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1.  Leaf Longevity as a Normalization Constant in Allometric Predictions of Plant Production 
PLoS ONE  2013;8(12):e81873.
In metabolic scaling theory the size-dependence of plant processes is described by a power function of form Y=YoMθ where Y is a characteristic such as plant productivity that changes with plant size (M) raised to the θth power and Yo is a normalization constant that adjusts the general relationship across environments and species. In essence, the theory considers that the value of θ arises in the size-dependent relationship between leaf area and vascular architecture that influences plant function and that Yo modulates this general relationship to account for ecological and evolutionary effects on the exchange of resources between plant and environment. Enquist and colleagues have shown from first principles that Yo is a function of carbon use efficiency, the carbon fraction of a plant, the area-specific carbon assimilation rate of a leaf, the laminar area of a leaf, and the mass of a leaf. We show that leaf longevity provides a functional integration of these traits that can serve as a simpler normalization in scaling plant productivity for individual species and potentially for mixed-species communities as well.
doi:10.1371/journal.pone.0081873
PMCID: PMC3849297  PMID: 24312595
2.  Experimental test for adaptive differentiation of ginseng populations reveals complex response to temperature 
Annals of Botany  2012;110(4):829-837.
Background and Aims
Local climatic adaptation can influence species' response to climate change. If populations within a species are adapted to local climate, directional change away from mean climatic conditions may negatively affect fitness of populations throughout the species' range.
Methods
Adaptive differentiation to temperature was tested for in American ginseng (Panax quinquefolius) by reciprocally transplanting individuals from two populations, originating at different elevations, among temperature treatments in a controlled growth chamber environment. Fitness-related traits were measured in order to test for a population × temperature treatment interaction, and key physiological and phenological traits were measured to explain population differences in response to temperature.
Key Results
Response to temperature treatments differed between populations, suggesting genetic differentiation of populations. However, the pattern of response of fitness-related variables generally did not suggest ‘home temperature’ advantage, as would be expected if populations were locally adapted to temperature alone.
Conclusions
Failure consistently to detect a ‘home temperature’ advantage response suggests that adaptation to temperature is complex, and environmental and biotic factors that naturally covary with temperature in the field may be critical to understanding the nature of adaptation to temperature.
doi:10.1093/aob/mcs155
PMCID: PMC3423813  PMID: 22811509
Adaptive differentiation; American ginseng; climate change; demography; growth chamber; local adaptation; Panax quinquefolius; temperature
3.  Contributions of leaf photosynthetic capacity, leaf angle and self-shading to the maximization of net photosynthesis in Acer saccharum: a modelling assessment 
Annals of Botany  2012;110(3):731-741.
Background and Aims
Plants are expected to maximize their net photosynthetic gains and efficiently use available resources, but the fundamental principles governing trade-offs in suites of traits related to resource-use optimization remain uncertain. This study investigated whether Acer saccharum (sugar maple) saplings could maximize their net photosynthetic gains through a combination of crown structure and foliar characteristics that let all leaves maximize their photosynthetic light-use efficiency (ɛ).
Methods
A functional–structural model, LIGNUM, was used to simulate individuals of different leaf area index (LAIind) together with a genetic algorithm to find distributions of leaf angle (LA) and leaf photosynthetic capacity (Amax) that maximized net carbon gain at the whole-plant level. Saplings grown in either the open or in a forest gap were simulated with Amax either unconstrained or constrained to an upper value consistent with reported values for Amax in A. saccharum.
Key Results
It was found that total net photosynthetic gain was highest when whole-plant PPFD absorption and leaf ɛ were simultaneously maximized. Maximization of ɛ required simultaneous adjustments in LA and Amax along gradients of PPFD in the plants. When Amax was constrained to a maximum, plants growing in the open maximized their PPFD absorption but not ɛ because PPFD incident on leaves was higher than the PPFD at which ɛmax was attainable. Average leaf ɛ in constrained plants nonetheless improved with increasing LAIind because of an increase in self-shading.
Conclusions
It is concluded that there are selective pressures for plants to simultaneously maximize both PPFD absorption at the scale of the whole individual and ɛ at the scale of leaves, which requires a highly integrated response between LA, Amax and LAIind. The results also suggest that to maximize ɛ plants have evolved mechanisms that co-ordinate the LA and Amax of individual leaves with PPFD availability.
doi:10.1093/aob/mcs106
PMCID: PMC3400442  PMID: 22665700
Acer saccharum; sugar maple; canopy architecture; functional–structural modelling; LIGNUM; scaling; photosynthetic light-use efficiency; leaf Amax; leaf angle; nitrogen; resource use; optimization; plant evolution; plasticity; acclimation
4.  Optimal photosynthetic use of light by tropical tree crowns achieved by adjustment of individual leaf angles and nitrogen content 
Annals of Botany  2009;103(5):795-805.
Background and Aims
Theory for optimal allocation of foliar nitrogen (ONA) predicts that both nitrogen concentration and photosynthetic capacity will scale linearly with gradients of insolation within plant canopies. ONA is expected to allow plants to efficiently use both light and nitrogen. However, empirical data generally do not exhibit perfect ONA, and light-use optimization per se is little explored. The aim was to examine to what degree partitioning of nitrogen or light is optimized in the crowns of three tropical canopy tree species.
Methods
Instantaneous photosynthetic photon flux density (PPFD) incident on the adaxial surface of individual leaves was measured along vertical PPFD gradients in tree canopies at a frequency of 0·5 Hz over 9–17 d, and summed to obtain the average daily integral of PPFD for each leaf to characterize its insolation regime. Also measured were leaf N per area (Narea), leaf mass per area (LMA), the cosine of leaf inclination and the parameters of the photosynthetic light response curve [photosynthetic capacity (Amax), dark respiration (Rd), apparent quantum yield (ϕ) and curvature (θ)]. The instantaneous PPFD measurements and light response curves were used to estimate leaf daily photosynthesis (Adaily) for each leaf.
Key Results
Leaf Narea and Amax changed as a hyperbolic asymptotic function of the PPFD regime, not the linear relationship predicted by ONA. Despite this suboptimal nitrogen partitioning among leaves, Adaily did increase linearly with PPFD regime through co-ordinated adjustments in both leaf angle and physiology along canopy gradients in insolation, exhibiting a strong convergence among the three species.
Conclusions
The results suggest that canopy tree leaves in this tropical forest optimize photosynthetic use of PPFD rather than N per se. Tropical tree canopies then can be considered simple ‘big-leaves’ in which all constituent ‘small leaves’ use PPFD with the same photosynthetic efficiency.
doi:10.1093/aob/mcn265
PMCID: PMC2707872  PMID: 19151040
Optimal resource allocation; nitrogen; photosynthetic capacity; leaf mass per area; tropical trees; radiation use efficiency; scaling; leaf angle; canopy architecture; big leaf model
5.  Contemporary perspectives on the niche that can improve models of species range shifts under climate change 
Biology Letters  2008;4(5):573-576.
Pioneering efforts to predict shifts in species distribution under climate change used simple models based on the correlation between contemporary environmental factors and distributions. These models make predictions at coarse spatial scales and assume the constancy of present correlations between environment and distribution. Adaptive management of climate change impacts requires models that can make more robust predictions at finer spatio-temporal scales by accounting for processes that actually affect species distribution on heterogeneous landscapes. Mechanistic models of the distribution of both species and vegetation types have begun to emerge to meet these needs. We review these developments and highlight how recent advances in our understanding of relationships among the niche concept, species diversity and community assembly point the way towards more effective models for the impacts of global change on species distribution and community diversity.
doi:10.1098/rsbl.2008.0181
PMCID: PMC2610068  PMID: 18664418
global change; species distribution; biodiversity; modelling; cross-scaling;
6.  Do Interspecific Differences in Sapling Growth Traits Contribute to the Co-dominance of Acer saccharum and Fagus grandifolia? 
Annals of Botany  2007;101(1):103-109.
Background and Aims
Acer saccharum and Fagus grandifolia are among the most dominant late-successional tree species in North America. The influence of sapling growth responses to canopy gaps on the co-dominance of the two species in an old-growth forest in southern Quebec, Canada was examined. Two predictions were evaluated: (a) F. grandifolia is more shade tolerant than A. saccharum due to greater sapling leaf area and net production per sapling in closed-canopy conditions; and (b) the height growth rate of A. saccharum in canopy gaps is greater than that of F. grandifolia due to increased net production per sapling.
Methods
Sapling crown allometry, net production and height growth rates were compared between and within the two species in closed canopy vs. canopy gaps. Standardized major axis regression was used to analyse differences in crown allometry.
Key Results
F. grandifolia had greater crown projection, sapling leaf area and net production rate per sapling than A. saccharum in closed-canopy conditions. In response to canopy gaps, net production per sapling increased to the same degree in both species. The net production per sapling of F. grandifolia thus was much greater than that of A. saccharum in both canopy gap and closed-canopy conditions. The height growth rate of both species increased in canopy gaps, but the degree of increase was greater in F. grandifolia than in A. saccharum.
Conclusions
F. grandifolia regenerated more successfully than A. saccharum in both closed-canopy conditions and canopy gaps, which indicates that the co-dominance of the two species cannot be maintained simply by interspecific differences in shade tolerance and growth in gaps. Previous research showed that although Fagus and Acer shared dominance at this site, their relative dominance shifted with edaphic conditions. This suggests that the widespread co-dominance of the two species in eastern North American forests is maintained by the joint influence of canopy disturbance and species-specific responses to the heterogeneity of moisture and fertility regimes within forested landscapes.
doi:10.1093/aob/mcm259
PMCID: PMC2701832  PMID: 17942590
American beech; crown architecture; crown allometry; height growth rate; net production rate; saplings; sugar maple

Results 1-6 (6)