Dryness affects trade-offs among soil functions via different mechanisms in semiarid and arid regions

Abstract

Soil is the basis of dryland ecosystems, which provide a variety of functions, such as nutrient cycling and hydrological regulation. Dryness poses a challenge to the ability of soil to support multiple functions simultaneously. However, little is known about how multiple soil functions respond to dryness and the factors influencing soil functions under different dryness levels, inhibiting our ability to better protect multiple soil functions. This study provides critical insights for predicting the evolution of soil multifunctionality under increasing aridity and formulating science-based adaptation strategies for dryland ecosystems. In this study, we investigated 58 sites in grassland areas in the drylands of China. We employed linear regression to analyze the effects of aridity on soil functions, used RMSE to assess trade-offs among soil functions across different aridity levels, and applied SEM to identify the driving mechanisms of soil functions. Our results showed that overall soil functions showed a significant decrease (R² = 0.42) as dryness intensified. Along the aridity gradient, there were trade-offs among soil functions, with soil nutrient retention higher than soil carbon sequestration capacity in the arid area but the opposite trend in the semiarid region. Aridity affected soil functions via different mechanisms under different aridity levels. In the arid zone, aridity had a direct negative effect (pathway coefficients −0.92 and −0.63, respectively) on soil moisture, while in the semiarid area, dryness negatively affected soil function through soil properties (silt) (pathway coefficients −0.25) and vegetation (plant cover, belowground biomass) (pathway coefficients −0.33 and −0.62, respectively). Our study provides evidence that a predicted drier climate will further limit soil functions and induce trade-offs among soil nutrients and soil carbon sequestration capacity along an aridity gradient. Based on the distinct mechanisms of soil functional degradation in arid and semiarid regions, differentiated ecological strategies should be appropriately implemented to maintain soil multifunctionality.