Abstract: With orthogonal experiment,this paper studied the effects of the concentrations of Mg²⁺,dNTP and primer,the anneal temperature,and the extending time and cycling times on RAPD of soil microbes.The results showed that the feasible PCR reaction system for soil microbes should be carried in 25 μl volume,which was composed of 7 ng soil microbial DNA template,20 pm random primer,l.5 uTaq enzyme,3.0 mmol·L^-1 Mg-CL₂,and 0.2 mmol·L^-1dNTP.The PCR reaction procedure was firstly,keeping 94 for 3 min to make soil microbial DNA denatualize followed by 39 cycles,each including 94 for 1 min,37 for 40 s,and 72 for 1.5 min,and finally,keeping 72 for 7 min for extending.

Key words: Watershed, Ecosystem, Forest, Water balance