Soil moisture spatial variability and affecting factors of natural larch forest in northern region of Daxinganling Mountains of northeastern China

In permafrost zone of northern region of Daxinganling Mountains, characteristics of soil moisture spatial variability and the influence of canopy structure, soil temperature, rainfall on soil moisture distribution of natural larch forest had been researched at the slope scale. The results indicated that soil moisture of 0 - 5 cm gradually reduced from upslope to lower slope. Compared sampling belt 12 with sampling belt 1, the soil moisture reduced by 19.95%. The soil moisture of 5 -10 cm and 10 -15 cm gradually increased from upslope to lower slope, and the contents of soil moisture increased by 15.55% and 29.16% respectively. Average soil moisture content of 0 - 15 cm fluctuated between 17.61% - 18.77% and had a gradually increasing trend from upslope to lower slope. The vertical variation coefficients of upslope and lower slope were significantly higher than middle slope. The vertical variation coefficients of sampling belt 1, 11, 12 were the highest and respectively 10.17%, 13.39% and 15.02%, and they belonged to the medium degree of variation. The degree of level variation among sampling belts were very low. The soil moisture of 0 -5 cm had a significant positive correlation with leaf area index(LAI) and a significant negative correlation with diffuse non -interceptance(DIFN). The soil moisture of 5 -10 cm and 10 -15 cm had a significant negative correlation with LAI , but it did not have a significant correlation with DIFN. Soil temperature had a significant negative correlation with soil moisture. The soil moisture of all sampling belts had reduced gradually in the four days after rainfall, the decreasing rate of surface soil moisture was significant larger than that of subsoil moisture, it indicated that the rainfall had a larger influence on surface soil moisture than subsoil moisture.