Carbon Dioxide Exchange of Ponderosa Pine as Affected by Sodium Chloride and Polyethylene Glycol
The effects of isosmotic solutions of sodium chloride and polyethylene glycol 4000 on ponderosa pine (Pinus ponderosa) were studied. Two-year-old seedlings were grown in sand cultures where the solutions of some cultures were decreased approximately - 1.5 bars each day for five consecutive days. Lowering the water potential in the root medium by using either sodium chloride or polyethylene glycol caused a decrease in net photosynthesis, dark respiration, and xylem water potential. Net photosynthesis was reduced at substrate water potentials of as high as -2.9 bars. Between -2.9 and -5.8 bars there was no change in net photosynthesis, whereas at -7.1 bars there was a second significant decrease in net photosynthesis. Dark respiration showed an initial increase at -1.5 bars and then a decrease from -2.9 to -7.1 bars. Seedlings that received foliar spray with solutions of sodium chloride had no significant changes in CO2 exchange rates or xylem water potentials. There was no detectable specific ion effect of the sodium or chloride ion on gas exchange in this short-term experiment other than through a reduction of the substrate water potential. Forest Sci. 27:139-146.
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