The photosynthetic activity of rice plants also correlates with methane production and emission (9).
If one hypothesizes that the allocation of photosynthates to various parts of the rice plant system increases with photosynthetic activity, the amount of biomass productivity and produced methane should both be proportional to the amount of solar radiation the plant receives.
This was found to be true. A 1% reduction in the solar radiation received during the critical growth period (heading 21 days) resulted in a 1.11% (r2 0.99) reduction in grain yield and a 1.70% (r2 0.75) reduction in methane emission. Although the effect of reduced radiation on methane emission is somewhat larger than that on grain yield, these results strongly suggest that rice grain filling and methanogenesis are similarly related to photosynthesis and that plant activity is tightly coupled to both methane production and emission.