The effect of seed source on transpiration rates of seedlings of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco)

Graduation date: 1968In this study transpiration rates were measured on Douglas-fir\ud seedlings from five seed sources. The seedlings were grown under\ud two environments, a growth chamber and outside in cold frames.\ud Transpiration was measured at two ages, 4 and 16 weeks. Comparison\ud of transpiration rates was made at low soil moisture stress.\ud Transpiration was measured using humidity sensing elements\ud to measure water vapor before and after passing the seedling. A\ud dual bath system was used to control the humidity.\ud Seedlings grown outside transpired significantly more (1% level)\ud than seedlings grown in a growth chamber. For all seed sources\ud combined (outside and growth-chamber-grown) the 16-week-old\ud seedlings transpired less than 4-week-old seedlings, however seedlings\ud from some sources showed increasing transpiration rates with\ud age. This was expressed in a highly statistical significant seed\ud source- environment-age interaction.\ud Among the outside grown seedlings the mesic seed sources\ud had higher transpiration rates than the seedlings from xeric sources.\ud When grown in the growth chamber the xeric sources had higher\ud transpiration rates. Transpiration rates of seedlings from mesic\ud sources were affected more by the growing conditions than seedlings\ud from xeric sources