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item Ziska, Lewis

Submitted to: Physiologia Plantarum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2003
Publication Date: 5/1/2003
Citation: Ziska, L.H. 2003. Canada thistle (cirsium arvense l. scop.) to recent increases in atmospheric carbon dioxide. Physiologia Plantarum. 119:105-112.

Interpretive Summary: Plants use atmospheric carbon dioxide (CO2) as fuel. They "breathe" CO2 in much the same way that humans breathe oxygen. Since the start of the industrial revolution, humans have poured a lot of CO2 in the atmosphere. Since plants like CO2, this will result in increased plant growth. Although some plants are good, others can have harmful effects on human society. Recent farmer surveys in North America and southern Canada have indicated one plant, Canada thistle, as the worst, most noxious, invasive weed in agriculture. We examined how this one weed might have responded to the rise in CO2 during the 20th century, and whether this response was dependent on nutrients (nitrogen). We found that while nitrogen did affect the overall growth of this weed, the ability to respond positively to recent changes in atmospheric CO2 was independent of nitrogen concentration. This suggests that rising CO2 in recent decades may have been a factor in the development and spread of this "nasty" weed.

Technical Abstract: A recognized invasive weed, Canada thistle was grown at ambient and pre-ambient concentrations of atmospheric carbon dioxide [CO2] (373 and 287 ppm, respectively) at three levels of supplemental nitrogen (N), (3, 6 and 14.5 mM) from seeding until flowering (ca 77 days after sowing, DAS). The primary objective was to determine if N supply limited the potential photosynthetic and growth response of this species to increases in atmospheric [CO2], which occurred during the 20th century (i.e. ~290 to ~370 ppm). Leaf photosynthesis increased both as a function of growth [CO2] and N supply through 46 DAS. Although by 46 DAS, photosynthetic acclimation was observed relative to a common measurement CO2 concentration, there was no interaction with N supply. Both [CO2] and N increased biomass, relative growth rates and leaf area while root:shoot ratio was increased by CO2 and decreased by increasing N; however, N supply did not effect the relative response to [CO2] for any measured vegetative parameter through 77 DAS. The amount of total above ground N increased at elevated [CO2] for all levels of supplemental N, due to the relative stimulation of shoot biomass, but the efficiency of N uptake per unit shoot biomass did not differ as a function of [CO2]. Overall, these data suggest that any potential response to increases in atmospheric [CO2] in recent decades was probably not limited by nitrogen for this invasive species.