Spatial and temporal distribution of carbon isotopes in soil organic matter at the Dinghushan Biosphere Reserve, South China

Abstract

The spatial and temporal distribution of carbon isotopes ( 13 C, 14 C) in soil organic matter (SOM) were studied based on SOM content, SOM D 14 C and SOM d 13 C of thinly layered soil samples for six soil profiles with different elevations at the Dinghushan Biosphere Reserve (DHSBR), South China. The results indicate that variations of SOM d 13 C with depth of the soil profiles at different elevations are controlled by soil development, and correlate well with SOM composition in terms of SOM compartments with different turnover rates, and SOM turnover processes at the DHSBR. The effect of carbon isotope fractionation was obvious during transformation of organic matter (OM) from plant debris to SOM in topsoil and SOM turnover processes after the topsoil was buried, which resulted in great increments of OM d 13 C, respectively. Increments of SOM d 13 C of topsoil from d 13 C of plant debris were controlled by SOM turnover rates. Both topsoil SOM d 13 C and plant debris d 13 C increase with elevation, indicating regular changes in vegetation species and composition with elevation, which is consistent with the vertical distribution of vegetation at the DHSBR. The six soil profiles at different elevations had similar characteristics in variations of SOM d 13 C with depth, alterations of SOM contents with depth and that SOM 14 C apparent ages increasing with depth, respectively. These are presumably attributed to the regular distribution of different SOM compartments with depth because of their regular turnover during soil development. Depth with the maximal SOM d 13 C value is different in mechanism and magnitude with penetrating depth of 14 C produced by nuclear explosion into atmosphere from 1952 to 1962, and both indicate controls of topography and vegetation on the distribution of SOM carbon isotopes with depth. Elevation exerts indirect controls on the spatial and temporal distribution of SOM carbon isotopes of the studied mountainous soil profiles at the DHSBR. This study shows that mountainous soil profiles at different elevations and with distinctive aboveground vegetation are presumably ideal sites for studies on soil carbon dynamics in different climatic-vegetation zones.

Buried Ancient Forest and Implications for Paleoclimate Since the Mid-Holocene in South China

“…These changes were likely related to climate events since the mid-Holocene as reported elsewhere (Bond et al 1997;deMenocal et al 2000). As shown in Figure 6, the drought events reflected from the historical evolution were consistent with the ice-rafting and cold events 3, 2, 1 recorded in the North Atlantic and north Africa, respectively (Bond et al 1997;deMenocal et al 2000).…”

“…These cold and drought events were also in agreement with little ice ages (H, F, D) speculated from written histories (Xu 1998). Termination of the ancient forest evolution at 1.1 ka likely represented another climate fluctuation before the Little Ice Age that occurred between AD 1300 and 1850 (Xu 1998;deMenocal et al 2000). It was mostly noted in the low-latitude areas (Haug et al 2001;Yancheva et al 2007) and corresponded to the final stage of the Maya collapse (Hodell et al 1995).…”

“…Coherent high-and low-latitude climate variability during the Holocene has been widely reported from corals, marine and lake sediments, and stalagmite records (deMenocal et al 2000;Bond et al 2001;Yu et al 2002;Wang et al 2005). However, evidence for unstable Holocene climate in southern China is still limited, and the interpretation of recently published high-resolution lake records is still under debate (Yancheva et al 2007;Zhang and Lu 2007;Zhou et al 2007).…”

Turnover Rate of Soil Organic Matter and Origin of Soil 14Co2 in Deep Soil from a Subtropical Forest in Dinghushan Biosphere Reserve, South China

“…Meanwhile, SOC content decreases exponentially with increasing depth from the maximal value 4.6% at the surface to 0.4% in the bottom and trends towards a stable value ( Figure 2). Sources of SOC are mainly controlled by vegetation and topography, and SOC  13 C values are associated with SOC sources, decomposition, and turnover process during soil development (Bird et al 2001;Chen et al 2005). With continuous coverage of the same plant type, the vertical variation of SOC  13 C is attributed to isotopic fractionation during SOC decomposition (Schweizer et al 1999;Hobbie et al 2004).…”

“…Then, the labile carbon decomposes, resulting in the further enrichment of 13 C and the greatest  13 C value generally, which indicates that most of the SOC has decomposed and the remaining SOC is mainly passive carbon with higher  13 C. The turnover rate of SOC then slows down, and the SOC content reduces slightly and tends to be stable along depth. When the passive carbon has decomposed, the SOC gradually becomes depleted in 13 C, probably due to the decomposition of SOC compartments with high  13 C value, which thus led to the decrease of SOC  13 C with increasing depth (Chen et al 2005). …”