Hairong Han

Ecological stoichiometry is an essential tool to understand carbon (C), nitrogen (N), and phosphorus (P) cycles and nutrient limitations. Plantations are usually managed to maintain specific age structures, but the impact of such management on microbial biomass and stoichiometric ratios remains unclear. We compared the stand ages of four Larix principis-rupprechtti Mayr. Plantations that were 15 years old, (young plantation, Lar15), 24 years old, (middle aged plantation, Lar24), 40 years old, (near-mature plantation, Lar40), and 50 years old, (mature plantation, Lar50), respectively, to determine the main factors that drive differences in the C:N:P stoichiometry of microorganisms. We demonstrated that the temperature, moisture, and nutrient concentrations in surface soil increased significantly with forest age. The stoichiometric ratios of elements in soil and microorganisms reached their maxima in the Lar40 and Lar50 plantations. Additionally, forest stand ages had a great influence on the biomass of microbial communities. Moreover, soil microbial community and soil abiotic factors are closely related to soil microorganisms’ C:N:P stoichiometric ratios. Specifically, changes in the microbial biomass C:N (MBC:MBN) were primarily correlated with bacteria, Gram-positive bacteria (G⁺), temperature, NH₄⁺-N, and moisture in soil. Shifts in G⁺, actinobacteria, soil temperature, and total phosphorus were primarily associated with variation in microbial biomass C:P (MBC:MBP). Alterations in microbial biomass N:P (MBN:MBP) were correlated with bacteria, NH₄⁺-N, water content, Gram-negative bacteria, and soil temperature. Overall, these results suggest that microbial elemental stoichiometric ratios could be affected by stand age and emphasize the importance of microbial communities and soil abiotic factors in shifting this dynamic change process.

Understanding the soil phosphorus (P) cycle is a prerequisite for the sustainable management of land resources. The sequential-extraction method was used to determine P fractions in 513 soils of Larix principis-rupprechtii Mayr. plantations. With these data, this study applied structural equation modeling to evaluate the interaction between various soil P fractions. Quantitative analysis was conducted on the importance of different soil P pools and P transformation pathways on soil P availability in a larch plantation. Our study showed that soluble inorganic P (Pi) was directly positively affected by labile Pi, labile organic P (Po), secondary mineral P, and primary mineral P, and was directly negatively affected by moderately labile Po. Soluble Pi was not directly affected by occluded P. The primary mineral P (β = 0.40) had the greatest total impact on soluble Pi, followed by secondary mineral P (β = 0.32) and labile P (labile Pi and Po, β = 0.31), and then occluded P (β = 0.11), with the total impact of moderately labile Po being relatively small (β = −0.06). In summary, this study reveals the important roles of soluble Pi in P transformations and in determining overall P availability in soils, as well as the extensive effects of weathering on soil P dynamics in L. principis-rupprechtii plantations.

Aims In order to better understand the changes in the potential carbon sequestration capacity of forest soil after the invasion of broad-leaved trees into pure larch plantations, the effects of broadleaf tree invasion on soil aggregate stability and carbon sequestration by soil organic carbon and active carbon components were studied. Methods In northern China, the pure Larix principis-rupprechtii plantations and the Larix principis-rupprechtii plantations invaded by Betula platyphylla at various degrees with the same site conditions were selected (Betula platyphylla had a mixed degree of 0.2 and 0.4, respectively). ANOVA, correlation analysis, principal component analysis and structural equation were conducted to interpret the relations between Betula platyphylla invasion and soil properties. Results The distribution of soil macroaggregates (> 0.25 mm) increased with the increase in the mixed degree of Betula platyphylla. The mixture of Betula platyphylla could effectively increase the organic carbon and active carbon components of the original soil and soil aggregates of different diameter classes. The forest growth in this study area was mainly limited by nitrogen. The invasion of Betula platyphylla had an indirect impact on soil carbon sequestration by affecting the soil physical and chemical properties and the aggregate stability. Conclusions The invasion of Betula platyphylla had significant positive effects on soil aggregate stability, erosion resistance and soil nutrient status in Larix principis-rupprechtii plantation. The coniferous and broad-leaved mixture was a good strategy to increase the soil quality and soil organic carbon sequestration of the Larix principis-rupprechtii plantation in this area.

Ecological engineering is a widely used strategy to address environmental degradation and enhance human well-being. A quantitative assessment of the impacts of ecological engineering on ecosystem services (ESs) is a prerequisite for designing inclusive and sustainable engineering programs. In order to strengthen national ecological security, the Chinese government has implemented the world’s largest ecological project since 1999, the Grain for Green Program (GFGP). We used a professional model to evaluate the key ESs in Lvliang City. Scenario analysis was used to quantify the contribution of the GFGP to changes in ESs and the impacts of trade-offs/synergy. We used spatial regression to identify the main drivers of ES trade-offs. We found that: (1) From 2000 to 2018, the contribution rates of the GFGP to changes in carbon storage (CS), habitat quality (HQ), water yield (WY), and soil conservation (SC) were 140.92%, 155.59%, −454.48%, and 92.96%, respectively. GFGP compensated for the negative impacts of external environmental pressure on CS and HQ, and significantly improved CS, HQ, and SC, but at the expense of WY. (2) The GFGP promotes the synergistic development of CS, HQ, and SC, and also intensifies the trade-off relationships between WY and CS, WY and HQ, and WY and SC. (3) Land use change and urbanization are significantly positively correlated with the WY–CS, WY–HQ, and WY–SC trade-offs, while increases in NDVI helped alleviate these trade-offs. (4) Geographically weighted regression explained 90.8%, 94.2%, and 88.2% of the WY–CS, WY–HQ, and WY–SC trade-offs, respectively. We suggest that the ESs’ benefits from the GFGP can be maximized by controlling the intensity of land use change, optimizing the development of urbanization, and improving the effectiveness of afforestation. This general method of quantifying the impact of ecological engineering on ESs can act as a reference for future ecological restoration plans and decision-making in China and across the world.