Arbuscular mycorrhizal fungi alter phosphorus relations of broomsedge (Andropogon virginicus L.) plants

Broomsedge (Andropogon virginicus L.) is a dominant grass revegetating many abandoned coal-mined lands in West Virginia, USA. Residual soils on such s ites are often characterized by low pH, low nutrients, and high aluminium. Experiments were conducted to assess the resistance of broomsedge to limite d phosphorus (Pi) availability and to investigate the role that arbuscular mycorrhizal (AM) fungi play in aiding plant growth under low Pi conditions. Pregerminated mycorrhizal and non-mycorrhizal seedlings were grown in a sa nd-culture system with nutrient solutions containing Pi concentrations rang ing from 10 to 100 muM for 8 weeks. Non-mycorrhizal plants exhibited severe inhibition of growth under Pi limitation (<60 <mu>M). Colonization by AM f ungi (combined Glomus clarum Nicolson & Schenck and Gigaspora gigantea (Nic ol. & Gerd.) Gerd. & Trappe) greatly enhanced host plant growth at low Pi c oncentrations, but did not benefit growth when Pi was readily available (10 0 muM). In comparison to non-mycorrhizal plants, mycorrhizal plants had hig her phosphorus use efficiency at low Pi concentrations and maintained nearl y constant tissue nutrient concentrations across the gradient of Pi concent rations investigated. Manganese (Mn) and sodium (Na) accumulated in shoots of nonmycorrhizal plants under Pi limitation. Mycorrhizal plants exhibited lower instantaneous Pi uptake rates and significantly lower C-min values co mpared to non-mycorrhizal plants. These patterns suggest that the symbiotic association between broomsedge roots and AM fungi effectively maintains nu trient homeostasis through changes in physiological properties, including n utrient uptake, allocation and use. The mycorrhizal association is thus a m ajor adaptation that allows broomsedge to become established on infertile m ined lands.