Trait Scaling Relationships Research Articles

Are shade tolerance and canopy gradient affecting twig-leaf trait scaling relationships in temperate forests?

Are shade tolerance and canopy gradient affecting twig-leaf trait scaling relationships in temperate forests?

Disentangling the effect of growth from development in size-related trait scaling relationships.

In plant ecology, the terms growth and development are often used interchangeably. Yet these constitute two distinct processes. Plant architectural traits (e.g. number of successive forks) can estimate development stages. Here, we show the importance of including the effect of development stages to better understand size-related trait scaling relationships (i.e. between height and stem diameter). We focused on one common savanna woody species (Senegalia nigrescens) from the Greater Kruger Area, South Africa. We sampled 406 individuals that experience different exposure to herbivory, from which we collected four traits: plant height, basal stem diameter, number of successive forks (proxy for development stage), and resprouting. We analysed trait relationships (using standardized major axis regression) between height and stem diameter, accounting for the effect of ontogeny, exposure to herbivory, and resprouting. The number of successive forks affects the scaling relationship between height and stem diameter, with the slope and strength of the relationship declining in more developed individuals. Herbivory exposure and resprouting do not affect the overall height-diameter relationship. However, when height and stem diameter were regressed separately against number of successive forks, herbivory exposure and resprouting had an effect. For example, resprouting individuals allocate more biomass to both primary and secondary growth than non-resprouting plants in more disturbed conditions. We stress the need to include traits related to ontogeny so as to disentangle the effect of biomass allocation to primary and secondary growth from that of development in plant functional relationships.

Rhizome trait scaling relationships are modulated by growth conditions and are linked to plant fitness.

Rhizomes are important organs allowing many clonal plants to persist and reproduce under stressful climates with longer rhizomes, indicating enhanced ability of the plants to spread vegetatively. We do not, however, know either how rhizome construction costs change with increasing length or how they vary with environmental conditions. We analysed the rhizome length vs. mass scaling relationship, the plasticity in the scaling relationships, their genetic basis and how scaling relationships are linked to plant fitness. We used data from 275 genotypes of a clonal grass Festuca rubra originating from 11 localities and cultivated under four contrasting climates. Data were analysed using standard major axis regression, mixed-effect regression models and a structural equation model. Rhizome construction costs increased (i.e. lower specific rhizome length) with increasing length. The trait scaling relationships were modulated by cultivation climate, and its effects also interacted with the climate of origin of the experimental plants. With increasing length, increasing moisture led to a greater increase in rhizome construction costs. Plants with lower rhizome construction costs showed significantly higher fitness. This study suggests that rhizome scaling relationships are plastic, but also show genetic differentiation and are linked to plant fitness. Therefore, to persist under variable environments, modulation in scaling relationships could be an important plant strategy.

Increase in light interception cost and metabolic mass component of leaves are coupled for efficient resource use in the high altitude vegetation

Global syntheses of leaf trait scaling relationships report an increase in light interception costs or ‘diminishing returns’ with increase in leaf area. However, variation in light interception costs across ecological gradients and plant strategies to cope up with these costs are not adequately understood. We analyzed leaf area (A) – leaf dry mass (M), leaf water mass (W) – M and W – A scaling relationships in plants occurring in a high altitude region of western Himalaya across environmental gradients to understand changes in light interception cost and metabolic mass component. M represents light interception cost, whereas, W is considered as a proxy of metabolic mass component for liquid phase being the ultimate source of metabolic activity. Trait values were measured from 9278 leaves belonging to 136 dominant species occurring at different sites, slope aspects, elevations and habitat types. Overall, light interception cost increased with increasing A (scaling exponent (α) < 1 in A–M relationship) and metabolic mass component increased disproportionately high with increasing M and A. We found significant differences in scaling exponents of leaf trait relationship between sites, elevations, slope aspects and habitat types, indicating that increase in light interception cost was more evident at higher elevations, southern slopes and open habitats. Further, with increase in light interception cost, metabolic mass component also increased (α > 1 in W–M and W–A relationships). The changes in scaling exponents of various leaf trait relationships across ecological gradients indicated that vegetation of different regions have differences in light interception cost and metabolic mass component. Moreover, increasing light interception cost (increase in mechanical and hydraulic tissues) with increasing A and increasing metabolic mass (leaf thickness) with increasing A and M are favored in high altitude vegetation. This could be a key strategy of high altitude plants for efficient resource capture and use in harsh environments.

Size-dependent variations in individual traits and trait scaling relationships within a shade-tolerant evergreen treespecies.

The plant size-trait relationship is a fundamental dimension in the spectrum of plant form and function. However, it remains unclear whether the trait scaling relationship within species is modified by tree size. Investigating size-dependent trait covariations within species is crucial for understanding the ontogenetic constraints on the intraspecific economic spectrum and, more broadly, the structure and causes of intraspecific trait variations. We measured eight morphological, stoichiometric, and hydraulic traits for 604 individual plants of a shade-tolerant evergreen tree species, Litsea elongata, in a subtropical evergreen forest of eastern China. Individual trait values were regressed against tree basal diameter to evaluate size-dependent trait variations. Standardized major axis regression was employed to examine trait scaling relationships and to test whether there was a common slope and elevation in the trait scaling relationship across size classes. Small trees tended to have larger, thinner leaves and longer, slenderer stems than larger trees, which indicates an acquisitive economic strategy in juvenile trees. Leaf nitrogen concentrations increased with plant size, which was likely due to a high ratio of structural to photosynthetic nitrogen in the evergreen leaves of large trees. Bivariate trait scaling was minimally modified by tree size, although the elevation of some relationships differed between size classes. Our results suggest that there are common economic and biophysical constraints on intraspecific trait covariation, independent of tree size. Small and large trees tend to be located at opposite ends of an intraspecific plant economic spectrum.

Phosphorus deficiency alters scaling relationships between leaf gas exchange and associated traits in a wide range of contrasting Eucalyptus species.

Phosphorus (P) limitation is known to have substantial impacts on leaf metabolism. However, uncertainty remains around whether P deficiency alters scaling functions linking leaf metabolism to associated traits. We investigated the effect of P deficiency on leaf gas exchange and related leaf traits in 17 contrasting Eucalyptus species that exhibit inherent differences in leaf traits. Saplings were grown under controlled-environment conditions in a glasshouse, where they were subjected to minus and plus P treatments for 15 weeks. P deficiency decreased P concentrations and increased leaf mass per area (LMA) of newly-developed leaves. Rates of photosynthesis (A) and respiration (R) were also reduced in P-deficient plants compared with P-fertilised plants. By contrast, P deficiency had little effect on the temperature sensitivity of R. Irrespective of P treatment, on a log-log basis A and R scaled positively with increasing leaf nitrogen concentration [N] and negatively with increasing LMA. Although P deficiency had limited impact on A-R-LMA relationships, rates of CO2 exchange per unit N were consistently lower in P-deficient plants. Our results highlight the importance of P supply for leaf carbon metabolism and show how P deficiencies (i.e. when excluding confounding genotypic and environmental effects) can have a direct effect on commonly used leaf trait scaling relationships.

Nitrogen and phosphorus availabilities interact to modulate leaf trait scaling relationships across six plant functional types in a controlled-environment study.

Nitrogen (N) and phosphorus (P) have key roles in leaf metabolism, resulting in a strong coupling of chemical composition traits to metabolic rates in field-based studies. However, in such studies, it is difficult to disentangle the effects of nutrient supply per se on trait-trait relationships. Our study assessed how high and low N (5mM and 0.4mM, respectively) and P (1mM and 2μM, respectively) supply in 37 species from six plant functional types (PTFs) affected photosynthesis (A) and respiration (R) (in darkness and light) in a controlled environment. Low P supply increased scaling exponents (slopes) of area-based log-log A-N or R-N relationships when N supply was not limiting, whereas there was no P effect under low N supply. By contrast, scaling exponents of A-P and R-P relationships were altered by P and N supply. Neither R:A nor light inhibition of leaf R was affected by nutrient supply. Light inhibition was 26% across nutrient treatments; herbaceous species exhibited a lower degree of light inhibition than woody species. Because N and P supply modulates leaf trait-trait relationships, the next generation of terrestrial biosphere models may need to consider how limitations in N and P availability affect trait-trait relationships when predicting carbon exchange.

Plant functional shifts in the invaded range: a test with reciprocal forest invaders of Europe and North America

Summary Comparative trait analyses of native and invasive plant species have enriched our understanding of the strategies that make plants successful in particular contexts. However, it is generally unknown whether traits associated with invasiveness arise de novo in the introduced range or represent a case of ‘pre‐adaptation’ of some species to become invasive. We compared the functional strategies of two invasive species, Prunus serotina, a tree native to Eastern North America (ENA) and invasive in European forests, and Rhamnus cathartica, a shrub native to Europe and invasive in ENA, in both their native and invasive ranges. We measured leaf functional traits related to plant carbon and nitrogen economics in populations across northeastern ENA (New York) and northern France. This reciprocal field approach is unique, comparing in situ physiology within and between each species' shared ranges. For both species, we found striking differences in leaf economic traits and intraspecific trait scaling relationships. Prunus serotina exhibited similar photosynthetic rates in New York (native range) and France (invasive range), but French populations had significantly greater leaf carbon investments in the form of increased leaf respiration, construction costs, and carbon concentrations. Rhamnus cathartica exhibited 50–60% higher photosynthetic rates in New York (invasive range) than France (native range), along with increased leaf nitrogen costs. New York populations also had significantly lower nitrogen resorption efficiency, with autumn leaf nitrogen concentrations 69% lower in France. Intraspecific trait differences between native and invasive ranges indicate shifts in resource‐use strategies between the native and invasive range are possible in invasive species. While further investigations with additional species would be needed to determine the role of phenotypic plasticity and prevalence of post‐introduction trait shifts, our results question the assumption that functional strategies of invasive species are conserved from the native range and highlight the utility of measuring in situ functional strategies of reciprocal invaders to provide mechanistic understanding of invasions.

Higher photosynthetic capacity and different functional trait scaling relationships in erect bryophytes compared with prostrate species

Ecophysiological studies of bryophytes have generally been conducted at the shoot or canopy scale. However, their growth forms are diverse, and knowledge of whether bryophytes with different shoot structures have different functional trait levels and scaling relationships is limited. We collected 27 bryophyte species and categorised them into two groups based on their growth forms: erect and prostrate species. Twenty-one morphological, nutrient and photosynthetic traits were quantified. Trait levels and bivariate trait scaling relationships across species were compared between the two groups. The two groups had similar mean values for shoot mass per area (SMA), light saturation point and mass-based nitrogen (N(mass)) and phosphorus concentrations. Erect bryophytes possessed higher values for mass-based chlorophyll concentration (Chl(mass)), light-saturated assimilation rate (A(mass)) and photosynthetic nitrogen/phosphorus use efficiency. N(mass), Chl(mass) and A(mass) were positively related, and these traits were negatively associated with SMA. Furthermore, the slope of the regression of N(mass) versus Chl(mass) was steeper for erect bryophytes than that for prostrate bryophytes, whereas this pattern was reversed for the relationship between Chl(mass) and A(mass). In conclusion, erect bryophytes possess higher photosynthetic capacities than prostrate species. Furthermore, erect bryophytes invest more nitrogen in chloroplast pigments to improve their light-harvesting ability, while the structure of prostrate species permits more efficient light capture. This study confirms the effect of growth form on the functional trait levels and scaling relationships of bryophytes. It also suggests that bryophytes could be good models for investigating the carbon economy and nutrient allocation of plants at the shoot rather than the leaf scale.

Functional trait scaling relationships across 13 temperate mosses growing in wintertime

AbstractMosses growing in wintertime exert important ecosystem function, but we know little about their fundamental functional trait levels and scaling relationships across species. Thus the present study chose 13 common mosses growing under a temperate deciduous forest in wintertime to measure their light‐saturated assimilation rate (Amass), dark respiration rate (Rdmass), major element concentrations and stoichiometric ratios (Cmass, Nmass, Pmass, C:P, C:P and N:P) and the shoot mass per area (SMA). Their bivariate log–log scaling relationships were determined by standardized major axes approach. We confirmed that except Cmass, the nutrient concentrations and metabolic rates of our mosses were higher than that of mosses growing at warmer sites but the SMA was lower than for Sphagnum species. Furthermore, the functional trait levels were totally lower than those of vascular plant leaves except Pmass. Besides, we found the Nmass and Pmass were significantly positively related to Amass and Rdmass but negatively associated with SMA. The C:P and N:P were also closely linked with Amass, Rdmass and SMA. The SMA was significantly related to Rdmass but not to Amass. Functional trait relationships across the current species deviated from previous studies of mosses but were generally analogous to those of vascular plant leaves only with different scaling. The findings suggest that mosses allocated a greater proportion of nutrients to metabolic components rather than to the non‐photosynthetic tissues. In addition, phosphorus was associated more closely with other functional traits than was nitrogen and might play a greater role to withstand the cold temperatures in wintertime for mosses.

Contrasting leaf trait scaling relationships in tropical and temperate wet forest species

Summary We investigated whether plants adapted to thermally contrasting environments (e.g. tropical‐temperate habitats) exhibit inherent differences in leaf trait scaling relationships. Thirteen tropical and 12 temperate species (all characteristic of wet forests) were grown in a glasshouse (25/20 °C day/night). A range of leaf traits were quantified, including mass‐based leaf nitrogen [N], mass per unit area (LMA), light‐saturated photosynthesis (A) and respiration (Rdark). Average area‐ and mass‐based rates of net CO2 exchange were higher in the temperate species, compared to their tropical counterparts. Average leaf [N] and LMA values were also higher in temperate species than in their tropical counterparts. The higher LMA in the metabolically more active temperate species was the most striking contrast to the patterns and predictions of the GLOPNET leaf trait data base, and was associated with different elevations (i.e. y‐axis intercepts) but not slopes of bivariate trait scaling relationships. As expected, mass‐based rates of A and Rdark scaled positively with increasing [N] and negatively with increasing LMA in both tropical and temperate species. No differences were found between temperate and tropical species groups in terms of log‐log scaling relationships linking A and Rdark to N. However, at any given LMA, mass‐based values of [N], A and Rdark were all higher in the temperate species than in their tropical counterparts. Underpinning higher A in temperate species was a higher capacity for carboxylation (Vcmax) and RuBP regeneration (Jmax), with Jmax:Vcmax being greater in temperate species. In conclusion, our results suggest that as a consequence of greater overall N investment as well as greater proportional N investment in metabolic capacity, cool‐adapted temperate wet forest species exhibit higher photosynthetic and respiration rates than their warm‐adapted tropical counterparts when compared in a common environment.

Different plant trait scaling in dry versus wet Central European meadows

AbstractQuestionTrait scaling relationships involve multiple trade‐offs and allometric constraints between the traits of co‐existing species. Alternative trait relationships, particularly between plant size and other traits, are expected in response to combinations of different biotic and abiotic filters. To what extent does the expected convergence in plant attributes to water shortage and disturbance produce different trait scaling relationships in dry vs wet meadows under various disturbance regimes?LocationsOne test meadow in South Bohemia and one in South Moravia (i.e. wet vs dry Central Europe meadows), Czech Republic.MethodsSelected species were sampled in mown and abandoned plots within each site. Several plant traits were measured to provide information on plant strategies related to growth, resource acquisition and carbon–water economy.ResultsTrait differentiation among co‐existing species was strong in both meadows, and generally stronger than differentiation caused by mowing and site effects. Different trait scaling relationships with plant height were observed across the meadows, particularly showing a more independent trait differentiation linked to water–carbon economy at the dry site. Mowing tended to reinforce the effect of water limitation on traits and on trait scaling. In contrast, mowing cessation tended to resemble the effect of humid conditions on trait relationships.ConclusionsThe results advocate incorporating trait scaling relationships between species into vegetation models and community assembly assessments, therefore accounting for processes of plant co‐existence along combined spectra of light, water and disturbance regimes. These gradients affect alternative life‐history strategies and possibly sustain different species co‐existence patterns based on different trait scaling. The results particularly advocate a convergence in traits and trait scaling relationships in response to the combination of disturbance and water limitation.

A general integrative model for scaling plant growth, carbon flux, and functional trait spectra

Linking functional traits to plant growth is critical for scaling attributes of organisms to the dynamics of ecosystems and for understanding how selection shapes integrated botanical phenotypes. However, a general mechanistic theory showing how traits specifically influence carbon and biomass flux within and across plants is needed. Building on foundational work on relative growth rate, recent work on functional trait spectra, and metabolic scaling theory, here we derive a generalized trait-based model of plant growth. In agreement with a wide variety of empirical data, our model uniquely predicts how key functional traits interact to regulate variation in relative growth rate, the allometric growth normalizations for both angiosperms and gymnosperms, and the quantitative form of several functional trait spectra relationships. The model also provides a general quantitative framework to incorporate additional leaf-level trait scaling relationships and hence to unite functional trait spectra with theories of relative growth rate, and metabolic scaling. We apply the model to calculate carbon use efficiency. This often ignored trait, which may influence variation in relative growth rate, appears to vary directionally across geographic gradients. Together, our results show how both quantitative plant traits and the geometry of vascular transport networks can be merged into a common scaling theory. Our model provides a framework for predicting not only how traits covary within an integrated allometric phenotype but also how trait variation mechanistically influences plant growth and carbon flux within and across diverse ecosystems.

Genotype to Phenotype: Physiological Control of Trait Size and Scaling in Insects

For almost a century, biologists have used trait scaling relationships (bi-variate scatter-plots of trait size versus body size) to characterize phenotypic variation within populations, and to compare animal shape across populations or species. Scaling relationships are a popular metric because they have long been thought to reflect underlying patterns of trait growth and development. However, the physiological mechanisms generating animal scaling are not well understood, and it is not yet clear how scaling relationships evolve. Here we review recent advances in developmental biology, genetics, and physiology as they pertain to the control of growth of adult body parts in insects. We summarize four mechanisms known to influence either the rate or the duration of cell proliferation within developing structures, and suggest how mutations in these mechanisms could affect the relative sizes of adult body parts. By reviewing what is known about these four processes, and illustrating how they may contribute to patterns of trait scaling, we reveal genetic mechanisms likely to be involved in the evolution of insect form.