Contributions of photosynthate carbon to methane emissions from rice paddies cultivated using different organic amendment methods: Results from an in-situ 13C-labelling study

Abstract

A field experiment was conducted in Shanghai, China, to examine whether different organic amendment methods can influence the emissions of methane (CH4) from a rice paddy by regulating the availability of photosynthate carbon (C), which is the methanogenic substrate for the production of CH4. Three treatments involving different organic amendment methods, rice–wheat without organic amendment (RW), rice–wheat with straw incorporation (RW-S) and Chinese milk vetch-rice with green manure incorporation (RM), were employed during the 2018 rice growing season. The results showed that, compared with the RW treatment, the RW-S and RM treatments significantly increased photosynthate C-induced CH4 emissions by factors of 5.55 and 1.74 in the tillering stage and 6.03 and 1.62 in the booting stage, respectively. However, the contribution ratios of the photosynthate C-induced CH4 fluxes to the gross fluxes of CH4 in descending order were RM > RW > RW-S, which can be attributed to background differences in CH4 fluxes among the different organic amendment methods. Compared with the tillering stage, the average contribution ratios of photosynthate C-induced CH4 emissions in the booting stage were 1.59, 4.43 and 2.46 times higher for the RW, RW-S and RM treatments, respectively. These results indicated that the different organic amendment methods affected CH4 emissions from the rice paddies not only via direct C inputs but also by influencing the availability of rice photosynthate C in rhizosphere.