Divergent non-structural carbohydrate allocation strategies in desert shrubs under coal mining-induced environmental gradients in Xinjiang, Northwestern China

Large-scale open-pit coal mining can create pronounced environmental gradients around mine sites. These gradients are often accompanied by coal-dust dispersion and elevated heavy-metal loads in surrounding soils, which may alter physiological and ecological processes of vegetation. As a key indicator of plant carbon balance, non-structural carbohydrates (NSC) provide valuable insights into plant adaptive strategies to mining-associated disturbances through their spatial distribution patterns. In this study, three typical desert shrubs, including Haloxylon ammodendron, Nitraria tangutorum, and Reaumuria songarica, were investigated in the Zhundong open-pit coal mining area of Xinjiang, China. Sampling transects were established in four directions, each comprising seven distance gradients, to collect branch and leaf samples for the analysis of NSC and its components, soluble sugars (SS), and starch (ST). The results revealed significant species- and organ-specific patterns in NSC dynamics. Variability was generally higher in branches than in leaves for NSC, SS, and ST, with R. songarica exhibiting the lowest overall variability. Spatially, NSC in branches and leaves exhibited pronounced species- and organ-specific differentiation along both directional and distance gradients. Branch NSC peaked upwind (N) in H. ammodendron and downwind (SE1; southeast transect 1) in R. songarica, reflecting their divergent adaptive strategies to heterogeneous mining environments. Furthermore, N. tangutorum consistently displayed higher NSC and component concentrations in both organs compared to the other species, while leaves universally contained higher concentrations than branches. Redundancy analysis and hierarchical partitioning identified the primary environmental predictors of NSC variation (based on the measured soil-derived variables) as heavy metals (Cr) for H. ammodendron, soil pH and nitrogen for N. tangutorum, and water and nutrient availability for R. songarica. Overall, branch NSC was mainly associated with heavy metals, whereas leaf NSC was more closely associated with water and nitrogen, exhibiting particular sensitivity to nitrogen availability. Importantly, this study elucidates the species- and organ-specific carbon allocation strategies of desert shrubs across mining-associated soil environmental gradients, providing physiological and ecological insights for vegetation restoration and ecological rehabilitation in arid open-pit mining regions.