SOM 14C apparent age

Little is known about the effect of leaching on distribution of SOM with depth, which is unfavorable for evaluating the potential capacity of soil to sequester carbon. Sporopollen (pollen and spores) are abundant in upper soils, and their vertical distributions are controlled substantially by leaching (Zheng et al. 2002). The distribution of sporopollen with depth may be a useful index of leaching potential. We intended to evaluate the effect of leaching on SOM vertical distribution, based on variations in SOC concentration and SOM 14C apparent age with depth. The distribution of sporopollen with depth can serve as a reference for our evaluation. 

Profile Vegetation type s13r O - topsoil (%o) s13r O - maximum (%o) s13r O - maximum s13r O -topsoil (%o) SOM 14C apparent ages of the bottom (yr B.P.)... 

Fig. 5. Variations of SOM 14C apparent ages with depth for the soil profiles with different elevations at the Dinghushan Biosphere Reserve (A GC Profile, B SL Profile, C WKS profile, D QYS profile).

The SOM 14C apparent age of soil section (0-0.05 m) is 80 yr B.R for WKS profile and 140 yr B.R for QYS profile, suggesting that the upper soil layers had been contaminated by some old carbons with negative A14C values. Contaminations from old carbon and bomb 14C can result in obvious alterations in SOM A14C values. However, SOM 513C value is relatively less susceptible to such contaminations, because the abundance of 13C is much greater than that of 14C in nature system. This indicates that 14C analysis alone is not adequate for studying SOM dynamics. 

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