Abstract: Peat forming and accumulation is one of main approaches of natural ecosystems on surface of the Earth to store the solar energy. A series of simultaneous field spot fixed experimental study were conducted at 4 wetlands respectively in different environment in Northeast China and North China from 1993 to 1996. Based on the experiments, it is researched that the relation of decomposition of herbaceous wetland plants and peat accumulation to the physiological properties of plants and environmental condition. Aquantitative model for relation of peat forming to the climate is established. Two species of mire plant, i.e. reed (Phragmites communis) and sedge (Carex schmidtii) were selected for the nelon bag test to determine the decomposition rate in 5 different kinds of microenvironment in the wetlands. The experiments show that the substantial composition and the anaerobic environment of roots are both not favorable to decay. The sequence of the micro environments on decomposition of plants is water surface>underground>groundsurface>underwater>abovewater. The dynamic change of decomposition is very obvious. In the first year, there are two decomposition rate peaks occured respectively during 0～10℃ period in spring and 20℃～20℃ period in summer. The changing curve of decomposition in the second year presented a monopeak form. When the temperature is much high for the humidity, the decomposition is fast; when the humidity is much high for the temperature, the restrained decomposition is advantageous for peat to form. Finally, a model for the global peat forming climate was established, that is V=(S-56 % )/T=0 009 28 in whichV : the humidity thermal ratio of peat forming climate; S: multiyear average of relative humidity during the >0℃ period; T: multiyear average of air temperature during the >0℃ period. When S >56%, and ( S -56%)/ T >0 009 28, the climate environment is favorable to peat forming; when S <56% or S >56% while ( S -56%)/ T <0 009 28, the climate is not favorable to peat forming.

Key words: herbaceous peat, decomposition of wetland plant, humidity thermal ratio of peat forming climate