Nitrogen addition improves drought tolerance in Camellia japonica (Naidong) seedlings

Abstract

The northernmost population of Camellia japonica globally is a unique ecotype within the species. Water deficit and atmospheric nitrogen deposition are two critical environmental factors that influence plant growth and primary productivity, particularly in the context of environmental change. However, the interactive effects of drought and nitrogen deposition on the physiology and growth of Naidong seedlings have not been investigated. To address this gap, we conducted a greenhouse experiment to investigate the individual and combined influences of different water and nitrogen (N) levels on growth, leaf morphology and physiology, and biomass and carbohydrate allocation of three-year-old Naidong seedlings. The results demonstrated that drought reduced height, basal diameter, specific leaf area, biomass accumulation, net photosynthesis, and non-structural carbohydrate (NSC) pool in the root of seedlings. However, water use efficiency (WUE) increased under slight drought conditions. Moderate (6 g N m−2 year−1) nitrogen addition enhanced seedling biomass accumulation, carbon fixation capacity, and WUE. Furthermore, a significant interaction between water and nitrogen deposition on Fv/Fm, soluble sugars concentration in the stem, and starch concentration in the root of Naidong seedlings was discovered. Drought and nitrogen deposition exhibited antagonistic effects on seedling biomass accumulation and photosynthetic capacity. The adverse impact of drought on growth and physiological responses could be partially compensated by increased nitrogen availability. This study highlights the need to include more variables when assessing a species' vulnerability to shifts in environmental conditions in the context of global change studies. Furthermore, our findings provide supportive data for the survival of C. japonica under future climate scenarios.