Mineral nutrient recycling within shoots of the moss Rhytidiadelphus squarrosus in relation to growth

Abstract

The intracellular and extracellular contents of K, Mg and Ca, dry weight and CO₂ exchange rates in successive 2-cm segments of Rhytidiadelphus squarrosus (Hedw.) Warnst, were recorded before and after storage of moss shoots collected from the field. Moss shoots sustained apical growth in the absence of aerial or substratum nutrient inputs and acropetal transfer of cations occurred at the expense of basal segments. Intact shoots of 12–17 cm initial length showed increased or decreased cation contents, respectively, in the uppermost segments according to whether infrequent or frequent watering regimes were employed. Excised shoots of 4 or 8 cm retained cations despite a frequent watering regime. Acropetal transfer of cations during growth of excised shoots was in proportion to the available cation pool. There was no evidence that nutrient limitation in the growing apex affected growth or metabolism. Pre-treatments which modified the initial Ca, Mg and K status of moss shoots did not influence the pattern of recovery of elements in newly-grown apices but showed that exchangeably bound extracellular cations were readily available for acropetal transfer. Results indicate that efficient internal recycling of nutrients can sustain growth. of bryophytes and are discussed in relation to the pathways and mechanisms of nutrient redistribution.