The influence of Bromus tectorum invasion on nitrogen dynamics in an arid grassland
Citation
L J Sperry, and R David Evans, The influence of Bromus tectorum invasion on nitrogen dynamics in an arid grassland: .
Summary
Destruction of habitats by invasion of non-native organisms may alter ecosystem processes. Biotic and abiotic shifts in the soil will influence available nitrogen pools, and plant species better adapted to the altered nitrogen regimes will be more competitive. We are interested in how a recent Bromus tectorum invasion will affect the nitrogen dynamics, and if the changes associated with invasion alter the competitive status of the native plants. B. tectorum, an annual grass, germinates in the fall, while most native grass species germinate and begin root activity in the spring. B. tectorum's extensive root system monopolizes the soil profile accessing available moisture and nitrogen throughout the winter. Plots were established along [...]
Summary
Destruction of habitats by invasion of non-native organisms may alter ecosystem processes. Biotic and abiotic shifts in the soil will influence available nitrogen pools, and plant species better adapted to the altered nitrogen regimes will be more competitive. We are interested in how a recent Bromus tectorum invasion will affect the nitrogen dynamics, and if the changes associated with invasion alter the competitive status of the native plants. B. tectorum, an annual grass, germinates in the fall, while most native grass species germinate and begin root activity in the spring. B. tectorum's extensive root system monopolizes the soil profile accessing available moisture and nitrogen throughout the winter. Plots were established along an invasion gradient that included two dominant grass species, Stipa spp. and Hilaria jamesii. We removed one meter soil cores, separated them by depth and incubated the soil for 30 days to monitor changes in mineralization. Total mineralization increased at 5-10 cm in the B. tectorum invaded plots for both native species. An increase in ammonification in S. spp., and nitrification in H. jamesii drove the shifts in mineralization rates. Isotopic analysis of plant tissues collected from the native plants showed H. jamesii was not affected by invasion, whereas the 15N of S. spp. increased 1.2 in invaded stands suggesting a shift in the nitrogen source available to S. spp. S. spp. may be more at risk to invasion than H. jamesii because it becomes active during the spring when B. tectorum has monopolized the soil profile. H. jamesii is most active after B. tectorum has set seed and before the next cohort has germinated. These results suggest B. tectorum may alter the soil nitrogen dynamics influencing the composition of the microbial pools as well as the ability of some native species to compete for nitrogen.
Published in 85th Annual Meeting of the Ecological Society of America, in 2000.