Inoculation of a perennial bunchgrass: Implications for plug-based restoration in arid environments

Plug- or container-based ecological restoration is widely used in attempts to increase rates of native grass establishment and persistence on biophysically disturbed sites. Our objective in this study was to evaluate the effects of soil inoculation of Digitaria californica (Arizona cottontop) plugs during the greenhouse phase of a plug-based restoration project, and determine if inoculation increases the chance of plug survival during extended dry periods. Locally harvested seed was placed in “Cone-Tainer” cells with a sterile soil mix consisting of local field soil and sand. In a completely randomized design, cells were either inoculated with water sieved through field soil, or inoculated with water sieved through sterilized field soil.  Plants were then watered as needed to provide adequate moisture for germination and subsequent growth. Germination rates, time to germination, seedling survival, and plant vigor were monitored prior to plants becoming rootbound. Watering was then halted to assess water stress through measurements of plant water potential following an extended dry period. Preliminary results suggest inoculated plugs were more vigorous with a higher rate of survival, and needed less time to germinate than the non-inoculated plugs. No difference in the overall germination rate or water stress was observed. These results suggest that soil inoculation may benefit D. Californica, especially in areas where water is the limiting factor, and that soil microorganisms have the potential to change its germination dynamics.