Acetylene‐Ethylene Assay Studies on Excised Root Nodules of Myrica asplenifolia L.

Abstract

Abstract The acetylene‐reducing activity of excised root nodules of Myrica asplenifolia L. [ Comptonia peregrina (L.) Coult.] was measured on a large number of samples both in the field and in the laboratory. The apparent K m for acetylene was determined to be 0.006 atm and was not significantly different in the presence or in the absence of 0.8 atm of N 2 . Maximum activity was obtained between 26 and 30C and between 0.15 and 0.25 atm O 2 . No significant diurnal fluctuation in activity could be detected. High variation (coefficient of variation ca. 50%) between replicate samples of field‐collected nodules was a consistent feature of estimates of acetylene‐reducing activity over a range of sites, sample weights, and sample numbers. Therefore, field‐collected nodules are unsuitable for physiological experiments unless the effect of the treatments on acetylene‐reducing activity is large. In ecological studies where field‐collected nodules must be used, extensive sampling is required to permit reliable estimates of the activity. The ratio of the rate of ethylene produced from acetylene to the rate of 15 N 2 incorporated was measured by exposing individual nodule samples sequentially to 15 N 2 , then acetylene. The mean ratio for 24 samples was 3.14 ± 0.30.