RESPONSES OF THE MOSSES BRACHYTHECIUM-RUTABULUM AND PSEUDOSCLEROPODIUM-PURUM TO A MINERAL NUTRIENT PULSE

1. The mosses Brachythecium rutabolum and Pseudoscleropodium were subjected to a nutrient 'pulse' consisting of eight daily additions of a solution of KH2PO4 and NH4NO3 at a concentration of 5 mM, and then grown for 10 weeks with daily distilled water misting but no further nutrient application. Biomass increase and tissue contents of N, P, K, Ca and Mg were determined during the experiment. 2. Relative growth rate in the nutrient-deficient environment was higher in Pseudoscleropodium than in Brachythecium. The nutrient pulse significantly stimulated subsequent growth of Pseudoscleropodium but not of Brachythecium. 3. Pseudoscleropodium showed a greater net uptake of P and, to a lesser extent, of N and conserved these elements more effectively under nutrient-deficient conditions than did Brachythecium. Evidence was obtained of the importance of cell wall cation-exchange capacity in sequestering nutrient cations and of the later movement of these cations into the cells. 4. The results are in accordance with the hypothesis that Pseudoscleropodium depends on unpredictable nutrient inputs in wet deposition whereas Brachythecium requires a more continuous nutrient supply which is probably obtained from its substratum.