The Blocking Effect is the Key Factor for the Sharp Descending of Soil Respiration Between Late Autumn and Early Winter in a Larch Forest

Throughout the year 2013 (from April to November), we measured the CO 2 efflux and investigated the soil physical properties weekly to characterize seasonal patterns of soil respiration and to examine blocking effect on winter soil respiration using Open Dynamic Chamber (ODC) method. We first affirmed that the local morning 10:00 o'clock with the smallest sampling errors of 0.5 to 2% was the optimal measurement point. The diurnal variation of soil respiration displayed as a single-crest curve which ascended with the increasing soil temperature in morning to a crest in early afternoon (about 13:30-15:30 o'clock), then descended. There was a significant difference in soil respiration among seasons. Hence, two separate models were used to describe the temperature sensitivity of R s (Q10) in growing season and non-growing season better. The fitted Q 10 value of Rs was 2.1 in time scale of a whole year. The obvious fluctuation of Q10 values between dormancy season (90.0) and growing season (1.6) indicated a high sensitivity of soil respiration to soil temperature in early winter. The maintenance respiration of roots in the dormant period was calculated as 0.11 µmol CO 2/m 2 /sec. The annual mean Rs and Ra were 2.53 and 1.12 µmol CO 2/m 2 /sec, separately. The proportion of R a in Rs had a relative smaller range of 14 to 55% in different seasons, higher in summer and lower in winter. The soil respiration decreased sharply in the early winter, especially after the melt of the first snow. In this study, we first defined the blocking effect of a thin ice layer on soil respiration and considered the transformation of soil water from liquid to solid as the reason of soil respiration descending in early winter. This theory may raise more concerns on the physical blocking effect on soil respiration in future researches.