Contribution of Root and Microbial Respiration to Soil CO 2 Efflux and Their Environmental Controls in a Humid Temperate Grassland of Japan

Abstract

Soil CO 2 efflux, root mass, and root production were investigated in a humid temperate grassland of Japan over a growing season (Apr. to Sep.) of 2005 to reveal seasonal changes of soil CO 2 efflux, to separate the respective contributions of root and microbial respiration to the total soil CO 2 efflux, and to determine the environmental factors that control soil respiration. Minimal microbial respiration rate was estimated based on the linear regression equations between soil CO 2 efflux and root mass at different experimental sites. Soil CO 2 efflux, ranging from 4.99 to 16.29 μmol CO 2 m −2 s −1, depended on the seasonal changes in soil temperature. The root mass at 0–10 cm soil depth was 0.82 and 1.27 kg m −2 in Apr. and Sep., respectively. The root mass at 0–10 cm soil depth comprised 60% of the total root mass at 0–50 cm soil depth. The root productivity at 0–30 cm depth varied from 8 to 180 g m −2 month −1. Microbial and root respiration rates ranged from 1.35 to 5.51 and 2.72 to 12.06 μmol CO 2 m −2 s −1, respectively. The contribution of root respiration to the total soil CO 2 efflux averaged 53%, ranging from 33% to 72%. The microbial respiration rate was exponentially related to soil temperature at 10 cm depth ( R 2 = 0.9400, P = 0.002, n = 6), and the root respiration rate was linearly related to the root production at 0–30 cm depth ( R 2 = 0.6561, P = 0.042, n = 6).