Root exudates, as an important form of material input from plants to the soil, regulate the carbon input and efflux of plant rhizosphere soil and play an important role in maintaining the carbon and nutrient balance of the whole ecosystem. Root exudates are notoriously difficult to collect due to their underlying characteristics (e.g., low concentration and fast turnover rate) and the associated methodological challenges of accurately measuring root exudates in native soils. As a result, up until now, it has been difficult to accurately quantify the soil organic carbon input from root exudates to the soil in most studies. In recent years, the contribution and ecological effects of root exudates to soil organic carbon input and efflux have been paid more and more attention. However, the ecological mechanism of soil organic carbon input and efflux mediated by root exudates are rarely analyzed comprehensively. In this review, the main processes and influencing factors of soil organic carbon input and efflux mediated by root exudates are demonstrated. Soil minerals and soil microbes play key roles in the processes. The carbon allocation from plants to soil is influenced by the relationship between root exudates and root functional traits. Compared with the quantity of root exudates, the response of root exudate quality to environmental changes affects soil carbon function more. In the future, the contribution of root exudates in different plants to soil carbon turnover and their relationship with soil nutrient availability will be accurately quantified, which will be helpful to understand the mechanism of soil organic carbon sequestration.

Grassland degradation represents a major challenge in grassland productivity. This process has dramatic impacts on energy flows and soil nutrient dynamics and therefore may directly or indirectly influence soil microbes residing in surface soils. Here we aim to (1) examine changes in soil microbial composition, diversity, and functionality in response to different levels of grassland degradation (i.e., non-degraded, moderately degraded and severely degraded) in a temperate grassland in Inner Mongolia, and (2) elucidate biotic and abiotic factors that are responsible to these changes. The composition structure of soil microbial community was determined by high-throughput sequencing. The functionality of bacterial communities was examined using the tool of FAPROTAX while functional guilds of fungal communities was quantified using the FUNGuild Pipeline. Grassland degradation significantly decreased soil bacterial diversity but had no effect on fungal diversity. Belowground biomass, soil organic carbon, and total nitrogen were positively related to changes in diversity of bacterial community. Grassland degradation significantly increased the relative abundance of Chloroflexi (from 2.48% to 8.40%), and decreased Firmicutes (from 3.62% to 1.08%) of bacterial community. Degradation also significantly increased the relative abundance of Glomeromycota (from 0.17% to 1.53%), and decreased Basidiomycota (from 19.30% to 4.83%) of fungal community. The relative abundance of pathogenic fungi (Didymella and Fusarium) decreased significantly in response to degradation. In addition, degradation had a significant impact on putative functionality of soil bacteria related to soil carbon and nitrogen cycling. Our results suggest that soil bacterial community was more sensitive than fungal community in response to degradation in this temperate grassland.

Assessing the health of the ecosystem based on the landscape pattern of national parks can facilitate policy makers in formulating more targeted conservation policies to better manage national park ecosystems. To analyze the landscape patterns and characteristics of the national park, the ecosystem health evaluation index system of the national park was constructed using the vigor-organization-resilience (VOR) model to evaluate the health status. In this study, the Shennongjia National Park in China was selected as a case study area to be assessed using the index system. The results revealed that the patches of construction land and farmland are the largest in number and the most complex in shape, reflecting the obvious fragmentation of construction land and farmland patches. All patch types in this national park were evenly distributed. The results of the analysis showed that the comprehensive index of national park heath, according to the VOR model, is 0.74, indicating that the ecosystems in this study area were in a good state of health. Ecosystems in strictly protected areas of this park had the highest ecosystem health index levels, while the traditional utilization areas had the lowest. Ecosystem health levels were characterized by significant spatial agglomeration characteristics, with high-high aggregation distribution areas, mainly clustered in strictly protected areas, and low-low aggregation distribution, mainly clustered in traditional utilization areas and marginal areas. This study provided a set of ecosystem health assessment systems and their practical use in China’s newly established national parks.