EFFECT OF NUTRIENTS ON CO2 ASSIMILATION BY MOSSES ON A SUB-ANTARCTIC ISLAND

N and P, especially when added together, significantly enhanced CO2 as similation rate in four moss species from a range of habitats on sub-A ntarctic Marion Island. NO3- always caused a greater increase in assim ilation rate than did NH4+, but this might have been due to Cl- added with the NH4+. Possibly for the same reason, K+ addition (as KCl) in s ome cases depressed CO2 assimilation rate compared with the controls ( tapwater addition), as did K + N or K + P compared with N or P alone. The degree to which the mosses were apparently sensitive to Cl- was re lated to their tissue water content and to the soil water content in t he habitats in which they occur. The results are discussed in the cont ext of extremely low levels of available soil nutrients in, and small precipitation inputs of nutrients to, plant communities predominated b y bryophytes on the island.