不同放牧强度下短花针茅荒漠草原植被-土壤系统有机碳组分储量特征

草地生态系统作为陆地生态系统的重要组成部分,在全球碳循环中发挥着重要作用。以内蒙古短花针茅荒漠草原不同放牧强度样地为研究对象,通过分析地上植物、凋落物、根系、土壤中有机碳和土壤轻组有机碳,研究草原植被-土壤系统有机碳组分储量的变化特征,从碳储量角度为合理利用草原提供指导。研究结果表明:(1)不同放牧强度荒漠草原地上植物碳储量为11.98—44.51 g/m~2,凋落物碳储量10.43—36.12 g/m~2,根系(0—40cm)碳储量502.30—804.31 g/m~2,且对照区(CK)均显著高于中度放牧区(MG)、重度放牧区(HG);(2)0—40cm土壤碳储量为7817.43—9694.16 g/m~2,其中轻度放牧区(LG)碳储量为9694.16 g/m~2,显著高于CK、HG(P0.05);(3)植被—土壤系统的碳储量为8342.14—10494.80 g/m~2,LGMGCKHG,有机碳主要储存于土壤当中,占比约90.54%—93.71%,适度放牧利用有利于发挥草地生态系统的碳汇功能;(4)土壤轻组有机碳储量为484.20—654.62 g/m~2,LG储量最高,表明适度放牧有助于草原土壤营养物质的循环和积累。

Organic carbon storage properties in Stipa breviflora desert steppe vegetation soil systems under different grazing intensities

Grassland ecosystem, an important component of terrestrial ecosystem, plays an essential role in global carbon cycle and balance. The Stipa breviflora desert steppe of Inner Mongolia is a transitional ecosystem from grassland to desert, which has infertile soil, weak stability, but high sensitivity to climate and environmental changes. Study on organic carbon storage of the steppe under different grazing intensities is very important for revealing the mechanism of grazing impact on carbon process of the desert steppe and can provide theoretical basis for reasonable conservation and utilization of grassland resources. According to the grassland plant species composition, community height, coverage, aboveground biomass, and density index, the steppe was divided into plots that were subjected to three grazing intensities, heavy grazing (HG), moderate grazing (MG), and light grazing (LG), and the experimental grassland which was fenced to exclude livestock grazing in 2008 was selected as the control sample (CK). The analyses of the aboveground biomass, litter, belowground biomass, soil organic carbon, and soil light fraction organic carbon were utilized to study the organic carbon storage properties in Stipa breviflora desert steppe vegetation soil systems under different grazing intensities. The results showed the following. The carbon storage was 11.98-44.51 g/m² in aboveground biomass, 10.43-36.12 g/m² in litter, and 502.30-804.31 g/m² in belowground biomass (0-40 cm); it was significantly higher in CK than in MG and HG. The carbon storage in the soil at a depth of 0-40 cm was 7817.43-9694.16 g/m², and it was significantly higher in LG than in CK and HG. The total carbon storage in the vegetation-soil system was 8342.14-10494.80 g/m² under different grazing intensities; it was the largest in LG, followed by MG, CK, and HG. About 90.54%-93.71% of the total carbon was reserved in soil. Light and moderate grazing intensities increased organic carbon level of the ecosystem due to the increase in the root:shoot ratio. The grazing intensities of plant root:shoot ratios decreased from HD (41.94) to MD (30.24), LD (24.33), and CK (18.07), thereby increasing the allocation of carbon amount into the ground. Increased organic carbon content in the ecosystem may also be due to animals trampling and breaking the litter and thus promoting litter decomposition and carbon and nutrients release into the soil. However, heavy grazing severely reduced the grassland vegetation leaf area and storage material, decreased plant net primary production, lowered material input to levels below the output, and decreased the ecosystem carbon storage. Each component of the system accounted for the percentage of ecosystem organic carbon storage in the following order: soil > root > aboveground vegetation > litter in different grazing intensities. Organic carbon storage accumulation in the vegetation had a short-term effect, while its accumulation in the soil was relatively slow. With increasing grazing intensity, aboveground vegetation, litter, and root organic carbon storage showed a decreasing trend, while soil organic carbon storage first increased and then decreased; MG was beneficial to the accumulation of soil organic carbon storage. The soil light fraction organic carbon storage was 484.20-654.62 g/m², and it was the highest in LG. With increasing grazing intensity, the soil light fraction organic carbon content, storage, and percentage of soil organic carbon storage first increased and then decreased, reaching the highest value in LG. MG intensity was beneficial to soil nutrient accumulation in the desert steppe.