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

Abstract

The trade-off between leaf number and individual leaf size on current-year shoots (twigs) is crucial to light interception and thus net carbon gain. However, a theoretical basis for understanding this trade-off remains elusive. Here, we argue that this trade-off emerges directly from the relationship between annual growth in leaf and stem mass, a hypothesis that predicts that maximum individual leaf size (i.e. leaf mass, Mmax, or leaf area, Amax) will scale negatively and isometrically with leafing intensity (i.e. leaf number per unit stem mass, per unit stem volume or per stem cross-sectional area). We tested this hypothesis by analysing the twigs of 64 species inhabiting three different forest communities along an elevation gradient using standardized major axis (SMA) analyses. Across species, maximum individual leaf size (Mmax, Amax) scaled isometrically with respect to leafing intensity; the scaling constants between maximum leaf size and leafing intensity (based on stem cross-sectional area) differed significantly among the three forests. Therefore, our hypothesis successfully predicts a scaling relationship between maximum individual leaf size and leafing intensity, and provides a general explanation for the leaf size-number trade-off as a consequence of mechanical-hydraulic constraints on stem and leaf growth per year.

Linking Leaf Water Potential, Photosynthesis and Chlorophyll Loss With Mechanisms of Photo- and Antioxidant Protection in Juvenile Olive Trees Subjected to Severe Drought

“…Stem elongation (cm) and the number of leaves per plant were measured for each plant at the beginning of stress (H i , L i ), at 30 days (H 30 , L 30 ) and at 60 days (H 60 , L 60 ) of drought. Stem growth rate (SGR) and leaf production rate (LPR) were estimated from these parameters according to the equations described by Sun et al (2019) and Rodrigues de Lima et al 2019.…”

Morphometry of leaf and shoot variables to assess aboveground biomass structure and carbon sequestration by different varieties of white mulberry (Morus alba L.)

“…Previously, Dombroskie and Aarssen (2012) found a leaf size-leafing intensity trade-off at the plant level in 16 broadleaf tree species in Canada. Similarly, Sun et al (2019) found a diminishing return between leaf size and leafing intensity in bamboo species.…”

Application of leaf size and leafing intensity scaling across subtropical trees

“…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).…”

“…Furthermore, the leaf–stem growth hypothesis showed that the scaling for the trade‐off between individual leaf mass and leafing intensity is governed by – α , where α is the exponents of total leaf mass versus stem mass (Sun et al., 2019a). Therefore, the isometric trade‐off in leaf size/number may deduce from the tightly isometric relationship between leaf and stem (Yang et al., 2008).…”

“…Mathematically, the maximum leaf mass in twig can have a statistically significant effect on the total leaf mass ( M leaf ) and thus leafing intensity. Recent studies have shown that maximum leaf mass and area are scales as the −1.0 power of leafing intensity (LIV and LIM) across three different forest types (Sun et al., 2019a). Following the same logic as above, it is reasonable to suppose that the minimum leaf mass in twig has a less impact on total leaf mass.…”