Microbial community shifts accompany divergent soil carbon recovery after aquaculture-pond restoration across China's coastal wetlands.

Abstract

Aquaculture-pond restoration may rebuild coastal soil carbon, but gains in soil organic carbon (SOC) do not necessarily indicate lower lability or uniform microbial responses. We compared aquaculture ponds and adjacent restored wetlands at 10 sites across temperate, subtropical, and tropical China. SOC, microbial biomass carbon (MBC), dissolved organic carbon (DOC), and easily oxidizable carbon (EOC) were measured at 0-15 and 15-30 cm in 160 samples, and carbon pool management index (CPMI) components were calculated. Surface-soil bacterial communities and FAPROTAX-inferred functions were characterized at three sites. Restoration increased SOC at most sites and surface MBC at five, but carbon-pool responses differed among regions. Operationally non-labile carbon (CSS = SOC - EOC), an operational estimate of less-labile carbon rather than a directly measured persistent carbon pool, increased at Yancheng, Minjiang River Estuary, Zhanjiang, and Dongzhai Port. Caofeidian, Hangzhou Bay, Zhangjiang River Estuary, and Beilun River Estuary had high carbon pool activity indices, producing CPMI values of 239.78-363.74% and indicating labile-carbon enrichment rather than uniform stabilization. Bacterial community structure was dominated by geographic separation: pond and restored samples remained close within sites, whereas alpha diversity decreased at Caofeidian, changed little at Minjiang River Estuary, and increased at Dongzhai Port. Restoration also altered dominant genera and inferred functions, including greater representation of plant-polymer degradation functions in some restored soils. DOC accounted for 46.25% of the fitted variation in the 10 dominant genera and was positively associated with Sulfurimonas, SOC, and CSS. Pond-to-wetland restoration therefore followed multiple carbon-recovery trajectories, ranging from labile-carbon pulses to accumulation of a less labile fraction. Assessments should integrate SOC quantity, carbon lability, and microbial associations.