Effects of all straw return on root secretions of wheat in different seasons

Root exudates play an important role in the exchange of substances and chemicals between plants and soil. Different straw returning modes change the growth environment of wheat roots, and wheat root exudates have different response characteristics to different straw returning modes. Screening for a suitable straw returning mode is a key issue for sustainable and high-quality development of wheat production. Metabolomics of root exudates can potentially help us to better understand the chemical interaction between roots, soils, and organisms in the rhizosphere. In this study, to investigate the effects of all straw return in different seasons of winter wheat-summer maize rotation system on wheat root exudates in the lime concretion black soil area in Huaibei Plain, four straw returning modes were developed, they included all wheat straw smashed mulching in summer maize season (T1), all wheat straw smashed mulching in summer maize season + all maize straw crushed burying in winter wheat season (T2), all maize straw crushed burying in winter wheat season (T3) and no straw returned to field (CK). The metabolomics of wheat root exudates collected under different straw returning modes was investigated based on non-targeted metabolomics combined with liquid chromatography-mass spectrometry. Multivariate statistical analysis methods were used to quantify the differences in metabolomics among different straw returning modes. The results showed that T1 treatment increased the root length and root dry weight of wheat during the overwintering period and resulted in higher root vigor compared to other treatments. T1, T2, and T3 detected 330, 110, and 89 differential metabolites compared with CK, respectively. Compared with CK, the relative contents of some oligosaccharides, such as stachyose and verbascose, in the root exudates of T1 increased, and the galactose metabolism and glycolytic pathways were greatly affected. The relative contents of proline, valine, isoleucine, glutamic acid, and glutamine of T1 increased, and the metabolism of arginine and proline, and D-glutamine and D-glutamate metabolism were affected greatly. The relative contents of 3-hydroxysebanoic acid, creatine phosphate, 3-isopropenylglutaric acid, 4-heptanoic acid, and cinnamic acid of T1 increased. The results indicated that all wheat straw smashed mulching changed the characteristics of wheat root exudates; increased the root length and dry weight of wheat by increasing the relative content of some sugars, amino acids, and organic acids; and maintained high root vitality under the condition of straw return. Metabolomic analysis of root exudates based on non-targeted metabolomics combined with liquid chromatography-mass spectrometry could provide an important theoretical basis for the study of the efficient utilization of straw resources and high yield, high quality, and high-efficiency development of wheat production in the lime concretion black soil area in Huaibei Plain.