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Abstract

Plant invasions have proven detrimental to numerous ecosystem processes; however, limited information exists on how plant invasions affect seed nutrients. We quantified nutrients in seeds of Indian ricegrass (Achnatherum hymenoides), green rabbitbrush (Chrysothamnus viscidiflorus), winterfat (Krascheninnikovia lanata), freckled milkvetch (Astragalus lentiginosus), and cheatgrass (Bromus tectorum) in sites invaded about 10 years by cheatgrass and in nearby sites with only widely scattered plants of cheatgrass. Seed chemistry differed significantly among the species tested. Overall, seeds of shrubs and freckled milkvetch had greater concentrations of N, P, and K, and lower C:N ratios than the grass species. On areas invaded by cheatgrass for 10 years, seeds trended towards decreased nutrients relative to seeds from non-invaded areas. Statistically, however, only winterfat, whose seeds from invaded areas had greater N and significantly lower C and C:N ratios, and cheatgrass, whose seeds from invaded areas had less P, were significantly different from non-invaded areas. Complimentary data suggests that cheatgrass invasion increases the availability of N, which explains an increase for seeds of winterfat; however, invasion also fosters high winterfat mortality. We suspect that high density of cheatgrass and cheatgrass litter on sites invaded for 10 years essentially ties-up large quantities of P, K and Mg, thus reducing amounts available for plant uptake. Overall, our data suggests declining nutritional value of seeds with plant invasion.

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