Plant Responses to Drought Under Climate Change in Mediterranean-Type Ecosystems

Competitor densities, habitat, and weather: effects on interspecific interactions between wild deer species

There is a growing interest on the potential interplay between weather, habitat, and interspecific competition on population dynamics of wild herbivores. Favorable environmental conditions may buffer the negative effects of competition; conversely, competition may be expected to be stronger under harsh environmental conditions. We investigated relationships between competitor abundance, weather, and habitat cover on density and local distribution of a medium‐sized herbivore, the roe deer Capreolus capreolus, as well as its spatial overlap with fallow deer Dama dama in a Mediterranean protected area. Over 11 years (2007–2017), roe deer density was not affected by spring–summer rainfall in the previous year and decreased with increasing density of fallow deer in the previous year. Hence, over the considered temporal scale, results supported a major role of competition over weather in influencing population trends of roe deer. At a finer spatial scale, roe deer occupancy was negatively affected by local abundance of fallow deer, especially in “poorer” habitats. We found a slight support for a positive effect of fallow deer density on interspecific spatial overlap. Moreover, fine‐scale spatial overlap between deer species increased with decreasing rainfall in spring–summer. Fallow deer were introduced to our study area in historical times and their role as superior competitors over roe deer has been found also in other study areas. We suggest a potential role of harsh weather conditions during the growing season of vegetation (i.e. scarce rainfall) in triggering the potential for ecological overlap, emphasizing the negative effects of interspecific competition.

Drought effect on plant biomass allocation: A meta-analysis

Drought is one of the abiotic stresses controlling plant function and ecological stability. In the context of climate change, drought is predicted to occur more frequently in the future. Despite numerous attempts to clarify the overall effects of drought stress on the growth and physiological processes of plants, a comprehensive evaluation on the impacts of drought stress on biomass allocation, especially on reproductive tissues, remains elusive. We conducted a meta-analysis by synthesizing 164 published studies to elucidate patterns of plant biomass allocation in relation to drought stress. Results showed that drought significantly increased the fraction of root mass but decreased that of stem, leaf, and reproductive mass. Roots of herbaceous plants were more sensitive to drought than woody plants that reduced reproductive allocation more sharply than the former. Relative to herbaceous plants, drought had a more negative impact on leaf mass fraction of woody plants. Among the herbaceous plants, roots of annuals responded to drought stress more strongly than perennial herbs, but their reproductive allocation was less sensitive to drought than the perennial herbs. In addition, cultivated and wild plants seemed to respond to drought stress in a similar way. Drought stress did not change the scaling exponents of the allometric relationship between different plant tissues. These findings suggest that the allometric partitioning theory, rather than the optimal partitioning theory, better explains the drought-induced changes in biomass allocation strategies.

Environmental alterations in biofuel generating molecules in Zilla spinosa

Now days, production of fuels and petrochemicals from renewable lignocellulosic biomass is an indispensable issue to meet the growing energy demand. Meanwhile, the changes in the climate and soil topography influence the growth and development as well as canopy level of the lignocellulosic biomass. In this study, Zilla spinosa Turr (Zilla) plants with similar age and size were collected from three main sectors (upstream, midstream, and downstream) of Wadi Hagul during spring (April) and summer (July) seasons. Environmental stresses evoked reduction in the energy trapping pigments concomitant with increments in chlorophyll fluorescence in summer harvested plants particularly at downstream. Furthermore, the biofuels generating compounds including carbohydrate, lignin, and lipid making the plant biomasses are greatly affected by environmental conditions. Greater amount of lignin was estimated in summer harvested Z. spinosa shoots particularly at downstream. Moreover, the total oil content which is a promising source of biodiesel was considerably decreased during summer season particularly at downstream. The physical properties of the lipids major constituent fatty acid methyl esters determine the biofuel properties and contribute in the adaptation of plants against environmental stresses. Hence, the analysis of fatty acid profile showed significant modifications under combined drought and heat stress displayed in the summer season. The maximum increase in saturated fatty acid levels including tridecanoic acid (C13:0), pentadeanoic acid (C15:0), palmitic acid (C16:0), and stearic acid (C18:0) were estimated in spring harvested Z. spinosa aerial portions particularly at midstream. In spite of the reduction in the total oil content, a marked increase in the value of unsaturated to saturated fatty acids ratio and thereby the unsaturation index were achieved during the dry summer period. Henceforth, these seasonal and spatial variations in fatty acids profiles may contribute in the acclimatization of Z. spinosa plants to soil water scarcity associated with heat stress experienced during summer. In addition, the alterations in the fatty acid profiles may match biofuel requirements. In conclusion, the most adequate growing season (spring) will be decisive for achieving high lipid productivity associated with improved biofuel quality in terms of high saturated fatty acids percentage that improves its cetane number. However, the dry summer season enhanced the accumulation of greater amount of lignin that may enhance the biodiesel quantity.

Diurnal and seasonal variations in the photosynthetic performance and water relations of two co-occurring Mediterranean shrubs, Erica multiflora and Globularia alypum

Diurnal and seasonal fluctuations in the photosynthetic performance and water relations of two co-occurring Mediterranean shrubs, Erica multiflora and Globularia alypum were monitored throughout two consecutive years at Garraf Natural Park in north-east Spain. Leaf gas exchange rates, chlorophyll fluorescence and shoot water potentials were measured once each season. Leaf nitrogen and carbon concentrations, leaf delta13C and delta15N and specific leaf area (SLA) were also measured once a year (August) on well developed mature leaves. Globularia alypum experienced seasonal fluctuations in their water potential, with the lowest values recorded in summer, whereas E. multiflora did not show significant differences in water potential among seasons. Moreover, lower water potentials were found in G. alypum than in E. multiflora throughout the entire study, suggesting that the latter behaved as a drought-avoiding species, whereas the former tolerated lower water potentials. In both species, maximum leaf gas exchange rates were observed in autumn and secondarily in spring; in contrast, photosynthetic and transpiration rates reached absolute minima in summer. The stronger fluctuations in water potential and leaf gas exchange rates found in G. alypum compared to E. multiflora, suggest that G. alypum is, sensu Levitt (1980), a water spender, whereas E. multiflora is a water conservative. This hypothesis is further supported by a higher integrated water-use efficiency (higher delta13C values) and a higher degree of sclerophylly (lower SLA) in E. multiflora in comparison with G. alypum. Globularia alypum showed higher leaf gas exchange rates and higher predawn potential photochemical efficiency (Fv/Fm) than E. multiflora during most of the study. In spring and autumn, predawn Fv/Fm values were within the optimal range, whereas chronic photoinhibition in summer and winter was detected in both species. However, whereas both species could maintain positive photosynthetic rates in winter, frequent negative values were found in summer, suggesting higher levels of stress during the drought period. These results together with the high correlations that were found between the net photosynthetic rates and several parameters of water availability (accumulated rainfall, soil moisture or midday water potential) provided further evidence of the key role of water availability in the regulation of the photosynthetic rates in these Mediterranean species. Warmer and drier conditions in future decades, as a consequence of climate change, may alter the present, slight competitive advantage of G. alypum and the fitness of both shrub species within semi-arid Mediterranean environments.

Identification, measurement and interpretation of tree rings in woody species from mediterranean climates

We review the literature dealing with mediterranean climate, vegetation, phenology and ecophysiology relevant to the understanding of tree-ring formation in mediterranean regions. Tree rings have been used extensively in temperate regions to reconstruct responses of forests to past environmental changes. In mediterranean regions, studies of tree rings are scarce, despite their potential for understanding and predicting the effects of global change on important ecological processes such as desertification. In mediterranean regions, due to the great spatio-temporal variability of mediterranean environmental conditions, tree rings are sometimes not formed. Often, clear seasonality is lacking, and vegetation activity is not always associated with regular dormancy periods. We present examples of tree-ring morphology of five species (Arbutus unedo, Fraxinus ornus, Quercus cerris, Q. ilex, Q. pubescens) sampled in Tuscany, Italy, focusing on the difficulties we encountered during the dating. We present an interpretation of anomalies found in the wood structure and, more generally, of cambial activity in such environments. Furthermore, we propose a classification of tree-ring formation in mediterranean environments. Mediterranean tree rings can be dated and used for dendrochronological purposes, but great care should be taken in selecting sampling sites, species and sample trees.