Herbaceous species richness enhances soil hydraulic conductivity by increasing soil pore connectivity

Abstract

Soil pore characteristics play a crucial role in determining soil hydrological processes. Plant diversity is recognized as a key factor in regulating soil hydraulic conductivity. However, the mechanisms by which plant diversity influencing soil pore characteristics and, consequently, hydraulic conductivity remain unclear. This study investigated the effects of herbaceous plant species richness on soil pore structure and its influence on both saturated and near-saturated hydraulic conductivity. A controlled experiment was conducted with four levels of herbaceous plant species richness (monoculture to four-species mixtures), coupled with soil pore analysis using X-ray computed tomography and measurements of saturated and near-saturated hydraulic conductivity. Our results showed that increasing plant diversity significantly increased soil porosity, particularly at plant richness levels of three and four species. This increase was primarily driven by an increase in connected porosity and a decrease in isolated porosity. Furthermore, the fractal dimension of both total pores and connected pores increased with increasing species richness. We found significant positive correlations between both near-saturated and saturated hydraulic conductivity and several pore characteristics including total porosity, connected porosity, connected pores, the fractal dimension, total biopores volume, and the specific characteristic of biopores. In-depth analysis indicated that saturated hydraulic conductivity was positively influenced by species richness, both directly through increased connected porosity and indirectly through changes in biopore volume, shape factor, and equivalent diameter. Additionally, species richness enhanced near-saturated hydraulic conductivity by increasing connected porosity and the shape factor of biopores. Our findings highlight the importance of plant diversity in regulating soil pore structure and enhancing hydraulic conductivity, contributing to a better understanding of the coupled plant-soil-hydrology processes and suggesting implications for sustainable ecosystem management.