Increasing Plant Size Research Articles

NOVEL METHOD OF MICRONUTRIENT APPLICATION INCREASES RADISH (RAPHANUS SATIVUS) AND SHIRONA (BRASSICA RAPA VAR. PEKINENSIS) BIOMASS

The practice of enriching nutrient-poor soils with large quantities of chemical fertilizer has contributed significantly to the boost in agricultural productivity witnessed over the last century. Plants also require minute quantities of micronutrients, such as iron (Fe), manganese (Mn), and zinc (Zn). Inadequate micronutrient concentrations in the soil are a crucial problem for crop production that can severely reduce yield and nutritional quality of crops. Modern agriculture can further promote micronutrient deficiency through excessive irrigation and imbalanced application of chemical fertilizers. Anecdotal evidence suggested that irrigation of crops with FFC H2O, a commercial product currently utilized by the agriculture, fishery, and food industries in Japan, improved crop yields. Our study quantified the biomass of radish and shirona plants watered with FFC H2O. These plants developed larger leaves, greater dry weight, and longer stems than plants watered with deionized H2O. Inductively coupled plasma mass spectroscopy revealed the presence of several biologically relevant micronutrients in FFC H2O. Radish plants watered with an FFC H2O solution that lacked micronutrients, or nutrient solutions that lacked either iron or zinc failed to increase plant size relative to controls. These results provide quantitative evidence that FFC H2O operates via micronutrient supplementation, and may alleviate micronutrient deficiencies through the addition of critical elements such as Fe and Zn. FFC H2O offers agriculturalists a simple and effective tool for the fortification of irrigation waters with micronutrients.

Does Increased Leaf Appearance Rate Enhance Adaptation to Postanthesis Drought Stress in Sorghum?

ABSTRACTIncreased leaf appearance rate (LAR) could reduce preanthesis water use of sorghum [Sorghum bicolor (L.) Moench] by restricting plant size via reduced tillering. The aim of this paper was to assess LAR as a potential pathway for adaptation to postanthesis drought stress. Four hybrids with different LAR were grown in four semicontrolled experiments under well‐watered conditions or postanthesis drought stress and in two irrigated field experiments. Observations included leaf area dynamics, transpiration, transpiration efficiency (TE), leaf N, biomass, and grain yield. ATx642 hybrids (0.0306 leaf °C d−1) had significantly greater LAR than AQL39 hybrids (0.0279 leaf °C d−1) and this increased early main shoot vigor. Under low plant density, this reduced tiller number and hence leaf area and biomass around anthesis. As hybrids had similar TE and differed little in phenology, this can reduce preanthesis water use. Water availability at flag leaf determined grain number per plant (adjusted R2 = 0.80, p < 0.01) and hence grain yield. However, the effect of increased LAR on reduced plant size was temperature dependent. Under high temperature, genotypic differences in tillering were reduced and main shoot leaf number increased more in hybrids with greater LAR. This increased responsiveness of leaf number could increase plant size and water use at anthesis. Hence, greater LAR may confer drought adaptation only in specific environments unless it is also associated with critical aspects of biomass partitioning.

Phenotypic plasticity of Chenopodium murale across contrasting habitat conditions in peri-urban areas in Indian dry tropics: Is it indicative of its invasiveness?

Phenotypic plasticity is an important plant trait associated with invasiveness of alien plants that reflects its ability to occupy a wide range of environments. We investigated the phenotypic response of Chenopodium murale to resource variability and ontogeny. Its plant-level and leaf-level traits were studied at high-resource (HR) and low-resource (LR) sites in peri-urban areas in Indian dry tropics. Plants at LR had significantly higher root length, root/shoot biomass ratio, stem mass and root mass fractions. Plants at HR had higher shoot length, basal diameter, leaf mass fraction and leaf area ratio. Leaf-level traits like leaf area and chlorophyll a were also higher here. Mean plasticity indices for plant- and leaf-level traits were higher at HR. With increasing total plant biomass, there was significant increase in the biomass of leaf, stem, root, and reproductive parts, and root and shoot lengths, whereas root/shoot length ratio, their biomass ratio, and leaf and root mass fractions declined significantly. Allocation to roots and leaves significantly decreased with increasing plant size at both sites. But, at any size, allocation to roots was greater at LR, indicative of optimization of capture of soil nutrients, whereas leaf allocation was higher at HR. Consistently increasing stem allocation equaled leaf allocation at comparatively higher shoot lengths at HR. Reproductive biomass comprised 10–12% of the plant’s total biomass. In conclusion, the success of alien weed C. murale across environmentally diverse habitat conditions in Indian dry tropics can be attributed to its high phenotypic plasticity, resource utilization capability in low-resource habitats and higher reproductive potential. These characteristics suggest that it will continue to be an aggressive invader.

Tree size and light availability increase photochemical instead of non-photochemical capacities of Nothofagus nitida trees growing in an evergreen temperate rain forest

Nothofagus nitida (Phil.) Krasser (Nothofagaceae) regenerates under the canopy in microsites protected from high light. Nonetheless, it is common to find older saplings in clear areas and adults as emergent trees of the Chilean evergreen forest. We hypothesized that this shade to sun transition in N. nitida is supported by an increase in photochemical and non-photochemical energy dissipation capacities of both photosystems in parallel with the increase in plant size and light availability. To dissect the relative contribution of light environment and plant developmental stage to these physiological responses, the photosynthetic performance of both photosystems was studied from the morpho-anatomical to the biochemical level in current-year leaves of N. nitida plants of different heights (ranging from 0.1 to 7 m) growing under contrasting light environments (integrated quantum flux (IQF) 5-40 mol m(-2). Tree height (TH) and light environment (IQF) independently increased the saturated electron transport rates of both photosystems, as well as leaf and palisade thickness, but non-photochemical energy flux, photoinhibition susceptibility, state transition capacity, and the contents of D1 and PsbS proteins were not affected by IQF and TH. Spongy mesophyll thickness and palisade cell diameter decreased with IQF and TH. A(max), light compensation and saturation points, Rubisco and nitrogen content (area basis) only increased with light environment (IQF), whereas dark respiration (R(d)) decreased slightly and relative chlorophyll content was higher in taller trees. Overall, the independent effects of more illuminated environment and tree height mainly increased the photochemical instead of the non-photochemical energy flux. Regardless of the photochemical increase with TH, carbon assimilation only significantly improved with higher IQF. Therefore it seems that mainly acclimation to the light environment supports the phenotypic transition of N. nitida from shade to sun.

Reproductive allometry in Pedicularis species changes with elevation

Summary1. Plants produce biomass and then allocate some of it to reproductive structures, so the relationship between reproductive (R) and vegetative (V) mass is a fundamental aspect of a plant’s reproductive strategy.2. Differences among populations or taxa in the allometric relationship between R and V have been attributed to environmental conditions. We hypothesize that populations and taxa living at high elevations should exhibit a lower log R vs. log V slope than those in more benign environments, because the environmental limits on size in alpine environments should favour a relatively large reproductive allocation at smaller sizes and a smaller investment in reproduction per additional unit of biomass accumulated.3. We investigated variation in the allometric relationship between R and V among 44 naturally occurring populations representing 24 species of Pedicularis in the Tibetan Plateau, to test the hypothesis that the slope of the relationship declines with increasing elevation.4. There was a significant negative relationship between the slope of the log R vs. log V relationship and elevation among populations, although the relationship among populations within species varied. We interpret this in terms of abiotic limitations on size and decreasing efficiency of resource allocation to reproduction with increasing plant size (measured as vegetative biomass) at high elevations. We also found a significant positive relationship between the y‐intercept of the regression of log R on log V and elevation across species, but the relationship was not significant among populations within species. The combination of the lower slopes and the higher y‐intercepts for high‐elevation populations means that plants growing at high elevations allocate proportionately more biomass to reproduction at smaller sizes and less at larger sizes than plants growing at lower elevations.5. Synthesis. The allometric slope (exponent) of the R–V relationship decreases with increasing elevation among Pedicularis populations and species, reflecting fundamental changes in the costs and benefits of increased vegetative biomass with elevation.

Point pattern analysis of several psammophyte populations in the riparian ecotone in the middle reaches of Yarlung Zangbo River of Tibet, China

Aims Artemisia wellbyi, A. younghusbandii and Sophora moorcroftiana are the major psammophyte populations on the aeolian desertified land in the riparian ecotone of the middle reaches of the Yarlung Zangbo River. Our ob-jectives were to determine how spatial scales are related to population patterns and how species spatially adapt to semi-arid conditions in the riparian ecotone, as well as to provide theoretical foundation for vegetation restoration on sand dunes in the study area. Methods We selected four representative plant communities under different habitat conditions in the riparian ecotone, measured the position, height and crown diameter of each individual in a 20 m × 30 m plot and studied the population structure, spatial distribution and association of these psammophyte populations using point pattern analysis.Important findings The population structure of A. wellbyi on semi-exposed sandy gravel land and semi-fixed sandy land is that of a growing population, while A. younghusbandii and S. moorcroftiana on fixed sandy land both have the structure of a declining population. Artemisia wellbyi and A. younghusbandii both have a clumped distri-bution at different scales, while the distribution pattern of S. moorcroftiana changed from clumped to random to clumped to random as the scale increased. Spatial distribution is mainly determined by the smaller size classes, while fluctuations or changes of population distribution are mainly determined by the larger size classes. There is a scale effect among the studied populations, and positive spatial association occurs mainly at certain scales. Spatial association is often affected by plant size and environmental heterogeneity. The spatial association of A. wellbyi and S. moorcroftiana on semi-exposed sandy gravel land or semi-fixed sandy land changes from independent to positive to independent to positive.The spatial association of A. wellbyi and Oxytropis sericopetala on semi-exposed sandy gravel land changes from positive to independent to positive to independent to negative, and that of A. younghus-bandii and S. moorcroftiana changes from positive to independent. The degree of aggregation weakens with in-creasing plant size. The smaller size class has a clumped distribution, and the larger has a random distribution or random and clumped. The positive spatial association between different size classes of the same species appears to weaken when the difference of plant size becomes greater and even changes into negative spatial association, while the spatial association of various size classes at a smaller scale often is positive or independent.

Plant growth regulators and flowering of Brunonia and Calandrinia sp.

Brunonia australis R. Br (Goodeniaceae) and Calandrinia (Portulacaceae), native to Australia, are potential new flowering potted plants. This research investigated the role of daylength and growth regulators, Gibberellic acid (GA 3) and paclobutrazol (Pac), to control vegetative growth, peduncle elongation and flowering of Brunonia and Calandrinia. Plants were grown under long days (16 h), short days (11 h) and 8 weeks under short day then transferred to long day (SDLDs). Plants in each daylength were treated with GA 3, Pac, and GA 3+ Pac. GA 3 was applied as 10 μL drop of 500 mg L −1 concentration to the newest mature leaf. A single application of Pac was applied as a soil drench at 0.25 mg a.i. dose per plant. Both Brunonia and Calandrinia flowered earlier in long days but still flowered in short days, so both can be classified as facultative LD plants. Brunonia under SDLDs were more vigorous and attractive than plants under LDs while still being more compact than plants under SDs. In Brunonia, GA 3 promoted earlier flowering and increased the number of inflorescences under SDs. Pac at 0.25 mg a.i. per plant applied alone or in combination with GA 3 had extended flower development in Brunonia, and resulted in a reduced number of inflorescences per plant compared to the control plants. Vegetative growth of Calandrinia was similar under LDs, SDs and SDLDs, whereas GA 3 application increased plant size. Pac-treated Calandrinia looked compact and attractive, and Pac application did not affect time to flower and flower number.

Snail grazing facilitates growth of a bloom-forming alga

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 420:83-89 (2010) - DOI: https://doi.org/10.3354/meps08894 Snail grazing facilitates growth of a bloom-forming alga Michele Guidone1,*, Carol S. Thornber1, Emily Field1,2 1Department of Biological Sciences, University of Rhode Island, Kingston, Rhode Island 02881, USA 2Department of Biological Science, Florida State University, Tallahassee, Florida 32306, USA *Email: mguidone@my.uri.edu ABSTRACT: Herbivory often has a negative effect on plants. However, there is a growing number of examples, primarily in terrestrial ecosystems, where herbivory causes an increase in plant size, growth rate, and/or reproductive output. In marine ecosystems, the positive effects of herbivores on macroalgae are not as well studied, although limited evidence exists for herbivore-induced increases in macroalgal growth rates via 2 mechanisms: nutrient addition via grazer defecation, and epiphyte removal. In this study, we examined the effects of grazing by the mud snail Ilyanassa obsoleta on Ulva lactuca, the dominant bloom-forming macroalga in many New England estuaries. We found that the presence of I. obsoleta had a significant positive, rather than negative, effect on U. lactuca. Through caging experiments, we established that this positive effect was not due to fecal nutrient inputs from the snail. Similarly, snail contact in the absence of grazing did not affect U. lactuca growth rates. In contrast, grazing by I. obsoleta significantly reduced the microalgal cover on heavily fouled U. lactuca blades, indicating that snail herbivory of microalgal films likely facilitates U. lactuca growth. Our study demonstrates the surprising, positive effect that an abundant herbivore can have on the growth of a macroalgal bloom species. KEY WORDS: Facilitation · Compensation · Herbivory · Algal bloom · Ulva lactuca · Ilyanassa obsoleta Full text in pdf format PreviousNextCite this article as: Guidone M, Thornber CS, Field E (2010) Snail grazing facilitates growth of a bloom-forming alga. Mar Ecol Prog Ser 420:83-89. https://doi.org/10.3354/meps08894 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 420. Online publication date: December 16, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

Determination of the critical nitrogen concentration of white cabbage

A measure of a crop's nitrogen (N) status can be obtained by relating the actual N concentration of the crop to the critical plant nitrogen concentration (PNC c), the minimum N concentration required for maximum growth. In annual crops, PNC c declines as plant size increases. Describing this decline is one of the main challenges for the implementation of the PNC c concept in fertilizer management strategies. From two field experiments with repeated harvests of Dutch white cabbage and with N supply ranging from limitation to excess, the relation between PNC c and weight per unit ground area of plant dry matter exclusive of roots ( W) was estimated as: PNC c = 5.1 W −0.33% for the linear growth phase ( W > 1.5 t ha −1; LAI > 1.4). From a third field experiment, a value of 4.5% N was estimated for PNC c for the pre-linear growth phase. Also a power function: LAR = 0.011 W −0.33 described the relationship between leaf area ratio and weight. The exponent of the power function determines the rate of the decline. Therefore, having the same value of the exponent: −0.33, LAR and PNC c declined at the same rates. The proportional decline in LAR and PNC c corresponded to a constant nitrogen content on a leaf area basis of 4.7 g N m −2 until onset of head formation.

Tolerance of selected weed species to broadcast flaming at different growth stages

Organic producers rank weeds as the most important pests that limit their crop production. In order to optimize the use of propane flaming as a weed control tool, the objective of this study was to test tolerance of selected weed species to broadcast flaming performed at different growth stages. Six annual species, including one grass [barnyardgrass ( Echinochloa crus-galli)] and five broadleaves [field bindweed ( Convolvulus arvensis), kochia ( Kochia scoparia), ivyleaf morning glory ( Ipomoea hederacea), velvetleaf ( Abutilon theophrasti) and Venice mallow ( Hibiscus trionum)] were flamed at three growth stages with six doses of propane. The propane doses applied were 0, 12, 31, 50, 68 and 87 kg/ha. Flaming treatments were applied utilizing a custom built flamer mounted on a four-wheeler moving at a constant speed of 6.4 km/h. Species response to propane were described by log-logistic models based on visual injury ratings and dry matter (DM) for each weed species. Overall response to flaming varied among species, growth stage and propane dose. Broadleaf weeds were more susceptible to flaming than the grass regardless of the growth stage. A dose of 76 kg/ha of propane was needed to obtain 90% DM reduction for 7-leaf (L) barnyardgrass compared to much lower doses of 40, 49, 55, 56 and 51 kg/ha propane for 8-L bindweed, 6-L kochia, 10-L morning glory, 7-L velvetleaf and 5-L Venice mallow, respectively. Moreover, the tolerance of both grassy and broadleaf weed species to broadcast flaming increased with increase in plant size. A 90% DM reduction in velvetleaf was obtained with 42, 56 and 102 kg/ha of propane for 5-L, 7-L and 16-L stages, respectively. The tested broadleaf weed species were effectively controlled (90% DM reduction) with propane dose of 30–60 kg/ha when flamed at early growth stages (3-L to 14-L), while the same dose of propane provided only 80% DM reduction in barnyardgrass when flamed at vegetative stages (4-L to 7-L). It was not possible to obtain 90% DM reduction in barnyardgrass when flamed at flowering stage with the propane doses tested in this experiment.

Cell Number Regulator1Affects Plant and Organ Size in Maize: Implications for Crop Yield Enhancement and Heterosis

Genes involved in cell number regulation may affect plant growth and organ size and, ultimately, crop yield. The tomato (genus Solanum) fruit weight gene fw2.2, for instance, governs a quantitative trait locus that accounts for 30% of fruit size variation, with increased fruit size chiefly due to increased carpel ovary cell number. To expand investigation of how related genes may impact other crop plant or organ sizes, we identified the maize (Zea mays) gene family of putative fw2.2 orthologs, naming them Cell Number Regulator (CNR) genes. This family represents an ancient eukaryotic family of Cys-rich proteins containing the PLAC8 or DUF614 conserved motif. We focused on native expression and transgene analysis of the two maize members closest to Le-fw2.2, namely, CNR1 and CNR2. We show that CNR1 reduced overall plant size when ectopically overexpressed and that plant and organ size increased when its expression was cosuppressed or silenced. Leaf epidermal cell counts showed that the increased or decreased transgenic plant and organ size was due to changes in cell number, not cell size. CNR2 expression was found to be negatively correlated with tissue growth activity and hybrid seedling vigor. The effects of CNR1 on plant size and cell number are reminiscent of heterosis, which also increases plant size primarily through increased cell number. Regardless of whether CNRs and other cell number-influencing genes directly contribute to, or merely mimic, heterosis, they may aid generation of more vigorous and productive crop plants.

Ontogenetic shift in the scaling of dark respiration with whole‐plant mass in seven shrub species

Summary 1. Recent evidence suggests that metabolic scaling exponents should shift from ≈ 1 to ∼¾ as plants grow from seedlings to mature trees. This study examines whether there is an ontogenetic shift in the scaling exponent of dark respiration with whole‐plant biomass and whether the allometry of dark respiration vs. plant total nitrogen content is consistent with these metabolic scaling relationships. 2. We examined seedling mass, dark respiration, biomass allocation, water and nitrogen contents, and relative growth rates for 351 seedlings of seven shrub species that span three orders of magnitude in total plant mass (i.e. <1 mg to >1 g). 3. Dark respiration increased with increasing seedling mass in each of three growth stages for each species. The scaling exponents for dark respiration vs. plant mass were c. 1·0 during the earliest stage of seedling development (<60 days after germination) but declined in the later two growth stages (>90 and <120 days after seed germination) for five of the seven species studied. However, the metabolic scaling relationship was isometric when the data were pooled for each species across all size classes. 4. With increasing plant size, the biomass allocated by each species to the metabolically active organ (leaf) generally scaled against whole plant biomass with a slope smaller than 1·0 but significantly larger than ¾. 5. Water and nitrogen contents declined with increasing seedling mass and whole plant dark respiration increased disproportionally (i.e. scaling slope >1) with increasing total plant water or nitrogen content, possibly because small seedlings have a lower water and nutrient‐use efficiency compared to larger ones in water‐ and nutrient‐ unlimited habitats. 6. The change in relative growth rate paralleled the ontogenetic shift in the dark respiration vs. mass relationship, which may explain the isometric metabolic scaling relationship if growth efficiency is inversely proportional to seedling mass. 7. We therefore demonstrate an ontogenetic shift in the metabolic scaling during plant ontogeny. Although the proximate mechanisms underlying the shift are not fully understood, we speculate that a contributing factor is the accrual of less metabolically active tissues or organs with increasing total body mass in the form of secondary tissues with high cell wall volume fractions (e.g. wood and phellum).

A review of light interception in plant stands from leaf to canopy in different plant functional types and in species with varying shade tolerance

AbstractChanges in the efficiency of light interception and in the costs for light harvesting along the light gradients from the top of the plant canopy to the bottom are the major means by which efficient light harvesting is achieved in ecosystems. In the current review analysis, leaf, shoot and canopy level determinants of plant light harvesting, the light‐driven plasticity in key traits altering light harvesting, and variations among different plant functional types and between species of different shade tolerance are analyzed. In addition, plant age‐ and size‐dependent alterations in light harvesting efficiency are also examined. At the leaf level, the variations in light harvesting are driven by alterations in leaf chlorophyll content modifies the fraction of incident light harvested by given leaf area, and in leaf dry mass per unit area (MA) that determines the amount of leaf area formed with certain fraction of plant biomass in the leaves. In needle‐leaved species with complex foliage cross‐section, the degree of foliage surface exposure also depends on the leaf total‐to‐projected surface area ratio. At the shoot scale, foliage inclination angle distribution and foliage spatial aggregation are the major determinants of light harvesting, while at the canopy scale, branching frequency, foliage distribution and biomass allocation to leaves (FL) modify light harvesting significantly. FL decreases with increasing plant size from herbs to shrubs to trees due to progressively larger support costs in plant functional types with greater stature. Among trees, FL and stand leaf area index scale positively with foliage longevity. Plant traits altering light harvesting have a large potential to adjust to light availability. Chlorophyll per mass increases, while MA, foliage inclination from the horizontal and degree of spatial aggregation decrease with decreasing light availability. In addition, branching frequency decreases and canopies become flatter in lower light. All these plastic modifications greatly enhance light harvesting in low light. Species with greater shade tolerance typically form a more extensive canopy by having lower MA in deciduous species and enhanced leaf longevity in evergreens. In addition, young plants of shade tolerators commonly have less strongly aggregated foliage and flatter canopies, while in adult plants partly exposed to high light, higher shade tolerance of foliage allows the shade tolerators to maintain more leaf layers, resulting in extended crowns. Within a given plant functional type, increases in plant age and size result in increases in MA, reductions in FL and increases in foliage aggregation, thereby reducing plant leaf area index and the efficiency of light harvesting. Such dynamic modifications in plant light harvesting play a key role in stand development and productivity. Overall, the current review analysis demonstrates that a suite of chemical and architectural traits at various scales and their plasticity drive plant light harvesting efficiency. Enhanced light harvesting can be achieved by various combinations of traits, and these suites of traits vary during plant ontogeny.

Biological stoichiometry of plant production: metabolism, scaling and ecological response to global change

Biological stoichiometry theory considers the balance of multiple chemical elements in living systems, whereas metabolic scaling theory considers how size affects metabolic properties from cells to ecosystems. We review recent developments integrating biological stoichiometry and metabolic scaling theories in the context of plant ecology and global change. Although vascular plants exhibit wide variation in foliar carbon:nitrogen:phosphorus ratios, they exhibit a higher degree of 'stoichiometric homeostasis' than previously appreciated. Thus, terrestrial carbon:nitrogen:phosphorus stoichiometry will reflect the effects of adjustment to local growth conditions as well as species' replacements. Plant stoichiometry exhibits size scaling, as foliar nutrient concentration decreases with increasing plant size, especially for phosphorus. Thus, small plants have lower nitrogen:phosphorus ratios. Furthermore, foliar nutrient concentration is reflected in other tissues (root, reproductive, support), permitting the development of empirical models of production that scale from tissue to whole-plant levels. Plant stoichiometry exhibits large-scale macroecological patterns, including stronger latitudinal trends and environmental correlations for phosphorus concentration (relative to nitrogen) and a positive correlation between nutrient concentrations and geographic range size. Given this emerging knowledge of how plant nutrients respond to environmental variables and are connected to size, the effects of global change factors (such as carbon dioxide, temperature, nitrogen deposition) can be better understood.

Ontogenetic changes in the numbers of short‐ vs. long‐shoots account for decreasing specific leaf area in Acer rubrum (Aceraceae) as trees increase in size

Specific leaf area (SLA) is reported to decrease with increasing plant size among dicot tree species despite a strong positive correlation between SLA and relative growth rate. This diminishing returns in SLA may result from changes in the relative numbers of different shoot types bearing leaves with different SLAs as trees increase in overall size. This ontogenetic shift hypothesis was examined for 15 Acer rubrum trees differing in basal stem diameter (0.01 m ≤ D ≤ 0.62 m). Detailed analyses of the largest tree showed that short-shoots produced leaves with significantly smaller SLA than the leaves produced by long-shoots regardless of the location of shoots within the canopy. A combination of random effect and split-plot (main-effect) ANOVA models showed that >94% of the variance observed for SLA was attributable to shoot type rather than to the location of leaves in the canopy. Further, with increasing trunk diameter, the number of short-shoots increased rapidly relative to the number of long-shoots. Although the leaves of short-shoots gain disproportionately more surface area per unit mass investment compared to the leaves produced by long-shoots, our data show that ontogenetic shifts occurring at the shoot and whole plant level account for size-dependent decreases in total canopy SLA.

Positive biodiversity–productivity relationship due to increased plant density

1. Positive effects of biodiversity on plant productivity may result from diversity-induced changes in the size or density of individual plants, yet these two possibilities have never been tested at the same time in a biodiversity experiment with a large species pool. Here, we distinguish between size effects and density effects on plant productivity, using data from 198 experimental grassland communities that contained 1–16 species. Plant modules such as tillers or rosettes were defined as relevant units, being equivalent to plant individuals in the majority of species. 2. In agreement with previous studies, we found positive effects of species richness on above-ground productivity. We show that this positive biodiversity effect resulted from diversity-induced increases in module density rather than from increases in module size. In contrast, variation in productivity within diversity levels was related to module size rather than module density. 3. The size–density relationships varied among plant functional groups and among species but their average response to increasing species richness paralleled the pattern observed at the level of the entire plant communities: species richness had a positive effect on above-ground species biomass and species module density but not on species module size. Twenty-four out of 26 overyielding species had denser populations and 25 out of 28 underyielding species had smaller modules in mixtures than in monocultures. 4. Synthesis: In grasslands, an increase in community productivity must involve an increase in plant size or density. We found that diversity-induced increases in productivity were related to diversity-induced increases in density, whereas diversity-independent increases in productivity were related to increases in plant size. Our results suggest that increased density of overyielding species in mixtures was the main driver of the positive biodiversity–productivity relationship in our experiment. We conclude that the mechanisms leading to enhanced productivity of species-rich as compared with species-poor communities cannot be derived from mechanisms explaining high productivity within communities that contain a particular number of species.

Scaling relations for a functionally two‐dimensional plant:Chamaesyce setiloba(Euphorbiaceae)

Many characteristics of plants and animals scale with body size as described by allometric equations of the form Y = βM(α), where Y is an attribute of the organism, β is a coefficient that varies with attribute, M is a measure of organism size, and α is another constant, the scaling exponent. In current models, the frequently observed quarter-power scaling exponents are hypothesized to be due to fractal-like structures. However, not all plants or animals conform to the assumptions of these models. Therefore, they might be expected to have different scaling relations. We studied one such plant, Chamaesyce setiloba, a prostrate annual herb that grows to functionally fill a two-dimensional space. Number of leaves scaled slightly less than isometrically with total aboveground plant mass (α ≈ 0.9) and substantially less than isometrically with dry total stem mass (α = 0.82), showing reduced allocation to leaf as opposed to stem tissue with increasing plant size. Additionally, scalings of the lengths and radii of parent and daughter branches differed from those predicted for three-dimensional trees and shrubs. Unlike plants with typical three-dimensional architectures, C. setiloba has distinctive scaling relations associated with its particular prostrate herbaceous growth form.

The Impact of Trade on Plant Scale, Production-Run Length and Diversification

This paper examines the effect of trade liberalization on plant scale, production-run length and product diversification. We first develop a model of trade in differentiated products with multiproduct plants. We then present empirical evidence using a large panel of Canadian manufacturing plants and their experience with the 1989 Canada-U.S. Free Trade Agreement (FTA). The model predicts that the bilateral tariff reduction reduces the product diversification of exporting plants, increases the production-run length and has an ambiguous effect on the size of those plants. It also reduces the product diversification and size of non-exporting plants, and has no effect on the production-run length of those plants. The empirical evidence on non-exporting plants provides broad support for the model. The evidence on exporting plants shows that exporters reduce product diversification, and increase production-run length and plant size, but those changes do not appear to be related to tariff cuts. Once in the export markets, plants respond to forces other than tariff cuts. Further tariff cuts have less effect on those plants.

Size-Dependent Sex Allocation in a Monoecious SpeciesSagittaria pygmaea(Alismataceae)

Sagittaria species have been reported to display remarkable variation in gender expression. Here, we investigated gender variation in Sagittaria pygmaea, the smallest sized monoecious species in the genus. We used the midvein length as an indicator of plant size and production of male and female flowers as an indicator of gender variation in a single inflorescence. We counted the total number of inflorescences to assess the effect of inflorescence variation on the gender variation pattern. Our results showed that variation in inflorescence number did not affect gender variation. Male flower production increased with increasing plant size, but female flower production did not. Plants of S. pygmaea might enhance their paternal reproductive success by increasing the number of male flowers with increasing plant size.

Interspecific competition changes reproductive output but does not increase reproductive costs in a grassland perennial

Abstract In plants, it is hypothesized that allocation trade-offs may appear only when expenditures like seed production are high or external resources are scarce. In this study, we tested whether reproductive costs are more pronounced under enhanced interspecific competition. In a common garden, we investigated phenotypic correlations between sexual reproduction, clonal growth and storage structures in the grassland perennial, Succisa pratensis . During the past 50 years, habitats of this species have faced an expansion of clonal grasses that increase competition intensity. We simulated this process by growing five populations of Succisa from high- and low-production habitats with its clipped and non-clipped competitor, Agrostis capillaris . In addition, we experimentally removed flower heads of Succisa plants from one population grown with and without A. capillaris . We demonstrated costs of sexual reproduction by flower-head removal (resulting in increased plant size and relative allocation to belowground structures) but not by phenotypic correlations. We found no evidence that reproductive costs increase in a competitive environment and the opposite pattern was shown in both approaches used. However, high competition intensity reduced relative investment to flower-head production. In plants from low-production habitats, competition also reduced the absolute number of flower heads and belowground biomass as a result of smaller plant size. We assume that populations from low-production habitats are more prone to extinction as they have a reduced likelihood of local persistence and of escape to more suitable habitats during advancing succession.