How cellulose‐based leaf toughness and lamina density contribute to long leaf lifespans of shade‐tolerant species

Abstract

Summary• Cell wall fibre and lamina density may interactively affect leaf toughness and leaf lifespan. Here, we tested this with seedlings of 24 neotropical tree species differing in shade tolerance and leaf lifespan under standardized field conditions (140-867 d in gaps; longer in shade). We quantified toughness with a cutting test, explicitly seeking a mechanistic linkage to fibre.• Lamina density, but not fracture toughness, exhibited a plastic response to gaps vs shade, while neither trait was affected by leaf age. Toughness corrected for lamina density, a recently recognized indicator of material strength per unit mass, was linearly correlated with cellulose content per unit dry mass.• Leaf lifespan was positively correlated with cellulose and toughness in shade-tolerant species but only weakly in gap-dependent species. Leaf lifespan was uncorrelated with lamina thickness, phenolics and tannin concentrations. In path analysis including all species, leaf lifespan was directly enhanced by density and toughness, and indirectly by cellulose via its effect on toughness. Different suites of leaf traits were correlated with early seedling survival in gaps vs shade.• In conclusion, cellulose and lamina density jointly enhance leaf fracture toughness, and these carbon-based physical traits, rather than phenolic-based defence, explain species differences in herbivory, leaf lifespan and shade survival.

Photosynthetic ecophysiology of evergreen leaves in the woody angiosperms – a review

“…Leaf toughness is also increased by greater tissue density per se through an increased concentration of wall cellulose in a unit of leaf volume (Onoda et al 2011;Kitajima et al 2012). Other wall fractions such as hemicellulose and lignin did not significantly influence toughness as measured in the latter study, however lignin is known to enhance bending resistance -another aspect of leaf mechanical resistance (Alvarez-Clare and Kitajima 2007).…”

“…Bending resistance and other leaf mechanical traits are also increased by the greater thickness of the lamina, independently of its density (Onoda et al 2011; see also Fig. 2 D, E, F for data from Kitajima et al 2012).…”

“…Leaf mechanical properties have been shown to depend on LMA (e.g. see data from Kitajima et al (2012) plotted in Fig. 2 A, B, C).…”

Different combinations of multiple defence traits in an extrafloral nectary‐bearing plant growing under various habitat conditions

“…Under severe light conditions, the expressions of physical and chemical defence traits are costly in non-shade tolerant plants such as herb and pioneer tree species. Kitajima et al (2012) suggested that carbon allocation to cell walls (i.e. leaf toughness) is costly, particularly in non-shade tolerant plants.…”

Biodiversity and the functioning of tropical forests

“…Specific leaf area (SLA) increases light interception efficiency and should therefore increase productivity, but it also relates to a high turnover rate which decreases biomass retention and therefore biomass stocks (Shipley 2006). High specific force to punch (FPs; a measure for leaf toughness) increases leaf defence and should decrease productivity, but tough structures may increase biomass retention and biomass stocks (Kitajima et al 2012). Leaf nitrogen (N leaf ) and leaf phosphorus (P leaf ) are used in photosynthesis and growth (Mercado et al 2011), and should in this way stimulate productivity but decrease longevity and therefore biomass stocks.…”