Non-Structural Carbohydrates and Growth Adaptation Strategies of Quercus mongolica Fisch. ex Ledeb. Seedlings under Drought Stress

Abstract

Under drought stress, plants can change their morphology, physiological characteristics, and carbon allocation to maintain survival and growth. Non-structural carbohydrates (NSC) are major substrates for plant metabolism and play an important role in seedling survival and growth under drought conditions. Mongolian oak (Quercus mongolica Fisch. ex Ledeb.), a constructive species distributed in northeast China, has a high drought tolerance. However, studies on seedling growth and the NSC dynamics of Mongolian oak under different drought intensities and durations are limited. To investigate this, our study measured photosynthetic characteristics, growth, biomass, and NSC concentrations for Mongolian oak seedlings on the 0, 15th, 30th, 45th, and 60th day of the experiment under three soil moisture conditions [75% ± 5% (CK), 50% ± 5% (W1), and 23% ± 5% (W2) of soil moisture field capacity (FC)]. Results showed that the growth and biomass gradually decreased as the soil moisture decreased, but the root: shoot ratio and root biomass allocation ratio gradually increased. In the W1 treatment (moderate drought), NSC content in the stems and taproots was 7.42% and 16.39% higher than those in CK at 60 days. However, in W2 treatment (severe drought), NSC content in the stems and taproots was significantly higher than those in CK during the whole period (p < 0.05), and they were 14.14% and 26.69% higher than those in CK at 60 days. We found that, under drought stress, Mongolian oak seedlings had lower growth but higher allocation to root biomass and higher NSC content in stems and roots. Furthermore, the root system became a vital carbon sink under drought stress and was beneficial for seedling survival.