Influence of plastic film mulching and planting density on yield, leaf anatomy, and root characteristics of maize on the Loess Plateau

In rainfed areas of northwestern China, maize production is constrained mainly by low temperature during early growth and water limitation during the entire growth period. Plastic film mulching is commonly used to increase maize yield in this area, because it increases topsoil temperature and moisture content as well as water use efficiency. However, the physiological and anatomical bases of maize yield improvement with plastic film mulching are not well understood. The effects of plastic film mulching and planting density on maize yield, photosynthetic characteristics, respiration, leaf anatomy, and root growth were studied in a two-year field experiment conducted on the Loess Plateau of China in 2017 and 2018. The experiment used a split-split plot design with two mulching treatments (plastic film mulching and no mulching), two planting densities (7.5 × 10⁴ and 10.5 × 10⁴ plants ha⁻¹), and two maize cultivars, Zhengdan 958 and Xianyu 335. Compared with no mulching, plastic film mulching increased maize yields by 31.1%–46.4% in 2017 and 3.6%–34.7% in 2018. Compared with low planting density, high planting density significantly increased and slightly reduced yields of both cultivars in the dry year 2017 and the rainy year 2018, respectively. Plastic film mulching increased photosynthesis and respiration as well as leaf stomatal density and aperture. Photosynthetic rate, dark respiration, and stomatal conductance and aperture were lower at high planting than at low planting density. Maize yield was positively correlated with photosynthesis, dark respiration, and stomatal aperture. Mulching increased root dry weight and length in the 0–20 cm soil layer and root activity at maturity. Overall, the changes in root growth and leaf anatomy resulted in increased photosynthesis and dark respiration, and the increased photosynthesis contributed to the increase in grain yield and biomass production under plastic film mulching conditions. Our results increase understanding of the physiological mechanisms by which plastic film mulching increases maize yield in water- and temperature-limited areas.