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Diurnal and ultradian rhythms in K + uptake by Trifolium repens under natural light patterns: Evidence for segmentation at different root temperatures
Author(s) -
Macduff J. H.,
Dhanoa M. S.
Publication year - 1996
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1034/j.1399-3054.1996.980211.x
Subject(s) - ultradian rhythm , trifolium repens , zoology , circadian rhythm , biology , diurnal cycle , darkness , diurnal temperature variation , botany , horticulture , atmospheric sciences , endocrinology , geology
The patterns and variability in the diurnal and ultradian fluctuations in net uptake of K + by 85‐day‐old plants of white clover ( Trifolium repens L. cv. Huia) were analysed during 21 days of vegetative growth under natural light conditions, at constant root temperaures of 13 and 25°C. Plants were established in flowing solution culture, and hourly rates of K + uptake from solutions containing 2.5‐6.5 µ M K + were automatically measured without physical disturbance. Total daily solar radiation ranged between 1.3 and 12.5 MJ m −2 day −1 over the 21 days of measurements. Substantial diurnal changes in rates of K + uptake, both absolutely and proportionately, were recorded on all but the day of lowest radiation (day 19), during which there was a period of net efflux of K + from the root system into the flowing nutrient solutions at both temperatures. Typically, uptake rates increased severalfold during the first half of the light period, followed by several hours of relative stability during the afternoon; then a rapid decline throughout the evening and first half of the night, and finally gradual decline during the second half of the night. The data from a sequence of typical days were normalised and indicated that the pattern could be resolved into 4 distinct and linear phases, successively: (1) rapid acceleration, (2) stable uptake, (3) rapid deceleration, and (4) slow deceleration. The full data set (days 1‐21) of hourly K + uptake rates was Fourier‐transformed and subjected to time‐series analysis to determine whether there were significant ultradian rhythms in K + uptake. Periodograms indicated a strong 24 h periodicity for uptake at both root temperatures. In addition, there were strong ultradian periodicities of 7 h for uptake at 13°C and 4 h for uptake at 25°C. The results are interpreted in terms of the possible mechanisms responsible for diurnal fluctuations in nutrient uptake.