ROOT RESISTANCE AS A CAUSE OF DECREASED WATER ABSORPTION BY PLANTS AT LOW TEMPERATURES

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Abstract
The rate of transpiration of potted sunflower and privet plants was reduced to 20-30% of the rate at 25[degree] C by cooling the soil nearly to freezing. The rate of water movement through living sunflower root systems attached to a vacuum pump was only 1/5 as great at 2[degree] as at 25[degree] C. The decrease in water movement was as great for root systems in water as for those in soil. The rate of water movement through dead roots was half as great near freezing as at 25[degree] C. The decreased rate of water movement through dead roots at low temps. is probably mainly due to the increased viscosity of the water; in living roots the added effects of decreased permeability of the cell membranes, probably caused by increased viscosity of the protoplasm and the colloidal gels of the cell walls, causes a much greater resistance to water movement than in dead roots. The decreased water intake through root systems at low soil or soln. temps. can, therefore, be adequately explained by the physical effects of low temp. on the viscosity of water 7 and the permeability of the root membranes. The effects of low temp. in decreasing root extension, root respiration, and active absorption appear to be of secondary importance as compared with the increased resistance to water movement through the roots.