Edge effects reduce plant diversity through cascading effects on microclimate and soil properties

Abstract Habitat fragmentation is a major threat to biodiversity, yet the edge effects on plant diversity remain unresolved. It is still unclear whether variation in plant diversity is driven directly by distance from the edge or indirectly through changes in soil properties and microclimatic conditions. We investigated 24 grassland fragments in agro-pastoral ecotone of Inner Mongolia to quantify the magnitude and distance of edge influence on plant diversity and to examine the mediating roles of soil and microclimatic conditions. Our results showed negative edge effects across plant diversity metrics, with mean distances of edge influence of less than 30 m. Environmental factors explained more variation in Shannon diversity and evenness than spatial distance, whereas species richness was more strongly associated with spatial distance. Edge effects operated through two pathways: a soil pathway, in which higher available phosphorus and soil water content near fragment edges had negative effects on the plant diversity, and a microclimate–soil pathway, in which lower relative humidity and light intensity near fragment edges affected plant diversity indirectly by altering available phosphorus. These findings identify an edge-sensitive zone extending approximately 30 m into grassland fragments and highlight the importance of managing soil nutrients and microclimatic conditions within this zone.