Carbon isotopic composition, turnover and origins of soil CO2 in a monsoon evergreen broadleaf forest in the Dinghushan Biosphere Reservoir, South China

Abstract

Carbon isotopic compositions of soil CO 2 in rainy season (July) from two natural soil profiles (DHLS & DHS) in the monsoon evergreen broadleaf forest in the Dinghushan Biosphere Reservoir (DBR), South China, are presented. Turnover and origins of soil CO 2 are preliminarily discussed in this paper. Results show that the content of soil CO 2 varies between 6120 and 18718 ppmv, and increases with increasing depth until 75 cm, and then it declines. In DHLS, soil CO 2 δ 13 C ranges from −24.71‰ to −24.03‰, showing a significant inverse correlation (R 2 ＝0.91) with the soil CO 2 content in the same layer. According to a model related to soil CO 2 δ 13 C, the soil CO 2 is mainly derived from the root respiration (>80%) in DHLS. While in DHS, where soil CO 2 δ 13 C ranges from −25.19‰ to −22.82‰, soil CO 2 is primarily originated from the decomposition of organic matter (51%-94%), excluding the surface layer (20 cm, 90%). Radiocarbon data suggest that the carbon in soil CO 2 is modern carbon in both DHLS and DHS. Differences in 14 C ages between the "oldest" and "youngest" soil CO 2 in DHLS and DHS are 8 months and 14 months, respectively, indicating that soil CO 2 in DHLS has a faster turnover rate than that in DHS. The Δ 14 C values of soil CO 2 , which range between 100.0‰ and 107.2‰ and between 102.5‰ and 112.1‰ in DHLS and DHS, respectively, are obviously higher than those of current atmospheric CO 2 and SOC in the same layer, suggesting that soil CO 2 is likely an important reservoir for Bomb-14 C in the atmosphere.Dinghushan Biosphere Reservoir, soil CO 2 , turnover, Bomb-14 CO 2 , 13 C & 14 C Citation:Ding P, Shen C D, Wang N, et al. Carbon isotopic composition, turnover and origins of soil CO 2 in a monsoon evergreen broadleaf forest in the

CO2 Transfer Characteristics of Calcareous Humid Subtropical Forest Soils and Associated Contributions to Carbon Source and Sink in Guilin, Southwest China

“…The δ 13 C-CO2 in the red soil below 50-60 cm tended to be stable; this finding is consistent with other studies in non-karst areas [29]. This stability with increasing soil depth may be attributed to the composition of stable carbon isotopes of CO2 produced from the soil or the limited impacts of the climate on the physical properties of deep soils.…”

Importance of Considered Organic Versus Inorganic Source of Carbon to Lakes for Calculating Net Effect on Landscape C Budgets

“…Generally, the contribution of root respiration to soil CO 2 emissions varies over a large range (<10% to >90%), with an overall mean of 48% as reported by Hanson et al (), who compiled data from 50 studies covering large areas of the globe. Ding et al () found that the contribution of root respiration to soil CO 2 emissions averaged >80% in densely vegetated parts of the evergreen broad lead forest, and the contribution was >90% in the upper 20 cm of soil, and decreased to 32% below 20 cm at sparsely vegetated sites in the Dinghushan area in southern China, geographically near to the study area. The phenomenon reported here, that root respiration contributed a large proportion of soil CO 2 in the catchment, is consistent with the observation that plants in karst areas tend to allocate more biomass in roots (Ni et al, ).…”

“…Therefore, it could be concluded that CO 2 in some lakes does not originate primarily from the input of soil organic matter from catchments, but from soil CO 2 . The CO 2 emissions in this kind of lake are one way that soil CO 2 returns to the atmosphere, although there are often small differences in isotopic compositions and ages of CO 2 between that evaded from waters and that evaded directly from soils (Leith et al, ) and between that produced in surface versus deep soils (Ding et al, ). This view is in accord with the conventional carbon cycle that blends outgassing from aquatic systems with terrestrial respiration (see Battin et al, ).…”