Abstract:

Chinese fir is an important timber species in south China.Since the productivity of Chinese fir plantation had been seriously declining after successive planting,the sustainable management of Chinese fir plantation becomes extremely important.In order to select the clones growing fast in degraded soil,High-nitrogen-efficiency-genotypes of Chinese fir clones were studied under three sorts of nitrogen stresses(glight nitrogen deficiency,medium nitrogen deficiency,heavy nitrogen deficiency)throught the physiological process analysis of Chinese fir clones.The results were as follows:there were significant differences in nitrogen utilization efficiencies among different Chinese fir clones.As the degree of nitrogen stress increased,nitrate reductase activities and light saturation points of different clones decreased,CO₂ compensation points increased and responses of different clones to nitrogen stresses became more obvious.The tested clones may be classified into three categories:strong,weak and intermediate capacity to nitrogen stresses according to their responses to nitrogen stress.Among the tested clones,No.163 and No.301 were the High-nitrogen-efficiency clones that could produce high yield in the site of low nitrogen concentration and ought to be popularized for poor site.These clones have practical significance to buffer the increasingly sever soil degradation and provide a new approach to control the productivity decline for successive planting of Chinese fir.

Key words: High-nitrogen-efficiency, Genotype, Chinese fir, Clones