Co-culture of rice and aquatic animals mitigates greenhouse gas emissions from rice paddies

Co-culture systems of rice and aquatic animals (CSRAA) constitute a type of cultivation system that is important for blue-green revolution, as they provide environmental sustainability, economic profitability, and increased food productivity. However, little research has been conducted on how and to what extent CSRAA influences greenhouse gas (GHG) emissions. Therefore, we conducted a global meta-analysis to examine the responses of N2O and CH4 emissions to the transformation of rice paddy fields into CSRAA. Twenty-three published articles were included, which accounted for 75 effect sizes across three types of CSRAA: rice-fish, rice-crayfish, and rice-crab. The effect size (response ratio) of GHG emissions between rice paddies and CSRAA was calculated. The results showed that the CSRAA reduced N2O and CH4 emissions by 17% and 11%, respectively. Moreover, the rice-crayfish systems were the most effective at reducing N2O (32%) and CH4 (45%) emissions. The observed reduction in GHG emissions may result from changes in critical environmental factors. The effect size of N2O emissions was significantly positively correlated with increases in water-dissolved oxygen (P=0.0082) and soil ammonium (P<0.0001), whereas that of CH4 emissions was significantly negatively associated with increases in soil ammonium (P=0.0055) and soil redox potential (P=0.0041). We observed a significant quadratic linear relationship between N2O emissions and soil nitrate concentrations (P=0.0456). Overall, our study demonstrated the potential of CSRAA to reduce GHG emissions.