Antioxidant activities and phenolics content of eight species of seaweeds from north Borneo

The antioxidant activity of eight edible species of Malaysian North Borneo seaweeds obtained from Sabah waters (Kudat, Tanjung Aru and Semporna) consisting of three red seaweeds (Eucheuma cottonii, E. spinosum and Halymenia durvillaei), two green seaweeds (Caulerpa lentillifera and C. racemosa) and three brown seaweeds (Dictyota dichotoma, Sargassum polycystum and Padina sp.) were determined. Methanol and diethyl ether were used as extraction solvent. The antioxidant activities were determined by two methods, TEAC (trolox equivalent antioxidant capacity) and FRAP (ferric reducing antioxidant power) assays. The total phenolic content of the extract was determined according to the Folin–Ciocalteu method and results were expressed as phloroglucinol equivalents. The methanolic extracts of green seaweeds, C. lentillifera and C. racemosa, and the brown seaweed, S. polycystum showed better radical-scavenging and reducing power ability, and higher phenolic content than the other seaweeds. The TEAC and FRAP assays showed positive and significantly high correlation (R ² = 0.89). There was a strong correlation (R ² = 0.96) between the reducing power and the total phenolic content of the seaweeds methanolic dry extracts. These seaweeds could be potential rich sources of natural antioxidants.     

Mass loss and nutrient release from decomposing evergreen and deciduous Nothofagus litters from the Chilean Andes

Abstract Leaf litter decomposition experiments were conducted on two deciduous (Nothofagus obliqua (roble)) and Nothofagus pumilio (lenga)) and one evergreen (Nothofagus dombeyi) Nothofagus (Nothofagaceae) species from a single Chilean forest in order to understand how congeneric trees with differing leaf lifespans impact the soil in which they grow. Single‐species litter samples were decomposed in a mixed hardwood forest in Ohio and in a deciduous‐evergreen Nothofagus forest in Chile. In the Ohio forest, the two deciduous species’ litters decomposed at k ≈ 1.00 per year and the evergreen at k ≈ 0.75 per year. In Chile k ranged from k ≈ 0.06 (N. obliqua) to k ≈ 0.23 (N. pumilio) per year. In both experiments, N and P were released faster from the deciduous litters than from evergreen litter. In Ohio, evergreen litter immobilized more N and P for a longer time period than did deciduous litter. As N. dombeyi stands tend to have lower available soil N and P in this particular mixed Nothofagus forest, the increased time of N and P immobilization by N. dombeyi litter suggests a feedback role of the tree itself in perpetuating low N and P soil conditions.     

秋茄落叶分解中营养元素释放的季节动态

研究了福建九龙江口林地红树植物秋茄落叶分解过程中K、Ca、Mg和P营养元素释放速率的季节动态。结果表明,腐解中叶片元素组成因不同营养元素损失率而变化较大。元素的损失总是快于干重损失,且损失速率为K>Mg>Ca和K>P。冬季P的损失快于Mg和Ca(P>Mg>Ca),夏季则相反(Mg>Ca>P),其余两季节差别不大。4个季节分解56天后,K、Ca、Mg、P分别损失达初始量的72—97％,51—88％,60—90％和64—79％。     

Nitrogen and phosphorus release from decaying water milfoil

To evaluate the net N and P contribution to water from herbicide-killed aquatic weeds, water milfoil containing 1.5% N and 0.30% P was killed with endothal and allowed to decompose, in the dark, in water only or sediment-water systems. Changes with time in dry weight, total N and P, and organic C in the plant material, and organic and inorganic forms of N and P in the water were determined. Plant decompostion was limited by N. Inorganic N was released by the sediment, and decomposition was more rapid when sediment was present. A smaller N requirement for decomposition under conditions of low O₂ was postulated as a possible explanation of the more rapid decomposition observed in the absence of aeration. The presence of plant P in excess of decomposition requirements resulted in rapid accumulation of organic P, followed by inorganic P, in the water. Organic N appeared in the water early in the experiments, but was depleted rapidly, and inorganic N was apparently immobilized as soon as it was formed. In the presence of sediment, organic N and inorganic P levels were much lower. On treating of water milfoil with herbicide, rapid P release can be expected. This P can either be utilized in further biomass production or be sorbed by the sediment. Insufficient data were available to reach definite conclusions regarding N. It would appear, however, that N release from decaying weeds is much slower than P.     

Nitrogen losses from perennial grass species

Nitrogen losses from plants may occur through a variety of pathways, but so far, most studies have only quantified losses of nutrients by above-ground litter production. We used ¹⁵N pulse labelling to quantify total nitrogen losses from above- and below-ground plant parts. Using this method we were able to include also pathways other than above-ground litter production. To test the hypothesis that species from nutrient-poor habitats lose less nitrogen than species from more fertile soils, six perennial grasses from habitats with a wide range of nutrient availability were investigated: Lolium perenne, Arrhenatherum elatius, Anthoxanthum odoratum, Festuca rubra, F. ovina and Molinia caerulea. The results of an experiment carried out in pots in a green-house at two fertility levels show that statistically significant losses occur through pathways other than above-ground litter production. In the low fertility treatment, most (70%) losses from L. perenne occurred by litter production, but in Ar. elatius, F. rubra, F. ovina and M. caerulea, more than 50% of labelled N losses took place by root turn-over, leaching or exudation from roots. When nutrient supply increased, the ¹⁵N losses in above-ground dead material increased in all species and in Ar. elatius, A. odoratum and F. rubra the ¹⁵N losses via other pathways decreased. Ranked according to decreasing turnover coefficient the sequence of species was: L. perenne, A. odoratum, F. rubra, F. ovina, Ar. elatius, M. caerulea. These results suggest that species adapted to sites with low availability of nutrients lose less nitrogen (including above- and below-ground losses) than species adapted to more fertile soils.     

Survival of seaweeds ingested by three species of tropical sea urchins from Brazil

Three species of sea urchins, Echinometra lucunter, Lytechinus variegatus, and Arbacia lixula, common on the southeastern coast of Brazil, were selected for experiments on seaweed survival after passage through their digestive tract. L. variegatus and E. lucunter have more than 80% of their diet composed of algae. C. 24% of the species of algae present in the digestive tract survived. A. lixula has only 29% of its diet composed by algae, but the survival rate of the algae is c. 50%.Although Rhodophyta represent 51% of the ingested algae, their survival rate in the faeces is only 19%, while the Chlorophyta, with a survival rate of 63%, comprise only about 26% of the diet. Most species of algae that survived ingestion were r-strategists.     

Digestive performance in five Mediterranean lizard species: effects of temperature and insularity

Temperature sensitivity of digestive processes has important ramifications for digestive performance in ectothermic vertebrates. We conducted a comparative analysis of temperature effects on digestive processes [gut passage times (GPTs) and apparent digestive efficiencies (ADEs)] in five lacertid lizards occurring in insular (Podarcis erhardii, P. gaigeae), and mainland (P. muralis, P. peloponnesiaca, Lacerta graeca) Mediterranean environments. GPTs were negatively correlated to temperature with mainland taxa having 10–20% longer GPTs than island taxa. In contrast to previous studies that estimate ADEs using bomb calorimetry, we compare ADEs by analyzing discrete efficiencies for lipids, sugars and proteins at three temperature regimes (20, 25, and 30°C); each of these categories produces different results. ADEs for lipids and sugars showed a monotonic increase with temperature whereas ADEs for proteins decreased with temperature. Island taxa had consistently higher ADEs than their mainland counterparts for lipids and for proteins but not for sugars. They are characterized by superior energy acquisition abilities despite significantly shorter GPTs. Their increased digestive performance relative to the mainland species appears to allow them to maximize energy acquisition in unproductive island environments where food availability is spatially and seasonally clustered.     

A seasonal study of the red seaweeds Solieria tenera and three species of Gracilaria from Jamaica

Three species of Gracilaria viz G. cervicornis, G. domingensis, G. verrucosa and Solieria tenera (Gigartinales, Rhodophyta) have been studied for their monthly variation in dry wt yields, ash, soluble carbohydrate, protein, lipid and insoluble carbohydrate contents for one year. The dry wt yields were higher in G. domingensis. Soluble carbohydrate and ash contents showed an inverse relationship in all the species. Protein content was lower, below 5% of the dry wt for all the species. A comparison of protein:carbohydrate ratios showed a similarity between morphologically similar G. domingensis and G. cervicornis in that there was less variation in the ratio. From this, it is assumed that flattened morphology probably is more efficient in maintaining nutrient balance to keep up the growth rates.     

Ultrastructure of ulvan: A polysaccharide from green seaweeds

Ultrastructural analysis of the gel forming green seaweed sulfated polysaccharide ulvan revealed a spherical‐based morphology (10–18 nm diameter) more or less aggregated in aqueous solution. At pH 13 in TBAOH (tetrabutyl ammonium hydroxyde) or NaOH, ulvan formed an open gel‐like structure or a continuous film by fusion or coalescence of bead‐like structures, while in acidic pH conditions, ulvan appeared as dispersed beads. Low concentrations of sodium chloride, copper or boric acid induced the formation of aggregates. These results highlight the hydrophobic and aggregative behavior of ulvan that are discussed in regard to the peculiar gel formation and the low intrinsic viscosity of the polysaccharide in aqueous solution. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 652–664, 2009. This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com     

Soil temperature and flooding effects on two species of citrus

Summary Rough lemon (Citrus jambhiri Lush.) and sour orange (C. aurantium L.) seedlings were grown at constant soil temperatures of 16, 24, and 33 C for 3 months. Shoot and root growth of rough lemon was greatest at 33 C while growth of sour orange was greatest at 24 C. There were no significant effects of soil temperature on shoot: root ratio, leaf water potential or stomatal conductance. The hydraulic conductivity of intact root systems of both species was highest when seedlings were grown at 16 C. Thus, acclimation through greater root conductivity at low soil temperature may have compensated for decreased root growth at 16 C and negated effects of soil temperature on plant water relations. Half the plants growing at each soil temperature were subsequently flooded. Within 1 week, the soil redox potential (Eh) dropped below zero mV, reaching a minimum Eh of –250mV after 3 weeks of flooded conditions. Flooded plants exhibited lower root conductivity, a cessation of shoot growth, lower leaf water potentials, lower stomatal conductances, and visual sloughing of fibrous roots. Decreases in root conductivity in response to flooding were large enough to account for the observed decreases in stomatal conductance.Florida Agricultural Experiment Stations Journal Series No. 4080.     

Nitrogen addition amplified water effects on species composition shift and productivity increase

增加氮素放大了水分对物种组成变化和生产力提高的影响 水分和氮素是旱地生态系统中的重要资源,二者对群落结构和生态系统功能的影响存在着复杂的交互作用。未来降水(降雨与降雪)变化将如何影响地上净初级生产力(ANPP)尚未研究清楚,尤其是当降水变化与氮沉降引起的氮有效性增加相互结合时。在本研究中,我们探讨了半干旱温带典型草原对增加降水(降雨与降雪)和氮素的响应,包括群落生产力、两种主要植物功能群、多年生根茎禾草(PR)和多年生丛生禾草(PB)的多度和地上生物量的变化。研究结果发现,夏季增雨略微增加了群落的ANPP,显著增加了PR的多度和地上生物量,而对PB的多度和地上生物量没有影响。夏季增雨提高了PR生物量在ANPP中的占比,降低了PB生物量的占比。春季增雪对上述两个植物功能群地上生物量均无显著影响,尽管它对群落ANPP有一定的提高。在夏季增雨条件下,氮素添加显著增加了群落ANPP,主要是由于增加了PR的生物量,说明氮和水分添加对群落ANPP存在较强的交互作用,并在很大程度上通过提高PR生物量来实现。我们发现随着降水量的增加,施氮对生产力的正效应呈非线性增加。上述结果表明,在未来大气氮沉降增加的情景下,降水增加对草地生产力的影响将得到进一步放大。     

Nutrient release from decomposing leaf litter of Banksia ornata,Dark Island heathland,South Australia

Distinct O₁ and O₂ layers, representing annual litter fall, enabled the sequential loss of biomass and nutrients (phosphorus and nitrogen) to be reconstructed in undisturbed litter layers of Banksia ornata in the Dark Island heathland, South Australia. Apart from an initial loss in biomass and nitrogen, the dry weight and nutrient content of the O₁ layer, exposed to the desiccating influence of the atmosphere, remained relatively constant until covered by the following year's leaf fall. Under the blanket of newly fallen leaves, biomass decomposition proceeded continuously through autumn, winter, spring, into the dry summer season. Even though the biomass of the decomposing leaf (O₂) layer decreased continuously, its nutrient content remained relatively constant until the summer season was reached when total decomposition and nutrient loss occurred. During spring, fine rootlets invaded the decomposing litter layer (O₂) and, together with decomposer fungi, bacteria and soil fauna, maintained the total nutrient content of the decomposing leaf at a constant level. By late spring-early summer shoot growth of the dominant heath species was initiated, inducing the mobilization of the nutrients stored in the decomposing litter layer.     

中国沿海海藻的种类与分布

我国沿海海藻现有记录835种。本文根据各海区的物种组成、物种的温度性质、特有属(种)的分布和各海区属的相似性比较,分析各海区海藻区系特点和亲缘关系。讨论了温度、海流和地理环境对海藻分布的影响。     

Microsatellite markers from expressed sequence tags (ESTs) of seaweeds in differentiating various Gracilaria species

Gracilaria is a red seaweed that has been cultivated worldwide and is commercially used for food, fertilizers, animal fodder, and phycocolloids. However, the high morphological plasticity of seaweeds often leads to the misidentification in the traditional identification of Gracilaria species. Molecular markers are important especially in the correct identification of Gracilaria species with high economic value. Microsatellite markers were developed from the expressed sequence tags of seaweeds deposited at the National Center for Biotechnology Information database and used for differentiating Gracilaria changii collected at various localities and two other Gracilaria species. Out of 33 primer pairs, only one primer pair gave significant results that can distinguish between three different Gracilaria species as well as G. changii from various localities based on the variation in repeated nucleotides. The unweighted pair group method using arithmetic mean dendrogram analysis grouped Gracilaria species into five main clades: (a) G. changii from Batu Besar (Malacca), Sandakan (Sabah), Bintulu (Sarawak), Batu Tengah (Malacca), Gua Tanah (Malacca), Middle Banks (Penang), Sungai (Sg.) Merbok (Kedah), Teluk Pelandok (Negeri Sembilan), Pantai Dickson (Negeri Sembilan), Sg. Kong-Kong (Johore), and Sg. Pulai (Johore); (b) Gracilaria manilaensis from Cebu, Philippines; (c) G. changii from Morib (Selangor); (d) Gracilaria fisheri from Pattani, Thailand; and (e) G. changii from Pantai Dickson (Negeri Sembilan), Gua Tanah (Malacca), Sg. Merbok (Kedah), Sg. Kong-Kong (Johore), and Sg. Pulai (Johore). This result shows that this primer pair was able to distinguish between three different species, which are G. changii from Morib (Malaysia), G. fisheri from Pattani (Thailand), and G. manilaensis from Cebu (Philippines), and also between different genotypes of G. changii. This suggested that the simple sequence repeat primer we developed was suitable for differentiating between different Gracilaria species due to the polymorphisms caused by the variability in the number of tandem repeats.     

Disentangling climate change effects on species interactions: effects of temperature, phenological shifts, and body size

Climate-mediated shifts in species’ phenologies are expected to alter species interactions, but predicting the consequences of this is difficult because phenological shifts may be driven by different climate factors that may or may not be correlated. Temperature could be an important factor determining effects of phenological shifts by altering species’ growth rates and thereby the relative size ratios of interacting species. We tested this hypothesis by independently manipulating temperature and the relative hatching phenologies of two competing amphibian species. Relative shifts in hatching time generally altered the strength of competition, but the presence and magnitude of this effect was temperature dependent and joint effects of temperature and hatching phenology were non-additive. Species that hatched relatively early or late performed significantly better or worse, respectively, but only at higher temperatures and not at lower temperatures. As a consequence, climate-mediated shifts in hatching phenology or temperature resulted in stronger or weaker effects than expected when both factors acted in concert. Furthermore, consequences of phenological shifts were asymmetric; arriving relatively early had disproportional stronger (or weaker) effects than arriving relatively late, and this varied with species identity. However, consistent with recent theory, these seemingly idiosyncratic effects of phenological shifts could be explained by species-specific differences in growth rates across temperatures and concordant shifts in relative body size of interacting species. Our results emphasize the need to account for environmental conditions when predicting the effects of phenological shifts, and suggest that shifts in size-structured interactions can mediate the impact of climate change on natural communities.     

Polysaccharides from the green seaweeds Codium fragile and C. vermilara with controversial effects on hemostasis

Codium fragile and Codium vermilara biosynthesize water-soluble sulfated arabinans and galactans (and/or sulfated arabinogalactans), (1 → 4)-d-glucans and β(1 → 4)-d-mannans. The former polysaccharides are composed by 3-linked β-d-galactopyranose and β-l-arabinopyranose residues, they are highly sulfated and substituted with pyruvic acid ketals. For both seaweeds, they have the same main structural units, but in different percentages. All the room-temperature water extracts from both seaweeds showed a dual haemostatic effect: they prevented coagulation, but they induced platelet aggregation. Anticoagulant activity and platelet aggregation were higher in the samples with polysaccharides richer in sulfate, mainly in those from C. vermilara, which have a higher degree of sulfation and arabinose content.     

Shared patterns of species turnover between seaweeds and seed plants break down at increasing distances from the sea

We tested for correlations in the degree of spatial similarity between algal and terrestrial plants communities along 5500 km of temperate Australian coastline and whether the strength of correlation weakens with increasing distance from the coast. We identified strong correlations between macroalgal and terrestrial plant communities within the first 100 km from shore, where the strength of these marine–terrestrial correlations indeed weakens with increasing distance inland. As such, our results suggest that marine‐driven community homogenization processes decompose with increasing distance from the shore toward inland. We speculate that the proximity to the marine environment produces lower levels of community turnover on land, and this effect decreases progressively farther inland. Our analysis suggests underlying ecological and evolutionary processes that give rise to continental‐scale biogeographic influence from sea to land.     

Nitrogen release from roots of alfalfa and soybean grown in sand culture

An enclosed root chamber containing sterile sand medium was used to study net nitrogen (N) release from actively growing root systems of ‘Saranac’ alfalfa (Medicago sativa L.) and ‘Fiskeby V’ soybean (Glycine max L. Merr.). Plants were inoculated with a rhizobial strain appropriate to each host, irrigated with N-free nutrient solution, and grown either to 85 or to 173 d after germination (alfalfa) or to physiological maturity (soybean). Alfalfa released 4.5% of symbiotically-fixed plant N into the root zone over its growth period; soybean released 10.4% of plant N. Root zone leachates were analyzed for total N and for amino acid and ammonium content. Significant ammonium-N release occurred from the alfalfa but not the soybean root system; little amino-N was released by root systems of either species. Shoot harvest and water deficit caused increased release of N from alfalfa roots. The results provide evidence that alfalfa and soybean released significant proportions of their N into the root zone, and indicate that while substantial ammonium-N was released from alfalfa roots, passive leakage of amino-N was not a primary mechanism for N release from root systems of either species. Cooperative investigation of USDA-ARS and the Minnesota Agric. Exp. Stn. (Scientific J. Series No. 16048). This research was supported in part by a Graduate School Fellowship to LSB from the Univ. of Minnesota.