JXB Advance Access originally published online on June 4, 2004
Journal of Experimental Botany, Vol. 55, No. 402, pp. 1557-1567, July 2004
Journal of Experimental Botany, Vol. 55, No. 402, © Society for Experimental Biology 2004; all rights reserved
RESEARCH PAPER |
Maintaining exponential growth, solution conductivity, and solution pH in low-ionic-strength solution culture using a computer-controlled nutrient delivery system

Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada
To whom correspondence should be addressed. Fax: +1 780 492 9234. E-mail: gregory.taylor{at}ualberta.ca
Studies of plant nutrient requirements in solution culture have often used nutrient concentrations many-fold higher than levels found in fertile soils, creating an artificial rooting environment that can alter patterns of nutrient acquisition. The relative addition rate (RAR) technique addresses this problem by providing nutrients in exponentially increasing quantities to plant roots in solution culture. A computer-controlled RAR nutrient delivery system has been developed to reduce workload and to facilitate more frequent nutrient additions (4x daily) than is possible with manual additions. In initial experiments, a minimum background solution containing 500 µM nitrogen and all other essential nutrients in optimal proportions was required for the healthy growth of Triticum aestivum. This requirement was reduced to 50 µM nitrogen when calcium in the background solutions was increased to 400 µM. Varying the abundance of ammonium and nitrate in both background and delivery solutions provided a means of controlling plant-induced pH changes in growth solutions. In optimized solutions, plant relative growth rates (RGR) in the order of 0.2 g g1 plant d1 were maintained over a 22 d experimental period. Variation in RARs provided a means of growing plants with varying RGRs under relatively constant conditions of solution electrical conductivity and pH.
Key words: Ammonium, nitrate, nitrogen, relative addition rate, RAR, Triticum aestivum