Differential carbon allocation in sandy ecosystems: Aboveground versus belowground herbaceous biomass mediated by vegetation coverage

Abstract

Understanding how climate and soil regulate plant biomass allocation is crucial for predicting carbon dynamics in water-limited sandy ecosystems. However, the pathways controlling herbaceous aboveground and belowground (0–20 cm soil layer) biomass remain poorly quantified. Based on surveys at 220 sites across four major sandy lands in northern China, the herbaceous community composition, aboveground biomass, belowground biomass, soil properties, and climatic variables were measured, and the direct and indirect effects were disentangled by using structural equation modeling to explore hypothesized associative pathways. Growing season precipitation enhanced aboveground biomass primarily by increasing herbaceous vegetation coverage, whereas mean annual temperature directly suppressed aboveground biomass but promoted belowground biomass, indicating a temperature-associated shift in biomass allocation. herbaceous vegetation coverage serves as an important integrative variable that integrates the effects of climate, soil texture, and geography, and transmits these signals to both the aboveground biomass and the belowground biomass. The community diversity index had a net negative effect on both types of biomass pools in these resource-limited communities, likely due to intensified interspecific competition. These findings reveal that herbaceous vegetation coverage functions as both an integrative ecosystem response variable and a key mediating variable through which environmental drivers are translated into divergent carbon allocation strategies. Therefore, targeted management of herbaceous vegetation coverage provides a viable intervention point to reshape biomass distribution patterns, thereby supporting the dual objectives of carbon sink enhancement and adaptive capacity under ongoing climate change in sandy lands.