The Loess Plateau is one of the main regions for growing apple trees in China, but a shortage of water resources and low utilization of nitrogen have restricted its agricultural development. A 2-year field experiment was conducted which included three levels of soil water content (SWC), 90–75%, 75–60%, and 60–45% of field capacity, and five levels of nitrogen application (N_app), 0.7, 0.6, 0.5, 0.4 and 0.3 kg/plant. The treatments were arranged in a strip-plot design with complete randomized blocks with three replications. For both years, the water and N_app had significant (P<0.05) effects on leaf area index (LAI), yield, water use efficiency (WUE) and nitrogen partial factor productivity (NPFP) while the interaction effect of water and N_app on yield, WUE and NPFP was significant (P<0.05) in 2018, and not in 2017. For the same SWC level, WUE first increased, then decreased as N_app increased, while NPFP tended to decrease, but the trend of LAI with different N_app was closely related to SWC. At the same N_app, the LAI increased as SWC increased, while the WUE and NPFP first increased, then decreased, but the yield showed different trends as the SWC increased. The dualistic and quadric regression equations of water and N_app indicate that the yield, WUE and NPFP cannot reach the maximum at the same time. Considering the coupling effects of water and N_app on yield, WUE and NPFP in 2017 and 2018, the SWC level shall be controlled in 75–60% of field capacity and the N_app is 0.45 kg/plant, which can be as the suitable strategy of water and N_app management for the maximum comprehensive benefits of yield, WUE and NPFP for apple trees in the Loess Plateau and other regions with similar environments.

To evaluate the physiological responses of Korshinsk peashrub (Caragana korshinskii Kom.) to water deficit, photosynthetic gas exchange, chlorophyll fluorescence, and the levels of superoxide anion (O₂^•−), hydrogen peroxide (H₂O₂), malondialdehyde (MDA), antioxidant enzymes, and endogenous hormones in its leaves were investigated under different irrigation strategies during the entire growth period. The results showed that leaf growth-promoting hormones were maintained at a higher level during the stages of leaf expansion and vigorous growth, and zeatin riboside (ZR) and gibberellic acid (GA) gradually decreased with an increase in water deficit. At the leaf-shedding stage, the concentration of abscisic acid (ABA) dramatically increased, and the ratio of ABA to growth-promoting hormones increased to a high level, which indicated that the rate of leaf senescence and shedding was accelerated. At the stages of leaf expansion and vigorous growth, the actual efficiency of photosystem II (PSII) (Φ_PSii) was downregulated with an increment in non-photochemical quenching (NPQ) under moderate water deficit. Excess excitation energy was dissipated, and the maximal efficiency of PSII (F_v/F_m) was maintained. However, with progressive water stress, the photo-protective mechanism was inadequate to avoid photo-damage; F_v/F_m was decreased and photosynthesis was subject to non-stomatal inhibition under severe water deficit. At the leaf-shedding stage, non-stomatal factors became the major factors in limiting photosynthesis under moderate and severe water deficits. In addition, the generation of O₂^•− and H₂O₂ in the leaves of Caragana was accelerated under moderate and severe water deficits, which caused an enhancement of antioxidant enzyme activities to maintain the oxidation–reduction balance. However, when the protective enzymes were insufficient in eliminating excessive reactive oxygen species (ROS), the activity of catalase (CAT) was reduced at the leaf-shedding stage. Taken all together, Caragana has strong drought resistance at the leaf expansion and vigorous growth stages, but weak drought resistance at the leaf-shedding stage.

To understand the physiological responses of seedlings to mechanical wounding, we analyzed photosynthesis, chlorophyll fluorescence, and endogenous hormones in tomato (Solanum lycopersicum L.) subjected to varying levels of mechanical pressure. The results showed that, at 4 h after wounding, excess excitation energy was dissipated as thermal energy through the reduction in the photosystem II (PSII) opening degree and the increase in non-photochemical quenching. Photodamage was avoided, and stomatal closure was the most prominent factor in photosynthesis inhibition. However, 12 h after wounding, the photoprotective mechanism was insufficient to mitigate the excess excitation energy caused by the wound, leading to photochemical damage to physiological processes. Meanwhile, the non-stomatal factor became the most prominent limiting factor for photosynthesis at 80 N pressure. At 12 and 36 h after wounding, the concentrations of abscisic acid (ABA), methyl jasmonate (MeJA), indole-3-acetic acid (IAA), zeatin riboside (ZR), and gibberellic acid (GA₃) in the stems showed a trend towards being increased, which promoted wound healing. However, after mechanical wounding, the ratio of stress- to growth-promoting hormones first increased and then decreased. This pattern can enhance stress resistance and promote cell division, respectively. Comprehensive analysis showed that the fluorescence parameter, photochemical quenching coefficient (Qp_Lss), was the most suitable indicator for evaluating mechanical wounding conditions.

To investigate the mechanism and influence of applying gamma-polyglutamic acid (γ-PGA) on soil water infiltration, laboratory experiments and numerical simulations were conducted using Hydrus-1D. These studies assessed the impact of various application rates of γ-PGA on soil water characteristic parameters. Orthogonal simulation experiments on soil bulk density, γ-PGA application rates, and burial depths were performed utilizing predefined soil water characteristic values (twelve groups: nine groups of numerical simulation experiments and three groups of laboratory verification tests), and the soil infiltration characteristics were analyzed. Concurrently, an empirical model was developed to elucidate the relationships between the empirical model parameters and influencing factors, as well as to examine the sensitivity of these factors to changes in soil infiltration rate. The relationship between cumulative infiltration and the distance of wetting front movement, based on the water balance equation, was refined. The results indicated that γ-PGA significantly affected soil water characteristic parameters, where the saturated water content and the reciprocal of soil intake suction increased with rising γ-PGA applications (p < 0.01), while the saturated hydraulic conductivity and the parameter n decreased (p < 0.01), with no notable changes in the retained water content (p > 0.05). The trend in cumulative infiltration influenced by various factors could be modeled by a capacitive charging model function, which yielded a superior fit. A negative correlation existed between the sensitivity index and all the influencing factors (p < 0.05), with the order of influence being soil bulk density, γ-PGA application rate, and γ-PGA burial depth, respectively. Utilizing the modified water balance equation, the ratio of cumulative infiltration to wetting front migration distance corresponded more closely with a power function. These findings provide a theoretical foundation for further studies on the effects of γ-PGA on crop growth characteristics in fields and the optimization of γ-PGA technical element combinations.

Green pepper (Capsicum annuum L.) is one of the major vegetables cultivated in sub-tropical monsoon climate regions. However, with the unreasonable use of water and nitrogen (N) fertilizer, efficient water and N fertilizer management systems need to be identified. The goal of this project was to investigate the coupling effects of different amounts of water and N on green pepper yield, water use efficiency (WUE), as well as N use efficiency (NUE) in sub-tropical monsoon climate regions. The optimum combination of water and N inputs was determined for multi-objective optimization through the multiple regression analysis and the combinations of likelihood functions. The pot experiment was conducted during the green pepper growing seasons (May–September) of 2019 and 2020 in a greenhouse at Nanchang, Jiangxi of China that included three water deficit levels, i.e., mild deficit (W1: 95~80%θFC, %θ field capacity simplified as %θFC), moderate deficit (W2: 80~65%θFC), and severe deficit (W3: 65~50%θFC), and four levels of nitrogen application (N_app) rate, i.e., 6.0 (N1), 3.0 (N2), 1.5 (N3), and 0.0 g plant⁻¹ (N4), for a total of twelve treatments (i.e., 3 × 4) with six replications. Results show that water levels have an extremely significant effect (p < 0.01) on green pepper yield and WUE, but no effect on NUE (p > 0.05). N treatments have significant effects on green pepper yield, WUE, and NUE. Meanwhile, the effects of water levels and N treatment interaction on WUE and NUE were extremely significant (p < 0.01), but varied on yield between the two years. The maximum yields (576.26 and 619.00 g plant⁻¹) occurred when the water level and N_app rate were 80~65%θFC and 6.0 g plant⁻¹. While the water level and N_app rate were 80~65%θFC and 3.0 g plant⁻¹, the WUEs and NUEs reached the maximum, which were 20.14 and 17.71 g L⁻¹, 76.54, and 77.73 g⁻¹ in 2019 and 2020. The dualistic and quadric regression equations of irrigation amount and N_app rate indicated that the yield, WUE and NUE cannot reach the maximum at the same time. By establishing a multiobjective optimization model using combinations of likelihood functions, it was concluded that the water level shall be controlled in 80~65%θFC and the N_app rate is 3.78 g plant⁻¹, which can be used as the suitable strategy of water and N management for the maximum comprehensive benefits of yield, WUE, and NUE for green pepper. The obtained optimum combination of water and N inputs can provide a scientific basis for irrigation and fertilization optimization and management in sub-tropical monsoon climate regions.

This study evaluates the impact of using biogas slurry (BS) instead of nitrogen fertilizer (NF) on wheat soil, and aims to provide an optimized fertilization strategy for green wheat production. Five fertilization modes were tested: basal fertilizer only (CK), NF at the full-bearing stage (CF), BS at the jointing stage + NF at the grouting period (S1), NF at the jointing stage + BS at the grouting period (S2), and BS at the full-bearing stage (S3). Wheat yield in S3 treatment was not significantly different from CF (9632.57 kg·ha⁻¹), but significantly increased starch content by 23.39% (p < 0.05). Analysis of soil nutrient content showed that S3 treatment elevated ammonium nitrogen (AN) content by 98.30% during the harvest period and maintained the highest urease activity (686.45 μg·g⁻¹·d⁻¹). Microbial community analysis showed that the bacterial Shannon index under S3 treatment reached 7.09, and the abundance of Actinomycetes reached 39.40%. The fungal Simpson index was 0.02, lower than that of other treatments (p < 0.01). A comprehensive evaluation led to the conclusion that a complete replacement of BS with NF synergistically improves soil quick-acting nutrient levels, enhances soil enzyme activities, and sustains high microbial diversity, whilst maintaining wheat yield.