Date of Award

Summer 1975

Document Type


Degree Name

Master of Science (MS)


Biological Sciences



Committee Director

Daniel E. Sonenshine

Committee Member

Gerald F. Levy

Committee Member

Paul W. Kirk, Jr.

Call Number for Print

Special Collections LD4331.B46 C96


Transpiration rates of loblolly pine (Pinus taeda L.) and sweetgum (Liguidambar styraciflua L.) were measured at two different water vapor pressure deficits (V.P.D.) in a controlled environment growth chamber using tritiated water as a tracer. The trees were maintained in a sealed plant bed containing a hydroponic nutrient solution. Samples of leaves, chamber air, spiked nutrient and control solutions were assayed for activity using liquid scintillation techniques. The transpiration rate of sweetgum (4.95 ml/hr/gm) was found to be 5 times greater than that of loblolly pine (1.03 ml/hr/gm) at the lower V.P.D. and 8 times greater at the higher V.P.D. (15.99 ml/hr/gm for sweetgum vs. 2.19 ml/hr/gm for pine). Transpiration in both species rose with increasing vapor pressure deficit although sweetgum increased its output by 3 times while pine only doubled its rate. Cyclical changes in transpiration rates were noted in both species; the sweetgum cycle peaked at 6 hour intervals and the pine cycle at 9 hour intervals.


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