MINERAL NUTRIENT ACQUISITION AND RETENTION BY BRYOPHYTES

Recent information on mineral nutrient acquisition and retention is reviewed in relation to the suspected importance of bryophytes in mineral relations of ecosystems. Nutrient inputs from various sources are discussed and the importance of determining the cellular locations of elements in experimental studies is emphasized. Mineral inputs from the substratum appear to be particularly important in rapidly growing species, e.g. Brachythecium rutabulum, which exploit seasonally deposited vascular plant litter. Slower-growing feather mosses, e.g. Pseudoscleropodium purum, may depend largely on wet deposition for minerals, although phosphate, which is present at low concentration in precipitation, is probably obtained principally from the substratum. The ecophysiological bases for the contrasting growth responses of different species to nutrient applications are poorly understood. Elevated cell wall cation exchange capacities (CEC) in bryophyte tissues in comparison to tracheophyte roots may be of significance in the sequestration and protoplasmic uptake of essential cations like Mg. In epilithic and woodland soil bryophytes the CEC decreases with decreasing Ca content and pH of the preferred substratum. It is possible that lowered CEC prevents excessive adsorption of the phytotoxic cation Al, which becomes increasingly available in acidic conditions, but this hypothesis has not yet been fully substantiated.