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Centaurea maculosa Lam. is a noxious weed in western North America that produces a phytotoxin, (+/-)-catechin, which is thought to contribute to its invasiveness. Areas invaded by C. maculosa often result in monocultures of the weed, however; in some areas, North American natives stand their ground against C. maculosa and show varying degrees of resistance to its phytotoxin. Two of these resistant native species, Lupinus sericeus Pursh and Gaillardia grandiflora Van Houtte, were found to secrete increased amounts of oxalate in response to catechin exposure. Mechanistically, we found that oxalate works exogenously by blocking generation of reactive oxygen species in susceptible plants and reducing oxidative damage...
1. Plant carbon (C) and nitrogen (N) inputs to soil interact with microbes and abiotic factors like climate and pH to influence soil fertility and plant productivity. Although root exudates and root litter are important factors affecting the cycling of nutrients critical to plant growth, many studies remain focused on effects of above-ground litter inputs. 2. Using two species that co-dominate alpine moist meadows as a model system (the phenolic-rich forb Geum rossii, and the fast-growing grass Deschampsia caespitosa), we asked whether C from G. rossii fine roots could reduce D. caespitosa growth. We hypothesized that root C would indirectly reduce D. caespitosa growth by stimulating soil microbes, thus restricting...
Centaurea diffusa is one of the most destructive invasive weeds in the western USA and allelopathy appears to contribute to its invasiveness (Callaway & Aschehoug 2000). Here we identify a chemical from the root exudates of C. diffusa, 8-hydroxyquinoline, not previously reported as a natural product, and find that it varies biogeographically in its natural concentration and its effect as an allelochemical. 8-Hydroxyquinoline is at least three times more concentrated in C. diffusa-invaded North American soils than in this weed's native Eurasian soils and has stronger phytotoxic effects on grass species from North America than on grass species from Eurasia. Furthermore, experimental communities built from North American...
The primary hypothesis for the astonishing success of many exotics as community invaders relative to their importance in their native communities is that they have escaped the natural enemies that control their population growth ? the `natural enemies hypothesis'. However, the frequent failure of introduced biocontrols, weak consumer effects on the growth and reproduction of some invaders, and the lack of consistent strong top-down regulation in many natural ecological systems indicate that other mechanisms must be involved in the success of some exotic plants. One mechanism may be the release by the invader of chemical compounds that have harmful effects on the members of the recipient plant community (i.e., allelopathy)....
The leaves, litter, and soil from within a community of Artemisia tridentata ssp. vaseyana were analyzed for secondary metabolic products. Methacrolein, five monterpenes, three sesquiterpene lactones, six coumarins, and one flavonoid were identified in the leaves; the contents of the litter were nearly identical. Soils collected directly beneath the shrubs contained the three sesquiterpene lactones, two coumarins and an unknown flavonoid. The litter and water extracts of the litter inhibited the germination of sagebrush seeds. Soils charged with monoterpenes from sagebrush leaves also inhibited seed germination. In addition, the monoterpene contents from eight sagebrush taxa collected from Western Montana are reported....