Nitrous oxide (N2O) is a potent greenhouse gas that significantly contributes to the global warming. Also, it enhances atmospheric PM2.5 accumulation, and aggravates stratospheric O3 depletion. Agroecosystems contribute the most important part to total anthropogenic N2O emissions (ca. 60%). Increasing photosynthate allocation to grains. i.e., harvest index (HI), has been widely regarded as an effective strategy of genetic and agronomic innovation for a further increase in crop yield. However, to our knowledge, no experiments have so far assessed the effects of altered photosynthate allocation on N2O emissions from croplands.
We conducted three independent but complementary experiments to assess the effects of different photosynthate allocation patterns on soil N2O emissions. In experiment 1, a field experiment with ten varieties was performed to determine the relationships between field N2O emissions and HI which is the ratio of grain yield to total aboveground biomass. In experiment 2, a rice variety (i.e. Yangdao 6) and its mutant with similar total biomass but significant differences in the grain yield were tested to examine the effect of photosynthate allocation on N2O emissions. In experiment 3, photosynthate allocations in rice and wheat were manipulated by removing spikelet to explore the resulting impact on N2O emissions.
Results/Conclusions
Results from the rice-variety experiment showed that N2O fluxes were significantly and negatively correlated with HI. N2O fluxes were significantly lower under the wild type variety with a high HI than the low-HI mutant. Also, spikelet removal drastically decreased grain yield and HI, but increased the N2O emission. A reduction in photosynthate allocation to grain by spikelet removal significantly increased new root growth and soil dissolved organic C and decreased plant N uptake, resulting in high soil denitrification potential. Our findings demonstrate that N2O emissions from cropland can be reduced by increasing photosynthate allocation to grains, indicating an opportunity of genetic and agronomic efforts to increase crop yield with less N2O emissions.