Root Resistance as a Cause of Decreased Water Absorption by Plants at Low Temperatures.

It is well known that low soil temperatures decrease the absorptionl of water by plants. Many years ago SACHS (24) reported that tobacco and gourd plants growing in moist soil under conditions favoring a low rate of transpiration wilted when the soil was cooled to 30 to 50 C., but recovered when the soil was warmed to 120 to 180 C. Cabbage and turnips were less affected, absorbing enough water at a soil temperature just above freezing to prevent wilting during times of moderate transpiration. A few years later VESQUE (29) made further studies using a potometer method in which the roots of Hedera helix were immersed in water and cooled to low temperatures. He reported that absorption by transpiring plants decreased as the temperature was decreased although some absorption occurred even at 0.50 C. The most rapid decrease occurred between 150 and 100 C. VESQUE stated that since temperatures higher than 150 C. sometimes resulted in an increase and sometimes in a decrease in absorption, it was impossible to decide as to the real effect. KOSAROFF (17), by the use of potometers, made an extensive investigation of the effects of low temperature on water intake through living root systems and root systems killed by scalding. He found that lowering the temperature from about 200 C. to freezing retarded the absorption of water by living root systems of Phaseolus and Pisum 25 or 30 per cent. but did not decrease the absorption of water through dead root systems. Lowered temperature decreased water intake through cut branches of woody plants, but not as much as through living root systems. KOSAROFF also reported that certain species including Sinapis alba and Chrysanthemum indicum were able to absorb water from soil at 10 C.; Chrysanthemutm indicum and Salix absorbed water from ice in which their roots were frozen. Since the claim that absorption occurred was based on recovery of wilted leaves in a humid atmosphere, it might be supposed that recovery was brought about by movement of water from stem to leaves rather than by absorption through the roots. KOSAROFF discounted this explanation, however, since shoots not in water or ice failed to recover their turgor in a saturated atmosphere. STAHL (25) reported guttation from the leaves of oats, barley, wheat, and Geranium pyrenaicum with roots in soil cooled to approximately 00 C. This, he believed, indicated that some absorption was occurring even at freezing. DUNCAN and COOKE (12) found that the rate of absorption by sugar cane