Evolutionary effects of nitrogen are not easily predicted from ecological responses.
AMERICAN JOURNAL OF BOTANY 2022;
109:1741-1756. [PMID:
36371717 PMCID:
PMC10099611 DOI:
10.1002/ajb2.16095]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/24/2022] [Revised: 08/27/2022] [Accepted: 08/30/2022] [Indexed: 06/16/2023]
Abstract
PREMISE
Anthropogenic nitrogen (N) addition alters the abiotic and biotic environment, potentially leading to changes in patterns of natural selection (i.e., trait-fitness relationships) and the opportunity for selection (i.e., variance in relative fitness). Because N addition favors species with light acquisition strategies (e.g., tall species), we predicted that N would strengthen selection favoring those same traits. We also predicted that N could alter the opportunity for selection via its effects on mean fitness and/or competitive asymmetries.
METHODS
We quantified the strength of selection and the opportunity for selection in replicated populations of the annual grass Setaria faberi (giant foxtail) growing in a long-term N addition experiment. We also correlated these population-level parameters with community-level metrics to identify the proximate causes of N-mediated evolutionary effects.
RESULTS
N addition increased aboveground productivity, light asymmetry, and reduced species diversity. Contrary to expectations, N addition did not strengthen selection for trait values associated with higher light acquisition such as greater height and specific leaf area (SLA); rather, it strengthened selection favoring lower SLA. Light asymmetry and species diversity were associated with selection for height and SLA, suggesting a role for these factors in driving N-mediated selection. The opportunity for selection was not influenced by N addition but was negatively associated with species diversity.
CONCLUSIONS
Our results indicate that anthropogenic N enrichment can affect evolutionary processes, but that evolutionary changes in plant traits within populations are unlikely to parallel the shifts in plant traits observed at the community level.
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