Morphological and physiological characteristics of tomato roots associated with potassium-acquisition efficiency

Acquisition of potassium (K) by roots plays the most important role in K efficiency of plants. However, limited information is available on morphological and physiological characteristics of roots in response to low-K stress. In this report, two tomato strains representing two distinct phenotypes of K-acquisition efficiency were studied using a sand±zeolite culture system. One was apparently morphological, manifested by rapidly proliferating root length and concomitantly greater root absorbing surface areas to capture K. The other was physiological, demonstrated by high net K-influx coupled with low pH around root surfaces. The high K-influx, in association with high root cation-exchange capacity for K, brought about significant amounts of K accumulation in apoplast and on root surfaces, and K depletion in a zone between 1 and 3 mm from root surfaces. The accumulated K, in turn, could serve as a K pool favorable to K uptake. Results from this study indicate that soil K deficiency has been a selective force that leads plants to evolve characteristics for the efficiency of K-acquisition. # 2000 Elsevier Science B.V. All rights reserved.