Assimilation and release of internal carbon dioxide by woody plant shoots

摘要

This study was undertaken to determine whether tree stems can reassimilate internal CO2produced by respiration or whether this CO2is evolved and could possibly interfere with measurements of leaf gas exchange. Radioactive CO2was added to the stem transpiration stream of slash pine seedlings (Pinus elliottiiEngelm.) and the distribution of14C studied in shoots and needles exposed to dark and light conditions.Photosynthesis decreases the amount of internal CO2evolved. Large amounts of14CO2from the transpiration stream are incorporated into organic compounds of needles and stems, primarily into ethanol-soluble sugars and organic acids, and in time, small amounts of14C occur in the ethanol-insoluble materials.These results indicate that respiratory CO2transported in the transpiration stream of woody plants can be reused in photosynthesis or possibly other metabolic processes. Internal CO2is also evolved to the atmosphere in large amounts, but related research indicates it diffuses primarily out of the stem tissue not the needles. The evolved CO2supplied from stems does not significantly affect short term measurements of needle gas exchange in pine seedlings.