关键词: 大叶相思, 根瘤, 固氮活性, 吸氢活性

Abstract: The main object of this study is to make some observations on the variation of nitrogen fixing activity in the nodules of A.auriculaeformis tinder different conditions, attempting to collect together some scientific data in time for selection of pioneer plants for afforestation on the red soil hilly lands of S. E. China. The life-span of root nodules in A.auriculaeformis was longer and might grow over winter. New nodules might occur on the top of old nodules. The nodules changed cosiderably in external shape during their growth, from single sphere or column to branchy or multibranchy. According to various shade of red in section and external shape, the nodules might be divided roughly into three physiological stages; juvenile, mature and senescent nodules. The highest C₂H₂-reducing activity, as determined by acetylene reduction assay, was observed in the mature nodules,the juvenile nodules ranked the second and the senescent nodules followed as the last. Effect of environmental factors on nitrogen fixation of A.auriculaeformis was investigated. In acid red soil with a pH between 4.6 and 5.7 A. auriculaeformis not only grew rapidly, but also the C₂H₂-reducing activity in nodules supported higher level. The seasonal variations in nodulation and nitrogen fixation of A. auriculaeformis grown in Xiamen area were observed. Results showed that more nodules formed and C₂H₂-reducing activity was higher in summer and autumn than in early spring and winter. The results of experiments in isolated nodules showed that C₂H₂-reducing activity supported higher level in 7 h after isolation from intact plants. Expression of hydrogen uptake (Hup) activity was found in nodules of A. auriculaeformis. Molecular hydrogen (H₂) markedly stimulated effect on the C₂H₂-reducing activity of nodules.

Key words: Acacia auriculaeformis, Nitrogen fixation, H₂ uptake