Factors influencing soil respiration in a pea field in the Loess Plateau

Based on the continuous measurement of soil respiration in a pea field on the Loess Plateau,northern China,using a closed chamber infrared CO2 gas analyzer in 2007,the temporal variation of soil respiration was studied and the influence of temperature and moisture determined,and soil properties analyzed.The diurnal variation of soil respiration in summer showed an asymmetric single-peak pattern with the minimum appearing at 0:00-3:00hand the maximum at 11:0-13:00h.The daily mean was close to the observed values at 9:00and 19:00h.In winter the minimum occured at 21:00-0:00and the maximum at 13:00-15:00,with the mean close to the values observed at 9:00and 17:00.Moreover,the soil respiration in winter accounted for about 8.9%of the total annual value,hence the soil respiration in winter should not be ignored.Meanwhile the diurnal soil respiration exhibited a negative numerical flux in winter,which,this paper contends,is mainly caused by the phenomenon that the alkaline soil(pH8.2)in this area promotes soil secondary carbonate which enables the soil to absorb CO2.This phenomenon may lead to an underestimate of soil respiration rate in this region,and more importantly,it may provide evidence for future research on missing carbon sinks.Soil respiration fluctuated widely during the flowering and seed production period of pea in this year.The annual mean soil respiration rate was near to the observed values of March 29,with a maximum of 0.92μmol CO2/(m2·s)on July 21 and a minimum of 0.01μmol CO2/(m2·s)on December 14.Analysis showed that soil temperature was the key factor in the diurnal variation of soil respiration.However,soil moisturecorrelated poorly with soil respiration.These results may provide basic data for the research of carbon cycle process and their mechanisms in farmland ecosystems.