Water and nitrogen addition differentially impact plant competition in a native rough fescue grassland |
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Authors: | Eric G Lamb Bryon H Shore James F Cahill |
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Institution: | (1) Department of Biology, University of Alberta, CW405 Biological Sciences Building, T6G 2E9 Edmonton, AB, Canada |
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Abstract: | We examined how water and nitrogen addition and water–nitrogen interactions affect root and shoot competition intensity and
competition–productivity relationships in a native rough fescue grassland in central Alberta, Canada. Water and nitrogen were
added in a factorial design to plots and root exclusion tubes and netting were used to isolate root and shoot competition
on two focal species (Artemisia frigida and Chenopodium leptophyllum). Both water and nitrogen were limiting to plant growth, and focal plant survival rates increased with nitrogen but not water
addition. Relative allocation to root biomass increased with water addition. Competition was almost entirely belowground,
with focal plants larger when released from root but not shoot competition. There were no significant relationships between
productivity and root, shoot, or total competition intensity, likely because in this system shoot biomass was too low to cause
strong shoot competition and root biomass was above the levels at which root competition saturates. Water addition had few
effects on the intensity of root competition suggesting that root competition intensity is invariant along soil moisture gradients.
Contrary to general expectation, the strength of root competition increased with nitrogen addition demonstrating that the
relationship between root competition intensity and nitrogen is more complex than a simple monotonic decline as nitrogen increases.
Finally, there were few interactions between nitrogen and water affecting competition. Together these results indicate that
the mechanisms of competition for water and nitrogen likely differ. |
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Keywords: | Aboveground competition Belowground competition Nitrogen fertilization Soil moisture |
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