Carbon-rich amendments increase soil ecosystem multifunctionality and cucumber yields under different soil conditions

Soil quality degradation is a global issue that leads to a decline in crop yields. Carbon-rich amendments (CRAs) are widely used to promote soil properties. However, the impacts of CRAs on soil ecosystem multifunctionality remain poorly understood. To address this issue, we examined the influence of various CRAs (i.e., straw, vermicompost and humic acid) on multiple soil functions and soil quality under three different soil conditions. The results showed that CRAs generally enhanced multiple soil functions (e.g., C and nutrient cycling, biodiversity maintenance, plant pathogen resistance and crop production) and increased the soil quality index area (SQI-area, an index representing areas on a radar diagram that integrates physicochemical, microbial, and nematode properties). On average, straw, vermicompost and humic acid enhanced ecosystem multifunctionality by 20.2 %, 38.1 %, and 28.9 %, respectively, and increased the SQI-area by 30.8 %, 61.2 %, and 42.3 %, respectively. The SQI-area exhibited a positive correlation with soil ecosystem multifunctionality. Furthermore, straw, vermicompost and humic acid led to yield increases of 11.1 %, 87.2 % and 75.6 % in acidic soil; 7.4 %, 66.7 % and 47.8 % in neutral soil; and 31.3 %, 62.4 % and 35.2 % in alkaline soil, respectively. Random forest modeling analysis, combined with structural equation modeling, depicted that soil physicochemical properties (e.g., porosity and soil organic C) rather than biological properties (e.g., biodiversity and nematode trophic groups) were the main driving factors for enhancing ecosystem multifunctionality and soil quality under the addition of CRAs. Our findings underscore the effectiveness of CRAs in supporting soil health and productivity through the promotion of physicochemical properties.