Water stress limits transpiration and growth of European larch up to the lower subalpine belt in an inner-alpine dry valley.

Climate change will further constrain water availability in dry inner-alpine environments and affect water relations and growth conditions in mountain forests, including the widespread larch forests. To estimate the effects of climate conditions on water balance and growth, variation in sap flow and stem radius of European larch was measured for 3 yr along an elevation transect from 1070 to 2250 m above sea level (asl) in an inner-alpine dry valley in South Tyrol/Italy. Additionally, long-term climate-growth relations were derived from tree cores. Sap flow and radial growth were reduced in dry periods up to an elevation of 1715 m, leading to maximum annual growth at 2000 m. In a wet year no growth difference between elevations was observed. Long-term tree ring data showed a positive growth response to precipitation up to 1715 m and to temperature only above 2000 m. Our results demonstrate that reduced water availability and higher atmospheric water demand limit larch at low elevation within dry Alpine regions. This indicates a general upward shift of this species' elevational amplitude upon climate change, and respective negative effects on future silvicultural use and ecosystem services at lower elevations in the European Alps.

Soil Respiration in European Grasslands in Relation to Climate and Assimilate Supply.

Soil respiration constitutes the second largest flux of carbon (C) between terrestrial ecosystems and the atmosphere. This study provides a synthesis of soil respiration (R(s)) in 20 European grasslands across a climatic transect, including ten meadows, eight pastures and two unmanaged grasslands. Maximum rates of R(s) (R(s(max) )), R(s) at a reference soil temperature (10°C; R(s(10) )) and annual R(s) (estimated for 13 sites) ranged from 1.9 to 15.9 µmol CO(2) m(-2) s(-1), 0.3 to 5.5 µmol CO(2) m(-2) s(-1) and 58 to 1988 g C m(-2) y(-1), respectively. Values obtained for Central European mountain meadows are amongst the highest so far reported for any type of ecosystem. Across all sites R(s(max) ) was closely related to R(s(10) ).Assimilate supply affected R(s) at timescales from daily (but not necessarily diurnal) to annual. Reductions of assimilate supply by removal of aboveground biomass through grazing and cutting resulted in a rapid and a significant decrease of R(s). Temperature-independent seasonal fluctuations of R(s) of an intensively managed pasture were closely related to changes in leaf area index (LAI). Across sites R(s(10) ) increased with mean annual soil temperature (MAT), LAI and gross primary productivity (GPP), indicating that assimilate supply overrides potential acclimation to prevailing temperatures. Also annual R(s) was closely related to LAI and GPP. Because the latter two parameters were coupled to MAT, temperature was a suitable surrogate for deriving estimates of annual R(s) across the grasslands studied. These findings contribute to our understanding of regional patterns of soil C fluxes and highlight the importance of assimilate supply for soil CO(2) emissions at various timescales.