Higher Specific Leaf Research Articles

Specific leaf area relates to the differences in leaf construction cost, photosynthesis, nitrogen allocation, and use efficiencies between invasive and noninvasive alien congeners

Comparisons between invasive and native species may not characterize the traits of invasive species, as native species might be invasive elsewhere if they were introduced. In this study, invasive Oxalis corymbosa and Peperomia pellucida were compared with their respective noninvasive alien congeners. We hypothesized that the invasive species have higher specific leaf (SLA) than their respective noninvasive alien congeners, and analyzed the physiological and ecological consequences of the higher SLA. Higher SLA was indeed the most important trait for the two invaders, which was associated with their lower leaf construction cost, higher nitrogen (N) allocation to photosynthesis and photosynthetic N use efficiency (PNUE). The higher N allocation to photosynthesis of the invaders in turn increased their PNUE, N content in photosynthesis, biochemical capacity for photosynthesis, and therefore light-saturated photosynthetic rate. The above resource capture-, use- and growth-related traits may facilitate the two invaders' invasion, while further comparative studies on a wider range of invasive and noninvasive congeners are needed to understand the generality of this pattern and to fully assess the competitive advantages afforded by these traits.

Feeding preferences of the Christmas beetle Anoplognathus chloropyrus (Coleoptera: Scarabaeidae) and four paropsine species (Coleoptera: Chrysomelidae) on selected Eucalyptus grandis clonal foliage

Summary Christmas beetles (Coleoptera: Scarabaeidae) (Anoplognathus spp.) and paropsine leaf beetles (Coleoptera: Chrysomelidae) are common defoliators of eucalypts, including several important plantation species, throughout south-eastern Australia. It has already been demonstrated that populations and individuals of several eucalypt species vary in susceptibility to defoliation by these leaf-chewing beetles. The objective of this study was to determine whether significant variation in resistance to insect herbivory was present in Eucalyptus grandis genotypes selected from the hardwood plantation program of State Forests of NSW. Grafted clones from three young trees with significantly less crown damage than neighbouring trees in a plantation established near Byron Bay, NSW, were tested for attractiveness to Anoplognathus chloropyrus adults in a binary choice experiment in the laboratory. Shoots from the resistant grafted ramets were paired with shoots from susceptible seedlings of similar age, and caged with feeding A. chloropyrus adults for 24 h. The Christmas beetles consumed significantly (P ≤ 0.05) less leaf area from the resistant shoots, compared to that consumed from the shoots from susceptible seedlings, when given access to both. The binary choice test method was also used to test feeding preferences of four paropsine chrysomelid species: Paropsis atomaria (adults and larvae), P. variolosa (larvae only), Paropsisterna beata (adults), and a Chrysophtharta sp. (adults), using the same E. grandis genotypes. No significant differences (P > 0.05) in feeding preferences were detected for P. variolosa larvae, P. atomaria adults, P. beata adults or the Chrysophtharta sp. adults. In contrast, P. atomaria larvae displayed a significant preference for foliage from the susceptible seedlings. In a larval development study using P. atomaria larvae, those reared on the susceptible foliage developed approximately five days faster and had significantly higher survival than those reared on resistant foliage. Several leaf traits were also compared between the two types of foliage. Leaves of similar age from the resistant clones did not differ significantly from the susceptible seedlings in terms of carbon to nitrogen content or concentrations of the monoterpene, 1,8-cineole. They did, however, have significantly higher specific leaf weight (SLW). SLW may have the potential for use in rapid screening of E. grandis genotypes for susceptibilty to defoliation by leaf-chewing beetles that prefer young soft foliage.

Leaf life span and nitrogen content in semideciduous forest tree species (Croton priscus and Hymenaea courbaril)

In comparison to deciduous species, evergreen plants have lower leaf nutrient contents and higher leaf life span, important mechanisms for nutrient economy, allowing the colonization of low fertility soils. Strategies to conserve nitrogen in two semideciduous tropical forest tree species, with different leaf life spans were analyzed. The hypothesis was the fact that the two species would present different nitrogen conservation mechanisms in relation to chemical (total nitrogen, protein, chlorophyll, and proteolytic activity), functional (leaf life span, N-use efficiency, and N-resorption efficiency), morphological (specific leaf mass) leaf characteristics, and total nitrogen in the soil. Hymenaea courbaril L. presented lower nitrogen compounds in leaves, longer leaf life span, higher N-use efficiency, and higher specific leaf mass, while absorbing proportionally less nitrogen from the soil than Croton priscus Croizat. These characteristics can contribute for a better nitrogen economy strategy of H. courbaril. No relationship was found between leaf life span and N resorption efficiency, nor between leaf life span, protease activity and nitrogen mobilization. The electrophoretic profiles of proteolytic enzymes in young leaves of the two species presented more bands with enzymatic activity than other kinds of leaves.

Recruitment and life-history traits of sparse plant species in subalpine grasslands

Recruitment is critical for the maintenance of plant populations and community diversity, but sexual regeneration is considered to be infrequent in climatically harsh habitats such as subalpine grasslands. This study examines the importance of regeneration through seed for 16 sparse herb species, and we asked whether their populations are limited by safe sites or the availability of seeds. Seedling recruitment and winter survival were recorded after sowing in an experimental split-plot design in (i) pasture grazed by livestock, and (ii) exclosed grassland cultivated for annual mowing. In addition we examined the effect of disturbance and local seedbank recruitment. All species were able to recruit and survive the first winter in at least some of the experimental plots, although none were initially present. Recruitment mainly occurred in disturbed plots, and disturbed pasture plots had a significantly higher recruitment than disturbed exclosures for all species except Silene dioica. We further examined whether specific plant traits were related to variation in recruitment. Lower recruitment in the disturbed exclosure was associated with higher specific leaf area, leaf dry weight, and seed number. In contrast, seeds sown in disturbed pasture recruited more independently of species traits. The exception was a negative correlation between recruitment and leaf dry weight, and an unexpected negative correlation with seed weight. We suggest that recruitment differences among habitats mainly reflect lower humidity in the exclosure. Consequently, small stature plants with small specific leaf area should have the highest recruiting probability when exposed to drought. The almost exclusive recruitment on disturbed plots indicates a strong competitive effect on the target species in vegetated plots, and suggests that safe sites for regeneration through seed are rare in subalpine grasslands.Key words: colonization, herbs, plant abundance and distribution, disturbance, pastures, cultivated exclosures, sowing experiment.

Branch growth and allocation patterns of saplings of two Abies species under different canopy conditions in a subalpine old-growth forest in central Japan

Branch growth and biomass allocation of saplings of two Abies species under three different canopy conditions (evergreen coniferous Abies canopy, deciduous broad-leaved Betula canopy, and canopy gaps) were examined in a subalpine old-growth forest in the northern Yatsugatake Mountains, central Japan. Both A. mariesii and A. veitchii saplings showed similar morphological plasticity: saplings growing in gaps had conical crowns, whereas those under evergreen and deciduous canopies had umbrella-shaped crowns. Both Abies species grew more in stem diameter than in stem height under evergreen and deciduous canopies. Under evergreen and deciduous canopies, A. veitchii saplings invested more biomass in stems and less in leaves and branches than did A. mariesii. The mean longevity of leaves and branches of A. veitchii saplings was shorter than that of A. mariesii saplings under evergreen and deciduous canopies. These results suggest that A. veitchii saplings have an efficient umbrella-shaped crown for light interception and invest relatively little biomass in leaves and branches compared with A. mariesii saplings in shaded conditions. However, branch mortality of A. veitchii saplings may be higher, because the species’ high leaf area ratio and specific leaf area may increase its susceptibility to herbivory and disease and also because the slender branches of A. veitchii saplings would be more likely to break under the weight of snow. The growth strategy of A. mariesii in shade is considered persistent, while that of A. veitchii saplings emphasizes height growth.

FROM FLUORESCENCE TO FITNESS: VARIATION IN PHOTOSYNTHETIC RATE AFFECTS FECUNDITY AND SURVIVORSHIP

Genetic variation in photosynthetic traits within populations provides the potential for evolution, but few studies relate phenotypic variation in these traits to variation in fitness. We tested the prediction that a lower photosynthetic rate reduces fecundity and survivorship by comparing wild-type (WT) Amaranthus hybridus family lines to those having a single-gene mutation that confers resistance to atrazine (R) and lowers the rate of photosynthetic carbon assimilation. Wild-type and R family lines with nearly uniform nuclear genomes were used to minimize the confounding effects of other loci. We established experimental populations in agricultural and one-year-old field plots and measured chlorophyll fluorescence, gas exchange, and the fecundity and survivorship of WT and R genotypes for two generations. The R genotype had a lower efficiency of electron transport through photosystem II, which translated into a 20–30% decrease in photosynthetic rate at light levels above 400 μmol·m−2·s−1. Compared to the WT, the R genotype also had lower water-use efficiency, higher specific leaf area, and greater leaf nitrogen concentration on a mass, but not area, basis. In five of six replicate populations, the R genotype had lower fecundity than the WT in the first generation. Survivorship of seed over winter was similar for the two genotypes, but survivorship of R seedlings during early establishment was lower than the WT in the agricultural field. The consistent pattern of selection against the R genotype during vegetative growth stages suggests that a lower photosynthetic rate reduces fitness. This selection, paired with heritable variation for photosynthetic traits within populations, provides a more complete scenario for the evolution of photosynthetic traits.

Crown development in tropical rain forest trees in gaps and understorey

Crown development was monitored for juvenile trees (4–18 m) of the canopy tree species Dicorynia guianensis and Vouacapoua americana in a tropical rain forest in French Guiana. A comparison was made between crown development in closed understorey forest sites (low light) and in canopy gaps (high light); development was expressed by plant traits at multiple levels of organisation. Dicorynia and Vouacapoua responded to gap creation at all organisational levels, but not for all traits. Both species increased their light interception efficiency in the understorey. Firstly, understorey trees produced relatively wide crowns because they did not favour the growth of shoots in the summit of the crown, as did gap trees. Secondly, they reduced self-shading (expressed by leaf area index) by lower sympodial unit production rates, lower leaf production rates per growth unit (only Vouacapoua), and smaller leaf size (only Dicorynia). The reduction in self-shading was weakened by other traits that had the opposite effect on self shading (e.g. longer leaf life span in understorey), and cannot be considered an adaptive response in itself. (3) Understorey trees of Vouacapoua reduced leaf display costs by producing a higher specific leaf area, a shorter space among leaves, a smaller leaf spacing to leaf size ratio, and a longer leaf life span. Thus, all traits contributed to the more economical use of carbon in the understorey. Dicorynia showed the same trends, but not significantly. These results suggest that light availability plays a major role in the development and morphology of trees through its influences at multiple levels of organisation within the crown hierarchy. The two species studied were rather similar in their response at crown level, while they sometimes differed in their responses at the underlying lower organisational levels. The response directions of some individual plant traits were similar for the tall trees studied here and small saplings studied elsewhere. Some of traits investigated here may not be important in the crown level responses of smaller seedlings and saplings, while they are important mechanisms for crown level responses in taller trees.

Ecophysiological Differences Among Growth Stages of Quercus laevis in a Sandhill Oak Community

DONOVAN, L. A. AND R. A. PAPPERT (Department of Botany, University of Georgia, Athens, GA 30602-7271). Ecophysiological differences among growth stages of Quercus laevis in a sandhill oak community. J. Torrey Bot. Soc. 125:3-10. 1998.-Plants in the sandhill habitats of the southeast are thought to be limited by soil resources such as water and nutrients. We measured ecophysiological characters related to resource use for several growth stages: Seedling Sprouts (small sprouts from small root collars), Stump Sprouts (small sprouts from large root collars) and Adults (large reproductively mature trees) of Quercus laevis (turkey oak) in SC. Adults did not differ from Stump Sprouts in water potentials, photosynthesis, stomatal conductance, or leaf nitrogen. In contrast, Seedling Sprouts differed from Stump Sprouts and Adults in June: lower predawn water potentials, lower rates of photosynthesis and stomatal conductance, higher specific leaf area, and lower leaf N concentration. The September growth stages rankings for these characters were generally similar to those in June, but variation within a growth stage was greater and thus Seedling Sprouts were only significantly different from the other two growth stages for leaf nitrogen. The differences between Seedling Sprouts and larger individuals may be due to differential access to soil resources as a function of rooting depth. Soil water availability was high in March, low in June, and higher again in September except at 1.25 m. Soil total N was higher at soil depth of 0-0.1 than 0.1-0.2 m in March, but did not differ between 0.25, 0.50, 0.75, 1.00 and 1.25 m in June. The differences in resource acquisition and resource use should relate to growth and survival of individuals within a population.

Effects of litter accumulation and water table on morphology and productivity of Phragmites australis

Phragmites australis (Common reed) occurs in the interface between water and land. The water depth gradient from deep water to dry land is inversely related to litter accumulation. Eutrophication can result in an excessive production of litter, which may have a large impact on the occurrence of P. australis in this gradient. In an outdoor pot experiment, it was investigated how water tables in combination with substrates containing variable amounts of litter affect morphology and productivity of P. australis. Vegetatively propagated P. australis was grown in pots filled with river sand, litter, and different mixtures of sand and litter (25, 50 and 75% by volume). Four water table treatments were applied; drained (–12 cm), waterlogged (0 cm), flooded (+12 cm), and weekly fluctuating drained and flooded conditions (–12/+12 cm of water relative to substrate level). When drained, no differences between substrate treatments were present. Waterlogging, flooding fluctuating water table treatments caused growth reduction in substrate containing litter. The plants formed short shoots and thin rhizomes. With increasing water table, allocation of dry matter to stems increased at the expense of leaves and rhizomes. At intermediate levels of litter in the substrate, allocation to leaves was lowest. In both instances a lower leaf weight ratio (LWR) was (partly) compensated for by a higher specific leaf area (SLA), resulting in less pronounced differences in leaf area ratio (LAR). Aquatic roots developed when plants were waterlogged or flooded, and increased when litter was present in the substrate. Aquatic roots were formed in the top soil layer when waterlogged. The percentage of aquatic roots increased with increasing amount of litter in the substrate when plants were flooded. It was concluded that the morphological responses of P. australis to litter strongly constrain its ability to maintain itself in deep water when the substrate contains litter. This might one of the explanations for the disappearance of P. australis along the waterward side of littoral zones.

Photosynthetic and structural acclimation to light direction in vertical leaves of Silphium terebinthinaceum.

The azimuth of vertical leaves of Silphium terebinthinaceum profoundly influenced total daily irradiance as well as the proportion of direct versus diffuse light incident on the adaxial and abaxial leaf surface. These differences caused structural and physiological adjustments in leaves that affected photosynthetic performance. Leaves with the adaxial surface facing East received equal daily integrated irradiance on each surface, and these leaves had similar photosynthetic rates when irradiated on either the adaxial or abaxial surface. The adaxial surface of East-facing leaves was also the only surface to receive more direct than diffuse irradiance and this was the only leaf side which had a clearly defined columnar palisade layer. A potential cost of constructing East-facing leaves with symmetrical photosynthetic capcity was a 25% higher specific leaf mass and increased leaf thickness in comparison to asymmetrical South-facing leaves. The adaxial surface of South-facing leaves received approximately three times more daily integrated irradiance than the abaxial surface. When measured at saturating CO2 and irradiance, these leaves had 42% higher photosynthetic rates when irradiated on the adaxial surface than when irradiated on the abaxial surface. However, there was no difference in photosynthesis for these leaves when irradiated on either surface when measurements were made at ambient CO2. Stomatal distribution (mean adaxial/abaxial stomatal density = 0.61) was unaffected by leaf orientation. Thus, the potential for high photosynthetic rates of adaxial palisade cells in South-facing leaves at ambient CO2 concentrations may have been constrained by stomatal limitations to gas exchange. The distribution of soluble protein and chlorophyll within leaves suggests that palisade and spongy mesophyll cells acclimated to their local light environment. The protein/chlorophyll ratio was high in the palisade layers and decreased in the spongy mesophyll cells, presumably corresponding to the attentuation of light as it penetrates leaves. Unlike some species, the chlorophyll a/b ratio and the degree of thylakoid stacking was uniform throughout the thickness of the leaf. It appears that sun-shade acclimation among cell layers of Silphium terebinthinaceum leaves is accomplished without adjustment to the chlorophyll a/b ratio or to thylakoid membrane structure.

The Effect of Reproduction on Canopy Structure, Allocation and Growth in Oenothera Biennis

SUMMARY (1) Time of reproduction in Oenothera biennis was controlled experimentally by gibberellic acid applications in a glasshouse experiment. Performance of vegetative plants and plants reproducing at various ages was compared by means of growth analysis. (2) Regardless of age, reproduction increased stem allocation and decreased root and leaf allocation. Early reproduction reduced growth relative to vegetative plants, while late reproduction had no effect on growth in the long term and enhanced growth in the short term. Seed output increased with age at reproduction up to a point after which there was little change. (3) The reduced growth of plants reproducing at an early age was due to a decrease in leaf area ratio, and the enhanced growth of older plants to a temporary increase. Specific leaf area in older plants increased with reproduction, temporarily overcompensating for the decrease in leaf allocation. There was a temporary increase in unit leaf rate in plants reproducing at a young age but not in plants reproducing at a late age. (4) Changes in specific leaf area were the result of a switch in leaf morphology between vegetative and reproductive plants. Vegetative plants produced leaves with petioles which increased in length with age. This morphology minimized self-shading in the vegetative rosettes. Leaves produced after reproduction had short petioles and, consequently, a higher specific leaf area. Plants reproducing at an early age produced few new leaves and exhibited little change in specific leaf area. (5) It is suggested that the beneficial effects of reproduction on canopy structure and photosynthesis that are observed in many species can compensate for the cost of reproduction, providing the accumulated nutrient reserves are sufficient to supply the reproductive structures.

Development of Mesophyll and Growth in Expanding Leaves Influenced by the Concentration of Potassium in Successive Leaves and Internodes in Nicotiana tabacum

Summary During initial expansion of leaves, the rate of cell division, the expansion of mesophyll cells and the development of intercellular space (ICS) was reduced by up to 35 % in tobacco (N. tabacum) plants when the concentration of K in the substrate solution was raised from 1 to 6 meq dm -3. This was accompanied by a higher specific leaf weight and a lower specific leaf area. The final number of palisade and spongy cells, however, was not influenced by the supply of K. During the major increase in area, expansion of mesophyll cells and the increase in volume of ICS in the high K plants was 50 % to 65 % greater than in plants supplied the lower concentration of K. With a phyllochron of one day, a leaf at the beginning of major expansion was one-third expanded and had been displaced from the apex towards the base by 5 or 6 nodes. The final area was reached by the leaf subtending nodes 10 to 12. The expansion of leaves in plants supplied a higher level of K was related to the progressive increase in concentration of K + in leaves and internodes as they are displaced towards the base of the shoot, which influences the translocation and allocation of metabolites in expanding leaves during the transition from sink to source.

Shoot development in Betula papyrifera. II. Comparison of vegetative and reproductive short-shoot growth

Short shoots of Betula papyrifera Marsh, may be vegetative or reproductive. The latter bear a female inflorescence. Early flushing and rapid growth of short-shoot buds depend on the age and position of the short shoot. Axillary short-shoot buds flush later than 2- to 4-year-old short-shoot terminal buds, which in turn flush later than 5- to 10-year-old shoots. Mean relative growth rate (RGR) of 5- to 10-year-old short-shoot buds is greater than that of younger short-shoot buds. It is suggested that older short-shoot buds are relatively autonomous and that the flushing long shoot exhibits an inhibitory influence on the proximal axillary buds and possibly on young short-shoot terminal buds. Reproductive short shoots differ from vegetative short shoots in that they have lower leaf area ratios and leaf RGR, higher specific leaf area, smaller leaf areas, and fewer side nerve pairs and they grow more in length than in width. These findings are related to reproductive cost. The developing inflorescences act as preferred "sinks" for resource allocation.

The Effect of Partial Defoliation on the Growth and Photosynthetic Efficiency of Bean Leaves

Removal of leaves above the first trifoliolate leaf of bean plants (Phaseolus vulgaris L `Canadian Wonder') induced more rapid leaf expansion, a larger final leaf area, higher dry weight, lower specific leaf area, and higher photosynthetic rates in the first trifoliolate leaf compared with undefoliated controls. Removal of the primary leaves just after they unfolded induced more rapid initial leaf expansion, smaller final leaf area, lower dry weight, higher specific leaf area, and initially higher but subsequently lower rates of photosynthesis in the first trifoliolate compared with undefoliated controls.