Intraspecific Relationships among Wood Density, Leaf Structural Traits and Environment in Four Co-Occurring Species of Nothofagus in New Zealand

Abstract

Plant functional traits capture important variation in plant strategy and function. Recent literature has revealed that within-species variation in traits is greater than previously supposed. However, we still have a poor understanding of how intraspecific variation is coordinated among different traits, and how it is driven by environment. We quantified intraspecific variation in wood density and five leaf traits underpinning the leaf economics spectrum (leaf dry matter content, leaf mass per unit area, size, thickness and density) within and among four widespread Nothofagus tree species in southern New Zealand. We tested whether intraspecific relationships between wood density and leaf traits followed widely reported interspecific relationships, and whether variation in these traits was coordinated through shared responses to environmental factors. Sample sites varied widely in environmental variables, including soil fertility (25–900 mg kg–1 total P), precipitation (668–4875 mm yr–1), temperature (5.2–12.4 °C mean annual temperature) and latitude (41–46 °S). Leaf traits were strongly correlated with one another within species, but not with wood density. There was some evidence for a positive relationship between wood density and leaf tissue density and dry matter content, but no evidence that leaf mass or leaf size were correlated with wood density; this highlights that leaf mass per unit area cannot be used as a surrogate for component leaf traits such as tissue density. Trait variation was predicted by environmental factors, but not consistently among different traits; e.g., only leaf thickness and leaf density responded to the same environmental cues as wood density. We conclude that although intraspecific variation in wood density and leaf traits is strongly driven by environmental factors, these responses are not strongly coordinated among functional traits even across co-occurring, closely-related plant species.

Climate‐driven trends in stem wood density of tree species in the eastern United States: Ecological impact and implications for national forest carbon assessments

“…Additionally, several studies have documented intra‐annual variation in the density of new growth related to climate manipulations (Bouriaud, Leban, Bert, & Deleuze, ; Skomarkova et al, ), and similar relationships are widely used in dendrochronological studies to reconstruct historical climate records (Briffa et al, ). Such experimental evidence, when taken in context with our results and other findings of biogeographical trends of within‐species trends in wood density reported in the literature (Richardson et al, ; Thomas et al, ), indicates that plastic physiological responses are at least in part responsible for driving broad patterns of wood density variation along latitudinal and environmental gradients (Chave et al, ; Muller‐Landau, ; Wiemann & Williamson, ; Williamson & Wiemann, ). This is significant because it suggests that intraspecific variation, whether related to phenotypic plasticity or to regional variation in genotype (Anderegg, ), can contribute to the biogeography of plant traits, rather than broad patterns only arising from species sorting along environmental gradients (Chave et al, ; Swenson & Enquist, ; Swenson et al, ).…”

“…Alternatively, our results might indicate that other accounted for (temperature) and unaccounted for (e.g., competition, soil fertility gradients) factors are stronger drivers of wood density trends at the regional scale. For example, Reich et al (2014) found that the impact of aridity on biomass allocation patterns in trees was limited compared with the direct and indirect effects of temperature gradients, whereas Kunstler et al (2016) (Richardson et al, 2013;Thomas et al, 2004), indicates that plastic physiological responses are at least in part responsible for driving broad patterns of wood density variation along latitudinal and environmental gradients (Chave et al, 2006;Muller-Landau, 2004;Wiemann & Williamson, 2002;Williamson & Wiemann, 2010). This is significant because it suggests that intraspecific variation, whether related to phenotypic plasticity or to regional variation in genotype (Anderegg, 2015), can contribute to the biogeography of plant traits, rather than broad patterns only arising from species sorting along environmental gradients (Chave et al, 2006;Swenson & Enquist, 2007;Swenson et al, 2012).…”

The anatomical and compositional basis of leaf mass per area

“…LMA varies considerably across sun leaves of given species; to estimate LMA for the leaves measured for anatomy, we developed empirical equations relating LMA to thickness for sun leaves of given species (Richardson et al . ). For 14–26 sun leaves of each species we averaged turgid leaf thickness (LT) measured at the base, middle and tip between second‐order veins using digital callipers (± 0.01 mm; Fisher Scientific, PA, USA).…”

Biophysical dependences among functional wood traits

“…The integration of wood traits as an independent variation axis orthogonal to leaf traits has been emphasized in plant ecology (Baraloto, Timothy Paine, et al., ; Chave et al., ; Fortunel, Fine, & Baraloto, ; Richardson et al., ). Wood density is often taken as a key functional wood trait.…”