The genus Sphagnum is an essential component in the formation and maintenance of high latitude peatlands, bogs and mires. The species grows in dense, extended mats of agglomerated shoots that allow it to retain water necessary for its growth. These mats are partly responsible for maintaining the right conditions for other species in these wetlands to thrive. In this issue of Physiologia Plantarum, Mironov et al. (2020) monitored the growth of Sphagnum riparium for a period of 4 years and revealed three distinct growth rhythms: a seasonal temperature dependent, a circalunar and a third one, synchronized with the circalunar. This synchronised nature of Sphagnum growth could contribute to its position as a key species in the maintenance of peatlands.Within Northern (high latitude) peatlands, the genus Sphagnum acts as an ecosystem engineer, rapidly forming an environment, both hydrological and biogeochemical, favourable to its growth (van Breemen 1995). As a consequence, the peat properties and plant species composition largely result from the growth of Sphagnum, a genus that can make up as much as 80% of the species composition in these areas (Weltzin et al. 2003). High latitude peatlands comprise almost one third of the global soil carbon pool and they provide an important sink for atmospheric carbon dioxide even though they cover only 2% of the total land mass (Yu et al. 2010). Sphagnum moss is harvested commercially and used, for example, as insulating material, an ingredient in potting mixes to enhance their moisture retaining value and as a critical substrate for growing mushrooms.As key-species in these environments, knowledge on the ecology, growth and development of Sphagnum spp. is of great interest to aid conservationists' efforts to restore damaged wetlands, necessary as climate change and overexploitation are straining the high latitude wetlands. It is estimated that as much as 52% of active peatlands have been lost to overexploitation (Chapman et al. 2003).To better understand the growth and development of these key species, the authors of this study have tried to assess the biological growth rhythm of Sphagnum riparium, a species covering 90% of their test site in Russian Karelia, using data from a 4-year period. The authors used the angle formed in the stem induced by the weight of the snow cover to measure the annual growth. The growth season starts when temperatures rise and the snow cover disappears, allowing for the use of this bend as 'starting point' of annual growth and the distance between consecutive curvatures as a measure of yearly growth. The authors revealed three growth rhythms (Fig. 1) of which the one contributing most to the annual growth was linked to the seasonal cycle of temperature, which relates to earlier studies into the effect of climate change and the possibility that the area of suitable climate for Sphagnum peatland could expand in the near future, provided that water availability is not greatly reduced (Oke and Hager 2017). The second rhythm, contributing substantially b...

The genesis of geotropic curvatures in the natural habitat of Sphagnum mosses is described in detail on the basis of in situ observations. A novel method of estimation of length increment of Sphagna shoots is developed, based on their geotropic curvatures, which are the markers of physical impacts. The snow load in northern areas is an example of the most typical impact on Sphagnum cover and further geotropic response of stems. Deviation in stem growth causes the curves which may form after snowmelt or under the snow layer. First attempt to use the snow induced markers, named further as "nival geotropic curvatures", for estimation of shoot increment rate of Sphagna stems were made in the late 20th century. However, first researchers ignored other than snow cover common factors that are responsible for the formation of similar markers during the growing season. Therefore, measuring increment from these markers may result in incorrect estimation, because they could be formed neither due to the snow load nor the beginning of the growing season. Our method takes into account these shortcomings. Several Sphagnum species were involved in the research for experimental comparison of the novel method with the classical tied thread method. Experimental plots were studied during a two-year period on Karelian mires. The length increment values obtained by both methods show some differences. Shoot increment values obtained by the method of the nival geotropic curvatures markedly exceed values obtained by the classical tied thread method in all cases. The difference ranged from 7.5 to 18.6 % in 2014 and from 20.8 to 45.8 % in 2015. The results could be explained by the negative effect of the tied thread method on the growth of moss, that was described in the literature. The coefficients of variation estimated by the method of nival curvatures are reliably lower than those obtained by the tied thread method for practically all samples. In 2014, mean value of the coefficients of variation were 20.3±4.2 % for samples obtained by tied thread method and 13.0±4.7 % for samples obtained by nival geotropic curvatures method. In 2015, the coefficients of variation were estimated at 21.1±5.3 % and 8.7±2.2 %, respectively.The differences are assumed to be due to the difference in the degree of impact on the structure of Sphagnum cover. РезюмеНа основании наблюдений in situ детально описан генезис геотропических изгибов стеблей в естественной среде обитания сфагнов. Разработан новый метод определения прироста побегов сфагновых мхов, в основу которого положено использование геотропических изгибов, образующихся в результате внешних физических воздействий. Снеговая нагрузка, характерная для северных регионов -пример наиболее типичного физического воздействия, вызывающего геотропическую реакцию побегов. Отклонение растущих побегов вызывает образование изгибов после снеготаяния или под снежным покровом. Первые попытки использования вызываемых действием снега маркеров (называемых нами в дальнейшем «нивальные геотропические изгибы») на ...

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In situ growth of Sphagnum riparium Ångstr. shoots were monitored during the 2015 and 2016 growing seasons in Karelia, Russia. It was established that shoot growth rates fluctuated with a period of around 30 days, that is, showed a circatrigintan rhythm. Such rhythms from mosses have not been previously reported. Correlation of growth rates with the percentage of the illuminated portion of the Moon was statistically significant (p<0.01) in both years. Shoot growth rates were reliably higher around the new Moon compared to the full Moon. This phenomenon may be due either to causality or to a pure coincidence of processes with similar rhythms.