DIFFERENTIAL RESPONSES TO NITROGEN FORM AND CONCENTRATION FOR ORYZOPSIS-HYMENOIDES AND ELYMUS-LANCEOLATUS

In a greenhouse experiment, effects of nitrogen form and concentration on productivity and dry matter allocation differed between two specie s native to semiarid ecosystems of the Great Basin. Aboveground produc tion of green surface area and of dry matter were consistently enhance d by increased nitrogen for the rhizomatous grass Elymus lanceolatus, but not for the bunchgrass Oryzopsis hymenoides. These differences wer e likely due to inherently low growth rates of O. hymenoides, Abovegro und dry matter allocation also differed between the two species. O. hy menoides had more leaves per tiller with increased nitrogen, whereas l eaf size but not number increased for E. lanceolatus, Furthermore, inc reases in tiller density with increased nitrogen for E. lanceolatus we re almost three times greater than those for O. hymenoides. E. lanceol atus, but not O. hymenoides, was sensitive to the form of nitrogen sup plied to the plants. When NH4-N was the only form of nitrogen supplied , high concentrations of NH4-N inhibited aboveground production of E. lanceolatus.