干旱区荒漠的非生物固碳能力一些学者至今怀疑,关键在于地上通量观测到的CO_2吸收结果是否在土壤碳库得到体现.本研究在我国西北干旱区,将荒漠划分为砾质荒漠(戈壁)、沙质荒漠(沙漠)和壤质荒漠三大类,从颗粒组成、总含盐量、有机碳和无机碳含量等方面测定分析,研究不同类型荒漠土壤有机碳和无机碳(soil inorganic carbon, SIC)密度和储量变化,并与高寒生态系统进行比较.结果表明,不同类型荒漠平均0~30 cm表土层和1 m深土壤SIC密度分别为2.8和10.1 kg C m~(-2).相比较,壤质荒漠的SIC密度最高, 1 m深土壤达到12.1 kg C m~(-2).针对土壤对CO_2的吸收和无机固定,提出土壤碳同化(soil carbon assimilation)概念.荒漠生态系统固碳是植物碳同化与土壤碳同化,即有机和无机过程的结合,荒漠土壤无机碳密度和储量是有机碳的5倍.土壤碳同化途径分为3个阶段: CO_2与H_2O反应阶段、CO_2或弱碳酸与土壤溶液阳离子反应阶段、生成溶解碳酸盐与沉淀碳酸盐附着于土壤颗粒和向下沉积阶段.土壤碳同化能力随着土壤有机碳含量、含盐量、水分、粉粒和黏粒含量的增加而提高.
英文摘要:
The inorganic carbon sequestration capacity of deserts in an arid region is now still questioned for their accuracy. The key question is whether the result of CO_2 absorption from aboveground flux observation can be reflected in the soil carbon pool or not. In the arid region of northwest China, desert is divided into three types based on the landscape and vegetation characteristics, namely gravel desert (Gobi), sand desert, and silt desert. By measuring and analyzing the soil particle composition, total salt content, organic carbon and inorganic carbon content, the changes in soil organic carbon (SOC) and soil inorganic carbon (SIC) density and their storage in different type deserts were studied, and then they were compared with that in the alpine ecosystem of southwest China. The results showed that the average SIC densities in 0-30 cm surface soil layer and 1 m soil depth in different type deserts were 2.8 and 10.1 kg C m~(-2), respectively. Comparatively, the SIC density of silt desert was the highest, and the value over 12 kg C m~(-2) in 1 m soil depth. In our study, the average total carbon densities in 0-30 cm desert soil layer was 3.5 kg C m~(-2), and in 1 m soil depth was 12.1 kg C m~(-2). According to the value of 100 g C m~(-2) a~(-1) to calculate, the carbon accumulation in 0-30 cm surface soil layer and 1 m soil depth need 35 years and 121 years, respectively. If the value is less than 100 g C m~(-2) a~(-1), a longer period is required, showed that it will take a long time for the formation of desert inorganic carbon pool. In terms of material content, the average bulk density in 1 m soil depth was 1.52 g cm-3, and the total carbon accumulated in desert soil accounted for 0.8% of soil mass in 121 years, of which the inorganic carbon accounted for 0.7% of soil mass. For the soil absorption and inorganic sequestration to CO_2, we proposed the concept of soil carbon assimilation. Carbon sequestration in desert ecosystems is plant carbon assimilation and soil carbon assimilation, which is a combination of organic and inorganic processes. The SIC density and storage of desert soil are five times that of SOC. The pathway of soil carbon assimilation can be divided into three stages: the reaction stage between CO_2 and H_2O, the reaction stage between CO_2 or weak carbonic acid and soil solution cation, and the stage that is the dissolved and precipitated carbonates which attached to soil particles and downward deposition. The soil carbon assimilation capacity was enhanced by increasing the soil organic carbon, salt content, water content, and soil silt and clay content. To recovering and conservation of desert vegetation, the desert is reclaimed into farmland under the carrying capacity of water resources, the SOC density was not only increased, the soil carbon assimilation capacity, SIC density and storage are also enhanced greatly. Under conditions of future climatic warming, soil inorganic carbon sequestration capacity will be increased and carbon sequestration capacity of the desert ecosystem will be enhanced with increasing precipitation in the arid region. The development of irrigated agriculture in the arid desert region will be beneficial to a collaborative improvement in production and ecological functions in the arid region.