title: A mechanistic study of plant and microbial controls over R* for nitrogen in an annual grassland.
abstract: Differences in species' abilities to capture resources can drive competitive hierarchies, successional dynamics, community diversity, and invasions. To investigate mechanisms of resource competition within a nitrogen (N) limited California grassland community, we established a manipulative experiment using an R* framework. R* theory holds that better competitors within a N limited community should better depress available N in monoculture plots and obtain higher abundance in mixture plots. We asked whether (1) plant uptake or (2) plant species influences on microbial dynamics were the primary drivers of available soil N levels in this system where N structures plant communities. To disentangle the relative roles of plant uptake and microbially-mediated processes in resource competition, we quantified soil N dynamics as well as N pools in plant and microbial biomass in monoculture plots of 11 native or exotic annual grassland plants over one growing season. We found a negative correlation between plant N content and soil dissolved inorganic nitrogen (DIN, our measure of R*), suggesting that plant uptake drives R*. In contrast, we found no relationship between microbial biomass N or potential net N mineralization and DIN. We conclude that while plant-microbial interactions may have altered the overall quantity of N that plants take up, the relationship between species' abundance and available N in monoculture was largely driven by plant N uptake in this first year of growth.
authors.affiliation: Department of Ecology, Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, California, United States of America.
authors.forename: Stephanie G
authors.initials: SG
authors.lastname: Yelenik
authors.affiliation: Department of Ecology, Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, California, United States of America.
authors.forename: Benjamin P
authors.initials: BP
authors.lastname: Colman
authors.affiliation: Department of Ecology, Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, California, United States of America.
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Levine
authors.affiliation: Department of Ecology, Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, California, United States of America.
authors.forename: Janneke
authors.initials: J
authors.lastname: HilleRisLambers
mesh_terms: D044822:Biodiversity; D018533:Biomass; D065948:Grassland; D008954:Models, Biological; D009584:Nitrogen / Q000378:metabolism*; D058458:Nitrogen Cycle; D010944:Plants / Q000145:classification / Q000378:metabolism*; D011157:Population Dynamics; D012621:Seasons; D012987:Soil / Q000737:chemistry*; D012988:Soil Microbiology; D013045:Species Specificity
chemical_list: D012987:Soil; D009584:Nitrogen