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- Climate models predict a further drying of the Mediterranean summer. One way for plant species to persist during such climate changes is through acclimation. Here, we determine the extent to which trait plasticity in response to drought differs between species and between sites, and address the question whether there is a trade‐off between drought survival and phenotypic plasticity.
- Throughout the summer we measured physiological traits (photosynthesis – Amax, stomatal conductance – gs, transpiration – E, leaf water potential – ψl) and structural traits (specific leaf area – SLA, leaf density – LD, leaf dry matter content – LDMC, leaf relative water content – LRWC) of leaves of eight woody species in two sites with slightly different microclimate (north‐ versus south‐facing slopes) in southern Spain. Plant recovery and survival was estimated after the summer drought period.
- We found high trait variability between species. In most variables, phenotypic plasticity was lower in the drier site. Phenotypic plasticity of SLA and LDMC correlated negatively with drought survival, which suggests a trade‐off between them. On the other hand, high phenotypic plasticity of SLA and LDMC was positively related to traits associated with rapid recovery and growth after the drought period.
- Although phenotypic plasticity is generally seen as favourable during stress conditions, here it seemed beneficial for favourable conditions. We propose that in environments with fluctuating drought periods there can be a trade‐off between drought survival and growth during favourable conditions. When climate become drier, species with high drought survival but low phenotypic plasticity might be selected for.
Background
Environmental stress is widely considered to be an important factor in regulating whether changes in diversity will affect the functioning and stability of ecological communities.Methodology/Principal Findings
We investigated the effects of a major environmental stressor (a decrease in water volume) on diversity-abundance and diversity-stability relations in laboratory microcosms composed of temperate multi-trophic rock pool communities to identify differences in community and functional group responses to increasing functional group richness along a gradient of environmental stress (low, medium, and high water volume). When a greater number of functional groups were present, communities were less temporally variable and achieved higher abundances. The stabilizing effect of increased functional group richness was observed regardless of the level of environmental stress the community was subjected too. Despite the strong consistent stabilizing effect of increased functional group richness on abundance, the way that individual functional groups were affected by functional group richness differed along the stress gradient. Under low stress, communities with more functional groups present were more productive and showed evidence of strong facilitative interactions. As stress increased, the positive effect of functional group richness on community abundance was no longer observed and compensatory responses became more common. Responses of individual functional groups to functional group richness became increasing heterogeneous are stress increased, prompting shifts from linear diversity-variability/abundance relations under low stress to a mix of linear and non-linear responses under medium and high stress. The strength of relations between functional group richness and both the abundances and temporal variability of functional groups also increased as stress increased.Conclusions/Significance
While stress did not affect the relation between functional group richness and stability per se, the way in which functional groups responded to changes in functional group richness differed as stress increased. These differences, which include increases in the heterogeneity of responses of individual functional groups, increases in compensatory dynamics, and increases in the strength of richness-abundance and richness-variability relations, may be critical to maintaining stability under increasingly stressful environmental conditions. 相似文献Aims
We assessed the temporal changes on microbial biomass in relation to changes in soil moisture, dissolved organic carbon and plant biomass during the summer season in a Mediterranean high-mountain grassland.Methods
Temporal variations were tested by two-way ANOVA. The relationships among microbial biomass, plant biomass, soil water content, soil organic carbon, dissolved organic carbon and total soil nitrogen during the summer season were assessed by means of structural equation modeling.Results
Microbial biomass did not show variation, while dissolved organic carbon and root biomass decreased throughout the summer. Aboveground plant biomass peaked in the middle of the summer, when soil water content was at its minimum. Soil water content directly and negatively affected soil microbial biomass, and positively affected dissolved organic carbon. Moreover soil microbial biomass and dissolved organic carbon were negatively related. Plant biomass effects on soil microbial biomass were driven by root biomass, which indirectly affected soil microbial biomass through effects on soil organic carbon and soil nitrogen.Conclusions
The temporal dynamic of microbial biomass during the summer season appeared to differ from previous observations in temperate alpine communities, and indicated the drought resistance of the microbial community during the summer in Mediterranean high-mountain grasslands. During the dry period, microbial biomass may play an alternative role in soil carbon conservation. 相似文献Questions
Rhododendron ponticum subsp. baeticum is an invasive shrub of growing concern in continental Europe, but little is known about its impact on native plant communities. Here we ask: do environmental conditions differ between forest stands invaded by it and uninvaded stands? Do these differences correlate with R. ponticum's cover? Are these differences associated with differences in taxonomic and functional diversity of vascular plant species of the herb layer? Can these vegetation changes be explained by the sorting of certain life-history traits by R. ponticum-induced environmental changes?Location
Several forests invaded by R. ponticum in the French Atlantic domain.Methods
We recorded vegetation composition and a number of environmental variables in 400-m2 plots that were established in 64 paired forest stands (32 invaded vs 32 uninvaded). We compiled traits from existing databases. We computed several metrics of taxonomic and functional diversity. We compared environmental variables and diversity metrics between invaded and uninvaded stands. We used correlation and regression analyses to relate them with R. ponticum's cover. We ran RLQ and fourth-corner analyses to explore the relationships between R. ponticum invasion, environmental variables, species traits, and vegetation composition.Results
Independent of its abundance, R. ponticum invasion was associated with lower light arrival at the forest floor and increased litter thickness. Concomitantly, species richness and diversity and trait diversity were reduced. The major driver of species assemblages was soil pH, which strongly interacted with the invasion gradient. R. ponticum did not sort species according to traits associated with shade tolerance and thick-litter tolerance. However, tree and shrub saplings were more abundant in invaded than uninvaded stands, at the expense of graminoid and fern species.Conclusions
As R. ponticum becomes the dominant shrub, it exerts new selection forces on life-history traits of extant species, mostly via reduced light availability, increased litter thickness, and physical competition, thereby reducing taxonomic and functional diversity of the herb layer, without impeding tree and shrub self-regeneration, at least in the short term. 相似文献Background
In the Mediterranean climate, plants have evolved under conditions of low soil-water and nutrient availabilities and have acquired a series of adaptive traits that, in turn exert strong feedback on soil fertility, structure, and protection. As a result, plant-soil systems constitute complex interactive webs where these adaptive traits allow plants to maximize the use of scarce resources.Scope
It is necessary to review the current bibliography to highlight the most know characteristic mechanisms underlying Mediterranean plant-soil feed-backs and identify the processes that merit further research in order to reach an understanding of the plant-soil feed-backs and its capacity to cope with future global change scenarios. In this review, we characterize the functional and structural plant-soil relationships and feedbacks in Mediterranean regions. We thereafter discuss the effects of global change drivers on these complex interactions between plants and soil.Conclusions
The large plant diversity that characterizes Mediterranean ecosystems is associated to the success of coexisting species in avoiding competition for soil resources by differential exploitation in space (soil layers) and time (year and daily). Among plant and soil traits, high foliar nutrient re-translocation and large contents of recalcitrant compounds reduce nutrient cycling. Meanwhile increased allocation of resources to roots and soil enzymes help to protect against soil erosion and to improve soil fertility and capacity to retain water. The long-term evolutionary adaptation to drought of Mediterranean plants allows them to cope with moderate increases of drought without significant losses of production and survival in some species. However, other species have proved to be more sensitive decreasing their growth and increasing their mortality under moderate rising of drought. All these increases contribute to species composition shifts. Moreover, in more xeric sites, the desertification resulting from synergic interactions among some related process such as drought increases, torrential rainfall increases and human driven disturbances is an increasing concern. A research priority now is to discern the effects of long-term increases in atmospheric CO2 concentrations, warming, and drought on soil fertility and water availability and on the structure of soil communities (e.g., shifts from bacteria to fungi) and on patching vegetation and root-water uplift (from soil to plant and from soil deep layers to soil superficial layers) roles in desertification. 相似文献Background and Aims
Summer dormancy is an adaptive trait in geophytes inhabiting regions with a Mediterranean climate, allowing their survival through the hot and dry summers. Summer dormancy in Poa bulbosa is induced by increasing day-length and temperature and decreasing water availability during spring. Populations from arid habitats became dormant earlier than those from mesic habitats. Relaxation of dormancy was promoted by the hot, dry summer conditions. Here we test the hypothesis that dormancy relaxation is also delayed in ecotypes of P. bulbosa inhabiting arid regions, as a cautious strategy related to the greater unpredictability of autumn rains associated with decreasing precipitation.Methods
Ecotypes collected across a precipitation gradient (100–1200 mm year−1) in the Mediterranean climate region were grown under similar conditions in a net-house in Israel. Differences among ecotypes in dormancy induction and dormancy relaxation were determined by measuring time to dormancy onset in spring, and time to sprouting after the first effective rain in autumn. Seasonal and ecotype variation in dormancy relaxation were assessed by measuring time to sprouting initiation, rate of sprouting and maximal sprouting of resting dry bulbs sampled in the net-house during late spring, and mid- and late summer, and planted in a wet substrate at temperatures promoting (10 °C) or limiting (20 °C) sprouting.Key Results
Earlier dormancy in the spring and delayed sprouting in autumn were correlated with decreasing mean annual rainfall at the site of ecotype origin. Seasonal and ecotype differences in dormancy relaxation were expressed in bulbs planted at 20 °C. During the summer, time to sprouting decreased while rate of sprouting and maximal sprouting increased, indicating dormancy relaxation. Ecotypes from more arid sites across the rainfall gradient showed delayed onset of sprouting and lower maximal sprouting, but did not differ in rate of sprouting. Planting at 10 °C promoted sprouting and cancelled differences among ecotypes in dormancy relaxation.Conclusions
Both the induction and the relaxation of summer dormancy in P. bulbosa are correlated with mean annual precipitation at the site of population origin. Ecotypes from arid habitats have earlier dormancy induction and delayed dormancy relaxation, compared with those from mesic habitats. 相似文献Key message
Warmer summer conditions result in increased terpene emissions except under severe drought, in which case they strongly decrease.Abstract
Water stress results in a reduction of the metabolism of plants and in a reorganization of their use of resources geared to survival. In the Mediterranean region, periods of drought accompanied by high temperatures and high irradiance occur in summer. Plants have developed various mechanisms to survive in these conditions by resisting, tolerating or preventing stress. We used three typical Mediterranean tree species in Israel, Pinus halepensis L., Quercus calliprinos and Quercus ithaburensis Webb, as models for studying some of these adaptive mechanisms. We measured their photosynthetic rates (A), stomatal conductance (g s), and terpene emission rates during spring and summer in a geophysical gradient from extremely dry to mesic from Yatir (south, arid) to Birya (north, moist) with intermediate conditions in Solelim. A and g s of P. halepensis were threefold higher in Birya than in Yatir where they remained very low both seasons. Quercus species presented 2–3-fold higher A and g s but with much more variability between seasons, especially for Q. ithaburensis with A and g s that decreased 10–30-fold from spring to summer. Terpene emission rates for pine were not different regionally in spring but they were 5–8-fold higher in Birya than in Yatir in summer (P < 0.05). Higher emissions were also observed in Solelim for the drought resistant Q. ithaburensis (P < 0.001) but not for Q. calliprinos. α-Pinene followed by limonene and 3-carene were the dominant terpenes. Warmer summer conditions result in increased Terpene emission rates except under severe drought, in which case they strongly decrease.Questions
Knowledge of how extreme drought events induce plant dieback and, eventually, plant mortality, may improve our forecasting of ecosystem change according to future climate projections, especially in Mediterranean drylands. In them, shrublands are the main vegetation communities in transition areas from a subhumid to semi-arid climate. This study analyzed differences in plant dieback after an unusual drought in 2014 and identified their main underlying factors in relation to three groups of explanatory variables: water availability, soil properties and vegetation structure attributes.Location
Four Mediterranean shrublands along a climatic gradient in SE Spain.Methods
At each experimental field site, we sampled a pool of vegetation structure characteristics, soil depth and soil surface properties, and we also determined water availability by continuously monitoring soil moisture and the microclimate conditions.Results
The climatic analysis showed that there was an extreme drought event in 2014, which was below the first percentile of the driest years. Under such conditions, vegetation dieback occurred at all the study sites. However, plant dieback differed between sites and plant biotypes. Subshrubs were the main affected biotype, with diebacks close to 60% at the driest sites, and up to 40% dieback for shrubs depending on their vertical development. Relative extractable water and bare soil surface cover were the best explanatory variables of plant community dieback but changed between plant biotypes. Vegetation structure variables related to plant vertical development (leaf area index [LAI], plant height, phytovolume) were significant explanatory variables of plant dieback in shrubs, subshrubs and grasses. Consecutive dry days fitted the best model to explain subshrub dieback.Conclusions
We found that rainfall pattern rather than total annual rainfall was the climatic factor that best determined water availability for plants in Mediterranean drylands. These results also pointed out the relevance of plant structure and soil properties for explaining ecosystem responses to extreme drought. 相似文献Climate change models predict a strong reduction of average precipitation, especially of the summer rainfall, and an increase in intensity and frequency of drought events in the Mediterranean region. The research aim was to understand how four dominant grass species (Arrhenatherum elatius, Cynosurus cristatus, Elymus repens, and Lolium perenne) in sub-Mediterranean meadows (central Apennines, Italy) modulate their resource acquisition and conservation strategies to short-term variation of the pattern of summer water supply. During summer 2016, using a randomized block design, we tested the effect of three patterns of summer water supply, differing in water amount and watering frequency, on leaf area, leaf dry mass, specific leaf area (SLA), leaf senescence, and plant height. Our results showed that dominant grass species can modulate their strategies to variation of the pattern of summer water supply, but the response of leaf traits and plant height is mediated by the set of functional characteristics of the species. E. repens and A. elatius, with summer green leaves, lower SLA, later flowering period, and deeper roots, were less influenced by changes in water amount. C. cristatus and L. perenne, which display acquisitive strategies (persistent leaves, higher SLA values), earlier flowering, and shallower roots were more influenced by changes in the pattern of summer water supply. Our results suggest that a short-term decrease in water availability might affect primarily species with trait syndromes less adapted to face summer drought.
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