Warming and drought alter C and N concentration, allocation and accumulation in a Mediterranean shrubland

0 Sardans, J Peñuelas, J. Estiarte, M Prieto, P 2008 Warming and drought alter C and N concentration, allocation and accumulation in a Mediterranean shrubland Global Change Biology 14 2304-2316 C/N, climate change, Dorycnium pentaphyllum, drought, Erica multiflora, Globularia alypum, Mediterranean shrubland, N, NUE, warming Â We investigated the effects of warming and drought on C and N concentrations, nitrogen use efficiency (NUE), and C and N accumulation in different ecosystem compartments. We conducted a 6-year (1999â��2005) field experiment to simulate the climate conditions projected by IPCC models for the coming decades in a Mediterranean shrubland. We studied the two dominant species, Globularia alypum and Erica multiflora, and an N-fixing species, Dorycniumpentaphyllum, also abundant in this shrubland. Warming (1 ÂºC) decreased N leaf concentrations by 25% and increased N stem concentrations by 40% in G. alypum. Although warming changed the available ammonium in soil in some seasons, it did not increase total soil N contents. Drought (19% average reduction in soil moisture) decreased leaf N concentrations in the two dominant shrub species, E. multiflora and G. alypum by 16% and 19%, respectively, and increased stem N concentrations by 56% and 40%, respectively. Neither warming nor drought changed the leaf N concentrations in the N-fixing species D. pentaphyllum, although warming increased stem N concentration by 9%. In G. alypum, the increase of stem N concentrations contributed to the observed increase of N accumulation in stem biomass in drought treatments with respect to control plots (8 kgNha). Neither warming nor drought changed NUE in the period 1999â��2005. Â Â Â Â Â Â Â Â Â Â Â Â Â Â