Spatial And Temporal Heterogeneity Of Soil Respiration On The Slope In The Hill-gully Areas Of Loess Plateau

Soil respiration is an important component of the terrestrial ecosystems carbon cycle and CO2 emissions from the soil exceed all the other terrestrial-atmospheric carbon exchanges.Any changes of land-use pattern play a great impact on soil carbon sources and sinks.In recent years,large-scale returning farmland to forests on Loess Plateau will necessarily make some important effects on carbon cycling and provide a feedback to global warming.Ansai Country is located in the typical loess hill-gullied region of the Loess Plateau.In order to understand the spatial and temporal patterns of soil respiration and the controlling environmental factors,we studied the daily variation and its relationship with soil temperature and water content on the slope of returning farmland to forests during growing season.Measurements of soil respiration were made with a LCpro+portable photosynthesis system that based on the principles of infra-red gas analyzer and its soil respiration chamber.The results showed that:(1) The soil respiration rate fluctuated among the measurement plots,and coefficient of variation was more than 20%in June and July.With the change of environmental factors,soil respiration rate in downhill more than uphill.(2) Through Geostatistics method to analysis soil respiration on the slope,the results showed that soil respiration rate in June from the aggregation of small scale transformation into gathering the larger scale distribution in July,with the stronger effect of rainfall,the pattern was changed into the aggregation of small scale type in August and September.(3) Temporal patterns of soil respiration could be expressed as single peak curve, and the times of the minimum soil respiration appeared at 8:00,the maximum at 14:00-16:00 during the growing season.Soil respiration was accorded with the dynamics of soil temperature,and had a significant exponential correlation with the temperature.(4) Soil respiration rate was controlled with the soil temperature and soil content at 10cm depth,but the effect of soil temperature on soil respiration rate is greater than that of soil water content.And the soil temperature can explained 90%of the variance of the diurnal soil respiration.But in the early of growing season,soil respiration was consisted with the soil moisture.As the rainfall leading to the increasement of soil moisture,the soil respiration rate in September was rapidly decreasing.(5) Based on the measurements,the results showed that soil respiration rate was consisted with soil erosion.In runoff plot with serious erosion,soil respiration changes remarkably in the growing season.