Soil salinization poses a severe threat to global wheat production, yet the physiological mechanisms underlying photosynthetic responses to neutral, alkaline, and combined salt stress remain poorly understood. This study systematically evaluated the photosynthetic physiology and salt tolerance of six spring wheat genotypes under three types of salt stress at varying concentrations. By integrating phenotypic data, gas exchange parameters, chlorophyll fluorescence indices, and biomass measurements, and applying structural equation modeling and multivariate analysis, key traits regulating biomass were identified. The results revealed significant interactions among salt stress type, genotype, and concentration on photosynthetic parameters. Structural equation modeling analysis revealed that under neutral salt stress, both gas exchange parameters and chlorophyll content had significant direct effects on seedling biomass, with standardized path coefficients of 0.421 and 0.400, respectively. Under alkaline and combined salt stresses, only chlorophyll content showed a significant direct effect on biomass, with standardized path coefficients of 0.873 and 0.790, respectively. Multiple regression analysis further identified key photosynthetic factors influencing growth under different stress types. Under neutral salt stress, phi (Ro) and E significantly affected biomass, whereas under alkaline and combined salt stresses, biomass was primarily co-regulated by phi (Ro) and phi (Eo). Based on a comprehensive evaluation of salt tolerance index, damage index, and biomass response, genotypes W06 and W02 exhibited the strongest overall salt tolerance. This study systematically elucidates the differential response mechanisms of photosynthesis in spring wheat under distinct salt stress types, providing an important theoretical basis and elite germplasm resources for breeding salt-tolerant wheat varieties.

The purpose of this study is to clarify the differential effects of the application rate of slow-release nitrogen fertilizer (SRF_N) on the nitrogen (N) accumulation dynamics, nutrient organ N distribution and transportation, yield, and N utilization efficiency of maize harvested using grain-type machines. This has significant implications for the scientific application of SRF_N, as well as for reducing its application rate and improving its efficiency, in the agro-pastoral transitional zone of northern China. In a long-term positioning experiment that began in 2018, five treatments consisting of different SRF_N application rates were set up, namely, N120 (120 kg ha⁻¹), N180 (180 kg ha⁻¹), N240 (240 kg ha⁻¹), N300 (300 kg ha⁻¹), and N360 (360 kg ha⁻¹), with no fertilization during the growth period used as control (CK) treatment. To explore the characteristics of nitrogen accumulation dynamics in maize populations and the main factors affecting maize yield formation under the different SRF_N application rate treatments, this study adopted a combination of quantitative analyses and model fitting, including logistic models, principal component analysis, and structural equation modeling. The research results show that SRF_N application increased the aboveground N accumulation of the maize population, and the fitting effect of the logistic models was significant. The maximum rate of N accumulation in both years showed a trend of first increasing and then decreasing with the increase in the SRF_N application rate. Compared with CK, SRF_N application reduced the proportion of N distribution in the nutrient organs during the R6 stage, and it increased the N transport from the nutrient organs to the grains after the VT-R1 stage. With the increase in the SRF_N application rate, both the economic yield and biological yield showed a single peak curve change and were maximized in the N240 treatment. The economic yield reached 15,342.07 kg ha⁻¹ in 2020 and 16,323.51 kg ha⁻¹ in 2021, increasing by 36.2% and 61.7% compared with CK, respectively. The apparent N fertilizer recovery rate, N uptake efficiency, N agronomic efficiency, and N fertilizer partial productivity all gradually decreased with the increase in the SRF_N application rate. In maize populations, an appropriate SRF_N application rate can adjust the characteristic parameters during the aboveground N accumulation rapid growth period, increase the N accumulation amount in aboveground parts, promote the transport of N from nutrient organs to grains, and improve yield. An application of 180–240 kg ha⁻¹ SRF_N is recommended for maize cultivation in the agro-pastoral transitional zone of northern China, as it is beneficial for stabilizing and increasing maize yield, as well as reducing the rate and improving the efficiency of N fertilizer.

Introduction: Straw returning is an important agricultural measure for improving soil health; however, the mechanism driving how it shapes the characteristics and multifunctionality of crop rhizosphere microbial communities in black-soil areas remains unclear. Methods: Through a 3-year field experiment, combined with high-throughput sequencing, co-occurrence network analysis, and multi-model coupling, this study systematically analyzed the effects of different straw-returning rates (no straw returning, half-dose straw returning, and full-dose straw returning) on the characteristics and multifunctionality of crop rhizosphere soil microbial communities in typical black-soil areas. Results: The results showed that the half-dose straw-returning treatment significantly increased soil microbial diversity, whereas the full-dose straw-returning treatment significantly enriched bacterial groups such as o_Rokubacteriales and f_Anaerolineaceae and fungal groups such as Ophiocordyceps and Gigaspora. Soil nitrate nitrogen, organic carbon, microbial biomass nitrogen, microbial biomass phosphorus, and invertase activity were important factors affecting soil multifunctionality. Furthermore, co-occurrence network analysis indicated that the nodes, edges, and average degree of the fungal community under the half-dose straw-returning treatment significantly increased by 9.41, 15.93, and 30.13%, respectively, compared with those in the no-straw-returning treatment. There was a significant positive correlation between the complexity of the fungal network and microbial network and the soil multifunctional index. Additionally, microbial network complexity is a direct key factor that drives improvements in soil multifunctionality, and microbial diversity indirectly enhances soil multifunctionality by regulating microbial network complexity. Moreover, soil multifunctionality was significantly positively correlated with crop biomass and grain yield. Discussion: This study elucidates the mechanism by which straw returning enhances black-soil fertility through the regulation of soil microbial networks, providing a theoretical basis and practical value for sustainable agricultural development and straw resource utilization in black-soil regions.