Abstract:
The effect of nitrogen on influencing the competitive balance between a shrub, Artemisia tridentata ssp. wyolningensis (ARTRW) and a perennial grass Stipa
thurberiana (STTH) in a sagebrush steppe community was determined. Nitrogen levels were altered on 5x5 in plots by applying 4.5 gun2 of nitrogen in the form of ammonium
or nitrate, or 45 gum2 of sugar. Treatments were compared with untreated control plots. Plant growth, production, leaf nitrogen content, soil water content and soil nitrogen
content were measured throughout growing season of 1987. Both forms of nitrogen, ammonium and nitrate, increased shoot densities, shoot length, ephemeral leaf number per terminal bud, reproductive shoots and leaf nitrogen content in ARTRW. Additions of nitrogen significantly increased
tiller density, reproductive shoots, biomass and leaf nitrogen content in STTH. Nitrate provided the greatest increase in reproductive shoots, for the two forms of
nitrogen. Reproductive tiller density in STTH increased 66% for ammonium and 250% for nitrate, and 56% for ainnionium and 193% for nitrate in ARTRW over control. Nitrogen form
did not appear to favor either the shrub or grass. Although both species responded positively to increases in available nitrogen, leaf area, above ground net annual
primary productivity and nitrogen uptake increased in ARTRW to a greater magnitude than STTH. Addition of sugar did not appear to decrease soil nitrogen availability comparing to control treatment in this research. Environmental conditions causing temporary increases in animonium and or
nitrate may drive the successional process towards a ARTRW dominated site.
