生态条件对马占相思结瘤固氮的影响

EFFECT OF ECOLOGICAL CONDITIONS ON NODULATION NITROGEN FIXATION OF ACACIA MANGIUM

本文研究了马占相思（Ａｃａｃｉａｍａｎｇｉｕｍ）结瘤固氮和生态条件的关系．结果显示．马占相思根瘤固氮活性的昼夜变化与固氮能源的供给有关，它受光、温影响较大，固氮活性昼夜变化的范围为１—５μｍｏｌＣ２Ｈ４·ｇ－１ｆｒｅｓｈｎｏｄｕｌｅｈ－１。固氮活性的季节性差异也很明显，且与温、湿度的变化关系密切，在温、湿度较好的５月—１０月．固氮活性较高．为３—１０μｍｏｌＣ２Ｈ４·ｇ－１ｆｒｅｓｈｎｏｄｕｌｅｈ－１．冬春的干旱和低温会影响根瘤的生长和存活．造成固氮活性降低甚至失去活性．不同年份和林地的根瘤生物量为１０４—６２５ｋｇ·ｈａ－１，以幼林期根瘤生物量较高．多数样地的根瘤生物量在３００ｈｇ·ｈａ－１以上．随着森林生态系统的发展．根系往土层深处生长以及林下草本和灌木层的增长等原因，根瘤生物量会受影响而有所下降。施肥松土能提高根瘤生物量５７—３４４ｋｇ·ｈａ－１，对增加固氮量有重大意义。

The nodulation and nitrogen fixation of Acacia mangium grown on the hill of Heshan Institute of Forestry in Guangdong was studied. The results showed that the diurnal variation of nodule nitrogenase activity for Acacia mangium was related to the energy supply of nitrogen fixation and depended on sunlight and temperature, the range for diurnal variation of nitrogenase activity being 1 to 5 μmol C2H4· g-1 fresh nodules h-1. Seasonal variation of nitrogenase activity was related to the temperature and humidity, it ranged from 3 to 10 μmol C2H4· g-1 fresh nodules h-1 in warm and rainy season from May to October.The growth retardation or death of the nodule and the degradation or loss of nitrogenase activity were affected by dry and low temperature in winter and spring. The nodule biomass for several plots in different years amounted to 104-625 kg·ha-1, and more biomass (over 300 kg·ha-1 ) appeared in early stage of the forest. Biomass decreased with the increase of forest age due to the herb and shrub developing and the root growth downward to the deep soil. Ditching and fertilizing increased the nodule biomass by 57-344kg·ha-1, which is significant for increasing the amount of nitrogen fixation.