pH Effect on Root Growth and Water Uptake by Plants

A direct pH effect upon root growth and water uptake by plants was demonstrated. When the OH‐ ion concentration increased sufficiently, the curtailment of water uptake was almost instantaneous. Extreme wilting of plants growing in nutrient solution occurred in a matter of 15 min after the addition of Na 2 CO 3 when temperatures were sufficiently high to cause rapid transpiration. Roots were damaged in a similar period of time as indicated by an over all discoloring of the root system and a blackening of root tips and small laterals. Plants treated with an equivalent amount of NaCl showed no adverse effects. Since the addition of Na 2 CO 3 to nutrient solutions produced excessively high pH values, a study of the effect of pH upon plant growth was made. Growth was curtailed at pH 9 and above. Wilt and root damage occurred at these pH values similar to that observed with Na 2 CO 3 treatments. The critical pH for tomato plants (lycopersicon esculentum) was 8.8 if the plants were established in nutrient solution for several days before treatments were added. For young developing roots, the critical pH was even lower, about 8.2. The only effect of different anions upon plant growth under these conditions proved to be a buffering effect upon the solution pH. Adventitious roots failed to grow in solutions buffered at 8.2 or above. New growth occurred readily at pH values below 8.0 with a concomitant revitalized plant growth.