Effects of Aquatic Animals on Soil Organic Carbon Mineralization in a Paddy Ecosystem

Mineralization of soil organic carbon (SOC) is an important component of the soil carbon cycle. Studies have shown that rice–fish cocultures increased SOC; however, the question of whether raising aquatic animals with rice affects SOC mineralization remains unresolved. In this study, we conducted a field experiment to test SOC mineralization under three types of rice–aquatic animal cocultures (i.e., rice–fish coculture, RF; rice–crayfish coculture, RC; and rice–turtle coculture, RT) and rice monoculture (RM). SOC fractions, soil aggregate structure and SOC mineralization were determined in the experiment. Total SOC and microbial biomass carbon (MBC) under RT were significantly higher than under other treatments, and no significant differences in other SOC fractions were found among the treatments. For soil aggregates, there were significant differences in the proportions of large macroaggregates (LMA), microaggregates (MiA), and mean weight diameter (MWD) among the treatments. The LMA proportion significantly reduced while the MiA increased under the RT treatment compared to other treatments. SOC mineralization rates significantly differed among the treatments, where the RT and RC treatments had significantly higher mineralization ratios and daily average mineralization rates than the RF and RM treatments. RDA indicated that SOC fractions and soil aggregate structure influenced SOC mineralization. Our results demonstrate that aquatic animals exert differential effects on SOC mineralization, primarily through altering soil aggregate structure and SOC fractions. These findings highlight that the effects of aquatic animals on SOC dynamics should be considered in the assessment of coculture outcomes.