THE EFFECTS OF NITROGEN AVAILABILITY AND COMPETITION ON FIRST YEAR PERRENNIAL BUNCHGRASS GROWTH AND ALLOCATION

Improving seedling survival of perennial bunchgrasses is a key goal of restoration programs in the Intermountain West. Two perennial bunchgrass species commonly used in restoration programs (Agropyron desertorum and Pseudoroegneria spicata) were exposed to two levels of N and competition treatments in a randomized complete block study in a pot study in eastern Oregon. I documented uptake, allocation and resorption of N in plants during the first year of growth. Agropyron desertorum had significantly higher rates of N uptake than P. spicata, but A. desertorum maintained lower tissue N concentrations, suggesting that P. spicata was more likely to enter into a period of luxury consumption. Results indicated that there may be an inherent trade-off between luxury consumption and resorption, in which high tissue N concentrations due to luxury consumption prevent plants from realizing more complete resorption. Plants of both species experiencing competition realized near or complete resorption, but also had plant-wide tissue concentrations near the minimum values attainable prior to death. These plants also had severely stunted growth. This study demonstrated that early competition results in compounding negative feedbacks for slow growing species, and that the slightly more plastic species (A. desertorum) may be better at coping with strong competitive stress. However, if either species is to be successful in a restoration setting, a strong focus should be placed on seeding times and methods, as well as seeding for communities with high functional trait diversity