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Dynamics of soil nitrogen availability during post-agricultural succession in a karst region, southwest China

Xiao, Kongcao, Li, Dejun, Wen, Li, Yang, Liqiong, Luo, Pan, Chen, Hao, Wang, Kelin
Geoderma 2018 v.314 pp. 184-189
dissolved organic nitrogen, mineralization, shrublands, cropland, nitrification, secondary forests, karsts, soil, ammonium, ecosystems, grasslands, nitrates, China
Soil nitrogen (N) availability is crucial in governing the dynamics of ecosystem structure and function. However, the variation pattern of soil N availability during post-agricultural succession has been poorly understood for karst regions. Here, soil N availability variables, including concentrations of soil total N (TN), dissolved inorganic N (DIN=ammonium (NH4+)+nitrate (NO3−)), dissolved organic N (DON), rates of net N mineralization and nitrification at different successional stages, i.e. cropland, grassland, shrubland and secondary forest were investigated at a regional scale, in order to get a general pattern of soil N availability dynamics following agricultural abandonment in the karst region of southwest China. Concentrations of soil TN, soil NO3−, DIN, net N mineralization and nitrification rates increased from grassland to forest. Soil NO3− concentration in secondary forest (37.71±5.01mgNkg−1) reached the level in cropland (31.01±2.93mgNkg−1). Soil NO3−:NH4+ ratio in grassland was not significantly different from 1, but increased directly and reached 13.02±1.16 in secondary forest, equivalent to the level in cropland (15.15±1.98). The dynamics of soil DIN:DON ratio followed the same pattern as soil NO3−:NH4+ ratio. Our study suggests that soil N availability increases and soil N cycling becomes progressively open following agricultural abandonment in the karst region, southwest China.