Mowing Reduces Exotic Annual Grasses but Increases Exotic Forbs in a Semiarid Grassland

Cheatgrass (Bromus tectorum) and other exotic winter‐active plants can be persistent invaders in native grasslands, growing earlier in the spring than native plants and pre‐empting soil resources. Effective management strategies are needed to reduce their abundance while encouraging the reestablishment of desirable native plants. In this 4‐year study, we investigated whether mowing and seeding with native perennial grasses could limit growth of exotic winter‐actives, and benefit growth of native plants in an invaded grassland in Colorado, United States. We established a split‐plot experiment in October 2008 with 3 mowing treatments: control, spring‐mowed, and spring/summer‐mowed (late spring, mid‐summer, and late summer), and 3 within‐plot seeding treatments: control, added B. tectorum seeds, and added native grass seeds. Cover of plant species and aboveground biomass were measured for 3 years. In March and June of 2010, 2011, and March of 2012, B. tectorum and other winter‐annual grasses were half as abundant in both mowing treatments as in control plots; however, cover of non‐native winter‐active forbs increased 2‐fold in spring‐mowed plots and almost 3‐fold in spring/summer‐mowed plots relative to controls. These patterns remained consistent 1 year after termination of treatments. Native cool‐season grasses were most abundant in spring‐mowed plots, and least abundant in control plots. There was higher cover of native warm‐season grasses in spring/summer‐mowed plots than in control plots in July 2011 and 2012. The timing of management can have strong effects on plant community dynamics in grasslands, and this experiment indicates that adaptive management can target the temporal niche of undesirable invasive species.     

Photosynthesis inCeratophyllum demersum. Carbon fixation rates in relation to the plants' physiological stage,and the contents of chlorophylland non-structural carbohydrates

Summary Since the role of the submerged aquatic macrophytes in the carbon cycle of lake Vechten (the Netherlands) is in study, attention is paid to several aspects of their productivity.Ceratophyllum demersum is a predominant macrophytic species in the littoral zone of this lake, occurring mainly from three to five metres depth. In situ measurements of its photosynthetic rate demonstrated a maximum in spring (May), followed by a distinct decrease early in summer and a second maximum in late summer. The spring maximum of the photosynthetic rate coincided with the maximum increase of plant biomass. Maximum biomass occurred in early autumn (August–September).Althoughinsitu measurements pointed to the upper plant portions (70 cm) as the most important with respect to photosynthetic activity, it was demonstrated under standard experimental conditions that lower portions might be equally active depending on the age of the plant. In the lake, light reduction with depth is one of the major causes in the commonly observed decrease in photosynthetic activity in lower plant parts.Comparison of the photosynthetic rates in plant tipsin situ and under standard experimental conditions indicated that in spring, both water temperature and the chlorophyll content of the plant limit photosynthesis. This was concluded since under experimental conditions (a) photosynthetic rate and chlorophyll content were strongly correlated during the first half of the growing season and (b) higher rates were measured thanin situ. In the subsequent stage, however, light and the distribution of non-structural carbohydrates (TNC) in the plant also play an important role.At the second half the growing season, the lower parts of plants growing in the lake lose gradually their buoyancy, caused by a deteriorating light climate resulting in a decreasing photosynthetic activity.     

Seasonal shifts in host usage in Uroleucon gravicorne (Homoptera: Aphididae) and implications for the evolution of host alternation in aphids

ABSTRACT.

• 1 Uroleucon gravicome (Patch) feeds on annual Erigeron species and on perennial Solidago species.
• 2 To test whether Solidago and Erigeron are analogous to winter and summer hosts of typical host-alternating aphids, reproductive performance, host preferences, and host associations were measured for E.strigosus, S.juncea and S.nemoralis during spring, summer and autumn.
• 3 Caged individuals can reproduce on both genera throughout the season, though colonies are rare on Solidago during summer.
• 4 Developmental rate, adult weight, and fecundity decline between May and August on all hosts; however, the drop is least on E.strigosus, intermediate on S.nemoralis, and greatest on S.juncea.
• 5 Throughout the season, reproductive performance is at least as great on Erigeron as on Solidago, the difference being least in spring.
• 6 Soluble nitrogen content shows the same seasonal trends as reproductive performance, declining in all hosts, but declining least in E.strigosus.
• 7 Preference tests and field records show that U.gravicorne moves from Solidago to Erigeron when the first alatae mature in late spring, feeds on Erigeron during the summer, and, in late summer, returns to Solidago where overwintering eggs are laid.
• 8 Solidago is not nutritionally superior during spring or autumn; its use during those seasons may result from the need for good oviposition sites.

     

Fire Season and Dominance in an Illinois Tallgrass Prairie Restoration

North American prairie remnants and restorations are normally managed with dormant‐season prescribed fires. Growing‐season fire is of interest because it suppresses dominant late‐flowering grasses and forbs, thereby making available light and other resources used by subdominant grasses and forbs that comprise most prairie diversity. Here we report a twofold increase in mean frequency and richness of subdominant species after late‐summer fire. Stimulation of subdominants was indiscriminate; richness of prairie and volunteer species increased in species that flowered in early, mid‐, or late season. Early spring fire, the management tool used on this site until this experiment, had no effect on subdominant richness or frequency. Neither burn treatment affected reproductive tillering of the tallgrasses Sorghastrum nutans or Panicum virgatum. Flowering of Andropogon gerardii increased 4‐fold after early‐spring fires and 11‐fold after late‐summer fires. These preliminary results suggest that frequency and species richness of subdominants can be improved by late growing‐season fire without compromising vigor of warm‐season tallgrasses.     

Variability in the chemistry of estuarine plants and its effect on feeding by Canada geese

Summary We investigated the influence of interspecific and seasonal variations in plant chemistry on food choices by adult and gosling Canada Geese, Branta canadensis, on Cape Cod, Massachusetts. The geese fed primarily on the abundant marsh grasses, Spartina spp., and rushes, Juncus gerardi, early in the growing season and switched to a greater dependence on eelgrass, Zostera marina, later. Forbs were generally avoided all season even when growing within patches of abundant species. The avoidance of forbs was related to their low abundance and their high concentrations of deterrent secondary metabolites. Differences in plant chemistry also determined the switch from marsh graminoids to Z. marina during the growing season. Marsh grasses were higher than Z. marina in nitrogen, particularly in the spring when the nitrogen requirement of geese is especially high. Z. marina was a better source of soluble carbohydrates and was the preferred food during the summer when the need to build up energy reserves may be more critical to geese than protein intake. Goslings, which require a diet higher in nitrogen than do adults, fed on marsh graminoids later into the growing season than the adults. The nitrogen content of the diets of goslings was significantly higher than that available to them in the plants, indicating that they selected for introgen. The diets of non-breeding adults in the spring and all geese in mid summer closely reflected the nutrient content of the plants. The diet of breeding adults was more similar to that of their goslings than to that of non-breeding adults. The effects of plant chemistry and the nutritional needs of geese on food choices were modified by the need to select a safe feeding site.     

Fungal root endophytes of the carnivorous plant Drosera rotundifolia

As carnivorous plants acquire substantial amounts of nutrients from the digestion of their prey, mycorrhizal associations are considered to be redundant; however, fungal root endophytes have rarely been examined. As endophytic fungi can have profound impacts on plant communities, we aim to determine the extent of fungal root colonisation of the carnivorous plant Drosera rotundifolia at two points in the growing season (spring and summer). We have used a culture-dependent method to isolate fungal endophytes and diagnostic polymerase chain reaction methods to determine arbuscular mycorrhizal fungi colonisation. All of the roots sampled contained culturable fungal root endophytes; additionally, we have provided molecular evidence that they also host arbuscular mycorrhizal fungi. Colonisation showed seasonal differences: Roots in the spring were colonised by Articulospora tetracladia, two isolates of uncultured ectomycorrhizal fungi, an unidentified species of fungal endophyte and Trichoderma viride, which was present in every plant sampled. In contrast, roots in the summer were colonised by Alatospora acuminata, an uncultured ectomycorrhizal fungus, Penicillium pinophilum and an uncultured fungal clone. Although the functional roles of fungal endophytes of D. rotundifolia are unknown, colonisation may (a) confer abiotic stress tolerance, (b) facilitate the acquisition of scarce nutrients particularly at the beginning of the growing season or (c) play a role in nutrient signalling between root and shoot.     

Geographic origin and past climatic experience influence the response to late spring frost in four common grass species in central Europe

Late spring frost events can affect vegetation. The response of grassland species, however, is generally unknown. We explore the late‐frost sensitivity of four common European grass species and investigate whether these species exhibit local adaptations to late frost on a continental scale and whether past climatic experience influences late frost sensitivity. Ecotypes of Arrhenatherum elatius, Alopecurus pratensis, Festuca pratensis, and Holcus lanatus from Spain, Italy, Bulgaria, Hungary, Sweden and Germany were exposed to late frost after drought and warming manipulations in the preceding growing season in a common garden experiment. Late frost reduced the productivity of the grasses on average by 20%. Ecotypes differed in their late‐frost sensitivity in three of the four species and local adaptations to late frost were identified. Previous exposure to drought and warming caused differences in late‐frost sensitivity in some cases. The impact of late frost events may increase in a warmer world due to an earlier onset of growing and no change in timing of late frost events. The history of climatic exposure can alter the performance of plants, possibly through epigenetic mechanisms. Based on the complex response pattern observed, a maximization of genetic diversity is proposed as a promising adaptation strategy against climate change.     

The Effect of Seasonal Shifts in Temperature on the Lipid Composition of Marine Macrophytes

The comparative study of lipid composition was carried out in four species of marine algae, Ahnfeltia tobuchiensis, Laminaria japonica, Sargassum pallidum, and Ulva fenestrata, as well as a higher plant grass wrack (Zostera marina). Plants were collected in the Japan Sea in spring at 2.9 and 5.5°C and in summer at 23°C. The main lipid components of membranes were determined, and the general patterns of the ratio of phospholipids (PL), glycolipids (GL), betaine (BL), and neutral (NL) lipids were discerned. The relative content of NL in all species (except A. tobuchiensis) was higher in summer. The level of triacylglycerols was as high as 18–37%. The content of individual classes of PL and GL varied between the spring and summer samples, the relative content of PL being higher in spring. In most species, the ratio of PL to GL decreased in summer. The content of free sterols did not depend on the season. The molar ratios of phosphatidylcholine and diacylglycerol-o-(hydroxymethyl)-(N,N,N-trimethyl)homoserine to free sterols varied from 0.9 to 1.7. The seasonal changes of lipid composition were apparently related to macrophyte adaptation to water temperature and to biology of their development.     

Leaf development of the ostrich fern Matteuccia struthiopteris (L.) Todaro

The timing of emergence of the three different leaf types of Matteuccia struthiopteris is described from plants sampled over the course of a growing season. Vegetative leaves were first to appear, followed five weeks later by sporophylls and cataphylls. Leaf number and type, and total leaf dry weight per plant were assessed in weekly transects. Vegetative fronds contributed the most to total leaf dry weight, which increased during the first four weeks, and then remained constant for the remainder of the season. Cataphylls, although numerous by the end of the season, contributed little weight. Sporophylls occurred on the widest plants with the most vegetative leaves and greatest leaf weight, whereas cataphylls occurred on most plants except the smallest. Experimentally defoliated plants were re-examined in late summer. Following initial harvest, plants often produced a second smaller set of leaves. These were restricted to vegetative leaves and cataphylls. Ability to reissue leaves, especially vegetative fronds, declined very quickly after the first few weeks in the growing season. Defoliated plants draw on the extensive reservoir of developing leaves which are found on the rhizome, thus possibly diminishing the ability of the plant to withstand regular harvesting of the young fronds for food. Individual leaves were tagged and measured over the growing season. Non-linear regression curves fitted to the growth data for the three types of leaves indicate that growth was described best by a monomolecular growth curve for the vegetative and fertile fronds. Cataphyllar growth could be described equally well by either a monomolecular or a logistic function.     

RAINFALL PERIODICITY AS A MAJOR FACTOR IN THE FORMATION OF FLOWERING RACES OF CAMPHORWEED (HETEROTHECA SUBAXILLARIS)

Plants of camphorweed (Heterotheca subaxillaris sensu latiore) were raised in a uniform garden at Northampton, Mass., from seed taken from 19 sites in different parts of the range of the species. Flowering races were observed. Flowering time at Northampton correlated with periodicities of rainfall at the seed source in most instances. The earliest-flowering plants were obtained from areas where above-average amounts of rainfall occur in spring, while the later-flowering plants came from sites where above-average rainfall occurs in mid- to late summer. Other workers have observed a correlation between the frost-free season and the formation of flowering races in prairie grasses, Eupatorium rugosum, and other plants. There is little correlation between the frost-free season and the formation of flowering races in Heterotheca and it is postulated that, within the range of camphorweed, periodicity of rainfall is a more critically limiting factor.     

Role of temperature in the germination ecology of three summer annual weeds

Summary Ambrosia artemisiifolia L., Chenopodium album L., and Amaranthus retroflexus L. are three summer annual weeds that occur in disturbed habitats. In nature, the peak germination season for A. artemisiifolia and C. album is in early to mid-spring, while in A. retroflexus the peak germination season is late spring to early summer. Furthermore, seeds of A. artemisiifolia germinate only in spring, while seeds of C. album and A. retroflexus germinate throughout the summer. In an attempt to explain the differential germination behavior of these three species in nature, changes in their germination responses to temperature during burial in a non-heated greenhouse from October 1974 to October 1975 were monitored. A high percentage of the seeds of all three species after-ripened during winter. Seeds of A. artemisiifolia and C. album germinated at temperatures characteristic of those in the field in early and mid-spring, but seeds of A. retroflexus required the higher temperatures of late spring and early summer for germination. Seeds of all three species germinated to higher percentages in light than in darkness. Non-dormant seeds of A. artemisiifolia that did not germinate in spring entered secondary dormancy. On the other hand, seeds of C. album and A. retroflexus that did not germinate when temperatures first became favorable for germination, did not enter secondary dormancy and, thus, retained the ability to germinate at summer field temperatures during summer. Thus, temporal differences in the germination behavior of these three species are caused by the differential reaction of the seeds to temperature during the annual temperature cycle.     

Photosynthetic responses of Mojave Desert shrubs to free air CO2 enrichment are greatest during wet years

It has been suggested that desert vegetation will show the strongest response to rising atmospheric carbon dioxide due to strong water limitations in these systems that may be ameliorated by both photosynthetic enhancements and reductions in stomatal conductance. Here, we report the long‐term effect of 55 Pa atmospheric CO₂ on photosynthesis and stomatal conductance for three Mojave Desert shrubs of differing leaf phenology (Ambrosia dumosa—drought‐deciduous, Krameria erecta—winter‐deciduous, Larrea tridentata—evergreen). The shrubs were growing in an undisturbed ecosystem fumigated using FACE technology and were measured over a four‐year period that included both above and below‐average precipitation. Daily integrated photosynthesis (A_day) was significantly enhanced by elevated CO₂ for all three species, although Krameria erecta showed the greatest enhancements (63% vs. 32% for the other species) enhancements were constant throughout the entire measurement period. Only one species, Larrea tridentata, decreased stomatal conductance by 25–50% in response to elevated CO₂, and then only at the onset of the summer dry season and following late summer convective precipitation. Similarly, reductions in the maximum carboxylation rate of Rubisco were limited to Larrea during spring. These results suggest that the elevated CO₂ response of desert vegetation is a function of complex interactions between species functional types and prevailing environmental conditions. Elevated CO₂ did not extend the active growing season into the summer dry season because of overall negligible stomatal conductance responses that did not result in significant water conservation. Overall, we expect the greatest response of desert vegetation during years with above‐average precipitation when the active growing season is not limited to ～ 2 months and, consequently, the effects of increased photosynthesis can accumulate over a biologically significant time period.     

Two types of matter economy for the wintering of evergreen shrubs in regions of heavy snowfall

Plant adaptation to an environment subject to heavy snowfalls was investigated in four species of evergreen shrubs growing in a Fagus crenata forest in an area of Honshu on the Sea of Japan. These shrubs stored carbohydrates in some organs before the snowy season and were covered with snow for 4–5 months. Aucuba japonica var. borealis, Camellia rusticana, and Ilex crenata var. paludosa maintained a reserve of carbohydrates during the snowy season. In Daphniphyllum macropodum var. humile, the reserve of carbohydrates decreased during winter. The respiration rates in the first three species decreased from autumn to winter, whereas the decrease in D. macropodum was slight. It was found that the first three species could use reserve carbohydrates for the growth of new shoots after the thaw, whereas in the last species the growth of new shoots depends on high photosynthetic activity in late spring. Our findings suggest some types of matter economy in evergreen shrubs for wintering in an environment of heavy snow.     

Phenology and photosynthetic activity in sterile and fertile sporophytes of Dryopteris filix-mas (L.) Schott

Summary This study describes the phenology of sporophytes of the fern Dryopteris filix-mas in relation to whole plant development. Sterile and fertile potted sporophytes were set out at an exposed site and the seasonal development of the fronds was measured from the commencement of unfolding, through the phase of increasing length, up to discoloration. The physiological activity of the fronds was determined by measuring photosynthetic gas exchange. The fronds of sterile sporophytes unfolded in April, about a week earlier than those of fertile plants, but the colour had already begun to turn in September and their life span was 1–2 months shorter. However, between mid-June and the end of August the sterile sporophytes put out several sets of new fronds: these overwintered without changing color and were still photosynthetically active in the following spring. All types of fronds were fully expanded 1–2 months from the beginning of unfolding and, with a natural supply of CO₂, had similar maximum net photosynthetic rates of 8–9 mol/m² · s. The decline in photosynthetic performance began before symptoms of senescence were visible and was due to decreased efficiency of the mesophyll. It is concluded that the phenology of D. filix-mas changes with transition from the sterile to the fertile phase. Whereas fertile sporophytes are genuinely summergreen, the sterile sporophytes with their summer fronds remain green throughout the winter and should therefore be termed semi-evergreen. The formation of overwintering summer shoots clearly extends the period of photosynthetic productivity of sterile sporophytes.     

Seasonal variation of the capture and field distribution of sterile Anastrepha ludens in Tamaulipas,Mexico

Anastrepha ludens (Loew) (Diptera: Tephritidae) is one of the most important citrus pest in Mexico. The sterile insect technique (SIT) is used against pest populations of fruit flies for suppression, eradication, containment and prevention to reduce damages in fruit‐growing areas. In this study, we analyzed the seasonal variation of captures and field distribution of sterile A. ludens released in different seasons of the year in north‐eastern Mexico. Chilled releases were conducted by air at constant densities per ha on a citrus area for a period of 32 weeks that included the coldest and warmest seasons that is winter, spring and summer. Multilure traps baited with torula yeast pellets were used to capture sterile flies. Fly capture data were compared over the three seasons and correlated with climate. The lowest number of captures of the sterile insect occurred in the summer and the highest in winter and spring. High and low temperatures were negatively correlated with fly captures. Field distribution was also negatively correlated with high temperatures in summer, but no relationships were observed in winter and spring. No relationships were observed between rainfall with capture and field distribution of sterile flies. These results indicate that summer is a season involving agro‐ecological and environmental constraints for the capture and field distribution of sterile flies. This study may be useful for enhancing release strategies and optimizing economic resources in north‐eastern Mexico. Further research on the behaviour of sterile flies under stressful environments is suggested.     

Effects of invasive species on plant communities: an example using submersed aquatic plants at the regional scale

Submersed aquatic plants have a key role in maintaining functioning aquatic ecosystems through their effects on the hydrological regime, sedimentation, nutrient cycling and habitat of associated fauna. Modifications of aquatic plant communities, for example through the introduction of invasive species, can alter these functions. In the Sacramento-San Joaquin River Delta, California, a major invasive submersed plant, Brazilian waterweed Egeria densa, has become widespread and greatly affected the functionality of the submersed aquatic plant community. Rapid assessments of the distribution and abundance of this species are therefore crucial to direct management actions early in the season. Given the E. densa bimodal growth pattern (late spring and fall growth peaks), summer assessments of this species may indicate which and where other submersed species may occur and fall assessments may indicate where this and other species may occur in the following spring, primarily because the Delta’s winter water temperatures are usually insufficient to kill submersed aquatic plant species. We assessed community composition and distribution in the fall of 2007 and summer of 2008 using geostatistical analysis; and measured summer biomass, temperature, pH, salinity, and turbidity. In the fall of 2007, submersed aquatic plants covered a much higher proportion of the waterways (60.7%) than in the summer of 2008 (37.4%), with a significant overlap between the seasonal distribution of native and non-native species. Most patches were monospecific, and multispecies patches had significantly higher dominance by E. densa, co-occurring especially with Ceratophyllum demersum. As species richness of non-natives increased there was a significant decrease in richness of natives, and of native biomass. Sustained E. densa summer biomass negatively affected the likelihood of presence of Myriophyllum spicatum, Potamogeton crispus, and Elodea canadensis but not their biomass within patches. Depth, temperature and salinity were associated with biomass; however, the direction of the effect was species specific. Our results suggest that despite native and invasive non-native submersed plant species sharing available niches in the Delta, E. densa affects aquatic plant community structure and composition by facilitating persistence of some species and reducing the likelihood of establishment of other species. Successful management of this species may therefore facilitate shifts in existing non-native or native plant species.     

Biological control of the black vine weevil, Otiorhynchus sulcatus (Coleoptera: Curculionidae) with entomopathogenic nematodes (Nematoda: Rhabditida)

Trials conducted under glasshouse conditions showed that control of Otiorhynchus sulcatus larvae in strawberry plants can be effective using Steinernema carpocapsae and Heterorhabditis megidis, given that temperature and moisture extremes are avoided. In field experiments, the double line T-Tape® drip irrigation system performed better than the single line T-Tape® system, effectively distributing the nematodes along and across strawberry raised beds, and placing them close to the root zone where O. sulcatus larvae feed. As soil temperatures are satisfactory for nematode infectivity from late spring to early autumn, nematode applications were aimed at late instar larvae during spring, and early instar larvae during summer. Late summer field treatment with S. carpocapsae induced 49.5% reduction of the early instar larvae, and field application of the same nematode species in late spring resulted in 65% control of late instar larvae. In the same trial, spring application of H. megidis caused 26% mortality of late instar larvae of O. sulcatus.     

Effects of Petunia cytoplasmic male sterile (CMS) cytoplasm on the development of sterile and fertility-restored P. parodii anthers

The developmental defects causing cytoplasmic male sterility in Petunia parodii are described in isonuclear fertile, sterile, and fertility-restored plants using both light- and scanning electron microscopy. The aberrant development of the sporogenous tissue and tapetal layer caused by the cytoplasmic male sterile cytoplasm in both Petunia hybrida and P. parodii nuclear backgrounds is similar in onset and progression. The degeneration of the sporogenous tissue and tapetal layer of sterile anthers is first apparent late in meiosis and results in highly abnormal sterile sporogenous tissue by tetrad stage of fertile anthers. The stomium and endothecium do not show major developmental differences between fertile and sterile anthers, but the inner connective tissue of sterile anthers contained calcium crystals not found at high abundance in fertile anthers. Ovoid bodies containing magnesium and phosphorus were seen only in the vascular bundles of fertile anthers. Material prepared for the scanning electron microscope by freeze drying showed better retention of fragile morphological features, while critical-point drying permitted examination of nonvolatile structures, such as cell walls.     

Reproductive ecology of the jacky dragon (Amphibolurus muricatus): an agamid lizard with temperature‐dependent sex determination

Abstract The jacky dragon, Amphibolurus muricatus (White, ex Shaw 1790) is a medium sized agamid lizard from the southeast of Australia. Laboratory incubation trials show that this species possesses temperature‐dependent sex determination. Both high and low incubation temperatures produced all female offspring, while varying proportions of males hatched at intermediate temperatures. Females may lay several clutches containing from three to nine eggs during the spring and summer. We report the first field nest temperature recordings for a squamate reptile with temperature‐dependent sex determination. Hatchling sex is determined by nest temperatures that are due to the combination of daily and seasonal weather conditions, together with maternal nest site selection. Over the prolonged egg‐laying season, mean nest temperatures steadily increase. This suggests that hatchling sex is best predicted by the date of egg laying, and that sex ratios from field nests will vary over the course of the breeding season. Lizards hatching from eggs laid in the spring (October) experience a longer growing season and should reach a larger body size by the beginning of their first reproductive season, compared to lizards from eggs laid in late summer (February). Adult male A. muricatus attain a greater maximum body size and have relatively larger heads than females, possibly as a consequence of sexual selection due to male‐male competition for territories and mates. If reproductive success in males increases with larger body size, then early hatching males may obtain a greater fitness benefit as adults, compared to males that hatch in late summer. We hypothesize that early season nests should produce male‐biased sex ratios, and that this provides an adaptive explanation for temperature‐dependent sex determination in A. muricatus.     

Comparative Study of Polysaccharides from Reproductive and Sterile Tissues of Five Brown Seaweeds

Sterile and reproductive tissues of five brown algae (Sargassum pallidum, Silvetia babingtonii, Fucus evanescens, Saccharina japonica, and Alaria ochotensis) from Russian Far East seas were compared for the content and monosaccharide composition of fucoidans as well as the content of laminarans and alginic acids. It was proved that reproduction has an apparent effect on fucoidan content and its monosaccharide composition. Fucoidan content in fertile tissues was shown to be 1.3–1.5 times as high as in sterile ones. Based on the present and previously reported data, we believe that fucoidan accumulation during the development of reproductive structure is a general trend for brown seaweeds. Reproduction also caused changes in the monosaccharide composition. As a result, fertile plants synthesized fucoidan with less heterogeneous monosaccharide composition in comparison with sterile ones. Structural changes of this polysaccharide are species-specific and perhaps depend on the type of the synthesized polysaccharide. The fertile plants of S. babingtonii yielded the highest fucoidan content [25% dry weight (dw)] among the tested species, whereas the maximum alginic acid content was found for the sterile tissues of S. japonica—up to 43% dw. There was no general trend in alginic acid content variation during sporulation. The alginic acid content was much higher in the sterile tissues of S. japonica in comparison with the fertile ones. On the contrary, the fertile tissues of A. ochotensis contained more alginic acid than the sterile ones.