The biology and ecology of weeping alkaligrass (Puccinellia distans) and Nuttall's alkaligrass (Puccinellia nuttalliana)

Weeping alkaligrass (Puccinellia distans) and Nuttall's alkaligrass (Puccinellia nuttalliana) infest Kentucky bluegrass seed fields of eastern Oregon. Weeping alkaligrass is an introduced species from Eurasia, whereas Nuttall's alkaligrass is native to semi arid environments of western North America. These species are often referred to collectively as 'alkaligrass'; however, for farmers of eastern Oregon, there is concern as to which species may prove to be more troublesome. Germination experiments conducted to determine the seed biology attributes of the two species revealed that both species exhibit relatively long afterripening characteristics and viable seed for at least 1 year when dry stored. Once adequately afterripened, weeping alkaligrass had greater germination at most temperature combinations, in particular at constant temperatures. Weeping alkaligrass also was more tolerant of extreme high temperatures, as well as drought and salt conditions. Field experiments exploring the fitness of these two species on sodic versus normal soil types, found that weeping alkaligrass benefited from normal soil conditions growing larger and producing up to 4 times the seed. Weeping alkaligrass also was able to adjust to a lower solute potential under sodic soil conditions, and maintain a higher relative water content under normal soil conditions. For both species, a strong inhibitor to plant establishment was competing vegetation. Observational studies revealed that depressional areas increased the likelihood of establishment of both species. While Nuttall's alkaligrass was positively associated with exchangeable sodium and negatively associated with exposed mineral soil, weeping alkaligrass exhibited the traits of a resource generalist, its abundance being negatively associated with competing vegetation. Results of a 2-year competition study comparing both species of alkaligrass with Kentucky bluegrass indicated that in year 1 Kentucky bluegrass grew slower than Nuttall's alkaligrass, and to a lesser extent weeping alkaligrass. Yet, by year 2, the average Kentucky bluegrass plant was vastly larger than either of the alkaligrasses, in particular weeping alkaligrass. As well, during the first year of establishment, Kentucky bluegrass biomass was equally reduced by both species of alkaligrass more so than by itself. Results from the second year indicate that Kentucky bluegrass had much higher survival rates than the two species of alkaligrass, especially weeping alkaligrass. In year 2, the original planting density of Kentucky bluegrass was the strongest indicator of potential biomass for all three species. In a comparison between year 1 and year 2 biomass, it was apparent that while weeping alkaligrass exhibited high levels of mortality, the original planting densities strongly impacted the year 2 biomass accumulation of both Kentucky bluegrass and Nuttall's alkaligrass. In conclusion, the traits of having wide ranging suitable germination conditions, a more dynamic phenotypic plasticity, increased fitness under agriculturally productive soils, traits of a resource generalist and lingering effects on the growth of both Nuttall's alkaligrass and Kentucky bluegrass, may make the introduced weeping alkaligrass a species of greater concern than the native Nuttall's alkaligrass for farmers of eastern Oregon.