Linking nitrogen partitioning and species abundance to invasion resistance in the Great Basin |
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Authors: | J J James K W Davies R L Sheley Z T Aanderud |
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Institution: | (1) USDA-Agricultural Research Service, Eastern Oregon Agricultural Research Center, 67826-A Hwy 205, Burns, OR 97720, USA;(2) W. K. Kellogg Biological Station, Michigan State University, Hickory Corners, MI 49060, USA |
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Abstract: | Resource partitioning has been suggested as an important mechanism of invasion resistance. The relative importance of resource
partitioning for invasion resistance, however, may depend on how species abundance is distributed in the plant community.
This study had two objectives. First, we quantified the degree to which one resource, nitrogen (N), is partitioned by time,
depth and chemical form among coexisting species from different functional groups by injecting 15N into soils around the study species three times during the growing season, at two soil depths and as two chemical forms.
A watering treatment also was applied to evaluate the impact of soil water content on N partitioning. Second, we examined
the degree to which native functional groups contributed to invasion resistance by seeding a non-native annual grass into
plots where bunchgrasses, perennial forbs or annual forbs had been removed. Bunchgrasses and forbs differed in timing, depth
and chemical form of N capture, and these patterns of N partitioning were not affected by soil water content. However, when
we incorporated abundance (biomass) with these relative measures of N capture to determine N sequestration by the community
there was no evidence suggesting that functional groups partitioned different soil N pools. Instead, dominant bunchgrasses
acquired the most N from all soil N pools. Consistent with these findings we also found that bunchgrasses were the only functional
group that inhibited annual grass establishment. At natural levels of species abundance, N partitioning may facilitate coexistence
but may not necessarily contribute to N sequestration and invasion resistance by the plant community. This suggests that a
general mechanism of invasion resistance may not be expected across systems. Instead, the key mechanism of invasion resistance
within a system may depend on trait variation among coexisting species and on how species abundance is distributed in the
system. |
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Keywords: | Cheatgrass Great Basin Medusahead Niche Nitrogen |
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