Effect of climatic factors on nitrogenase and hydrogenase activities in nodules of Acacia confusa, A. auriculaeformis and Dalbergia balansae were investigated. Hydrogen uptake activity was found in the nodules of all the three leguminous trees. In the presence of exogenous hydrogen, nitrogenase activity in nodules increased markedly, indicating that hydrogenase played an important role in increasing the efficiency of nitrogen-fixation in symbiotic system. Seasonal changes were obvious in nodulation and nitrogen fixation of leguminous species grown in Xiamen area． Results showed that more nodules produced and higher C2H2-reducing activity were observed in summer and autumn than in early spring and winter．The optimun temperature for both nitrogenase and hydrogenase activities in nodules was 25-30℃．Minor soil water deficit did not affect the C2H2-reducing activities，but serious soil drought markedly reduced the activities of nitrogen-fixation and hydrogen uptake．Shading reduced both nitrogenase and hydrogenase activities in nodules.
