title: Relative growth rate variation of evergreen and deciduous savanna tree species is driven by different traits.
abstract: OBJECTIVE
  Plant relative growth rate (RGR) depends on biomass allocation to leaves (leaf mass fraction, LMF), efficient construction of leaf surface area (specific leaf area, SLA) and biomass growth per unit leaf area (net assimilation rate, NAR). Functional groups of species may differ in any of these traits, potentially resulting in (1) differences in mean RGR of groups, and (2) differences in the traits driving RGR variation within each group. We tested these predictions by comparing deciduous and evergreen savanna trees.
  
  
  METHODS
  RGR, changes to biomass allocation and leaf morphology, and root non-structural carbohydrate reserves were evaluated for juveniles of 51 savanna species (34 deciduous, 17 evergreen) grown in a common garden experiment. It was anticipated that drivers of RGR would differ between leaf habit groups because deciduous species have to allocate carbohydrates to storage in roots to be able to flush leaves again, which directly compromises their LMF, whereas evergreen species are not subject to this constraint.
  
  
  RESULTS
  Evergreen species had greater LMF and RGR than deciduous species. Among deciduous species LMF explained 27 % of RGR variation (SLA 34 % and NAR 29 %), whereas among evergreen species LMF explained between 2 and 17 % of RGR variation (SLA 32-35 % and NAR 38-62 %). RGR and LMF were (negatively) related to carbohydrate storage only among deciduous species.
  
  
  CONCLUSIONS
  Trade-offs between investment in carbohydrate reserves and growth occurred only among deciduous species, leading to differences in relative contribution made by the underlying components of RGR between the leaf habit groups. The results suggest that differences in drivers of RGR occur among savanna species because these have different selected strategies for coping with fire disturbance in savannas. It is expected that variation in the drivers of RGR will be found in other functional types that respond differently to particular disturbances.
authors: Community Ecology & Conservation Group, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun 666303, Yunnan, China Resource Ecology Group kylewtomlinson@gmail.com.
authors: Kyle W
authors: KW
authors: Tomlinson
authors: Forest Ecology and Forest Management Group, Wageningen University, PO Box 47, 6700 AA Wageningen, The Netherlands.
authors: Lourens
authors: L
authors: Poorter
authors: Forest Ecology and Forest Management Group, Wageningen University, PO Box 47, 6700 AA Wageningen, The Netherlands.
authors: Frans
authors: F
authors: Bongers
authors: Department of Botany, University of Brasília, 70910-970, Federal District, Brazil.
authors: Fabian
authors: F
authors: Borghetti
authors: Resource Ecology Group.
authors: Loes
authors: L
authors: Jacobs
authors: Resource Ecology Group.
authors: Frank
authors: F
authors: van Langevelde
mesh_terms: D000704:Analysis of Variance; D050260:Carbohydrate Metabolism; D017753:Ecosystem; D016014:Linear Models; D018515:Plant Leaves / Q000033:anatomy & histology; D019655:Quantitative Trait, Heritable; D036226:Seedlings / Q000254:growth & development; D013045:Species Specificity; D013997:Time Factors; D014197:Trees / Q000254:growth & development*
keywords: Carbohydrate storage; RGR; deciduous; ecological traits; evergreen; functional types; plant growth variation; relative growth rate; savanna trees