Winter soil CO2 efflux and its contribution to annual soil respiration in different ecosystems of a forest-steppe ecotone, north China

Abstract

Abstract Most soil respiration measurements are conducted during the growing season. In tundra and boreal forest ecosystems, cumulative winter soil CO2 fluxes are reported to be a significant component of their annual carbon budgets. However, little information on winter soil CO2 efflux is known from mid-latitude ecosystems. Therefore, comparing measurements of soil respiration taken annually versus during the growing season will improve the accuracy of ecosystem carbon budgets and the response of soil CO2 efflux to climate changes. In this study we measured winter soil CO2 efflux and its contribution to annual soil respiration for seven ecosystems (three forests: Pinus sylvestris var. mongolica plantation, Larix principis-rupprechtii plantation and Betula platyphylla forest; two shrubs: Rosa bella and Malus baccata; and two meadow grasslands) in a forest-steppe ecotone, north China. Overall mean winter and growing season soil CO2 effluxes were 0.15–0.26 μmol m−2 s−1 and 2.65–4.61 μmol m−2 s−1, respectively, with significant differences in the growing season among the different ecosystems. Annual Q10 (increased soil respiration rate per 10 °C increase in temperature) was generally higher than the growing season Q10. Soil water content accounted for 84% of the variations in growing season Q10 and soil temperature range explained 88% of the variation in annual Q10. Soil organic carbon density to 30 cm depth was a good surrogate for SR10 (basal soil respiration at a reference temperature of 10 °C). Annual soil CO2 efflux ranged from 394.76 g C m−2 to 973.18 g C m−2 using observed ecosystem-specific response equations between soil respiration and soil temperature. Estimates ranged from 424.90 g C m−2 to 784.73 g C m−2 by interpolating measured soil respiration between sampling dates for every day of the year and then computing the sum to obtain the annual value. The contributions of winter soil CO2 efflux to annual soil respiration were 3.48–7.30% and 4.92–7.83% using interpolated and modeled methods, respectively. Our results indicate that in mid-latitude ecosystems, soil CO2 efflux continues throughout the winter and winter soil respiration is an important component of annual CO2 efflux.