WIKINDX Resources
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Evans, R. D., Rimer, R., Sperry, L., & Belnap, J. (2001). Exotic plant invasion alters nitrogen dynamics in an arid grassland. Ecological Applications, 11(5), 1301–1310.
Added by: Eric Peterson 2007-10-19 22:08:32 Last edited by: Eric Peterson 2007-10-19 22:11:31
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Categories: General
Keywords: Bromus tectorum; Canyonlands National Park, changes in biomass and chemistry; N mineralization; plant-available N fo, USA; denitrification enzyme activity; desert vegetation; ecosystem carbon; ecosystem nitrogen; grasslands; invasive species; litter, Utah
Creators: Belnap, Evans, Rimer, Sperry
Collection: Ecological Applications
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Number of views: 129
Popularity index: 84.31%
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Abstract
The introduction of nonnative plant species may decrease ecosystem stability
by altering the availability of nitrogen (N) for plant growth. Invasive species can impact
N availability by changing litter quantity and quality, rates of N2-fixation, or rates of N
loss. We quantified the effects of invasion by the annual grass Bromus tectorum on N
cycling in an arid grassland on the Colorado Plateau (USA). The invasion occurred in 1994
in two community types in an undisturbed grassland. This natural experiment allowed us
to measure the immediate responses following invasion without the confounding effects of
previous disturbance. Litter biomass and the C:N and lignin:N ratios were measured to
determine the effects on litter dynamics. Long-term soil incubations (415 d) were used to
measure potential microbial respiration and net N mineralization. Plant-available N was
quantified for two years in situ with ion-exchange resin bags, and potential changes in rates
of gaseous N loss were estimated by measuring denitrification enzyme activity. Bromus
invasion significantly increased litter biomass, and Bromus litter had significantly greater
C:N and lignin:N ratios than did native species. The change in litter quantity and chemistry
decreased potential rates of net N mineralization in sites with Bromus by decreasing nitrogen
available for microbial activity. Inorganic N was 50% lower on Hilaria sites with Bromus
during the spring of 1997, but no differences were observed during 1998. The contrasting
differences between years are likely due to moisture availability; spring precipitation was
15% greater than average during 1997, but 52% below average during spring of 1998.
Bromus may cause a short-term decrease in N loss by decreasing substrate availability and
denitrification enzyme activity, but N loss is likely to be greater in invaded sites in the
long term because of increased fire frequency and greater N volatilization during fire. We
hypothesize that the introduction of Bromus in conjunction with land-use change has established
a series of positive feedbacks that will decrease N availability and alter species
composition.
Added by: Eric Peterson
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