Objectives Nebkhas, which are widely distributed in desert ecosystems, play a pivotal role in sustaining regional ecological stability by mitigating wind erosion, enhancing soil fertility, and fostering biodiversity. Soil stoichiometric characteristics serve as critical indicators of nutrient cycling dynamics and ecosystem resilience within nebkha systems. This study focuses on the Nitraria tangutorum nebkhas, a dominant shrub species in arid regions, aiming to elucidate soil stoichiometric patterns and their underlying drivers.
Methods Field sampling was conducted across five spatially distinct nebkhas in the eastern Qaidam Basin, China. Soil samples were collected from three microhabitats: within nebkha mounds, the subsurface zone beneath nebkhas, and the inter-nebkha substrate. Vertical profiles (0−135 cm) were analyzed for total nitrogen (TN), total phosphorus (TP), organic carbon (SOC), available nitrogen (AN), available phosphorus (AP), and available potassium (AK). Stepwise regression analysis identified key soil factors influencing stoichiometric ratios, while Spearman correlation analysis assessed relationships between nutrient ratios and environmental variables. Structural equation modeling (SEM) quantified the direct and indirect effects of soil physicochemical properties (e.g., cation exchange capacity, bulk density, soil moisture, root biomass, and litter accumulation) on stoichiometric dynamics.
Results 1) The average contents of TN, TP and SOC in Nitraria tangutorum nebkhas were 0.11−0.13 g/kg, 0.38−0.43 g/kg, and 1.48−1.76 g/kg, respectively, lower than other deserts in TN and SOC. TP content in nebkhas was significantly depleted compared to underground section of inter-nebkhas (P<0.05). AN, AP and AK contents are in range of 2.98−4.31 mg/kg, 2.67−3.93 mg/kg, and 68.68−87.03 mg/kg, respectively, at the levels of extreme deficiency, deficiency and slight deficiency. AP content in nebkhas was significantly higher than in underground section (P<0.05), and AK content in nebkhas was significantly higher than underground section beneath (P<0.05) and inter-nebkhas (P<0.001). The mean Stoichiometric ratios values (C/N: 14.64−15.45, C/P: 3.86−4.48, and N/P 0.25−0.32) revealed the deficiency degree of nutrients in order of N>C>P. C/N ratios exceeded those in natural deserts but were lower than in oasis plantations, while C/P and N/P ratios were universally lower than in other desert soils. N/P in nebkha mounds surpassed subsurface values (P<0.05). 2) TN, SOC, AN, AP, AK, C/P, and N/P exhibited a "decrease-increase-decrease" trend with depth, whereas TP declined uniformly and C/N increased. Nutrient accumulation peaked in surface (0−5 cm) and deep (110−130 cm) layers. Root volume, diameter, biomass, and litter weight as well as soil moisture varied significantly across soil layers (P<0.05), with the 100−135 cm layer harboring dense root networks and elevated moisture. 3) Soil stoichiometry was jointly influenced by nutrient availability (AN, TP, SOC) and physicochemical factors (cation exchange capacity, bulk density, moisture, root biomass, litter mass). SEM highlighted root distribution and litter accumulation as primary mediators of moisture heterogeneity, thereby regulating nutrient cycling and stoichiometric ratios.
Conclusions The Nitraria tangutorum nebkhas exhibit pronounced nutrient scarcity (TN, TP, SOC, AN, AP), with nitrogen emerging as the primary growth-limiting factor. Vertical nutrient dynamics reveal a stratified pattern: subsurface P depletion, surface and deep nutrient enrichment, and mid-profile minima. The heterogeneous distribution of roots and litter, coupled with soil moisture gradients, drives these stoichiometric shifts. These findings underscore the vulnerability of nebkha ecosystems to nutrient stress and emphasize the need for conservation strategies that prioritize soil fertility restoration and belowground biodiversity protection.
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