Abstract:

Stem respiration is an important part of the carbon balance research of forest community and ecosystem. A new method to estimate stem respiration, demonstrated in the United States, namely mass balance approach, was introduced in this paper, including the theory, measurement methods and some study cases. Mass balance theory considers that the CO₂ production of a segment of stem tissue should be sum of CO₂ fluxes, including CO₂ leaving the segment by diffusion through bark (efflux to atmosphere), CO₂ entering and leaving the segment in flowing sap (influx and efflux transported) and the CO₂ increased or decreased in mean sap concentration over time (storage flux). The key item of mass balance approach is to determine the CO₂ flux of sap flow (storage and transport flux and efflux). There are two methods to estimate CO₂ concentration in sap flow by mass balance approach: 1) Directly measurement using instruments; 2) Indirectly estimation by calculating the efflux deference between the sap flow ceased or at vary low velocity (night time) and the sap is flowing (day time). Mass balance approach provides a more accurate method to evaluate stem respiration and makes the results more reasonable.

Key words: stem respiration, mass balance approach, CO₂ flux