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, 9 (3), 1095-1109
eCollection

Effects of Soil Nitrogen on Diploid Advantage in Fireweed, Chamerion angustifolium (Onagraceae)

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Effects of Soil Nitrogen on Diploid Advantage in Fireweed, Chamerion angustifolium (Onagraceae)

Alex L Bales et al. Ecol Evol.

Abstract

In many ecosystems, plant growth and reproduction are nitrogen limited. Current and predicted increases of global reactive nitrogen could alter the ecological and evolutionary trajectories of plant populations. Nitrogen is a major component of nucleic acids and cell structures, and it has been predicted that organisms with larger genomes should require more nitrogen for growth and reproduction and be more negatively affected by nitrogen scarcities than organisms with smaller genomes. In a greenhouse experiment, we tested this hypothesis by examining whether the amount of soil nitrogen supplied differentially influenced the performance (fitness, growth, and resource allocation strategies) of diploid and autotetraploid fireweed (Chamerion angustifolium). We found that soil nitrogen levels differentially impacted cytotype performance, and in general, diploids were favored under low nitrogen conditions, but this diploid advantage disappeared under nitrogen enrichment. Specifically, when nitrogen was scarce, diploids produced more seeds and allocated more biomass toward seed production relative to investment in plant biomass or total plant nitrogen than did tetraploids. As nitrogen supplied increased, such discrepancies between cytotypes disappeared. We also found that cytotype resource allocation strategies were differentially dependent on soil nitrogen, and that whereas diploids adopted resource allocation strategies that favored current season reproduction when nitrogen was limiting and future reproduction when nitrogen was more plentiful, tetraploids adopted resource allocation strategies that favored current season reproduction under nitrogen enrichment. Together these results suggest nitrogen enrichment could differentially affect cytotype performance, which could have implications for cytotypes' ecological and evolutionary dynamics under a globally changing climate.

Keywords: adaptation; autopolyploidy; fitness; global change; resource allocation strategies; soil nitrogen.

Figures

Figure 1
Figure 1
Study species, Chamerion angustifolium (Onagraceae)
Figure 2
Figure 2
Ploidy and soil nitrogen treatment interactions on (a) the number of flowers produced per plant, (b) the number of outcrossed seeds produced per fruit, (c) maximum seed production (MSP), and (d) flowering phenology of fireweed (Chamerion angustifolium). We report p‐values from ploidy × soil N treatment interactions, LS means ±1 SE's, and significant independent contrasts between cytotypes within nitrogen treatments when significant (p < 0.05) with separate letters; full statistical details are reported in Table 2
Figure 3
Figure 3
Ploidy and soil nitrogen treatment interactions on fireweed's (Chamerion angustifolium) (a) shoot biomass to root biomass (log‐transformed), (b) shoot‐N to total root‐N (log‐transformed), (c) maximum seed production (MSP) to total plant biomass, and (d) maximum seed production (MSP) to total plant N. We report p‐values from ploidy × soil N treatment interactions, LS means ±1 SE's, and significant independent contrasts between cytotypes within nitrogen treatments when significant (p < 0.05) with separate letters; full statistical details are reported in Table 3

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