Soil Organic Carbon Characteristics And Its Responses To Simulated Warming On Alpine Grassland Of The Qinghai-tibet Plateau

Global warming has become a common concern of scientists all over the world, and has an important influence on terrestrial ecosystem carbon cycle. Alpine grassland soils on the Qinghai-Tibet Plateau(QTP) of western China bear a large organic carbon pool and have an important role in the global carbon cycle, so it is necessary to study the characteristics of the soil organic carbon for Qinghai-Tibet Plateau. We examined the soil total organic carbon, Active organic carbon(water-soluble organic carbon, easily oxidizable organic carbon), Humic fractions carbon(Humic acid carbon, Fulvic acid carbon and Humin carbon), and HAC/FAC ratio aggregate-associated carbon, the water stability of soil aggregates, and the chemical composition of soil Humic acid(HA) or Humic, as well as their relationships with the environmental factors(i.e., precipitation, temperature, and plant biomass) along the level grassland transect(i.e., alpine meadow, alpine steppe, and alpine desert), the vertical grassland transect(4500, 4650,4800 and 4950 m) and different simulation temperature(no warming, winter warming and year warming) for Qinghai-Tibet Plateau. The results are as follows:1. The contents of soil total organic carbon, Active organic carbon, Humic fractions carbon, and aggregate-associated carbon, the proportions of macroaggregates(2-0.25) and microaggregates(0.25-0.053 mm), and the aggregate stability indices(i.e., mean weight diameter, geometric mean diameter, percentage of >0.25 mm water stable aggregates, and stability ratio of water stable aggregate) increased in the order alpine desert<alpine steppe<alpine meadow. The alkyl C, O-alkyl C, and aliphatic C/aromatic C ratio increased in the order alpine desert<alpine meadow<alpine steppe, and the reverse was true for the aromatic C and HB/HI ratio. There were significantly correlations between the contents of SOC and its fractions, the proportions of macro- and micro-aggregates, and the aggregate stability indices with mean annual precipitation(MAP) and above-ground biomass(AGB). These results suggest that alpine meadow soils contain a large amount of labile, resistant, and aggregate-associated carbon, and exhibit a high soil aggregation and aggregate stability. The aliphaticity and hydrophobicity degrees of HA from alpine meadow soils are between those of HA from alpine steppe and alpine desert soils. MAP and AGB are important environmental factors to impact SOC contents, soil aggregation, and aggregate stability across grasslands types on the QTP.2. The contents of soil total organic carbon, Active organic carbon, Humic fractions carbon, Aggregate associated carbon, increased with the rise of different altitude of Qinghai-Tibet Plateau. There were significantly positive correlations between the water-soluble organic carbon, Humic acid carbon and fulvic acid carbon with mean annual precipitation(MAP) and above-ground biomass(AGB). There were significantly negative correlations between easily oxidizable organic carbon, humic acid carbon and fulvic acid carbon with annual average temperature. There were no significantly correlations between other components of carbon content and with the environmental factors(i.e., precipitation, temperature, and plant biomass).3. The water-soluble organic carbon, mean weight diameter and geometric mean diameter of soil aggregates have significantly increased, but the particle size ratio of 0.25-0.053 mm have significantly decreased in winter warming compared with no warming experiment. The water-soluble organic carbon, the particle size ratio of <0.053 mm have significantly increased in year warming compared with no warming experiment of Tibetan alpine meadow. The particle size ratio of <0.25 mm have significantly increased, but mean weight diameter and geometric mean diameter have significantly decrease in year warming compared with winter warming experiment. These results suggest that water-soluble organic carbon and aggregate stability have significantly increased in winter warming,but the aggregate stability have significantly decrease in winter warming experiment...