ABUNDANCE, BIOMASS, AND PRODUCTIVITY OF ENDOLITHIC AND EPILITHIC LOWER PLANTS ON THE TEMPERATE-ZONE CLIFFS OF THE NIAGARA ESCARPMENT, CANADA

To investigate the cover, frequency, biomass, and productivity of endo lithic and epilithic lower plants on temperate zone cliff faces, rock samples were randomly collected from the Niagara Escarpment in souther n Ontario, Canada. Chlorophyll was extracted using dimethyl sulfoxide (DMSO), and CO2 gas exchange was measured in the laboratory using infr ared gas analysis. Epilithic surface cover averaged 26% for cyanobacte ria, 3% for green algae, and 20% for lichens. Endoliths were present b elow 6% of the surface area, with chasmoendoliths about twice as commo n as cryptoendoliths. Fungi were by far the most common organisms. The cliffs contained 73.0 mg chi a and 19.8 mg chi b per square meter; 15 % and 23% of these, respectively, were in the endolithic zone. Biomass of primary producers (algae, cyanobacteria, and lichen photobionts) w as 1.5-73 g dry mass m(-2) total, and 0.3-14 g m(-2) in the endolithic zone alone. Photosynthetic carbon uptake was 0.0021 mg CO2 cm(-2) h(- 1) at 700 mu mol m(-2) s(-1) photosynthetically active radiation (PAR) . At PAR = 130 mu mol m(-2) s(-1), a small amount of carbon was releas ed (0.5 mg CO2 m(-2) s(-1)); dark respiration was 0.0096 mg CO2 cm(-2) h(-1). The upper limit for carbon fixation by primary producers was e stimated from this to be 2.3 mg CO2 cm(-2) yr(-1), but endolithic and epilithic zones as a whole were shown to be net consumers of CO2. Cove r, occurrence, biomass, and productivity of endoliths and epiliths sho wed most of their variability on a scale smaller than a square meter; there was little or no consistent variation from north to south or fro m cliff top to bottom. Seasonal changes were absent when chlorophyll a nd gas exchange rates were expressed on a unit cliff surface basis. Ga s exchange on a chlorophyll a basis, as well as the chi a:phaeophytin a ratio, showed a general decline between spring and fall.