|其他摘要||Soil carbon is the world's largest carbon source. Soil respiration has been viewed as a vital ecological progress in the global carbon cycle and climate evolution. Previous researches on dynamic changes of soil organic carbon and characteritics of soil respiration of the shelter forest ecosystem in the extreme arid region are quite inadequate, which would be necessary for carbon cycle on regional scale or world scale. Therefore, this study based on the world's second-largest flow desert hinterland，the Tarim desert highway shelter forest was chosen as the study object and the experimental design were mainly based on different plantation time of the shelter forest.
The objects of this thesis are preliminarily understanding: (1) the ability of soil carbon sequestration during the process of the development of the sandy soil, by studding the dynamic changes of soil organic carbon in Tarim desert highway shelter forest; (2) the influence of shelt forst on the carbon release characteristics of sandy soil by simulating plant litter decomposition process under the influence of saline water irrigation. The study fruits of this project will enrich basic data of carbon balance in extreme arid region, help to improve theoretical system of carbon cycling in in extreme arid region, furthermore, provide scientific decision-making basis for sustainable management of the Tarim desert highway shelter forest ecological project.
The main results of this study are:
(1) The soil organic carbon storks increased a little with the years of plantation only in Tamarix chinensis Lour. (T.c.) Shelter forest. The range of the change is 1192-2316 g/m2, average value is 1704 g/m2. The carbon storks size order of three kinds of plant is Calligonum mongolicunl Turcz. (C.m.) > Tamarix chinensis Lour. (T.c.) > Haloxylon ammodendron (C. A. Mey.) Bunge. (H.a.). Soil organic carbon content only decreased with soil depth in 0 to 50 cm and didn’t changed obviously below 50 cm.
(2) The soil passive organic carbon, including micro-aggregate organic carbon (OCMIA), humus organic carbon (OCHS), resistance to oxidation carbon (OCNaClO) and resistance to hydrolysis carbon (OCHCl) increased with years of plantation in the soil surface layer (0-10 cm). OCMIA and OCHS increased year by years, OCNaClO and OCHCl increased in 5 to 7 years and then no obvious change. The degree of correlation between all kinds of SOC fractions is with significance prominence, and the correlation between OCMIA and TOC, OCHS and TOC is higher than OCHCl and TOC,
OCNaClO and TOC. The relative content of OCMIA and OCNaClO in TOC is higher than OCHS and OCHCl, the relative content of OCHCl is the lowest.
(3) The relative content of functional C=O groups (C=O/C-O-C) decreased first and then increased with years of plantation; and the ratio of the polymerization methylene in carbon branched chain to methyl at the end of the carbon chain (CH2 / CH3) was highest in 7 years and decreases a little and stable gradually.
(4) In the end of summer, autumn and early winter (from June 30 to November 18), with the increase of litter decomposition time, the soil respiration rate was reduced with fluctuation monthly. With soil depth increasing, in the end of summer and early autumn (from June 30 to September 10), the rate was surface layer greater than sub-surface. In the end of summer and early autumn (from June 30 to August 10), the influence of three kinds of plants to soil respiration was T.c. > C.m. > H.a.. With the increase of irrigation water salinity, fresh water soil respiration rate was significantly higher than salt. The difference between two kinds of salt- water was not obvious. The rate after applying nitrogen fertilizer will increase obviously.
(5) In autumn, the daily variation of soil respiration rate was single-peak curve model. The maximum appears at 14-16 h pm, decreased to minimum 22-24 h pm. With depth increase, the rate reduced. With the increase of irrigation water salinity, the soil respiration rate decreased which showed more apparent in the sub-surface layer. The influence of three plants on soil respiration was H.a. >T.c.> C.m.
(6) The monthly changes of soil respiration rate with the soil and air temperature presented complicated model, can use four kinds of curve fitting, which are compound, growth, exponential and logistic curve respectively. The relationship between daily variation of respiration rate of soil irrigated by salt water and temperature is three function of Rs = b3T3 + b2T2 + b1T + a. The decision coefficients (R2) of the fitting curve of each treat with temperature in 5 cm depth are the highest, and with the air temperature are lowest. In two decomposition layers, the fitting accuracy of the change of the surface soil respiration rate with temperature is higher. The average value of R2 in the fitting curve of T.c. is maximum than other plants; H.a. is minimal.|