59 research outputs found
On the photosynthetic responses of crops to intracanopy lighting with light emitting diodes
No full text Key words: Cucumis sativus, intracanopy lighting, light-emitting diodes (LEDs), light distribution, light interception, light quality, photosynthesis, photosynthetic acclimation Assimilation lighting is a production factor of increasing importance in Dutch greenhouse horticulture. Assimilation lighting increases production levels, improves product quality and opens possibilities for year round production. As a drawback, this use of assimilation lighting increases energy inputs and CO2-emission. Intracanopy lighting (with LEDs) is a technique to enhance the light use efficiency by changing the position of (a part of ) the lamps from above to within the canopy of greenhouse grown crops. Intracanopy lighting (IL) firstly reduces reflection and transmission losses of the supplemental lighting on crop level. These losses are high in traditional top-lighting systems, hence IL yields a higher light absorption on crop level. Secondly, IL creates a more homogenous vertical light distribution which can result in higher light use efficiencies. The aim of present study was to obtain insights in photosynthetic acclimation in response to irradiance level and spectrum in the framework of the applicability of LEDs as light source for intracanopy lighting in indeterminate growing vegetable crops. Intracanopy lighting may vary in (1) position within the crop, in (2) irradiance level and in (3) spectrum. Leaves deeper in the canopy are older. If leaf age negatively affects the photosynthetic capacity (Amax), then potential positions of IL-lamps reduce. By growing tomato plants horizontally so that irradiance was similar for all leaves from 0-70 days old, it is concluded that during the normal life-span of tomato leaves in cultivation, irradiance and not ageing is the most important factor affecting Amax. In winter, natural irradiances are low so that new developing leaves acclimate to low irradiances. Later on in their life time these leaves could be exposed to higher irradiances owing to IL. The question arose if cucumber leaves which develop under low irradiance can acclimate to a moderate irradiance. Acclimation of photosynthesis occurred within 7 days but photosynthesis at moderate irradiance and Amax did not reach to that of leaves developed under moderate irradiance. This reveals the importance of photosynthetic acclimation during the leaf developmental phase for crop productivity in scenarios with realistic, moderate fluctuations in irradiance that leaves can be exposed to. By growing plants under seven different combinations of red and blue light, blue light is shown to have both a qualitative and a quantitative effect on leaf development. Only leaves developed under red light (0% blue) displayed a dysfunctional photosynthetic operation (“red light syndrome”), which was largely alleviated by only 7% blue. Quantitatively, leaf responses to an increasing blue light percentage resembled responses associated with an increase in irradiance. Leaves developed under red light exposed to a mixture of red and blue (RB) completely recovered within 4 days after exposure to RB-light but remained limited in other leaf parameters, showing limitations in plasticity due to constraints arising from the prior leaf development. Leaves developed under RB also revealed the “red light syndrome” within 7 days of red illumination. Lastly, the effects of intracanopy lighting with LEDs on the production and development of a cucumber crop was investigated in winter. In the IL-treatment, LEDs supplied 38% of the supplemental irradiance within the canopy; the remaining 62% was supplied as top lighting by High-Pressure Sodium (HPS) lamps. The control was 100% top lighting (HPS lamps). Intracanopy lighting resulted in a greater Amax for leaves at deeper canopy layers but did not increase total biomass or fruit production. This was partly due to a reduced light interception caused by extreme leaf curling, which counteracted the expected higher light absorption by the crop, and partly to a lower dry matter partitioning to the fruits, and thus a greater dry matter partitioning to the leaves compared to the control. The effect of these factors on fruit yield was quantified using a explanatory crop model. Model calculations revealed a large negative effect on the fruit yield due to the greater partitioning to the leaves, whereas the negative effect of leaf curling was small. The effect of a greater Amax at deeper canopy layers was slightly positive. The last however might have indirectly caused the greater partitioning to the leaves as the greater Amax was associated with a preserved leaf mass per area. </p
Legen van een zandvang
No full textNadat in hoofdstuk 1 een beschrijving van een zandvang is gegeven, komt in de volgende twee hoofdstukken de karakteristieke methode dan ook uitgebreid aan de orde, en is dan vooral van belang voor een beter inzicht in het probleem. In hoofdstuk 2 wordt aan de hand van een literatuuronderzoek een aantal schematisaties van de gebruikte basisvergelijkingen bekeken, terwijl in hoofdstuk 3 de randvoorwaarden en beginvoorwaarden worden geformuleerd. Aan het eind van dit hoofdstuk komt de problematiek rond de karakteristieke methode naar voren. In hoofdstuk 4 wordt nagegaan of verwaarlozingen of benaderingen mogelijk zijn, waardoor toepassing van de karakteristieke methode nog tot de mogelijkheden zou kunnen behoren. Het negatieve resultaat hiervan heeft geleid tot de keuze van een numeriek schema welke behandeld wordt in hoofdstuk 5: de differentiaalvergelijkingen worden met behulp van het Preissmanschema in differentievorm geschreven, terwijl voor het oplossen van de differentievergelijkingen het Newton-Raphson proces toegepast wordt. De resultaten van het onderzoek worden weergegeven in hoofdstuk 6. Een aantal berekeningen zijn uitgevoerd, met als belangrijkste conclusie dat, onafhankelijk van datgene wat er in de zandvang gebeurt, bij een gegeven debiet de spuisluis maatgevend is voor de hoeveelheid sediment dat getransporteerd wordt.VloeistofmechanicaHydraulic EngineeringCivil Engineering and Geoscience
Scriptie: Oorzaken van doodgaan van humaan mesenchymale stamcellen na implantatie en effecten hiervan
No full textDe begeleider en/of auteur heeft geen toestemming gegeven tot het openbaar maken van de scriptie.
The supervisor and/or the author did not authorize public publication of the thesis.
Verplicht, maar toch vrijblijvend: Een verkenning van de meerwaarde van intervisie voor gezinshuisouders
No full textIn dit verkennende onderzoek is zicht gekregen op de meerwaarde van intervisie voor gezinshuisouders. Er is een literatuuronderzoek gehouden naar de werkzame bestanddelen voor intervisiegroepen. Daarnaast is er er een enquête gehouden over het nut van intervisienetwerken voor gezinshuisouders. Hier hebben 70 gezinshuisouders aan meegewerkt. En tenslotte zijn er vervolgens diepte-interviews gehouden met 8 gezinshuisouders.
Bijgevoegd is ook een visuele samenvatting van het rapport
On the photosynthetic and devlopmental responses of leaves to the spectral composition of light
No full textKey words: action spectrum, artificial solar spectrum, blue light, Cucumis sativus, gas-exchange, light-emitting diodes (LEDs), light interception, light quality, non-photosynthetic pigments, photo-synthetic capacity, photomorphogenesis, photosystem excitation balance, quantum yield, red light. A wide range of plant properties respond to the spectral composition of irradiance, such as photosynthesis, photomorphogenesis, phototropism and photonastic movements. These responses affect plant productivity, mainly via changes in the photosynthetic rate per unit leaf area, light interception, and irradiance distribution through the canopy. The spectral environment of plants is dependent on location (e.g. latitude), changes over time (e.g. Sun-angle), shading by other leaves, and, in the case of protected cultivation, the use of growth lamps. Therefore, not only the acclimation of developing leaves to light spectrum is important for plant productivity and survival, but also the capability of mature leaves to respond to changes in spectrum. This thesis focuses on the acclimation of photosynthesis per unit leaf area to the growth-light spectrum, the consequences of spectral acclimation for the wavelength dependence of photosynthetic quantum yield, and photomorphogenetic versus leaf photosynthetic acclimation in relation to biomass production. Cucumis sativus is used as a model plant. Additionally, the consequences of the choice and quality of the actinic light used during photosynthesis measurements are explored. By growing plants under seven different combinations of red and blue light, blue light is shown to have both a qualitative and a quantitative effect on leaf development. Only leaves developed under red alone (0% blue) displayed a dysfunctional photosynthetic operation, which was largely alleviated by only 7% blue. Quantitatively, leaf responses to an increasing blue light percentage resembled responses associated with an increase in irradiance. Next, the wavelength dependence of the quantum yield for CO2 fixation (α) is analysed in detail. Leaves grown under artificial shadelight, which overexcites photosystem I (PSI), had a higher α at wavelengths overexciting PSI (≥690 nm) and a lower PSI:PSII ratio compared with artificial sunlight and blue light grown leaves. At wavelengths overexciting PSII, α of the sun and blue grown leaves was higher. The photosystem excitation balance is quantitatively shown to determine α at those wavelengths where absorption by carotenoids and non-photosynthetic pigments is insignificant (≥580 nm). The wavelength dependences of the photosystem excitation balance calculated via an in vivo and an in vitro approach were substantially in agreement with each other, and where not, carotenoid absorption and state transitions are likely to play a role. Not only is the photosynthetic rate per unit leaf area is important for plant productivity, but also photomorphogenesis. We have engineered an artificial solar (AS) spectrum under which plants produced a dry weight that was, respectively, 2.3 and 1.6 times greater than that of plants grown under fluorescent tubes and high pressure sodium light. This striking difference was due to a morphology of the AS-plants that was more efficient in light interception, and not related to photosynthesis per unit leaf area. These results highlight the importance of a spectrum that is more natural than that of usual growth-lamps for research and possibly also for horticultural production. A technically orientated part of this thesis presents a simple method to quantify the light distribution in leaf chambers, which is shown to be important for the accuracy of photosynthesis measurements by gas-exchange. The match between growth-light and measuring-light spectrum is likewise shown to be important. A mismatch can have significant consequences for the estimate of α in situ, but only minor consequences for the estimate of the light-saturated photosynthetic rate. The relationship between the electron transport rate calculated using chlorophyll fluorescence measurements and the CO2 fixation rate also changed considerably with changes in measuring-light spectrum. The use of erroneous estimates of α as input for crop growth models is shown to have disproportionately large consequences for predictions of plant growth. <br/
Linking leaf initiation to the aerial environment: when air temperature is not the whole story
No full textThe initiation of new leaves, which takes place at the shoot apical meristem, is essential for plant growth and development. Leaf initiation rate (LIR) is very sensitive to meristem temperature. However, in practice meristem temperature is hardly ever monitored and air temperature is often used instead. It can be questioned whether relating LIR solely to air temperature is valid. This thesis aims at linking LIR to the aerial environment in two main horticultural crops: tomato and cucumber. It was shown that meristem temperature often differs from air temperature, depending on other environmental factors (e.g. radiation, humidity and wind speed) and species-specific traits. LIR was solely influenced by meristem temperature even when it largely deviated from air temperature. In addition, LIR was reduced at low light levels. Consequently, air temperature is not the whole story when relating leaf initiation to the environment. </p
Continuous light on tomato : from gene to yield
No full textLight essentially sustains all life on planet earth surface. Plants transform light energy into chemical energy through photosynthesis. Hence, it can be anticipated that extending the daily photoperiod, using artificial light, results in increased plant productivity. Although this premise is true for many plant species, a limit exists. For instance, the seminal work of Arthur et al. (1930) showed that tomato plants develop leaf injuries if exposed to continuous light (CL). Many studies have investigated the physiological mechanism inducing such CL-induced injury. Although important and valuable discoveries were done over the decades, by the time the present project started, a detailed and proven physiological explanation of this disorder was still missing. Here, I present the results of a 5-year effort to better understand the physiological basis of the CL-induced injury in tomato and develop the tools (genetic and conceptual) to cultivate tomatoes under CL. After an exhaustive literature search, it was found that Daskaloff and Ognjanova (1965) reported that wild tomato species are tolerant to CL. Unfortunately, this important finding was ignored by numerous studies done after its publication. Here, we used the CL-tolerance found in wild tomatoes as a fundamental resource. Hence, the specific objectives of this thesis were to (i) better understand the physiological basis of the CL-induced injuries in tomato, (ii) identify the gene(s) responsible for CL-tolerance in wild tomato species, (iii) breed a CL-tolerant tomato line and (iv) use it to cultivate a greenhouse tomato crop under CL. Chapter 1 describes how innovation efforts encountered the unsolved scientific enigma of the injuries that tomato plants develop when exposed to CL. The term CL-induced injury is defined, and a detailed description of the symptoms observed in this disorder is shown. Additionally, an overview of the most important studies, influencing the hypotheses postulated and/or tested in this dissertation, is presented. Finally, a description and motivation of the main questions that this dissertation pursued to answer is presented alongside a short description of the strategy chosen to answer them. Chapter 2 reviews the literature, published over the last 80 years, on CL-induced injury using modern knowledge of plant physiology. By doing so, new hypotheses aiming to explain this disorder are postulated in addition to the ones collected from literature. Additionally, we highlight that CL is an essential tool for understanding the plant circadian clock, but using CL in research has its challenges. For instance, most of the circadian-clock-oriented experiments are performed under CL; consequently, interactions between the circadian clock and the light signalling pathway are overlooked. This chapter is published here. Chapter 3 explores the benefits and challenges of cultivating CL-tolerant tomato under CL. Considering that current commercial tomato varieties need six hours of darkness per day for optimal growth, photosynthesis does not take place during a quarter of the day. Hence, if tomatoes could be grown under CL, a substantial increase in production is anticipated. A simulation study is presented, which shows that if an ideal continuous-light-tolerant tomato genotype is used and no crop adaptations to CL are assumed, greenhouse tomato production could be 26% higher when supplementing light to 24 h day-1 in comparison with a photoperiod (including supplementary lighting) of only 18 h day-1. In addition, the expected changes in greenhouse energy budgets and alterations in crop physiological responses that might arise from cultivating tomatoes under continuous light are discussed. This chapter is published here. Chapter 4 maps the locus conferring CL-tolerance in wild tomatoes to chromosome seven, and shows that its introgression into modern tomato cultivars enhances yield by 20%, when grown under CL. In addition, genetic evidence, RNAseq data, silencing experiments and sequence analysis all point to the type III Light-Harvesting Chlorophyll a/b Binding protein 13 (CAB-13) gene as a major factor responsible for the tolerance. In Arabidopsis thaliana this protein is thought to have a regulatory role in balancing light harvesting by photosystems I and II. The likely mechanisms that link CAB-13 with CL-tolerance are discussed. This chapter is published here. Chapter 5 investigates from which part of the plant CL-tolerance originates and whether this trait acts systemically. By exposing grafted plants bearing both tolerant and sensitive shoots to CL, the trait was functionally located to the shoot rather than the roots. Additionally, an increase in continuous-light tolerance was observed in sensitive plants when a continuous-light-tolerant shoot was grafted on it. Our results show that in order to increase yield in greenhouse tomato production by using CL, the trait should be bred into scion rather than rootstock lines. Chapter 6 discusses the factors that differ between injurious and non-injurious light regimes. Each of these factors may potentially be responsible for triggering the injury in CL-grown tomato and was experimentally tested here. In short, these factors include (i) differences in the light spectral distribution between sunlight and artificial light, (ii) continuous signalling to the photoreceptors, (iii) constant supply of light for photosynthesis, (iv) constant photo-oxidative pressure, and (v) circadian asynchrony — a mismatch between the internal circadian clock frequency and the external light/dark cycles. The evidence presented here suggests that the continuous-light-induced injury does not result from the unnatural spectral distribution of artificial light or the continuity of the light per se. Instead, circadian asynchrony seems to be the factor inducing the injury. As the discovered diurnal fluctuations in photoinhibition sensitivity of tomato seedlings are not under circadian control, it seems that circadian asynchrony does not directly induce injury via photoinhibition as it has been proposed. Chapter 7 investigates a possible role for phytochromes (PHY) in CL-induced injury in tomato. Mutant and transgenic tomato plants lacking or over-expressing phytochromes were exposed to CL, with and without far-red light enrichment, to test the role of individual phytochromes on the induction and/or prevention of injury. PHYA over-expression confers complete tolerance to CL regardless the light spectrum. Under CL with low far-red content, PHYB1 and PHYB2 diminished and enhanced the injury, respectively, yet the effects were small. These results confirm that phytochrome signaling networks are involved in the injury induction under CL. The link between CAB-13 and PHYA is discussed. Chapter 8 investigates the role of carbohydrate accumulation in the induction of CL-induced injury in tomato by using untargeted metabolomics and transcriptomics data. These data reveal a clear effect of CL on sugar metabolism and photosynthesis. A strong negative correlation between sucrose and starch with the maximum quantum efficiency of photosystem II (Fv /Fm) was found across several abnormal light/dark cycles, supporting the hypothesis that carbohydrates play an important role in CL-induced injury. I suggest that CL-induced injury in tomato is caused by a photosynthetic down-regulation showing characteristics of both cytokinin-regulated senescence and light-modulated retrograde signaling. Molecular mechanisms linking carbohydrate accumulation with photosynthetic down-regulation are discussed. Chapter 9 provides a synthesis of the most important findings and proposes a generic model of CL-induced injury in tomato. I propose that CL-induced injury in tomato arises from retrograde signals that counteract signals derived from the cellular developmental program that promote chloroplast development, such that chloroplast development cannot be completed, resulting in the chlorotic phenotype. Finally, perspectives on what future directions to take to further elucidate the physiological basis of this trait and successfully implement it in greenhouses are presented.</p
Efficient tools to simulate main crops in Portugal for decision support systems
No full textPhD Thesis Agricultural Production Chains - From Fork to FarmAgricultural systems are inherently vulnerable to climate variability and climate change is expected to increase this vulnerability. Various studies warn the anthropogenic-driven global warming with elevated CO2 concentration and altered regional precipitation pattern, are expected to negatively affect local crop productivity and thus exacerbate food insecurities in many regions worldwide, particularly for Mediterranean basin. Mediterranean basin is one of the most prominent climate change “hotspot” due to ongoing and projected changes in both climate means and variabilities, comprising a robust climate change signal of an overall warming and drying trend, accompanied by more frequent occurrence of severe drought and extreme high temperatures. Specifically, these projected changes are expected to be more pronounced in southern Europe, such as in Portugal, where annual mean temperature has increased at a rate more than double the global warming rate in the past decades, along with the observed decreases in precipitation and its enhanced inter-annual variability. Therefore, it is urgently needed to carry out the assessment of climate change impacts on agricultural production and explore suitable adaptation strategies, whereas the related studies so far remain scarce in Portugal. We had chosen three important cropping systems for Portuguese agriculture, i.e. irrigated maize, rainfed wheat and perennial forage grassland, while representative study sites in their current principal growing regions were identified accordingly. The overall methodology follows combined use of climate and crop models, where the spatially-downscaled bias-corrected climate change projections from climate models were utilized to drive crop model simulations at study sites, which were prior calibrated using local observed weather, soil and management data. For employed process-based crop models, both STICS and AquaCrop were applied for the irrigated maize production, whereas the other two cropping systems were only analyzed using STICS model. It was noteworthy one major strength from current studies consisted in, on top of projected mean climate changes, we had consistently incorporated the effects of potential changes in climate variability and its associated extreme weather events into the simulated impacts (e.g. yield changes) for a more reliable assessment. The results indicate threats and risks of future climate change are substantially high for agriculture production in Portugal. Because an overall negative climate change impact from the mid until the end of 21st century is obtained for all three important cropping systems, corresponding to moderate-to-severe yield losses with increased inter-annual variabilities. Yield losses are greater in magnitude with higher year-to-year variability, in the second half of the century than in the first half, and in a high emission pathway than in a low emission scenario. The CO2 fertilization effect is unlikely to compensate these yield reductions, where it brings more yield increment for C3 species (wheat and defined grass mixture) than for C4 (maize). Specifically, majority of negative impacts are derived from the shortened growth duration for irrigated maize under a warmer climate, and from intensified drought and heat stresses during a sensitive period (grain-filling) for rainfed wheat or during an unfavorable summer period for perennial grassland. These aspects correspond to the vulnerabilities of cropping systems facing climate change. It is interesting to note though higher temperature is clearly detrimental to irrigated maize production, it facilitates advanced phenology of perennial grass shifting towards the favorable cool and wet winter period for enhanced production or it may also help rainfed wheat crop to mature earlier to avoid excessive terminal stresses. Yet the magnitude of climate change impacts on agricultural productivity remains uncertain, varying with analyzed cropping systems, locations and management practices, applied climate models (including downscaling approaches) and crop models (including partial or full calibration), selected time periods and emission pathways. Adaptation strategies provide potential to mitigate these negative impacts, and development of appropriate and risk-focused adaptation policy should address previously identified vulnerabilities and prioritize available options for an integrated and comprehensive strategy. For annual cereal crops, increased irrigation amount at various levels has been firstly tested for irrigated maize cropping system under climate change, taking into account crop water demand and projected seasonal rainfall distribution. Though increased irrigation is able to mitigate yield reductions and maintain current yield levels, crop WUE considerably declines as a result of diminished yield responsiveness to seasonal water input with shorter growth duration. In view of increasing risks of water scarcity and decreasing portion of fresh water available for agriculture in the Mediterranean basin, solely increased irrigation supply might not be a feasible strategy, whereas the adaptive response for maize should be prioritized to promote water-saving techniques and maximize WUE for stabilizing yields (marginal reductions allowed). Combining optimized irrigation strategy (e.g. deficit irrigation) and installed efficient facilities (e.g. drip irrigation system) with other adaptation options, including introducing longer cycle cultivars and advanced sowing dates to counterbalance the shortened growing duration, is recommend, but should be further rigorously examined. For the rainfed wheat cropping system, adaptation priority should address the exacerbated risks of drought and heat stresses during the sensitive anthesis and grain-filling periods. The terminal stress escaping strategy is proposed by firstly testing early flowering cultivars (also known as short-cycle genotypes), where the trade-off between lower risk of exposure to terminal stress and higher risk of reduced yield potential tends to be positive, leading to net yield gains. Still, this option needs to be combined with other adaptation opportunities including early sowing date, wheat cultivars with less or no vernalization requirement (e.g. using spring wheat) and supplementary irrigation during the sensitive stage. Early sowing is expected to achieve the same stress escaping goals by anticipation of growth cycle. But winter warming during early sowing window could potentially slow vernalization fulfillment, with limited benefits to advance the susceptible stages. Using earlyflowering spring wheat cultivars (the earliness threshold must be carefully defined) thus can help advocating early sowing practice that potentially make use of more autumn-winter rainfall. Nevertheless, the proposed stress escaping strategy is found to be comparatively more useful to avoid enhanced terminal heat stress (>38º last over a short period) than prolonged terminal drought stress, where the latter can be alleviated with optimized supplemental irrigation. Adaptation strategy for perennial forage grassland should take advantage of opportunity and tackle the challenge, both arising from climate change. Benefiting from advanced phenology towards winter and early spring with alleviated cold stress and enriched ambient CO2 concentration, adaptation measures should focus on maximizing growth potential during this favorable period. These include optimized resource use (balanced early fertilization strategy with limited N leaching) and using grass-legume mixture for flexible forage utilization and better exploiting the stimulated CO2 responsiveness. In contrast, to cope with the challenge of exacerbated risks of summer heat and drought stresses, future breeding programs should ensure a diversification (intra- and interspecific variations) of available germplasms in phenology (fit new seasonal climate pattern), heat tolerance and dehydration tolerance for principal forage species. Specifically, continuous improvement of drought persistence and summer dormancy traits should gain more importance for rainfed Mediterranean grassland. Moreover, these drought survival traits should be integrated into plant materials with deeper root system to enhance water uptake (e.g. more of tall fescue), but it may raise forage quality issues that remain unassessed. Besides, we also hypothesize it is possible to adapt to summer drought from a management perspective without the needs to improve and diversify the species and variety mixture. The findings suggest that provided minimum soil moisture is guaranteed by supplemental irrigation to ensure adequate drought survival rate and standing density, breeding efforts should be more motivated towards heat tolerance, particularly in southern Portugal. Meanwhile, this measure is likely to result in a considerable increase in irrigation need, rendering a similar water-restriction issue facing irrigated maize. Crop yield projections and explored adaptation strategies are essential to assess the regional food security prospects and provide crucial information to support planning and implementing suitable adaptation strategies for farmers and policymakers in Portugal and in Mediterranean basin that is known to be susceptible to climate change. Despite the uncertainties in the magnitude of yield impacts and quantitative effectiveness of adaptations, the proposed and recommended adaptation strategies can represent promising opportunities to maintain or increase production in future climate while minimize environment impacts. Future research efforts should be directed towards using multi-model ensembles (both crop and climate models) to quantify the uncertainties and make the estimations more robust and reliable, but sustained and extensive international cooperation is required. Moreover, stronger link of field experimentation with crop modelling is essential for a more mechanistic understanding of crop response to climate change, as well as the integration of crop model into economic modelling for complex farm-level assessment. These shall all contribute to appropriate manage the climate risks and comprehensively improve the resilience of cropping systemOs sistemas agrícolas são inerentemente vulneráveis à variabilidade climática e espera-se que a mudança climática aumente essa vulnerabilidade. Vários estudos alertam para o facto de que o aquecimento global de causas antropogénicas, a elevada concentração atmosférica de CO2 e padrões de precipitação regional alterados deverão afetar negativamente a produtividade local das culturas e, assim, exacerbar inseguranças alimentares em muitas regiões do mundo, particularmente na bacia do Mediterrâneo. A bacia do Mediterrâneo é um dos mais proeminentes "hotspots" das alterações climáticas, devido às mudanças climáticas em curso e projetadas, tanto na média como na variabilidade, compreendendo um sinal robusto de mudanças climáticas com uma tendência geral de aquecimento e secura, acompanhada pela ocorrência mais frequente de secas severas ou extremas e temperaturas muito altas. Especificamente, espera-se que estas mudanças projetadas sejam mais pronunciadas no sul da Europa, como em Portugal, onde a temperatura média anual aumentou a uma taxa de mais do dobro da taxa de aquecimento global nas últimas décadas, juntamente com os decréscimos observados na precipitação e maior variabilidade interanual. Por conseguinte, é necessário avaliar os impactos das alterações climáticas na produção agrícola e explorar estratégias de adaptação adequadas, enquanto os estudos efetuados até agora permanecem escassos em Portugal. Escolhemos três importantes sistemas de cultivo para a agricultura portuguesa, nomeadamente o milho de regadio, trigo de sequeiro e pastagens forrageiras perenes, sendo os locais de estudo escolhidos representativos das suas principais regiões de crescimento. A metodologia geral segue o uso combinado de modelos de clima e de culturas, onde as projeções climáticas de elevada resolução espacial e corrigidas de viés foram utilizadas como forçamentos das simulações de modelos de culturas, tendo sido estes previamente calibrados usando dados meteorológicos, de solo e de práticas agrícolas locais. Para a produção de milho de regadio foram utilizados os modelos de culturas dinâmicos STICS e AquaCrop, enquanto os outros dois sistemas de cultivo foram analisados apenas com o modelo STICS. É importante salientar que os resultados do presente estudo incorporaram nos impactos simulados os efeitos das alterações não apenas na média, mas também na variabilidade climática e seus extremos (por exemplo, mudanças de produção), o que permite uma avaliação mais rigorosa. Os resultados indicam que as ameaças e os riscos das alterações climáticas são elevados para a produção agrícola em Portugal, dado que se verifica um impacto global negativo para os três sistemas de cultivo estudados, correspondendo a perdas de rendimento moderadas a severas, com elevadas variabilidades inter anuais. As perdas de rendimento são maiores, com maior variabilidade interanual na segunda metade do século do que na primeira metade, e para um cenário de emissão elevada do que num cenário de baixa emissão. É improvável que o efeito da fertilização com CO2 compense estas reduções de rendimento, com um maior rendimento para as espécies C3 (trigo e pastagem) do que para a C4 (milho). Mais especificamente, a maioria dos impactos negativos resulta do encurtamento do período de crescimento do milho de regadio sob um clima mais quente, e da intensificação do stresse hídrico e térmico durante o período sensível para o trigo de sequeiro ou para as pastagens perenes. Esses aspetos correspondem às vulnerabilidades dos sistemas de cultivo face às alterações climáticas. É interessante notar que temperaturas mais altas são claramente prejudiciais à produção de milho de regadio, mas facilitando a antecipação da fenologia das pastagens perenes, melhorando a produção durante para o período favorável de inverno fresco e húmido. Estas novas condições também podem ajudar o trigo de sequeiro a amadurecer mais cedo, evitando valores excessivos de stresse. No entanto, a magnitude dos impactos da mudança climática na produtividade agrícola permanece incerta, dependendo do sistema de cultivo, local e práticas culturais, modelos climáticos aplicados (incluindo abordagens de downscaling) e modelos de culturas (incluindo calibração parcial ou total), períodos de tempo selecionados e cenários de emissão. As estratégias de adaptação fornecem potencial para mitigar esses impactos negativos. O desenvolvimento de medidas de adaptação apropriadas e focadas no risco deve ter em conta as vulnerabilidades previamente identificadas e priorizar as opções disponíveis para uma estratégia integrada e abrangente. Para as culturas anuais de cereais, o aumento dos volumes de rega em vários níveis foi primeiramente testado para o sistema de cultivo de milho de regadio em cenários de alterações climáticas, tendo em consideração as necessidades de água da cultura e a projeção da distribuição sazonal de precipitação. Embora o aumento da rega seja capaz de mitigar as reduções de rendimento e manter os níveis atuais, a WUE da cultura decresce consideravelmente como resultado da menor resposta ao fornecimento de água devido ao encurtamento da época de crescimento. Devido ao risco crescente de escassez de água e à redução da água disponível para a agricultura na bacia do Mediterrâneo, o aumento do recurso à rega pode não ser uma estratégia viável, devendo ser priorizadas estratégias de gestão de água e maximização da WUE com vista à estabilização dos rendimentos (reduções marginais permitidas). Combinar estratégias de irrigação otimizadas (por exemplo, irrigação deficitária) e instalações eficientes (por exemplo, sistema de rega gota a gota) com outras opções de adaptação, incluindo a introdução de variedades de ciclo mais longo e datas de sementeira mais precoces de forma a contrabalançar o encurtamento do período de crescimento é recomendável. Para o sistema de cultivo do trigo de sequeiro, a prioridade de adaptação deve abordar os riscos exacerbados stresse térmico e hídrico durante os períodos sensíveis de antese e enchimento de grãos. A estratégia para evitar o stresse terminal é proposta testando primeiramente variedades de floração precoce (também conhecidas como genótipos de ciclo curto), onde o trade-off entre menor risco de exposição ao stresse terminal e maior risco de redução do potencial produtivo tende a ser positivo, levando a ganhos líquidos de rendimento. Ainda assim, esta opção precisa ser combinada com outras estratégias de adaptação, incluindo a data de semeadura antecipada, cultivares de trigo com menor ou nenhum requisito de vernalização (por exemplo, usando trigo de primavera) e irrigação suplementar durante o período mais sensível. Uma sementeira mais precoce deverá permitir evitar o stresse terminal por antecipação do ciclo de crescimento. No entanto, o aquecimento de inverno durante a janela de sementeira precoce poderá potencialmente abrandar a vernalização, com benefícios limitados no avanço das fases suscetíveis. A utilização de variedades de trigo de primavera com floração precoce (o limiar de antecipação deve ser cuidadosamente definido) advogam sementeira precoce, o que permite a utilização da precipitação de outono-inverno. No entanto, a estratégia proposta para evitar o stresse é comparativamente mais útil para evitar o aumento do stresse térmico terminal (> 38ºC por um período curto) do que o stresse prolongado por seca, onde este último pode ser aliviado com rega suplementar otimizada. A estratégia de adaptação para pastagens forrageiras perenes deve aproveitar a oportunidade e enfrentar o desafio, ambos decorrentes da mudança climática. Beneficiando-se de fenologia avançada em relação ao inverno e início da primavera, com menor stresse por frio e maior concentração atmosférica de CO2, as medidas de adaptação devem-se concentrar na maximização do potencial de crescimento durante este período favorável. Estes incluem o uso otimizado de recursos (estratégia balançada de fertilização precoce com limitação da lixiviação de N) e o uso de mistura de gramíneas e leguminosas para utilização de forragens flexíveis e melhor exploração da resposta estimulada de CO2. Em contraste, para lidar com o desafio dos riscos exacerbados de calor no verão e stresse hídrico, futuros programas de melhoramento devem garantir uma diversificação (intra e inter varietal) dos germoplasmas disponíveis em fenologia (ajuste ao novo padrão climático sazonal), tolerância ao calor e tolerância à desidratação para espécies forrageiras. Concretamente, a melhoria contínua das características de persistência à seca e de dormência de verão devem ganhar mais importância para as pastagens mediterrâneas de sequeiro. Além disso, estas características de sobrevivência à seca devem ser integrados em materiais vegetais com sistema radicular mais profundo para aumentar a absorção de água (por exemplo, festuca mais alta), mas isso pode resultar em problemas de qualidade da forragem que ainda permanecem por avaliação. Além disso, também formulamos a hipótese de que é possível a adaptação à seca de verão a partir de uma perspetiva de gestão sem a necessidade de melhorar e diversificar a mistura de espécies e variedades. Os resultados sugerem que, desde que a humidade mínima do solo seja garantida pela rega suplementar para garantir a taxa adequada de sobrevivência à seca e a densidade de planta, os esforços de melhoramento devem ser mais motivados para a tolerância ao calor, particularmente no sul de Portugal. Ao mesmo tempo, esta medida provavelmente resultará num aumento considerável na necessidade de rega, tornando-se num problema similar de restrição de água enfrentado pelo milho de regadio. As projeções de colheira e as estratégias de adaptação exploradas são essenciais para avaliar as perspetivas regionais de segurança alimentar e fornecer informações cruciais para apoiar o planeamento e a implementação de estratégias adequadas de adaptação para agricultores e decisores políticos em Portugal e na bacia do Mediterrâneo. Apesar das incertezas na magnitude dos impactos na produção e na eficácia quantitativa das adaptações, as estratégias de adaptação propostas e recomendadas podem representar oportunidades promissoras para manter ou aumentar a produção no clima futuro, minimizando ao mesmo tempo os impactos ambientais. Esforços de investigação futuros devem ser direcionados para o uso de ensembles de modelos (tanto modelos agrícolas quanto climáticos) para melhor quantificar as incertezas e tornar as estimativas mais robustas e confiáveis. Não obstante, é necessária uma cooperação internacional vasta e sustentável. Além disso, uma forte ligação entre a experimentação de campo e a modelação de culturas é essencial para uma compreensão mais mecanicista da resposta da cultura às alterações climáticas, bem como a integração dos modelos de cultura na modelação económica. Todos estes devem contribuir para gerir adequadamente os riscos climáticos e melhorar a resiliência dos sistemas de cultiv
Efficient tools to simulate main crops in Portugal for decision support systems
No full textPhD Thesis Agricultural Production Chains - From Fork to FarmAgricultural systems are inherently vulnerable to climate variability and climate change is expected to increase this vulnerability. Various studies warn the anthropogenic-driven global warming with elevated CO2 concentration and altered regional precipitation pattern, are expected to negatively affect local crop productivity and thus exacerbate food insecurities in many regions worldwide, particularly for Mediterranean basin. Mediterranean basin is one of the most prominent climate change “hotspot” due to ongoing and projected changes in both climate means and variabilities, comprising a robust climate change signal of an overall warming and drying trend, accompanied by more frequent occurrence of severe drought and extreme high temperatures. Specifically, these projected changes are expected to be more pronounced in southern Europe, such as in Portugal, where annual mean temperature has increased at a rate more than double the global warming rate in the past decades, along with the observed decreases in precipitation and its enhanced inter-annual variability. Therefore, it is urgently needed to carry out the assessment of climate change impacts on agricultural production and explore suitable adaptation strategies, whereas the related studies so far remain scarce in Portugal. We had chosen three important cropping systems for Portuguese agriculture, i.e. irrigated maize, rainfed wheat and perennial forage grassland, while representative study sites in their current principal growing regions were identified accordingly. The overall methodology follows combined use of climate and crop models, where the spatially-downscaled bias-corrected climate change projections from climate models were utilized to drive crop model simulations at study sites, which were prior calibrated using local observed weather, soil and management data. For employed process-based crop models, both STICS and AquaCrop were applied for the irrigated maize production, whereas the other two cropping systems were only analyzed using STICS model. It was noteworthy one major strength from current studies consisted in, on top of projected mean climate changes, we had consistently incorporated the effects of potential changes in climate variability and its associated extreme weather events into the simulated impacts (e.g. yield changes) for a more reliable assessment. The results indicate threats and risks of future climate change are substantially high for agriculture production in Portugal. Because an overall negative climate change impact from the mid until the end of 21st century is obtained for all three important cropping systems, corresponding to moderate-to-severe yield losses with increased inter-annual variabilities. Yield losses are greater in magnitude with higher year-to-year variability, in the second half of the century than in the first half, and in a high emission pathway than in a low emission scenario. The CO2 fertilization effect is unlikely to compensate these yield reductions, where it brings more yield increment for C3 species (wheat and defined grass mixture) than for C4 (maize). Specifically, majority of negative impacts are derived from the shortened growth duration for irrigated maize under a warmer climate, and from intensified drought and heat stresses during a sensitive period (grain-filling) for rainfed wheat or during an unfavorable summer period for perennial grassland. These aspects correspond to the vulnerabilities of cropping systems facing climate change. It is interesting to note though higher temperature is clearly detrimental to irrigated maize production, it facilitates advanced phenology of perennial grass shifting towards the favorable cool and wet winter period for enhanced production or it may also help rainfed wheat crop to mature earlier to avoid excessive terminal stresses. Yet the magnitude of climate change impacts on agricultural productivity remains uncertain, varying with analyzed cropping systems, locations and management practices, applied climate models (including downscaling approaches) and crop models (including partial or full calibration), selected time periods and emission pathways. Adaptation strategies provide potential to mitigate these negative impacts, and development of appropriate and risk-focused adaptation policy should address previously identified vulnerabilities and prioritize available options for an integrated and comprehensive strategy. For annual cereal crops, increased irrigation amount at various levels has been firstly tested for irrigated maize cropping system under climate change, taking into account crop water demand and projected seasonal rainfall distribution. Though increased irrigation is able to mitigate yield reductions and maintain current yield levels, crop WUE considerably declines as a result of diminished yield responsiveness to seasonal water input with shorter growth duration. In view of increasing risks of water scarcity and decreasing portion of fresh water available for agriculture in the Mediterranean basin, solely increased irrigation supply might not be a feasible strategy, whereas the adaptive response for maize should be prioritized to promote water-saving techniques and maximize WUE for stabilizing yields (marginal reductions allowed). Combining optimized irrigation strategy (e.g. deficit irrigation) and installed efficient facilities (e.g. drip irrigation system) with other adaptation options, including introducing longer cycle cultivars and advanced sowing dates to counterbalance the shortened growing duration, is recommend, but should be further rigorously examined. For the rainfed wheat cropping system, adaptation priority should address the exacerbated risks of drought and heat stresses during the sensitive anthesis and grain-filling periods. The terminal stress escaping strategy is proposed by firstly testing early flowering cultivars (also known as short-cycle genotypes), where the trade-off between lower risk of exposure to terminal stress and higher risk of reduced yield potential tends to be positive, leading to net yield gains. Still, this option needs to be combined with other adaptation opportunities including early sowing date, wheat cultivars with less or no vernalization requirement (e.g. using spring wheat) and supplementary irrigation during the sensitive stage. Early sowing is expected to achieve the same stress escaping goals by anticipation of growth cycle. But winter warming during early sowing window could potentially slow vernalization fulfillment, with limited benefits to advance the susceptible stages. Using earlyflowering spring wheat cultivars (the earliness threshold must be carefully defined) thus can help advocating early sowing practice that potentially make use of more autumn-winter rainfall. Nevertheless, the proposed stress escaping strategy is found to be comparatively more useful to avoid enhanced terminal heat stress (>38º last over a short period) than prolonged terminal drought stress, where the latter can be alleviated with optimized supplemental irrigation. Adaptation strategy for perennial forage grassland should take advantage of opportunity and tackle the challenge, both arising from climate change. Benefiting from advanced phenology towards winter and early spring with alleviated cold stress and enriched ambient CO2 concentration, adaptation measures should focus on maximizing growth potential during this favorable period. These include optimized resource use (balanced early fertilization strategy with limited N leaching) and using grass-legume mixture for flexible forage utilization and better exploiting the stimulated CO2 responsiveness. In contrast, to cope with the challenge of exacerbated risks of summer heat and drought stresses, future breeding programs should ensure a diversification (intra- and interspecific variations) of available germplasms in phenology (fit new seasonal climate pattern), heat tolerance and dehydration tolerance for principal forage species. Specifically, continuous improvement of drought persistence and summer dormancy traits should gain more importance for rainfed Mediterranean grassland. Moreover, these drought survival traits should be integrated into plant materials with deeper root system to enhance water uptake (e.g. more of tall fescue), but it may raise forage quality issues that remain unassessed. Besides, we also hypothesize it is possible to adapt to summer drought from a management perspective without the needs to improve and diversify the species and variety mixture. The findings suggest that provided minimum soil moisture is guaranteed by supplemental irrigation to ensure adequate drought survival rate and standing density, breeding efforts should be more motivated towards heat tolerance, particularly in southern Portugal. Meanwhile, this measure is likely to result in a considerable increase in irrigation need, rendering a similar water-restriction issue facing irrigated maize. Crop yield projections and explored adaptation strategies are essential to assess the regional food security prospects and provide crucial information to support planning and implementing suitable adaptation strategies for farmers and policymakers in Portugal and in Mediterranean basin that is known to be susceptible to climate change. Despite the uncertainties in the magnitude of yield impacts and quantitative effectiveness of adaptations, the proposed and recommended adaptation strategies can represent promising opportunities to maintain or increase production in future climate while minimize environment impacts. Future research efforts should be directed towards using multi-model ensembles (both crop and climate models) to quantify the uncertainties and make the estimations more robust and reliable, but sustained and extensive international cooperation is required. Moreover, stronger link of field experimentation with crop modelling is essential for a more mechanistic understanding of crop response to climate change, as well as the integration of crop model into economic modelling for complex farm-level assessment. These shall all contribute to appropriate manage the climate risks and comprehensively improve the resilience of cropping systemOs sistemas agrícolas são inerentemente vulneráveis à variabilidade climática e espera-se que a mudança climática aumente essa vulnerabilidade. Vários estudos alertam para o facto de que o aquecimento global de causas antropogénicas, a elevada concentração atmosférica de CO2 e padrões de precipitação regional alterados deverão afetar negativamente a produtividade local das culturas e, assim, exacerbar inseguranças alimentares em muitas regiões do mundo, particularmente na bacia do Mediterrâneo. A bacia do Mediterrâneo é um dos mais proeminentes "hotspots" das alterações climáticas, devido às mudanças climáticas em curso e projetadas, tanto na média como na variabilidade, compreendendo um sinal robusto de mudanças climáticas com uma tendência geral de aquecimento e secura, acompanhada pela ocorrência mais frequente de secas severas ou extremas e temperaturas muito altas. Especificamente, espera-se que estas mudanças projetadas sejam mais pronunciadas no sul da Europa, como em Portugal, onde a temperatura média anual aumentou a uma taxa de mais do dobro da taxa de aquecimento global nas últimas décadas, juntamente com os decréscimos observados na precipitação e maior variabilidade interanual. Por conseguinte, é necessário avaliar os impactos das alterações climáticas na produção agrícola e explorar estratégias de adaptação adequadas, enquanto os estudos efetuados até agora permanecem escassos em Portugal. Escolhemos três importantes sistemas de cultivo para a agricultura portuguesa, nomeadamente o milho de regadio, trigo de sequeiro e pastagens forrageiras perenes, sendo os locais de estudo escolhidos representativos das suas principais regiões de crescimento. A metodologia geral segue o uso combinado de modelos de clima e de culturas, onde as projeções climáticas de elevada resolução espacial e corrigidas de viés foram utilizadas como forçamentos das simulações de modelos de culturas, tendo sido estes previamente calibrados usando dados meteorológicos, de solo e de práticas agrícolas locais. Para a produção de milho de regadio foram utilizados os modelos de culturas dinâmicos STICS e AquaCrop, enquanto os outros dois sistemas de cultivo foram analisados apenas com o modelo STICS. É importante salientar que os resultados do presente estudo incorporaram nos impactos simulados os efeitos das alterações não apenas na média, mas também na variabilidade climática e seus extremos (por exemplo, mudanças de produção), o que permite uma avaliação mais rigorosa. Os resultados indicam que as ameaças e os riscos das alterações climáticas são elevados para a produção agrícola em Portugal, dado que se verifica um impacto global negativo para os três sistemas de cultivo estudados, correspondendo a perdas de rendimento moderadas a severas, com elevadas variabilidades inter anuais. As perdas de rendimento são maiores, com maior variabilidade interanual na segunda metade do século do que na primeira metade, e para um cenário de emissão elevada do que num cenário de baixa emissão. É improvável que o efeito da fertilização com CO2 compense estas reduções de rendimento, com um maior rendimento para as espécies C3 (trigo e pastagem) do que para a C4 (milho). Mais especificamente, a maioria dos impactos negativos resulta do encurtamento do período de crescimento do milho de regadio sob um clima mais quente, e da intensificação do stresse hídrico e térmico durante o período sensível para o trigo de sequeiro ou para as pastagens perenes. Esses aspetos correspondem às vulnerabilidades dos sistemas de cultivo face às alterações climáticas. É interessante notar que temperaturas mais altas são claramente prejudiciais à produção de milho de regadio, mas facilitando a antecipação da fenologia das pastagens perenes, melhorando a produção durante para o período favorável de inverno fresco e húmido. Estas novas condições também podem ajudar o trigo de sequeiro a amadurecer mais cedo, evitando valores excessivos de stresse. No entanto, a magnitude dos impactos da mudança climática na produtividade agrícola permanece incerta, dependendo do sistema de cultivo, local e práticas culturais, modelos climáticos aplicados (incluindo abordagens de downscaling) e modelos de culturas (incluindo calibração parcial ou total), períodos de tempo selecionados e cenários de emissão. As estratégias de adaptação fornecem potencial para mitigar esses impactos negativos. O desenvolvimento de medidas de adaptação apropriadas e focadas no risco deve ter em conta as vulnerabilidades previamente identificadas e priorizar as opções disponíveis para uma estratégia integrada e abrangente. Para as culturas anuais de cereais, o aumento dos volumes de rega em vários níveis foi primeiramente testado para o sistema de cultivo de milho de regadio em cenários de alterações climáticas, tendo em consideração as necessidades de água da cultura e a projeção da distribuição sazonal de precipitação. Embora o aumento da rega seja capaz de mitigar as reduções de rendimento e manter os níveis atuais, a WUE da cultura decresce consideravelmente como resultado da menor resposta ao fornecimento de água devido ao encurtamento da época de crescimento. Devido ao risco crescente de escassez de água e à redução da água disponível para a agricultura na bacia do Mediterrâneo, o aumento do recurso à rega pode não ser uma estratégia viável, devendo ser priorizadas estratégias de gestão de água e maximização da WUE com vista à estabilização dos rendimentos (reduções marginais permitidas). Combinar estratégias de irrigação otimizadas (por exemplo, irrigação deficitária) e instalações eficientes (por exemplo, sistema de rega gota a gota) com outras opções de adaptação, incluindo a introdução de variedades de ciclo mais longo e datas de sementeira mais precoces de forma a contrabalançar o encurtamento do período de crescimento é recomendável. Para o sistema de cultivo do trigo de sequeiro, a prioridade de adaptação deve abordar os riscos exacerbados stresse térmico e hídrico durante os períodos sensíveis de antese e enchimento de grãos. A estratégia para evitar o stresse terminal é proposta testando primeiramente variedades de floração precoce (também conhecidas como genótipos de ciclo curto), onde o trade-off entre menor risco de exposição ao stresse terminal e maior risco de redução do potencial produtivo tende a ser positivo, levando a ganhos líquidos de rendimento. Ainda assim, esta opção precisa ser combinada com outras estratégias de adaptação, incluindo a data de semeadura antecipada, cultivares de trigo com menor ou nenhum requisito de vernalização (por exemplo, usando trigo de primavera) e irrigação suplementar durante o período mais sensível. Uma sementeira mais precoce deverá permitir evitar o stresse terminal por antecipação do ciclo de crescimento. No entanto, o aquecimento de inverno durante a janela de sementeira precoce poderá potencialmente abrandar a vernalização, com benefícios limitados no avanço das fases suscetíveis. A utilização de variedades de trigo de primavera com floração precoce (o limiar de antecipação deve ser cuidadosamente definido) advogam sementeira precoce, o que permite a utilização da precipitação de outono-inverno. No entanto, a estratégia proposta para evitar o stresse é comparativamente mais útil para evitar o aumento do stresse térmico terminal (> 38ºC por um período curto) do que o stresse prolongado por seca, onde este último pode ser aliviado com rega suplementar otimizada. A estratégia de adaptação para pastagens forrageiras perenes deve aproveitar a oportunidade e enfrentar o desafio, ambos decorrentes da mudança climática. Beneficiando-se de fenologia avançada em relação ao inverno e início da primavera, com menor stresse por frio e maior concentração atmosférica de CO2, as medidas de adaptação devem-se concentrar na maximização do potencial de crescimento durante este período favorável. Estes incluem o uso otimizado de recursos (estratégia balançada de fertilização precoce com limitação da lixiviação de N) e o uso de mistura de gramíneas e leguminosas para utilização de forragens flexíveis e melhor exploração da resposta estimulada de CO2. Em contraste, para lidar com o desafio dos riscos exacerbados de calor no verão e stresse hídrico, futuros programas de melhoramento devem garantir uma diversificação (intra e inter varietal) dos germoplasmas disponíveis em fenologia (ajuste ao novo padrão climático sazonal), tolerância ao calor e tolerância à desidratação para espécies forrageiras. Concretamente, a melhoria contínua das características de persistência à seca e de dormência de verão devem ganhar mais importância para as pastagens mediterrâneas de sequeiro. Além disso, estas características de sobrevivência à seca devem ser integrados em materiais vegetais com sistema radicular mais profundo para aumentar a absorção de água (por exemplo, festuca mais alta), mas isso pode resultar em problemas de qualidade da forragem que ainda permanecem por avaliação. Além disso, também formulamos a hipótese de que é possível a adaptação à seca de verão a partir de uma perspetiva de gestão sem a necessidade de melhorar e diversificar a mistura de espécies e variedades. Os resultados sugerem que, desde que a humidade mínima do solo seja garantida pela rega suplementar para garantir a taxa adequada de sobrevivência à seca e a densidade de planta, os esforços de melhoramento devem ser mais motivados para a tolerância ao calor, particularmente no sul de Portugal. Ao mesmo tempo, esta medida provavelmente resultará num aumento considerável na necessidade de rega, tornando-se num problema similar de restrição de água enfrentado pelo milho de regadio. As projeções de colheira e as estratégias de adaptação exploradas são essenciais para avaliar as perspetivas regionais de segurança alimentar e fornecer informações cruciais para apoiar o planeamento e a implementação de estratégias adequadas de adaptação para agricultores e decisores políticos em Portugal e na bacia do Mediterrâneo. Apesar das incertezas na magnitude dos impactos na produção e na eficácia quantitativa das adaptações, as estratégias de adaptação propostas e recomendadas podem representar oportunidades promissoras para manter ou aumentar a produção no clima futuro, minimizando ao mesmo tempo os impactos ambientais. Esforços de investigação futuros devem ser direcionados para o uso de ensembles de modelos (tanto modelos agrícolas quanto climáticos) para melhor quantificar as incertezas e tornar as estimativas mais robustas e confiáveis. Não obstante, é necessária uma cooperação internacional vasta e sustentável. Além disso, uma forte ligação entre a experimentação de campo e a modelação de culturas é essencial para uma compreensão mais mecanicista da resposta da cultura às alterações climáticas, bem como a integração dos modelos de cultura na modelação económica. Todos estes devem contribuir para gerir adequadamente os riscos climáticos e melhorar a resiliência dos sistemas de cultiv
Caspase inhibitors affect the kinetics and dimensions of tracheary elements in xylogenic Zinnia (<it>Zinnia elegans</it>) cell cultures
No full textAbstract Background The xylem vascular system is composed of fused dead, hollow cells called tracheary elements (TEs) that originate through trans-differentiation of root and shoot cambium cells. TEs undergo autolysis as they differentiate and mature. The final stage of the formation of TEs in plants is the death of the involved cells, a process showing some similarities to programmed cell death (PCD) in animal systems. Plant proteases with functional similarity to proteases involved in mammalian apoptotic cell death (caspases) are suggested as an integral part of the core mechanism of most PCD responses in plants, but participation of plant caspase-like proteases in TE PCD has not yet been documented. Results Confocal microscopic images revealed the consecutive stages of TE formation in Zinnia cells during trans-differentiation. Application of the caspase inhibitors Z-Asp-CH2-DCB, Ac-YVAD-CMK and Ac-DEVD-CHO affected the kinetics of formation and the dimensions of the TEs resulting in a significant delay of TE formation, production of larger TEs and in elimination of the 'two-wave' pattern of TE production. DNA breakdown and appearance of TUNEL-positive nuclei was observed in xylogenic cultures and this was suppressed in the presence of caspase inhibitors. Conclusions To the best of our knowledge this is the first report showing that caspase inhibitors can modulate the process of trans-differentiation in Zinnia xylogenic cell cultures. As caspase inhibitors are closely associated with cell death inhibition in a variety of plant systems, this suggests that the altered TE formation results from suppression of PCD. The findings presented here are a first step towards the use of appropriate PCD signalling modulators or related molecular genetic strategies to improve the hydraulic properties of xylem vessels in favour of the quality and shelf life of plants or plant parts.</p
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