An integrative measurement of stomatal regulation of water loss will also be of relevance in studies concerning plant response to variation in the growth environment. Again, a technique that overcomes the difficulties of field measurement of gs using gas exchange techniques would be valuable. Many studies of plant and ecosystem function use measurements of shoot gs as a basic tool in understanding carbon and water fluxes. An integrative measure of gs, requiring little (and unskilled) labor in the field, would be of great merit. However, the same cautions as outlined above for breeding applications apply to ecophysiological applications.

A further application of interest in ecophysiological studies is using A18Op to interpret studies of ecosystem fluxes and isotope ratios of CO2 and water. The stable oxygen isotope ratio of ecosystem CO2 and H2O may allow partitioning of the fluxes into the components of photosynthesis and respiration (for CO2) or transpiration and soil evaporation (for H2O). However, to interpret variation in C18OleO and H18OleO, the leaf water AlsO must be known. A18Op may provide an integrative measure of A18Ol, and would therefore dispense with time-consuming diurnal sampling of leaf water for isotope analysis.

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