Affiliation: | 1. School of Geography, Nanjing Normal University, Nanjing, China;2. School of Geography, Nanjing Normal University, Nanjing, China Jiangsu Center for Collaborative Innovation in Geographical Information Resource Development and Application, Nanjing, China Key Laboratory of Virtual Geographic Environment (Nanjing Normal University), Ministry of Education, Nanjing, China Liebig Centre for Agroecology and Climate Impact Research, Justus Liebig University, Giessen, Germany Contribution: Writing - review & editing, Conceptualization;3. Liebig Centre for Agroecology and Climate Impact Research, Justus Liebig University, Giessen, Germany Institute of Plant Ecology, Justus Liebig University Giessen, Giessen, Germany School of Biology and Environmental Science and Earth Institute, University College Dublin, Dublin, Ireland Contribution: Writing - review & editing |
Abstract: | Carbon (C) is an important factor controlling heterotrophic nitrification in soil, but the effect of individual C components (e.g., labile and recalcitrant C) is largely unclear. We carried out a C amendment experiment in which either labile C (glucose) or a recalcitrant C (cellulose and biochar) was added to a subtropical forest soil. A 15N-, 13C-tracing and MiSeq sequencing study was performed to investigate soil gross heterotrophic nitrification rates, carbon utilization for soil respiration and microbial biomass production and microbial composition, respectively. After 2 days, results showed a significant increase of gross heterotrophic nitrification rate in glucose (GLU) (on average 3.34 mg N kg−1 day−1), cellulose (CEL) (on average 0.21 mg N kg−1 day−1) and biochar (BIO) (on average 0.13 mg N kg−1 day−1) amendment in comparison with the unamended soil (CK) (on average 0.01 mg N kg−1 day−1; p < 0.05). The contribution of heterotrophic nitrification to total soil nitrification was significantly larger in GLU (average 85.86%), CEL (average 98.52%) and BIO (average 81.25%) treatments compared with CK (average 33.33%; p < 0.01). After 2-month amendment, the gross rates remarkably decreased in GLU (average 0.02 mg N kg−1 day−1), and the contribution to total nitrification (average 8.73%) were significantly lower than that in CK (p < 0.05). A decrease in the proportion of heterotrophic nitrification to total nitrification in soil was also observed in CEL (average 38.40%) and BIO (6.74%) treatments. Nevertheless, BIO amendment (compared to CK, GLU and CEL) showed the highest gross heterotrophic nitrification rate, accompanied by a notably higher abundance of specific heterotrophic nitrifiers, i.e. Trichoderma, Aspergillus and Penicillium. These results point to a stimulatory effect of C addition on soil heterotrophic nitrification in the short term, while the stimulatory impact of C amendment diminishes with the decline in easily available C. In addition, a shift of the microbial composition in the long term can possibly be sustained for longer if additional recalcitrant C is available to heterotrophic nitrifiers. The dynamic response of heterotrophic nitrification to labile and recalcitrant C in this study offered an explanation for the positive effect of plantation and plant root exudation on the process. |