Mechanisms of environmental factors affecting uptake and utilization of N and P by vegetable crops

The intensive vegetable cultivation using high fertilizer input were selected to study the effects of environmental factors on transformation, uptake, and utilization of N and P in soils. The objective of the study was to provide a theoretical basis and technical support for improving fertilizer use efficiency. Soil water contents in the incubation experiments were kept constant in this study. Two greenhouse vegetable soils were used. The soils had different soil N mineralization microbial communities—difference in community compositions induced by soil type was greater than those induced by soil moisture changes. Multivariate analysis of community-level physiological profile and phospholipid fatty acid data indicated that soil moisture regime had a significant effect on soil microbial community substrate utilization pattern and microbial community composition. Hydroponic experiments were carried out to investigate the effects of three ratios of nitrate to ammonium (75/25, 50/50, 25/75) on biomass, photosynthetic system, and antioxidant defense systems with Chinese cabbage grown under different light (full light, 15% full light) and moisture (0% PEG, 2.5% PEG) conditions.

Plant growth and photosynthetic ratio were greatly inhibited under conditions of shade (15% full light) and water stress (2.5% PEG), whereas appropriate NO₃^-/NH₄⁺ ratio (75/25) could improve shoot growth and root growth and activities, and enhance the photosynthetic intensity. Under shading (15% full light) and water stress (2.5% PEG), higher contents of ROS (H₂O₂, O₂^-), and MDA, and lower contents of antioxidants and activities of antioxidative enzymes were observed in the low and high N treatments. In combined stresses of shading and water stress, the lower ROS and MDA contents, and higher biomass, root growth, antioxidant (AsA, GSH) contents, antioxidative enzyme (POD, APX and GR) activities and the total antioxidant capacity evaluated as the 2, 2-diphenyl-1-picrylhydrazyl-radical scavenging activity and the ferric reducing/ antioxidant power in cabbage seedlings were found at NO³-/NH₄⁺ ratio (75/25) in the nutrient solution. These results suggest that appropriate NO₃^-/NH₄⁺ ratio (75/25) in the nutrient solution could improve plant growth by enhancing the antioxidant defense capacity, which prevents ROS accumulation under adverse environmental conditions. Zhejiang-25