Mingdan Song

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.

The Muli mining area on the Qinghai–Tibet Plateau lies within a permafrost region where long-term coal mining has severely degraded native grassland ecosystems. To identify an effective restoration strategy, this study evaluated plant and soil ecological stoichiometry and stoichiometric homeostasis under different combinations of fertilization and seeding rates. A two-factor field experiment was conducted with three fertilization levels (F1–F3) and three seeding rates (S1–S3), using bare slag (BS) and natural grassland (NG) as reference controls. The F3S3 treatment produced the highest aboveground biomass (AGB), representing a 293.55% increase relative to NG. The F2S2 treatment significantly increased plant nitrogen (PN) and phosphorus (PP) contents. In addition, plant carbon-to-nitrogen (PC:PN), carbon-to-phosphorus (PC:PP), and nitrogen-to-phosphorus (PN:PP) ratios under the F2S2, F1S2, and F3S3 treatments, respectively, were closest to those of NG. The PN:PP ratio ranged from 6.05 to 8.20 (<14), indicating that plant growth in the restored plots remained primarily nitrogen-limited. Soil stoichiometric ratios (SOC:TN, SOC:TP, and TN:TP) under the F1S3, F1S1, and F1S2 treatments, respectively, were most similar to those of NG. Principal component analysis (PCA) showed that F3S3 produced the greatest short-term improvement in plant productivity and soil fertility, whereas F2S2 showed the most favorable stoichiometric homeostasis and C:N:P balance relative to natural grassland. Random forest modeling further identified soil total phosphorus, SOC:TN, and available phosphorus as the main factors controlling AGB formation. Overall, F3S3 is suitable for rapid short-term vegetation recovery, whereas F2S2 is more advantageous for long-term restoration when vegetation–soil stoichiometric balance and homeostatic stability are considered. Therefore, restoration projects in similar alpine permafrost mining areas should prioritize the F2S2 treatment to improve both ecological function and system stability.