Understanding the drivers of ecosystem multifunctionality in the Mongolian steppe: The role of grazing history and resource input

Predicting the comprehensive driver of ecosystem multifunctionality is crucial for effective grassland management. However, the underlying biotic and abiotic mechanisms of ecosystem multifunctionality under global change and land use remain poorly understood. In this study, a 3-year field experiment was conducted in a semi-arid steppe in Inner Mongolia to investigate the relative importance of different biotic and abiotic factors in regulating aboveground ecosystem multifunctionality (AEM) and belowground ecosystem multifunctionality (BEM) in response to resource input after long-term grazing. The experiment involved three grazing intensities (1.5 low, 4.5 moderate, and 9.0 high sheep/ha) with a 7-year difference in grazing history. Precipitation (W) and nitrogen deposition (N) were manipulatively increased during the growing season. The study focused on exploring the effects of various biotic factors (e.g. species richness, functional diversity, plant functional groups) and abiotic factors (e.g. soil environment variables) on AEM and BEM. The results revealed asymmetric responses of AEM and BEM to resource input. Resource input enhanced AEM, but not BEM. However, increasing grazing intensity substantially reduced BEM, though we noted that AEM and BEM decreased the most under moderate grazing. Interestingly, the study found consistent responses of single ecosystem functions and ecosystem multifunctionality to resource input across the three grazing blocks. Structural equation modeling (SEM) analysis indicated that species richness primarily enhanced AEM, while soil environment played a major role in promoting BEM across different grazing history intensities and the whole grazed system. Multiple biotic and abiotic factors with varying relative importance in different grazing history scenarios controlled AEM and BEM. Species richness exhibited a strong influence on AEM and BEM, but within a narrow effect threshold range, whereas soil environment had a lesser effect size but a wider threshold range. This study provides the first evidence that grazing history and resource enrichment jointly regulate AEM and BEM. The findings highlight the importance of considering biodiversity conservation, soil health, and land use history in management practices aimed at maintaining ecosystem multifunctionality under climate change and human activities scenarios.