| To explore the effect of straw returning on the physiological characteristics of wheat seedlings subjected to freezing stress in early spring, a comparative analysis was conducted based on a 15 year long term field experiment at the Crop Cultivation Science Observation Station of the Ministry of Agriculture and Rural Affairs in East China region. From 2023 to 2024, four different straw returning modes were evaluated for their effects on the growth and physiological traits of wheat seedlings under freezing stress in early spring: full pulverization and surface coverage of wheat straw(T1), full pulverization and surface coverage of wheat straw and corn straw(T2), full pulverization and subsoil incorporation of corn straw(T3), and no incorporation of either wheat or corn straw(CK). Principal component analysis(PCA) was employed to construct a comprehensive evaluation model for the effect of different straw returning modes on the physiological indices of wheat under the conditions of freezing stress(-3 ℃) in early spring. The results indicated that straw returning had a significant influence on the development of wheat spikes and the accumulation of dry matter in above ground parts and roots under the freezing stress in early spring. After the freezing injury, compared with CK, the spike length growth rate in T1, T2, and T3 treatments increased by 36.19%, 40.38%, and 60.67%, respectively. The dry matter weight of above ground parts and roots in wheat treated with T1 and T3 increased, with an increase rate of 15.14% and 19.12% for above ground parts, and 13.05% and 10.26% for roots, respectively. Compared to no straw returning, straw returning enhanced the antioxidant enzyme activity and the content of osmotic regulatory substances in wheat leaves and roots under freezing stress in early spring, while reducing the content of malondialdehyde(MDA). Specifically, the activities of superoxide dismutase(SOD) and peroxidase(POD) in leaves and roots in T1 treatment increased, with an increase rate of 140.08% and 71.47% for leaves, and 26.69% and 35.60% for roots compared to CK respectively, while the MDA content decreased significantly by 37.87% and 99.57%. The content of soluble protein and proline in leaves and roots in the T1 treatment increased significantly, with an increase rate of 40.55% and 64.44% for leaves, and 55.11% and 83.71% for roots, respectively. PCA revealed that the comprehensive physiological index for different treatments ranked as T1>T3>T2>CK. In summary, straw returning increased the antioxidant enzyme activity and the content of osmotic regulatory substances in wheat at the regreening stage, enhancing its cold resistance, which in turn promoted the development of wheat spikes and the accumulation of plant dry matter under freezing stress in early spring. Moreover, the full pulverization and surface coverage of wheat straw was proved to be the most effective treatment. |
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