Biomass Allocation in Four Prairie Grasses under Drought Stress

In grasses, food reserves in crowns and rhizomes support herbage production and allow regrowth in the spring. One important factor leading to the relative competitiveness of Kentucky bluegrass and smooth brome is that they initiate spring regrowth earlier than their native counterparts in the mixed-grass prairie. It still remains to be tested if there is a greater biomass investment to crowns or rhizomes in the exotic grasses as compared to the native species. We report on a study of the effect of drought stress on vegetative biomass allocation in two native grass species, western wheatgrass (Pascopyrum smithii (Rydb.) A. Löve) and green needlegrass (Nassella viridula (Trin.) Barkworth), and two exotic species, Kentucky bluegrass (Poa pratensis L.) and smooth brome (Bromus inermis Leyss.). All four species are dominant in the mixed-grass prairie. Green needlegrass is a bunch-type grass while the remaining three species are strongly rhizomatous. We tested the following three hypotheses: