Scaling of leaf area with biomass in trees reconsidered: constant metabolically active sapwood volume per unit leaf area with height growth.

The article focuses on the scaling relationship between leaf area and metabolically active sapwood volume (VMASW) in woody plants, challenging the common assumption of hypoallometric scaling between metabolic rate and body mass. Using tetrazolium staining to distinguish metabolically active sapwood, the study on 22 individuals of Ricinus communis demonstrates that total leaf area scales isometrically (slope ≈ 1) with VMASW, rather than increasing disproportionately with sapwood volume as traditionally estimated. This finding suggests that natural selection favors maintaining a constant balance between carbon assimilation in leaves and carbon consumption by metabolically active sapwood as trees grow taller, with implications for understanding plant carbon economy, reproductive output, drought vulnerability, and allometric theory. The study also highlights that traditional methods overestimate sapwood metabolic activity and calls for further research across species to validate the generality of the leaf area–VMASW isometric relationship.