Correlations between lunar phases and rhythmicities in plant growth under field conditions

Abstract

A previous investigation of fluctuations in temperature and changes in growth in seven herbaceous species under field conditions revealed a periodic lack of correlation between the two variants. An original step-by-step periodogram analysis of the curves of correlation obtained by plotting growth rate against temperature has been used in the present study. Temperature has been expressed considering the maximum and minimum daily air temperature and the upper and lower threshold values at which the temperature effect on growth is considered to be null. The growth curves, which express observed stem elongation, have been transformed to daily values of growth rate. Using a modified equation of the "logistic curve," which best fits the observed growth pattern, a theoretical representation of growth has been applied to the data. The correlation coefficient has been calculated plotting the values of temperature summation against those of growth rate for periods of 7 days. The stem growth of the seven species has revealed rhythmic components of 29.5-, 14.7-, 9.7-, and 7.3-day periods. The first two components of 29.5 and 14.7 days, which are the most evident, appear to be best correlated with the phases of the new and full moon. This fact suggests that some unknown periodic environmental change is directly or indirectly connected with the position of the moon. The other two shorter components in growth, of 9.7 and 7.3 days, may be endogenous rhythms that are expressive of the overall physiology of stem development of each species.