<b>Effects of nitrogen addition on soil microbial carbon dynamics in terrestrial ecosystems in China</b>
Creators: name: Lu, Xiaofei
Publisher: name: figshare
Year: 2024
Subjects: classificationCode: 410101
subject: Carbon sequestration science

description: <b>Abstract:</b><b> </b><b><i>Background, aim, and scope </i></b>Elevated atmospheric nitrogen (N) deposition profoundly affects the carbon (C) cycling of terrestrial ecosystems in China. While previous studies have noted the positive effects of N deposition on aboveground C sequestration, how the increase of exogenous N input impacts soil microbial C dynamics remains unclear. Quantifying the responses of microbial C utilization to N addition would contribute to predicting the terrestrial C budget under elevated N deposition. <b><i>Materials and methods</i></b> In this study, we constructed a dataset comprising 114 studies by searching peer-reviewed publications that reported manipulative N-addition experiments in the terrestrial ecosystem in China. A meta-analysis method was performed to assess the effects of N addition on soil microbial C dynamics and underlying mechanisms. <b><i>Results </i></b>Our results revealed that N addition significantly decreased the soil microbial biomass C (MBC) by an average of 5%, but significantly increased microbial necromass C (MNC) by an average of 7%. As the increased N-addition rates and length, the negative effect of N addition on MBC increased. However, the MNC significantly increased with N-addition rates and length. Furthermore, N deposition significantly changed the soil extracellular enzyme activities. The activity of β-glucosidase significantly increased by an average of 6%, but the activity of polyphenol oxidase significantly decreased by an average of 7%. N deposition had minor effects on soil microbial structure, since the abundance of total phospholipid fatty acids (PLFAs), bacterial PLFAS, and fungal PLFs did not significantly change under N addition across all the studies. In addition, soil organic C (SOC) was also significantly increased by N addition, with a negative and positive relationship with MBC and MNC, respectively. <b><i>Discussion </i></b>Being consistent with many global meta-analyses, our results revealed that N deposition strongly limited soil microbial growth, via substantially decreasing MBC in the terrestrial ecosystems of China. However, the response of MNC to N addition differed from MBC. Previous studies have suggested that N deposition enhanced SOC storage through increased organic matter input and reduced soil C decomposition. Although these results are the great explanation for the increase in SOC accumulation, they ignore the contribution of C fraction from soil microbial necromass. We found that SOC was increased with the increased MNC under N addition, which suggests that microbial-driven C inputs may also be one of the important ways to promote SOC storage in terrestrial ecosystems. Furthermore, N deposition would regulate the microbial C utilization strategy through the shifts of extracellular enzyme activities, since N addition significantly increased the activities of β-glucosidase that targets cellulose but decreased the activities of polyphenol oxidase that degrades lignin. It indicates that soil microbes would degrade more phytogenous C under N deposition to meet its N demand. <b><i>Conclusions </i></b>Exogenous N input caused by increased atmospheric N deposition obviously impacted the C dynamics of soil microbial communities. In general, N addition significantly decreased MBC, but increased the MNC in terrestrial ecosystems. The response magnitudes of variables depended on the differences among ecosystem types and N addition regimes. Increased available N element affected the soil microbial C utilization strategies by changing the activities of soil extracellular enzymes. N addition would facilitate soil microbial decomposition of simple compounds while reducing the decomposition of recalcitrant compounds. The responses of MNC and SOC to N addition had a significant positive relationship, and hence increased MNC would contribute to the SOC storage. <b><i>Recommendations and perspectives </i></b>In this study, we meta-analyzed data from 114 N-manipulation experiments countrywide to assess the effects of N deposition on soil microbial C dynamics. N deposition substantially changed microbial growth and its C utilization strategies. Increased MNC from the stimulation of microbial C mineralization was conducive to SOC accumulation. Our findings highlight that microbiogenic C from microbial necromass was an important component of increased SOC under N deposition.