Spatiotemporal variations in solute chemistry of stemflow and throughfall within a xerophytic shrub ecosystem in Northern China

Numerous studies have demonstrated the chemical alteration of throughfall and stemflow by vegetation in forested ecosystems. However, less is known about the temporal variations and spatial patterning of solute chemistry in stemflow and throughfall within arid ecosystems where water and nutrient availability are generally limited. This study systematically examined the variations of various cations (K⁺, Na⁺, Ca²⁺, Mg²⁺, and NH₄⁺), anions (NO₃⁻, SO₄²⁻, and Cl⁻), pH, total nitrogen (TN), total phosphorus (TP), and total organic carbon (TOC) in stemflow and throughfall by a xerophytic shrub species (Caragana korshinskii Kom.) within a desert ecosystem of northern China. We found that after accounting for the effects of sampling date and shrub variations, stemflow was significantly chemically enriched compared to throughfall (p < 0.001). TN, TP, TOC, cations and anions in stemflow exhibited significant decreasing trends during the course of individual rainfall events (p < 0.001), while pH of stemflow showed a significant increasing trend (p < 0.001). Throughfall ion concentrations demonstrated radial spatial differentiation below the canopy, with TOC, TN, K⁺, Na⁺, Ca²⁺, NO₃⁻, and Cl⁻ showing a significant decreasing trend from the shrub base to the canopy outer edge (p < 0.001), whereas TP, Mg²⁺, and SO₄²⁻ displayed no clear trend along this radial gradient. In general, ionic concentrations in stemflow and throughfall initially increased and then tended to stabilize with a prolonged antecedent dry period length, whereas pH showed the opposite trend. For all solutes examined, flux-based enrichment ratios of stemflow to gross rainfall (E_P) and to throughfall (E_T) averaged 24.1 and 10.2, respectively. This study provides insights into the dynamic processes of nutrient enrichment driven by canopy rainfall partitioning and the shrub “fertile island” effect in arid ecosystems.