Responses of Downy Brome to Nitrogen and Water

Abstract

Downy brome (Brooms tectorum L.) is an alien grass that dominates disturbed ground in shrub-steppe ecosystems of the western United States. Responses of downy brome to added nitrogen and water were evaluated using intact soil cores obtained from an old field. Gas exchange data were gathered at the leaf and canopy scales. Stomata1 conductance and net photosynthesis rates were greater at the leaf scale than at the canopy scale, decreased with time from germination, and were weakly affected by treatments. Water-use efficiency was weakly related to time from germination and treatments. Biomass was greater in the nitrogen-plus-water (7.4 g) treatment, compared with water (3.6 g), nitrogen (4.5 g), and control (3.3 g) treatments. The leaf-area indes varied like biomass at the end of the esperiment. Shoot nitrogen was the same in the nitrogen (2.5%) and nitrogen-pluswater (2.5%) treatments, nearly twice the level in the control (1.5%) and water (1.3%) treatments. Nitrogen-use efficiency was highest in the control (67) and water (80) treatments and lowest in the nitrogen (41) and nitrogen-plus-water (43) treatments. The most significant conclusion of this work is that gas exchange was strongly related to the time from germination and little affected by water and nitrogen while growth characters were strongly affected only when water and nitrogen were added together. (Bromrrs tectorunt L.) have come to dominate resource-limited rangelands in the western United States (Klemmedson and Smith 1964, Mack 1981, Billings 1990). Downy brome shoot and root biomass increased with additional nitrogen in the field (Hulbert 1955). Biomass production was significantly related to stored soil moisture (Cline and Rickard 1973, Uresk et al. 1979). Cline and Rickard (1973) found that nitrogen was more limiting than soil water for shoot biomass production over several years of observation in the field. Past studies have investigated the response of downy brome production to nitrogen and water, separately. There have been no studies investigating the interaction of nitrogen and water on the physiology and growth of downy brome. The purpose of this study was to investigate the growth and gas exchange response of downy brome to separate and combined additions of nitrogen and water. We examined growth and gas exchange responses to water and nitrogen as a function of the time from germination. Gas exchange observations were taken at leaf and canopy scales.

Invasion resistance and persistence: established plants win, even with disturbance and high propagule pressure

“…As an annual species, cheatgrass generally has greater dependence on plant-available soil nutrients for successful establishment and persistence than perennial species (Marschner 1995). Past research has shown both soil nutrient concentration and native species competition to be important in regulating invasions (Link et al 1995;Booth et al 2003a;Chambers et al 2007); possibly their combined influences provided both community resiliency and resistance to cheatgrass invasion in our study.…”

“…Cheatgrass outcompetes many native perennial grass seedlings, but performs worse when competing with mature native plants (Booth et al 2003a;Lowe et al 2003;Humphrey and Schupp 2004). Furthermore, cheatgrass success is promoted by high soil nutrient levels, particularly nitrate, which often increases in the soil immediately after fire (Link et al 1995;Lowe et al 2003;Beckstead and Augspurger 2004;Gundale et al 2008).…”

Contrasting effects of resource availability and plant mortality on plant community invasion by Bromus tectorum L.

“…The spread and success of B. tectorum in this region is thought to be due largely to disturbances in the form of grazing and increased fire frequency (Mack 1986;D'Antonio and Vitousek 1992;Mack et al 2000). In some cases, B. tectorum success has been linked to increases in nitrogen (N) (NPS 2000;Lowe et al 2003;Monaco et al 2003;Beckstead and Augspurger 2004) and water (Link et al 1995;Chambers et al 2007), but the nature of the response of B. tectorum to increasing levels of these resources is not known (e.g., linear, nonlinear or threshold dynamics).…”

A spring rainfall pulse causes greater in situ photosynthetic upregulation for Bromus tectorum compared to co-occurring native herbaceous species

“…However, we know little about the in situ patterns of photosynthesis for B. tectorum and the native herbaceous species at this site. Despite some greenhouse experiments (Dakheel et al, 1994;Link et al, 1995;Rice et al, 1992;Smith et al, 1987), we are not aware of any reports of the in situ patterns of photosynthesis for B. tectorum. Likewise, much of the research on B. tectorum has focused on invasions at lower elevations (Booth et al, 2003;Humphrey and Schupp, 2004;Mazzola et al, 2011;Rau et al, 2011), where impacts are extensive.…”