title: Plasticity in seedling morphology, biomass allocation and physiology among ten temperate tree species in response to shade is related to shade tolerance and not leaf habit.
abstract: Mechanisms of shade tolerance in tree seedlings, and thus growth in shade, may differ by leaf habit and vary with ontogeny following seed germination. To examine early responses of seedlings to shade in relation to morphological, physiological and biomass allocation traits, we compared seedlings of 10 temperate species, varying in their leaf habit (broadleaved versus needle-leaved) and observed tolerance to shade, when growing in two contrasting light treatments - open (about 20% of full sunlight) and shade (about 5% of full sunlight). We analyzed biomass allocation and its response to shade using allometric relationships. We also measured leaf gas exchange rates and leaf N in the two light treatments. Compared to the open treatment, shading significantly increased traits typically associated with high relative growth rate (RGR) - leaf area ratio (LAR), specific leaf area (SLA), and allocation of biomass into leaves, and reduced seedling mass and allocation to roots, and net assimilation rate (NAR). Interestingly, RGR was not affected by light treatment, likely because of morphological and physiological adjustments in shaded plants that offset reductions of in situ net assimilation of carbon in shade. Leaf area-based rates of light-saturated leaf gas exchange differed among species groups, but not between light treatments, as leaf N concentration increased in concert with increased SLA in shade. We found little evidence to support the hypothesis of a increased plasticity of broadleaved species compared to needle-leaved conifers in response to shade. However, an expectation of higher plasticity in shade-intolerant species than in shade-tolerant ones, and in leaf and plant morphology than in biomass allocation was supported across species of contrasting leaf habit.
authors.affiliation: Institute of Dendrology, Polish Academy of Sciences, Kórnik, Poland.|Department of Ecosystem Science and Management, Texas A&M University, College Station, TX, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Chmura
authors.affiliation: Department of Ecosystem Science and Management, Texas A&M University, College Station, TX, USA.|Department of Forest Sites and Ecology, Faculty of Forestry, Poznań University of Life Sciences, Poznań, Poland.
authors.forename: J
authors.initials: J
authors.lastname: Modrzyński
authors.affiliation: Institute of Dendrology, Polish Academy of Sciences, Kórnik, Poland.
authors.forename: P
authors.initials: P
authors.lastname: Chmielarz
authors.affiliation: Department of Ecosystem Science and Management, Texas A&M University, College Station, TX, USA.|Hawkesbury Institute for the Environment, Western Sydney University, Penrith, NSW, Australia.
authors.forename: M G
authors.initials: MG
authors.lastname: Tjoelker
mesh_terms: D018533:Biomass; D002244:Carbon / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D010788:Photosynthesis; D018515:Plant Leaves / Q000033:anatomy & histology / Q000254:growth & development / Q000502:physiology / Q000528:radiation effects; D018517:Plant Roots / Q000033:anatomy & histology / Q000254:growth & development / Q000502:physiology / Q000528:radiation effects; D018526:Plant Transpiration; D036226:Seedlings / Q000033:anatomy & histology / Q000254:growth & development / Q000502:physiology / Q000528:radiation effects; D013472:Sunlight; D064028:Tracheophyta / Q000033:anatomy & histology / Q000254:growth & development / Q000502:physiology* / Q000528:radiation effects; D014197:Trees; D014329:Tropical Climate
chemical_list: D002244:Carbon; D009584:Nitrogen
keywords: Allometry; broadleaved; conifers; growth; partitioning; shade tolerance