Functional linkages between leaf traits and net photosynthetic rate: reconciling empirical and mechanistic models

Abstract

Summary1. We had two objectives: (i) to determine the generality of, and extend the applicability of, a previously reported empirical relationship between leaf-level net photosynthetic rate ( A M , nmol g − 1 s − 1 ), specific leaf area (SLA, m 2 kg) and leaf nitrogen mass fraction ( N M , mmol g − 1 ); and (ii) to compare these empirical results with a mechanistic model of photosynthesis in order to provide a mechanistic justification for the empirical pattern. 2. Our results were based on both literature and original data. There were a total of 160 and 87 data points for the leaf-level and whole-plant data, respectively. 3. Our multiple regression for single leaves was ln( A M ) = 0·66 + 0·71 ln(SLA) + 0·79 ln( N M ), r 2 = − 0·80; only the intercept (0·11) differed for the whole-plant data. These results are not significantly different from previously published relationships. 4. We then converted the mechanistic model of Evans and Poorter, and a modified version which includes leaf lamina thickness ( T ) and leaf dry matter (tissue) concentration ( C M ), into directed acyclic graphs. We then derived reduced graphs that involved only T , C M , SLA, N M and A M . These were tested using structural equation modelling, with measured lamina thickness ( T ′ ) and leaf dry matter ratio (LDMR, g dry mass g − 1 fresh mass) as indicators of T and C M . The original Evans-Poorter model was rejected, but the modified version fitted the structural relationships well. The same qualitative models also applied to the whole-plant data, although the path coefficients sometimes differed. 5. Using simulations, we show that the original Evans-Poorter model predicts a positive correlation between SLA and N M that maximizes A M . The data closely follow this predicted relationship. The correlation between the actual values of A M (standardized units) and the predicted values obtained from the modified Evans-Poorter model was 0·74 and increased to 0·82 once three outlier points were removed. 6. These results provide a mechanistic explanation for the empirical trends relating leaf form and carbon fixation, and predict that SLA and leaf N must be quantitatively co-ordinated to maximize C fixation.

Plant- and stand-level variation in biophysical and physiological traits along tree density gradients in the Cerrado

“…the independent variable increase and the dependent variable decrease). to both a high leaf area displayed per unit mass invested (and hence efficient light capture) and high photosynthetic capacity (Reich et al, 1997(Reich et al, , 1999Shipley et al, 2005). Consistent with this general relationship, Franco et al, (2005) found that maximum net CO 2 assimilation increased with SLA for evergreen and deciduous species in the same area of this research.…”

“…Stem conductivity and total leaf surface area influence leafspecific hydraulic conductivity, a major determinant of leaf gas exchange capacity. Specific leaf area reflects properties of leaves as they are impacted by leaf water status and photosynthetic capacity (Reich et al, 1997(Reich et al, , 1999Shipley et al, 2005). To avoid the potential pitfalls of using correlations between scaling variables as indicators of causation, we established an a priori network of cause and effect relationships between biophysical, morphological and physiological traits of Neotropical savanna woody plants.…”

Response of Leaf Functional Traits of Cerasus yedoensis (Mats.) Yü Li to Serious Insect Attack

“…Thus, after a serious insect attack occurred, damaged C. yedoensis contained larger quantities of material investment per unit area to perform a highly efficient anti-herbivore defense underrious insect attack. This high material investment per unit area is necessary to yield low leaf moisture and SLA, but high leaf thickness, single leaf wet weight, and single leaf dry weight compared with the results described in previous studies [7,[14][15]. Furthermore, leaves with low SLA contain more ructural carbohydrates, such as lignin and cellulose in their cell walls , than those with high SLA [23].…”

“…In this study, the following hypotheses were presented: 1) Leaf moisture and SLA of damaged leaves may be lower than those of healthy leaves; by contrast, leaf thickness, and single leaf wet and dry weight of damaged leaves may be higher than those of healthy leaves because damaged leaves should invest great biomass on leaf structures per unit area to exhibit a highly efficient anti-herbivore defense under seriuos insect attack. Furthermore, thick leaves or leaves with denser tissues contained greater dry biomass per unit area and lower SLA levels than thin leaves [14][15]. 2) Damaged leaves may display a higher phenotypic plasticity in leaf functional characteristics (SLA, as the preferred agent of plant growth and defense strategies) [7][8][10][11] than healthy leaves to develop a highly efficient anti-herbivore defense; this result could occur because the enhanced phenotypic plasticity for any functional characteristic could benefit plants by allowing these organisms to maximize fitness in the environment [16,17].…”

Changing gears during succession: shifting functional strategies in young tropical secondary forests

“…Previous studies (Becknell and Powers 2014;Whitfeld et al 2014) also have reported either anomalous variation or increases in the CWM of leaf N, possibly due to an increase in the abundance of N-fixing species (Batterman et al 2013) or increases in soil pH. The expectation that leaf N will decrease during succession is predicated upon its positive correlation with A mass (Wright et al 2004), although recent studies have demonstrated that this relationship is also mediated by leaf structural attributes, density, and thickness, which comprise LMA (Poorter et al 2009;Shipley et al 2005Shipley et al , 2006. When controlling for variation in LMA, we found that correlations between leaf N and A mass for both size classes were conditionally independent (Online Resource 5).…”