Plastic-soil mulching increases the photosynthetic rate by relieving nutrient limitations in the soil and flag leaves of spring wheat in a semiarid area

Purpose The stoichiometric characteristics of plants are significantly affected by soil nutrients and moisture, which regulate photosynthesis. In wheat, they can be assessed to determine environmental adaptability. Methods The selected spring wheat was investigated in a field experiment conducted from 2015 to 2017 in a semiarid area. The three treatments were (1) plastic-soil mulching (PMS), (2) gravel mulching (SM), and (3) without mulching (CK). The soil chemical properties and the net photosynthetic rate in flag leaves were recorded; the stoichiometric parameters of soil and flag leaves were calculated. Results The soil organic carbon (C) of PMS increased significantly in the 0–30-cm profile when compared with SM and CK, respectively. The soil nitrogen (N)/phosphorus (P) ratio of PMS increased in the filling stage when compared with SM and CK, respectively. The C/N ratio in flag leaves of wheat under PMS significantly decreased and increased compared with SM and CK at the filling stage during a wet year, respectively, and significantly decreased compared with CK during a drought year. The C/N and C/P ratios were significantly correlated between soil and wheat flag leaves in SM, and the net photosynthetic rates and the C/N, C/P, and N/P ratios of flag leaves under PMS and SM were also significantly correlated. Conclusions The PMS treatment relieved soil nutrient limitations in flag leaves and increased the net photosynthetic rate by optimizing foliar C/N, C/P, and N/P ratios. This resulted in increased photosynthesis under drought conditions and significantly increased the yield and water-use efficiency.