Mixed model results of variation in aboveground biomass (AGB), belowground biomass (BGB), total biomass (TB) and root:shoot (R:S) between the factors genetic lineage, carbon dioxide (CO₂), nitrogen (N) and all interactions, using the random term species(genetic lineage) to test the genetic lineage effect (random effect not shown).

<p>Bold underlined values are significant and degrees of freedom are denoted as subscript of each F value.</p

General linear model results of variation in aboveground biomass (AGB), belowground biomass (BGB), total biomass (TB) and root:shoot (R:S) between the factors of species, carbon dioxide (CO₂), nitrogen (N) and all interactions.

<p>Bold, underlined values indicate statistical significance (α = 0.05); degrees of freedom are denoted as subscript of each F value.</p

Mixed model results of variation in aboveground biomass (AGB), belowground biomass (BGB), total biomass (TB) and root:shoot (R:S) between the factors subgenus, carbon dioxide (CO₂), nitrogen (N) and all interactions, using the random term species(subgenus) to test the subgenus effect (random effect not shown).

<p>Bold underlined values are significant and degrees of freedom are denoted as subscript of each F value.</p

Effect sizes (standardized z-scores) of species total biomass responses to added soil N (30 kg/ha/month; upper panel) and elevated CO₂ (700 ppm; lower panel) for native species monocultures (black) and mixtures with the non-native <i>E. nitens</i> (gray).

<p>Error bars represent ±1 SEM.</p

Productivity responses to global change scenarios are contingent upon species evolutionary history and novel biotic interactions.

<p>Overall, monocultures (pairs of conspecific individuals) of species in the subgenus <i>Symphyomyrtus</i> (top right panel) in elevated CO₂ conditions exhibit the strongest responses to N. On average, these monocultures produce 126% more biomass than all other species pairs in high N and elevated CO₂ treatments (1.301±0.205 g and 0.576±0.061 g, respectively). Above- and belowground biomass follow similar patterns. Error bars represent ±1 SEM.</p

Linear mixed effects model results of eucalypt productivity (total, aboveground and belowground; TB, AGB, and BGB, respectively) and biomass allocation (root to shoot ratio; R∶S) across CO₂, soil N, species pair type (monoculture vs. mixture with the non-native <i>E. nitens</i>) treatments and native species subgenus (N = 190).

<p>In a greenhouse experiment, 28 native Tasmanian eucalypt species within two subgenera (S), <i>Symphyomyrtus</i> and <i>Eucalyptus</i>, were treated with factorial combinations of ambient or elevated CO₂ (C; 420 or 700 ppm, respectively) and low or high soil N (N; 3 or 30 kg/ha/mo), and paired with a conspecific or a non-native (<i>E. nitens</i>) individual (M). In these models, whole-pot biomass measurements and ratios of root to shoot biomass were averaged for each native species in each treatment combination, cube root transformed, and blocked by species. P values are shown in bold and are significant at α≤0.05.</p>δ<p>TB, total biomass; AGB, aboveground biomass; BGB, belowground biomass; R∶S, root to shoot ratio; M, species pair type (native species monoculture vs. mixture with <i>E. nitens</i>); C, CO₂ treatment (420 or 700 ppm); N, nitrogen treatment (3 or 30 kg ha⁻¹ mo⁻¹).</p><p>Linear mixed effects model results of eucalypt productivity (total, aboveground and belowground; TB, AGB, and BGB, respectively) and biomass allocation (root to shoot ratio; R∶S) across CO₂, soil N, species pair type (monoculture vs. mixture with the non-native <i>E. nitens</i>) treatments and native species subgenus (N = 190).</p

Linear mixed effects model results of subgenus-level eucalypt productivity (total, aboveground and belowground; TB, AGB, and BGB, respectively) and biomass allocation (root to shoot ratio; R∶S) across CO₂, soil N, and species pair type (monoculture vs. mixture with the non-native <i>E. nitens</i>).

<p>In a greenhouse experiment, 28 native Tasmanian eucalypt species within two subgenera (S), <i>Symphyomyrtus</i> and <i>Eucalyptus</i>, were treated with factorial combinations of ambient or elevated CO₂ (C; 420 or 700 ppm, respectively) and low or high soil N (N; 3 or 30 kg/ha/mo), and paired with a conspecific or a non-native (<i>E. nitens</i>) individual (M). In these models, whole-pot biomass measurements and ratios of root to shoot biomass were averaged for each native species in each treatment combination, cube root transformed, and blocked by species. P values are shown in bold and are significant at α≤0.05.</p>δ<p>TB, total biomass; AGB, aboveground biomass; BGB, belowground biomass; R∶S, root to shoot ratio; M, species pair type (native species monoculture vs. mixture with <i>E. nitens</i>); C, CO₂ treatment (420 or 700 ppm); N, nitrogen treatment (3 or 30 kg ha⁻¹ mo⁻¹).</p><p>Linear mixed effects model results of subgenus-level eucalypt productivity (total, aboveground and belowground; TB, AGB, and BGB, respectively) and biomass allocation (root to shoot ratio; R∶S) across CO₂, soil N, and species pair type (monoculture vs. mixture with the non-native <i>E. nitens</i>).</p

Evolutionary History and Novel Biotic Interactions Determine Plant Responses to Elevated CO₂ and Nitrogen Fertilization

<div><p>A major frontier in global change research is predicting how multiple agents of global change will alter plant productivity, a critical component of the carbon cycle. Recent research has shown that plant responses to climate change are phylogenetically conserved such that species within some lineages are more productive than those within other lineages in changing environments. However, it remains unclear how phylogenetic patterns in plant responses to changing abiotic conditions may be altered by another agent of global change, the introduction of non-native species. Using a system of 28 native Tasmanian <i>Eucalyptus</i> species belonging to two subgenera, <i>Symphyomyrtus</i> and <i>Eucalyptus</i>, we hypothesized that productivity responses to abiotic agents of global change (elevated CO₂ and increased soil N) are unique to lineages, but that novel interactions with a non-native species mediate these responses. We tested this hypothesis by examining productivity of 1) native species monocultures and 2) mixtures of native species with an introduced hardwood plantation species, <i>Eucalyptus nitens</i>, to experimentally manipulated soil N and atmospheric CO₂. Consistent with past research, we found that N limits productivity overall, especially in elevated CO₂ conditions. However, monocultures of species within the <i>Symphyomyrtus</i> subgenus showed the strongest response to N (gained 127% more total biomass) in elevated CO₂ conditions, whereas those within the <i>Eucalyptus</i> subgenus did not respond to N. Root:shoot ratio (an indicator of resource use) was on average greater in species pairs containing <i>Symphyomyrtus</i> species, suggesting that functional traits important for resource uptake are phylogenetically conserved and explaining the phylogenetic pattern in plant response to changing environmental conditions. Yet, native species mixtures with <i>E. nitens</i> exhibited responses to CO₂ and N that differed from those of monocultures, supporting our hypothesis and highlighting that both plant evolutionary history and introduced species will shape community productivity in a changing world.</p></div

Belowground biomass responses to elevated CO₂ and N.

<p>Interaction plots of least squares means (± standard error for C–F) of the belowground biomass of species (A and B), genetic lineages (C and D) and subgenera (E and F) with control N and 30 kg ha⁻¹ of N added (High N) under both ambient (left panels) and elevated CO₂ (right panels). Standard errors are not presented on the species panels (A–B) due to space constraints. Each colour and line (solid/dashed) combination represents each species, genetic lineage or subgenus.</p