Are endemics functionally distinct? Leaf traits of native and exotic woody species in a New Zealand forest

<div><p>Recent studies have concluded that native and invasive species share a common set of trait relationships. However, native species in isolated regions might be functionally constrained by their unique evolutionary histories such that they follow different carbon capture strategies than introduced species. We compared leaf traits relating to resource investment, carbon return, and resource-use efficiency in 16 native (endemic) and three non-native (invasive) species in a temperate forest in Canterbury, South Island, New Zealand. Trait differences were more closely associated with leaf habit than nativity. Deciduous species (including invaders) exhibited greater maximum photosynthetic rates at similar resource costs, which resulted in greater nitrogen- and energy-use efficiencies than evergreen natives. Leaf area was the only trait that differed significantly by nativity (over two-fold larger in invaders). Invaders and deciduous natives both occupied the ‘fast return’ end of the leaf economics spectrum in contrast to the native evergreens which had comparatively slow return on investment. Dominant woody invaders in this forest are physiologically distinct from many New Zealand endemic species, which are overwhelmingly evergreen. It remains unclear whether these trait differences translate to an ecological divergence in plant strategy, but these results suggest that ecophysiological tradeoffs are likely constrained by biogeography.</p></div

Woody species measured, including invasive status, biogeographic origin, growth form, and number of replicate individuals.

<p>Woody species measured, including invasive status, biogeographic origin, growth form, and number of replicate individuals.</p

Mean values (± 1 SE) of photosynthetic, biochemical, structural, and resource-use efficiency leaf traits among native and invasive species.

<p>Mean values (± 1 SE) of photosynthetic, biochemical, structural, and resource-use efficiency leaf traits among native and invasive species.</p

Are endemics functionally distinct? Leaf traits of native and exotic woody species in a New Zealand forest - Fig 4

<p><b>Standardized major axis (SMA) relationships for area-based light-saturated maximum photosynthetic rate (A</b>_{<b>max,area</b>}<b>) and leaf resource cost traits (a, e) dark respiration rate (R</b>_{<b>d,area</b>}<b>), (b, f) nitrogen concentration (N</b>_<b>area</b><b>), (c, g) construction cost (CC</b>_<b>area</b><b>), and (d, h) specific leaf area (SLA).</b> Points refer to species- (a-d) or individual-level (e-h) estimates. Native deciduous species are denoted by black text and open triangles, invasive species by closed triangles, and native evergreen species (open circles) are shown in grey. Light gray error bars denote 95% credible intervals on posterior means from light response curve models. Only significant SMA lines are drawn (deciduous, solid black line; evergreen, dashed grey line). SMA analyses were performed only for relationships showing at least moderate correlation (R²>0.1, <i>P</i><0.1). Significance tests indicate differences in slope, elevation (y-intercept), or shift along common slope. +<i>P</i><0.1; * <i>P</i><0.05; <i>**P</i><0.01<i>; ***P</i><0.001. Note axes are on log scale.</p

Species-level average modeled light response curves for 3 invasive (non-grey) and 15 native (grey) species.

<p>Curves estimate each species’ area-based net photosynthetic rates (A_net) response to irradiance (photosynthetic photon flux density, PPFD), using all data with random effects for species. Only deciduous species are labeled, following codes listed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0196746#pone.0196746.t001" target="_blank">Table 1</a>. Corresponding parameter estimates for each species are illustrated in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0196746#pone.0196746.g002" target="_blank">Fig 2</a>.</p

Are endemics functionally distinct? Leaf traits of native and exotic woody species in a New Zealand forest - Fig 5

<p><b>Standardized major axis (SMA) relationships between (a) N</b>_<b>mass</b><b>and SLA and (b) N</b>_<b>area</b><b>and SLA.</b> Deciduous individuals are denoted by triangles (native closed, invasive open points) and native evergreen species (open circles) are shown in grey. +<i>P</i><0.1; * <i>P</i><0.05<i>; ***P</i><0.001. Note axes are on log scale.</p

Means and 95% credible intervals by species grouped by nativity and leaf habit.

<p>(a) area-based maximum photosynthetic rate (A_max,area), (b) area-based dark respiration rate (R_d,area), (c) apparent quantum yield (ϕ), (d) light compensation point (LCP), (e) mass-based maximum photosynthetic rate (A_max,mass), and (f) mass-based dark respiration rate (R_d,mass). Vertical lines show group level averages.</p