“The effect of water potential on the water balance of lichens and mosses – distribution patterns of internal and external water”

Abstract

Lichen-forming fungi and mosses form a major part of the terrestrial non-vascular vegetation and are thought to have a significant impact on global biogeochemical cycles, such as the nitrogen and carbon cycle. However, in order to draw quantitative conclusions about their ecosystem functions, it is essential to understand the metabolic processes underlying their growth. The dynamic water balance of lichens and mosses is a crucial factor in this regard since the metabolic processes of the organisms can only occur in phases with sufficient water saturation. Water can occur inside the cells (internal) in the symplast and in pores in the cell wall (apoplast water), and also externally in the capillaries of the intercellular space. It is poorly known, however, how atmospheric demand for water, related to water potential ( ψ ), affects the dynamic distribution of internal and external water in lichens and mosses and which consequences this may have for their water balance. Here, we examined water absorption of Pleurozium schreberi , Cladonia portentosa and Peltigera rufescens under a gradient of ψ in the laboratory. Results show that for all species, relative water content decreased with decreasing ψ. Both internal and external water contents thereby showed a consistent pattern across the range of ψ- values tested here. This indicates that, although a proportion of the internal water has already evaporated and therefore the turgor pressure is altered, in all three species a proportion of external water is retained by capillary forces even at low ψ .

Effect of light stress on maximum photochemical efficiency of photosystem II and chloroplast structure in cryptogams Cladonia mitis and Pleurozium schreberi

“…Additionally, it is believed to create a functional disconnection of components of the photochemical apparatus (Sigfridsson, 1980;Bilger et al, 1989). On the other hand, soaked P. schreberi sample showed lower Fv/Fm values in each light, which may be the result of the supersaturation phenomenon (Green et al, 2011) and limited CO2 diffusion (Green et al, 2011;Möller et al, 2022). The results presented here did not confirm the second research hypothesis that lichens in any type of light show higher values of photosynthetic activity than mosses.…”

Effect of light stress on maximum photochemical efficiency of photosystem II and chloroplast structure in cryptogams Cladonia mitis and Pleurozium schreberi

“…Additionally, it is believed to create a functional disconnection of components of the photochemical apparatus (Sigfridsson 1980;Bilger et al 1989). On the other hand, soaked P. schreberi thallus mosses showed lower Fv/Fm values in each light, which may be the result of the supersaturation phenomenon (Green et al 2011) and limited CO2 diffusion (Green et al 2011;Möller et al 2022). The results presented here did not con rm the second research hypothesis that lichens in any type of light show higher values of photosynthetic activity than mosses, however, they partially con rmed the third hypothesis, as we found that the lichens that were soaked in water exhibited a signi cant increase in photosynthetic activity when compared to the non-soaked specimens.…”