Nutrient Solution pH Control using Dipolar Buffers in Studies ofTrifolium repensL. Nitrogen Nutrition

Abstract

In studies of Trifolium repens nitrogen nutrition, the control of nutrient solution pH using dipolar buffers, was evaluated in tube culture under sterile conditions. Five buffers; MES, ADA, ACES, BES and MOPS with pKas (20 °C) of 6-15, 6-60, 6-90, 715 and 7-20 respectively, at a concentration of 20 mol m3, were provided to inoculated Trifolium repens growing in nutrient solution containing 713 mol m-3 nitrogen as (NH4)2S04. Initial pH of each solution was adjusted to the appropriate buffer pKa. Two buffers, ADA and ACES completely inhibited plant growth. The remaining buffers had little effect in limiting pH change, although plant dry matter was higher and nodule numbers lower in the presence of these buffers. MES and MOPS were supplied to nutrient solutions with and without 713 mol m-3 (NH4)2S04, at concentrations ranging from 0-12 mol m 3. MES at 9 mol m-3 and 12 mol m-3 reduced growth of plants reliant on the symbiosis for providing nitrogen. The provision of MES to plants provided with NH4 significantly increased plant yield and reduced nodule number at all concentrations. MOPS did not affect plant yield or nodule number. The use of dipolar buffers in legume nitrogen nutrition studies is considered in terms of buffering capacity, and the side effects on plant growth and symbiotic development.