Metabolomics reveals changes in soil metabolic profiles during vegetation succession in karst area.

Soil metabolites are critical in regulating the dynamics of ecosystem structure and function, particularly in fragile karst ecosystems. Clarification of response of soil metabolism to vegetation succession in karst areas will contribute to the overall understanding and management of karst soils. Here, we investigated the metabolite characteristics of karst soils with different vegetation stages (grassland, brushwood, secondary forest and primary forest) based on untargeted metabolomics. We confirmed that the abundance and composition of soil metabolites altered with vegetation succession. Of the 403 metabolites we found, 157 had significantly varied expression levels across vegetation soils, including mainly lipids and lipid-like molecules, phenylpropanoids and polyketides, organic acids and derivatives. Certain soil metabolites, such as maltotetraose and bifurcose, were sensitive to vegetation succession, increasing significantly from grassland to brushwood and then decreasing dramatically in secondary and primary forests, making them possible indicators of karst vegetation succession. In addition, soil metabolic pathways, such as galactose metabolism and biosynthesis of unsaturated fatty acids, also changed with vegetation succession. This study characterized the soil metabolic profile in different vegetation stages during karst secondary succession, which would provide new insights for the management of karst soils.

Comparative genomics analysis reveals genetic characteristics and nitrogen fixation profile of Bradyrhizobium.

Bradyrhizobium is a genus of nitrogen-fixing bacteria, with some species producing nodules in leguminous plants. Investigations into Bradyrhizobium have recently revealed its substantial genetic resources and agricultural benefits, but a comprehensive survey of its genetic diversity and functional properties is lacking. Using a panel of various strains (N = 278), this study performed a comparative genomics analysis to anticipate genes linked with symbiotic nitrogen fixation. Bradyrhizobium's pan-genome consisted of 84,078 gene families, containing 824 core genes and 42,409 accessory genes. Core genes were mainly involved in crucial cell processes, while accessory genes served diverse functions, including nitrogen fixation and nodulation. Three distinct genetic profiles were identified based on the presence/absence of gene clusters related to nodulation, nitrogen fixation, and secretion systems. Most Bradyrhizobium strains from soil and non-leguminous plants lacked major nif/nod genes and were evolutionarily more closely related. These findings shed light on Bradyrhizobium's genetic features for symbiotic nitrogen fixation.

Improving modeling of ecosystem gross primary productivity through re-optimizing temperature restrictions on photosynthesis.

The terrestrial ecosystem gross primary productivity (GPP) plays an important role in the global carbon cycle and ecosystem functions. However, the estimates of GPP still have large uncertainties due to insufficient understanding of the photosynthesis-temperature relationship and maximum light use efficiency (LUEmax). We used satellite-derived proxies of GPP to derive optimum, minimum, and maximum temperature for photosynthesis at the ecosystem scale, which was then used to construct a new temperature stress expression. This study improves the MODIS-based light use efficiency model through coupling the optimized LUEmax with the new proposed temperature stress expression. The new model (R2 = 0.81, RMSE = 17.8 gC m-2 (16 d)-1) performed better than the MODIS GPP products (R2 = 0.67, RMSE = 30.4 gC m-2 (16 d)-1), especially for evergreen broadleaf forests and croplands. The mean annual GPP over China is 5.7 ± 0.27 PgC, and the GPP significantly increased by 0.046 ± 0.006 PgC year-1 during 2001-2018. This study provides a potential method for future projections of terrestrial ecosystem functioning.

Improvements in soil quality with vegetation succession in subtropical China karst.

Secondary vegetation succession can alter soil functions and quality. However, data on changes to soil quality at different stages of vegetation succession in karst areas of southwest China is limited. This study aimed to evaluate the effects of different vegetation succession on soil quality and further to identify the factors that influencing soil quality. Secondary forest, shrub, grass, and cropland (as a reference) were selected and sampled in the subtropical karst of southwest China. Soil quality index (SQI) was developed by two methods of Total Data Set (TDS) and Minimum Data Set (MDS). Based on principal component analysis (PCA), soil organic carbon, silt, available phosphorous, available potassium, soil thickness, and soil water content were identified as the most representative indicators for the MDS. Both methods showed that the highest SQI values were observed in secondary forest, followed by shrub and grass, and the cropland values were the lowest. This showed vegetation succession significantly influenced on soil physiochemical properties and thus on soil quality. MDS could adequately represent TDS to quantify the effects of vegetation succession on soil quality since similar SQI results were derived from the two methods (R2 = 0.68, P < 0.01). The influencing factors explained about 75% of the total variation in SQI using a generalized linear model. Vegetation types accounted for the largest proportion of the SQI variability followed by restoration time, indicating these factors significantly affect soil quality during vegetation succession. In general, vegetation succession significantly influenced soil properties, and also has long-term and positive effects on soil quality during vegetation restoration. This study helps to understand the changes in soil quality during vegetation succession and provides guidance for the sustainable management of revegetation in subtropical karst regions in China.

Effects of vegetation restoration on soil quality in degraded karst landscapes of southwest China.

Vegetation restoration was implemented to control soil erosion in the karst regions of southwest China. It is essential to assess the soil function and quality scientifically during this process and to adopt suitable management practices for this area. However, few studies have been conducted to comprehensively evaluate the effect of vegetation restoration on soil quality in this severely eroded karst area. By taking 302 soil samples from 11 vegetation types, this study investigated the influence of different types of vegetation restoration on soil quality using an integrated soil quality index (SQI) and a generalized linear model (GLM). Vegetation types had significant effects on soil properties and thus on soil quality. SQI was developed by using TN, TP, TK, AP, and clay content; TN had highest weighting values (0.58), which indicated that it contributed the most to final SQI. The highest and lowest SQI values were observed for primary forest and cropland, respectively. Overall, vegetation restoration (e.g., natural restoration, artificial forests and artificial grassland) improved soil quality significantly. A GLM model explained 73.20% of the total variation in SQI, and vegetation type explained the largest proportion (46.39%) of the variation, which implies that the vegetation restoration practices can greatly enhance the soil quality in karst landscapes of southwest China. The results of this study may be used to improve implication of ecological restoration and management in degraded regions.