Leaf cellulose density as the key determinant of inter- and intra-specific variation in leaf fracture toughness in a species-rich tropical forest

Abstract

Leaves as the main photosynthetic organ of plants must be well protected against various hazards to achieve their optimal lifespans. Yet, within-species variation and the material basis of leaf strength have been explored for very few species. Here, we present a large dataset of leaf fracture toughness from a species-rich humid tropical forest on Barro Colorado Island, Panama, reporting both among-and within-species variation in relation to light environment (sun-lit canopy versus shaded understorey) and ontogeny (seedlings versus adults). In this dataset encompassing 281 free-standing woody species and 428 species-light combinations, lamina fracture toughness varied ca 10 times. A central objective of our study was to identify generalizable patterns in the structural and material basis for interspecific variation in leaf lamina fracture toughness. The leaf lamina is a heterogeneous structure in which strong materials in cell walls, such as cellulose and lignin, contribute disproportionately to fracture toughness. We found significant increases in leaf fracture toughness from shade to sun and from seedling leaves to adult leaves. Both within and across species, leaf fracture toughness increased with total bulk density (dry biomass per unit volume) and cellulose mass concentration, but decreased with mass concentrations of lignin and hemicelluose. These bivariate relationships shift between light environments, but leaf cellulose density (cellulose mass per unit leaf volume) exhibits a common relationship with lamina fracture toughness between light environments and through ontogeny. Hence, leaf cellulose density is probably a universal predictor of leaf fracture toughness.

Decomposing leaf mass into metabolic and structural components explains divergent patterns of trait variation within and among plant species

“…2010), but higher in shade than sun at the wet site (Fig. S4b; as observed by Kitajima et al ., 2016). In summary, the decrease in optimal LL with increasing light (Kikuzawa 1991) appears sufficient by itself to create a LL counter-gradient, but the counter-gradient appears to be enhanced in some assemblages by greater structural mass fractions in shade vs. sun leaves.…”

“…A simpler alternative would be to modify our model (see methods) to account for variation in cell wall thickness (T CW ): for a given cell size, increasing T CW would lead to an increase in lamina density, cellulose per volume, toughness, and LL (Kitajima and Poorter 2010; Kitajima et al . 2012, 2016), and a decrease in mesophyll conductance and A max (Evans et al ., 2009; Terashima et al ., 2011; Onoda et al ., 2017).…”

Functional composition of epiphyte communities in the Colombian Andes

“…3). This trait gradient shows the influence of structural and chemical components that enhance leaf mass, and thus leaf toughness (Poorter et al 2009, Kitajima et al 2016. The prevalence of tougher leaves at sites with homogeneous height distributions indicates that these sites may be more homogeneously "canopy-like," as is expected in shorter forests at higher elevations.…”

Retrieving Foliar Traits of Quercus garryana var. garryana across a Modified Landscape Using Leaf Spectroscopy and LiDAR

“…Correlation between the leaf structure (p = 0.069) functional trait category and the CDF is suggestive, implying that Q. garryana individuals may also change their leaf structure based on proximity to competitors, with leaf structural values associated with stress tolerance decreasing with distance ( Figure 3) [39,40]. This is interesting as leaf structure is related to a leaf's defensive capabilities and longevity [13,54,55]. These findings suggest that individuals closer to the CDF have a higher stress tolerance, which could be caused by a more favorable microclimate compared to individuals living in the open meadow.…”

“…One technique that has benefited from these recent developments is the use of spectroscopy to identify plant functional traits [8][9][10][11]. These traits, which relate to plant growth and development strategies, provide biologically relevant information relating to photosynthesis and environmental drivers such as nutrient, water and stress regimes [12][13][14][15]. When evaluated at a site-or landscape-level, plant functional traits can be used to map functional diversity, community assembly and other ecosystem characteristics linked with biodiversity [16].…”