Allometric estimation of total leaf area in the neotropical palm Euterpe oleracea at La Selva, Costa Rica

We estimated the magnitude of the total leaf area of the neotropical palm Euterpe oleracea and examined its allometry relative to the variation in stem height and diameter at La Selva Biological Station in Costa Rica. The allometric relationships between frond leaf area and frond length (from tip to base), and between frond leaf area and number of leaflets, were determined by natural logarithmic regressions to estimate the total area of each frond. Palm total leaf area was then estimated by adding the area of the composing fronds. We fit 14 separate regression models that related one or more of the morphological variables (number of fronds, diameter at breast height, stem height) to the total leaf area. Our results show that palm total leaf area is directly proportional to the number of fronds and palm size as reflected in stem height and diameter. Eight out of the 14 models had r ² values of >0.90 and incorporated a diverse combination of predictor variables. Simple linear regression models were more congruent with the observed values of total leaf area, whereas natural logarithmic models overestimated the value of total leaf area for large palms. Both approaches show a high degree of association among morphological characters in E. oleracea supporting the hypothesis that palms behave like unitary organisms, and are morphologically constrained by the lack of secondary meristems. To afford attaining canopy heights, woody palms need to show a high degree of phenotypic integration, shaping their growth and allometric relationships to match spatial and temporal changes in resources.     

Alginate content and composition ofMacrocystis pyrifera from New Zealand

Tissue samples ofMacrocystis pyrifera from 2 sites in southern New Zealand and harvested over a period of 12 months were analysed for alginate content and composition (M:G ratio). Plants were divided into three frond classes of different length and each frond was further separated into age categories of blades and stipes (viz young, mature and old blades; mature and old stipes). Within each size class, younger blades had higher alginate content than older blades. Stipes did not show such variation with age. Alginate from younger blades and stipes had higher proportions of mannuronic acid residues than those from old blades and stipes. The range of M:G ratios for age categories of either blades or stipes from longer fronds was greater than those for smaller fronds. Alginate content and M:G ratios of stipes were always higher than for blades. The difference between M:G ratios of blades and stipes was greater for smaller fronds than for longer ones. Differences between collection sites and seasonal trends are also discussed.author for correspondence     

Regeneration and reproduction of Mazzaella cornucopiae (Rhodophyta, Gigartinaceae) after frond harvesting

The effects that different intensities of frond harvesting have on frond regeneration and subsequent production of reproductive structures were investigated for the red intertidal alga Mazzaella cornucopiae (Postels & Ruprecht) Hommersand from British Columbia, Canada. Harvesting was done by pruning fronds in the late spring (when stand biomass is highest) of 1993 at two intensities: total and partial collection of fronds, in this second case leaving all frond biomass less than 1 cm high in place. Holdfasts were not damaged. Total percent cover of thalli, frond density, mean frond length, and stand biomass for these experimental quadrats were statistically similar to values for control quadrats in the spring of 1994. These results suggest that one total harvest of fronds per year, done in late spring without damaging holdfasts, may give the highest sustainable yield of biomass. The effects of harvesting intensity on reproduction were variable and difficult to explain. Neither the appearance nor the abundance of cystocarpic fronds were affected by frond pruning, compared with control areas, but pruning did affect the appearance and the abundance of tetrasporic fronds. Partial pruning resulted in a longer presence of tetrasporic fronds, whereas total pruning was associated with their complete absence. Results are compared with those for the few other species of the Gigartinaceae for which experimental harvesting has been done. This revised version was published online in August 2006 with corrections to the Cover Date.     

Plant response to overcrowding – Lemna minor example

Plants adopt various strategies in response to increasing density. We tested that response in two populations of Lemna minor L. – a free floating aquatic plant that frequently experiences intraspecific competition for space. Surface area of fronds and colonies, colony size (the number of fronds per colony), the rate of reproduction (based on the number of produced fronds) and growth rate (enlargement of surface area of all colonies) were the analysed factors presumably affected by density. The study was performed in natural stands and in experimental conditions with the use of two contrasting plant densities. Plants growing in natural conditions produced fronds of smaller and less variable surface area as a response to overcrowding but the number of fronds per colony was unrelated to plant density. Stable experimental conditions facilitated formation of fronds and colonies larger than in the field but frond detachment decreasing colony size was more intensive at high than at low density. This strategy allowed plants to more efficiently occupy limited available space. No self-thinning was observed during experimental cultures. Due to increasing frond area in cultures, growth rate was always higher than the rate of plant reproduction. Both were strongly negatively affected by high density. Performed calculations indicate that density-dependent growth inhibition starts when L. minor colonies cover the available water surface with a mono-layer mat. Some types of responses were found to significantly differ between analysed populations, which was also shown by genetic differences tested with he ISSR-PCR technique. Possible causal relationship between plant strategies and their genomic structure needs, however, further studies.     

A field study on the growth and development ofDumontia contorta

Young, crustose plants ofDumontia contorta grown in the laboratory from carpospores were transferred in September 1983 to their natural habitat in Lake Grevelingen (SW Netherlands). The number of upright fronds per crust, length of upright fronds, and diameter of crusts were determined monthly until October 1984 and the presence of tetrasporangia was noted. Although fronds were initiated from crusts throughout the period of short daylengths (<13 h light per day, i.e. from September to March), the majority of the fronds was initiated in October and November when short daylengths coincided with optimum temperatures for frond initiation (ca 10–20°C). By April, i.e. within 5–6 months, these plants had reached maximum sizes and had become fertile; subsequently, the plants decayed. The successively smaller numbers of fronds that were formed in December and January also reached maximum sizes after ca 5–6 months, i.e. by May and June, but these fronds remained much smaller than the fronds initiated in October–November, possibly because of lower temperatures and light levels at the start of their growth. It is suggested that the fronds have a fixed maturation period (ca 5–6 months) irrespective of their size and the moment of their initiation. Crusts were shown to “oversummer” and to produce new fronds at the onset of shortday conditions in September 1984. Dedicated to Dr. Dr. h. c. Peter Kornmann on the occasion of his eightieth birthday.     

Quantitative trait locus analysis of leaf dissection in tomato using Lycopersicon pennellii segmental introgression lines

Leaves are one of the most conspicuous and important organs of all seed plants. A fundamental source of morphological diversity in leaves is the degree to which the leaf is dissected by lobes and leaflets. We used publicly available segmental introgression lines to describe the quantitative trait loci (QTL) controlling the difference in leaf dissection seen between two tomato species, Lycopersicon esculentum and L. pennellii. We define eight morphological characteristics that comprise the mature tomato leaf and describe loci that affect each of these characters. We found 30 QTL that contribute one or more of these characters. Of these 30 QTL, 22 primarily affect leaf dissection and 8 primarily affect leaf size. On the basis of which characters are affected, four classes of loci emerge that affect leaf dissection. The majority of the QTL produce phenotypes intermediate to the two parent lines, while 5 QTL result in transgression with drastically increased dissection relative to both parent lines.     

DEMOGRAPHY OF FRONDS OF SARGASSUM LAPAZEANUM FROM SOUTHERN BAJA CALIFORNIA, MEXICO, DURING EARLY STAGES

In terms of biomass, Sargassum lapazeanum (Phaeophyceae, Fucales) is one of the most important seaweeds in La Paz Bay, on the southeastern coast of the Baja California Peninsula, Mexico. This species can be found year-round in shallow subtidal sites. Standing biomass is lowest between fall and winter and highest between spring and summer. We are currently studying the annual demography of fronds as a necessary step to understanding the mechanisms of population regulation. Work is being done on a bed of about 90 m in length and three m in width. At this stage of abstract submission, we can report results for winter only. Random samples were collected in February and in March 2000 to estimate stand biomass, frond density, and size (frond length) structure. In addition, we labeled fronds with numbered plastic tags to estimate their rates of growth and of mortality during this period. Rates of recruitment were estimated from a combined analysis of the above. In February, fronds were all shorter than 6.5 cm. Between February and March, mean total frond density increased from 122 to 776 fronds m⁻² (n = 30 quadrats). The mean recruitment rate was 667 fronds m⁻², the mean growth rate was 0.5 cm day⁻¹ (n = 60 fronds), and the mean mortality rate was 43 fronds m⁻². From last year's preliminary observations, we expect to observe peaks of biomass and of reproduction in late spring, followed by negative growth rates and high mortality rates during summer.     

Scaling of Frond Form in Hawaiian Tree Fern Cibotium glaucum: Compliance with Global Trends and Application for Field Estimation

Large‐fronded tree ferns are critical components of many tropical forests. We investigated frond and whole‐plant allometries for Hawaiian keystone species Cibotium glaucum, for prediction and to compare with global scaling relationships. We found that C. glaucum fronds maintain geometric proportionality across a wide range of plant and frond sizes. These relationships result in strong allometries that permit rapid field estimation of frond size from simple linear dimensions. C. glaucum frond allometries complied with intra‐ and interspecific global trends for leaf area versus mass established for much smaller‐leafed species, indicating ‘diminishing returns’ in photosynthetic area per investment in mass for larger fronds. The intraspecific trend was related to declining water content in larger fronds, but not to a significantly larger investment in stipe or rachis relative to lamina. However, C. glaucum complied with the global interspecific trends for greater allocation to support structures in larger leaves. Allometries for frond number and size versus plant height showed that as plants increase in height, frond production and/or retention progressively declines, and the increases of leaf size tend to level off. These frond and whole plant‐level relationships indicate the potential for estimating frond area and mass at landscape scale to enrich studies of forest dynamics.     

Changes in habitat complexity negatively affect diverse gastropod assemblages in coralline algal turf

The physical structure of a habitat generally has a strong influence on the diversity and abundance of associated organisms. I investigated the role of coralline algal turf structure in determining spatial variation of gastropod assemblages at different tidal heights of a rocky shore near Sydney, Australia. The structural characteristics of algal turf tested were frond density (or structural complexity) and frond length (the vertical scale over which structural complexity was measured). This definition of structural complexity assumes that complexity of the habitat increases with increasing frond density. While frond length was unrelated to gastropod community structure, I found significant correlations between density of fronds and multivariate and univariate measures of gastropod assemblages, indicating the importance of structural complexity. In contrast to previous studies, here there were negative relationships between the density of fronds and the richness and abundance of gastropods. Artificial habitat mimics were used to manipulate the density of fronds to test the hypothesis that increasing algal structural complexity decreases the richness and abundance of gastropods. As predicted, there were significantly more species of gastropods in loosely packed than in tightly packed turf at both low- and mid-shore levels. Despite large differences between gastropod assemblages at different tidal heights, the direction and magnitude of these negative effects were similar at low- and mid-shore levels and, therefore, relatively independent of local environmental conditions. These novel results extend our previous understanding of the ecological effects of habitat structure because they demonstrate possible limitations of commonly used definitions of structural complexity, as well as distinct upper thresholds in the relationship between structural complexity and faunal species richness.     

Nodular somatic embryogenesis and frond regeneration in duckweed,Lemna gibba G3

Duckweed(Lemna gibba) is a useful model system for elucidating plant development, but the techniques needed for regenerating fronds from calli are not yet well established. This study examined the effects of auxin, sucrose, and gelling agents on callus and frond formation inL. gibba G3. After three weeks of culturing on a solid medium, two types of calli were observed: watery, pale-green, and undifferentiated; or white, compact calli that were organized into nodules and which resembled somatic embryogenie calli. Homogeneous callus lines were produced through selective subculture. To induce nodular calli, auxin (2,4-D) was absolutely required, with an effective concentration of 5 to 20 μM; induction was found to be possible with up to a maximum concentration of 4.4%. The calli were then maintained on a medium with a reduced 2,4-D concentration (1 μM), and were transferred every three weeks. Optimal callus induction and growth were obtained by using 3% sucrose with a combination of 0.15% Gelrite and 0.4% agar. Fronds, however, could be regenerated only on distilled water solidified with a combination of 0.4% agar and 0.15% Gelrite. On this medium, 87% of the callus expiants regenerated into fronds after four weeks of culture. These new fronds were morphologically normal but small, approximately 15 to 20% of the size of stock fronds. Continued culture of these fronds in an SH medium produced normal duckweeds, and histological examination of the cultures revealed several distinct types of callus nodules. Nonetheless, because zygotic embryogenesis inL. gibba does not produce distinct bipolar structures, the developmental pathway of frond regeneration from these nodular cultures remains unknown.     

Reconstructing the Pennsylvanian-Age Filicalean Fern Botryopteris tridentata (Felix) Scott

Numerous anatomically preserved fragments of the Middle Pennsylvanian age filicalean fern, Botryopteris tridentata, occur in coal balls collected at the Pittsburgh and Midway Coal Company mine near Baxter Springs, Kansas. Included are the first fertile specimens of the species, evidence of complete vegetative frond architecture, and fronds that are specialized for vegetative propagation. Rhizomes are erect and unbranched, have helical phyllotaxis and short internodes, and typically display an ectophloic solenostele. Fronds are tripinnately compound with lobed pinnules that have open, dichotomous venation. Fertile pinnae or individual pinnules are interspersed among vegetative frond segments and produce sori of annulate sporangia beneath veins on the abaxial pinnule surface. Fertile pinnule lobes are rolled toward the abaxial surface to enclose the sori. Sporangia have a horizontally elongated biseriate annulus located near the short broad stalk and produce tetrahedral-shaped trilete spores with coarse spines. Epiphyllous branches diverge from the stipe or rachis, and some fronds produce only branches. This fern is reconstructed as having short stems. Helically arranged fronds are either pinnately dissected with lobed vegetative pinnules and abaxially rolled fertile pinnules or are specialized for vegetative propagation. The latter functioned as the foliar equivalent of stolons. While some characters of the B. tridentata plant are similar to those of Botryopteris forensis, generitype of the Botryopteridaceae, others are more comparable to those of Psalixochlaena cylindrica, generitype of Psalixochlaenaceae, suggesting the need for reevaluation of systematic relationships among species of the Botryopteridaceae and Psalixochlaenaceae.     

WATER MOTION AND MORPHOLOGY IN CHONDRUS CRISPUS (RHODOPHYTA)1

Morphological variability of intertidal Chondrus crispus Stackh. fronds along a small open rocky coast was related to wave exposure and emersion. Cluster analysis revealed two well-defined morphologies: filiform and planiform, named the N morphotype and B morphotype, respectively. We propose a rapid method of classifying fronds based on the morphology of the cross section at half the height on the thallus. The N morphotype is characterized by fewer dichotomies per unit length, a circular cross section with a large inner cortex, and narrow fronds. It is abundant at low intertidal and exposed sites. The B morphotype is characterized by more dichotomies, smaller sizes, a subelliptical or flattened cross section, and broad fronds. It is abundant at high intertidal sites in sheltered areas. Regression analysis revealed a major effect of water movements on frond morphology with respect to tidal level, which was more evident at high intertidal levels. No relationships were observed between morphology and life history phases.     

Field studies of the relationship between herbivore damage and tannin concentration in bracken (Pteridium aquilinum Kuhn)

Summary The acceptance of secondary plant metabolites as herbivore deterrents rests primarily on their deleterious effects on herbivores. Efforts to demonstrate differential fitness in natural plant populations with varying concentrations of tannin have failed, since coevolved plant predators may physiologically or behaviorally circumvent the defense, which results in apparently equal amounts of damage to defended and undefended individuals. In this study, two approaches were used to overcome this difficulty. 1) Theoretically, more energy should be allocated to the defense of parts which contribute more heavily to the plant's fitness. Bracken fern clones produce fronds throughout the growing season. Fronds which are produced early should be more heavily defended than late-emerging fronds which will return less photosynthate per unit cost of production. The results of this study do not support this prediction; it appears that the production of tannin is more closely linked to environmental factors such as water stress than to date of frond emergence. Fronds which emerged in August contained as much tannin as fronds which emerged in May. 2) By recording the temporal occurrence of herbivore damage in bracken ferns, it was found that in fronds which escaped attack until after reaching maturity there was a significant negative correlation between tannin concentration in the frond and the amount of damage experienced. This result supports the generally accepted assumption that herbivory has been a selective force in the evolution of tannin as a defensive substance.     

Translocation of C in Macrocystis pyrifera (Giant Kelp)

The pattern of import and export of ¹⁴C-labeled assimilates in Macrocystis pyrifera (L.) C. A. Agardh in southern California was studied by labeling single blades on fronds, in situ, with [¹⁴C]NaHCO₃ for 24 hours. The pattern was found to be similar to that known in dicotyledons: actively growing tissue imported and did not export. As a blade reached maturity it began to export, at first only acropetally to the apex which formed it, later also down the frond to sporophylls and frond initials at the base of the frond, and into the apical regions of juvenile fronds; finally there was a phase of declining export, late in the life of the blade, when transport was only downward. Young fronds imported from older fronds until they were approximately 3 meters long, by which time they had developed mature, upward exporting blades. No translocation was found from a younger frond to an older frond, nor was there transport upward from a blade on a frond lacking the apical region.     

Effects of medium components and light on callus induction, growth, and frond regeneration in Lemna gibba (Duckweed)

Summary Basal media, plant growth regulator type and concentration, sucrose, and light were examined for their effects on duckweed (Lemna gibba) frond proliferation, callus induction and growth, and frond regeneration. Murashige and Skoog medium proved best for callus induction and growth, while Schenk and Hildebrandt medium proved best for frond proliferation. The ability of auxin to induce callus was associated with the relative strength of the four auxins tested, with 20 or 50 μM 2,4-dichlorophenoxyacetic acid giving the highest frequency (10%) of fronds producing callus. Auxin combinations did not improve callus induction frequency. Auxin in combination with other plant growth regulators was needed for long-term callus growth; the two superior plant growth regulator combinations were 10 μM naphthaleneacetic acid, 10 μM gibberellic acid, and 2 μM benzyladenine with either 1 or 20 μM 2,4-dichlorophenoxyacetic acid. Three percent sucrose was best for callus induction and growth. Callus induction and growth required light. Callus that proliferated from each frond’s meristematic zone contained a mixture of dedifferentiated and somewhat organized cell masses. Continual callus selection was required to produce mostly dedifferentiated, slow-growing callus cell lines. Frond regeneration occurred on Schenk and Hildebrandt medium without plant growth regulators but was promoted by 1 μM benzyladenine. Callus maintained its ability to regenerate fronds for at least 10 mo. Regenerated fronds showed a slower growth rate than normal fronds and a low percentage of abnormal morphologies that reverted to normal after one or two subcultures.     

The effects of cutting and asulam on numbers of frond buds and biomass of fronds and rhizomes of bracken Pteridium aquilinum

The effects of cutting and the herbicide asulam for the control of a dense uniform stand of bracken Preridium aquilinum were investigated experimentally over a 6 —yr period in Norfolk, England. Bracken is a particularly difficult species to control by either mechanical or herbicidal means because of its extensive and complex rhizome network, containing large reserves of dry matter and a large number of frond buds. Cutting bracken in the summer removed dry matter from the system and reduced frond vigour but did not reduce the number of frond buds to a critical level. Whereas the first few cuts substantially reduced the standing crop of fronds, relatively stable standing crops of fronds were observed in future years despite continued cutting. Asulam caused a 99% reduction in the standing crop of fronds in the year after spraying, but in the absence of further treatment, fronds recovered to pre-spray levels after 6 yr. Asulam caused severe localised damage to frond buds and rhizome apices, but otherwise the rhizome network remained intact. New sections of frond bearing rhizome (short shoots) developed on storage rhizome (long shoots) deep in the soil of both the asulam plots and those cut.     

Reproduction ofChondrus crispus Stackhouse (Rhodophyta,Gigartinales) in sublittoral Prince Edward Island,Canada

The influence of size (as biomass), morphology and depth on reproductive patterns was examined in populations ofChondrus crispus in the sublittoral zone of Prince Edward Island, Canada. Fronds of ≥ 10 mg wet wt were considered, and a minimum biomass could not be related to reproduction. However, as frond biomass increased, the frequency of reproductive structures also increased. Reproductive maturity was related to the number of dichotomies. Fronds with less than two dichotomies were only occasionally reproductive, while those with two or more dichotomies could bear sori. Depth in the Prince Edward Island environment had no apparent influence on reproductive maturity, and there was no apparent relationship between depth and the vertical distribution of cystocarpic or tetrasporic fronds.     

Protein and nitrate content of lemna sp. As a function of developmental stage and incubation temperature

Lemna protein per frond and per root increases with developmental stage until plants are at least two generations old. Protein per frond, per root, and per unit dry weight is greater in plants grown at 23.9 C than at 18.3 C. More protein is found in fronds than in roots, and more nitrate occurs in roots than in fronds. Nitrate per root increases with developmental stage and is higher (per root) in plants grown at 23.9 C than in those grown at 18.3 C. The distribution of generations within a growing population is constant for at least eight doubling times. Whether populations multiply slowly at 15.6 C or more rapidly at 23.9 C, fronds which have not yet produced progeny form 62% of the population; fronds which are one generation old form 24% of the population; and fronds which are two generations old form 9% of the population.     

The relationship between stand biomass and frond density in the clonal alga Mazzaella cornucopiae (Rhodophyta,Gigartinaceae)

The negative relationship between stand biomass and plant density observed in terrestrial plants was tested among fronds of a clonal red alga, Mazzaella cornucopiae. Stand biomass and frond density were estimated bimonthly for 1 year on 7 permanent quadrats. A positive linear correlation was found between biomass and density for the whole data set, suggesting the lack of self-thinning among fronds of this intertidal alga at natural densities. Higher frond densities could favor increased water retention among fronds, thus minimizing desiccation during low tides. In this way, stands could maintain higher production of biomass. Fronds may also be cushioned better against wave action at higher frond densities, thus decreasing the detachment of larger fronds. The temporal variation of the relationship between biomass and density was plotted separately for these 7 quadrats. Four quadrats showed positive linear correlation between both variables (the other three quadrats showed non-significant positive linear correlation). Their four slopes are statistically similar to that found for the entire data set. It is possible, then, that there is only one positive slope for the biomass-density relationship in this population. If this is true, standing biomass could be estimated from the density of fronds.