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• The transport and distribution of 13 C and 15 N under rice straw return (SR) is clarified. • SR improved the partitioning of 13 C and 15 N in rice plants. • SR significantly improved photosynthetic C transfer to soil by 9.8%. • SR increased rice yields by enhancing 13 C accumulation. Straw return has demonstrated significant potential for enhancing carbon (C) sequestration and nitrogen (N) uptake while concurrently promoting plant productivity. However, the specific transport and distribution of C produced by photosynthesis and exogenous N within the rice plant-soil system under straw return remains unclear. A long-term straw return pot trial experiment was conducted in a double cropping rice system, incorporating treatments of inorganic fertilizer application with straw removal (F), straw burning and ash return with reducing inorganic fertilizers (SBR), and straw return with reducing inorganic fertilizers (SR) to investigate C sequestration and exogenous N uptake using 13 C pulse and 15 N isotope tracer techniques. The SR treatment had significantly higher soil 13 C abundance, by 24.4 and 25.4% respectively, 13 C concentrations in aboveground plant parts, by 18.4 and 35.8% respectively, and 15 N concentrations in rice panicles, by 12.8 and 34.3% than the SBR and F treatments. This enhancement contributed to a higher total organic C concentration and increased rice grain yield in the SR treatment. Furthermore, the SR treatment had significantly higher photosynthetic C, by 9.8%, which was directly transferred to soil C. The SR treatment had a higher distribution of photosynthetic C in the leaves and stems, but a lower distribution in the panicle compared to the SBR treatment. This finding is advantageous for sequestering photosynthetic C into the soil through straw return; conversely, opposite trends were observed in 15 N distribution. In addition, rice plants in the SR treatment had increased N uptake from urea and soil N sources, enhancing N recovery by 9.2 and 12.5% respectively and reducing soil N residues. Correlation analysis showed that the SR treatment increased the concentrations of 13 C in leaves and roots while decreasing the 15 N abundance in all rice organs, thereby contributing to an increase in rice yield. The partial least square path model suggested that the increase in rice yield under the SR treatment was primarily linked to 13 C accumulation within the rice plant-soil system. The results suggest that straw return increases the sequestration of photosynthetic C and exogenous N in the rice plant-soil system and increases N utilization efficiency, which subsequently improves both rice and soil productivity.
Yang et al. (Wed,) studied this question.