PARENT SESSION
Poster Session #45: Gas Exchange.
Friday, August 10, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall

Photosynthesis of cryptobiotic crusts in a seasonally inundated system of pans and dunes in the western Mojave Desert. I: Laboratory studies.

Sharifi, Rasoul¹, Brostoff, William², Rundel, Philip¹, ^{1 2}

ABSTRACT- Cryptobiotic crusts are a dominant component of a unique system of dunes and intermittently inundated pans and playas situated on Pleistocene Lake Thompson bed at Edwards Air Force Base, California. Previous work reported on basic ecological parameters including distribution, abundance, and species composition of these algal (cyanobacterial)-dominated cryptobiotic crusts. As a step toward building an ecological model in support of the military installation natural resources management plan, we determined the photosynthetic rate of the algal crusts under controlled laboratory conditions. We examined the relation between the environmental conditions of light intensity, crust moisture content, antecedent crust moisture content, and atmospheric CO₂ concentration; on photosynthetic rates. Maximal photosynthetic rates were 4.97 and 7.75 mol m-2 s-1 for cryptobiotic crusts collected from dunes (upland crusts) and from pans (aquatic remnant crusts), respectively, which corresponds well with the upper range of previous reports for such algal crusts. Light saturation levels were about 1500 and 1500-2000 mol m-2 s-1 for cryptobiotic crusts from both the dunes and the pans respectively. Optimal moisture content of the crusts for photosynthesis was 15-30% and 90-100% for crusts from dunes and pans respectively; both lower and higher moisture contents resulted in decreased rates of photosynthesis. With increasing CO₂ concentrations up to at least 1000 ppm, photosynthesis of both types of crusts increased linearly to rates several times that of rates at ambient CO₂ concentrations.

KEY WORDS: Cryptobiotic crust, photosynthesis, Mojave Desert, water content