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The fate of leaf-litter N under contrasting pedo-climatic conditions in south-western Siberia

Brédoire, Félix, Zeller, Bernd, Kayler, Zachary E., Barsukov, Pavel A., Nikitich, Polina, Rusalimova, Olga, Bakker, Mark R., Bashuk, Alexander, Sainte-Marie, Julien, Didier, Serge, Legout, Arnaud, Derrien, Delphine
Soil biology & biochemistry 2019 v.135 pp. 331-342
drought, forest steppe, forests, freezing, grasses, land use change, models, organic matter, snowmelt, soil profiles, stable isotopes, summer, surface area, taiga, terrestrial ecosystems, topsoil, winter, Siberia
Nitrogen (N) made available through the decomposition of organic matter is a major source for plants in terrestrial ecosystems. N cycling in Siberia is however poorly documented despite the region representing a substantial surface area of the globe.We studied the influence of pedo-climate (using two forest-steppe and two southern taiga sites) and vegetation type (aspen forest and grassland) on the redistribution of N released from decomposing 15N-labelled leaf-litter in south-western (SW) Siberia. A model of N dynamics was fit to field measurements that yielded estimates of N mean residence time (MRT) within litter and soil layers, as well as the proportion of N transferred from one layer to another.The release of N from the aspen litter was slower in the forest-steppe (MRT in litter: 2.9–4.6 years) than in the southern taiga (0.9–1.5 years), likely because winter soil freezing and summer drought slowed decomposition in the forest-steppe. In contrast, no difference between the bioclimatic zones was observed for the grass litter (MRT 1.2–1.6 years), suggesting litter chemistry outweighs pedo-climate in these zones. While most of the vertical transfer of N down the soil profile occurred during the vegetative season, important losses were observed after snow-melt. Over three years, the transfer of N within the soil profile was deeper in the southern taiga sites than in the forest-steppe, and in forest than in grassland. In the topsoil, the MRT of N was longer in grassland (4.9–9.4 years) than in forest (1.5–2.1 years) but there were no pronounced differences between bioclimatic zones.The detailed and quantitative view of current N cycling in SW Siberia provided in this study may serve as the basis for informing ecosystem models that anticipate future climate and land-use changes.