Seasonality of vertically partitioned soil CO₂ production in temperate and tropical forest

Abstract

Soil CO₂ production seasonality at a number of depths was investigated in a temperate forest in Japan and in a tropical montane forest in Thailand. The CO₂ production rates were evaluated by examining differences in the estimated soil CO₂ flux at adjacent depths. The temperate forest had clear temperature seasonality and only slight rainfall seasonality, whereas the tropical montane forest showed clear rainfall seasonality and only slight temperature seasonality. In the temperate forest, the pattern of seasonal variation in soil respiration was similar at all depths, except the deepest (0.65 m–), and respiration was greater in summer and less in winter. The contribution of the shallowest depth (around 0.1 m) was more than 50% of total soil-surface CO₂ flux all year round, and the annual mean contribution was about 75%. CO₂ production mostly appeared to increase with temperature in shallower layers. In contrast, in the tropical forest, soil CO₂ production seasonality appeared to differ with depth. The CO₂ production rate in the shallowest layer was high during the rainy season and low during the dry season. Soil CO₂ production at greater depths (0.4 and 0.5 m–) showed the opposite seasonality to that in the shallower layer (around 0.1 m). As a result, the contribution from the shallow depth was greatest in the tropical forest during the rainy season (more than 90%), whereas it decreased during the dry season (about 50%). CO₂ production appeared to be controlled by soil water at all depths, and the different ranges of water saturation seemed to cause the difference in seasonality at each depth. Our results suggest the importance of considering the vertical distribution of soil processes, particularly in areas where soil water is a dominant controller of soil respiration.

Keywords:

• Belowground processes
• Soil carbon
• Soil CO₂
• Soil organic matter
• Soil respiration

Acknowledgments

We are grateful to all members of the Fukuroyamasawa project and the Kog-Ma project. Part of this research was supported by Research Fellowships of the Japan Society for the Promotion of Science for Young Scientists. Part of this work was supported by Grants-in-Aid for Scientific Research (#06404012, #11460063, #14360081) from the Ministry of Education, Culture, Sports, Science, and Technology, of Japan. Part of this research was conducted as one of the GAME-Tropics activities funded by the Japanese Ministry of Education, Culture, Sports, Science, and Technology, under Grants-in-Aid for Scientific Research (#07041106 and #10041219, Leader: Prof. K. Musiake, The University of Tokyo), with cooperation from the National Research Council of Thailand. We sincerely thank two anonymous reviewers for their helpful comments on earlier drafts of this manuscript.