Morphological and physiological traits account for similar nitrate uptake by crested wheatgrass and cheatgrass

Authors: Leffler, Alan; Monaco, Thomas; James, Jeremy

Submitted to: Wildland Shrub Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 7/15/2011
Publication Date: 11/15/2011
Citation: Leffler, A.J., Monaco, T.A., James, J.J. 2011. Morphological and physiological traits account for similar nitrate uptake by crested wheatgrass and cheatgrass. Wildland Shrub Symposium Proceedings. XVII.

Interpretive Summary: Crested wheatgrass stands are largely resistant to invasion by the annual grass cheatgrass while perennial grasses native to the Intermountain West are not. Resistance to invasion by crested wheatgrass may be related to its ability to acquire soil nitrogen. Nitrogen uptake is closely linked to morphology of roots and leaves and theory predicts annual grasses to have much higher rates of nitrogen uptake than perennial grasses such as crested wheatgrass. We find that cheatgrass and created wheatgrass can have similar rates of nitrogen uptake and despite crested wheatgrass being a perennial, it is morphologically more similar to cheatgrass than to native perennial grasses. Morphology, however, only accounts for 57% of the variation in nitrogen uptake and physiological similarity of these species should be examined more closely.

Technical Abstract: Millions of hectares throughout the Intermountain West are either dominated or threatened by the invasive annual grass Bromus tectorum (cheatgrass). This invasion is largely linked to disturbance and few regions appear immune. Disturbance liberates resources in a community and cheatgrass appears exceptionally able to capitalize on these resources. One species, however, is consistently competitive with cheatgrass. Agropyron cristatum (crested wheatgrass), an improved plant material developed from several populations in central Asia is drought resistant, grazing tolerant, and largely excludes cheatgrass in stands established within the Great Basin. While previous studies document high resource uptake ability by crested wheatgrass, it remains unknown if high uptake in this species is due to morphological or physiological adaptation. We examine N uptake and tissue morphology by four grasses common in the Intermountain West including cheatgrass and crested wheatgrass; we also include two native grasses, Pseudoroegneria spicata (bluebunch wheatgrass) and Elymus elymoides (bottlebrush squirreltail). We observed similar rates of N uptake by cheatgrass and crested wheatgrass and uptake by these species was greater than the native perennials. A multivariate analysis suggests, of the three perennial grasses examined here, crested wheatgrass is morphologically most similar to cheatgrass, but that morphology only accounts for 57% of the variation in N uptake capacity among species. Consequently, physiological traits such as induction of N uptake or N efflux likely play a role in the ability of crested wheatgrass to achieve N uptake rates similar to cheatgrass.