The purpose of this study was to identify the physiological mechanism underlying the effects of high temperature and waterlogging on summer maize. The stem development and yield of the maize hybrid Denghai 605 in response to high-temperature stress, waterlogging stress, and their combination applied for six days at the third-leaf, sixth-leaf, and tasseling stages were recorded. The combined stresses reduced lignin biosynthetic enzyme activity and lignin accumulation, leading to abnormal stem development. Reduction of the area and number of vascular bundles in stems led to reduced dry matter accumulation and allocation. Decreased grain dry weight at all three stages reduced grain yield relative to a control. In summary, high temperature, waterlogging, and their combined stress impaired stem development and grain yield of summer maize. The combined stresses were more damaging than either stress alone.

A field experiment was performed to investigate the physiological mechanism of the simultaneous stresses of waterlogging and shading on leaf photosynthetic and senescence during three growth stages of summer maize. The responses of leaf gas exchange parameters and antioxidant enzyme activities of the summer maize hybrids Denghai 605 (DH605) to waterlogging (W), shading (S), and their combination (W + S) for 6 days at the third leaf stage (V3), the sixth leaf stage (V6), and the tasseling stage (VT) were recorded. Shading, waterlogging, and their combination disturbed the activities of protective enzymes and increased the contents of H₂O₂ and O₂⁻, accelerating leaf senescence and disordering photosynthetic characteristics. Under waterlogging, shading and their combination, leaf P_n, the photo-assimilates and grain yield was decreased. The greatest reduction for waterlogging and the combined stresses occurred at V3 and that for shading stress occurred at VT. The individual and combined stresses reduced the activities of protective enzymes and inhibited photosynthesis, reducing the accumulation of photosynthetic compounds and thereby yield. Waterlogging and the combined stresses at the V3 stage showed the greatest effect on leaf photosynthetic and senescence, followed by the V6 and VT stages. The greatest effect for shading stress occurred at VT, followed by the V6 and V3 stages, and the combined influence of shading and waterlogging was greater than that of either single stress.

Stable yield of staple grains must be ensured to satisfy food demands for daily dietary energy requirements against the backdrop of global climate change. Summer maize, a staple crop, suffers severe yield losses due to extreme rainfall events, threatening food security. A randomized block experiment with four treatments: control, no water stress (CK); waterlogging for 6 days at the third leaf, sixth leaf stage, and 10th day after tasseling, was conducted to investigate the mechanism of waterlogging-induced yield losses of summer maize. Waterlogging delayed plant growth and impaired tassel and ear differentiation, leading to high grain yield losses of Denghai 605 (DH605). Waterlogging at third leaf (V3) stage reduced the photosynthesis of DH605, reducing total dry matter weight. Waterlogging at V3 stage reduced sucrose-cleaving enzymes activities in spike nodes and ears, reducing the carbon partitioned to ears (–53.1%), shanks (–46.5%), and ear nodes (–71.5%) but increasing the carbon partitioned to ear leaves (9.6%) and tassels (43.9%) in comparison with CK. The reductions in total carbon assimilate together with the reduced carbon partitioning to ears resulted in poor development of spikes (with respectively 15.2% and 20.6% reductions in total florets and fertilized florets) and lengthened the anthesis–silking interval by around 1 day, leading to high yield losses.

The standard cultivation system in the North China Plain is double cropping of winter wheat and summer maize. The main effects of this cultivation system on root development and yield are decreases in soil nutrient content and depth of the plow layer under either long-term no-tillage or rotary tillage before winter wheat sowing and no tillage before summer maize sowing. In this study, we investigated the combined effects of tillage practices before winter wheat and summer maize sowing on soil properties and root growth and distribution in summer maize. Zhengdan 958 (ZD958) was used as experimental material, with three tillage treatments: rotary tillage before winter wheat sowing and no tillage before summer maize sowing (RTW + NTM), moldboard plowing before winter wheat sowing and no tillage before summer maize sowing (MPW + NTM), and moldboard plowing before winter wheat sowing and rotary tillage before summer maize sowing (MPW + RTM). Tillage practice showed a significant (P < 0.05) effect on grain yield of summer maize. Grain yields under MPW + RTM and MPW + NTM were 30.6% and 24.0% higher, respectively, than that under RTW + NTM. Soil bulk density and soil penetration resistance decreased among tillage systems in the order RTW + NTM > MPW + NTM > MPW + RTM. Soil bulk densities were 3.3% and 515% lower in MPW + NTM and MPW + RTM, respectively, than that in RTW + NTM, and soil penetration resistances were respectively 17.8% and 20.4% lower, across growth stages and soil depths. Root dry matter and root length density were highest under MPW + RTM, with the resulting increased root activity leading to a yield increase of summer maize. Thus the marked effects of moldboard plowing before winter-wheat sowing on root length density, soil penetration resistance, and soil bulk density may contribute to higher yield.

The objective of this study was to understand the effects of plant spacing on grain yield and root competition in summer maize (Zea mays L.). Maize cultivar Denghai 661 was planted in rectangular tanks (0.54 m × 0.27 m × 1.00 m) under 27 cm (normal) and 6 cm (narrow) plant spacing and treated with zero and 7.5 g nitrogen (N) per plant. Compared to normal plant spacing, narrow plant spacing generated less root biomass in the 0–20 cm zone under both N rates, slight reductions of dry root weight in the 20–40 cm and 40–70 cm zones at the mid-grain filling stage, and slight variation of dry root weights in the 70–100 cm zone during the whole growth period. Narrow plant spacing decreased root reductive activity in all root zones, especially at the grain-filling stage. Grain yield and above-ground biomass were 5.0% and 8.4% lower in the narrow plant spacing than with normal plant spacing, although narrow plant spacing significantly increased N harvest index and N use efficiency in both grain yield and biomass, and higher N translocation rates from vegetative organs. These results indicate that the reductive activity of maize roots in all soil layers and dry weights of shallow roots were significantly decreased under narrow plant spacing conditions, resulting in lower root biomass and yield reduction at maturity. Therefore, a moderately dense sowing is a basis for high yield in summer maize.