Enhanced deposition of nitrate alters microbial cycling of N in a subtropical forest soil.

Gao, Wenlong; Kou, Liang; Zhang, Jinbo; Müller, Christoph; Wang, Huiming; Yang, Hao; Li, Shenggong

In China, atmospheric deposition of NO is increasing rapidly. However, information on how microbial N cycling in forest soils may respond to increasing deposition of NO is currently lacking. Determination of process- and pool-specific N transformation rates can provide additional insights into the controls on the production and consumption of inorganic N, and microbial function. Here, we present results from a laboratory N tracing study with a soil (0-10 cm) from a subtropical forest receiving fertilization for more than 2.5 years at a rate of 0, 40, and 120 kg NO -N ha year. The process- and pool-specific N transformation rates were quantified with a N tracing model. The directions of changes in microbial mineralization of labile and recalcitrant organic N were opposite under increased NO additions. Microbial mineralization of labile organic N first decreased, then increased, while microbial mineralization of recalcitrant organic N showed the opposite in response to increasing NO additions. Ammonium immobilization into labile and recalcitrant organic N was not changed by increased NO additions. Nitrate additions did not affect heterotrophic and gross nitrification, but stimulated autotrophic nitrification. Nitrate immobilization decreased under increased NO additions, with a greater reduction under low NO addition treatment compared to high NO addition treatment. Overall, our results reflect a contrasting change in microbial mineralization of liable and recalcitrant organic N under increased NO additions, and a contrasting effect of low and high NO additions on microbial mineralization of liable and recalcitrant organic N. It also has implications for our understanding of NO deposition-induced nonlinear changes in net production and loss of NO in subtropical/tropical forest soils.

FOREST soils; NITROGEN cycle; MINERALIZATION; SOIL fertility; SOIL productivity; ACID deposition

Biology & Fertility of Soils, 2016, Vol 52, Issue 7, p977

0178-2762

Academic Journal

10.1007/s00374-016-1134-4