Nutrient retention by Pseudoscleropodium purum and its relation to growth

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Abstract
A complete mineral nutrient fertilizer solution was added to carpets of Pseudoseleropodium purum growing in Windsor Forest, Berkshire, to study the efficiency of nutrient capture from dilute solutions and its effect on growth. In the experiment different frequencies of application were balanced by employing different concentrations of fertilizer so that all treatment plots received the same quantities of nutrients over a six-month period. At the end of the experiment the concentrations of macronutrients (N, P, K, Mg, Ca) within the moss tissues were determined and shoot growth was assessed by the tagged shoot method. Significant luxury uptake occurred only in the case of P where shoot concentrations in fertilized plots were 50% above the control. Smaller net increases were noted for other elements, particularly Mg. Shoot N concentration was hardly affected by fertilizer application possibly due to efficient internal recycling of the element in P. purum. Levels of exchange ably held cations were not markedly increased by fertilizer addition in the field experiment but when shoots were incubated with fertilizers in the laboratory for 30 min the concentrations of exchangeable Ca and Mg rose appreciably and exchangeable K fell. These changes appear to be quickly reversed under field conditions without transfer of cations to the protoplasts. The importance of elevated cation exchange capacity in the initial sequestration of nutrient cations is, therefore, questioned. Growth stimulation due to fertilizer treatment was negligible. Maximum net uptake of P, Mg and Ca occurred when plots were watered at weekly intervals with a dilute fertilizer and least occurred where a concentrated solution was applied at less frequent intervals implying that contact time between P. purum and its potential nutrients is an important factor. The period elapsing between fertilizer additions may also have significance, however, due to leaching away of nutrients and the re-establishment of a natural ionic balance at the cell wall exchange sites. Levels of nutrient absorption and growth were greatest at a site where the moss remained moist longest. This result indicates that the ability of P. purum to absorb and utilize additional nutrients is governed by general metabolic performance which is itself restricted by water supply in Windsor Forest.