Leaf area ratio and net assimilation rate of 24 wild species differing in relative growth rate

Summary Which factors cause fast-growing plant species to achieve a higher relative growth rate than slow-growing ones? To answer this question 24 wild species were grown from seed in a growth chamber under conditions of optimal nutrient supply and a growth analysis was carried out. Mean relative growth rate, corrected for possible ontogenetic drift, ranged from 113 to 356 mg g^–1 day^–1. Net assimilation rate, the increase in plant dry weight per unit leaf area and unit time, varied two-fold between species but no correlation with relative growth rate was found. The correlation between leaf area ratio, the ratio between total leaf area and total plant weight, and relative growth rate was very high. This positive correlation was mainly due to the specific leaf area, the ratio between leaf area and leaf weight, and to a lesser extent caused by the leaf weight ratio, the fraction of plant biomass allocated to the leaves. Differences in relative growth rate under conditions of optimum nutrient supply were correlated with the soil fertility in the natural habitat of these species. It is postulated that natural selection in a nutrient-rich environment has favoured species with a high specific leaf area and a high leaf weight ratio, and consequently a high leaf area ratio, whereas selection in nutrient-poor habitats has led to species with an inherently low specific leaf area and a higher fraction of root mass, and thus a low leaf area ratio.     

What determines interspecific variation in relative growth rate of <Emphasis Type="Italic">Eucalyptus</Emphasis> seedlings?

The present study examines relative growth rate (RGR) and its determinants in seedlings of nine Eucalyptus species. Species were selected from mesic (1,800 mm a⁻¹ rainfall) through to semi-arid habitats (300 mm a⁻¹), and thus, notionally vary in “stress” tolerance. Seedlings were grown in a glasshouse during early summer and received between 33 mol and 41 mol PAR m⁻² day⁻¹ . The mean RGR varied among species—from a minimum of 66 mg g⁻¹ day⁻¹ in E. hypochlamydea to a maximum of 106 mg g⁻¹ day⁻¹ in E. delegatensis. RGR was positively related to rainfall at the sites of seed collection. Neither specific leaf area (SLA) nor net assimilation rate was related to rainfall or RGR. While the absence of relationships with SLA and net assimilation rate contrasts with other studies and species, we cannot rule out the effects of sample size (n=9 species) and modest ranges in SLA and RGR. The ratio of leaf mass to total mass (LMR) varied from 0.49±0.07 g g⁻¹ in E. socialis to 0.74±0.04 g g⁻¹ in E. delegatensis and was strongly positively related with rainfall (r ²=0.77). Interspecific differences in RGR were strongly related to LMR (positive relationship, r ²=0.50) and the rate of dry matter production per mol of leaf nitrogen (positive relationship, r ²=0.64). Hence, the slow RGR of low-rainfall species was functionally related to a lower growth rate per mol of leaf nitrogen than high-rainfall species. Furthermore, slow RGR of low-rainfall species was related to greater allocation to roots at the expense of leaves. Increasing allocation to roots versus leaves is likely an adaptation to soil and atmospheric water deficits, but one that comes at the expense of a slow RGR.     

Modulation of relative growth rate and its components by water stress in Mediterranean species with different growth forms

Effects of water availability on seedling growth were analysed in eight Mediterranean species naturally occurring in the Balearic Islands. Seedlings were grown outdoors during summer under two irrigation treatments: field capacity and 35% of field capacity. The relative growth rate (RGR) strongly depended on the growth form, from highest values in herbs to lowest in woody perennials. The main component associated with interspecific variation in RGR was the specific leaf area (SLA), and a quantitative grouping of the different growth forms appeared along the regression line between both parameters. The slow-growing species, i.e. woody perennial shrubs, had the lowest SLA and the fast-growing perennial herbs, the highest, while woody semi-deciduous shrubs appeared intermediate. Decreases in RGR due to water stress were analysed in terms of the relative contribution of the leaf mass ratio (LMR), SLA and the net assimilation rate (NAR). Pooling all species, the decrease in RGR caused by water deficit was mainly explained by decreases in SLA. However, this general pattern was strongly dependent of growth form. Thus, in the woody perennial plants, the decrease in RGR was accompanied by a three-fold decrease in NAR which, however, increased in perennial herbs. SLA increased with decreasing water supply in woody perennial plants, and decreased in woody semi-deciduous shrubs and perennial herbs. Finally, decreases in LMR partly explained decreases in RGR in perennial herbs and woody perennial shrubs. This different response of the different growth forms may reflect differences in seedling adaptation and surviving strategies to drought periods.     

Components of variation in seedling potential relative growth rate: phylogenetically independent contrasts

Variation between species in seedling potential relative growth rate (RGR) is among the most important spectra of plant adaptation. Investigations are reported into the components responsible for this variation, using phylogenetically independent contrasts (PICs). The two species for each PIC were selected to diverge in seed mass at least four-fold, seed mass being a known correlate of RGR. Consistent with previous reports, the main influence on RGR differences between species was leaf area per unit leaf mass (SLA), rather than net assimilation rate per leaf area (NAR_a). The PIC design showed that SLA differences both underpinned old RGR divergences between orders and families, and also were repeatedly responsible for more recent RGR divergences between genera and species.     

Growth characteristics,nutrient allocation and photosynthesis ofCarex species from floating fens

Summary The purpose of this study was to investigate various growth parameters, dry matter and nitrogen, phosphorus and potassium allocation and photosynthesis ofCarex acutiformis, C. rostrata andC. diandra growing in fens with, in this order, decreasing nutrient availability and decreasing aboveground productivity. Plants were grown from cuttings at optimum nutrient conditions in a growth chamber. Growth analysis at sequential harvests revealed that the species had no inherently different relative growth rates which could explain their different productivity, but that their LAR (LWR and SLA) decreased in the orderC. acutiformis, C. rostrata, C. diandra and their NAR increased in this order. All growth parameters decreased during plant growth even under the controlled conditions of the experiment.C. acutiformis allocated relatively much dry matter to the leaves,C. rostrata to the rhizomes andC. diandra to the roots. This may, in part, explain the higher aboveground biomass production ofC. acutiformis in the field. Nitrogen, but not phosphorus and potassium, allocation patterns were different for the three species.C. diandra, the species from the nitrogen-poorest site, had the highest leaf N content of the three species and also a higher chlorophyll content. Related to this, this species had the highest photosynthetic activity of whole plants both when collected from the field and when grown in the growth chamber. The nitrogen productivity was similar for the three species and the photosynthetic nitrogen use efficiency, determined forC. acutiformis andC. diandra, was similar for these two species.C. diandra had the most finely branched root system, i.e., the highest specific root length of the three species and its root surface area to leaf surface area ratio was also the highest. All three species showed higher nitrate reductase activity in the leaves than in the roots when grown on nutrient solution. The growth ofC. diandra at a relatively nutrient-poor site and a rather open low vegetation is assumed to be adapted to its habitat by a relatively high NAR made possible by a high rate of photosynthesis concurrent with a high leaf N content. The growth ofC. acutiformis at a relatively nutrient-rich site and a more dense and higher vegetation is adapted to its habitat by a high LAR.     

Responses of photosynthesis,leaf conductance and growth to different salinities in three coastal dune plants

The effects of soil-water salinity on growth and photosynthesis of three coastal dune plants were examined by salt-treatment in order to clarify the causal relationship between salinity and plant distribution in a dune habitat. Plants were cultivated hydroponically at three salinity levels: 0, 10 and 100 mM NaCl. With the 100 mM salt treatment,Calystegia soldanella (C₃ species) had the highest relative growth rate (RGR) (0.085 g g⁻¹ d⁻¹), followed byCarex kobomugi (C₃) (0.066), andIschaemum anthephoroides (C₄) (0.060). This order coincides with the distribution pattern of the three species on coastal dunes;Calystegia soldanella is generally distributed in more seaward areas whereasI. anthephoroides occurs further inland. The order of RGR was determined exclusively by leaf area ratio (LAR) among the three species. Due to its C₄ pathway,I. anthephoroides had higher net photosynthetic rate (Pn) and net assimilation rate (NAR) than the two C₃ plants at all NaCl concentrations, despite its low RGR. This apparent discrepancy is explainable by differences of LAR among the three species; LAR ofI. anthephoroides was lowest, and about half that ofCalystegia soldanella. These results suggest that LAR is one of the main determinants of salt tolerance based on RGR, whereas Pn or NAR may not be significant. This article is dedicated to Professor Hideo Iwaki, University of Tsukuba, in appreciation of the sincere encouragement he has given to the authors.     

Modelling the relative growth rate as a function of plant nitrogen concentration

The relationship between the relative growth rate (RGR) and the nitrogen concentration of the whole plant (PNC) was analyzed by using experimentally determined relations (1) between the PNC and the fraction of dry matter (LWR) and nitrogen in leaves, (2) between the specific leaf area (SLA) and the leaf nitrogen concentration (LNC) and (3) between the net assimilation rate (NAR) and the LNC on an area basis. A strong dependence of RGR on nitrogen concentration resulted from the increase in NAR, LWR and SLA with increasing PNC. A curvilinear relationship between RGR and PNC gave an optimum curve for nitrogen productivity against PNC.     

Net assimilation rate and relative nitrogen assimilation rate in relation to the dry matter production of alfalfa cultivars

Summary Twelve alfalfa cultivars inoculated with an indigenous strain (RM9) ofRhizobium meliloti, were compared for their seedling morphological characters, and growth characters, including net assimilation rate (NAR), relative growth rate (RGR), leaf area ratio (LAR) and relative nitrogen assimilation rate (R_N). Highly significant differences were obtained between cultivars for most characters.Simple correlation showed that NAR influenced RGR (r=0.91) more than leaf area ratio (LAR) (r=–0.44), and that most characters measured were highly correlated with seedling dry weight. Factor analysis showed that NAR, RGR and R_N contributed 25% of the total variation in the dependence structure. The grouping indicated that the higher the NAR and R_N the greater was the RGR. Path-coefficient analysis showed that NAR had more important direct and indirect effects than R_N in dry matter accumulation. The relationship implied that selection for plants with high NAR, or high efficiency in converting light energy to dry matter production could contribute greater N₂ fixation in alfalfa.     

Potassium requirements for growth and its related processes determined by plant analysis in wheat

Summary Potassium requirements for growth—dry matter (DM) and leaf area (LA) and related processes — relative leaf growth rate (RLGR), relative growth rate (RGR), net assimilation rate (NAR) and crop growth rate (CGR) were determined by plant analysis during the entogeny of wheat. Wheat (Triticum aestivum cv. HD 2329) plants were supplied with different amounts of K from deficient to adequate through nutrient solution. Samples were taken at specific stages for K determinations. The DM and LA were recorded at 45d, 75d and 105d. The growth related processes RGR, NAR and CGR were estimated between 30–45d, 45–75d and 75–105d. In case of RLGR the observations were carried out between 15–30d, 30–45d and 45–75d. These physiological processes and grain yield were correlated with K concentration in whole plant at 30 and 45d and top two leaves at 75 and 105d. The results indicated that k status in plants influences growth mostly through leaf area formation which inturn influences successively RLGR, RGR and CGR and finally grain yield. For vegetative growth the optimum concentration required in plants was always lower than the optimum for grain production.     

Relative growth rate in relation to physiological and morphological traits for northern hardwood tree seedlings: species,light environment and ontogenetic considerations

The influence of ontogeny, light environment and species on relationships of relative growth rate (RGR) to physiological and morphological traits were examined for first-year northern hardwood tree seedlings. Three Betulaceae species (Betula papyrifera, Betula alleghaniensis and Ostrya virginiana) were grown in high and low light and Quercus rubra and Acer saccharum were grown only in high light. Plant traits were determined at four ages: 41, 62, 83 and 104 days after germination. In high light (610 mol m^–2 s^–1 PPFD), across species and ages, RGR was positively related to the proportion of the plant in leaves (leaf weight ratio, LWR; leaf area ratio, LAR), in situ rates of average canopy net photosynthesis (A) per unit mass (A_mass) and per unit area (A_area), and rates of leaf, stem and root respiration. In low light (127 mol m^–2 s^–1 PPFD), RGR was not correlated with A_mass and A_area whereas RGR was positively correlated with LAR, LWR, and rates of root and stem respiration. RGR was negatively correlated with leaf mass per area in both high and low light. Across light levels, relationships of CO₂ exchange and morphological characteristics with RGR were generally weaker than within light environments. Moreover, relationships were weaker for plant parameters containing a leaf area component (leaf mass per area, LAR and A_area), than those that were solely mass-based (respiration rates, LWR and A_mass). Across light environments, parameters incorporating the proportion of the plant in leaves and rates of photosynthesis explained a greater amount of variation in RGR (e.g. LWR^*A_mass, R²=0.64) than did any single parameter related to whole-plant carbon gain. RGR generally declined with age and mass, which were used as scalars of ontogeny. LWR (and LAR) also declined for seven of the eight species-light treatments and A declined in four of the five species in high light. Decreasing LWR and A with ontogeny may have been partially responsible for decreasing RGR. Declines in RGR were not due to increased respiration resulting from an increase in the proportion of solely respiring tissue (roots and stems). In general, although LWR declined with ontogeny, specific rates of leaf, stem, and root respiration also decreased. The net result was that whole-plant respiration rates per unit leaf mass decreased for all eight treatments. Identifying the major determinants of variation in growth (e.g. LWR^*A_mass) across light environments, species and ontogeny contributes to the establishment of a framework for exploring limits to productivity and the nature of ecological success as measured by growth. The generality of these relationships both across the sources of variation we explored here and across other sources of variation in RGR needs further study.     

Growth and nutrition of birch seedlings in relation to potassium supply rate

Summary Growth of hydroponically cultivated birch seedlings (Betula pendula Roth.) at sub- and supra-optimum potassium supply rates was investigated. Potassium was supplied either as a relative addition rate (r _k = 5, 10, 15 and 20% increase day^-1) or as fixed concentrations (0.2, 3, 6, 12 and 15 mM) in the culture solution. After an acclimation period the growth rate of the seedlings in the suboptimum treatments reached values close to the treatment variable, the relative rate of K-addition. Deficiency symptoms, in the form of chlorosis and necroses along the leaf margins, developed initially in all suboptimum treatments, but very few new symptoms appeared once the seedlings had reached the phase of steady-state nutrition and growth. At supra-optimum K-supply levels, i.e. at 0.2–15 mM K in the culture solution, no symptoms of deficiency or toxicity developed, and the relative growth rate of the seedlings remained maximum. The relative growth rate of the seedlings was linearly related to the plant K-status for K contents ranging from 0.2 to 1.0% of dry weight (DW). At higher internal K-concentrations, 1.0–3.0% DW, no further increase in relative growth rate was achieved. A shortage of K resulted in a decrease in the net assimilation rate. This effect was counterbalanced by the absence of shift in he leaf weight ratio as well as by the production of relatively thin leaves. The fraction of dry matter allocated to roots decreased in K-limited plants, as did the leaf contents of soluble carbohydrates and starch.     

The effect of nitrogen nutrition on growth and biomass partitioning of annual plants originating from habitats of different nitrogen availability

Summary The hypothesis was tested that faster growth of nitrophilic plants at high nitrogen (N) nutrition is counterbalanced by faster growth of non-nitrophilic plants at low N-nutrition. Ten annual plant species were used which originated from habitats of different N-availability. The species' preference for N was quantified by the N-number of Ellenberg (1979), a relative measure of nitrophily. The plants were cultivated in a growth cabinet at five levels of ammonium-nitrate supply. At low N-supply, the relative growth rate (RGR) was independent of nitrophily. At high N-supply, RGR tended to be higher in nitrophilic than in non-nitrophilic species. However, the response of RGR to N-supply was strongly and positively correlated with the nitrophily of species. Increasing N-supply enhanced partitioning to leaf weight per total biomass (LWR) and increased plant leaf area per total biomass (LAR). Specific leaf weight (SLW) and LWR were both higher in non-nitrophilic than in nitrophilic species at all levels of N-nutrition. NAR (growth per leaf area or net assimilation rate) increased with nitrophily only under conditions of high N-supply. RGR correlated positively with LAR, irrespective of N-nutrition. Under conditions of high N-supply RGR correlated with SLW negatively and with NAR positively.     

Dry matter allocation and nitrogen productivity explain growth responses to photoperiod and temperature in forage grasses

The mechanisms responsible for fluctuations in species composition of semi-natural grassland are not well understood. To identify plant traits that determine the poor competitive ability of Festuca pratensis compared to Dactylis glomerata especially during summer, the growth of both grasses was monitored over time and at different temperatures and photoperiods. Plants of both grasses were grown from seed with non-limiting nutrient supply at three day/night temperatures (11/6, 18/13 and 25/20°C) and two photoperiods (16 and 12 h). F. pratensis had a significantly lower relative growth rate than D. glomerata, mainly due to its lower specific leaf area and reduced nitrogen productivity. At high temperature, F. pratensis had a considerably lower root weight ratio than D. glomerata leading to substantially slower root growth. F. pratensis responded to a shorter photoperiod with an increase in the net assimilation rate, whereas D. glomerata responded with an increase in specific leaf area. The low competitive ability of F. pratensis compared to D. glomerata was mainly associated with its lower specific leaf area and nitrogen productivity. The stronger decline of its competitive ability during summer was probably related to the decreased allocation of dry matter to the roots at higher temperatures which leads to slower root growth compared to D. glomerata. Received: 7 September 1998 / Accepted: 29 July 1999     

Traits and growth of liana regeneration in primary and secondary forests of Central Amazonia

Question: Do traits of liana regeneration differ among secondary forest types of varying land‐use history and primary forest? Location: Eighty kilometers north of Manaus, Brazil. Methods: We compared plant functional traits and growth rates of liana regeneration (<1.7‐m length) among two secondary forest types and primary forest. Secondary forest types were: Vismia (on land formerly clear‐cut, used for pasture and intensively burned) and Cecropia (no pasture usage or intensive fires after clear‐cut). Results: A principal components analysis indicated that most of the primary forest species exhibited a similar habit and were characterized by short shoots and small, round leaves with low specific leaf area, whereas secondary forest species had a broad range of trait values. At the plot level, primary and secondary forest communities were separated mainly by plant length and leaf size. Plant size varied more within secondary than within primary forest plots. The two secondary forest types could not be separated based on the traits of liana regeneration. Relative growth rate (RGR) did not correlate significantly with any measured plant trait, except for a negative relation to initial length. RGR increased with decreasing canopy cover and was highest in Vismia forest plots. Conclusion: Plant functional traits of liana regeneration were more similar in the primary forest and differed substantially from secondary forests, yet canopy cover only partly explained the observed differences.     

Intra-specific variation in relative growth rate: impact on competitive ability and performance of Lychnis flos-cuculi in habitats differing in soil fertility

Plant species from unproductive or adverse habitats are often characterized by a low potential relative growth rate (RGR). Although it is generally assumed that this is the result of selection for specific trait combinations that are associated with a low rate of net biomass accumulation, few studies have directly investigated the selective (dis-)advantage of specific growth parameters under a set of different environmental conditions. Aim of the present study was to quantify the impact of inherent differences in growth parameters among phenotypes of a single plant species, Lychnis flos-cuculi, on their performance under different soil nutrient conditions. Growth analysis revealed significant variation in RGR among progeny families from a diallel cross between eight genotypes originating from a single population. Differences in RGR were due to variation in both leaf area ratio (LAR) and in net assimilation rate (NAR). A genetic trade-off was observed between these two components of growth, i.e. progeny families with high investment in leaf area had a lower rate of net biomass accumulation per unit leaf area. The degree of plasticity in RGR to nutrient conditions did not differ among progeny families. Inherent differences in growth parameters among progeny families had a significant impact on their yield in competition with Anthoxanthum odoratum and Taraxacum hollandicum. In nutrient-rich conditions, progeny families with an inherently high leaf weight ratio (LWR) achieved higher yield in competition, but variation in this trait could not explain differences in competitive yield under nutrient-poor conditions. Inherent differences in growth parameters among progeny families were poorly correlated with differences in survival and average rosette biomass (a good predictor of fecundity) among these progeny families sown in four field sites along a natural gradient of soil fertility. In the more productive sites none of the growth parameters was significantly correlated with rosette biomass, but in the least productive site progeny families with an inherently high specific leaf area (SLA) tended to produce smaller rosettes than low-SLA families. These results are consistent with the view that a selective advantage may accrue from either high or low values of individual RGR components, depending on habitat conditions, and that the selective advantage of low trait values in nutrient-poor environments may results in indirect selection for low RGR in these habitats.     

Nitrogen allocation,partitioning and use efficiency in three invasive plant species in comparison with their native congeners

In this study, we hypothesized that invasive species may allocate a higher fraction of leaf nitrogen (N) to photosynthesis than phylogenetically related native species. To test this hypothesis, we determined N allocation and other ecophysiological traits of three invasive species in comparison with their respective native congeners by measuring response curves of photosynthesis to intercellular CO₂ concentration. The invasive species of Peperomia and Piper indeed allocated a higher fraction of leaf N to photosynthesis and were more efficient in photosynthetic N (N _P) partitioning than their native congeners. The two invasive species partitioned a higher fraction of N _P to carboxylation and showed a higher use efficiency of N _P, while their native congeners partitioned a higher fraction of N _P to light-harvesting components. The higher N allocation to photosynthesis and the higher N _P partitioning to carboxylation in the two invaders were associated with their higher specific leaf area. Nitrogen allocation and partitioning were the most important factors in explaining the differences in light-saturated photosynthetic rate and photosynthetic N use efficiency (PNUE) between the two invasive species and their native congeners. The differences in N allocation-related variables between the invasive and native species of Amaranthus could not be evaluated in this study due to the method. Except PNUE, resource capture- and use-related traits were not always higher in all three invasive species compared to their native congeners, indicating that different invasive species may have different syndrome of traits associated with its invasiveness.     

Relationships of leaf dark respiration to leaf nitrogen, specific leaf area and leaf life-span: a test across biomes and functional groups

Based on prior evidence of coordinated multiple leaf trait scaling, we hypothesized that variation among species in leaf dark respiration rate (R _d) should scale with variation in traits such as leaf nitrogen (N), leaf life-span, specific leaf area (SLA), and net photosynthetic capacity (A _max). However, it is not known whether such scaling, if it exists, is similar among disparate biomes and plant functional types. We tested this idea by examining the interspecific relationships between R _d measured at a standard temperature and leaf life-span, N, SLA and A _max for 69 species from four functional groups (forbs, broad-leafed trees and shrubs, and needle-leafed conifers) in six biomes traversing the Americas: alpine tundra/subalpine forest, Colorado; cold temperate forest/grassland, Wisconsin; cool temperate forest, North Carolina; desert/shrubland, New Mexico; subtropical forest, South Carolina; and tropical rain forest, Amazonas, Venezuela. Area-based R _d was positively related to area-based leaf N within functional groups and for all species pooled, but not when comparing among species within any site. At all sites, mass-based R _d (R _d-mass) decreased sharply with increasing leaf life-span and was positively related to SLA and mass-based A _max and leaf N (leaf N _mass). These intra-biome relationships were similar in shape and slope among sites, where in each case we compared species belonging to different plant functional groups. Significant R _d-mass−N _mass relationships were observed in all functional groups (pooled across sites), but the relationships differed, with higher R _d at any given leaf N in functional groups (such as forbs) with higher SLA and shorter leaf life-span. Regardless of biome or functional group, R _d-mass was well predicted by all combinations of leaf life-span, N _mass and/or SLA (r ²≥ 0.79, P < 0.0001). At any given SLA, R _d-mass rises with increasing N _mass and/or decreasing leaf life-span; and at any level of N _mass, R _d-mass rises with increasing SLA and/or decreasing leaf life-span. The relationships between R _d and leaf traits observed in this study support the idea of a global set of predictable interrelationships between key leaf morphological, chemical and metabolic traits. Received: 23 May 1997 / Accepted: 16 December 1997