Enhancing Drought Resilience in Calligonum mongolicum through Nitrogen-Mediated Amelioration of Metabolic Stress: A Comprehensive Exploration of Phytohormones, Sugar Metabolism and Antioxidants Responses

Abstract

Abstract Groundwater resources sustain phreatophytes in arid ecosystems. Nevertheless, how phreatophyte seedlings respond to topsoil water and nutrients before reaching groundwater remains elusive. This study unraveled the effects of three irrigation levels (well-watered, medium-drought, and severe-drought) and N-fertilization on multiple physio-biochemical responses in Calligonum mongolicum seedlings. Drought-stressed seedlings significantly enhanced reactive oxygen species, lipid peroxidation, and oxidized ascorbate-glutathione in shoots and roots, leading to impaired chlorophyll pigments, water status, and biomass, compared to control. They displayed higher abscisic acid, salicylic acid, jasmonic acid, and strigolactones but reduced indole acetic acid (IAA), cytokinin (CTKs), and zeatin riboside (ZR) in shoots and roots, and gibberellic acid (GA) and brassinosteroids (BR) in shoots. Lower starch and higher fructose, glucose, and sucrose, are possibly due to dynamic changes in carbohydrate metabolizing enzymes. Further, significantly upregulated superoxide dismutase (SOD), catalase, and ascorbate peroxidase (APX) in shoots, while glutathione-peroxidase and glucose-6-phosphate dehydrogenase observed in shoots and roots under either stress. Lower SOD and APX in roots; PPO in shoots while other enzymes of the ascorbate-glutathione cycle in shoots and roots following either stress, suggesting the sensitivity of the anti-oxidant mechanism. Conversely, N-addition enhanced the productivity of drought-stressed seedlings by improving their chlorophyll pigments, and endogenous hormones (IAA, GA, CTK, BR, and ZR), which may account for their better growth. Moreover, upregulated O2•−-H2O2-scavenging mechanism, and soluble sugar, resulting in better status and biomass. Hence, N-supplementation could be an effective strategy to enhance drought-resistance in Calligonum seedlings to restore their communities in hyper-arid conditions under future climate change.