攀枝花苏铁(Cycas panzhihuaensis)的根瘤和固氮作用

 分布在南亚热带金沙江干热河谷的攀枝花苏铁，普遍受蓝细菌侵染形成特殊的多级分枝珊瑚状根瘤簇。当年生树苗活瘤重可达8克／株，100年生370克／株。固氮活性在秋季一般为1.8—11.1μmol C2H4／g·f·w·h-1，它明显受光照和湿度影响，昼夜动态是白天活性明显比夜间高。苏铁固氮量从0.64—18.69毫克／株·小时，它在生态系统的氮循环中起良好作用。

THE ROOT NODULES AND THE NITROGEN FIXATION PROPERTY OF THE CYCAS PANZHIHUAENSIS

The cycas distributed in the dry-hot inshajiang river valley in the south-subtropical region of China,infected by the cyanobacteria,form especial coral-like nodule clusters with multiply branches. The nodules are most numerous within 10cm below the soil surface. The living nodules of current seedlings amounted to 8 g per plant and those of over 100 year plants averaged 370 g. The nitrogen fixation activity is usually from 1.8 to 11.1 μmol/g·f·w·h-1 in the autumn, and is obviously influenced by light and soil moisture, Daily variation of N2-fixing activity has shown that it is mhcu higher in daytime than at night. Nitrogen fixation amount for the cycas varied from 0.64 to 18.68 mg/plant·h-1.This suggests that it may play a certain role in the nitrogen cycle of