Desiccation Effects and Cation Distribution in Bryophytes

Abstract

SUMMARYAnalysis of the cations in a range of bryophytes, using a differential ion displacement technique, has shown that potassium is mainly soluble within the cells, calcium is bound, exchangeably, to sites in the cell wall and is insoluble within the cell and magnesium is present in all three locations. After desiccation, soluble ions either leak into the rehydrating solution (e.g. potassium and some magnesium) or become bound to the cell-wall exchange sites (e.g. most of the magnesium). Leakage of intracellular ions can be used as a measure of membrane damage. An index of desiccation resistance (based on potassium retention within the cells after storage at 52 and 100% r.h.) is related to the availability of water in each bryophyte's habitat and is significantly correlated with the total potassium content of the plant. Reduced cation leakage occurred after material was transferred from either 52 or 0 % r.h. to 100 % r.h., indicating the ability of bryophytes to recover from such desiccation stress. An index of recovery is presented which shows that naost bryophytes, unless excessively stressed, are able to repair the damage caused by desiccation.

Inorganic ion composition in Tardigrada: cryptobionts contain large fraction of unidentified organic solutes

“…carnivorous insects generally contain low levels of K + (Sutcliffe, 1962). Conversely, phytophagous tardigrades are known to feed on bryophytes that are typically high in K + and low in Na + (Brown and Buck, 1979), and were therefore, analogous to phytophagous insects (Sutcliffe, 1962), expected to reflect this Total osmotic concentration of the external and internal fluids, as well as the osmotic contribution of the respective ions to the total internal concentration in each of the investigated species of tardigrades. Corresponding data on hemolymph concentration and composition of selected species of crustaceans, insects and onychophorans are included for comparative purposes.…”

Assessment of the terrestrial impact of a nuclear power plant caesium 137 and caesium 134 atmospheric releases

“…One can mention a limited range of variations of the concentration power of 137 Cs and 134 Cs (ratio ~ 2-3) in similar environmental conditions [14,2], except for Sphagnum spp. (~5-10 fold less contaminated), a captation increase with altitude [27,32,9,23,5,19], with the inclination (inclined < vertical < horizontal) [12,16], the density and the thickness [12,5] of the moss carpet, a positive Kd between leaves and stems [11], a decreasing concentration of 137 Cs with the growth rate [16,26], a higher concentration in older parts of Hylocomium splendens [18] and a significant attraction of N, K and P for young stems' leaves observed in five Sphagnum species [20], in the context of a 137 Cs/ 40 K or total K competition [2,10,4,32,25,21], a primary concentration of intra-cellular caesium in cell-walls liable of ionic exchanges [6,8], an increase of intra-cellular, or on the contrary the migration of intra-cellular potassium and an increase of the bioavailability of extra-cellular potassium with the level of desiccation [3], in the context of a 137 Cs/K ratio higher in dead material than in living one in Pleurozium schreberi [21]. However, the edaphic influence of the medium on caesium captation by mosses [9,27,14], as well as the influence of the sampling location (such as its position relating to a forest canopy) [14,12] remain controversial.…”

Effects of Intermittent Desiccation on Nutrient Economy and Growth of Two Ecologically Contrasted Mosses

“…As exchangeable K + content was also significantly elevated (B. rutabulum by 1200 %, P. purum by 410 %) in the intermittently desiccated controls (dCON) it is likely that this difference was caused by moisture stress. Probably, during rehydration, potassium ions leak through the plasmalemma and are sequestered by the cell wall (Brown and Buck, 1979). Intracellular K + content showed highly significant species and treatment differences and a significant interaction term (Table 2).…”

“…In strongly desiccation-tolerant mosses like Tortula ruralis most of the leakage occurs within 5 min of rehydration after which membrane integrity is restored and considerable reabsorption has been observed (Oliver et al, 1993). Brown and Buck (1979) noted that when the cations K + and Mg# + leaked from the protoplasts in laboratory experiments, they were frequently sequestered on the fixed negative charges of the cell walls. Few direct observations of rehydration leakage have been made in the field.…”

“…A factor that has rarely been considered in the mineral nutrition of bryophyte colonies is the impact of the repeated cycles of wetting and drying that are a normal feature of the lives of poikilohydric organisms. On rehydration after a period of desiccation, both desiccation-tolerant and -sensitive bryophytes leak considerable quantities of cell electrolytes and organic solutes to the bathing medium in laboratory experiments (Gupta, 1976(Gupta, , 1977(Gupta, , 1981Brown and Buck, 1979 ;Schonbeck and Bewley, 1981 ;Dhindsa, 1991 ;Oliver, Mishler and Quisenberry, 1993). In strongly desiccation-tolerant mosses like Tortula ruralis most of the leakage occurs within 5 min of rehydration after which membrane integrity is restored and considerable reabsorption has been observed (Oliver et al, 1993).…”