Photosynthesis of cryptobiotic soil crusts in a seasonally inundated system of pans and dunes in the western Mojave Desert, CA: Field studies

Maximal photosynthetic rates (Pmax), which did not vary greatly with season, were 3.57 and 3.99 μmol CO2 m−2 s−1 for crusts on dunes and in pans, respectively. Mean photosynthetic rates for three types of crust on dunes, smooth and flat, pedicillated, and unconsolidated, were 1.31, 1.47, and 1.29 μmol CO2 m−2 s−1, respectively. Pmax of crusts on dunes and pans occurred at soil MCs of 110% and 20%, respectively, both lower and higher MCs resulted in decreased rates of photosynthesis. The relation between atmospheric CO2 concentration and net photosynthesis was linear (r2=0.88 and 0.97 for crusts on dunes and pans, respectively) through at least 1000 ppm CO2. We measured positive net photosynthesis at temperatures from 0 to 46 °C and found no clear optimum within this range when crusts were provided with optimal moisture and light conditions. Photosynthetic rates in this field study were somewhat lower than those measured in the laboratory, but both optimum MC and the relation between ambient CO2 and net photosynthetic rate were similar. Respiration rates were generally less than 10% those of photosynthetic rates. Based on data herein and climatic information, we estimated the potential net primary productivity of crusts on dunes to be 11.7 g C m−2 yr−1. The photosynthetic rate of the unconsolidated crust type, for which no data have been published, was similar to the other crust types. This finding, together with previous information that the chlorophyll values of this and other crust forms were similar, suggests that ecological studies, as well as conservation and restoration efforts, give these the same attention as the other crust types.