Net nitrogen mineralization and nitrification rates in forest soil in northeastern Taiwan

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We used a laboratory incubation approach to measure rates of net N mineralization and nitrification in forest soils from Fu-shan Experimental Forest WS1 in northern Taiwan. Net mineralization rates in the O horizon ranged from 4.0 to 13.8 mg N kg−1 day−1, and net nitrification rates ranged from 2.2 to 11.6 mg N kg−1 day−1. For mineral (10–20 cm depth) soil, net mineralization ranged from 0.06 to 2.8 mg N kg−1 day−1 and net nitrification rates ranged from 0.02 to 2.8 mg N kg−1 day−1. We did not find any consistent differences in N mineralization or nitrification rates in soils from the upper and lower part of the watershed. We compared the rates of these processes in three soil horizons (to a soil depth of 30 cm) on a single sampling date and found a large decrease in both net N mineralization and nitrification with depth. We estimated that the soil total N pool was 6,909 kg N ha−1. The present study demonstrates the importance of the stock of mineral soil N in WS1, mostly organic N, which can be transformed to inorganic N and potentially exported to surface and ground water from this watershed. Additional studies quantifying the rates of soil N cycling, particularly multi-site comparisons within Taiwan and the East Asia–Pacific region, will greatly improve our understanding of regional patterns in nitrogen cycling.