Stress-induced reactions of mosses to periodic short-term and long-term drying depending on the water regime of their habitats

Abstract

Bryophytes are poikilohydric higher plants and their water content as well as metabolic activity depend on the water regime of the environment. The aim of the study was to establish the features of stress-induced reactions of mosses under controlled conditions of short-term and long-term drying depending on the water regime of their habitats. A culture of shoots of the same age from agar mediums the same level of relative humidity was used to study the effect of periodic drying. Dehydration was carried out within 24 hours, removing the polyethylene cover from the pots with moss culture. Plant watering was carried out twice a week in the variant of the experiment with short-term drying: immediately after dehydration and on the third day after drying. In the variant with long-term drying plants were watered once a week – on the third day after 24-hour dehydration. Control plants were sprayed twice a week. A significant decrease in the size of shoots, leaves and an increase in the density of moss turf under the influence of short-term and long-term drying have been established, based on the analysis of morphometric parameters of Barbula unguiculata Hedw. and Physcomitrella patens (Hedw.) Bruch & Schimp. In the moss Weissia longifolia Mitt. long-term drying caused a slight increase in leaf size and elongation of shoots, comparing with control and short-term drying, and at the same time activated the formation of chloronеmal dendroids, which proved its greatest adaptability and ability to adapt to perio­dic changes in humidity. A higher sensitivity of the pigment system of B. unguiculata and P. patens to drying compared to W. longifolia was established. It was found that in the pigment system of the hygromesophytic moss P. patens the significant role belongs to chlorophyll b and pheophytin b, functioning of the assimilation complex of the xeromesophytic moss Barbula unguiculata depends on chlorophyll a and pheophytin a, in xerophytic moss W. longifolia – due to the stability of chlorophyll a and the strength of the bound of carotenoids with protein complexes of the pigment system. The dependence of the component composition of the pigment apparatus, the strength of the bond of pigment-protein complexes (PPC), the activity of chlorophyllase, and the total carbohydrate content of the studied mosses on the duration of drying and their species characteristics was determined.