Mironov, V.L., S.I. Grabovik, P.А. Ignashov & L.V. Kantserova. Geotropic curvatures of Sphagnum: environmental features of their genesis and trial application for estimation shoot length increment
Arctoa (2016) 25: 353–363
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.