A Contribution to the Biology of Nitella hookeri A. Br. in the Rotorua Lakes, New Zealand

Abstract

Nitella hookeri A. BR., a native charophyte of the Rotorua lakes in the North Island of New Zealand, was investigated in terms of its nutrient requirements under laboratory culture in non-arenic conditions. Optimum growth in phosphate, nitrate, ammonia, iron and magnesium occurred at 20 mg l−1 or lower. Higher concentrations of these ions were markedly inhibitory to growth when compared with the optimum. Calcium and potassium gave growth at higher levels and over a wider range of concentrations. Sulphate and sulphur-amino acids do not promote growth above the levels of the basal medium (1.2 mg l−1 sulphur as SO2−4). Amino acids did not appear to provide a nitrogen source for the plant. The optimum phosphate concentration was one thousand times higher than previously reported values. This may be due to the presence of arsenic in the vegetative propagules used from Lake Rotoiti. Iron toxicity effects may have resulted from the presence of EDTA. The results are considered in relation to the known levels of nutrients present in lake waters. Only phosphorus appears directly correlated with the natural distribution of the plant but it is suggested that anaerobic lake substrates may contribute iron and ammonia to the plants and further explain their distribution.