Intensive Nutrient Input Strengthens the Organic Carbon Sequestration Potential in Fishpond Sediments

Abstract

Burial in sediments as organic carbon (OC) is the key pathway for C reduction. However, the C fixation mechanisms in fishpond sediments remain unclear. In this study, sediments were taken from fishponds raising different fish species. Different OC fractions including microbial biomass C (MBC), enzymatic activities, and C uptake indices including microbial C use efficiency (CUE) were obtained. The microbial communities were identified using 16S rRNA high‐throughput sequencing. The genes, cbbL and cbbM, encoding Calvin‐Benson‐Bassham (CBB) cycle were analyzed to decipher the community assembly regulation of C‐fixing bacteria. Results indicated that the fishpond cultivating Channel catfish had higher OC and nutrients. Higher MBC and C uptake factors indicated that high nutrients facilitated MBC synthesis and OC burial via microbial activities. Different from enzymes involved in C and N cycles, alkaline phosphatase (AP) displayed a significantly positive correlation with OC fractions. This cooperativity revealed that AP dominated the organic phosphorus mineralization and phosphate increase in water, thereby promoting C assimilation and burial into sediments. Additionally, 16S rRNA and CBB cycle genes revealed that the microbial community structure remarkably varied with fishpond types. The nutrient‐rich fishpond exhibited a greater abundance of dominant bacterial genera. Aquaculture types coupling nutrient differences induced the microbial community regulation, which further triggered the CUE response and MBC enrichment. Generally, nutrient‐driven MBC accumulation and microflora shifts were key drivers of OC sequestration. These findings provide new insights into the mechanisms of OC fixation in fishponds and suggest potential Nature‐based Solutions for enhancing global C reduction management.