Are nitrate production and retention processes in subtropical acidic forest soils responsive to ammonium deposition?. (September 2016)

• Record Type: Journal Article
• Authors: Gao, Wenlong; Kou, Liang; Yang, Hao; Zhang, Jinbo; Müller, Christoph; Li, Shenggong
• Is Part Of: Soil biology and biochemistry. Volume 100(2016)
• Page Start: 102
• Page End: 109
• Publication Date: 2016-09
• Subjects: N deposition -- Gross N transformations -- DNRA -- 15N tracing model -- Acid soil of subtropical forest; Soil biochemistry -- Periodicals; Soil biology -- Periodicals; Sols -- Biochimie -- Périodiques; Sols -- Biologie -- Périodiques; Sols -- Microbiologie -- Périodiques; Bodembiologie; Biochemie; 631.46
• DOI: 10.1016/j.soilbio.2016.06.002
• Languages: English
• ISSNs: 0038-0717

Abstract

Abstract: Changes in soil N-cycling and retention processes in subtropical/tropical acidic forest ecosystems under anthropogenic N inputs are not well understood. We conducted a laboratory 15 N tracing study on an acid soil (pH values: 4.6 to 5.0) from a subtropical forest fertilized for more than 2.5 years at a rate of 0, 40, and 120 kg NH4 ClN ha −1 yr −1, respectively. To get a better resolution of mechanistic changes in soil N cycling and retention processes under NH4 + additions, we used a conceptual 15 N tracing model to quantify process-specific and pool-specific N transformation rates in soils. Gross N mineralization rates decreased at high NH4 + additions, which were paralleled by a reduction in fungal biomass and mineralization of recalcitrant organic N. Gross NH4 + immobilization rates did not show a change with increasing NH4 + additions. Interestingly, soil NO3 − production (heterotrophic, autotrophic, and gross nitrification) and retention (NO3 − immobilization and dissimilatory nitrate reduction to ammonium) showed insensitivity to increasing additions of NH4 + . The mechanisms behind the lack of response of heterotrophic nitrification were unclear, but possibly related to the absence of significant changes in soil C: N ratio and soil acidity under increased NH4 + additions. Because of the low autotrophic nitrification potential and the lack of NH4 + limitation to autotrophic nitrifiers, autotrophic nitrification was unresponsive to NH4 + additions. NO3 − immobilization rates appeared to be controlled by the NO3 − produced from heterotrophic nitrification, as indicated by the positive relationship between NO3 − immobilization and heterotrophic nitrification ( R 2 = 0.59, p = 0.015), thus showing a lack of a change under increased NH4 + additions. DNRA seemed to be inherently less responsive to environmental changes such as NH4 + deposition. Our work demonstrates that enhanced NH4 + deposition has a low potential to stimulate soil NO3 − production and weaken soil retention of NO3 − in this, and perhaps other subtropical/tropical acidic forest ecosystems. Highlights: We conducted a 15 N tracing study on a NH4 + amended, subtropical acid forest soil. Gross N transformations were quantified with a process-based 15 N tracing model. NH4 + additions inhibited mineralization of recalcitrant organic N. NH4 + additions did not stimulate autotrophic and heterotrophic nitrification. NH4 + additions did not alter the rates of NO3 − immobilization and DNRA.