气态有机物组成对生物过滤及菌体密度的影响

以堆肥-火山灰为填料的生物过滤器连续处理含甲苯、乙酸乙酯和异丙醇的气体,观测生物过滤效果和填料的菌系状态变化.结果表明:在甲苯和乙酸乙酯共存的条件下,生物过滤器优先去除乙酸乙酯;当进气中同时存在甲苯、乙酸乙酯和异丙醇时,优先去除乙酸乙酯和异丙醇.填料中各种微生物的菌体密度与过滤去除的有机物组成和浓度有关.霉菌和酵母菌竞争利用乙酸乙酯和异丙醇的能力较强,放线菌和细菌对甲苯的竞争利用能力较强.进气中高浓度的有机物会使填料中的菌体密度增大.在处理甲苯、乙酸乙酯和异丙醇的生物过滤器的各段填料中,菌体密度按细菌、霉菌、酵母菌、放线菌的顺序而降低. 图 1表 3参 17     

Riparian forest composition affects stream litter decomposition despite similar microbial and invertebrate communities

Cross-boundary flows of energy and nutrients link biodiversity and functioning in adjacent ecosystems. The composition of forest tree species can affect the structure and functioning of stream ecosystems due to physical and chemical attributes, as well as changes in terrestrial resource subsidies. We examined how variation in riparian canopy composition (coniferous, deciduous, mixed) affects adjacent trophic levels (invertebrate and microbial consumers) and decomposition of organic matter in small, coastal rainforest streams in southwestern British Columbia. Breakdown rates of higher-quality red alder (Alnus rubra) litter were faster in streams with a greater percentage of deciduous than coniferous riparian canopy, whereas breakdown rates of lower-quality western hemlock (Tsuga heterophylla) litter were independent of riparian forest composition. When invertebrates were excluded using fine mesh, breakdown rates of both litter species were an order of magnitude less and were not significantly affected by riparian forest composition. Stream invertebrate and microbial communities were similar among riparian forest composition, with most variation attributed to leaf litter species. Invertebrate taxa richness and shredder biomass were higher in A. rubra litter; however, taxa evenness was greatest for T. heterophylla litter and both litter species in coniferous streams. Microbial community diversity (determined from terminal restriction fragment length polymorphisms) was unaffected by riparian forest or litter species. Fungal allele richness was higher than bacterial allele richness, and microbial communities associated with lower-quality T. heterophylla litter had higher diversity (allele uniqueness and richness) than those associated with higher-quality A. rubra litter. Percent variation in breakdown rates was mostly attributed to riparian forest composition in the presence of invertebrates and microbes; however, stream consumer biodiversity at adjacent trophic levels did not explain these patterns. Riparian and stream ecosystems and their biotic communities are linked through exchange and decomposition of detrital resources, and we provide evidence that riparian forest composition affects stream ecosystem catabolism despite similarities in microbial and invertebrate communities.     

Plant-soil microorganism interactions: heritable relationship between plant genotype and associated soil microorganisms

Although soil microbial communities are known to play crucial roles in the cycling of nutrients in forest ecosystems and can vary by plant species, how microorganisms respond to the subtle gradients of plant genetic variation is just beginning to be appreciated. Using a model Populus system in a common garden with replicated clones of known genotypes, we evaluated microbial biomass and community composition as quantitative traits. Two main patterns emerged. (1) Plant genotype influenced microbial biomass nitrogen in soils under replicated genotypes of Populus angustifolia, F1, and backcross hybrids, but not P. fremontii. Genotype explained up to 78% of the variation in microbial biomass as indicated by broad-sense heritability estimates (i.e., clonal repeatability). A second estimate of microbial biomass (total phospholipid fatty acid) was more conservative and showed significant genotype effects in P. angustifolia and backcross hybrids. (2) Plant genotype significantly influenced microbial community composition, explaining up to 70% of the variation in community composition within P. angustifolia genotypes alone. These findings suggest that variation in above- and belowground traits of individual plant genotypes can alter soil microbial dynamics, and suggests that further investigations of the evolutionary implications of genetic feedbacks are warranted.     

Net energetic advantage drives honey bees (Apis mellifera L) to nectar larceny in Vaccinium ashei Reade

Carpenter bees (Xylocopa spp.) act as primary nectar thieves in rabbiteye blueberry (Vaccinium ashei Reade), piercing corollas laterally to imbibe nectar at basal nectaries. Honey bees (Apis mellifera L) learn to visit these perforations and thus become secondary nectar thieves. We tested the hypothesis that honey bees make this behavioral switch in response to an energetic advantage realized by nectar-robbing flower visits. Nectar volume and sugar quantity were higher in intact than perforated flowers, but bees (robbers) visiting perforated flowers were able to extract a higher percentage of available nectar and sugar so that absolute amount of sugar (mg) removed by one bee visit is the same for each flower type. However, because perforated flowers facilitate higher rates of bee flower visitation and the same or higher rates of nectar ingestion, they are rendered more profitable than intact flowers in temporal terms. Accordingly, net energy (J) gain per second flower handling time was higher for robbers on most days sampled. We conclude that the majority evidence indicates an energetic advantage for honey bees that engage in secondary nectar thievery in V. ashei.Communicated by R. Page     

Comparison on bacterial community of rhizosphere and bulk soil of poplar plantation based on pyrosequencing北大核心CSCD

By the 454 pyrosequencing technology, this research compared the bacterial communities in poplar plantation rhizosphere and bulk soil for an accurate understanding of bacterial community colonization in the two soil environments. The species annotation showed that rhizosphere soil contained 145 bacterial genera and bulk soil contained 141 bacterial genera, with 8 common genera shared by both at a relative abundance of more than 4%. The 8 genera in common were Acidobacterium GP1, Acidobacterium GP3, Acidobacterium GP6, Gemmatimonas, Bradyrhizobium, Burkholderia, Streptomyces and Acidobacterium GP4. The relative abundance of the same bacterial community was significantly different between rhizosphere and bulk soil environments. Alpha diversity analysis showed that the bacterial community diversity of rhizosphere soil was higher than that of bulk soil, but the difference was not significant. The results of bacterial communities sorting could reflect the variation of soil bacterial communities from rhizosphere to the bulk and the spatial variation among different sampling points, indicating a contribution of about 21.2% variance of bacterial communities by the effect of rhizosphere. Beta diversity analysis showed great difference between rhizosphere and bulk soil samples in bacterial community composition. There were 15 genera specific to rhizosphere soil and 11 to bulk soil. The abundance of 23 genera, mainly cellulose degrading bacteria and nitrogen-fixing bacteria, changed significantly. Selectivity of root to rhizosphere microorganisms is an important mechanism leading to significant differences in the rhizosphere microbial community composition and structure, which may significantly impact the carbon and nitrogen cycles of the root-soil interface.     

Microbial community composition and function across an arctic tundra landscape

Arctic landscapes are characterized by a diversity of ecosystems, which differ in plant species composition, litter biochemistry, and biogeochemical cycling rates. Tundra ecosystems differing in plant composition should contain compositionally and functionally distinct microbial communities that differentially transform dissolved organic matter as it moves downslope from dry, upland to wet, lowland tundra. To test this idea, we studied soil microbial communities in upland tussock, stream-side birch-willow, and lakeside wet sedge tundra in arctic Alaska, USA. These are a series of ecosystems that differ in topographic position, plant composition, and soil drainage. Phospholipid fatty acid (PLFA) analyses, coupled with compound-specific 13C isotope tracing, were used to quantify microbial community composition and function; we also assayed the activity of extracellular enzymes involved in cellulose, chitin, and lignin degradation. Surface soil from each tundra ecosystem was labeled with 13C-cellobiose,13C-N-acetylglucosamine, or 13C-vanillin. After a five-day incubation, we followed the movement of 13C into bacterial and fungal PLFAs, microbial respiration, dissolved organic carbon, and soil organic matter. Microbial community composition and function were distinct among tundra ecosystems, with tussock tundra containing a significantly greater abundance and activity of soil fungi. Although the majority of 13C-labeled substrates rapidly moved into soil organic matter in all tundra soils (i.e., 50-90% of applied 13C), microbial respiration of labeled substrates in wet sedge tundra soil was lower than in tussock and birch-willow tundra; approximately 8% of 13C-cellobiose and approximately 5% of 13C-vanillin was respired in wet sedge soil vs. 26-38% of 13C-cellobiose and 18-21% of 13C-vanillin in the other tundra ecosystems. Despite these differences, wet sedge tundra exhibited the greatest extracellular enzyme activity. Topographic variation in plant litter biochemistry and soil drainage shape the metabolic capability of soil microbial communities, which, in turn, influence the chemical composition of dissolved organic matter across the arctic tundra landscape.     

Nectar secondary compounds affect self-pollen transfer: implications for female and male reproduction

Pollen movement within and among plants affects inbreeding, plant fitness, and the spatial scale of genetic differentiation. Although a number of studies have assessed how plant and floral traits influence pollen movement via changes in pollinator behavior, few have explored how nectar chemical composition affects pollen transfer. As many as 55% of plants produce secondary compounds in their nectar, which is surprising given that nectar is typically thought to attract pollinators. We tested the hypothesis that nectar with secondary compounds may benefit plants by encouraging pollinators to leave plants after visiting only a few flowers, thus reducing self-pollen transfer. We used Gelsemium sempervirens, a plant whose nectar contains the alkaloid gelsemine, which has been shown to be a deterrent to foraging bee pollinators. We found that high nectar alkaloids reduced the total and proportion of self-pollen received by one-half and one-third, respectively. However, nectar alkaloids did not affect female reproduction when we removed the potential for self-pollination (by emasculating all flowers on plants). We then tested the assumption that self-pollen in combination with outcrossed pollen depresses seed set. We found that plants were weakly self-compatible, but self-pollen with outcrossed pollen did not reduce seed set relative to solely outcrossed flowers. Finally, an exponential model of pollen carryover suggests that high nectar alkaloids could benefit plants via increased pollen export (an estimate of male function), but only when pollinators were efficient and abundant and plants had large floral displays. Results suggest that high nectar alkaloids may benefit plants via increased pollen export under a restricted set of ecological conditions, but in general, the costs of high nectar alkaloids in reducing pollination balanced or outweighed the benefits of reducing self-pollen transfer for estimates of female and male reproduction.     

Macrophyte species composition and structure along littoral region in relation to limnological variables of a tropical wetland ecosystem

The composition and structure of macrophyte communities of the littoral region of Bhindawas wetland (India) was investigated. Two hypotheses were tested: (1) if limnological variables such as water chemistry and soil parameters are important determinants of species composition and abundance and (2) what is the variance in species richness and composition within the wetland. Twenty-eight macrophyte species belonging to 17 different families were identified with relatively low species diversity and richness (H′?=?2.09; Margalef index?=?1.12). Eichhornia crassipes, attained the highest relative frequency (22.69%), followed by Salvinia natans, Paspalum paspaloides, Phragmites karka, Cynodon dactylon and Cyperus alopecuroides. The first and second axis of CCA ordination explained 38.4% and 28.5% of the total variance of species–limnological variables relationship, respectively. Water-related variables (dissolved oxygen, pH and nitrate concentration) and soil nutrient factors (soil carbon and phosphorus levels) were significantly correlated to macrophyte distribution. Sampling sites formed two distinct groups based on cluster analysis, indicating varying ecological conditions. Generally, composition and abundance of macrophytes evince highly productive nature of the lake, while dominance of invasive species like E. crassipes and S. natans indicates high influence of increased nutrient levels and anthropogenic activities in the catchment on lake macrophyte composition.     

Changes in microbial community characteristics and soil organic matter with nitrogen additions in two tropical forests

Microbial communities and their associated enzyme activities affect the amount and chemical quality of carbon (C) in soils. Increasing nitrogen (N) deposition, particularly in N-rich tropical forests, is likely to change the composition and behavior of microbial communities and feed back on ecosystem structure and function. This study presents a novel assessment of mechanistic links between microbial responses to N deposition and shifts in soil organic matter (SOM) quality and quantity. We used phospholipid fatty acid (PLFA) analysis and microbial enzyme assays in soils to assess microbial community responses to long-term N additions in two distinct tropical rain forests. We used soil density fractionation and 13C nuclear magnetic resonance (NMR) spectroscopy to measure related changes in SOM pool sizes and chemical quality. Microbial biomass increased in response to N fertilization in both tropical forests and corresponded to declines in pools of low-density SOM. The chemical quality of this soil C pool reflected ecosystem-specific changes in microbial community composition. In the lower-elevation forest, there was an increase in gram-negative bacteria PLFA biomass, and there were significant losses of labile C chemical groups (O-alkyls). In contrast, the upper-elevation tropical forest had an increase in fungal PLFAs with N additions and declines in C groups associated with increased soil C storage (alkyls). The dynamics of microbial enzymatic activities with N addition provided a functional link between changes in microbial community structure and SOM chemistry. Ecosystem-specific changes in microbial community composition are likely to have far-reaching effects on soil carbon storage and cycling. This study indicates that microbial communities in N-rich tropical forests can be sensitive to added N, but we can expect significant variability in how ecosystem structure and function respond to N deposition among tropical forest types.     

Bottom-up effects of plant genotype on aphids, ants, and predators

Theory predicts that bottom-up ecological forces can affect community dynamics, but whether this extends to the effects of heritable plant variation on tritrophic communities is poorly understood. In a field experiment, I contrasted the effects of plant genotype (28 genotypes; 1064 plants), aphid density, and the presence/absence of mutualistic ants in affecting the per capita population growth of a specialist aphid herbivore, as well as the effects of plant genotype on the third trophic level. Plant genotype strongly affected aphid population growth rate, explaining 29% of the total variation in growth rate, whereas aphid density and ant-aphid interactions explained substantially less variation (< 2%) in aphid population growth rate. Plant genotype also had direct and indirect effects on the third trophic level, affecting the abundance of aphid-tending ants and the richness of predators. Multiple regression identified several heritable plant traits that explained 49% of the variation in aphid growth rate and 30% of the variation in ant abundance among plant genotypes. These bottom-up effects of plant genotype on tritrophic interactions were independent of the effects of either initial aphid density or the presence/absence of mutualistic ants. This study shows that plant genotype can be one of the most important ecological factors shaping tritrophic communities.     

枯草芽孢杆菌Bs-15对板栗土壤微生物种群数量及功能多样性的影响

土壤微生物是维持土壤质量的重要组成部分,是土壤中生物活性的具体体现。土壤微生物多样性的变异可反映其对环境的响应与适应,能敏感反映生态系统的功能演变和生态环境的变化。本研究采用固体平板法研究了枯草芽孢杆菌（Bacillus subtilis）Bs-15对板栗（Castanea mollissimaBL）土壤微生物种群数量的影响,并通过BIOLOG ECO微孔板法分析Bs-15对板栗土壤功能多样性的影响。结果表明,接种Bs-15后,土壤中细菌数量比对照略有增加,但差异不显著;接种后放线菌的数量与对照相比有所减少,第7天达到极显著（p〈0.01）差异,之后差异变小,第14 d开始,处理与对照之间放线菌数量基本持平;真菌数量则先增加后减少,第7天开始接种后的真菌数量与对照相比达极显著（p〈0.01）差异。BIOLOG ECO微孔板分析显示,Bs-15使得土壤中微生物的AWCD值变大,72小时以后,AWCD值与对照相比差异达到极显著（p〈0.01）水平;接种Bs-15后增大了土壤微生物多样性指数,其中Shannon多样性指数、Simpson多样性指数和McIntosh多样性指数分别增加了4.09%、6.01%和7.20%,对对照相比差异均达到极显著水平（p〈0.01）,Simpson均匀度和McIntosh均匀度分别增加了2.07%和2.53%,与对照相比差异均达到显著水平（p〈0.05）。本研究结果表明,Bs-15不但提高了板栗土壤微生物的整体活性,丰富了土壤微生物种群,有利于保持和促进土壤肥力和健康状况;还提高了板栗土壤微生物功能多样性,使板栗土壤微生态系统功能更加稳定。     

Influence of invasive plant Coreopsis grandiflora on functional diversity of soil microbial communities

Biological invasions are increasingly attracting the ecologists' attention. Invasive plants threaten the natural ecosystems not only by competing with the native plants, but also by altering the structure and function of soil microbial communities belowground. In this study, we studied the effects of the invasive plant Coreopsis grandiflora (C. grandiflora) on the functional diversity of soil microbial communities in Laoshan mountain in the province of Shandong, North of China. We sampled soil from plots that were invaded or not invaded by C. grandiflora. The functional diversity of microbial communities in the sampled soils was assessed by the Biolog procedure test. By the ANOVA analysis of average well color development (AWCD), Shannon index (H'), Shannon evenness (E), principle components analysis of the level physiological profiles (CLPP) and correlation analysis between the studied parameters, we found that the invasive species C. grandiflora enhanced the functional diversity of soil microbial communities where the habitat was invaded by the C. grandiflora. The study indicated thatthe successful invasive plants have profound effects on the function of soil microbial communities.     

Microbial community variation and its relationship with nitrogen mineralization in historically altered forests

Past land use can impart soil legacies that have important implications for ecosystem function. Although these legacies have been linked with microbially mediated processes, little is known about the long-term influence of land use on soil microbial communities themselves. We examined whether historical land use affected soil microbial community composition (lipid profiles) and whether community composition was related to potential net nitrogen (N) mineralization rates in southern Appalachian (USA) forest stands abandoned from agriculture or logging and reforested >50 yr ago. Microbial community composition was determined by a hybrid procedure of phospholipid fatty acid (PLFA) and fatty acid methyl ester (FAME) analysis. We found that community composition varied significantly with past land use. Communities in formerly farmed stands had a higher relative abundance of markers for gram-negative bacteria and a lower abundance of markers for fungi compared with previously logged and reference (i.e., no disturbance history) stands. Potential net N mineralization rates were negatively correlated with fungal and gram-negative bacterial markers in both farmed and reference stands, and fungal abundance and soil bulk density effectively predicted mineralization rates in all stands. Our results indicate that the alteration of microbial communities by historical land use may influence the ecosystem processes they mediate. This is in contrast to typical expectations about microbial community resilience to change. Here, the decrease in fungal abundance observed from disturbance appeared to result in decreased nitrogen mineralization over the long term.     

Honeybees modify gustatory responsiveness after receiving nectar from foragers within the hive

Food quality is a relevant characteristic to be transferred within eusocial insect colonies because its evaluation improves the collective foraging efficiency. In honeybees, colony mates could directly acquire this resource characteristic during trophallactic encounters with nectar foragers. In the present study, we focused on the gustatory responsiveness of bees that have unloaded food from incoming foragers. The sugar sensitivity of receiver bees was assessed in the laboratory by using the proboscis extension response paradigm. After unloading, hive bees were captured either from a colony that foraged freely in the environmental surroundings or from a colony that foraged at an artificial feeder with a known sucrose solution. In the first situation, the sugar sensitivity of the hive bees negatively correlated with the sugar concentration of the nectar crops brought back by forager mates. Similarly, in the controlled situation, the highest sucrose concentration the receivers accepted during trophallaxis corresponded to the highest thresholds to sucrose. The results indicate that first-order receivers modify their sugar sensitivity according to the quality of the food previously transferred through trophallaxis by the incoming foragers. In addition, trophallaxis is a mechanism capable of transferring gustatory information in honeybees. Its implications at a social scale might involve changes in the social information as well as in nectar distribution within the colony.     

Microbial community dynamics at high organic loading rates revealed by pyrosequencing during sugar refinery wastewater treatment in a UASB reactor

High strength sugar refinery wastewater was treated in a mesophilic UASB. Pyrosequencing reveals microbial community succession with OLR increase. Diversity of microbial communities in OLR12 is much higher than those in OLR36 and OLR54.0 kgCOD/(kg VSS·d). Fermentative bacteria could deal with increasing OLR through the increase of microbial diversity and quantity. Hydrogen-producing acotogens and methanogens mainly coped with high OLR shocks by increasing the quantity of community The performance and microbial community structure in an upflow anaerobic sludge blanket reactor (UASB) treating sugar refinery wastewater were investigated. The chemical oxygen demand (COD) removal reached above 92.0% at organic loading rates (OLRs) of 12.0–54.0 kgCOD/(m³·d). The volatile fatty acids (VFAs) in effluent were increased to 451.1 mg/L from 147.9 mg/L and the specific methane production rate improved by 1.2–2.2-fold as the OLR increased. The evolution of microbial communities in anaerobic sludge at three different OLRs was investigated using pyrosequencing. Operational taxonomic units (OTUs) at a 3% distance were 353, 337 and 233 for OLR12, OLR36 and OLR54, respectively. When the OLR was increased to 54.0 kgCOD /(m³·d) from 12.0 kgCOD/(m³·d) by stepwise, the microbial community structure were changed significantly. Five genera (Bacteroides, Trichococcus, Chryseobacterium, Longilinea and Aerococcus) were the dominant fermentative bacteria at the OLR 12.0 kgCOD/(m³·d). However, the sample of OLR36 was dominated by Lactococcus, Trichococcus, Anaeroarcus and Veillonella. At the last stage (OLR= 54.0 kgCOD/(m³·d)), the diversity and percentage of fermentative bacteria were markedly increased. Apart from fermentative bacteria, an obvious shift was observed in hydrogen-producing acetogens and non-acetotrophic methanogens as OLR increased. Syntrophobacter, Geobacter and Methanomethylovorans were the dominant hydrogen-producing acetogens and methylotrophic methanogens in the samples of OLR12 and OLR36. When the OLR was increased to 54.0 kgCOD/(m³·d), the main hydrogen-producing acetogens and hydrogenotrophic methanogens were substituted with Desulfovibrio and Methanospirillum. However, the composition of acetotrophic methanogens (Methanosaeta) was relatively stable during the whole operation period of the UASB reactor.     

Dark, bitter-tasting nectar functions as a filter of flower visitors in a bird-pollinated plant

Floral nectar is offered by plants to animals as a reward for pollination. While nectar is typically a clear liquid containing sugar and trace amounts of amino acids, colored nectar has evolved in several plant families. Here we explore the functional significance of the phenolic compounds that impart a dark brown color to the nectar of the South African succulent shrub Aloe vryheidensis. Flowers of this aloe are visited for their nectar by a suite of short-billed birds that are occasional nectarivores, including bulbuls, white-eyes, rock thrushes, and chats. Dark-capped Bulbuls were more likely to probe model flowers containing dark nectar than those containing clear nectar, suggesting a potential signaling function for dark nectar. However, the main effect of the phenolics appears to be to repel "unwanted" nectarivores that find their bitter taste unpalatable. Nectar-feeding honey bees and sunbirds are morphologically mismatched for pollinating A. vryheidensis flowers and strongly reject its nectar. However, the frugivorous and insectivorous birds that effectively pollinate this aloe are seemingly unaffected by the nectar's bitter taste. Thus the dark phenolic component of the nectar appears to function as a floral filter by attracting some animals visually and deterring others by its taste.     

Increasing litter species richness reduces variability in a terrestrial decomposer system

Debate on the relationship between diversity and stability has been driven by the recognition that species loss may influence ecosystem properties and processes. We conducted a litterbag experiment in the Scottish Highlands, United Kingdom, to examine the effects of altering plant litter diversity on decomposition, microbial biomass, and microfaunal abundance. The design of treatments was fully factorial and included five species from an upland plant community (silver birch, Betula pendula; Scots' pine, Pinus sylvestris; heather, Calluna vulgaris; bilberry, Vaccinium myrtillus; wavy-hair grass, Deschampsia flexuosa); species richness ranged from one to five species. We tested the effects of litter species richness and composition on variable means, whether increasing litter species richness reduced variability in the decomposer system, and whether any richness-variability relationships were maintained over time (196 vs. 564 days). While litter species composition effects controlled variable means, we revealed reductions in variability with increasing litter species richness, even after accounting for differences between litter types. These findings suggest that higher plant species richness per se may result in more stable ecosystem processes (e.g., decomposition) and decomposer communities. Negative richness-variation relationships generally relaxed over time, presumably because properties of litter mixtures became more homogeneous. However, given that plant litter inputs continue to enter the belowground system over time, we conclude that variation in ecosystem properties may be buffered by greater litter species richness.     

The communal crop: modulation of sucrose response thresholds of pre-foraging honey bees with incoming nectar quality

We examined whether the quality (concentration) of incoming sucrose solutions returned by foraging honey bees affected the response thresholds of pre-foraging members of the colony. Six pairs of colonies were given ad libitum access to sucrose solution feeders. A colony from each pair was switched from 20–50% sugar concentration feeders while the other continued to have access to 20% sucrose feeders. Proboscis extension response (PER) scores to an increasing series of sucrose concentrations were significantly higher in pre-foragers of colonies foraging on 20% sucrose throughout compared to pre-foragers in colonies where foraging was switched to 50% sucrose. Although all colonies had honey stores, the concentration of sugar solution in non-foraging bees crops were significantly lower in bees from colonies foraging on 20% sucrose compared to those from colonies foraging on 50% sucrose. Because response thresholds to sugar of young bees were modulated by the concentration of sucrose solution returned to colonies, we repeated the 2000 study of Pankiw and Page that potentially confounded baseline response thresholds with modulated scores due to experience in the colony. Here, we examined PER scores to sucrose in bees within 6 h of emergence, prior to feeding experience, and their forage choice 2 to 3 weeks later. Pollen foragers had higher PER scores as newly emerged bees compared to bees that eventually became nectar foragers. These results confirm those of the 2000 study by Pankiw and Page. Combined, these experiments demonstrate that variation in pre-forager sucrose response thresholds are established prior to emerging as adults but may be modulated by incoming resources later on. Whether this modulation has long-term effects on foraging behavior is unknown but modulation has short-term effects and the potential to act as a means of communication among all bees in the colony.Communicated by M. Giurfa     

Seaweeds as a reservoir of Candida yeasts in inshore waters

The yeast populations on 9 species of seaweeds and in seawater were estimated by cultural methods over a 16-month period in Narragansett Bay, Rhode Island (USA). Maximal numbers occurred on rhodophytes and a chlorophyte, while the lower numbers on phaeophytes were attributed to the release of inhibitory polyphenolic materials. All divisions of algae showed a similar seasonal variation in yeast populations, correlated with trends in solar radiation and water temperature which would affect both the host and its microflora. The exposure of intertidal algae to unseasonable air temperatures apparently has a detectable effect on their microflora. The population changes in the water surrounding the seaweeds paralleled those on the plants. Only colorless yeasts of the genus Candida were observed, except for brief occurrences of the pink yeast Rhodotorula in late spring, when it accounted for 3 to 35% of the yeast community. Ninety five percent of the 362 representative isolates were strains of Candida. The published properties of the 84 species accepted in the genus Candida were compared with those of the marine isolates using numerical analysis. There were 7 groups: 1 solely of named species, 3 small groups with both named species and marine isolates, and 3 large groups with only one or two named species that contained 75% of the seaweed and sea-water isolates. An apparent successional sequence for three groups may be due to differences in their biochemical activity. The same three groups were preferentially enriched by 5 of the algal species. The role of this persistent yeast population as a reservoir of inshore yeasts is discussed.     

Trace Metal Uptake By Pichia Spartinae, an Endosymbiotic Yeast in the Salt Marsh Cord Grass Spartina Alterniflora

The ascosporogenous marine yeast Pichia spartinae is a dominant endosymbiont of the marsh grass Spartina alterniflora. Results of previous studies suggested that P. spartinae is involved in iron transport processes in the grass. of particular interest has been the mechanisms of metal uptake and metabolism by the yeast, and the ecological and plant biochemical significance of these processes. This investigation examined the uptake of iron and other metals (Zn, Cu, Cd, Ni, Pb, Cr) by P. spartinae, and provides data on possible mechanisms of this activity. the results suggest a) the yeast can assimilate divalent and trivalent forms of inorganic iron, as well as large organic-Fe(III) complexes, b) the uptake of inorganic trivalent iron under soluble iron-deficient conditions proceeded by a different mechanism than that of soluble Fe(II), with intracellular loadings of iron much increased under the former conditions; c) trivalent iron uptake is not mediated by hydroxamate siderophores at levels detectable by sensitive screening assays; d) the assimilation of some trace metals (Cu, Zn, Cd, Ni) is likely to be mediated by low molecular weight cysteine rich proteins, possibly metallothionein, and; e) siderophores from other fungi can provide iron for P. spartinae. the iron assimilation data suggested that multiple mechanisms are involved, and are influenced by the concentration and speciation of iron in the system. in general, iron assimilation mechanisms are comparable to those described for closely related yeasts, such as Saccharomyces cerevisiae. Among other things, these results indicated that future studies of trace metal mobilization and plant assimilation in salt marsh ecosystems must account for the activities of microbial symbionts associated with the plants.