Characterizing Of Soil Organic Carbon Contents And Respiration At Sejila Mountain,in Southeastern Tibet

Tibetan Plateau(TP)is considered as the third pole of the planet due to its unique terrestrial ecosystems characterized by high elevation(i.e.4,000 m on average)and extensive coverage(2.9×106 km2).As the largest plateau in size and youngest in age,TP is of major significance in determining ecosystem patterns in Asia and the globe.However,the original ecosystem of TP had been modifying greatly due to growing climate change and anthropogenic activities,thereby affecting the organic carbon cycling of the soil and further exacerbating climate change.The dissertation is conducted to elaborate on the soil organic carbon(SOC)content under different elevations in TP,and on the sensitivity of soil respiration(RT)and decomposition to temperature changes,with the objective of providing a scientificbasis for assessing the distribution,dynamics,and future changes of SOC of the Plateau.The different types of vegetation between the elevation of 3,000 m and 4,600 m on Sejila Mountain in southeast of TP are selected as the object of investigation.This dissertation investigated the SOC content and major influencing factors,assessed the contribution of litter respiration(RL)of different types of forest to the total carbon emission of R-T,and explored the sensitivity to the temperature of the soil basal respiration(RB).The major results are as follows:(1)The mean content of SOC in the 0-10 cm soil and 10-20 cm soil at theSejila Mountain is(8.15±3.17)%and(5.01±2.21)%,respectively,with relatively high organic carbon density,i.e.,(4.44±0.61)kg m-2 and(3.51±0.88)kg m-2 respectively.The SOC content increased with increasing elevation in the forest soil between the elevations of 3 550-4 300 m.SOC content is affected by undergrowth vegetation,micro-topography conditions,and other factors.The SOC content under different types of vegetation is as forest>temperate grassland>farmland>subalpine meadow.(2)In the soil of forest and grassland,the CH3 and CH2 group and amide-C=O group decrease with soil depth.The relative content of each organic carbon group is highest in the forest,followed by temperate grassland and subalpine grass bush.In the 0-10 cm soils,the relative content of the main organic carbon group is as deformation vibration aliphatic-C>stretching vibration aliphatic-C>amide-C=O.(3)Litters in the forest had a significant effect on Rs;that is,a significant difference is observed between total soil respiration(R-T),respiration of litter(RL),and soil respiration(Rs).The RL of coniferous forest is less than that of broad-leaved forest,that is,coniferous forestlitters have relatively low decomposition rate.The RL/RT in different types of forest is Rhododendron>Piceaasperata Mast>Quercusspinosa>Abiesgeorgei Orr,and the average value is 59.25%,33.26%,20.00%and 17.64%,respectively.The respiration rate of broadleaved mixed forest decreases with the depth of soil and the respiration of 0-10 cm soil accounts for 45.63%-75.23%of total respiration.However,the Q10 may increase in>5 cm soil depth.(4)The RB of 0-5 cm and 5-10 cm soil at elevation of 3 800 m,3 990 m,and 4 090 m decreases along with the increase in elevation(R3800 m>R3990m>R4090m),but the 10-20 cm soil does not show the uniform variations.When incubation time is prolonged,the RB decreases rapidly,particularly in 0-7 day ofincubation.The RB has a highly significant exponential relationship with incubation time.The RB rate decreases with soil depth increased and increases with the rise of incubation temperature.At a low temperature,the RB Q10 is higher than that at high temperature in 5-10 cm and 10-20 cm layer,and within the range of 15 ?-25 ?,Q10 increases along with the elevation in 0-5 cm layer.(5)The results of the soil respiration rate simulation based on atmosphere temperature and precipitation show that the soil respiration rate in high elevation areas is lower than that in low elevation.Between the elevation of 3 300-4 400 m,the mean annual soil respiration rate is 1.26 g C m-2 d-1 and the annualmean respiration emission is 4.60 Mg C ha-1.The temperature and precipitation models for soil respiration could enable the effective assessment ofassess the soil respiration in high elevation areas(>3 700 m),but the assessment result is relatively low in low elevation areas.