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

In trees, the trade-off between leaf number and individual leaf size on current year shoots (twigs) is crucial to light interception. This relationship has consequences on leaf energy balance as well as carbon uptake at the whole plant level. Previous studies have suggested that it is advantageous for plants to have smaller but more numerous leaves. This is because these leaves contribute to the maintenance of axillary buds. In other words, the more leaves, the more buds. Yet much variation in leaf size and number across and within species has been observed, and so the theoretical basis for the leaf size and number trade-off continues to remain elusive.

Y. S. Chen collecting the current-year twig from tree canopy in the National Nature Reserve of Wuyi Mountain, China. Image credit: J. Sun.

In a recent study published in AoBP, Sun et al. present a model (Stem-Leaf Growth Hypothesis, SLGH) to provide a theoretical explanation for the trade-off between the maximum leaf size vs. leafing intensity. The authors found that the scaling exponents of maximum leaf size vs. the leafing intensity are nearly close to -1.0 and are insensitive to forest types and different elevations. These results successfully provide a general explanation for this trade-off, as a consequence of mechanical-hydraulic constraints on stem and leaf growth rates. The authors suggest that future work should test this model further by comparing data from different plant families and species groups.

Researcher highlight

Jun Sun

Jun Sun conducted his PhD in ecology at the Fujian Normal University, China graduating in September 2018. Jun currently holds a research assistant position with Professor Dongliang Cheng in the College of Geography Sciences at the Fujian Normal University. 

Jun’s scientific interests are centered on evolutionary ecology, especially plant functional traits in relation to environment change. Recently, he has been trying to link traditional plant life history strategy theories and allometric growth law, aiming to explore a fundamental mechanism underlying plant evolutionary strategies. He is also interested in linking plant traits that modulate forest soil carbon fluxes, and how nutrient cycling processes, such as litter soluble organic carbon and nitrogen, stimulate soil organic matter decomposition rates.