Vegetative Blades Research Articles

Desiccation and thermo-tolerance of Fucus guiryi (Phaeophyceae) from its southernmost populations (Canary Islands, Eastern Atlantic)

Abstract Populations inhabiting the periphery of a species’ distribution suffer the immediate pressure of the environmental changes. Studying their physiology under stressful conditions is essential in the context of climate change. We characterized two morphotypes with measurements of length, thickness and width of the thallus of the macroalga Fucus guiryi in two localities (north and south) in Tenerife (Canary Islands), the southern limit of distribution of the species. We hypothesized that the individuals from the north locality, especially the large morphotype, would be more vulnerable to desiccation and high temperatures than those from the south. Tolerance to desiccation was tested through two long desiccation experiments and by comparing the vegetative and reproductive blades. Tolerance to high temperatures was tested by keeping the individuals in seawater (26–32 °C) for 24 h. The recovery of physiological functions after the stressful conditions was estimated through maximal photochemical efficiency of PSII. Results indicate that both of the two morphometrically differentiated morphotypes were tolerant to prolonged desiccation; however, the small one was more affected, particularly in the northern locality. The reproductive blades were hardly affected, indicating greater tolerance to desiccation than the vegetative blades. Fucus guiryi showed tolerance to high temperatures (32 °C) suggesting plasticity to future warming scenarios.

Ecological, physiological, and biomechanical differences between gametophytes and sporophytes of Chondrus ocellatus (Gigartinales, Rhodophyta)1.

Although variation among habitats in the ratio of gametophytes to sporophytes has been reported in various gigartinacean species, factors controlling the phase ratio remain poorly understood. Over 18months, we examined the phase ratio of Chondrus ocellatus at three sites: a sheltered intertidal site, Hiruga A; an exposed intertidal site, Hiruga B; and a subtidal site, Shikimi. The mean proportion of gametophytes at Hiruga A (73.1%) was significantly higher than that at Shikimi (51.2%) and Hiruga B (44.7%). Due to a significantly higher water retention ability of the gametophytes, it was expected that the gametophytes would exhibit higher desiccation tolerance. After dehydration treatments, however, neither the photosynthetic rate of vegetative blades nor the survival rate of spores was significantly different between the phases. Measurements of blade strength indicated that the sporophytic blades were less stiff and more flexible, and a culture experiment revealed that the sporophytic germlings showed a significantly higher growth rate. Flexible blades and fast-growing germlings are considered advantageous for colonizing wave-swept intertidal habitats, so these properties may have caused the different fluctuation pattern of phase ratio among the sites. The present data demonstrate that biomechanical and physiological differences between the two phases of C. ocellatus make one phase advantageous in certain environmental conditions, and that these differences likely cause an unequal ratio of isomorphic phases.

Structural features of the vegetative bodies of Hibiscus syriacus L. (Sev. Malvaceae Juss.) growing under the conditions in Uzbekistan

The article studies the anatomical structure of the vegetative organs, stems, leaves and leaf blades of Hibiscus syriacus L. in Uzbekistan for the first time.

Salinity and temperature tolerance of the invasive alga Undaria pinnatifida and native New Zealand kelps: Implications for competition

Invasive species are generally believed to be more tolerant to varying abiotic conditions than native species. Here, we report the combined effect of temperature (5, 15, 20 and 25 °C) and salinity (33, 24, 18, 12 and 6 SA) on the performance of the invasive kelp Undaria pinnatifida and two native kelp species (Lessonia variegata, Ecklonia radiata) from Tauranga Harbour, New Zealand (37°38′S, 176°10′E, 2014). Vegetative blade discs were exposed to temperature and salinity treatments in a 10-day laboratory experiment, and the physiological response was assessed employing photosynthetic (Fv/Fm, ETRmax) as well as biochemical parameters (chlorophyll a, xanthophylls and antioxidant pool size). U. pinnatifida sustained a high photosynthetic quantum yield in most treatments, with a negative synergistic effect on photosynthetic yield observed at 25 °C and low salinities (12, 6 SA). E. radiata died in salinities below 18 SA, except at 5 °C and L. variegata was highly susceptible to elevated temperatures (20, 25 °C). Antioxidant pool size showed species-specific responses to the experimental conditions, being most resilient in U. pinnatifida. Overall, U. pinnatifida displayed broader tolerance to the experimental salinity and temperature conditions than native kelps. The abilities to cope with a wide range in abiotic factors and to thrive in estuarine conditions might contribute to higher competitive strength compared to native kelps leading to its invasion success, especially with regard to ocean warming.

Nipped in the bud: mesograzer feeding preference contributes to kelp decline.

Small invertebrate grazers can disproportionately reduce plant fitness by discriminately consuming valuable tissues, but the context and attendant consequences of this activity at higher levels of ecological organization rarely are considered. To assess the impact of a gastropod mesograzer Lacuna vincta on fecundity and potential reproductive output of the habitat-forming kelp Saccharina latissima, we measured the intensity and distribution of grazing damage on kelp blades at five sites of varying kelp density, during the annual reproductive peak (October-November) in Nova Scotia. We found most grazing damage on reproductive individuals consisted of superficial excavations, and was concentrated on the central sorus (region where sporangia develop) compared to the vegetative blade margins. Grazing intensity on sori (percent grazed) averaged 29.6% across sites and sampling periods. The distribution of grazing on non-reproductive individuals was opposite to that of reproductive ones, indicating that snails shift feeding from blade margins to the center as sori develop. Choice and no-choice feeding assays in the laboratory revealed that focused grazing on sori is likely due to an active feeding preference for sporogenous over vegetative tissue. This preference was correlated with the distribution of chemical defense between tissues (phlorotannin content was ~2.5 times higher in vegetative tissue than sori), but not nutritional quality (no difference in C/N ratio). We deduce, with support from histological observations, that consumption of sorus tissue by L. vincta reduces fecundity of S. latissima. Extrapolating our results to estimate potential reproductive output within kelp beds suggests that spore supply and recruitment limitation may be predominantly imposed by the scarcity of reproductive individuals in the most degraded kelp beds. However, loss of reproductive output to grazing could extend recruitment limitations that impede recovery of waning kelp populations in Nova Scotia.

Sorus formation on the holdfast haptera of the kelp Ecklonia radicosa (Phaeophyceae, Laminariales)

AbstractKelps usually form sori on their vegetative blades or sporophylls, and occasionally on stipes, with a notable exception being the primitive kelp

UV Sensitivity of Vegetative and Reproductive Tissues of Two Antarctic Brown Algae is Related to Differential Allocation of Phenolic Substances.

UV sensitivity of the vegetative and reproductive tissues of two Antarctic brown macroalgae was compared. Photosynthesis as well as the content and localization of phenolic substances were determined. Responses to UV radiation were quantified as chlorophyll fluorescence (Fv /Fm ). Ascoseira mirabilis showed high UV tolerance, while in Cystosphaera jacquinotii Fv /Fm decreased by 15-21%, the receptacles being more tolerant than the vegetative blades. The phlorotannin contents showed an opposite pattern: the soluble fraction dominated in C.jacquinotii while in A.mirabilis the insoluble fraction was more abundant. Soluble phlorotannins were higher in the reproductive than in vegetative tissues in both species. Images of tissue cross-sections under violet-blue light excitation confirmed a high allocation of phenolic compounds (as blue autofluorescence) in C.jacquinotii, both in reproductive and vegetative blades. The allocation and proportions of the soluble and insoluble phlorotannins could be related with the observed UV tolerance of the vegetative and reproductive tissues.

Prevailing sea surface temperatures inhibit summer reproduction of the kelp Laminaria digitata at Helgoland (North Sea).

The impact of abiotic factors on kelp sporophyte reproduction has rarely been investigated. Laminaria digitata (Hudson) J.V. Lamouroux is one of the few summer fertile Laminaria species worldwide and reproduction is subjected to relatively high water temperatures. We investigated the impact of prevailing summer temperatures (~18°C in August) on the induction of sporangia, meiospore release, and germination at the island of Helgoland (North Sea). At Helgoland, fertile sporophytes are found between April and December with a maximum in late summer. While released meiospore numbers were constant between June and October, germination rates decreased significantly in summer. Short-term exposure of mature sori to 17°C-22°C induced a significantly higher meiospore release indicating enhancement of sporulation by elevated temperatures. Induction of sporangia on vegetative blade disks was not possible at 20°C, and fertility was only 20% at 18°C-19°C, but it was 100% in cool temperatures of 1°C-10°C. It was shown for the first time in a kelp species that "sporogenesis" is the life-cycle process with the narrowest temperature window compared to growth or survival of the sporophyte or reproduction, growth, and survival of the gametophyte. We incorporated several parameters (induction time, fertile area, and relative fertility) into a "Reproductive efficiency index." This indicates that sporogenesis of L.digitata is a cold-adapted process with an optimum at (5)-10°C. The results show that the population at Helgoland is at its reproduction limit despite the existence of other geographically more southerly located populations.

Shifts in morphological and mechanical traits compensate for performance costs of reproduction in a wave‐swept seaweed

Summary In addition to metabolic costs associated with reproduction, morphological and mechanical changes accompanying reproductive effort can affect an organism's performance. Reproductive effort may have unavoidable costs in plants and plant‐like taxa (i.e. extra mass or drag); however, the extent to which an organism can ameliorate these consequences by additional modifications of shape or tissue properties remains unknown in seaweed and plant taxa. We investigated mechanical and morphological changes associated with reproduction and how these shifts influence functional performance in the winged kelp, Alaria marginata. Compared to vegetative blades, reproductive blades were similar in width but were longer and had greater surface area. Reproductive sporophylls were also thicker and less ruffled. Tissue extensibility and breaking stress were not different in reproductive vs. vegetative blades. However, reproductive tissue exhibited greater tensile stiffness, flexural stiffness and force to break. Reproductive blades experienced greater drag (despite decreased flapping) than did vegetative blades, but did not experience greater size‐specific drag. Tissues cut into experimental blades of the same size and shape experienced greater drag when cut from reproductive tissue suggesting that the change in shape associated with the onset of reproduction ameliorates the cost of increased tissue stiffness. Nonetheless, increased blade breaking force in reproductive individuals resulted in increased blade safety factors (breaking force/drag experienced) in reproductive compared to non‐reproductive sporophylls. Synthesis: In A. marginata, decreased flexibility and increased surface area are mechanical costs associated with reproduction. Decreased blade ruffliness and increased strength associated with the onset of reproduction in A. marginata ameliorate the concomitant mechanical costs of decreased flexibility and increased size. Shifts in mechanical and morphological traits among plants and plant‐like taxa may allow them to increase reproductive output without decreasing functional performance.

Species-specific defense strategies of vegetative versus reproductive blades of the Pacific kelps Lessonia nigrescens and Macrocystis integrifolia

Chemical defense is assumed to be costly and therefore algae should allocate defense investments in a way to reduce costs and optimize their overall fitness. Thus, lifetime expectation of particular tissues and their contribution to the fitness of the alga may affect defense allocation. Two brown algae common to the SE Pacific coasts, Lessonia nigrescens Bory and Macrocystis integrifolia Bory, feature important ontogenetic differences in the development of reproductive structures; in L. nigrescens blade tissues pass from a vegetative stage to a reproductive stage, while in M. integrifolia reproductive and vegetative functions are spatially separated on different blades. We hypothesized that vegetative blades of L. nigrescens with important future functions are more (or equally) defended than reproductive blades, whereas in M. integrifolia defense should be mainly allocated to reproductive blades (sporophylls), which are considered to make a higher contribution to fitness. Herein, within-plant variation in susceptibility of reproductive and vegetative tissues to herbivory and in allocation of phlorotannins (phenolics) and N-compounds was compared. The results show that phlorotannin and N-concentrations were higher in reproductive blade tissues for both investigated algae. However, preferences by amphipod grazers (Parhyalella penai) for either tissue type differed between the two algal species. Fresh reproductive tissue of L. nigrescens was more consumed than vegetative tissue, while the reverse was found in M. integrifolia, thus confirming the original hypothesis. This suggests that future fitness function might indeed be a useful predictor of anti-herbivore defense in large, perennial kelps. Results from feeding assays with artificial pellets that were made with air-dried material and extract-treated Ulva powder indicated that defenses in live algae are probably not based on chemicals that can be extracted or remain intact after air-drying and grinding up algal tissues. Instead, anti-herbivore defense against amphipod mesograzers seems to depend on structural traits of living algae.

Survivorship and Predation Changes in Five Populations of Botrychium dissectum in Eastern Pennsylvania

This study of five populations of Botrychium dissectum was initiated in 1977 as part of a general environmental monitoring program at the Susquehanna Steam Electric Station. The Botrychium populations were discovered in the course of general flora surveys. Plants of this species were remarkably common in old fields and second growth woodlands on the site; therefore, I decided to monitor these populations in several successional habitats and their fate over several years. Part of the rationale of this study was simply that populations of Botrychium dissectum were observed in several plant communities that I could reasonably expect to remain undisturbed at a protected site. The study area is located in the Susquehanna River valley, 8 km north of Berwick, Salem Township, Luzerne County, in east-central Pennsylvania. Botrychium dissectum produces a single leaf each year from a short underground rhizome. This leaf emerges in mid to late summer, unfolds, and, if a fertile segment is present, spores are shed in early autumn. The fertile segment then withers, but the vegetative blade remains throughout the winter and following spring, senescing as the new leaf emerges. It should be emphasized that if this leaf is damaged or lost, the plant has no photosynthetic organ until the next summer. If the first leaf is damaged as soon as it emerges, occasionally plants will produce a small second leaf. Although this study was initiated with the idea of following the fate (longevity) and production of fertile fronds of plants in several populations, the study has been sidetracked by the discovery that many of the plants were eaten in the autumn soon after the leaf emerged and expanded. The plants have high survival under these conditions; this will be the chief topic of this paper.

Identification of associating carbohydrate sequences with labelled oligosaccharides

The gelling subunit of alginate, the major cell-wall polysaccharide of brown algae, was used as a molecular marker for identification of this cell-wall carbohydrate subunit at the cellular level. Short polyguluronate chains were conjugated to fluorescein and used as a probe to identify the gelling regions of alginate in tissue sections from a brown alga. The specificity of the probe for gelling subunits was demonstrated by lack of cell-wall labelling in the absence of calcium, correlation between divalent-cation binding affinities of polyguluronate with labelling intensity, and lack of labelling by fluorescein-conjugated nongelling subunits. The probe labelling-pattern also differed from sulfated fucan distribution. Extracellular matrix and cell walls were labelled on sections of vegetative blade, stipe and reproductive frond of Fucus gardneri Silva. Probe labelling was rapid, being virtually complete within 5 min. Probe labelling in seawater differed markedly from labelling at lower ionic strength and is interpreted as reflecting alginategelling properties in natural conditions. High-and low-affinity binding sites are discussed in terms of gelling-subunit length and steric availability. Fluorescein-conjugated polygalacturonate, which also forms calcium dimers, labelled extracellular alginate by formation of mixed polygalacturonate-polyguluronate dimers. Binding by the alginate hybridization probe differs from nucleic-acid hybridization in divalent-cation bridging and the lack of both a conformational transition and polymer polarity.

Algal Chemical Defense Against Herbivores: Allocation of Phenolic Compounds in the Kelp Alaria marginata

Higher concentrations of phenolic compounds were found in the reproductive fronds (sporophylls) of the intertidal kelp Alaria marginata than were found in the vegetative blades. The sporophylls were consumed by herbivorous snails at a lower rate than were the vegetative blades, in both field and laboratory studies. These results indicate that differential internal production of defensive compounds in a marine alga can significantly affect the pattern of herbivory on the plant.

LIFE HISTORY AND HYBRIDIZATION STUDIES ONGIGARTINA STELLATAANDPETROCELIS CRUENTA(RHODOPHYTA) IN THE NORTH ATLANTIC1

ABSTRACTFourteen isolates of the crustose marine red algaPetrocelis cruentaJ. Agardh from various localities in the British Isles, France (including the type locality), Spain and Portugal gave rise in culture to dioecious foliose plants identifiable asGigartina stellata(Stackhouse) Batters although two isolates formed only sterile foliose blades. A total of 145 isolates ofGigartina stellatawere also grown in culture from various localities in the U.S.A. (Maine), the British Isles, Iceland, Denmark, France, Spain and Portugal using both carpospores and vegetative blade apices. Two basic types of life history were found among these isolates: a direct‐type life history involving the formation of further foliose plants from carpospores, some isolates of which also form spermatangia on the same papillae as the cystocarps; and a heteromorphic‐type in which only crustose plants resemblingPetrocelis cruentaare formed from carpospores. Only heteromorphic‐type life histories were found from Spain and Portugal. Both life history types were found in plants from the U.S.A., the British Isles and northern France. Only direct‐type life histories were found in plants from Iceland and Denmark. SomePetrocelis‐like crusts derived from field collectedG. stellatacarpospores andPetroceliscrusts of hybrid progeny formed tetrasporangia in 8:16 h LD, 10° C but not in 8:16 h LD, 15° C; 16:8 h LD 10° C or 15° C; and 10:6.5:1: 6.5 h LDLD, 10° C. The spores thus formed were viable and produced normal dioecious male and female gametophytes. Short day and low temperature conditions appear necessary for tetrasporogenesis. The results from crossing experiments with 32 male and 27 female isolates of the heteromorphic‐type derived from bothG. stellataandP. cruentashowed that two virtually non‐interbreeding populations with a high degree of geographical separation exist in the north‐eastern Atlantic. Morphological differences between plants from each population are described. On the basis of culture and crossing results,Petrocelis cruentaJ. Agardh is placed in synonymy withGigartina stellata(Stackhouse in Withering) Batters.

Sources of variability in macroalgal primary productivity: Sampling and interpretative problems

Previous macroalgal production studies have been plagued by broad ranges of variability within experimental replicates that often exceed the seasonal or other parameters under investigation. As a first step toward understanding the factors responsible, eight rocky intertidal and subtidal macroalgae were examined for intrinsic sources of variation in photosynthetic performance and respiration relative to season, age, thallus part, reproductive state, external morphology, crowding, macrohabitat, microhabitat, desiccation, and physical injury. Corallina officinalis L. var. chilensis (Decaisne) Kützing and Egregia menziesii (Turn). Areschoug showed different seasonal production patterns with the minimum for Corallina and the maximum for Egregia occurring in the summer. The productivity of juvenile E. menziesii was 2.5 times higher than in structurally-differentiated mature individuals. Halidrys dioica Gardner had 2.8 times greater productivity in terminal vegetative branches than in basal fronds, while mature branches of E. menziesii were only half as productive as the young less-differentiated branches, indicating that as fronds mature, photosynthesis per unit of weight is effectively lowered as a result of increases in structural components. If the values for the least and most active thallus parts were used separately in production calculations, discrepancies of 250% for Halidrys and 130% for Egregia would be the result. The fertile terminal branches of H. dioica produced at a higher rate than either the basal fronds or vegetative terminal branches. Conversely, sporophylls of Macrocystis pyrifera (L.) C. Agardh showed no measurable net photosynthesis while vegetative blades fixed 2.01 mg C g dry wt.−1 h−1. Respiration rates in fertile blades of both H. dioica and M. pyrifera were significantly lower than in vegetative fronds. More robust and highly-branched thalli of Gigartina canaliculata Harvey showed significantly (P < 0.05) greater photosynthetic rates than did the tougher more wiry individuals. The clumped form of Gelidium pusillum (Stackhouse) Le Jolis produced and respired at only half the rate of separate individuals. Subtidal populations of Colpomenia sinuosa (Roth) Derbès & Solier had both higher net production and respiration rates than intertidal thalli, while subtidal and intertidal Codium fragile (Sur.) Hariot did not show such differences. In Colpomenia, the intertidal form was thicker and heavier per unit area, resulting in self-shading that reduced the weight-based production. The shade-acclimated populations of Corallina officinalis var. chilensis showed much lower photosynthetic performances in full sunlight than did thalli acclimated to direct insolation. We found that desiccation significantly reduced net productivity in the lower intertidal species H. dioica. Physical damage reduced the photosynthetic performance of C. sinuosa by one-half while nearly doubling its respiration. An understanding of variations such as those documented by this study is necessary for accurate analyses of macroalgal energetics and for the development of predictive insights into evolutionary strategies of carbon allocation. Therefore, much of the previous research on marine macroalgal productivity should be re-assessed in view of difficulties arising from environmental and intrinsic sources of metabolic variation.