Grasslands of the central and southern Great Plains (US) are being invaded by exotic, C4 grasses such us Old World bluestems (OWB, Bothriochloa spp; Kleberg bluestem, Dichanthium annulatum) and buffelgrass (Pennisetum ciliare), as well as encroached by native C4 grasses (e.g. tanglehead, Heteropogon contortus).  These exotic, perennial grasses native to Europe and Asia were introduced to the U.S. and planted extensively  throughout the Great Plains. Until recently, studies on these species have focused primarily on forage potential, rather than invasibility. Recent evidence indicates these species are highly invasive and reduce native plant and animal diversity. A greenhouse study was conducted to determine if these species inhibit growth of native grasses through soil alterations. This study examined soil from 5 prairies in OK, KS, and TX characterized by undisturbed native prairie with adjacent areas intensively invaded (encroached). We collected soil from 1) beneath native grasses (control) and 2) beneath the invading (encroaching) grass.  These soils were 1) sterilized, 2) sterilized and inoculated with nonsterile soil collected beneath native grasses, thereby returning native soil microorganisms, or 3) left non-amended (non-sterile soil).  Plants were grown for 14 weeks, harvested to collect above-, and belowground biomass, and % mycorrhizal root colonization.

Results/Conclusions

Generally, the perennial grasses (OWB, buffelgrass, tanglehead, and native) exhibited reduced growth in sterilized soil, indicating dependence on mycorrhizal fungi. However, the growth and reproduction of the perennial native, hooded windmillgrass (Chloris cucullata), was not dependent on the mycorrhizal symbiont.  All species had reduced total biomass when grown in soil collected under the non-native Kleberg bluestem.  Most native grasses were reduced in growth and root colonization by mycorrhizal fungi when planted into invaded soils. This adverse effect was partially alleviated by the addition of native microbes.  A strong, linear relationship between mycorrhizal colonization and plant productivity was observed.  Addition of native soil microbes improved plant growth and mycorrhizal colonization in most plant-soil combinations. Our results indicate that invasive (encroaching) grasses alter soil biota and produce a species-specific growth and reproduction response of native grasses.  These results suggest successful restoration of invaded areas may require the use of soil remediation techniques designed specifically for the invasive species of interest.