Effects of abiotic factors on acetylene reduction by cyanobacteria epiphytic on moss at a subantarctic island.

Acetylene reduction (AR) rates by cyanobacteria epiphytic on a moss at Marion Island (46 degrees 54' S, 37 degrees 45' E) increased from -5 degrees C to a maximum at 25 to 27 degrees C. Q(10) values between 0 and 25 degrees C were between 2.3 and 2.9, depending on photosynthetic photon flux density. AR rates declined sharply at temperatures above the optimum and were lower at 35 degrees C than at 0 degrees C. Photosynthetic photon flux density at low levels markedly influenced AR, and half of the maximum rate occurred at 84 mumol m s, saturation occurring at ca. 1,000 mumol m s. Higher photosynthetic photon flux density levels decreased AR rates. AR increased up to the highest sample moisture content investigated (3,405%), and the pH optimum was between 5.9 and 6.2. The addition of P, Co, and Mo, individually or together, depressed AR.