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Responses of soil N transformations and N loss to three years of simulated N deposition in a temperate Korean pine plantation in northeast China

Song, Lei, Zhang, Jinbo, Müller, Christoph, Jin, Guangze
Applied soil ecology 2019
Pinus koraiensis, ammonium, dissolved organic nitrogen, gas emissions, growing season, microorganisms, mineralization, nitrate reduction, nitrates, nitric oxide, nitrification, nitrous oxide, quantitative polymerase chain reaction, runoff, soil, stable isotopes, China
Nitrogen (N) losses are related to N deposition and activity of microbes that affect N dynamics. However, the effects of N deposition on gross N dynamics and mechanisms of N losses are not fully understood. Here, we quantified N losses from runoff and gaseous N (NO, N2O) emissions, assessed gross N transformation rates using 15N tracing, and recorded microbe abundance using real-time PCR in a temperate Korean pine plantation treated with zero N (control), low-N (20 kg N ha−1 yr−1), moderate-N (40 kg N ha−1 yr−1) and high-N (80 kg N ha−1 yr−1). The results showed that total N loss (N2O, NO and surface runoff) during the growing season was higher with N addition, where it was 0.86 kg N ha−1 in control and 1.83 kg N ha−1 in the high-N treatment. NH4+ and DON losses from surface runoff and NO loss from gas emissions were higher with N addition, whereas gross N mineralization and autotrophic nitrification rates were lower. Gross mineral N immobilization and dissimilatory nitrate reduction to ammonium rates were very low, and immobilization of NH4+ and NO3− varied among the treatments. The contrast between stimulated mineral N losses and suppressed mineral N production processes (mineralization and nitrification) with N addition showed that greater mineral N losses were likely related to losses from recently added N, rather than from old N converted from the native N pool, as a result of mineralization and nitrification processes. Suppressed NH4+ and NO3− immobilizations in some treatments also contributed to greater N losses.