77 research outputs found
OPTIMIZATION OF GREEN ROOF INSTALLATIONS IN THE MEDITERRANEAN CLIMATE
No full textLe coperture a verde pensile sono impianti vegetali realizzati sui tetti degli edifici mediante l'uso di una serie di stratigrafie specifiche. É stato dimostrato che i tetti verdi forniscono benefici ecologici, economici e sociali, ma l'applicazione della tecnologia è ancora poco diffusa nelle regioni a clima arido. Le attività di ricerca condotte nel corso della presente tesi hanno permesso di sviluppare nuovi criteri per la realizzazione di coperture a verde pensile in area mediterranea.
Per aumentare le capacità di ritenzione idrica del substrato, mantenendo spessori limitati, è stata valutata la possibilità di ricorrere a miscele di substrato e polimeri idrofili (SAP). I SAP hanno portato all’aumento della quantità di acqua disponibile per la vegetazione ottimizzando lo stato idrico delle piante di Salvia officinalis durante i periodi aridi, specialmente se cresciute su spessori di substrato limitati.
Essendo la riduzione degli spessori di substrato uno dei principali obiettivi della ricerca sul verde pensile, sono stati valutati lo stato idrico, l’evapotraspirazione e l’accrescimento di specie arbustive cresciute su spessori di substrato ridotti. I dati sperimentali hanno dimostrato come in condizioni di aridità lo stato idrico delle piante è risultato essere più favorevole nei sistemi caratterizzati da spessori ridotti, in quanto essi promuovono un minore accumulo di biomassa vegetale e quindi un minor consumo di acqua, se paragonati a spessori superiori.
Con l'obiettivo di dimostrare l'importanza della selezione delle specie vegetali accoppiata a una appropriata scelta del substrato, due specie arbustive sono state fatte crescere in due substrati che differivano in termini di caratteristiche di ritenzione idrica. I risultati hanno evidenziato come il tipo di substrato influenzi in maniera significativa lo stato idrico della vegetazione. Per approfondire le conoscenze sull'adattamento allo stress idrico della pianta modello S. officinalis è stato condotto uno studio ecofisiologico sulla specie, anche in ambiente naturale, che ha evidenziato come le foglie risultano essere più vulnerabili allo stress idrico in termini di perdita di efficienza di trasporto dell'acqua se paragonate ai fusti. Si può quindi concludere che la tolleranza alla aridità di S. officinalis è, almeno in parte, conseguenza della segmentazione idraulica.
Nelle regioni a clima mediterraneo, temperature elevate e deficit idrico impongono l’utilizzo nei sistemi a verde pensile di una vegetazione con buona tolleranza all’aridità e alle temperature estreme. Il presente lavoro, sulla base di uno studio che ha coinvolto 11 specie, vuole contribuire alla ottimizzazione del processo di selezione delle piante arbustive più idonee. Misure dello stato idrico, test di sopravvivenza su spessori di substrato ridotti e lo studio di parametri fisiologici, hanno evidenziato come i tratti che garantiscono efficienza/sicurezza al trasporto dell'acqua risultano essere buoni indicatori del tasso di accrescimento delle piante e del consumo dell’acqua, ma le alte temperature del substrato influenzano in maniera molto più significativa la sopravvivenza delle piante su un inverdimento pensile. La tolleranza specie-specifica dell'apparato radicale al calore, nonché la resistenza delle foglie allo stress idrico, sono caratteristiche funzionali essenziali per garantire un'adeguata copertura del verde pensile.
La tutela della biodiversità e la formazione di habitat sono due dei benefici ecologici apportati dalle coperture a verde pensile. Nel corso della ricerca sono stati analizzati lo sviluppo e la composizione floristica di coperture a piante erbacee e succulente sviluppate su volumi di substrato ridotti. L’utilizzo di una miscela di semi di specie erbacee ha permesso di ottenere una buona copertura del substrato e lo sviluppo di una comunità con elevata biodiversità
Plastic response of xylem anatomy to growth constraints and its effects on the vulnerability to embolism formation in Fraxinus ornus
No full textImpact of green roof layering on plant water status and drought survival
No full textThe influence of different green roof layering types on the amount of water available to plants was investigated in the specific climatic context of the Mediterranean region. Water status, productivity and survival rate of Salvia officinalis L. plants growing in experimental green roof modules were monitored between early spring and late summer. Experimental data showed that: (a) substrate and water retention layer retained respectively 34% and 90% in volume of water potentially available to plants; (b) water retention
layer had a positive effect on plant water status and survival; (c) the design of the overall green roof system, and in particular the characteristics of the drainage layer, influenced the amount of water transferred between different green roof elements, thus significantly influencing the amount of water available to plants. In particular, significant amounts of water were shown to be transferred from the retention layer
into the cavities of the plastic drainage layer in response to temperature fluctuations, leading to day/night cycles of water evaporation/condensation. Targeted modifications of the geometrical and technical features of drainage elements were shown to be potentially useful to improve plant survival during intense and/or prolonged drought events
Shoot desiccation and hydraulic failure in temperate woody angiosperms during an extreme summer drought
No full textPlant water status and hydraulics were measured in six woody angiosperms growing in a karstic woodland, during an extreme summer drought. Our aim was to take advantage of an unusual climatic event to identify key traits related to species-specific mortality risk.
The damage suffered by different species was assessed in terms of percentage of desiccated individuals. Stem water potential (Ystem) and loss of hydraulic conductivity (PLC) were measured in healthy and desiccated individuals. Vulnerability to cavitation was assessed in terms of stem water potential inducing 50% PLC (Y50). Wood density (WD) was also measured.
Species-specific percentage of desiccated individuals was correlated to Y50 and WD. Crown desiccation was more widespread in species with less negative Y50 and lower WD. Desiccated individuals had lower Ystem and higher PLC than healthy ones, suggesting that hydraulic failure was an important mechanism driving shoot dieback. Drought-vulnerable species showed lower safety margins (Ystem - Y50) than resistant ones.
Y50, safety margins and WD emerge as convenient traits to be used for tentative predictions of differential species-specific impact of extreme drought events on a local scale. The possibility that carbohydrate depletion was also involved in induction of desiccation symptoms is discussed
When smaller is better: leaf hydraulic conductance and drought vulnerability correlate to leaf size and venation density across four Coffea arabica L. genotypes
No full textLeaf hydraulic conductance (Kleaf) and drought vulnerability in terms of leaf water potential inducing 50% loss of Kleaf (P50), were assessed in four genotypes of Coffea arabica L. We tested three hypotheses: (1) leaf P50 is lower in small leaves with higher vein densities; (2) lower P50 translates into lower Kleaf, limiting gas exchange rates and higher leaf mass per unit area (LMA); (3) P50 values are coordinated with symplastic drought tolerance. We found partial support for Hypotheses 1 and 3, but not for Hypothesis 2. Significant correlations existed among leaf size, vein network and drought resistance. Smaller leaves displayed higher major vein density, higher Kleaf and more negative P50. Kleaf was correlated with leaf gas exchange rates. A negative relationship was observed between Kleaf and LMA, whereas P50 was found to be positively correlated with LMA. Across coffee genotypes, reduced leaf surface area and increased vein density shifts P50 towards more negative values while not translating into higher LMA or lower Kleaf. Breeding crop varieties for both increased safety of the leaf hydraulic system towards drought-induced dysfunction and high gas exchange rates per unit of leaf area is probably a feasible target for future adaptation of crops to climate change scenarios
Un giardino per Pegaso: verde pensile mediterraneo
No full textLa realizzazione di coperture a verde pensile nell’area mediterranea richiede un approccio basato sulla conoscenza della risposta delle piante allo stress idrico e della capacità delle stratigrafie utilizzate di garantire adeguate quantità di acqua effettivamente disponibile per la vegetazione. Recenti studi relativi allo stato termodinamico dell’acqua nelle piante e nei diversi componenti delle stratigrafie invitano a considerare da nuove prospettive la progettazione del verde pensile mediterraneo
Droughts, heat waves and plant hydraulics: impacts and legacies
No full textExtreme drought events accompanied by heat waves are posing a serious threat to tree survival in several forest biomes. Drought-induced tree mortality is thought to be driven by both hydraulic failure caused by extensive xylem embolism, and carbon starvation induced by prolonged stomatal closure to prevent or in response to massive
xylem cavitation. Biotic attacks frequently accompany the terminal phases of tree decline and death. In this paper, we discuss the potential legacies of extreme droughts on plants’ vulnerability to successive stress events. By revising the current literature and presenting data recently obtained on Fraxinus ornus L., we argue that extreme droughts
imply an hydraulic legacy in terms of increased vulnerability to cavitation and decreased hydraulic efficiency, possibly leading to long-term reduction of photosynthetic rates and further depletion of non-structural carbohydrates (NSC) pools. In turn, the ‘energetic’ legacy of reduced NSC availability is hypothesized to impair mechanisms underlying
embolism repair, thus potentially exacerbating the hydraulic legacies. Future studies are called to elucidate the feedback and loops underlying progressive degradation of the hydraulic and metabolic networks of plants
Consistent decrease in conifer embolism resistance from the stem apex to base resulting from axial trends in tracheid and pit traits
No full textIntroduction: Drought-induced embolism formation in conifers is associated
with several tracheid and pit traits, which vary in parallel from stem apex to base.
We tested whether this axial anatomical variability is associated with a progressive
variation in embolism vulnerability along the stem from apex to base.
Methods: We assessed the tracheid hydraulic diameter (Dh), mean pit membrane
area (PMA) and the xylem pressure at 50% loss of conductivity (P50) on
longitudinal stem segments extracted at different distances from the stem apex
(DFA) in a Picea abies and an Abies alba tree.
Results: In both trees, Dh and PMA scaled with DFA0.2. P50 varied for more than 3
MPa fromthe treetop to the stembase, according to a scaling of -P50 with DFA-0.2.
The largest Dh, PMA and P50 variation occurred for DFA<1.5 m. PMA and Dh scaled
more than isometrically (exponent b=1.2). Pit traits vary proportionally with
tracheid lumen diameter.
Discussion and conclusions: Apex-to-base trends in tracheid and pit traits, along
with variations in P50, suggest a strong structure-function relationship that is
influenced by DFA. Although the effect of DFA on P50 has not been extensively
explored previously, we propose that analyzing the relationship between P50 and
DFA could be crucial for a comprehensive assessment of embolism vulnerability
at the individual level
Make it simpler: alien species decrease functional diversity of coastal plant communities
No full textQuestions: 1) Are there differences in abundance-weighted functional trait values between native and alien species in coastal plant communities? 2) Which functional traits are associated with a higher level of invasion in these communities? 3) Do functional diversity patterns differ between native and alien species? 4) Is alien species occurrence linked to small-scale functional homogenization effects on the resident native species? Location: N-Adriatic coastal ecosystems (Marano and Grado lagoon, Friuli Venezia Giulia region, Italy) Methods: We sampled coastal vegetation within two habitats (foredunes and saltmarshes) along 9 belt transects in two sampling sites. Plant species richness and abundance were assessed in 128 plots along with a suite of plant functional traits. We tested for differences in CWMs between native and alien species within the two habitats, and a Linear Mixed Model (LMMs) provided insights on traits fostering the invasion success among alien species. To check for potential functional homogenization driven by alien species invasion, we explored functional diversity patterns of native and alien species (alpha and beta functional diversity) and the relationship between alpha functional diversity and alien cover. Results: Alien species had lower functional diversity than natives and were characterized by lower leaf construction costs coupled with lower drought resistance and higher water transport efficiency. The most abundant aliens were the ones minimizing carbon investment for leaf construction. In addition, we also found evidence for small-scale functional homogenization driven by alien invasion. Conclusions: Our results suggested that native species adopt a resource conservative strategy whereas alien species are characterized by a higher resource acquisition capacity (i.e. acquisitive strategy). Our data also confirmed that alien species are less functionally diverse than natives, Functional diversity of coastal plant communities potentially driving the community towards small-scale functional homogenization, resulting in a loss of species and a reduction in the functional space
Drought Stress and the Recovery from Xylem Embolism in Woody Plants
No full textWater is transported from roots to foliage through the xylem under negative pressure (= tension). Under this metastable status, water is prone to sudden phase change to water vapor (cavitation). In plants, air can also be aspirated into functioning xylem conduits through inter-conduit pit membranes, and the resulting embolism blocks water transport through the conduit and reduces plant hydraulic conductance and productivity. Xylem embolism and hydraulic failure are major factors contributing to tree mortality and forest decline under global-change-type droughts. However, some plants can tolerate even high embolism levels under drought, recovering hydraulic functionality upon partial or total rehydration via embolism repair and xylem refilling. Here, we review current evidence of embolism repair, highlighting possible physiological mechanisms and suggesting some functional and anatomical determinants making embolism reversal a feasible and successful drought resilience mechanism in some plants
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