Abstract
Rice paddies are a major source of anthropogenic nitrous oxide (N2O) emissions, especially under alternate wetting-drying irrigation and high N input. Increasing photosynthate allocation to the grain in rice (Oryza sativa L.) has been identified as an effective strategy of genetic and agronomic innovation for yield enhancement; however, its impacts on N2O emissions are still unknown. We conducted three independent but complementary experiments (variety, mutant study, and spikelet clipping) to examine the impacts of rice plant photosynthate allocation on paddy N2O emissions. The three experiments showed that N2O fluxes were significantly and negatively correlated with the ratio of grain yield to total aboveground biomass, known as the harvest index (HI) in agronomy (P < 0.01). Biomass accumulation and N uptake after anthesis were significantly and positively correlated with HI (P < 0.05). Reducing photosynthate allocation to the grain by spikelet clipping significantly increased white root biomass and soil dissolved organic C and reduced plant N uptake, resulting in high soil denitrification potential (P < 0.05). Our findings demonstrate that optimizing photosynthate allocation to the grain can reduce paddy N2O emissions through decreasing belowground C input and increasing plant N uptake, suggesting the potential for genetic and agronomic efforts to produce more rice with less N2O emissions.
Highlights
Rice paddies are a major source of anthropogenic nitrous oxide (N2O) emissions, especially under alternate wetting-drying irrigation and high N input
In experiment 1, we performed a rice variety experiment at the Dangyang (10 varieties) and Jinxian (9 varieties) sites under field conditions to determine the relationships between field N2O emissions and the ratio of grain yield to total aboveground biomass, known as the harvest index (HI)
The mean N2O fluxes were significantly and negatively correlated with the HI at both sites (P < 0.01). This correlation indicates that more photosynthate allocation to rice grain reduces paddy N2O emissions
Summary
Rice paddies are a major source of anthropogenic nitrous oxide (N2O) emissions, especially under alternate wetting-drying irrigation and high N input. Increasing photosynthate allocation to the grain in rice (Oryza sativa L.) has been identified as an effective strategy of genetic and agronomic innovation for yield enhancement; its impacts on N2O emissions are still unknown. Plants affect denitrification by providing C as an energy source for denitrifiers through root exudates and/or dead root cells and by mediating soil N availability through N uptake[20,21] This process suggests that the living plants’ photosynthetic products or biomass and their allocation affect N2O emissions. Enhanced photosynthate partitioning to the grain could indirectly stimulate total crop photosynthesis, which may increase plant N uptake and, in turn, reduce soil N availability and N2O production[25,26,27]. In experiment 3, we altered rice plant photosynthate allocation by clipping spikelets to explore the underlying mechanisms of photosynthate allocation under field and pot conditions
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