Functional diversity overrides community-weighted mean traits in linking land-use intensity to hydrological ecosystem services

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Land-use intensification can importantly influence terrestrial ecosystem services by altering plant functional traits. Although we know that functional traits influence both ecosystem properties and services, we do not fully understand the mechanistic pathways governing these relationships nor how they will respond to global climate change. To identify the impact pathways of land-use intensity on hydrological services under changing precipitation regimes, we monitored hydrological services in 15 plots of different land-use types during 25 precipitation events (6 light, 8 moderate, and 11 heavy rains). Bayesian structural equation modeling was used to quantify the direct and indirect effects between land-use intensity, functional trait components (community weighted mean [CWM] and functional diversity [FD]), ecosystem properties (canopy density, litter fall and fine-root density), and hydrological services under different rainfall intensities. The impact of land-use intensity on hydrological service provisioning was regulated by plant functional traits regardless of intensity rainfall. Under light and moderate rain, FD significantly influenced hydrological services by altering canopy density and fine-root density, but we found no significant effect of CWMs. Under heavy rain, FD had significant, and greater, impacts on hydrological services than CWM of traits, although CWM of traits influenced hydrological services provision indirectly by altering canopy density and fine-root density. Land-use intensity indirectly affected hydrological services mainly by altering FD regardless of rainfall intensification, suggesting that the reduction of niche differentiation caused by land-use intensity is the main mechanism of hydrological services degradation. Our results suggested that the effect of land-use intensity on hydrological services are likely to change with increasing frequency of extreme precipitation events because of the different underlying mechanism at play and emphasize the importance of FD in maintaining hydrological services in respond to global environmental changes.