Winter Soil CO2 Flux from Different Mid-Latitude Sites from Middle Taihang Mountain in North China

Huitao Shen,Huaru Wang,Jiansheng Cao,Xinhua Zeng,Wanjun Zhang

doi:10.1371/journal.pone.0091589

Abstract

Winter soil respiration is a very important component of the annual soil carbon flux in some ecosystems. We hypothesized that, with all other factors being equal, shorter winter SR result in reduced contribution to annual soil C flux. In this study, the contribution of winter soil respiration to annual soil respiration was measured for three sites (grassland: dominated by Artemisia sacrorum, Bothriochloa ischaemum and Themeda japonica; shrubland: dominated by Vitex negundo var. heterophylla; plantation: dominated by Populus tomatosa) in a mountainous area of north China. Diurnal and intra-annual soil CO2 flux patterns were consistent among different sites, with the maximum soil respiration rates at 12∶00 or 14∶00, and in July or August. The lowest respiration rates were seen in February. Mean soil respiration rates ranged from 0.26 to 0.45 µmol m−2 s−1 in the winter (December to February), and between 2.38 to 3.16 µmol m−2 s−1 during the growing season (May-September). The winter soil carbon flux was 24.6 to 42.8 g C m−2, which contributed 4.8 to 7.1% of the annual soil carbon flux. Based on exponential functions, soil temperature explained 73.8 to 91.8% of the within year variability in soil respiration rates. The Q10 values of SR against ST at 10 cm ranged from 3.60 to 4.90 among different sites. In addition, the equation between soil respiration and soil temperature for the growing season was used to calculate the “modeled” annual soil carbon flux based on the actual measured soil temperature. The “measured” annual value was significantly higher than the “modeled” annual value. Our results suggest that winter soil respiration plays a significant role in annual soil carbon balance, and should not be neglected when soil ecosystems are assessed as either sinks or sources of atmospheric CO2.

Highlights

Soil respiration (SR) provides the main C flux from terrestrial ecosystems to the atmosphere [1,2] and is one of the major components to consider in understanding ecosystematmosphere C exchange [3]
Monson et al [8] suggested that winter soil respiration could offset a major portion of the carbon fixed during the growing season, and significantly contribute to the annual carbon cycling
Temporal Dynamics of SR The diurnal pattern of SR for all three sites was described by asymmetric single-peak curves (Figure 2)

Summary

Introduction

Soil respiration (SR) provides the main C flux from terrestrial ecosystems to the atmosphere [1,2] and is one of the major components to consider in understanding ecosystematmosphere C exchange [3]. Monson et al [8] suggested that winter soil respiration could offset a major portion of the carbon fixed during the growing season, and significantly contribute to the annual carbon cycling. Mid-latitude ecosystems, on the other hand, are dominated by a shorter winter season and a thinner snow depth. These mid-latitude ecosystems are considered to be major terrestrial carbon sinks in the northern hemisphere [12]. Little is known about the winter SR and its contribution to annual soil C flux in different mid-latitude ecosystems, which may yield inaccurate regional and global C budget predictions [13,14]

Methods

Results

Discussion

Conclusion