The Influence of the Mineral Composition of the Medium on the Growth of Planktonic Algae: Part II. The Influence of the Concentration of Inorganic Nitrogen and Phosphate Phosphorus

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Abstract
The influence of the conc. of N and P in the medium on the growth of 7 common algae (Pediastrum boryanum, Staurastrum paradoxum, Botryo-coccus brauni, Nitzchia palea, Fragilaria crotonensis, Tabel-laria flocculosa and Asterionella gracillima) was investigated using media made with pure inorganic chemicals as described in Part I (Jour. Ecol. 30, 2). The ranges of conc. used in the expts. generally included that found in natural waters. The bearing of the exptl. results on the occurrence of planktonts in nature is discussed in relation to the conc. of N and P observed in fresh waters. The upper limits of conc. of N and P for optimum growth are always higher than the highest conc. occurring in ordinary waters, so that plankton growth is unlikely ever to be unfavorably affected by too high a conc. of N or P in nature. The conc. of N and P in nearly all natural waters frequently falls below or never reaches the lower limit for an optimum growth, so that, when other conditions are suitable for growth, a limiting effect due to deficiency of these elements may be expected in all natural waters during certain periods of the year. Optimum growth of all the organisms studied can be obtained in nitrate-N conc. 0.9-3.5 ppm. and P cone. 0.09-1.8 ppm., while a limiting effect on all of them will be discernible in N conc. from 0.1 ppm. downwards and in P conc. from 0.009 ppm. downwards. The opt. ranges differ slightly for different organisms. The ranges are also affected by the forms of N used. Ammoniacal N can be directly utilized. When NH4 salts are used, the opt. ranges of conc. of N and P are narrower than when nitrates are used, the lower limit of N conc. being higher and the upper limit of P conc. lower. No increase or decrease in the conc. of N or P, and no change in the value of the N/P ratio in the medium can markedly affect the growth of planktonts, so long as these elements remain within the opt. range for their growth. When the concs. of these elements are below the optimum range, it is mainly the deficiency of N or P or both that limits the growth, but not the N/P ratio. Marked inhibiting effect will occur in high conc. of N or P above 45 ppm.