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Current and Recent Research Projects

visit the  SDSU Santa Margarita Ecological Reserve web site

Research in coastal sage scrub (CSS) ecosystems 

The role of cryptobiotic soil crusts and vascular plants in patterning microbial communities in CSS ecosystems

We are investigating how cryptobiotic crusts of varying levels of successional development and the dominant vascular plants of the CSS affect soil microbial communities and processes.

Soil crusts grow in bare patches between shrubs in CSS.  These crusts are held together by polysaccharides produced by cyanobacteria, algae and lichens, and harbor unique microbial communities.

Effects of Invasive plant species and fire on microbial communities and soil processes in CSS

We are studying how disturbance by fire and invasion in CSS affects microbial communities, and how these changes might feed back to influence the plant communities and the ecosystem.  Much of this research is performed with the cooperation of the Soil Ecology and Restoration Group (SERG) and the laboratories of Douglas Deutschman and Janet Franklin

CSS ecosystems are endangered by human development, disturbance and invasion by exotic plant species.

Publications resulting from this work:

Dane LS, Lipson DA (2006) The role of cryptobiotic soil crusts and vascular plants in patterning soil microbial processes in a coastal sage scrub ecosystem. (in review)

ABSTRACT: Cryptobiotic soil crusts have many biologic components whose life histories are well understood, yet very little is known about the heterotrophic bacterial species that inhabit soil crust communities. The purpose of this research was to understand the carbon cycling and functional heterotrophic diversity associated with cyanobacteria-dominated and lichen-dominated soil crusts in a coastal sage scrub ecosystem and to compare the functioning of soils associated with crusts and vascular plants. This master’s thesis tested whether soil heterotrophic activity is related to the photosynthetic activity of primary producers in soil crusts, and whether lichen dominated soil crusts and cyanobacteria dominated soil crusts differ functionally. All soil crust samples were collected at the Santa Margarita Ecological Reserve in Riverside County, CA in February, March and May 2004. A total of 54 samples were collected in paired units representing sections of the crust community where cyanobacteria-dominated and lichen-dominated crusts coexist adjacent to one another, along with a control taken from underneath the vascular plant canopy (Salvia mellifera) for each paired crust sample. Results showed quantitative and qualitative effects of primary producers on carbon cycling that vary over the season. Substrate-induced respiration (SIR) was used as an indicator of heterotrophic biomass and activity. Chlorophyll was used as an indicator of primary production. Simple regressions of SIR with chlorophyll a + b showed significant linear relationships during the early, relatively moist growing season only. Multiple regression demonstrated chlorophyll and moisture content as significant predictors of heterotrophic activity early in the season. Only chlorophyll was a significant indicator of heterotrophic activity in the mid-season, and organic matter became the only indicator later in the season. Levels of cellulase and invertase enzyme activities were consistently higher in the lichen-dominated crusts, as was heterotrophic consumption of the algal produced compounds: fucose, ribitol, and galacturonic acid. Discriminant analysis clustered lichen dominated soil crusts on the basis of substrate use profiles throughout all sampling dates. On the other hand, cyanobacteria dominated samples were clustered only during the early-season, and soils beneath Salvia mellifera varied greatly in their substrate use profiles throughout all sample dates. These results suggest that photosynthesis does control microbial biomass activities of soil crusts while environmental conditions are moist. These results also suggest that lichen dominated and cyanobacteria dominated soil crusts do differ functionally.

Lipson DA, Dane LS, Lopez A, Maya Y (2006) Novel diversity of bacterial 16S rRNA and rbcL genes from cryptobiotic soil crusts. (in preparation).