Nitrogen deposition does not reduce water deficit in Ailanthus altissima seedlings

- Water deficit restrained growth and physiology of A. altissima.
- N load facilitated growth and physiology of A. altissima.
- High N addition did not inhibit growth of A. altissima.
- A. altissima was not affected by the interactions between water deficit and N load.

Water deficit and nitrogen (N) deposition are two important factors affecting plant growth in the context of global change. Here we selected Ailanthus altissima, a locally important tree species in North China, to study the combined effects of soil water status and N addition on plant growth. Ailanthus altissima seedlings were exposed to two soil moisture conditions (35% and 75% of the saturated soil moisture content) and three N treatments (0, 5, and 15 g N m−2 year−1) in a greenhouse experiment. After 50 d of treatment, plant growth, biomass production and allocation, and leaf physiological parameters were determined. Water deficit significantly restricted some parameters of growth and biomass accumulation, like height and basal diameter, total biomass, lateral root biomass, leaf biomass, and stem biomass. Some physiological parameters were also affected significantly by water deficit, leaf N content and qP decreased as soil moisture decreased and WUE was highest in water deficit condition. However, the high N load increased crown area and total biomass, lateral root biomass, and root biomass. With respect to physiological parameters, net photosynthetic rate, leaf N content, ΦPSII and ETR were clearly higher in the high N addition group than in the control group. Overall, an interaction between water deficit and N load had no significant effects on plant growth. Based on the present study with A. altissima seedlings, considering their rapid growth rate, we conclude that this species is better adapted than other deciduous trees to water deficit and high N additions under future global change scenarios, making it suited for vegetation restoration and reconstruction projects in the warm temperate zone of China.