Abstract
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.
Highlights
Soil Respiration (Rs) is an ecosystem process that releases CO2 from soil via root Respiration (Ra), microbial decomposition of litter and soil organic matter (Rh) and fauna respiration
In 24 h, the rate of Rs had the minimum around 04:30 o’clock and it followed the increasing trend of soil temperature to a peak around early afternoon, but leveled off with slight fluctuations while soil temperature kept increasing in the afternoon
The optimal measurement point confirmed by comparing the daily mean of Rs with point measurements was local morning 10:00 o’clock, at which the measurements had the smallest sampling errors of 0.5 to 2% (Fig. 1)
Summary
Soil Respiration (Rs) is an ecosystem process that releases CO2 from soil via root Respiration (Ra), microbial decomposition of litter and soil organic matter (Rh) and fauna respiration. There are two keys for the extraordinary active research on soil respiration in the past decades. One is that it is among the least understood subjects in ecosystem ecology and the other is that it represents the second largest flux of carbon cycling between the atmosphere and terrestrial ecosystems (Luo, 2007). Soil respiration displays strong temporal variation over time. The diurnal variation must be accounted appropriately to avoid errors when point measurements of soil respiration are used to estimate annual soil carbon efflux. There is no certain time point that is given to determine the diurnal mean of soil respiration. Assuring an optimal sampling point can estimate the annual CO2 efflux more precisely, and can save the sampling time and labor
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