PARENT SESSION
Oral Session #51: Invasions: Population and community interactions.
Presiding: T. Stohlgren
Wednesday, August 7. 8:00 AM to 11:30 AM. Graham Meeting Room, TCC.

The role of plant-microbe interactions in invasion of California serpentine grasslands.

Batten, Kit^*,1, Scow, Kate¹, Harrison, Susan², ¹ Department of Land, Air, and Water Resources, Davis, CA² Department of Environmental Science and Policy, Davis, CA

ABSTRACT- Plant invasions present a serious threat to native ecosystem structure and function. To gain insight on the mechanisms and effects of invasion, current research has focused on the 'invasibility' of ecosystems, traits that facilitate the 'invasiveness' of certain plant species, and the consequences of invasion on diversity and ecosystem processes. Virtually unexplored is the potential role of rhizosphere microbial communities in facilitating invasive species or in resisting invasion into native plant communities. The objective of this study was to compare the composition of microbial communities in the rhizosphere of invasive and native plant species in serpentine soils. Serpentine soils are highly infertile (low calcium:magnesium ratio, low nitrogen content, and high levels of chromium and nickel) and tend to be host to a large number of native endemics. We focused on two invasive species, goatgrass (Aegilops triuncialis) and yellow starthistle (Centaurea solstitialis), both of which are frequent invaders of serpentine soils. The soil rhizosphere microbial communities associated with goatgrass and starthistle were compared to those of native plants (Plantago erecta, Lasthenia californica, Lotus wrangelianus, and Hemezonia congesta) that appeared to be competitively excluded by these species in the field. Phospholipid Fatty Acid analysis (PLFA) was used to compare the rhizosphere microbial communities of invasive and native plants, and soil chemical properties were also measured. Correspondence Analyses (CA) indicated that plants more strongly influenced soil microbial community composition than plot location. Starthistle appeared to share the same rhizosphere microbial community with the native species it excluded; whereas, goatgrass appeared to alter the microbial community in the invaded areas, potentially to the detriment of the native species. These data suggest that invasive plant species may interact with soil microbes in different ways to increase their invasive ability. We propose two such mechanisms that may apply to goatgrass and starthistle invasions in serpentine soils.

KEY WORDS: Aegilops triuncialis, Centaurea solstitialis, Invasive Species Ecology, Soil Microbial Ecology