title: Correlation between relative growth rate and specific leaf area requires associations of specific leaf area with nitrogen absorption rate of roots.
abstract: Close correlations between specific leaf area (SLA) and relative growth rate (RGR) have been reported in many studies. However, theoretically, SLA by itself has small net positive effect on RGR because any increase in SLA inevitably causes a decrease in area-based leaf nitrogen concentration (LNCa), another RGR component. It was hypothesized that, for a correlation between SLA and RGR, SLA needs to be associated with specific nitrogen absorption rate of roots (SAR), which counteracts the negative effect of SLA on LNCa. Five trees and six herbs were grown under optimal conditions and relationships between SAR and RGR components were analyzed using a model based on balanced growth hypothesis. SLA varied 1.9-fold between species. Simulations predicted that, if SAR is not associated with SLA, this variation in SLA would cause a47% decrease in LNCa along the SLA gradient, leading to a marginal net positive effect on RGR. In reality, SAR was positively related to SLA, showing a 3.9-fold variation, which largely compensated for the negative effect of SLA on LNCa. Consequently, LNCa values were almost constant across species and a positive SLA-RGR relationship was achieved. These results highlight the importance of leaf-root interactions in understanding interspecific differences in RGR.
authors.affiliation: Department of Plant Ecology, Forestry and Forest Products Research Institute, Tsukuba, Ibaraki 305-8687, Japan.|Department of Natural Science, International Christian University, Osawa 3-10-2, Mitaka, Tokyo 181-8585, Japan.
authors.forename: Yoko
authors.initials: Y
authors.lastname: Osone
authors.affiliation: Department of Plant Ecology, Forestry and Forest Products Research Institute, Tsukuba, Ibaraki 305-8687, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Ishida
authors.affiliation: Nikko Botanical Garden, Graduate school of science, University of Tokyo, Nikko, Tochigi 321-1435, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Tateno
mesh_terms: D009584:Nitrogen / Q000378:metabolism*; D063245:Plant Development; D018515:Plant Leaves / Q000033:anatomy & histology* / Q000254:growth & development*; D018517:Plant Roots / Q000378:metabolism*; D010944:Plants / Q000378:metabolism
chemical_list: D009584:Nitrogen