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

Abstract : 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 N-15-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.
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Félix Brédoire, Bernd Zeller, Zachary E. Kayler, Pavel A. Barsukov, Polina Nikitich, et al.. The fate of leaf-litter N under contrasting pedo-climatic conditions in south-western Siberia. Soil Biology and Biochemistry, Elsevier, 2019, 135, pp.331-342. ⟨10.1016/j.soilbio.2019.05.022⟩. ⟨hal-02265508⟩



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