With the increase of world food demand, the intensity of cultivated land use also increased. To improve soil nutrient concentrations and crop yield, several straw returning techniques have been developed. Studies have shown that straw returning is beneficial to soil, but few studies have focused on the relationship between microbes and fertility in seasonal freeze-thaw periods. A two-year cropland experiment was set up that comprised three different straw return strategies, namely covering tillage with straw return for two years (CS), rotary tillage and straw return for two years (RS), rotary covering tillage with straw return (first year covering and the second year rotary tillage) (CRS), and conventional tillage with no straw return (CK). Illumina Miseq high throughput sequencing of 16S rRNA was applied to assess bacteria community structure. The relationship between bacteria community structure and changes in soil fertility induced by different straw incorporating during seasonal trends was studied. Our results showed that soil bacterial communities varied significantly during the soil seasonal freeze-thaw period in the northwest of Jilin province, China, and were influenced, to some extent, by the different straw returning procedures. Multidimensional analysis revealed that total phosphorus (TP), available nitrogen (AN), and total nitrogen (TN) were the major drivers of bacterial community structure. The co-occurrence network was divided into several modules. Notably, the major bacterial modules varied significantly in different sampling periods and different treatments. These results suggested that specific bacterial groups could contribute to soil fertility in relation to environmental fluctuations. Some bacterial groups (e.g., Pyrinomonadales, Rhizobiales, Sphingomonadales, and Xanthomonadales, in order level) were directly linked with specific environmental factors, indicating the key roles of these groups in soil fertility. In summary, the soil bacterial communities varied significantly during the freeze-thaw period and might play important roles in the degradation of straw. Thus, the straw return could enhance soil fertility.

Long-term intensive cultivation has caused soil fertility decline and structural degradation in the Songnen Plain, thereby constraining maize root development and yield formation. As a fundamental conservation tillage practice, straw return enhances soil function by incorporating exogenous organic matter and regulating root-shoot physiological processes. However, the mechanism underlying yield improvement through root–photosynthesis–nitrogen synergy remains insufficiently understood. A field experiment was conducted to assess the effects of conventional tillage (CT), straw incorporation (SI), straw mulching (SM), and deep straw incorporation (DF) on maize physiological traits and yield. Compared with CT, DF markedly enhanced root morphology and physiology, increasing the root length, surface area, volume, and root-shoot ratio by 16.46%, 23.87%, 26.64%, and 51.34%, respectively. The root bleeding intensity increased by 23.63%, whereas amino acid and nitrate contents in the bleeding sap increased by 29.20% and 65.93%, respectively, indicating improved root nutrient transport capacity. The enhanced root system positively influenced shoot photosynthesis by increasing the chlorophyll SPAD value by 16.05%, net photosynthetic rate (P_n) by 11.28%, and the activities of RuBP, PEP, nitrate reductase (NR), and glutamine synthetase (GS) by 10.59%, 24.36%, 29.94%, and 12.47%, respectively. These synergistic improvements significantly promoted post-anthesis biomass accumulation and yield formation. DF increased nitrogen and dry matter accumulation at the R3 stage by 26.61% and 15.67%, respectively, and resulted in an average yield increase of 8.34%, which was primarily due to an 11.96% increase in 100-grain weight. Although SI and SM also improved certain physiological indices, their effects were weaker than those of DF. RF analysis identified sap nitrate content (RNO), bleeding intensity (RBI), root length (RL), and root volume (RV) as key yield determinants. PLS-SEM further revealed that straw return enhanced root morphology and bleeding traits (path coefficients: 0.96 and 0.82), which subsequently improved leaf photosynthetic traits (path coefficients: 0.52 and 0.39) and biomass accumulation (path coefficient: 0.71). Collectively, these improvements promoted post-anthesis nitrogen accumulation and dry matter partitioning into grains. These findings elucidated the physiological mechanism by which deep straw incorporation increased maize yield through root system optimization, providing a theoretical basis for conservation tillage optimization in the thin-layer Mollisol region of the Songnen Plain.

Background and objective: Phosphorus (P) deficiency is a major constraint on rice growth and productivity. Clarifying the physiological basis of root–shoot coordination under phosphorus limitation is essential for improving phosphorus-use efficiency in rice. Methods: Following a preliminary phenotypic screening of 156 rice germplasm resources, four rice cultivars representing two contrasting low-P tolerance groups were selected, including two tolerant cultivars (J873 and J705) and two sensitive cultivars (T35 and L20). The physiological responses of these four cultivars to low-P stress were systematically compared using the Claassen–Barber nutrient depletion method, gas exchange measurements, and enzymatic assays. Results: Phosphorus deficiency was associated with marked changes in root phosphorus uptake kinetics. The tolerant cultivars developed an uptake pattern characterized by the coexistence of high uptake capacity (high I _max ) and high affinity (low K _m ), improving phosphorus acquisition efficiency. In leaves, these cultivars maintained higher stomatal conductance, supporting transpiration-driven nutrient transport, and exhibited greater acid phosphatase activity, consistent with enhanced intracellular phosphorus recycling. Along with delayed leaf senescence, these responses alleviated the biochemical limitations on photosynthesis, with the net photosynthetic rate at day 21 remaining 39.47–45.09% higher than that of the sensitive cultivars. Metabolic analysis indicated that enhanced sucrose phosphate synthase activity was accompanied by a 42.18–43.10% increase in the root-to-shoot ratio, reflecting greater carbon allocation to roots, while the accumulation of free amino acids contributed to the maintenance of carbon–nitrogen metabolic balance. Structural equation modeling indicated that under low-P conditions, biomass accumulation was jointly regulated by photosynthetic carbon assimilation and coordinated carbon–nitrogen metabolic processes. Conclusion: Coordinated regulation of root phosphorus uptake kinetics and SPS-mediated carbon partitioning is a key physiological strategy underlying rice adaptation to low-P conditions.

Soil respiration is a major pathway of carbon loss from agricultural soils and is substantially influenced by tillage practices. However, the short-term effects of different tillage system transitions on soil respiration and maize yield remain unclear. A field experiment was therefore conducted with five treatments: conventional tillage–conventional tillage (CK), mulching–mulching (CS), conventional tillage–rotary tillage (NR), rotary tillage–rotary tillage (RS), and mulching–rotary tillage (CRS). Soil respiration, maize growth, and yield were monitored throughout the growing season. The results showed that tillage transition significantly altered the soil respiration rate and its component structure. Higher soil respiration increased CO₂ release, raised canopy CO₂ concentration, and accelerated dry matter accumulation. The RS exhibited the highest soil respiration, with a peak rate of 16.83 μmol m⁻² s⁻¹, of which root respiration accounted for 64.16%, and improved soil porosity and promoted aboveground biomass accumulation. The CRS treatment achieved the highest leaf area index, dry matter accumulation, and yield, representing a 51.49% increase over the control, and had the lowest Q₁₀ value (2.97), indicating that respiration under this treatment was more regulated by substrate availability than by temperature. The CS treatment minimized carbon loss while maintaining grain yield. Overall, tillage transitions that improve soil aeration and root activity were generally associated with higher maize yields, but different pathways created distinct trade-offs among respiration, carbon turnover, and harvestable yield. These findings suggest that conservation tillage transitions have considerable potential for balancing yield maintenance with soil respiration regulation, providing useful guidance for sustainable high-yield maize production in semi-arid regions.