Forest stock volume (FSV) is a major indicator of forest ecosystem health and it also plays an important part in understanding the worldwide carbon cycle. A precise comprehension of the distribution patterns and variations of FSV is crucial in the assessment of the sequestration potential of forest carbon and optimization of the management programs of the forest carbon sink. In this study, a novel vegetation index based on Sentinel-2 data for modeling FSV with the random forest (RF) algorithm in Helan Mountains, China has been developed. Among all the other variables and with a correlation coefficient of r = 0.778, the novel vegetation index (NDVI_RE) developed based on the red-edge bands of the Sentinel-2 data was the most significant. Meanwhile, the model that combined bands and vegetation indices (bands + VIs-based model, BVBM) performed best in the training phase (R² = 0.93, RMSE = 10.82 m³ha⁻¹) and testing phase (R² = 0.60, RMSE = 27.05 m³ha⁻¹). Using the best training model, the FSV of the Helan Mountains was first mapped and an accuracy of 80.46% was obtained. The novel vegetation index developed based on the red-edge bands of the Sentinel-2 data and RF algorithm is thus the most effective method to assess the FSV. In addition, this method can provide a new method to estimate the FSV in other areas, especially in the management of forest carbon sequestration.

Reforestation has been widely adopted to restore soil fertility and ecosystem service function in the rocky desertification region of southwestern China. However, there has been limited research concerning the stoichiometry of carbon (C), nitrogen (N), and phosphorus (P) and nutrient resorption rate of plantations in karst ecosystems. In this study, we selected plantations of Pinus yunnanensis Franch. (PY) and Eucalyptus maideni F. Muell. (EM) in Yunnan Province. The C, N, and P concentrations and the C:N:P stoichiometry in different soil layers (0–10 cm, 10–20 cm, and 20–30 cm) were examined. The nutrient limitation and nutrient resorption efficiency were also analyzed. The leaf C and N concentrations in the PY plantation were higher than that in the EM plantation; the P concentration demonstrated the opposite trend, both in green and senesced leaves. Soil C, N, and P concentrations in the EM plantation were much greater than in the PY plantation at all three depths and decreased with the depth of the soil. In addition, the high ratios of C:P, N:P, C:Available P, and N:Available P in soil coupled with the ratios of N:P in leaves indicate that the EM plantation has a greater P deficiency than the PY plantation. In the EM plantation, the relatively low P concentrations in senesced leaves indicates efficient TP (Total phosphorus) resorption, which highlights that the high reuse proficiency of P could have favored moderating P limitation in the karst ecosystem. This research aids in understanding the stoichiometric characteristics that mediate forest properties, and provides a basis for management of vegetation in karst ecosystems.

The Aeronautical Reconnaissance Coverage Geographic Information System (ArcGIS) 10.2 and Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) model are used to comprehensively evaluate ecosystem services in the Dongting Lake Wetland, focusing on water yield, soil conservation, carbon storage, and snail control and schistosomiasis prevention. The spatial and temporal variations of these services, as well as their variations between different land use types in a period of 10 years from 2005 to 2015, are investigated, and the value of such services is then estimated and analyzed. The results of this study show various temporal and spatial trends in the ecosystem services, such as (1) the overall increase of all these services during the study period (although significant in some services, such as schistosomiasis patient reduction, by 86.8%; and, very slight in some others such as soil conservation, only by 0.02%); (2) different orders of the services values that are based on different land use types; and, (3) the temporal changes in the proportion of the values of different ecosystem services with respect to the total services value. Besides, it is concluded that the evaluation of ecosystem services of a certain wetland is heavily dependent on the characteristics of the area where the wetland is located, and the assessment indicators and methods should be selected based on such characteristics through the analysis of the results and a comparison with the findings of literature.

Microbial functional diversity is significantly associated with both nutrient cycling and organic matter decomposition. However, how different forests as well as the soil parent materials influence the soil microbial carbon metabolism remains poorly understood. In this study, a natural secondary forest and a Pinus yunnanensis plantation, with similar climatic conditions under contrasting parent materials (clasolite in the non-karst areas and limestone in the karst areas) in Yunnan Province, China, were investigated. The soil microbial carbon metabolism diversity was assessed by the Biolog^® ECO-plates. During the dry season, the soil microbial communities used carbon substrate in secondary forest and Pinus yunnanensis plantation, showing no significant difference, both in non-karst and karst areas. The microbial communities in the non-karst area were more efficient in utilizing carbon substrates than those in the karst area with the same vegetation types, resulting in the higher accumulation of organic carbon in the karst area. The six categories of most frequently utilized carbon substrates were carbohydrates, carboxylic acids, and amino acids in both the non-karst and the karst areas. The soil basal respiration of the secondary forest was higher than that of the Pinus yunnanensis plantation, both in the non-karst and the karst areas. In addition, the driving factors of the soil microbial community functional diversity in the non-karst and karst areas are different. Our findings suggest that soil microbial functional diversity is governed by vegetation types as well as by soil properties in subtropical forests. Moreover, calcareous soil holds a higher proportion of recalcitrant organic carbon, which is difficult to utilize by microorganisms.

Soil extracellular ecoenzymatic activities (EEA) are major players in the biogeochemical cycles and are closely related to the metabolic demand and nutrient supply in microbes. However, their effects on biogeochemistry along the elevation gradient on mountain ecosystems in arid regions remain unclear. To address this, we investigated the variations of soil microbial resource limitation and the relative contributing factors along the elevation gradient of the Helan Mountains, northwest China. The results showed that the relative abundance of total microbial, bacterial, fungal, actinomycetes, and N-acquiring enzymatic activities (N-Acetyl-β-D-glucosaminidase and Leucine- α-aminopeptidase, that are NAG and LAP, respectively) in the soil first increased and then decreased with an increase in elevation. This variation pattern could be due to the changes in soil temperature and moisture along the elevation gradient. Soil enzyme stoichiometry and resource allocation further revealed that the microbial metabolism activity in the Helan Mountains was limited by carbon (C) and phosphorus (P). Furthermore, the two limited elements were significantly higher at the mid and high altitudes (2,139–2,438 m) than at low altitudes (1,380–1,650 m). Additionally, redundancy analysis revealed that the soil water content and bulk density played a crucial role in microbial community structures, while the soil pH had the most influence on soil EEA and ecoenzymatic stoichiometry. Our findings revealed the patterns of soil microbial community structure, extracellular enzyme activities, and microbial metabolism at various elevations, which will help in understanding the microbial resource limitation and nutrient cycling in mountain ecosystems in arid regions.

Tropical old-growth forests are essential for global carbon regulation. Although there is increasing evidence that species and functional diversity, stand structural diversity, functional compositions, and elevation play roles in ecosystem functioning, the relative strengths of these drivers and the underlying mechanisms (mass-ratio hypothesis or niche complementarity hypothesis) are not clear. Aboveground carbon storage, species diversity, stand structural diversity, community-weighted mean (CWM), and functional diversity (FDvar) of 12 leaf traits were analyzed using data from 56 old-growth forest communities in the Dawei Mountain area of Southwest China. Multiple regression models were used to test the relative importance of the predictor variables and the structural equation model was used to explore the direct and indirect influences on aboveground carbon storage. High structural diversity moderately enhanced aboveground carbon storage. CWM leaf nitrogen concentration in young leaves weakly affected aboveground carbon storage. Our final multiple regression model showed that aboveground carbon storage is mostly affected by diameter at breast height (DBH) diversity, followed by FDvar of dry matter concentration in mature leaves and CWM nitrogen concentration in young leaves. The structural equation model indicated that elevation negatively affects aboveground carbon storage via diameter at breast height (DBH) diversity. Our results suggest that niche complementarity effects moderately drive aboveground carbon storage in tropical old-growth forests, but do not fully support the importance of the mass-ratio hypothesis.