Community-specific hydraulic conductance potential of soil water decomposed for two Alpine grasslands by small-scale lysimetry

For central Europe in addition to rising temperatures an increasing variability in precipitation is predicted. This will increase the probability of drought periods in the Alps, where water supply has been sufficient in most areas so far. For Alpine grasslands, community-specific imprints on drought responses are poorly analyzed so far due to the sufficient natural water supply. In a replicated mesocosm experiment we compared evapotranspiration (ET) and biomass productivity of two differently drought-adapted Alpine grassland communities during two artificial drought periods divided by extreme precipitation events using high-precision small lysimeters. The drought-adapted vegetation type showed a high potential to utilize even scarce water resources. This is combined with a low potential to translate atmospheric deficits into higher water conductance and a lower biomass production as those measured for the non-drought-adapted type. The non-drought-adapted type, in contrast, showed high water conductance potential and a strong increase in ET rates when environmental conditions became less constraining. With high rates even at dry conditions, this community appears not to be optimized to save water and might experience drought effects earlier and probably more strongly. As a result, the water use efficiency of the drought-adapted plant community is with 2.6 gDW kg−1 of water much higher than that of the non-drought-adapted plant community (0.16 gDW kg−1). In summary, the vegetation's reaction to two covarying gradients of potential evapotranspiration and soil water content revealed a clear difference in vegetation development and between water-saving and water-spending strategies regarding evapotranspiration

Vegetation effects on the water balance of mountain grasslands depend on climatic conditions

Mountain regions are key for humanity's water supply, and their water yield depends on climatic, soil and vegetation effects. Here we explore the effects of vegetation composition and structure on the water balance of high elevation grasslands with different climatic conditions across the Alps. Using a total of 220 deep seepage collectors with intact soil-vegetation monoliths in different types of mountain grasslands in the Austrian, French and Swiss Alps, we solved the water balance equation for evapotranspiration (ET) and related the results to biomass, the abundance of certain plant functional types and structural and functional vegetation properties. While daily mean ET during the growing season was similar at all sites, ET to precipitation ratios were significantly higher and ET to potential ET ratios significantly lower at the drier French sites than at the more humid Swiss and Austrian site. Large variability of ET, seepage and soil moisture within all sites pointed at a high influence of vegetation on the water balance. While ET increased significantly with biomass at all sites, the influence of other vegetation properties was site specific. At the more humid, subalpine Austrian site the effects of vegetation on ET were stronger and more diverse than at the higher elevation Swiss site and the drier French sites, where climatic drivers dominated ET. The potential to influence ET and water yield of mountain areas by manipulating the plant canopy with systematic land management is therefore higher in regions with good growing conditions than in areas with harsh climate

The 2018 European heatwave led to stem dehydration but not to consistent growth reductions in forests

Heatwaves exert disproportionately strong and sometimes irreversible impacts on forest ecosystems. These impacts remain poorly understood at the tree and species level and across large spatial scales. Here, we investigate the effects of the record-breaking 2018 European heatwave on tree growth and tree water status using a collection of high-temporal resolution dendrometer data from 21 species across 53 sites. Relative to the two preceding years, annual stem growth was not consistently reduced by the 2018 heatwave but stems experienced twice the temporary shrinkage due to depletion of water reserves. Conifer species were less capable of rehydrating overnight than broadleaves across gradients of soil and atmospheric drought, suggesting less resilience toward transient stress. In particular, Norway spruce and Scots pine experienced extensive stem dehydration. Our high-resolution dendrometer network was suitable to disentangle the effects of a severe heatwave on tree growth and desiccation at large-spatial scales in situ, and provided insights on which species may be more vulnerable to climate extremes

Phenotypic plasticity of European larch radial growth and wood density along a‐1,000 m elevational gradient

Phenotypic plasticity is a key mechanism for sedentary long-living species to adjust to changing environment. Here, we use mature Larix decidua tree-ring variables collected along an elevational transect in the French Alps to characterize the range of individual plastic responses to temperature. Stem cores from 821 mature Larix decidua trees have been collected from four plots distributed along a 1,000-m elevational gradient in a natural forest to build up individual linear reaction norms of tree-ring microdensity traits to temperature. The sign, magnitude and spread of variations of the slopes of the individual reaction norms were used to characterize variation of phenotypic plasticity among plots and traits. Results showed a large range of phenotypic plasticity (with positive and negative slopes) at each elevational plot and for each tree-ring variable. Overall, phenotypic plasticity tends to be larger but positive at higher elevation, negative at the warmer lower sites, and more variable in the center of the elevation distribution. Individual inter-ring reaction norm is a valuable tool to retrospectively characterize phenotypic plasticity of mature forest trees. This approach applied to Larix decidua tree-ring micro-density traits along an elevation gradient showed the existence of large inter-individual variations that could support local adaptation to a fast-changing climate.Estación Experimental Agropecuaria BarilocheFil: Escobar Sandoval, Margarita. Institut National de la Recherche Agronomique (INRA); FranciaFil: Pâques, Luc. Institut National de la Recherche Agronomique (INRA); FranciaFil: Fonti, Patrick. Swiss Federal Institute for Forest Snow and Landscape Research; SuizaFil: Martinez Meier, Alejandro. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bariloche. Área de Recursos Forestales. Grupo de Ecología Forestal; ArgentinaFil: Rozenberg, Philippe. Institut National de la Recherche Agronomique (INRA); Franci