Influence of drought stress and N addition on the gas exchange, biochemical and growth traits in Quercus ithaburensis

Forest tree species are likely to be affected by drought due to global climate change. Drought and nitrogen (N) affect plant growth. Therefore, we should understand the mechanisms underlying the N availability and species response to drought for plant development. This paper had two objectives. First, it determined the effects of N addition on water potential, gas exchange parameters, soluble sugar and photosynthetic pigment content, leaf N concentration, and growth parameters under drought stress and well-watered conditions. Second, it searched the drought response of Quercus ithaburensis Decne. subsp. macrolepis (Kotschy) Hedge&Yaltırık seedlings under N conditions with drought stress. In a greenhouse, one-year-old seedlings were exposed to two drought stress and nitrogen addition and three drought cycles. Drought stress significantly reduced stem water potential, relative water content, net photosynthetic rate, stomatal conductance, transpiration rate, leaf area, root collar diameter, seedling height, shoot and root dry weight. On the other hand, it increased water use efficiency and soluble sugar content. N addition is effective on soluble sugar content and photosynthetic pigment content, and promoted leaf N concentra­tions. Nitrogen addition under well-watered conditions stimulated the growth of Q. ithaburensis seedlings. Drought stress changed the physiological response of Q. ithaburensis seedlings (decreased water potential, net photosynthetic rate, stomatal conductance, and transpiration rate) in the short term, although nitrogen addition under drought stress has not changed the decreasing trend overall.