典型麻竹林土壤植硅体碳的空间异质性特征

Spatial Variability of Phytolith-occluded Organic Carbon in Soil under Typical Dendrocalamus latiflorus Munro Groves

土壤植硅体碳(Phytolith Occluded Organic Carbon,Phyt OC)是土壤稳定性碳库的重要来源之一,对于增强土壤碳汇,维持全球CO2平衡具有重要意义。为了了解土壤植硅体碳的空间分布,基于地统计学方法,结合Arc GIS 10.0空间分析软件,分析典型麻竹主产区——福建南靖县麻竹林不同土层的土壤植硅体碳的空间变异性。结果表明:南靖县麻竹土壤植硅体碳平均含量介于0.30~0.75g kg-1之间,变异系数介于80.38%~87.46%,表现为中等程度的变异性;地统计分析得出块基比介于8.7%~74.9%,有较强的空间自相关性,且参数比均较小,模型拟合度较好;0~100 cm土层土壤植硅体碳平均储量为4.23 t hm-2;土壤植硅体碳含量随土壤剖面深度的增加而降低,土壤植硅体碳、土壤植硅体和土壤全硅的空间分布图较为相似,它们之间也呈极显著正相关关系(p<0.01)。样地的竹林年龄与表层的土壤植硅体碳呈现显著正相关关系(p<0.05)。样地的海拔与表层的土壤植硅体碳呈现显著负相关关系(p<0.05)。

[Objective] As phytolith features super tolerance to high temperature, oxidation and decomposition, the organic carbon occluded inside the phytolith shell may exist and accumulate in soils and sediments for thousands of years and is hence named as Phytolith occluded organic carbon （ PhytOC ） , which is, therefore, regarded as an important soil organic carbon pool, and contributes significantly to the carbon sink in the soil and global CO2 balance. Forest ecosystem is a mainstay of the terrestrial ecosystem. However, the area of forests on the globe is shrinking drastically today, while the area of bamboo groves is still on a rising trend. So, bamboo groves are a growing carbon sink and playing a critical role in carbon cycling in the terrestrial ecosystem. As Dendrocalamus latiflorus Munro grows very fast and features large volumes of biomass, well-developed root system and outstanding ecological functions, it is favored to be one of the bamboo species extensively cultivated in South China. Nanjing County is known as ＂Land of Dendrocalamus latiflorus Munro in China＂ and one of the largest Dendrocalamus latiflorus Munro cultivation region in Fujian Province. In this paper an attempt was made to explore characteristics of the spatial distribution of PhytOC in the soil under the bamboo groves, aiming at providing some scientific basis for assessing the pool of PhytOC in the bamboo ecosystems of China. [ Method ] A total of 100 tracts of Dendrocalamus latiflorus Munro groves in Nanjing County was selected as object for the study. Soils in different soil layers were sampled for extraction and isolation of PhytOC using the microwave digestion method and then the centrifuging-heavy liquid floatation extraction method. In order to extract fairly pure phytolith, the floatation extraction process was performed twice, using heavy liquid, Zinc bromide, 2.35 and 1.60 in specific gravity sequently to remove impurities.The isolated constant in w Alkali Dissol pure phytolith was put into a ventilated oven at 65℃ for 48 hours till they were fully dried and eight. And then, the phytolith was weighed after the samples cooled down in a vacuum dryer. The ution Spectrophotometry method was applied to analysis of the PhytOC and then spatial variability of the PhytOC in the bamboo soil analyzed using the software of ArcGIS 10.0 and the Geostatistic method. [Result] Results show that average content of PhytOC in the soil varied from 0.30 - 0.75 g kg-1 with soil layer under Dendrocalamus latiflorus Munro groves in Nanjing County, with variation coefficients ranging from 80.38% to 87.46%, which indicates a moderate degree of variability. Geostatistical analysis reveals that PhytOC contents in the 10 - 30 cm, 60 - 100 cm and 0 - 100 cm soil layers fit exponential models; in the 0 - 10 cm soil layer fit the Gaussian model; and in the 30 - 60 cm soil layer fit spherical models. Nugget/Sill ratio of the PhytOC varied from 8.7% to74.9%, displaying strong and moderate spatial correlation; moreover their SM/SRMS ratios were low, indicating that the models fit well. In the 0- 100 cm soil layer under the bamboo groves, the pool of PhytOC reached 4.23 t hm-2, significantly higher than that under the Chinese fir forest, Masson pine forest, broadleaf forest and mixed conifer-broadleaf forest. Kriging reveals that the contents of PhytOC displayed a decreasing trend with soil depth, which is quite similar to the distributions of phytolith and total silicon in the top-soil. Besides that, a ultra-significantly positive correlation （p 〈 0.01 ） was observed between them, and a significant positive relationship, too, between the content of PhytOC in the 0 - 100 cm soil layer and age of the bamboo forest, but a significantly negative one between the content of PhytOC and elevation of the groves （p 〈 0.05 ） . [Conclusion] All the findings in this study suggest that to raise the content of soil silicon may help increase the content of soil phytolith and soil PhytOC in the top- soil; and that Dendrocalamus latiflorus Munro groves can hold a large pool of PhytOC, because the plant per se has a high content of PbytOC, and the soil under the groves is highly capable of fixing and accumulating PhytOC, as well. Therefore, the Dendrocalamus latiflorus Munro ecosystem plays an important role in expanding the stable organic carbon pool in the soil.