Abstract
The Tibetan Plateau reacts particularly sensitively to possible effects of climate change. Approximately two thirds of the total area is affected by permafrost. To get a better understanding of the role of permafrost on soil organic carbon pools and stocks, investigations were carried out including both discontinuous (site Huashixia, HUA) and continuous permafrost (site Wudaoliang, WUD). Three organic carbon fractions were isolated using density separation combined with ultrasonic dispersion: the light fractions (<1.6 g cm−3) of free particulate organic matter (FPOM) and occluded particulate organic matter (OPOM), plus a heavy fraction (>1.6 g cm−3) of mineral associated organic matter (MOM). The fractions were analyzed for C, N, and their portion of organic C. FPOM contained an average SOC content of 252 g kg−1. Higher SOC contents (320 g kg−1) were found in OPOM while MOM had the lowest SOC contents (29 g kg−1). Due to their lower density the easily decomposable fractions FPOM and OPOM contribute 27% (HUA) and 22% (WUD) to the total SOC stocks. In HUA mean SOC stocks (0–30 cm depth) account for 10.4 kg m−2, compared to 3.4 kg m−2 in WUD. 53% of the SOC is stored in the upper 10 cm in WUD, in HUA only 39%. Highest POM values of 36% occurred in profiles with high soil moisture content. SOC stocks, soil moisture and active layer thickness correlated strongly in discontinuous permafrost while no correlation between SOC stocks and active layer thickness and only a weak relation between soil moisture and SOC stocks could be found in continuous permafrost. Consequently, permafrost-affected soils in discontinuous permafrost environments are susceptible to soil moisture changes due to alterations in quantity and seasonal distribution of precipitation, increasing temperature and therefore evaporation.
Highlights
The relationship between soil organic carbon (SOC) stocks and site characteristics has been well investigated in the temperate zones at local and regional scale (e.g. [1,2,3,4]), but much less studies exist about the role of SOC in high-cold alpine regions (e.g. [5,6,7,8])
Soil Organic Carbon Content and SOC/N Ratios The SOC content of bulk soil decreased with increasing depth at both sites (Fig. 2)
Highest contents occurred in the occluded particulate organic matter (OPOM) fractions (320 g kg21), free particulate organic matter (FPOM) followed with 252 g kg21, while they were lowest in the mineral associated organic matter (MOM) fractions (29 g kg21)
Summary
The relationship between soil organic carbon (SOC) stocks and site characteristics has been well investigated in the temperate zones at local and regional scale (e.g. [1,2,3,4]), but much less studies exist about the role of SOC in high-cold alpine regions (e.g. [5,6,7,8]). [1,2,3,4]), but much less studies exist about the role of SOC in high-cold alpine regions Studies in Arctic regions have shown that permafrost-influenced alpine ecosystems are highly sensitive to global climate change [9]. The Tibetan Plateau is a sensitive area in terms of possible effects of global climate change. It is the largest and highest plateau on earth and covers an area of 2.5 million square kilometers with an average altitude of more than 4000 m a.s.l. comprising about a quarter of China’s mainland [18]. In this study permafrost is classified after the Chinese Permafrost Classification which differs from the classification of the International Permafrost Association (IPA). In this study permafrost is classified after the Chinese Permafrost Classification which differs from the classification of the International Permafrost Association (IPA). 50–90% of permafrost is required for classifying discontinuous permafrost after IPA Permafrost Classification; 30–70% is required after Chinese Permafrost Classification [28]
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