Plant invasion in mountain ecosystems reduces soil micro‐food web complexity at higher elevations

Abstract Anthropogenic activities have accelerated plant invasions in mountain ecosystems, impacting the structure and functions of native plant communities. Changes in above‐ground vegetation can drive shifts in below‐ground biota, yet the effects of plant invasions on soil micro‐food web structure and complexity along elevational gradients and the underlying mechanisms remain poorly understood. This study examined the differences between the communities of native herbaceous plants invading Ageratina adenophora along an elevational gradient in the Gaoligong Mountains. We surveyed the composition of the plant community, measured the physicochemical properties of the soil and the enzyme activities of carbon and nitrogen acquisition. The complexity of the soil micro‐food web complexity index (including bacteria, fungi, nematodes and protists) using high‐throughput sequencing and network analysis. Structural equation modelling and two‐way ANOVA were used to analyse the effects of elevation, invasion and their interaction on the micro‐food web. We found that native plant diversity, soil micro‐food web complexity and soil carbon‐ and nitrogen‐acquiring enzyme activities all increased significantly with elevation. However, invasion by A. adenophora both reduced native plant diversity and altered the original elevation pattern of the soil micro‐food web. At the highest elevation (2300 m), the complexity index of the soil micro‐food web in native communities was approximately 4.8 units higher than in invaded communities, while the activities of the C‐acquiring enzymes of the soil were 135% higher and the activities of the N‐acquiring enzymes 119% higher. The complexity of the soil micro‐food web was directly influenced by plant diversity, soil nutrient cycling capacity and multitrophic diversity, whereas environmental factors such as mean temperature and soil moisture exerted indirect effects through soil nutrient status and cycling processes. Our findings demonstrate that the invasion of A. adenophora primarily affects high‐elevation ecosystems by reducing native herbaceous plant diversity, thus reducing the complexity of the micro‐food web of the soil and altering the carbon and nitrogen cycling of the soil. This study advances the mechanistic understanding of how plant invasions impact soil food webs and associated mountain ecosystem processes, providing insights into invasion management and control strategies. Read the free Plain Language Summary for this article on the Journal blog.