The Biology of Moonlight?
The moon may have effects on animal behavior (see here for example), but does it affect plants?
Last time I introduced the scientific literature on the subject by referring to a 1946 paper by Beeson (see ref. 1 below) published in the journal Nature. In this paper Dr. Beeson divided the information regarding the moon’s effects on plants into three categories: (a) myth or beliefs, (b) experiments by people believing in biodynamics, and (c) professional plant scientists with no ties to biodynamics.
Let’s see what’s out there from group (c), starting with the sunlight reflected by the moon.
Is Moonlight Bright Enough to Affect Plants?
From laboratory experiments, it’s known that light intensities as low as 0.1 lux (approximately 0.01 foot-candle) during the night can influence photoperiodic time measurement in some plants and animals.
Yet the intensity of light from a full moon on a cloudless night may reach 0.3 lux at latitude of 50′, and more than three times this value in tropical regions.
This fact led E. Bunning and his colleagues (ref 2 below) to inquire whether moonlight can disturb time measurement. Surprisingly, their investigations revealed that some plants have adaptive mechanisms that apparently prevent moonlight from interfering with photoperiodism.
Photoperiodic perception occurs in the leaves. In the leguminous plants soybean, peanut, and clover, “sleep movements” change the position of the leaves from horizontal during the, day to vertical at night. This behavior reduces the intensity of light falling on the leaf surface from an overhead lamp (an “artificial moon”) by 85% to 95%, to an intensity below threshold for interference with time measurement.
In some nyctinastic plants such as Albizzia, Sainanea, and Cassia, leaflets not only orient vertically at night, but also rotate on their axes so that paired leaflets fold together, with the upper surfaces shading each other, an interesting behavior in view of the fact that the upper surface is more sensitive to light breaks than is the lower surface.
Some long-night plants (a.k.a., short-day plants) flower most prolifically when grown with low intensity light (approximately 0.5 lux) rather than complete darkness during the night. In these plants, moonlight probably increases the number of flowers produced by a short-day regime.
However, flowering of Pharbitis nil (Morning Glory) plants was slightly inhibited by exposure to the light of the full moon for 8 or more hours with a single dark period of 16, 14 or 13 h. It is suggested that in the natural environment moonlight may have at most only a slight delaying effect on the time of flower induction in short-day plants (see ref. 3 below).
In a brief review, Wolfgang Schad (ref. 4) cites evidence for the effects of moonlight on biological rhythms in plants. He is co-author of the book Moon Rhythms in Nature: How Lunar Cycles Affect Living Organisms
Bottom Line: Although it is not clear why low light intensities affect flowering more than darkness, these examples provide some rational basis for the belief of planting particular seeds by the light of the full moon. Another full moon one lunar cycle later could have effects on flowering.
References
1. Beeson, C.F.C. (1946) “The moon and plant growth.” Nature vol. 158, pp. 572-573. (PDF)
2. Bunning, E. and I. Moser (1969) “Interference of Moonlight with the
Photoperiodic Measurement of Time by Plants, and their Adaptive
Reaction.” Proceedings of the National Academy of Sciences (USA) vol. 62, pp. 1018-1022. (PDF)
3. Kadman-Zahavi, A. and D. Peiper (1987) “Effects of Moonlight on Flower Induction in Pharbitis nil, Using a Single Dark Period.” Annals of Botany vol. 60, pp. 621-623.
4. Schad, W. (1999) “Lunar influence on plants.”, Earth, Moon, and Planets vol. 85-86, pp. 405-411. (PDF)
Next Time: Does the moon’s gravity affect plants?
