Critical Leaf Water Content for Maize Photosynthesis under Drought Stress and Its Response to Rewatering

Crop photosynthesis is closely related to leaf water content (LWC), and clarifying the LWC conditions at critical points in crop photosynthesis has great theoretical and practical value for accurately monitoring drought and providing early drought warnings. This experiment was conducted to study the response of LWC to drought and rewatering and to determine the LWC at which maize photosynthesis reaches a maximum and minimum and thus changes from a state of stomatal limitation (SL) to non-stomatal limitation (NSL). The effects of rehydration were different after different levels of drought stress intensity at different growth stages, and the maize LWC recovered after rewatering following different drought stresses at the jointing stage; however, the maize LWC recovered more slowly after rewatering following 43 days and 36 days of drought stress at the tasselling and silking stages, respectively. The LWC when maize photosynthesis changed from SL to NSL was 75.4% ± 0.38%, implying that the maize became rehydrated under physiologically impaired conditions. The LWCs at which the maize Vcmax25 reached maximum values and zero differed between the drought and rewatering periods. After exposure to drought stress, the maize exhibited enhanced drought stress tolerance, an obviously reduced suitable water range, and significantly weakened photosynthetic capacity. These results provide profound insight into the turning points in maize photosynthesis and their responses to drought and rewatering. They may also help to improve crop water management, which will be useful in coping with the increased frequency of drought and extreme weather events expected under global climate change.

Potentials of straw return and potassium supply on maize (Zea mays L.) photosynthesis, dry matter accumulation and yield

Maize (Zea mays L.) is considered one of the most important grains in the world. Straw return and potassium fertilization can enhance the maize yield. Therefore, three field experiments were carried out in the three years (2018–2020) to study the effects of straw return at two methods and four levels of potassium fertilization on photosynthesis, dry matter accumulation and yield of the maize ‘Xianyu 335’. To conduct the field trials, a split plot system in five replications was established. Two straw return methods (straw return with deep tillage and straw mulching with no tillage) were in the main plots, and four potassium fertilization levels (0, 30, 45 and 60 kg/ha) were in the subplots. Each sub-plot consisted of 10 rows with 5 m length and 0.6 m width, and each sub-plot area was 30 m2 in the three years. The results indicated that the straw return methods and the potassium supply significantly affected the maize photosynthesis, dry matter accumulation and yield in the three years. Under the same potassium supply, straw return with deep tillage significantly improved the maize photosynthesis, dry matter accumulation and yield compared to straw mulching with no tillage. The above characteristics improved with increased potassium supply. The treatment of SFK60 recorded the highest values for the parameters of maize photosynthesis, dry matter accumulation and yield during the three harvest seasons. The treatment of SFK45 reached maximum profit of maize planting, which was 12088.77 yuan/ha. Therefore, SFK45 was an effective way to ensure the stable and higher yields of maize and to maximize the income of farmers.

Variable photosynthetic sensitivity of maize (Zea mays L.) to sunlight and temperature during drought development process

The complex interaction process of the abiotic factors (sunlight, air temperature and soil water) in regulating maize (Zea mays L.) photosynthesis has not been fully understood. Our field experiment explored the changed sensitivity (or role) of the abiotic factors in regulating maize photosynthesis under a drought development process. The experiment established a scenario with a long-term drought and an instantaneous cloud cover. The results revealed that long-term drought stress causes the sensitivity (or role) of sunlight and temperature exchanged in regulating maize photosynthesis. The maize photosynthesis was more sensitive to instantaneous sunlight rather than temperature in the absence of drought. However, a diminishing photosynthetic sensitivity to sunlight but an increasing photosynthetic sensitivity to temperature was observed with drought development process. The variable photosynthetic sensitivity indicated that the roles of temperature and sunlight in regulating maize photosynthesis were exchanged, so it is expected that higher photosynthetic rate could be achieved by adjusting temperature rather than sunlight after severe drought. Nevertheless, further studies are needed to provide more evidence and mechanism explanations.

Silicon Improves Maize Photosynthesis in Saline-Alkaline Soils

The research aimed to determine the effects of Si application on photosynthetic characteristics of maize on saline-alkaline soil, including photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (E), and intercellular CO2concentration (Ci) of maize in the field with five levels (0, 45, 90, 150, and 225 kg·ha−1) of Si supplying. Experimental results showed that the values ofPn,gs, andCiof maize were significantly enhanced while the values ofEof maize were dramatically decreased by certain doses of silicon fertilizers, which meant that Si application with proper doses significantly increased photosynthetic efficiency of maize in different growth stages under stressing environment of saline-alkaline soil. The optimal dose of Si application in this experiment was 150 kg·ha−1 Si. It indicated that increase in maize photosynthesis under saline-alkaline stress took place by Si application with proper doses, which is helpful to improve growth and yield of maize.