Effects of land use and climate on carbon and nitrogen pool partitioning in European mountain grasslands

European mountain grasslands are increasingly affected by land-use changes and climate, which have been suggested to exert important controls on grassland carbon (C) and nitrogen (N) pools. However, so far there has been no synthetic study on whether and how land-use changes and climate interactively affect the partitioning of these pools amongst the different grassland compartments. We analyzed the partitioning of C and N pools of 36 European mountain grasslands differing in land-use and climate with respect to above- and belowground phytomass, litter and topsoil (top 23 cm). We found that a reduction of management intensity and the abandonment of hay meadows and pastures increased above-ground phytomass, root mass and litter as well as their respective C and N pools, concurrently decreasing the fractional contribution of the topsoil to the total organic carbon pool. These changes were strongly driven by the cessation of cutting and grazing, a shift in plant functional groups and a related reduction in litter quality. Across all grasslands studied, variation in the impact of land management on the topsoil N pool and C/N-ratio were mainly explained by soil clay content combined with pH. Across the grasslands, below-ground phytomass as well as phytomass- and litter C concentrations were inversely related to the mean annual temperature; furthermore, C/N- ratios of phytomass and litter increased with decreasing mean annual precipitation. Within the topsoil compartment, C concentrations decreased from colder to warmer sites, and increased with increasing precipitation. Climate generally influenced effects of land use on C and N pools mainly through mean annual temperature and less through mean an- nual precipitation. We conclude that site-specific conditions need to be considered for understanding the effects of land use and of current and future climate changes on grassland C and N pools.Peer reviewe

Rooting characteristics and their drivers for important vegetation communities in European Alps

The data collection contains 171 root samples, where the root mass, the root length and the root depth are given. Furthermore, the database contains the main environmental parameters that influence rooting (climate, land use, soil, vegetation composition). The rooting data are provided separately for three root categories: (1) very fine roots (diameter between 0 - 1 mm), (2) fine roots (diameter between 1 - 5 mm), and (3) coarse roots (diameter between 5 - 20 mm). Roots of woody species with a diameter larger than 20 mm were not considered, as the distribution and diameter of coarse roots (especially trees) in the soil vary greatly spatially. The rooting samples were taken between 1994 and 2017 in the most widespread vegetation communities and land-use types in 13 Alpine study sites along a north-south transect from Tyrol (Austria) via South Tyrol to Trentino (both in Italy). 15 samples were taken from arable land, 56 samples from intensively used hay meadows, 15 samples from extensively managed hay meadows, 16 samples from lightly stocked pastures, 32 samples from agriculturally unused grasslands, and 37 samples from forests. The roots were collected with core samplers of 6.8–7.7 cm diameter and a maximum core depth of 70 cm. In the laboratory, the soil cores were split into the O-horizon (if present) and mineral soil layers of various thicknesses (0–3 cm, 3–8 cm, 8–13 cm, 13–23 cm, 23–38 cm, 38–53 cm, and >53 cm). Root extraction was performed manually with the roots cleared of soil in sieving cascades under running water. The root mass was weighed and based on the mass, the root length and root depth distribution were determined according to the method of Tasser et al. (2005). As environmental parameters 79 potential impact variables on rooting, including 19 site variables, six land-use variables and 53 vegetation variables, are present in the database. The vegetation variables are based on vegetation relevées after Braun-Blanquet, in whose center the root samples were taken. Meteorological parameters were measured in the most study sites at a distance of < 150 m from the rooting samples using different microclimate stations. For detailed soil characterization, soil profiles were investigated directly at the sample site or at a representative site with the same land-use type and identical plant communities in the immediate vicinity (<50 m distance). For all soil samples, we analyzed pore size distribution, soil bulk density, soil particle density, total soil porosity, soil texture, and soil organic C and pH. Furthermore, we calculated mean Ellenberg's indicator values (EIV) for temperature (T), moisture (F), soil reaction (R) and soil productivity or fertility (N) for all study sites. Past and present management practices at the study sites were recorded by interviewing landowners