CRYPTOGAMIC CRUSTS OF SEMIARID AND ARID LANDS OF NORTH AMERICA

Abstract

Question (Bell): What types of biomass measuring techniques have been tried, which work best, and what are some of the confounding factors involved in working with these crusts? Answer: Several methods have been tried. Biomass can be quantified in direct counts using quantitative counting chambers (such as hemacytometer) and fluorescence microscopy. This gives some indication of numbers and kinds of organisms, although only the common cyanobacterial and diatom species can be identified with confidence. Obtaining biovolume estimates can be done with this method but is very laborious. Another direct method is chlorophyll a determination. This is the easiest and fastest method, but has the drawback that lichen phycobionts and free-living algae are not separated nor are any species or even coarse taxonomic groups determined. Cell counts using dilution plate methods work well for the chlorophytes and xanthophytes, although quantification by species has not been done because these algae can only be identified after unialgal culturing. Dilution plate counts for cyanobacteria are not effective because it is nearly impossible to disperse the cyanobacteria into small colony-forming units. I feel that in any determination of biomass for comparative purposes it is probably best to use two methods, with chlorophyll a determination being one of those methods simply because of its ease of use and reproducibility in different laboratories. Question:(Bell): Are there biomass estimates of the algae in the various crust types or within different regions of a single crust of any type? Answer: To my knowledge, there are not. Beymer and Klopatek (1991) have estimated biomass using chlorophyll a in the pedicelled crusts in pinyon–juniper woodlands, and currently Klopatek. Belnap, and myself are independently using chlorophyll a to estimate biomass in other types of crusts and vascular plant communities. However, comparative studies of several crust types in various vascular plant communities or of a single crust type in different regions using the same methodology have yet to be undertaken.