1,720,973 research outputs found
Identification of microRNAS differentially regulated by water deficit in relation to mycorrhizal treatment in wheat
No full textArbuscular mycorrhizal fungi (AMF) are soil microrganisms that establish symbiosis with plants positively influencing their resistance to abiotic stresses. The aim of this work was to identify wheat miRNAs differentially regulated by water deficit conditions in presence or absence of AMF treatment. Small RNA libraries were constructed for both leaf and root tissues considering four conditions: control (irrigated) or water deficit in presence/absence of mycorrhizal (AMF) treatment. A total of 12 miRNAs were significantly regulated by water deficit in leaves: five in absence and seven in presence of AMF treatment. In roots, three miRNAs were water deficit-modulated in absence of mycorrhizal treatment while six were regulated in presence of it. The most represented miRNA family was miR167 that was regulated by water deficit in both leaf and root tissues. Interestingly, miR827-5p was differentially regulated in leaves in the absence of mycorrhizal treatment while it was water deficit-modulated in roots irrespective of AMF treatment. In roots, water deficit repressed miR827-5p, miR394, miR6187, miR167e-3p, and miR9666b-3p affecting transcription, RNA synthesis, protein synthesis, and protein modifications. In leaves, mycorrhizae modulated miR5384-3p and miR156e-3p affecting trafficking and cell redox homeostasis. DNA replication and transcription regulation should be targeted by the repression of miR1432-5p and miR166h-3p. This work provided interesting insights into the post-transcriptional mechanisms of wheat responses to water deficit in relation to mycorrhizal symbiosis
Morphological and physiological root traits and their relationship with nitrogen uptake in wheat varieties released from 1915 to 2013
Full text linkIdentifying genotypes with a greater ability to absorb nitrogen (N) may be important to reducing N loss in the environment and improving the sustainability of agricultural systems. This study extends the knowledge of variability among wheat genotypes in terms of morphological or physiological root traits, N uptake under conditions of low soil N availability, and in the amount and rapidity of the use of N supplied with fertilizer. Nine genotypes of durum wheat were chosen for their different morpho-phenological characteristics and year of their release. The isotopic tracer15 N was used to measure the fertilizer N uptake efficiency. The results show that durum wheat breeding did not have univocal effects on the characteristics of the root system (weight, length, specific root length, etc.) or N uptake capacity. The differences in N uptake among the studied genotypes when grown in conditions of low N availability appear to be related more to differences in uptake efficiency per unit of weight and length of the root system than to differences in the morphological root traits. The differences among the genotypes in the speed and the ability to take advantage of the greater N availability, determined by N fertilization, appear to a certain extent to be related to the development of the root system and the photosynthesizing area. This study highlights some variability within the species in terms of the development, distribution, and efficiency of the root system, which suggests that there may be sufficient grounds for improving these traits with positive effects in terms of adaptability to difficult environments and resilience to climate change
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Polyester microplastic fibers in soil increase nitrogen loss via leaching and decrease plant biomass production and N uptake
Full text linkMicroplastic contamination, like other global change factors, can induce effects on ecosystem functions and processes, affecting various soil biophysical properties. However, effects of such contaminants on nutrient cycles in agroecosystems are still poorly understood. We here performed two pot experiments to investigate the effect of polyester microplastic fibers (PMFs) on soil physical properties, nitrogen cycle, and plant performance in a maize-based agroecosystem. Moreover, we followed the N loss via leaching in soil contaminated or not with PMFs by simulating heavy rainfall events that mimic a future scenario of climate change. Our results show that soil contaminated with PMFs (at a concentration of 0.5% w/w) can jeopardize agroecosystem sustainability by affecting soil physical properties and in particular soil macro- and microporosity, the nitrogen cycle, and plant performance. In particular, we found that soil PMF contamination limited crop growth and N uptake by circa 30%, and consequently increased N loss via leaching. Overall, our findings show that soil contamination with PMFs may pose problems to future agricultural challenges like food security and environmental protection
Polypropylene microfibers negatively affect soybean growth and nitrogen fixation regardless of soil type and mycorrhizae presence
Full text linkRecent studies have indicated that soil contamination with microplastics (MPs) can negatively affect agricultural productivity, although these effects vary greatly depending on the context. Furthermore, the mechanisms behind these effects remain largely unknown. In this study, we examined the impact of two concentrations of polypropylene (PP) fibers in the soil (0.4 % and 0.8 % w/w) on soybean growth, nitrogen uptake, biological nitrogen fixation (BNF), and water use efficiency by growing plants in two soil types, with and without arbuscular mycorrhizal fungi (AMF). PP contamination consistently reduced vegetative growth (-12 %, on average compared to the control), with the severity of this effect varying significantly by soil type (more pronounced in Alfisol than in Vertisol). The extent of BNF progressively reduced with the increase in PP contamination level in both soils (on average, -17.1 % in PP0.4 and -27.5 % in PP0.8 compared to the control), which poses clear agro-environmental concerns. Water use efficiency was also reduced due to PP contamination but only in the Alfisol (-9 %, on average). Mycorrhizal symbiosis did not seem to help plants manage the stress caused by PP contamination, although it did lessen the negative impact on BNF. These findings are the first to demonstrate the effect of PP on BNF in soybean plants, underscoring the need to develop strategies to reduce PP pollution in the soil and to mitigate the impact of PP on the functionality and sustainability of agroecosystems
Mycorrhizae differentially influence the transfer of nitrogen among associated plants and their competitive relationships
Full text linkThe formation of a common mycorrhizal network among roots of different plant species growing close to each other can influence plant community dynamics, regulating plant relationships through the differential transfer of nutrients from one plant to another. However, knowledge of the mechanisms that regulate this process is poor. Here we quantify the contribution of arbuscular mycorrhizae to the transfer of N among heterospecific plants growing adjacent to each other and examine whether the differential transfer of N within the plant community via mycorrhizae can alter competitive relationships among plant species. Plants of four species (wheat, pea, flax, and chicory) were grown in four-compartment pots (one species per compartment) under three conditions: no belowground interaction permitted among the compartments (Clo-sys); belowground interaction limited to soil microorganisms (including arbuscular mycorrhizal [AM] fungi) and soil solution (Res-sys); and belowground interaction permitted, so the crossing of roots, soil microorganisms, and soil solution was allowed (Ope-sys). Each condition was tested in both the absence ( myc) and presence (+myc) of AM symbiosis. The transfer of N from pea to the three non-legume companion species (assessed via direct 15N labelling) was greater in Ope-sys than Res-sys for wheat and chicory but not for flax. In general, N transfer was greater in +myc than –myc in all species. In wheat the positive effects of AM symbiosis on N transfer were pronounced in Ope-sys but not in Res-sys, whereas in flax and chicory mycorrhization had similar effects in both Ope-sys and Res-sys. In Res-sys and in the absence of AM symbiosis, wheat intercepted about 50% of the total N transferred from pea, chicory about 40%, and flax about 10%. Mycorrhization altered these ratios, reducing the proportion of N transferred to wheat while increasing the proportion transferred to the other two species (especially to chicory), thus favouring the weakest components of the mixture. Similar effects of AM symbiosis were observed in Ope-sys. Our study shows that AM symbiosis affects the distribution of N and as a consequence the competitive relationships among adjacent plants of different species
Conventional tillage versus no-tillage: Nitrogen use efficiency component analysis of contrasting durum wheat genotypes grown in a Mediterranean environment
Full text linkVery little information is available for Mediterranean areas about the soil N dynamics and crop N use efficiency during the transition phase from conventional tillage (CT) to no-tillage (NT). Hence, a 2-yr experiment was conducted under semiarid Mediterranean conditions in three sites to study how soil N dynamics, crop N uptake, grain yield, and N use efficiency vary with N-fertilization rate and crop genotype in the switch year from CT to NT. Treatments consisted of two tillage systems (CT and NT), five N-fertilization rates (0, 40, 80, 120, and 160 kg N ha−1), and two durum wheat (Triticum durum Desf.) genotypes (one modern variety and one old landrace). Irrespective of the genotype, NT reduced compared to CT both wheat N uptake and grain yield under low soil N availability. The greater soil N supply under CT was the main reason for this outcome, so much so that the differences between CT and NT for these traits gradually decreased with the increase of N fertilization rate, practically disappearing at 80 kg N ha−1). The analysis of the N use efficiency components corroborated this hypothesis showing clearly that the yield advantage observed in CT depended mainly on the increase in N supply in soil under CT than NT condition. The two wheat genotypes responded similarly to varying soil tillage system. However, the adverse effects of NT practice were more evident in the modern variety than the old landrace. This study ultimately indicates that in the Mediterranean areas the switch year from CT to NT regime is rather delicate. Given that the lack of soil cultivation considerably reduces the soil N availability, hence, using NT technique alone as a substitute for CT is not agronomically feasible. Instead, an optimal application of NT is achievable by acting simultaneously on other factors of the cropping management, particularly the N-fertilization strategy, to maximize the crop N use efficiency and increase crop yield, which are essential requirements for a more sustainable agriculture
Nitrogen Type and Availability Drive Mycorrhizal Effects on Wheat Performance, Nitrogen Uptake and Recovery, and Production Sustainability
Full text linkPlant performance is strongly dependent on nitrogen (N), and thus increasing N nutrition is of great relevance for the productivity of agroecosystems. The effects of arbuscular mycorrhizal (AM) fungi on plant N acquisition are debated because contradictory results have been reported. Using 15N-labeled fertilizers as a tracer, we evaluated the effects of AM fungi on N uptake and recovery from mineral or organic sources in durum wheat. Under sufficient N availability, AM fungi had no effects on plant biomass but increased N concentrations in plant tissue, plant N uptake, and total N recovered from the fertilizer. In N-deficient soil, AM fungi led to decreased aboveground biomass, which suggests that plants and AM fungi may have competed for N. When the organic source had a low carbon-to-nitrogen ratio, AM fungi favored both plant N uptake and N recovery. In contrast, when the organic source had a high carbon-to-nitrogen ratio, a clear reduction in N recovery from the fertilizer was observed. Overall, the results indicate an active role of arbuscular mycorrhizae in favoring plant N-related traits when N is not a limiting factor and show that these fungi help in N recovery from the fertilizer. These results hold great potential for increasing the sustainability of durum wheat production
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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