Effects of returns of full straws of different seasons on summer maize root exudates

Root exudates are carriers of material exchange, and could improve the rhizosphere environment and play an important role in the response of plants to environmental changes through chemical information exchange and energy transfer between plants and microenvironments. Different straw-returning modes change the growth environment of summer maize roots. Furthermore, the composition and quantity of maize root exudates have different response characteristics to different straw-returning modes. Screening suitable straw-returning modes is a key issue that needs to be clarified to obtain a high yield, high quality, and efficient development of maize production. In this study, we explored the effects of returens of full straw from different seasons on maize root secretions in the lime concretion black soil area in the Huaibei Plain. Four straw returning modes were developed for collecting root exudates: wheat single-season straw full smashed mulching and returning to the field (T1), wheat straw full smashed mulching and returning to the field + maize straw full crushed burying and returning to the field (T2), maize single-season straw full crushed burying and returning to the field (T3), and straw not returned to the field (CK). The metabolomics of root exudates collected under different straw-returning modes was investigated using non-targeted metabolomics combined with gas chromatography-mass spectrometry (GC-MS). The results showed that root length, surface area, dry matter weight, root vigor of T1 and T2 treatments were significantly increased compared with CK by 9.8%, 21.2%, 20.9%, 16.4%, and 12.4%, 23.9%, 29.2%, 21.3%, respectively. T1, T2, and T3 screened 60, 38, and 39 differential metabolites, respectively, compared to CK. There were nine categories of differential metabolites, and returning straw to the field mainly influenced carbohydrates and amino acids in root exudates. Compared with CK, T1, T2, and T3 treatments were significantly enriched in 45, 56, and 39 metabolic pathways, respectively. Straw returns mainly influenced carbohydrate and amino acid metabolic pathways. Compared with CK, glycerol and melibiose in the root exudates of T2 treatment were upregulated, which upregulated the galactose metabolism pathway. The upregulation of amino acids in the root exudates of T2 treatment, such as L-tyrosine and L-glutamine, significantly increased the metabolism of alanine, aspartic acid, glutamic acid, and tyrosine. Organic acids in the root exudates of the T2 treatment, such as 5-aminosalicylic acid, succinic acid, and aminoethyl phosphate, were upregulated. The results indicated that T2 treatment promoted the growth of maize roots by increasing the relative content of sugars, amino acids, and organic acids in maize root exudates, increasing the accumulation of dry matter in the aboveground and underground parts, coordinating the relationship between the aboveground and underground parts, and promoting the coordinated growth of roots and canopies. This study provides a theoretical basis for the efficient utilization of straw resources and the high yield, high quality, and efficient development of summer maize in the lime concretion black soil area of the Huaibei Plain.