Non-structural carbohydrates (NSC) in plant tissue are frequently quantified to make inferences about plant responses to environmental conditions. Laboratories publishing estimates of NSC of woody plants use many different methods to evaluate NSC. We asked whether NSC estimates in the recent literature could be quantitatively compared among studies. We also asked whether any differences among laboratories were related to the extraction and quantification methods used to determine starch and sugar concentrations. These questions were addressed by sending sub-samples collected from five woody plant tissues, which varied in NSC content and chemical composition, to 29 laboratories. Each laboratory analyzed the samples with their laboratory-specific protocols, based on recent publications, to determine concentrations of soluble sugars, starch and their sum, total NSC. Laboratory estimates differed substantially for all samples. For example, estimates for Eucalyptus globulus leaves (EGL) varied from 23 to 116 (mean = 56) mg g(-1) for soluble sugars, 6-533 (mean = 94) mg g(-1) for starch and 53-649 (mean = 153) mg g(-1) for total NSC. Mixed model analysis of variance showed that much of the variability among laboratories was unrelated to the categories we used for extraction and quantification methods (method category R(2) = 0.05-0.12 for soluble sugars, 0.10-0.33 for starch and 0.01-0.09 for total NSC). For EGL, the difference between the highest and lowest least squares means for categories in the mixed model analysis was 33 mg g(-1) for total NSC, compared with the range of laboratory estimates of 596 mg g(-1). Laboratories were reasonably consistent in their ranks of estimates among tissues for starch (r = 0.41-0.91), but less so for total NSC (r = 0.45-0.84) and soluble sugars (r = 0.11-0.83). Our results show that NSC estimates for woody plant tissues cannot be compared among laboratories. The relative changes in NSC between treatments measured within a laboratory may be comparable within and between laboratories, especially for starch. To obtain comparable NSC estimates, we suggest that users can either adopt the reference method given in this publication, or report estimates for a portion of samples using the reference method, and report estimates for a standard reference material. Researchers interested in NSC estimates should work to identify and adopt standard methods.

These data demonstrate that variation in leaf size is associated with major changes in within-leaf support investments and in large modifications in integrated leaf chemical and structural characteristics. These size-dependent alterations can importantly affect general leaf structure vs. function scaling relationships. These data further demonstrate important life-form effects on and climatic differentiation in foliage support costs.

Summary• The implications of extensive variation in leaf size for biomass distribution between physiological and support tissues and for overall leaf physiological activity are poorly understood. Here, we tested the hypotheses that increases in leaf size result in enhanced whole-plant support investments, especially in compound-leaved species, and that accumulation of support tissues reduces average leaf nitrogen (N) content per unit dry mass ( N M ), a proxy for photosynthetic capacity.• Leaf biomass partitioning among the lamina, mid-rib and petiole, and whole-plant investments in leaf support (within-leaf and stem) were studied in 33 simple-leaved and 11 compound-leaved species.• Support investments in mid-ribs and petioles increased with leaf size similarly in simple leaves and leaflets of compound leaves, but the overall support mass fraction within leaves was larger in compound-leaved species as a result of prominent rachises. Within-leaf and within-plant support mass investments were negatively correlated. Therefore, the total plant support fraction was independent of leaf size and lamina dissection. Because of the lower N M of support biomass, the difference in N M between the entire leaf and the photosynthetic lamina increased with leaf size.• We conclude that whole-plant support costs are weakly size-dependent, but accumulation of support structures within the leaf decreases whole-leaf average N M , potentially reducing the integrated photosynthetic activity of larger leaves.

Morphological and photosynthetic acclimation of current-year needles to canopy gradients in light availability (seasonal mean integrated quantum flux density, Q(int)) was studied in the temperate conifer, Pinus sylvestris L., at two sites of contrasting nutrient availability. The nutrient-rich site supported a monospecific P. sylvestris stand on an old-field. The trees were approximately 30 years old and 19-21 m tall. Mean foliar N and P contents (+/- SD) were 1.53 +/- 0.11% and 0.196 +/- 0.017%, respectively. The nutrient-poor site was located on a raised bog supporting a sparse stand of 50- to 100-year-old trees, with a height of 1-2 m, and mean needle N and P contents of 0.86 +/- 0.12% and 0.074 +/- 0.010%, respectively. At both sites, needle thickness (T) and width (W) increased with increasing Qint, and leaf dry mass per unit leaf area (MA) was also greater at higher irradiance. The light effects on MA-the product of needle density (D) and volume to total area ratio (V/AT)-resulted primarily from large increases in V/AT with Qint rather than from modifications of D, which was relatively insensitive to light. Although needle morphology versus light relationships were qualitatively similar at both sites, needles were shorter, and the slopes of W, T, MA and V/AT versus light relationships were lower, at the nutrient-poor than at the nutrient-rich site, indicating that the plasticity of foliar morphological characteristics was affected by nutrient availability. As a result of lower plasticity, needles at the nutrient-poor site were narrower, thinner, and had lower MA at high irradiance than needles at the nutrient-rich site. The maximum carboxylase activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Vcmax) and the maximum photosynthetic electron transport rate (Jmax) scaled positively with foliar N and P contents. The correlations were generally stronger with P than with N, suggesting that needle photosynthetic capacity was more heavily limited by the availability of P than of N. The Jmax/Vcmax ratio was positively related to the foliar P/N ratio, indicating that Jmax was more strongly suppressed than Vcmax under conditions of low P availability. Phosphorus and N deficiency also limited the plasticity of foliar photosynthetic characteristics. There was a moderate increase in needle photosynthetic capacity of up to 1.6-fold from the bottom to the top of the canopy at the nutrient-rich site, but net assimilation rates were essentially independent of canopy position at the nutrient-poor site. Stomatal constraints on photosynthesis were similar between the sites, indicating that photosynthetic acclimation was curtailed at the biochemical level. We conclude that the foliar capacity for morphological and physiological acclimation to high light significantly decreases with decreasing nutrient availability in P. sylvestris, and that both N and P availability are potentially important determinants of foliar carbon gain capacities.

Summary 1.A trade-off between the investments in functional and support structures is a major determinant of leaf physiological activities. A variety of leaf shapes and venation densities occur in coexisting vegetation, but the costs and benefits of various leaf shapes and venation architectures are poorly understood. As the lever arms (location of leaf mass centre) become effectively longer as the maximum of lamina mass distribution shifts farther from the lamina base, we hypothesized that the fraction of lamina biomass in the mid-rib ( F MR ) is larger in leaves in which the centroid of lamina mass is located at, or greater than, half-leaf length ('elliptic' leaves) compared with leaves having the centroid of lamina mass located closer to the leaf base ('ovate' leaves). We further hypothesized that minor vein density ( ρ V ) is larger in leaves with lower F MR , compensating for lower investments in central support. Finally, we predicted that ρ V is lower in parallel/ palmate-veined than in pinnate-veined leaves, due to a more uniform distribution of large veins in parallel/palmate-veined leaves. 2. F MR and ρ V were studied in 44 herbs and woody seedlings with an overall variation in lamina fresh mass ( M FL ) of more than five orders of magnitude, and a sixfold variation in leaf longevity. Species were separated between pinnate-veined elliptic and ovate leaves, and parallel-or palmate-veined elliptic and ovate leaves. 3. Contrary to the hypothesis, support investment in the mid-rib was similar among leaf shapes, and scaled positively with leaf size and negatively with leaf longevity. However, F MR and ρ V were negatively associated. Fractional biomass investment in the mid-rib scaled with lamina size (fresh and dry mass and area), but at a common lamina size F MR was larger in pinnate-veined elliptic than in parallel/palmate-veined elliptic leaves. In addition, ρ V was larger in pinnate than in parallel/palmate-veined leaves, and the differences in lamina carbon content further suggested an overall greater investment of lamina biomass in the minor veins of pinnate-veined leaves.4. These data demonstrate that the effect of leaf shape on biomass investments in central support is less significant than predicted by biomechanical models, partly because of the trade-off between the biomass investments in central support and minor veins, which compensate for differences in lamina shape. These data collectively indicate that leaf size, longevity, shape and venation pattern can importantly modify the distribution of foliage biomass between support and functional tissues, and thus can alter foliage physiological activity and leaf functioning in environments with different resource availability.