Soil respiration in a successional tropical forest in Thailand

Soil respiration (SR) in forests contributes significant emissions of
carbon from terrestrial ecosystems into the atmosphere. Soil respiration
is highly sensitive to environmental changes because it is affected by
many factors, including soil temperature, soil moisture, microbial
community, surface litter and vegetation type. Indeed, a small change in
SR may have large impacts on the global carbon balance, further
influencing feedbacks to climate change. Thus, detailed characterization
of SR responses to changes in environmental conditions is needed to
accurately estimate carbon dioxide emissions from forest ecosystems.
However, data for such analyses are still limited, especially in tropical
forests of Southeast Asia where various stages of forest succession exist
due to previous land-use changes. In this preliminary study, we measured
SR and some environmental factors including soil temperature (ST), soil
moisture (SM) and organic matter content (OM) in three successional
tropical forests in both wet and dry seasons. We also analyzed the
relationships between SR and the three environmental variables. Results
showed that SR was higher in the wet season and in older forests. While no
response of SR to ST was found in younger forest stages, SR of the
old-growth forest significantly responded to ST, plausibly due to the
non-uniform forest structure, including gaps, that resulted in a wide
range of ST. Across forest stages, SM was the limiting factor for SR in
the wet season whereas SR significantly varied with OM in the dry season.
Overall, our results indicated that the responses of SR to environmental
factors were mediated by seasons and forest succession. These findings
call for further investigations on SR and its variations with
environmental factors in tropical forests with detailed temporal and
spatial scales, particularly in Southeast Asia where patches of
successional stages dominate.