Spatially different responses of nitrogen processing to precipitation during glacial-interglacial cycles on the Chinese Loess Plateau

Abstract

Abstract Terrestrial nitrogen (N) cycling is closely associated with precipitation and crucial to ecosystem, which has been receiving great concerns at the backdrop of global climate change. In addition to modern investigations, paleo record of N cycling may provide valuable clues about how ecosystem N responds to climate change. Here we measured soil organic nitrogen (TON) and its isotope value (δ15Norg) in two loess-paleosol sequences (LPS), i.e. the Yuanbao (YB) and Luochuan (LC) sequences, on the Chinese Loess Plateau (CLP) accumulated during the glacial-interglacial cycles. Both sequences showed higher magnetic susceptibility in paleosol and lower in loess, but with overall higher values in the wetter site of LC, suggesting higher precipitation during warm periods for both sites, as well as higher precipitation at site LC than at site YB. TON increased with increase of paleo-precipitation in both sequences, but the fraction of microbial derived ON, estimated from (C/N)org, increased faster than plant-derived ON at site YB but slower at site LC. δ15Norg was used to estimate microbial mediated gaseous N loss, showing greater losses at higher paleo-precipitation at site YB and a reverse trend at site LC. Thereby, both (C/N)org and δ15Norg suggest a quicker response of microbes than plants to precipitation at the drier site YB but conversely at the wetter site LC. Such a spatially different responses of nitrogen processing to precipitation would be a reference for projection of future terrestrial ecosystem response to climate change.