Physiological Responses of Eucalyptus grandis Hill ex Maiden Saplings to Nitrogen Fertilization and Drought Stress

The effect of nitrogen (N) addition and short-term drought stress on growth and other physiological processes in Eucalyptus grandis Hill ex Maiden saplings was investigated. The experiment consisted of nine treatment combinations with three levels of N (0, 0.65 and 1.3 g per pot) and three levels of drought stress (soil moisture at 40%, 60% and 80% field capacity, FC). N fertilization promoted growth in terms of height and basal diameter, and net photosynthetic rate (Pn) of E. grandis saplings across all water treatments. Compared with those that were not given N, the metabolism of N-treated saplings appeared to be more active and possessed better osmoregulatory ability due to higher leaf water potential (LWp) and Pn across all water treatments. N addition (especially 1.3 g N) was likely to have a promotive action on water consumption in the saplings by enhancing gas exchange, resulting in reduced leaf relative water content (LRWC) and leaf vapor pressure deficit (VpdL) in the face of severe drought. N application does not appear to benefit E. grandis saplings under severe drought condition. Key Words: drought stress, Eucalyptus grandis, N application, photosynthetic characteristics, water physiology