Nutrient solution pH control using dipolar buffers in studies of Trifolium repens L. nitrogen nutrition

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 pK2s (20 °C) of 6.15, 6.60, 6.90, 7.15 and 7.20 respectively, at a concentration of 2.0 mol m−3, were provided to inoculated Trifolium repens growing in nutrient solution containing 7.13 mol m−3 nitrogen as (NH4)2SO4. Initial pH of each solution was adjusted to the appropriate buffer pK2 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 7.13 mol m−3 (NH4)2SO4, 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.