Recent records of environmental contamination noted a moderate decrease of SO2 pollution, whereas the burden of atmospheric heavy metals is still considerable. The present review refers to the entrapment, uptake, and accumulation of heavy metals by lichen thalli, made apparent by parameters of lichen vitality and stress. The particulate nature of airborne heavy metals is made evident by parameters referring to the entrapment of heavy-metal containing particles by lichen thalli. The mechanism of uptake of heavy metals, investigated by means of controlled experiments, refers to extracellular and intracellular uptake. The rate of absorption and the accumulation of heavy metals is dependent on morphological features of lichen thalli in addition to kind and intensity of emission sources and to nonanthropogenic factors such as climate and topography. The role of lichens as biomonitors is demonstrated by the case of lead. In contrast to data obtained by retrospective studies, using lichens as biomonitors of heav...

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Biomonitoring Atmospheric Heavy Metals with Lichens: Theory and Application

Bryophytes face the same basic problems of life on land as flowering plants. Water is essential for metabolism, but is in limited and erratic supply in the above-ground environment where the leaves must be exposed in order to photosynthesize. Bryophytes and vascular plants exemplify two alternative patterns of adaptation to these conditions. Vascular plants have evolved roots and an efficient conducting system, bringing water from the soil where it is in relatively plentiful and constant supply. Bryophytes have evolved to utilize water where and when it is available above ground; some are confined to moist habitats, but many can tolerate drying out, and some are extremely desiccation-tolerant and highly adapted to a poikilohydric existence. But this contrast between vascular plants and bryophytes is by no means sharp. Polytrichum and Dawsonia species and various other large bryophytes have efficient water-conducting systems and maintain turgor for much of the year in many habitats. Conversely, many small vascular plants evade the problems of drqught in moist habitats, or by passing the summer as desiccation-tolerant seeds, and there are a number of scattered genera of poikilohydric vascular plants.

Physiological Ecology: Water Relations, Light and Temperature Responses, Carbon Balance

Bryophytes and nutrient cycling

Vascular plants represent one strategy of adaptation to the uneven and erratic supply of water on land. Desiccation-tolerant (DT) bryophytes represent an alternative, photosynthesising and growing when water is freely available, and suspending metabolism when it is not. By contrast with vascular plants, DT bryophytes are typically ectohydric, carrying external capillary water which can vary widely in quantity without affecting the water status of the cells. External water is important in water conduction, and results in bryophyte leaf cells functioning for most of the time at full turgor; water stress is a relatively brief transient phase before full desiccation. All bryophytes are C3 plants, and their cells are essentially mesophytic in important physiological respects. Their carbohydrate content shows parallels with that of maturing embryos of DT seeds. Initial recovery from moderate periods of desiccation is very rapid, and substantial elements of it appear to be independent of protein synthesis. Desiccation tolerance in effect acts as a device that evades the problems of drought, and in various adaptive features DT bryophytes are more comparable with (mesic) desert ephemerals or temperate winter annuals (but on a shorter time scale, with DT vegetative tissues substituting for DT seeds) than with drought-tolerant vascular plants.

The bryophyte paradox: tolerance of desiccation, evasion of drought

The physiological basis of bryophyte production

Summary
Analysis 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 most bryophytes, unless excessively stressed, are able to repair the damage caused by desiccation.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.1979.tb07565.x

G. W. Buck

Papers

Desiccation effects and cation distribution in bryophytes