喀斯特峰丛洼地不同植被类型碳格局变化及影响因子

Carbon storage and its controlling factors under different vegetation types in depressions between karst hills,southwest China

采用样方法研究了西南喀斯特峰丛洼地草地、灌丛、次生林、原生林4种植被类型碳格局及其土壤碳的影响因子。结果表明:草地、灌丛、次生林、原生林4类生态系统总碳储量分别为133.84、160.79、179.08和261.24 Mg C/hm2,其中植被碳储量为5.02、6.59、20.87和60.20 Mg C/hm2,占总碳储量的3.75%—23.04%,随植被正向发展而增加;地被物碳储量为1.76、0.95、2.60和0.82 Mg C/hm2,仅占总碳储量的0.32%—1.45%;土壤层碳储量为127.06、153.25、151.61和200.21 Mg C/hm2,占76.64%—94.93%,随植被正向发展呈增加趋势,但对整个生态系统碳储量贡献率减少;由草地向原生林发展过程中,地下部分碳储量均大于地上部分碳储量,地上部分所占比例逐渐提高,地下部分所占比例逐渐减少;相关分析表明,土壤有机碳含量、储量与土壤容重、土壤深度存在良好的线性关系,喀斯特峰丛洼地石灰土土壤有机碳含量与水稳性团聚的分布关系密切,土壤氮素是影响有机碳含量的主要因素,<2 mm细根和土壤微生物对石灰土土壤有机碳的积累具有重要的作用。

The karst region in southwest China is the world＇s largest geology-controlled eco-environment. This area＇s basic characteristics include： the shortage of soil resources; low vegetation cover and highly diverse microhabitats. The historical irffluence of human direct/indirect disturbances has negatively affected the karst forest causing different degrees of degradation. This has resulted in the forest forming coexisting communities at different stages or forms reflecting different successional stages. Therefore, vegetation restoration/reconstruction and the comprehensive control of karst rock desertification has rapidly developed in this region of southwest China. However, the role of karst ecosystems in the global carbon-cycle under different vegetation types remains unclear. The quantification of karst areas for carbon storage and distribution is important in studies on karst carbon cycling. To quantify carbon storage in karst areas we used plot inventory,harvest methods and an allometric approach to measure carbon density and allocation at four different vegetation types including grasslands, shrublands, secondary and primary （climax community）forests located in depressions between karst hills. In addition, we investigated the effect of different parameters such as soil physicochemical properties and biological characteristics on soil carbon. The results showed that the total carbon storage in grasslands, shrublands, secondary and primary forest were 133.84, 160.79, 179.08 and 261.24 Mg C/hm^2, respectively, with the vegetation developing into a higher stage. The storage of carbon in vegetation was 5.02, 6.59, 20.87 and 60.20 Mg C/hm^2（ grasslands, shrublands, secondary and primary forests, respectively） accounting for 3.75, 4.10, 13.89 and 23.04% of the total carbon storage in grassland, shrublands, secondary and primary forest, respectively. The carbon storage in the litter for grasslands, shrublands, secondary and primary forests was 1.76, 0.95, 2.60 and 0.82 Mg C/hm^2, respectively, contributing 0.32- 1.45% to the total carbon density. The soil organic carbon content decreased with increasing soil depth at different stages of vegetation restoration, with the carbon storage of mineral soils at 127.06, 153.25, 151.61 and 200.21 Mg C/hm^2, （grassland, shrub, secondary and primary forest respectively） This accounted for 94.93% （grassland） 95.31% （shrubs）, 84.66% （secondary forest） and 76.64% （primary forest） of the total carbon storage. The soil carbon pool increased with vegetation development into a higher stage, but showed a proportional decrease with restoration. The underground carbon content was higher compared with that above-ground, while the proportion of carbon storage above-ground gradually increased. However, the underground carbon content decreased from grasslands to primary forest. Correlation analysis showed a significant positive or negative linear association between soil carbon content, carbon storage, soil bulk density and soil depth. In the depressions between the karst hills, the calcareous soil organic carbon content showed a significant association with water-stable aggregation （〈 0.25, 0.25-0.5, 0.5-1, 1-2, 2-5, 5-8, 〉8 ram）. Soil nitrogen was the main factor affecting soil organic carbon content. Fine roots （ 〈 2 mm） and soil microorganism showed a significant role in organic carbon accumulation in calcareous soil. In the karst region of southwestern China, the carbon sequestration potential is significant under the conditions of reduced human disturbance and reasonable management strategies promoting rapid vegetation recovery, ecological reconstruction and increased carbon storage.