秦岭火地塘林区油松林下主要灌木碳吸存

林下灌木是森林生态系统的重要组成部分,在维持森林碳平衡中发挥着重要作用.为估算林下灌木的固碳功能,采用TOC-VT H-2000A型TOC/TON分析仪,测定了油松林下主要灌木不同器官的含碳率;根据野外实测资料,建立了油松群落内主要灌木测树因子与其器官生物量的回归模型;计算了2006年和2007年,灌木层CO2年吸存量.结果表明:5种灌木叶、茎、根和皮的平均含碳率为:41.80%～46.25%,39.24%～49.22%,39.56%～46.71%和36.65%～48.23%;刚毛忍冬(Lonicera Hispida pall)各器官的含碳率最高,栓翅卫矛(Euonymus alatus)的叶和茎,白檀 (Symplocos paniculata)的根和皮含碳率最低;不同灌木同一器官和同一灌木不同器官的含碳率均存在显著差异;不同灌木同一器官平均含碳率差值最高达10.58%,同一灌木不同器官平均含碳率差值最高达6.47%;模拟显示:灌木器官的生物量和测树因子间的关系可用复合式、幂、二次方程、三次方程、对数方程、指数方程和倒数方程来描述;残差和误差分析表明,均方差根不大于1.70,模型有效性指数均接近于1,残差系数均接近于0,灌木根、茎、叶和皮的生物量模型估计值与实测值间相对误差的绝对值分别为3.89%～8.58%,0.57%～6.84%,4.69%～9.09%和4.50%～7.03%.回归模型的决定系数(R2)都在0.90以上,估计精度在95%以上,建立的油松群落内主要灌木测树因子与其器官生物量的回归模型,具有较高的估计精度和较好的适用性;研究区2006～2007年,主要灌木CO2年吸存量为10.138 Mghm-2.

Carbon dioxide sequestration of main shrub species in a natural secondary Pinus Tabulaeformis forest at the Huoditang forest zone in the Qinling Moutains

Understorey shrub species play a vital role in maintaining the carbon balance between a forest ecosystem and the atmosphere. To estimate the amount of CO_2 sequestrated by shrub species, samples were collected from 294 plots at the Qinling National Forest Ecosystem Research Station, Huoditang forest zone, Ningshaan County, China (33°18′-33°28′ N, 109°20′ -109°29′ E). The carbon content ratio (CCR) of shrub organs was measured using a TOC/TON analyzer (TOC-VT H-2000A, Shimadzu Corporation, Japan). Biomass models describing the relationship among shrub organs and their morphological indices (height, DBH, canopy width, etc.) were established. The amount of carbon dioxide sequestrated by the shrub species between 2006 and 2007 was calculated. The CCR in five shrub species ranged from 41.80%-46.25% (roots), 39.24%-49.22% (stems), 39.56% to 46.71% (leaves), and 36.65%-48.23% (tegument), respectively. The highest CCR value occurred in all the organs of Lonicera hispida pall. The lowest CCR values were obtained from the leaves and stem of Euonymus phellomas, and the root and tegument of Symplocos paniculata. Significant differences in the CCR occurred both in the same organs of various shrub species and in the various organs of the same shrub species. The greatest difference in the mean CCR of the same organ among different shrub species and various organs of the same shrub species was 10.58% and 6.47%, respectively. The relationship of organ biomass to the morphological indices of different shrub species could be better shown using compound, power, quadratic, cubic, logarithmic, exponential and inverse models, respectively. Residual errors were analyzed.The maximum value of RMSE (root mean square error) was not more than 1.70. All EF (modeling efficiency)and CRM(coefficient of residual mass)values were close to 1 and 0, respectively. The absolute values for relative error in shrub organ biomass between the model-estimated and the field-measured ranged from 3.89%-8.58% (roots), 0.57%-6.84% (stems), 4.69%-9.09% (leaves) and 4.50%-7.03% (tegument). The models′ determining coefficients and estimating accuracy exceeded 0.90 and 95%, respectively. Residual and error analysis demonstrated that these models achieved higher accuracy and had better applicability. However, the samples are from special forest types (Pinus tabulaeformis forest and mixed forests of Pinus tabulaeformis and Quercus aliena var. Acuteserrata) in the experimental area and the indices are limited in some scale. These models could not be used generally. Moreover, no model could be fit to the relationship of organ biomass and the morphological indices of fasciculate shrub species (such as Rosa swginzowii, etc.) making CO_2 sequestration difficult to estimate. Between 2006 and 2007, in the experimental area, the main understorey shrub species in the Pinus tabulaeformis forest sequestrated 10.138 Mghm-2year-1of carbon dioxide.