Affecting Factors Of Soil Respiration In The Water-wind Erosion Crisscross Region

Water-wind erosion crisscross area is located in the north of the Loess Plateau, which is one of the most serious soil erosion areas in the Loess Plateau. Since Grain to Green project has conducted many years, the land use patterns in this region have changed in some extent. The diurnal dynamic characteristics and seasonal characteristics, affecting mechanism, soil carbon sink of soil respiration needed to be studied in the changing of the vegetation type. For that reason, this research had chosen 16 kinds of typical land use patterns to study diurnal dynamic and seasonal characteristics of soil respiration, as well as the influence of environmental factors and soil carbon sink. Besides, we investigated the amount of vegetation above-ground biomass and its influencing factors in different land use patterns.The diurnal dynamic change of soil respiration rate were very obvious and emerged the single-peak type curve in 7 kinds of typical land use patterns in the water-wind erosion crisscross region on the Loess Plateau. Soil respiration rate was the highest at 12:00 ~ 15:00 and the lowest at 4:00 ~ 6:00. In our research, we found the soil respiration rate value at 9:00 ~ 10:00 (Beijing time) was closest to the daily value of soil respiration. The soil respiration rate of 7 kinds of typical land use patterns had positive significant correlation with soil temperature at 6 cm depth (p<0.01). As the soil water content increasing, the soil respiration rate and its Q10 rose first, but after they all decreased. In August, soil respiration rate was significantly higher than soil respiration rate in September in the same land use patterns (p<0.05), and the diurnal variation of soil respiration rate had significant difference among different land use patterns in the same months (p<0.05). The rainfall could reduce the soil respiration rate.Soil respiration rate during the vegetation growing season followed a trend of multiple peaks under different land use patterns. The higher value of soil respiration appeared from July to August, and the lowest appeared in October. In June to September, soil respiration rate was significantly difference in the same land use patterns (p<0.05), and the season variation of soil respiration rate had significant difference among different land use patterns in the same months (p<0.05).There were significantly (p<0.05) or highly significant (p<0.01) correlations between soil respiration rate and the temperature of the air or soil at 5, 10, 15 cm soil depths. The results indicated that the exponent function could simulate their relationships best. Soil respiration rate of Salix babylonica land and Artemisia desterorum land had a negative relationship with soil water content. The RS=a + b·TS+c·WS function could simulate their relationships best among soil respiration with soil tempreture and soil water content. Soil temperature and soil moisture could explain 46%~89% variation of soil respiration in June to October。Soil respiration had significant relationship with soil organic carbon content and total nitrogen. Soil respiration with total soil ammonium nitrogen, C/N and ammonium hydroxide had negative correlation, but not significant. Soil respiration and the total porosity had significant relationship (y=0.2613+0.0211x, R2=0.0856*),but had negative correlation with soil bulk density (y=0.2613+0.0211x, R2=0.0856*). Soil respiration rate and the vegetation leaf area index were significantly and linearly correlated.There was a significant positive correlation between above-ground dry biomass and 0-100 cm soil water storage, soil organic carbon content, total nitrogen and the height of vegetation in the study area. Bare net ecosystem showed significantly carbon "source "; and farmland, terraced farmland were the weak performance of the carbon "sink"; but Medicago sativa land, abandoned land, Stipa bungeana land, wasted land had a significant carbon "sinks". The result showed that soil carbon emissions and absorption pattern was changed and could be helpful for soil carbon "collect" function in the Process of Returning Farmland to Forest and Grassland.