Straw Incorporation Effects on Net Photosynthetic Carbon Assimilation and Maize Growth

Xin-Xin Wang,Tingting An,Danlei Wang,Jiaqi Li,Hongtao Zou,Zed Rengel,Wei Qin

doi:10.3389/fagro.2022.805320

Abstract

Returning straw into soil could increase soil organic carbon (SOC) and promote crop growth. However, little has been reported on the source of C for increased SOC (straw C or crop photosynthetic C). To investigate the assimilation of photosynthetic C and its distribution in soil in the maize growth season, we set up a 1-year 13C pulse-labeling experiment in a consecutive maize-straw-returning long-term trial. Four treatments were included: no straw return (control), straw mulching on the soil surface (cover), return in 0–20 cm layer (shallow), and 20–40 cm layer (deep). We found that the deep straw incorporation significantly (P &lt; 0.05) increased maize 100-grain weight (by 7.8%), yield in the coming year (by 10.5%), and SOC (by 13.4%) compared with the control. During the growing season, the deep straw incorporation increased photosynthetic 13C assimilation in shoots by 17.4% and the partitioning of photosynthetic 13C to soil by 7.9% at early jointing, and by 11.5% at maturity. The contribution of photosynthetic C to microbial biomass C (MBC) and dissolved organic C (DOC) was highest at jointing, and at harvest amounted to 39.1 % of MBC and 28.8% of DOC. The results highlighted the importance of regulating the soil carbon dynamics via the deep straw return strategy. In conclusion, deep straw incorporation significantly increased photosynthetic efficiency and facilitated partitioning of photosynthetic C to roots and soil, thus promoting maize growth and yield.

Highlights

China produces more than 800 million tons of crop straw annually, accounting for about 30% of the world’s total straw production (Bi et al, 2009), and the amount is still growing at a net rate of 12.5 million tons per year (Xia et al, 2014)
The objectives of this study were: (1) to characterize the effects of straw return to various soil depths on maize growth and grain yield; (2) to determine changes in the photosynthetic C partitioning in maize shoots, roots, grains, soil organic carbon (SOC), dissolved organic C (DOC), and microbial biomass C (MBC); and (3) to elucidate temporal dynamics of 13C partitioning in the maize-soil system
Deep straw incorporation showed significantly higher 100-grain weight compared with the control in 2018 (Figure 1D); in 2019, the deep straw return treatment had similar 100grain weight, but a longer ears compared with the control (Supplementary Table 1)

Summary

Introduction

China produces more than 800 million tons of crop straw annually, accounting for about 30% of the world’s total straw production (Bi et al, 2009), and the amount is still growing at a net rate of 12.5 million tons per year (Xia et al, 2014). The straw contains considerable amounts of nitrogen (N), phosphorus (P), potassium (K), and other nutrient resources, which are equal to 40% of the national fertilizer consumption (Xu et al, 2016; Jia et al, 2018). Crop straw is an important component of the C cycle. Alterations in soil C pools influence plant growth and development, soil fertility, and nutrient cycling. The partitioning of photosynthetic C to roots, as well as to soil, remains poorly understood due to the complexity of the soil organic C pools.

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Results

Conclusion