Stem Diameter (and Not Length) Limits Twig Leaf Biomass

Abstract

The relationship between leaf and stem biomass as well as the relationship between leaf biomass and stem length and diameter are important to our understanding of a broad range of important plant scaling relationship because of their relationship to photosynthesis and thus growth. To understand how twig architecture (i.e., current year leaves, and stem diameter and length) affects stem diameter and length, and leaf number and biomass, we examined the twigs of 64 woody species collected from three forest types along an elevational gradient in the Wuyi Mountains, Jiangxi Province, China. We also compared the scaling relationships we observed with biomass allocation patterns reported at the whole tree level. Our results revealed isometric relationship between leaf and stem biomass on twigs despite differences in forest communities and despite changes in environmental factors along an elevational gradient. Across the 64 species, from twigs to individual trees, leaf biomass scaled approximately as the 2.0-power of stem diameter (but not for stem length or leaf number). These results help to identify a general rule that operates at two different levels of biological organization (twigs and whole trees). The scaling relationship between leaf biomass and stem diameter in twigs is insensitive to differences in species composition, elevation, or forest type. We speculate that this rule emerges because stem diameter serves as a proxy for the amount of resources supplied per unit cross section to developing leaves and for the flow of photosynthates from mature leaves to the rest of the plant body.

Stem and leaf growth rates define the leaf size vs. number trade-off

“…It is reasonable to suppose that the resources hydraulically supplied by twigs depend on stem cross-sectional area and thus cross-sectional area is correlated with stem and leaf growth rates, a supposition that has been demonstrated empirically (Brodribb and Feild 2000; Normand et al 2008; Fan et al 2017). Previously, we argued that stem diameter (thus stem cross-sectional area) is the primary constraint on the total leaf biomass in twigs (Sun et al 2019). Our data also show that stem cross-sectional area scales isometrically with respect to stem mass (Fig.…”

“…M S = ρ V S . The hypothesis that annual stem growth (and thus stem mass) scales isometrically with respect to stem cross-sectional area ( A S ) as a consequence of hydraulic constraints on water and nutrient transport was tested and supported in previous studies (Fan et al 2017; Sun et al 2019) (i.e. M S ∞ A S ).…”

Application of leaf size and leafing intensity scaling across subtropical trees

“…The results indicate that the potential maximum total leaf mass (maximum leaf mass × leaf number) might be usually constrained by stem hydraulic or mechanical traits (Fan et al., 2017; Westoby et al., 2002) in different leaf habit groups. For example, prior studies suggest that leaf size generally scaled positively with respect to the diameter of the stem (Sun et al., 2019b; White, 1983), and in some plants, both mechanical and hydraulic constraints may be responsible for the limited maximum leaf size (Niinemets et al., 2002). Thus, constrained by maximum leaf size expand, the upper limit for the range of leaf size and number may be insensitive to different leaf habit groups.…”

“…The dominant species (e.g., Rhododendron simiarum , Schima superba , Cyclobalanopsis glauca , Symplocos sumuntia , Cyclobalanopsis multinervis , Tsuga chinensis , Taxus wallichiana , Acer elegantulum , Illicium angustisepalum ) and site characteristics of the Wuyishan National Nature Reserve were listed in Sun et al. (2019a,b).…”

“Diminishing Returns” in the Scaling between Leaf Area and Twig Size in Three Forest Communities Along an Elevation Gradient of Wuyi Mountain, China

“…), and a deciduous forest (DF; 1818 m a.s.l.). A total of 32, 20, and 23 species (including overlapping species) were respectively sampled in EF, MF, and DF ( [17]. The stand densities were 3033 trees/hm 2 , 1133 trees/hm 2 , and 2725 trees/hm 2 for EF, MF, and DF, respectively, with corresponding mean plant heights of 7.87 m, 10.56 m, and 6.94 m. Three 20 m × 20 m plots were established in each forest type, with at least a 20 m spacing between plots.…”