Characteristics Of Soil Respiration Along Eroded Sloping Land With Different SOC Background On The Hilly Loess Plateau

Aiming at scientific problems ofcharacteristics of soil respiration along eroded sloping land with different SOC background on the hillyloess plateau, we chose the Ansai County of a typical hilly and gully area to carry the experiment. We studied the dynamic characteristics of soil respiration in different parts of the eroded slope and under different soil organic carbon background at different time scales, to understand the effect of soil carbon emission factors of erosion slope and the effect of erosion slope soil carbon sink. The research results could provide basis forthe research of carbon storage under erosion and the evaluation of regional environment under soil erosion. And the same time, they also provided the background knowledge of reducing the content of carbon dioxide in the atmosphere and slowing down the green house effect. The main conclusions were as follows:1、Soil respiration response to erosion showed obviously on-site and off-site effects along the eroded sloping land. The soil respiration rate in different parts of the slope was the desposition area > control area > erosion area. The soil respiration in different parts of the slope all had strong response to the precipitation events.Thenonlinear model Rs= ae^bTW^ccould explain the relationship between soil respiration and soil temperature and moisture in spring, summer and autumn.The model Rs=a+bT+cW could explain the relationship between soil respiration and soil temperature and moisture in winter.Soil respiration in the deposition area was higher than the soil respiration of the control area, and soil respiration in the control area was higher than the soil respiration of the erosion area. The coefficient of variation of soil respiration in the erosion area was higher than the coefficient of variation of soil respiration in deposition area and control area. With the increase of organic carbon, the soil respiration rate under different eroded slope positions increased gradually.2)Soil respiration in the deposition and erosion areahad strong response to precipitation events. The response of the soil respiration in thedeposition area tothe precipitation event would reach the peak value, when the soil moisture was 17.7¹7.8%.And the responseof the soil respiration in theerosion area tothe precipitation event would reach the peak value, when the soil moisture was 14.2¹4.4%. Due to the different sensitivity of soil respiration in deposition and erosion areato soil moisture,soil respiration in erosion area reached its peak first, after the occurrence of heavy rainfall and strong rainfall.3)Thenonlinear modelRs= ae^bTW^ccould explain the relationship between soil respirationand soil temperature and moisture in spring, summer and autumn.The modelRs=a+bT+cWcouldexplain the relationship between soil respirationand soil temperature and moisture inwinter.2、Soil respiration at different time scaleshad obvious spatial heterogeneity.The time of daily dynamics of soil respiration in different seasons arrivingthe minimum and peak arrival were different, which showed that the time of minimum and the peak arrived were early in summer and the later in winter. The soil respiration rate was maintained at a high level throughout the day. In winter soil respiration rate was negative.The overall performance of soil respiration rate in different seasons is summer > spring / autumn > winter.The minimum value appeared in December, and the maximum value appeared in June.Diurnal variation of soil respiration had the same trend at different slope positions under the same organic carbon level.The diurnal variation of soil respiration was mainly affected by the soil temperature.Soil respiration reached the minimum value at 6 in spring and summer, 1hour earlier than soil respiration in autumn and winter.And soil respiration reached the peak at 13 in summer, 1 hour earlier than soil respiration in spring and autumn, 2 hours earlier than soil respiration in winter. 2)Diurnal variation of soil respiration had the same trend under different organic carbon level, increasing with organic carbon levelincreased. In summer, soil respiration maintained a high level. But soil respiration in winter showed negative value in the range of-0.7⁰umol.s-1.m-2.3)Monthly dynamic changes of soil respiration had the same trend at different slope positions under the same organic carbon level.In summer, monthly dynamic changes of soil respiration and monthly dynamic changes ofsoil moistureat the appropriate slope had the same trend. But in spring, autumn and winter,monthly dynamic changes of soil respiration and monthly dynamic changes of soil temperature 0-5cm at the appropriate slope had the same trend.4)Monthly dynamic changesof soil respiration had the same trend under differentorganic carbon level and in different seasons. Soil respiration was highest in summer, followed by in spring, in autumn and in winter. 5)Inter-annualdynamic changes of soil respiration had the same trend at different slope positions under the same organic carbon level. The minimum value appeared in December, and the maximum value appeared in June.Inter-annualdynamic changesof soil respiration had the same trend under differentorganic carbon level. Soil respiration in 6-8 monthswas at the highest level of a year, and was at the lowest level in December and January of a year.3、Erosion slope average annual soil respiration was mostly affected by the soil temperature, explained 50.6% of the variability of soil respiration.Soil moisturecould explain 26.2% of soil respirationvariability.Soil organic carboncould explain 23.2% of soil respirationvariability. But soil respiration had different sensitivity to soil temperature in different seasons. Soil respiration was significantly correlated with soil organic carbon and soil temperature in different seasons.There was a significant correlation between soil respirationalong eroded sloping and soil organic carbon and soil temperature in different seasons. And there was a significant correlation between soil respirationalong eroded sloping and soil water content in spring, summer and winter.But there was no significant correlation between soil respirationalong eroded slopingand soil moisture in autumn. 2)The soil respiration along eroded sloping was different to the soil temperature sensitivityin different seasons, and was very sensitive to soil temperature in autumn, and was not sensitive to soil temperature in winter. 3)The contribution of soil temperature, soil moisture and soil organic carbon to soil respiration was different in different seasons.Soil temperature had the greatest contribution to soil respiration in spring and autumn, and had the minimum contribution to soil respiration in summer and winter.Soil moisture contributed most to soil respiration in deposition area in summer and winter.Soilorganic carbon contributed most to soil respirationin theerosion area in summer and winter. 4)Soil temperature was the most important factor affecting soil respirationalong eroded sloping, which could explain soil respiration variation 50.6%, followed by soil moistureand soil organic carbon, which could explain soil respirationalong eroded sloping variation 26.2% and 23.2%respectively.4、The deposition was the carbon sourceprocess, and the erosion was the carbon sinkprocess. Carbon source and sink related the carbon organic level.The net emission of carbon was positivein different seasons along eroded sloping, and it was the effect of carbon source. The net emission of the erosion area wasalmostnegative in different seasons along eroded sloping, which was the carbon sink effect.2)Carbon source and sink related the carbon organic level.The net emission of erosion along eroded slopingwas the carbon sink under moderate organic carbon level（Soil organic carbon content was between3.03g·kg-1and 6.82g·kg-1）, and was the carbon source under high organic carbon level（Soil organic carbon content was higher than 9.69g·kg-1）.