To investigate the accumulation, distribution, and translocation of nitrogen (N) from chemical fertilizers and green manure in wheat plants, we conducted an experiment using leguminous green manure crop hairy vetch and wheat as test materials. During the anthesis and maturity stages of wheat, the 15N enrichment and Nitrogen content of wheat plant samples were determined in different organs, and 15N enrichment and nitrogen content of soil samples were measured at maturity. The accumulation and distribution characteristics of nitrogen from different sources during the wheat growth stages were investigated to explore the impacts of green manure and chemical fertilizers on wheat growth and nitrogen uptake. The results showed that nitrogen from chemical fertilizers in the soil-plant system exhibited the following pattern: plant absorption > soil residue > loss, while nitrogen from green manure showed: soil residue > loss > plant absorption. Wheat had higher absorption of nitrogen from chemical fertilizers compared to green manure. The absorption of nitrogen from chemical fertilizers by wheat ranged from 46.00% to 54.08%, while the absorption of nitrogen from green manure ranged from 20.71% to 28.21%. The residual nitrogen from green manure in the soil (38.47% to 58.22%) was higher than that from chemical fertilizers (31.44% to 40.69%), and the nitrogen loss from green manure (21.07% to 33.31%) was higher than that from chemical fertilizers (5.22% to 22.56%). Supply of nitrogen from the two sources could coordinate the distribution of nitrogen in various organs and increase the proportion of nitrogen allocation in grains. This was beneficial for facilitating nutrient transfer to reproductive organs.

To evaluate the ameliorative effects of different green manure crops on continuously cropped protected pepper soil and to identify suitable green manure species for plateau-protected cultivation systems, a one-factor randomized complete block design was conducted with five treatments: common vetch (L1), pea (L2), hairy vetch (L3), radish (L4), and a control without green manure (CK). Soil physicochemical properties, enzyme activities, and microbial community composition were determined at the full-bloom stage before green manure incorporation. Compared with CK, L1 reduced soil pH from 8.63 to 8.34 and decreased total salt content by 45.5%, increased alkali-hydrolyzable nitrogen by 40.93%, and significantly enhanced catalase activity. L3 increased available phosphorus by 23.72% and urease and sucrase activities by 71.32% and 56.31%, respectively, while significantly affecting fungal β-diversity and community composition. Community composition analysis showed that L3 increased the relative abundances of the bacterial genus Rhizobium and the fungal genus Rhizophagus, while reducing the relative abundance of Ascomycota and several potentially pathogen-associated fungal taxa. Redundancy analysis and Mantel tests indicated that bacterial community composition was mainly associated with soil total salt content, alkaline phosphatase, and available phosphorus, whereas fungal community composition was more closely related to urease and alkaline phosphatase. Random forest analysis and partial least squares path modeling further suggested that sucrase, urease, and catalase were important factors closely associated with changes in the soil quality index (SQI). Overall, common vetch performed better in reducing soil salinity, increasing alkali-hydrolyzable nitrogen, and improving the soil quality index and may therefore be considered a suitable green manure species for improving continuously cropped protected pepper soil on the Qinghai Plateau. Hairy vetch showed advantages in increasing available phosphorus and regulating fungal community composition, indicating its potential suitability for protected soils with limited phosphorus availability.

The Qinghai–Tibet Plateau is a key component of global plateau ecosystems, but the synergistic yield-enhancing mechanism integrating aboveground photosynthetic productivity and belowground increase in soil organic carbon stock under combined green manure and wheat straw incorporation remains unclear. Based on a field experiment established in 2021, four treatments were designed (green manure return (G), straw return (W), combined return (GW), and no-return control (N)) to systematically investigate the effects of return methods on the photosynthetic characteristics, carbon-cycling functional genes, and grain yield of spring wheat. All return treatments significantly increased spring wheat yield, dry matter accumulation, and yield components, with GW showing the greatest effect. The return treatments also increased the net photosynthetic rate, stomatal conductance, transpiration rate, and chlorophyll content, while decreasing intercellular CO₂ concentration. Straw return improved bacterial community evenness; the GW treatment increased microbial β-diversity, enriched Chloroflexi and Fusarium, and constructed a functionally complementary microbial community. Green manure return increased the community richness of the cbbS gene, while straw return reduced the community evenness of the ppdK gene; different return materials directionally reshaped carbon-cycling microbial communities. rbcL was predominantly affiliated with Bradyrhizobium; korA, ppdK, and sdhA were mainly hosted by Nocardioides; Amaricoccus was the dominant genus carrying cbbS, while Flavobacterium prevailed in communities harboring accA and gapA. Co-occurrence network analysis revealed that green manure or straw return alone formed compact networks with high clustering coefficients and short path lengths, dominated by Rokubacteriota and Dormibacterota; the GW network exhibited lower average degree and shorter path length, with Saccharimonadales replacing the original dominant taxa to form a modular structure characterized by low redundancy and high efficiency. Soil organic carbon stock increased under all treatments, with the greatest increment observed under GW. In summary, combined green manure and wheat straw return enhances spring wheat yield by strengthening aboveground photosynthetic performance and optimizing yield components, while simultaneously activating belowground carbon-cycling functional genes, restructuring microbial co-occurrence networks, and promoting soil organic carbon accumulation.

To explore low-carbon spring wheat production strategies for the ecologically fragile Qinghai Plateau, a two-year field experiment was conducted using a split-plot design. The main plots were set with three nitrogen (N) application levels: N0 (0 kg·ha⁻¹, no N input), N1 (157.5 kg·ha⁻¹, 30% N reduction relative to conventional rate), and N2 (225 kg·ha⁻¹, the conventional rate). The subplots comprised four green manure mixed cropping patterns: sole cropped common vetch (CK), common vetch mixed with hull-less barley (HB), common vetch mixed with hairy vetch (HV), and common vetch mixed with rapeseed (RS). Averaged across green manure treatments, N1 reduced global warming potential (GWP) by 14.56% and greenhouse gas intensity (GHGI) by 16.89% compared with N2. Under the N1 treatment, compared with CK, RS reduced cumulative CO₂ emissions by 7.77% and GWP by 7.45%, maintained wheat grain yield comparable to those under N2, and obtained the minimum GHGI which was 2.92% lower than CK. Regarding soil properties, all green manure patterns significantly increased soil available phosphorus (AP) and available potassium (AK) compared with CK. Specifically, HB increased AP by 12.81% and AK by 16.38%, and RS also increased AP by 4.37% and AK by 2.36%. In addition, HB enhanced soil organic matter (SOM) by 5.85%, ammonium nitrogen (NH₄–N) by 8.13%, and nitrate nitrogen (NO₃–N) by 4.34%. Soil NH₄–N and NO₃–N were identified as key drivers of GHGI across treatments. On the Qinghai–Tibet Plateau, a 30% N reduction combined with target-oriented green manure mixtures—RS for emission mitigation and HB for high yield and fertility—offers a viable low-carbon strategy for spring wheat production.