Abstract: The development of niche theory and its application in forest ecological study are reviewed in this paper.It is pointed out that the functional action of plant unit was not involved in previous niche concepts, The particularities of niche of plant unit are discussed and a new method is developed to determine it with pho-tosynthetic production as a functional index. This method can be applied to studv the mechanisms of in-ter／intra－species competition, community structure and dynamics in forest ecosyStem.

Key words: heterotrophic nitrobacteria, nitrification, subculture, stability.