Nitrogen deposition in low-phosphorus tropical forests benefits soil C sequestration but not stabilization

The stability of soil organic carbon (SOC) plays a vital role in C sequestration, and largely depends on the availability of soil nitrogen (N) and phosphorus (P). Understanding how different fractions of SOC respond to N and P availability and the underlying microbial mechanism is crucial for mitigating climate changes. Here, we assessed how soil N and P availability modifies different SOC fractions and the soil microbial communities in a tropical forest. We measured soil chemical properties, SOC fractions, microbial PLFA abundance, fungal rDNA and its predicted gene abundance, and extracellular enzyme activities within a field N and P addition experiment. P addition decreased the concentration of recalcitrant SOC and greatly increased the soil oxidative extracellular enzyme activities, while N addition increased active SOC, mainly light fractions, and decreased soil phenol oxidase activity. P addition also induced the greatest abundance of oxidoreductases. Additionally, the transferases, lyases, hydrolases, isomerases, and ligases were also expressed at higher levels after P addition. The results indicate that enhanced soil microbial activities after P addition accelerated recalcitrant SOC decomposition by higher oxidative enzyme activities. Given the increasing N deposition, tropical forests that characterized by a low P have a great potential to sequester more SOC which will mitigate climate change. However, the increase in SOC might be vulnerable to disturbance, because most of the increased C is the active SOC.

Automated summary

The availability of soil nitrogen and phosphorus has a significant impact on the stability of soil organic carbon. This study examined how different fractions of soil organic carbon and the soil microbial communities in a tropical forest are affected by soil nitrogen and phosphorus availability. The results showed that phosphorus addition increased soil microbial activities and promoted the decomposition of recalcitrant soil organic carbon, while nitrogen addition increased the abundance of active soil organic carbon.