| Abstract |
The number of aerobic free-living nitrogen fixation bacteria and factors in soil at different stands covered with Pinus rigida, Quercus acutissima and Zoysia japonica in Cheongju area were investigated from Feb. to Sept 1981. 1. The numbers of N₂-fixation bacteria, according to the seasonal changes, increased gradually from winter to spring and summer. But the growth pattern revealed some differences in accordance with plant cover stands : the numbers increased abruptly in May at Pinus, May-June at Quercus and Apr. May at Zoysia stand. The pick of numbers represented in Aug. Sept, at Pinus, Jul-Aug. at Quercus and May-Jun. at Zoysia stand, respectively. 2. The interrelationship between the monthly changes of enviotnmental factors and numbers of N₂-fixation bacteria at different stands, mainly depends upon the soil temperature than other soil factors (r=0.71-0.84). The numbers of N₂-fixation bacteria may increase 5-7 times according to increase 10℃ of soil temperature, and optimal range was 20-30℃ for growth. Equation of the interrelation between soil temperature and numbers could be stated as follows : log y=ax + b. 3. In the case of high soil temperature, the bacterial numbers presented high level in drought periods. Therefore, the N₂-fixation bacterial species in these soil seem to consist of resistant to desication. 4. The influence of soil organic matter for growth of N₂-fixation bacteria indicated low corelation. The reason may seen the content of organic matter in these soil existed abundantly above the quantities of limitation for growth. 5. In artifical gradients, the N₂-fixation bacteria were predominated at 20-30℃ same as natural condition, pH7-8, and 20-30% of soil water contents. 6. The vertical distribution of bacteria marked decreasing trends from surface to lower layers, and the decreasing degree was shown well in Zoysia, Quercus and Pinus stand in order. But in the trees, the numbers increased at 30cm layer estimated the region of root than 20cm layer. 7. Both catalase negative and positive group of N₂-fixation bacteria in soil increased according to the rise of the soil temperature. Catalase positive group was revealed as dominant group in winter, and catalase negative group revealed in summer. The change of dominant pattern was shown during Feb. to Apr. |
