Soil gross N ammonification and nitrification from tropical to temperate forests in eastern China

Abstract

Abstract1. Nitrogen (N) ammonification and nitrification are two primary microbial processes controlling the availability of soil ammonium (NH 4 + ), a key nutrient for vegetative growth. The large-scale patterns of gross ammonification (GA) and gross nitrification (GN) rates represent soil microbial adaptations to different vegetative and environmental conditions. In this study, we investigated GA and GN rates in nine forest soils along a 3,700-km north-south transect in eastern China. We used 15N-labelling techniques, along with field experiments and laboratory incubations, to assess in situ and potential rates of the GA and GN. The mean in situ GA rate was 4.9 ± 0.5 mg N kg −1 day −1, whereas the mean potential rate of GA was 32.0 ± 8.6 mg N kg −1 day −1. The mean in situ GN rate was 1.7 ± 0.3 mg N kg −1 day −1(potential GN rate: 3.2 ± 0.6 mg N kg −1 day −1). GA was significantly higher than GN along the transect, and there were high variations in GA and GN among different forests. Significant relationships were identified between meteorological factors (temperature and precipitation) and the GA and GN rates during the sampling month (August 2013). However, the mean GA rate in primary forest was significantly lower in the Huzhong (HZ), Dongling (DL), Taiyue (TY) and Dinghu (DH) sites compared with other sites, whereas with the exception of the Liangshui (LS) sampling site, the mean GN rate in primary and secondary forests showed the same trends. Significant differences in GA rates were found between primary and secondary forests at the LS and Changbai (CB) sites, and differences were detected in GN rate at the HZ, LS and Jiulian (JL) sites. Structural equation modelling analysis suggested that soil N contents, microbialbiomass N pool sizes and bacterial abundance are the primary determinants of the in situ rates of GA and GN. The strong control of edaphic factors on GA and GN indicates a need to improve soil N models with more explicit representation of edaphic factors and their control on soil N transformations. K E Y W O R D Sammonification, forest, microbe, nitrification, nitrogen, productivity, transect | INTRODUCTIONNitrogen (N) is one of the most important nutrients in terrestrial ecosystems (Vitousek & Howarth, 1991) and is subjected to competitive partitioning between plants and soil micro-organisms (Harrison, Bol, & Bardgett, 2007;Kuzyakov & Xu, 2013). Gross ammonification (GA) and gross nitrification (GN) rates are key soil microbial processes controlling the availability of ammonium (NH 4 + ) in soils and thus the primary productivity of terrestrial ecosystems. Microbial ammonification is a key process in N cycling, as it defines the formation of NH 4 + from organic matter, with ammonium being the preferred N form for plant and microbial metabolism and protein synthesis (Dannenmann et al., 2009). Microbial ammonification is also defined as N mineralization (Kirkham & Bartholomew, 1954 (Larsen et al., 2011;Yin et al., 2013), whereas a few other studies have shown that warming can suppress ammonif...

Environmental effects on soil microbial nitrogen use efficiency are controlled by allocation of organic nitrogen to microbial growth and regulate gross N mineralization

“…In their data synthesis Booth et al (2005) also found that gross N mineralization was negatively related to soil C/N, after correcting for effects of SOC quantity. Although microbial biomass N (Wang et al, 2018) and soil pH (Cheng et al, 2013) were reported also as important effectors of gross N mineralization, these were not confirmed by our dataset. Overall, microbial growth and gross N mineralization are crucial drivers and outputs of microbial NUE but they correlate with microbial NUE in opposite directions (Table S1).…”

Global patterns and controlling factors of soil nitrification rate

“…Soil MBN is one of the primary determinants of soil nitrification rate at a global scale, which is consistent with the findings in nine forest soils along a 3,700 km transect in Eastern China using the 15 N‐labeling approach (Wang, Wang, et al, 2018). The positive relationship between soil nitrification rate and MBN is also confirmed in forest soils along an elevation in the Cordillera de Consuelo (Baldos, Corre, & Veldkamp, 2015).…”

Plant diversity influenced gross nitrogen mineralization, microbial ammonium consumption and gross inorganic N immobilization in a grassland experiment

“…7 ) agrees well with the frequently reported finding that there is a negative relationship between the litter C:N ratio and N mineralization rates (Silver and Miya 2001 ; Van der Krift et al 2001 ; Chen et al 2017 ), because a high C:N ratio of plant tissue reflects a low litter quality (Abera et al 2014 ; Zhu et al 2014 ) . The fact that roots and root exudates play a vital role in regulating N mineralization (Oelmann et al 2011 ) through their influence on microbial biomass and activity (Bais et al 2006 ; Wang et al 2018 ) further supports the important role of root properties in explaining the plant species richness effect on gross N mineralization rates. The SEM also showed another significant pathway which illustrated a positive relationship between plant species richness and gross N mineralization rates via microbial biomass C. Higher plant diversity increased microbial biomass C (Strecker et al 2016 ), which further increased gross N mineralization rates (Booth et al 2005 ).…”