THE EFFECTS OF PHOSPHORUS AND FORM OF NITROGEN SUPPLY ON LEAF CELL-SIZE AND NUTRIENT CONTENT IN TRIFOLIUM-REPENS AND LOTUS-ULIGINOSUS

White clover (Grasslands Huia) and lotus (Grasslands Maku) were grown in pots of soil at a range of phosphorus supply, and reliant on symbio tic nitrogen fixation (SN plants) or entirely on mineral nitrogen (MN plants). Shoots increased in weight with phosphorus supply. White clov er MN shoots were bigger than those of SN plants except at the lowest level of phosphorus supply; lotus MN shoots were only bigger than SN s hoots at the highest level of phosphorus supply. Leaf growth rate and size increased with phosphorus supply but were not significantly affec ted by the nitrogen treatments. Estimates of cell size were made by de termining DNA concentration, by digestion of tissue followed by counti ng and by taking vinyl impressions of epidermal cell surfaces. Lotus c ells are bigger than those of white clover. 'Digested' cell sizes were not significantly affected by changes in phosphorus supply. Epidermal cell size increased with phosphorus supply, but the relationship was, weaker in SN than in MN plants. Methods which give values for 'averag e' cell size are capable of detecting large-scale differences, but met hods able to resolve cell heterogeneity are necessary for an accurate picture of the relationship between leaf growth and cellular nutrition . Average concentrations of total and inorganic phosphorus on a DNA ba sis did not differ between the species, contrary to concentrations on a dry weight basis, indicating that differences in phosphorus efficien cy can be partly explained on the basis of average differences in cell size. Differences in inorganic phosphorous on a DNA basis at higher l evels of supply suggested an additional intrinsic difference in cellul ar accumulation of inorganic phosphorus between the two species.