Effects of arbuscular mycorrhizal fungi on CH4 emissions from rice paddies

Arbuscular mycorrhizal fungi (AMF) play a key role in soil carbon storage and release; however, they have never been considered as a factor affecting methane (CH4) emissions from rice paddies. To reveal the role of AMF, the diurnal variations of CH4 emissions from the noninoculated and inoculated rice field plots were compared at midseason drainage, reflooding stage, and end-of-season drainage. The results showed that the diurnal variation patterns in the two treatments both closely tracked soil water content at midseason drainage and end-of-season drainage, while correlated very well with the stomatal conductance of rice at reflooding stage. There were no significant differences between treatments in soil water content and stomatal conductance. However, the diurnal CH4 emission fluxes at the three stages ranged from 4.8 to 39.3, 0.9 to 12.4, and 0.2 to 2.3 mg m(-2) h(-1) in the noninoculated plots, and those in the inoculated plots ranged from 2.1 to 18.7, 0.9 to 5.0, and 0.3 to 1.2 mg m(-2) h(-1). The significant differences resulted from carbon-to-nitrogen ratios (C:N) of the noninoculated and inoculated soil, which had a negative linear correlation with maximum diurnal CH4 fluxes. Compared with the noninoculated treatment, inoculating with AMF significantly increased soil C: N by improving the dry matter of rice, which intensified N limit for CH4 production.