Variation in leaf and twig CO2 flux as a function of plant size: a comparison of seedlings, saplings and trees

Abstract

Rates of tissue-level function have been hypothesized to decline as trees grow older and larger, but relevant evidence to assess such changes remains limited, especially across a wide range of sizes from saplings to large trees. We measured functional traits of leaves and twigs of three cold-temperate deciduous tree species in Minnesota, USA, to assess how these vary with tree height. Individuals ranging from 0.13 to 20 m in height were sampled in both relatively open and closed canopy environments to minimize light differences as a potential driver of size-related differences in leaf and twig properties. We hypothesized that (H1) gas-exchange rates, tissue N concentration and leaf mass per unit area (LMA) would vary with tree size in a pattern reflecting declining function in taller trees, yet maintaining (H2) bivariate trait relations, common among species as characterized by the leaf economics spectrum. Taking these two ideas together yielded a third, integrated hypothesis that (H3) nitrogen (N) content and gas-exchange rates should decrease monotonically with tree size and LMA should increase. We observed increasing LMA and decreasing leaf and twig Rd with increasing size, which matched predictions from H1 and H3. However, opposite to our predictions, leaf and twig N generally increased with size, and thus had inverse relations with respiration, rather than the predicted positive relations. Two exceptions were area-based leaf N of Prunus serotina Ehrh. in gaps and mass-based leaf N of Quercus ellipsoidalis E. J. Hill in gaps, both of which showed qualitatively hump-shaped patterns. Finally, we observed hump-shaped relationships between photosynthetic capacity and tree height, not mirroring any of the other traits, except in the two cases highlighted above. Bivariate trait relations were weak intra-specifically, but were generally significant and positive for area-based traits using the pooled dataset. Results suggest that different traits vary with tree size in different ways that are not consistent with a universal shift towards a lower 'return on investment' strategy. Instead, species traits vary with size in patterns that likely reflect complex variation in water, light, nitrogen and carbon availability, storage and use.

Global variability in leaf respiration in relation to climate, plant functional types and leaf traits

“…To create a global leaf respiration and associated leaf traits (Glo-bResp) database, we combined data from recent field campaigns (Table S1) with previously published data (Table S2). Data were obtained from recent publications Slot et al, 2013Slot et al, , 2014bWeerasinghe et al, 2014) and the TRY trait database (Kattge et al, 2011) that included published studies (Mooney et al, 1983;Oberbauer & Strain, 1985, 1986Chazdon & Kaufmann, 1993;Kamaluddin & Grace, 1993;Kloeppel et al, 1993;Garc ıa-N uñez et al, 1995;Kloeppel & Abrams, 1995;Zotz & Winter, 1996;Grueters, 1998;Miyazawa et al, 1998;Reich et al, 1998a;Bolstad et al, 1999;Craine et al, 1999;Mitchell et al, 1999;Niinemets, 1999;Wright et al, 2001Wright et al, , 2004Wright et al, , 2006Meir et al, 2002Meir et al, , 2007Wright & Westoby, 2002;Veneklaas & Poot, 2003;Tjoelker et al, 2005;Poorter & Bongers, 2006;Swaine, 2007;Sendall & Reich, 2013). The combined database contains data from 100 thermally contrasting sites (899 species representing 136 families, and c. 1200 species-site combinations) from biomes ranging from 69°N to 43°S and from sea level to 3450 m above sea level (asl) ( Fig.…”

Variations in leaf economics spectrum traits for an evergreen coniferous species: Tree size dominates over environment factors

“…Therefore, tree size was a stronger driver of leaf traits than environmental factors. The most likely reason for this is that previous studies usually used seedlings, which might be more sensitive to environmental variables than mature trees, and information on large trees is still limited (Díaz et al, ; Drake et al, ; Sendall & Reich, ). Furthermore, an evaluation of environmental variables, especially light intensity, is often difficult for larger trees.…”

“…However, there seems to be no consensus on the effect of tree size on other traits. Mass‐based leaf N content (N mass ) was positively related to tree size in evergreen trees (He & Yan, ; Kenzo et al, ) and in a deciduous tree (Sendall & Reich, ), whereas no significant correlation was found in two evergreen conifers (Niinemets, ). The size dependence of N mass was different between two tropical tree species (Martin & Thomas, ) and between two deciduous tree species (Park et al, ).…”

Trade‐offs in juvenile growth potential vs. shade tolerance among subtropical rain forest trees on soils of contrasting fertility

“…Despite the clear evidence that differences in growth–light relationships among species correspond with habitat light affinity, it is important to note that shade tolerance is known to vary with ontogeny (Lusk ). We measured a relatively narrow range of sapling size, but traits associated with shade tolerance, such as leaf gas exchange and specific leaf area, may still have varied among our sampled trees due to size differences (Thomas ; Sendall & Reich ). Likewise, ontogenetic patterns of RGR and allocation may differ for species with different shade tolerance rankings.…”