土壤与植物根系特征及碳积累探究

为研究土壤与植物根系生长及有机碳输入之间的关系，2011年分别将构树（Broussonetia papyrifera）、铁仔（Myrsine africana）、紫花苜蓿（Medicago sativa）、皇竹草（Pennisetum sinese）移栽入贵州大学林学院苗圃基地，采用石灰土（岩溶地区土壤）与硅质黄壤（非岩溶地区土壤）进行培育，然后对根系生长特征和根系对土壤有机碳积累进行了研究。研究结果表明，构树根系在岩溶地区土壤比非岩溶地区土壤发达，即岩溶地区土壤根系碳沉积比非岩溶高。岩溶地区土壤上，紫花苜蓿死亡根系体积最大，其根系对土壤有机碳积累贡献最大。构树根系生长无论在哪种土壤均随土层深度增加而增加，使得森林土壤深层有机碳含量比草地高。因此，可确定土壤有机碳积累与植被生长环境和植被种类密切相关。 

Root characteristics and carbon accumulation in relation to soils

To study the relationship between the input of soil organic carbon and growth of plant root systems in different soils, four kinds of plants, including Broussonetia papyrifera, Myrsine africana, Medicago sativa and Pennisetum sinese, were shifted and cultivated in calcareous and siliceous yellow soils at the cultivation base of Guizhou University in 2011. This place is of subtropical humid monsoon climate, at an altitude of 1,100 m, with an annual average temperature (MAT) of 14.9 ℃ and the annual average precipitation (MAP) of 1,178.3 mm, respectively. The monitoring system (CI-600) was installed in October 2011. For each experimental unit, a plexiglass tube, with a length of 1 meter and diameter of 0.1 meter, was inserted at an angle of 45° down to the ground, with an insert length 65 cm. During the period from January 2014 to December 2014, the root growth characteristics were observed with a plant root scanning system. The resulting data were analyzed with software WINRHIZO TRON 2009a. The dead roots were dug out for the determination of their bulk density, annual dead volume and root carbon density. The results suggest that the root system of Broussonetia papyrifera cultivated in calcareous soil grew better in comparison than that in siliceous yellow soil. It means that the soil organic carbon concentration in the karst mountainous area is larger than that in non-karst area. However, the annual dead roots volume of Medicago sativa cultivated in calcareous soil was larger than that of vegetation species, and its root has the largest contribution to soil carbon sequestration. As an arbor tree species, the root of Broussonetia papyrifera always increased with depth no matter in what soil it was cultivated with. We consider that this should be one of the key reasons why concentrations of soil organic carbon in forest lands are usually higher than those in grass lands at deeper soils. The root system of Broussonetia papyrifera cultivated in calcareous soil developed better in comparison with that of Broussonetia papyrifera cultivated in the sandy clay loam soil. In karst areas, the contributions of plants to soil carbon accumulation follow the order of Medicago sativa> Myrsine africana > Broussonetia papyrifera > Pennisetum sinese. Therefore, it is concluded that the accumulation of soil organic carbon is closely related with growth environments and species of vegetation.