林木非同化器官CO_2通量的测定方法及对结果的影响

Methods for the determination of CO_2 flux from non-photosynthetic organs of trees and their influences on the results

林木非同化器官的气体交换特性是研究森林 CO2 通量过程中的一个必须考虑的因子 ,但是目前对于如何测定并没有标准方法。综述研究根系呼吸的 6类 10种方法、研究树干和树枝呼吸的 2类方法 ,并对各种方法的优缺点和最新研究成果进行了讨论。在此基础之上 ,收集前人研究结果 (6 5个根系呼吸占土壤总呼吸比例的数据 ,5 9个美国黄松 (Pinus ponderosa)树干呼吸数据 )对不同研究方法对测定结果的可能影响进行了评述。根系呼吸对土壤呼吸的贡献率在 5 %～ 90 %之间 ,而近 6 0 %的研究结果显示土壤呼吸中根呼吸所占比例为 4 0 %～ 70 %。不同研究方法测定的根系呼吸结果不同 ,其中 ,使用同位素标记法测定的根系呼吸占土壤总呼吸的比例最低 (4 0 %) ,而根系排除法和树干环剥法测定结果最高 ,较同位素标记法 (人工同位素标记法和天然同位素丰度法 )的测定结果高 33%,较根系分离法的测定结果高 7%,表明根系排除法和树干环剥法对根际环境的扰动破坏可能导致估计偏高 ,而根系分离法中根系死亡导致呼吸速率降低和根系受伤导致呼吸增加之间的补偿作用 ,仅仅使测定结果稍微偏高。对树干呼吸的统计结果显示 ,当以树干表面积为基准时 ,离体测定结果较活体测定结果平均高 74 %(p=0 .0 13) ;而当用边材体积为基准时 。

The CO 2 exchange feature of non-photosynthetic organs of trees is important in monitoring forest CO 2 flux. However, up to date, no standard method has been suggested in these measurements. Six categories of 10 methods for separating root respiration from soil respiration, and 2 methods for measuring stem or branch respiration were reviewed. The advantage and disadvantage of each method and its recent advance were also discussed. Under the light of these discussion, data from previous references (65 data of root respiration and 59 stem respiration data of Pinus ponderosa)were collected to analyze the influence of different methods to the results. The results showed that root respiration contributed 5% to 90% of total soil respiration, and near 60% data ranged from 40%～70%. Study methods showed somewhat influences on the results of root respiration. The contribution of root respiration to total soil respiration was ca. 40% measured by the isotopic labeling methods, but this value was enhanced by 33% for those measured by the root exclusion methods and the stem girdling method, and 7% higher than that measured by the root separation method. This finding indicates that the root exclusion methods and the stem girdling method may overestimate the root respiration since they disturbed the root system and rhizosphere. Comparing with in vivo method, the stem respiration rate was overestimated by 72% using the in vitro method based on stem surface area; while, it was overestimated by 56 times based on sap wood volume for the in vitro method in same study. Therefore, it is necessary to fully considerate the method-induced difference when comparisons are carried out by different methods.