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

摘要： 本文报道大叶相思的结瘤固氮和氢酶活性的研究结果。大叶相思结瘤状况与其他含羞草亚科的树种相似,刚形成的幼瘤为单生球状或椭圆形,以后顶端伸长或分叉,呈分叉状、姜状和扇状。同一植株的不同成熟度根瘤的固氮活性也不同,成熟壮瘤固氮活性最高,幼瘤次之,衰老瘤最低。不同立地条件下种植的大叶相思根瘤固氮活性虽有差异,但生长在pH 4.7的酸性红壤中的大叶相思,根瘤固氮活性仍具有较高水平。大叶相思根瘤固氮活性也有明显的季节变化,夏秋较高,春冬较低。根瘤离体后7小时内固氮活性变化不大,甚至在离体后21小时内仍维持一定水平的固氮活性。大叶相思根瘤具有吸氢酶,其吸H₂活性在最初3小时内随时间延长而升高,3-7小时内仍维持一定水平。在根瘤固氮系统中注入外源分子H₂,可提高固氮酶活性,外源H₂最适浓度为7.5%。由于其根瘤具有催化吸收分子H₂的氢酶系统,能吸收利用固氮反应所放出的大量H₂,因而能更有效地利用光合产物于固氮过程。大叶相思根瘤离体后能较长时间维持高的固氮活性水平,可能与其吸H₂酶系统有关。

关键词: 大叶相思, 根瘤, 固氮活性, 吸氢活性