Martin T A, Teskey R O, Dougherty P M
School of Forest Resources, University of Georgia, Athens, GA 30602, USA.
Tree Physiol. 1994 May;14(5):481-95. doi: 10.1093/treephys/14.5.481.
Temperature-independent fluctuations in stem CO(2) efflux were measured in Pinus taeda L. seedlings. Stem CO(2) efflux was measured during high and low transpiration rates, high and low net photosynthesis rates, and normal and interrupted substrate supply conditions. Stem CO(2) efflux rates were an average of 6.7% lower during periods of high transpiration compared to periods of low transpiration. This difference in stem CO(2) efflux rates was not due to water stress. The most likely cause was movement of respiratory CO(2) in the transpiration stream. Interruption of substrate supply to the stem by phloem girdling reduced stem CO(2) efflux rates. Increasing net photosynthesis rates from low to high had no effect on stem CO(2) efflux, but decreasing net photosynthesis from high to low caused relatively small reductions in stem CO(2) efflux. These results indicate that diurnal changes in net photosynthesis rate may play a small role in temperature-independent afternoon depressions of stem CO(2) efflux. The transport of respiratory CO(2) by the transpiration stream compromises measurements of woody tissue respiration obtained by commonly accepted gas exchange techniques. This phenomenon could also affect measurement of leaf net photosynthesis and branch woody tissue respiration.
在火炬松幼苗中测量了茎干二氧化碳通量与温度无关的波动情况。在高蒸腾速率和低蒸腾速率、高净光合速率和低净光合速率以及正常和中断底物供应条件下测量了茎干二氧化碳通量。与低蒸腾时期相比，高蒸腾时期的茎干二氧化碳通量速率平均低6.7%。茎干二氧化碳通量速率的这种差异并非由于水分胁迫。最可能的原因是呼吸产生的二氧化碳在蒸腾流中的移动。通过韧皮部环剥中断茎干的底物供应会降低茎干二氧化碳通量速率。将净光合速率从低提高到高对茎干二氧化碳通量没有影响，但将净光合速率从高降低到低会使茎干二氧化碳通量有相对较小的降低。这些结果表明，净光合速率的昼夜变化可能在与温度无关的下午茎干二氧化碳通量降低中起较小作用。蒸腾流对呼吸产生的二氧化碳的运输会影响通过常用气体交换技术获得的木质组织呼吸测量结果。这种现象也可能影响叶片净光合以及枝条木质组织呼吸的测量。
