Responses of seedling growth and physiological characteristics of perennial species Sophora alopecuroides to warming and nitrogen deposition in temperate arid habitats, China

Abstract Background It is now undisputed that global warming and nitrogen deposition are having a significant impact on ecosystems. Therefore, it is important to gain a better understanding of how plants are responding to these changes. Of particular interest is Sophora alopecuroides, a common and invasive native plant species found in the temperate desert steppes and arid zone temperate steppes of northwestern China. It is of great importance to gain insight into the growth and physiological responses of its seedlings when exposed to conditions of warming and nitrogen deposition. This knowledge is crucial to elucidate the invasion mechanisms of the species and to assess the potential ecological security risks. To study these effects in depth, treatments of nitrogen (N) addition, warming (W), and a synergistic approach of warming and nitrogen (WN) were established. Results The W and WN treatments demonstrated no statistically significant difference in germination rate, index, or potential relative to the control (CK), whereas the N treatment exhibited a notable reduction in germination rate. The W and WN treatments were found to significantly enhance several key growth parameters, including root-to-shoot ratio, stem diameter, plant height, and axial root length. In contrast, the N treatment was observed to significantly reduce these same parameters, with the exception of stem length. In comparison to the control treatment, the nitrogen treatment resulted in an increase in leaf biomass, whereas the water treatment led to a reduction in leaf number. The W and WN treatments were observed to significantly enhance both above-ground and below-ground biomass. The N treatment also resulted in an improvement in leaf biomass ratio and root-to-shoot ratio, while the WN treatment increased stem biomass ratio and root biomass ratio. The N treatment resulted in a reduction in chlorophyll, soluble sugar, and soluble protein contents. In contrast, the W treatment led to a significant decrease in malondialdehyde levels, while the WN treatment increased nitrate reductase activity. Both the N and W treatments elevated enzyme activity, but also had a stronger inhibitory effect on superoxide dismutase enzyme activity. Conclusions The treatments of warming, nitrogen addition, and their combination resulted in significant alterations to the germination characteristics, biomass accumulation, and physiological metabolism of S. alopecuroides. These findings are of great significance for advancing our comprehension of the species' influence on ecosystems and for the formulation of efficacious management and control strategies.