Year-round soil and ecosystem respiration in a temperate broad-leaved Korean Pine forest

Abstract

As part of ChinaFlux program, forest soil and ecosystem respiration were measured using two sets of eddy covariance systems in a 300-year-old mixed forest in northeast China in 2003, and soil respiration was also measured in situ by chamber method. The forest showed a clear old-age effect, i.e. high assimilation and respiration rates. The estimates of annual gross carbon gain and loss at the forest were 1511 and 1327 gC m −2. The annual soil respiration was 1017 gC m −2, which accounted for 76% of the total ecosystem respiration. The forest showed a reasonable positive carbon uptake during growing season, but even during the coldest winter month, it still acted as a sink for a few hours around noon. The annual net carbon sequestration was 184.4 gC m −2. Close relations were found between 5 cm depth soil temperature and soil respiration, as well as ecosystem respiration, both can be well explained by first-order exponential equations. A more reasonable method to calculate Q 10 values of soil based on weighted mean respiratory contribution rates of temperature in each layer was suggested. There was moderate correlation between soil respiration rates and volumetric soil water content. Very dry or very wet soil generally depressed the soil respiration. However, when soil temperature increased, the wet forest soil ( W s > 0.35 m 3 m −3) had greater respiratory potential. When the atmosphere was regularly mixed by turbulence, soil respiration measured by EC was in good agreement with the chamber data. On a daily basis, the soil respiration data obtained from below-canopy EC system is quite acceptable.