Are nitrate production and retention processes in subtropical acidic forest soils responsive to ammonium deposition?

Abstract

N tracing model Acid soil of subtropical forest a b s t r a c tChanges 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 NH 4 CleN ha À1 yr À1 , respectively. To get a better resolution of mechanistic changes in soil N cycling and retention processes under NH 4 þ 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 NH 4 þ additions, which were paralleled by a reduction in fungal biomass and mineralization of recalcitrant organic N. Gross NH 4 þ immobilization rates did not show a change with increasing NH 4 þ additions. Interestingly, soil NO 3 À production (heterotrophic, autotrophic, and gross nitrification) and retention (NO 3 À immobilization and dissimilatory nitrate reduction to ammonium) showed insensitivity to increasing additions of NH 4 þ . 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 NH 4 þ additions. Because of the low autotrophic nitrification potential and the lack of NH 4 þ limitation to autotrophic nitrifiers, autotrophic nitrification was unresponsive to NH 4 þ additions.NO 3 À immobilization rates appeared to be controlled by the NO 3 À produced from heterotrophic nitrification, as indicated by the positive relationship between NO 3 À immobilization and heterotrophic nitri-thus showing a lack of a change under increased NH 4 þ additions. DNRA seemed to be inherently less responsive to environmental changes such as NH 4 þ deposition. Our work demonstrates that enhanced NH 4 þ deposition has a low potential to stimulate soil NO 3 À production and weaken soil retention of NO 3 À in this, and perhaps other subtropical/tropical acidic forest ecosystems.

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

“…3). Previous studies have suggested that NO 3 − immobilization depends directly on heterotrophic nitrification for substrate generation, and both pathways are functionally linked in subtropical/tropical acidic forest soils (Gao et al 2016). At our site, NO 3 − immobilization rates were higher in the control plots with higher heterotrophic nitrification rates, and were lower in the N addition plots with lower heterotrophic nitrification rates (Fig.…”

Nitrogen fertilization changes the molecular composition of soil organic matter in a subtropical plantation forest

“…The high rate of N fertilization led to a significant accumulation of soil NO 3 − , as well as soil acidification in the subtropical plantation forest (Table 1), which was closely related to the ecosystem N cycle. Soil NO 3 − content depends on the budget between production (heterotrophic and autotrophic nitrification) and retention (NO 3 − immobilization and dissimilatory nitrate reduction to ammonium) processes (Gao et al, 2016). On the basis of 15 N tracing experiments, several previous studies reported that low N availability led to a low autotrophic nitrification rate in the acidic subtropical forest soils (Levy-Booth, Prescott, & Grayston, 2014;Zhang, Hu, Shen, & He, 2012), whereas the dissimilatory nitrate reduction to ammonium process decreased with increasing N availability (Gao et al, 2016).…”

Terrestrial N cycling associated with climate and plant‐specific N preferences: a review

“…The medians of gross rates of soil N transformations in different wet and dry climate zones: rates of (a) mineralization, (b) immobilization of NH 4 + , (c) heterotrophic nitrification, (d) oxidation of NH 4 + to NO 3 − and (e) immobilization of NO 3 − , and (f) ratio of rates of oxidation of NH 4 + to NO 3 − to gross rate of N mineralization. Data are cited from 16 publications (Zhang et al , 2013a; Zhang et al , ; Wang et al , ; Zhang et al , ; Gao et al , ; Huygens et al , ; Huygens et al , ; Rütting et al , ; Staelens et al , ; Zhang et al , ; Müller et al , ; Rütting & Müller, 2008; Müller et al , ; Müller et al , ; Gao et al , ; Wang et al , a) (Table S1, Supporting Information). Most data were obtained within China, but other data were measured in Germany, Chile, Belgium and Northern Ireland.…”

“…rate of NH 4 + oxidation and climate zones) can also prevail in agricultural soil. (Zhang et al, 2013a;Zhang et al, 2016b;Wang et al, 2016;Zhang et al, 2015b;Gao et al, 2016b;Huygens et al, 2008;Huygens et al, 2007;Rütting et al, 2008;Staelens et al, 2012;Zhang et al, 2016a;Müller et al, 2004;Rütting & Müller, 2008;Müller et al, 2009;Müller et al, 2014;Gao et al, 2016a;Wang et al, 2017aa) (…”