Relationship between C:N/C:O stoichiometry and ecosystem services in managed production systems

Light grazing intensity enhances ecosystem services in semi-arid grasslands through plant trait associations

Grasslands provide multiple ecosystem services (ESs) including provisioning, regulating, supporting, and cultural services that are largely affected by livestock grazing. Linking plant functional traits (PFTs) to ecosystem processes and functions has attracted extensive ecological research to explore the responses and inter-relations of ecosystem services to environmental and management changes. However, little information is available on the links between PFTs and ESs in most ecosystems. We conducted a grazing experiment to investigate the response of PFTs at different levels, including in plant organs (leaves and stems), individual plants, and the overall community in a typical steppe region of Inner Mongolia. Additionally, we examined the effect of animal grazing at four intensities (nil, light, moderate, and heavy) and explored the dynamic interconnections between PFTs and ecosystem services in grasslands. Our analysis revealed that the highest total ecosystem service and provisioning service were achieved under light- and moderate-grazing treatments, respectively. Heavy grazing also increased provisioning service but with a large decline in regulating and total ecosystem services. These changes in ESs were closely associated with grazing-induced variations in PFTs. Compared to no grazing, light grazing increased plant size-related functional traits, such as height, leaf length, leaf area, stem length, and the ratio of stem length to diameter. In contrast, heavy grazing decreased these PFTs. Provisioning and regulating services were determined by plant above-ground community function and structural properties, while supporting service was jointly affected by the below-ground community and soil properties. Our results indicate that light grazing should be recommended for the best total ESs, although moderate grazing may lead to high short-term economic benefits. Moreover, PFTs are powerful indicators for provisioning and regulating services. These findings provide a valuable reference for developing effective management practices to achieve targeted ESs using PFTs as indicators.

Soil microbial C:N ratio is a robust indicator of soil productivity for paddy fields

Maintaining good soil productivity in rice paddies is important for global food security. Numerous methods have been developed to evaluate paddy soil productivity (PSP), most based on soil physiochemical properties and relatively few on biological indices. Here, we used a long-term dataset from experiments on paddy fields at eight county sites and a short-term dataset from a single field experiment in southern China, and aimed at quantifying relationships between PSP and the ratios of carbon (C) to nutrients (N and P) in soil microbial biomass (SMB). In the long-term dataset, SMB variables generally showed stronger correlations with the relative PSP (rPSP) compared to soil chemical properties. Both correlation and variation partitioning analyses suggested that SMB N, P and C:N ratio were good predictors of rPSP. In the short-term dataset, we found a significant, negative correlation of annual rice yield with SMB C:N (r = −0.99), confirming SMB C:N as a robust indicator for PSP. In treatments of the short-term experiment, soil amendment with biochar lowered SMB C:N and improved PSP, while incorporation of rice straw increased SMB C:N and reduced PSP. We conclude that SMB C:N ratio does not only indicate PSP but also helps to identify management practices that improve PSP.