Growth of Sphagnum riparium is strongly rhythmic: Contribution of the seasonal, circalunar and third rhythmic components

Continuous high-resolution monitoring of Sphagnum growth can provide insights into the biological rhythms of moss growth. Moss Sphagnum riparium is a convenient model for growth monitoring. Application of the method of geotropic curvatures has enabled a three-year monitoring with two to five-day intervals. We measured the increment in ca. 85000 shoots and produced ca. 3500 growth rate estimates, making this study a champion in precision compared to previous efforts. The zeitgeber for seasonal growth rhythms is the temperature seasonal cycle (R 2 =0.21–0.52). When the temperature changes by 10 ° C, moss growth rate is modified by 0.10–0.17cm/day according to the linear model, and 1.47–2.06-fold in the exponential model. The zeitgeber for circalunar rhythms is the lunar synodic cycle (R 2 =0.14–0.26). The average amplitude of the fluctuations it induces in the growth rate is 0.0425– 0.0572cm/day, which is equivalent to the effect of a 3.43–4.53 ° C change in temperature. The third rhythm can be distinguished in periodograms. Its period ranges from 10 to 16 days, but we did not detect the zeitgeber. In total, three rhythms explain 51–78% of the growth rate. We believe that the strong rhythmicity in Sphagnum growth is associated with shoot growth synchronization.