Low Light Availability Research Articles

The community-level effect of light on germination timing in relation to seed mass: a source of regeneration niche differentiation.

Within a community, species may germinate at different times so as to mitigate competition and to take advantage of different aspects of the seasonal environment (temporal niche differentiation). We illustrated a hypothesis of the combined effects of abiotic and biotic competitive factors on germination timing and the subsequent upscale effects on community assembly. We estimated the germination timing (GT) for 476 angiosperm species of the eastern Tibetan Plateau grasslands under two light treatments in the field: high (i.e. natural) light and low light. We also measured the shift in germination timing (SGT) across treatments for all species. Furthermore, we used phylogenetic comparative methods to test if GT and SGT were associated with seed mass, an important factor in competitive interactions. We found a significant positive correlation between GT and seed mass in both light treatments. Additionally, small seeds (early germinating seeds) tended to germinate later and large seeds (late germinating seeds) tended to germinate earlier under low light vs high light conditions. Low light availability can reduce temporal niche differentiation by increasing the overlap in germination time between small and large seeds. In turn, reduced temporal niche differentiation may increase competition in the process of community assembly.

Effect of light availability on dissolved organic carbon release by Caribbean reef algae and corals

Dissolved organic carbon (DOC) release of three algal and two coral species was determined at three light intensities (0, 30-80, and 200-400 [Mu]mol photons m-2 s-1) in ex situ incubations to quantify the effect of light availability on DOC release by reef primary producers. DOC release of three additional algal species was quantified at the highest light intensity only to infer inter-specific differences in DOC release. For species tested at different light intensities, highest net release of DOC occurred under full light (200-400 [Mu]mol photons m-2 s-1). DOC released by benthic algae under full light differed (up to 16-fold) among species, whereas DOC release by scleractinian corals was minimal (Orbicella annularis Ellis and Solander, 1786) or net uptake occurred (Madracis mirabilis Duchassaing and Michelotti, 1860) independent of light availability. DOC concentrations and light intensities were also measured in situ near seven benthic primary producers, sediment, and in the water column at nine sites evenly distributed along the leeward coast of Curacao. In situ DOC concentrations increased with light availability, although the magnitude of this positive effect differed among species and bottom types tested. In situ DOC concentrations were on average lower in November-December [87 (SD 45) [Mu]mol L -1 ] compared to May-June [186 (SD 136) [Mu]mol L-1], which can, at least partly, be explained by the lower light availability in the latter period. Our results suggest that DOC release by Caribbean benthic primary producers varies considerably among species and depends on light availability in reef algae.

Effects of light and prey availability on Arctic freshwater protist communities examined by high-throughput DNA and RNA sequencing

Protists in high-latitude lakes are constrained by cold temperatures, low inorganic nutrient supply and low light availability for much of the year due to ice cover and polar darkness. The lengthening ice-free periods in these freshwater ecosystems due to a warming climate results in increased light availability, but the overall impacts on phytoplankton and other protists are unknown. We experimentally investigated protist community responses to changes in light and prey availability in a dilution series in Ward Hunt Lake (latitude 83°05'N), in the Canadian High Arctic. The communities at the end of the experiment were characterized using high-throughput pyrosequencing of the V4 region of the 18S rRNA gene as a measure of taxonomic presence, and of 18S rRNA (from RNA converted to cDNA) as a taxon-specific indicator of community response. At the end of the experiment under low irradiance, cDNA reads were dominated by photosynthetic dinoflagellate genera, except at the greatest dilution where Cercozoa were most abundant. In contrast, the cDNA reads in the high light treatments were dominated by chrysophytes. Given the known trophic differences among dinoflagellates, cercozoans and chrysophytes, this apparent environmental selection implies that the rise in underwater irradiance associated with increasing ice-free conditions may affect microbial food web structure and function in polar lakes.

In vitro culture: an epigenetic challenge for plants

In vitro plant cell and tissue culture techniques are the basis of many micropropagation and breeding programs for scientific research. Plant tissue culture (PTC) involves organogenesis and embryogenesis, and the outcome depends on the different conditions to which the tissue is exposed. PTC is a stressful environment—high relative humidity, low ventilation rate, high concentrations of plant growth regulators, and low light availability—for plants that need to rapidly change their molecular regulation in order to respond fast and efficiently during cell division and growth. For instance, somatic embryogenesis (SE), which plays an important role in plant multiplication, requires complex cellular, biochemical and molecular processes for embryo formation and development. New data has come out about a connection between plant morphogenesis and epigenetics. Epigenetics is a very sensitive regulatory mechanism, which in most of cases is affected by the environment. Although it is known that, under plant morphogenesis, the genome has little or no change, DNA methylation and histone modifications are very susceptible to those in vitro environmental conditions. In the present review, we highlight the most used in vitro systems such as organogenesis and SE in plants and discuss how epigenetics plays a pivotal role in the phenotype outcome. Furthermore, we discuss the big role that the small RNAs have during cell division and propagation and propose different challenges and opportunities to study epigenetics in plant cell tissue and organ cultures.

Natural History Survey of the Ornamental Grass Miscanthus sinensis in the Introduced Range

AbstractMiscanthus sinensis is a perennial grass native to Asia, but since its introduction to the United States in the late 19th century, it has become both a major ornamental crop and invasive species. Previous studies of the ecology of M. sinensis in both its introduced and native ranges have suggested that it may be occupying a novel ecological niche in the introduced range. Miscanthus sinensis and its daughter species, Miscanthus × giganteus, are under evaluation as bioenergy crops; therefore, characterization of the ecology and environmental niche of M. sinensis is essential to mitigate the risk of fostering future invasion in the United States. In July 2011, we surveyed 18 naturalized M. sinensis populations spanning the U.S. distribution, covering a 6° latitudinal gradient from North Carolina to Massachusetts. Miscanthus sinensis populations ranged in size from 3 to 181,763 m2 with densities between 0.0012 and 2.2 individuals m−2, and strongly favored highly disturbed and unmanaged habitats such as roadsides and forest edges. Population size and individual plant morphology (i.e., tiller height, basal diameter, and tiller number) were not affected by soil characteristics and nutrient availability, though increased tree canopy cover was associated with reduced population size (P < 0.0001). Plant size and vigor were not significantly affected by low light availability, which supports previous suggestions of shade tolerance of M. sinensis. In summary, M. sinensis can tolerate a broad range of climatic conditions, light availability, and nutrient availability in the eastern United States, suggesting risk of further invasion beyond its current distribution in the United States.

Phenology as a strategy for carbon optimality: a global model

Abstract. Phenology is essential to our understanding of biogeochemical cycles and the climate system. We develop a global mechanistic model of leaf phenology based on the hypothesis that phenology is a strategy for optimal carbon gain at the canopy level so that trees adjust leaf gains and losses in response to environmental factors such as light, temperature and soil moisture, to achieve maximum carbon assimilation. We fit this model to five years of satellite observations of leaf area index (LAI) using a Bayesian fitting algorithm. We show that our model is able to reproduce phenological patterns for all vegetation types and use it to explore variations in growing season length and the climate factors that limit leaf growth for different biomes. Phenology in wet tropical areas is limited by leaf age physiological constraints while at higher latitude leaf seasonality is limited by low temperature and light availability. Leaf growth in grassland regions is limited by water availability but often in combination with other factors. This model will advance the current understanding of phenology for ecosystem carbon models and our ability to predict future phenological behaviour.

Biogeochemical characterization of the riverine particulate organic matter transferred to the NW Mediterranean Sea

Abstract. A large amount of terrestrial organic matter is annually delivered by rivers to the continental shelf, where this material is either degraded, buried or transferred to the deep sea by hydrodynamic processes such as storms. The relative amount of terrestrial organic matter in the marine sediments is often determined by analysing the stable isotopes (δ13C and δ15N) and the C / N ratio of organic matter because the various particulate organic matter (POM) sources have distinct isotopic compositions. With the objective to refine and better interpret POM sources in the marine environment, we have characterized monthly terrestrial POM delivered by eight rivers discharging to the NW Mediterranean Sea: the Rhône, Hérault, Orb, Aude, Têt, Fluvià, Ter and Tordera rivers. These rivers were simultaneously sampled from November 2008 to December 2009 and the concentrations of total suspended matter (TSM), particulate organic carbon (POC) and nitrogen (PN), as well as their stable isotopic ratios (δ13C and δ15N) were determined. During the survey, three rainstorm events with winds coming from the E–NE and the S–SE impacted the NW Mediterranean. Depending on the direction of incoming winds, the fluvial response (amount of water discharge and TSM) was different. Rivers draining the Alps (Rhône River) and Central Massif (Hérault, Orb, and Aude rivers) were mostly impacted by rainstorms associated with winds coming from the S–SE, while rivers draining the Pyrenees (Têt, Fluvià, and Ter rivers) and the Montseny Massif (Tordera River) were impacted by rainstorms associated with winds coming from the E–NE. In addition, the spatial evolution of water discharges shows a different hydrological regime of the Rhône River, with relatively constant and high water stages and TSM concentrations when compared to coastal rivers, characterized by long periods of low water stages. TSM concentrations are positively correlated to water discharges (high water flows resuspended riverbed sediments) but show an inverse relationship with POC and PN relative contents (mostly due to dilution and by low availability of light in river waters during flood events). TSM in most of the coastal rivers have on average 2.5–3 times higher POC and PN mean contents than the Rhône River (8.5 and 1.5%, respectively, for coastal rivers compared to 3.6 and 0.5%, respectively, for the Rhône River). This discrepancy may be caused by the long drought periods in small coastal Mediterranean watersheds that enhance the eutrophication in studied coastal rivers. The δ13C ratios of organic matter also reflect this discrepancy between high and low water stages with values ranging from −33.2 to −24.5‰. The enriched 13C values (−26.3 ± 0.4‰ for the Rhône River and −26.9 ± 1.2‰ for coastal rivers), measured during high water stages, express mostly a mixture of terrestrial source (plant remains and soils) whereas depleted 13C values (∼ −30‰) associated with low water stages exhibit a source with predominant freshwater algae. The high δ15N mean values (>8‰) found in Têt, Ter and Tordera rivers may underline the importance of denitrification processes as a consequence of the eutrophication and anthropogenic impact.

Structural, compositional and trait differences between native‐ and non‐native‐dominated grassland patches

Summary Non‐native species with growth forms that are different from the native flora may alter the physical structure of the area they invade, thereby changing the resources available to resident species. This in turn can select for species with traits suited for the new growing environment. We used adjacent uninvaded and invaded grassland patches to evaluate whether the shift in dominance from a native perennial bunchgrass, Nassella pulchra, to the early season, non‐native annual grass, Bromus diandrus, affects the physical structure, available light, plant community composition and community‐weighted trait means. Our field surveys revealed that the exotic grass B. diandrus alters both the vertical and horizontal structure creating more dense continuous vegetative growth and dead plant biomass than patches dominated by N. pulchra. These differences in physical structure are responsible for a threefold reduction in available light and likely contribute to the lower diversity, especially of native forbs in B. diandrus‐dominated patches. Further, flowering time began earlier and seed size and plant height were higher in B. diandrus patches relative to N. pulchra patches. Our results suggest that species that are better suited (earlier phenology, larger seed size and taller) for low light availability are those that coexist with B. diandrus, and this is consistent with our hypothesis that change in physical structure with B. diandrus invasion is an important driver of community and trait composition. The traits of species able to coexist with invaders are rarely considered when assessing community change following invasion; however, this may be a powerful approach for predicting community change in environments with high anthropogenic pressures, such as disturbance and nutrient enrichment. It also provides a means for selecting species to introduce when trying to enhance native diversity in an otherwise invaded community.

Three-dimensional winter modeling and the effects of ice cover on hydrodynamics, thermal structure and water quality in Lake Erie

A 3-dimensional numerical model of Lake Erie was set up for a winter season using a coupled hydrodynamic and water quality model (ELCOM-CAEDYM) and validated against observations. The model was successful in predicting average lake surface temperature (root mean square deviation, RMSD<0.87°C) when compared with the available observed temperature profile (RMSD<0.78°C). The ice cover hind cast favorably agrees with observations (ice coverage RMSD=3.1×103km2, ~10% of the lake surface, and thickness RMSD=2.1cm). This study illustrates the importance of the inclusion of ice cover when simulating hydrodynamics and lake water quality. For example, the water level oscillations were significantly reduced under ice cover conditions. Although the model is not calibrated for water quality during winter conditions, the predicted variations in DO and Chl-a are qualitatively in agreement for all three basins of Lake Erie. Similar to recent field observations, our model results also suggest that despite low temperatures and low under-ice light availability, winter conditions can support high phytoplankton biomass in the central basin which is at least comparable to that typically observed in the summer. Our results also indicate that simulations without ice-cover during the winter results in higher phytoplankton biomass in the central basin compared to that in the scenario with ice. This suggests that changes in the extent of ice cover, its thickness and duration will influence winter productivity with the consequences for hypoxia to develop later in the season.

Phytoplankton composition changes during water level fluctuations in a high-altitude, tropical reservoir

To understand the responses of phytoplankton to water level fluctuations (WLFs) in tropical conditions at high altitude, limnological monitoring was performed monthly in Valle de Bravo (VB) reservoir, a waterbody affected by relatively strong WLFs due to water scarcity in central Mexico during 2008–2009. The thermal behaviour of the reservoir was warm, monomictic (Nov–Feb), and water levels fell to 12 m below capacity. Observed hypolimnetic temperature increases in VB are considered indirect evidence of boundary mixing events, previously attributed to internal waves driven by strong diurnal winds along a 7 km fetch. Unusually low biomasses were observed during circulation, probably due to low light availability (Zeu/Zmix < 1), grazing, and relatively low temperatures (<20 °C). In contrast, enhanced phytoplankton biomass was observed throughout stratification, which could be explained by nutrient inputs to the epilimnion through boundary mixing, as previously proposed for VB, and by higher (>20 °C) temperatures. Dominant species were Cyclotella ocellata, Fragilaria crotonensis, Woronichinia naegeliana, and Microcystis wesenbergii. Nitrogen-fixing cyanobacteria (Nostocales), a recurrent problem in this reservoir, were markedly less abundant than during high-water periods (2002–2005), probably due to dissolved inorganic nitrogen (DIN) inputs from the hypolimnion. A profuse formation of heterocysts was observed at the same time that DIN and the DIN to soluble reactive phosphorus ratio (DIN:SRP) were low (<2 μmol L−1 and ~1 respectively), suggesting heterocyst development could be a complementary proxy to assess DIN limitation. Intense water level decreases in this reservoir resulted in increasing biomasses of planktonic diatoms and a significant decrease in noxious algae such as Nostocales, thus ameliorating the water quality of the reservoir.

Clonal integration of Fragaria orientalis in reciprocal and coincident patchiness resources: cost-benefit analysis.

Clonal growth allows plants to spread horizontally and to experience different levels of resources. If ramets remain physiologically integrated, clonal plants can reciprocally translocate resources between ramets in heterogeneous environments. But little is known about the interaction between benefits of clonal integration and patterns of resource heterogeneity in different patches, i.e., coincident patchiness or reciprocal patchiness. We hypothesized that clonal integration will show different effects on ramets in different patches and more benefit to ramets under reciprocal patchiness than to those under coincident patchiness, as well as that the benefit from clonal integration is affected by the position of proximal and distal ramets under reciprocal or coincident patchiness. A pot experiment was conducted with clonal fragments consisting of two interconnected ramets (proximal and distal ramet) of Fragaria orientalis. In the experiment, proximal and distal ramets were grown in high or low availability of resources, i.e., light and water. Resource limitation was applied either simultaneously to both ramets of a clonal fragment (coincident resource limitation) or separately to different ramets of the same clonal fragment (reciprocal resource limitation). Half of the clonal fragments were connected while the other half were severed. From the experiment, clonal fragments growing under coincident resource limitation accumulated more biomass than those under reciprocal resource limitation. Based on a cost-benefit analysis, the support from proximal ramets to distal ramets was stronger than that from distal ramets to proximal ramets. Through division of labour, clonal fragments of F. orientalis benefited more in reciprocal patchiness than in coincident patchiness. While considering biomass accumulation and ramets production, coincident patchiness were more favourable to clonal plant F. orientalis.

Importance of underwater light field in selecting phytoplankton morphology in a eutrophic reservoir

This study attempted to reveal the effect of solar radiation fluctuation on the dynamics of phytoplankton communities expressed as cell morphology in eutrophic water bodies where the impacts of nutrients could be considered as small. Two morphological descriptors were proposed, cellular projected area ( $$\varphi_{\rm p}$$ ) and flattening index (f), which were able to he cellular light-harvesting potential and energy requirement, respectively. A model was established to describe the effects of natural light availability on selecting phytoplankton assemblages with underwater field and mixing process in the water column considered. Based on the data collected from the eutrophic Yanghe Reservoir, the model was derived as $$V=37.92\lambda\varphi_{\rm p} (R^2 = 0.673, P < 0.01),$$ where V is bio-volume, λ is a function of solar elevation angle (θ) and mixing/euphotic depth ratio (z mix/z eu) in water, and $$\varphi_{\rm p}.$$ Post-analysis of the model results revealed that species with large $$\varphi_{\rm p}$$ and f in general have advantages in spring and winter when underwater light availability is low; by contrast, those with small $$\varphi_{\rm p}$$ and f have advantages in summer. Larger $$\varphi_{\rm p}$$ and f mean that the cells could harvest more light energy and consumed less, allowing them to be selected under low light availability; and vice versa. We thus concluded that the underwater light field probably the most important factor in selecting phytoplankton morphology in eutrophic water bodies.

The physiology of invasive plants in low-resource environments.

While invasive plant species primarily occur in disturbed, high-resource environments, many species have invaded ecosystems characterized by low nutrient, water, and light availability. Species adapted to low-resource systems often display traits associated with resource conservation, such as slow growth, high tissue longevity, and resource-use efficiency. This contrasts with our general understanding of invasive species physiology derived primarily from studies in high-resource environments. These studies suggest that invasive species succeed through high resource acquisition. This review examines physiological and morphological traits of native and invasive species in low-resource environments. Existing data support the idea that species invading low-resource environments possess traits associated with resource acquisition, resource conservation or both. Disturbance and climate change are affecting resource availability in many ecosystems, and understanding physiological differences between native and invasive species may suggest ways to restore invaded ecosystems.

&lt;b&gt;Spatial and temporal fluctuation of phytoplankton functional groups in a tropical reservoir&lt;/b&gt; - doi: 10.4025/actascibiolsci.v35i3.12988

Along the horizontal axis of reservoirs are generally recognized three zones (fluvial, transition and lacustrine) with distinct hydrodynamic and physical, chemical and biological properties. Quarterly samplings were conducted in 2002, in the limnetic region from each zone, at different depths of a tropical reservoir. To test the hypothesis that highest biomass (biovolume) of phytoplankton are found in the transition zone, the PERMANOVA analysis was realized. 106 taxa were recorded. Significant differences between biovolume values of the three zones were not verified (pseudo F = 0,89; p = 0,55). Higher values of biomass were obtained in lacustrine and transition zones of the reservoir. The functional group (FG) N (Cosmarium spp.) was dominant in these zones, in rain period, and related to low phosphorus concentration, high transparency and water column stability. Low biovolume values in reservoir characterized oligotrophic conditions in all zones of the reservoir, most of the period. The dominance of FGs Y, Lo, E, P and A, as evidenced by the CCA, was associated with low light availability and higher nutrients concentrations.

Growth characteristics of Adiantum reniforme var. sinensis and A. capillus‐veneris in response to light and soil moisture

Adiantum reniforme var. sinensis (Adiantaceae) is an endangered fern endemic to the Three Gorges region in southwest China. To elucidate possible ecophysiological mechanisms restricting its distribution, effects of the availability of light (28%, 14% and 7% of open field) and soil moisture (60% and 40% of field capacity) on dry matter production and allocation, leaf morphology and water use efficiency (WUE) were examined in A. reniforme var. sinensis and its widespread congener A. capillus‐veneris. Both species had lower root/shoot ratio (R/S) and higher specific leaf area (SLA) when grown at low light. However, A. reniforme var. sinensis showed less plasticity for total leaf area (LA) and leaf area ratio (LAR) than A. capillus‐veneris, and its root mass, total mass and WUE decreased as light availability decreased. Under water stress, all traits of both species except WUE were significantly affected. However, drought stress decreased total mass of A. capillus‐veneris but did not have a significant effect on A. reniforme var. sinensis. Compared with A. capillus‐veneris, A. reniforme var. sinensis had significantly higher R/S but lower values for other analyzed traits. These results suggest that A. reniforme var. sinensis is relatively superior in drought tolerance but inferior at low light, allowing it to persist in habitats with low soil moisture and high light availability but with few coexisting species present.

Lack of superiority of invasive over co-occurring native riparian tree seedling species

The invasive tree species Acer negundo, Ailanthus altissima, Elaeagnus angustifolia and Robinia pseudoacacia are nowadays spreading in inner Spain riparian forests, where they co-occur with the natives Fraxinus angustifolia, Populus alba and Ulmus minor. In these forests, the natural light and soil moisture conditions are being altered by different human activities, as river channelization and regulation. These new environmental conditions may favor invasive species to the detriment of natives. In order to predict potential shifts of species composition in inner Spain riparian forests, we experimentally compared seedling and sapling performance across the four invasive and the three native mentioned species. Seeds were sown along an experimental gradient with four levels of light (100, 65, 35, 7 % of full irradiance) factorially combined with two levels of soil moisture (61 and 40 % of soil gravimetric water content). We compared plant biomass at the end of the first and second growing seasons, relative growth rates, biomass allocation to roots (RWR), stems (SWR) and leaves (LWR), time to emergence (Temerg) and net assimilation rate per unit of leaf mass (NARm) between origins and across species. Biomass accumulation greatly varied across species. However, invaders did not grow on average more than natives. Under high resource conditions, all species tended to grow more and similarly. Only the native U. minor and the invader A. negundo were not hampered by low moisture and/or low light availabilities. The absence of superiority of invaders over natives suggests that the former will not displace the latter in inner Spain riparian forests. However, human activities promoting shade and drought stress in floodplains may benefit the invasive A. negundo in the long term, as the growth of its seedlings is less declined by these conditions than the growth of the rest of the studied species. Thus, management effort should be focused in monitoring and preventing this species spread.

Distribution and identity of Bacteria in subarctic permafrost thaw ponds

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 69:231-245 (2013) - DOI: https://doi.org/10.3354/ame01634 Distribution and identity of Bacteria in subarctic permafrost thaw ponds Paul-Georges Rossi1, Isabelle Laurion1, Connie Lovejoy2,* 1Centre d’études nordiques, Institut national de la recherche scientifique, Centre Eau Terre Environnement, Québec, Quebec G1K 9A9, Canada 2Québec-Océan, Département de Biologie and Institut de Biologie Intégrative et des Systèmes (IBIS), Université Laval, Québec, Quebec G1V 0A6, Canada *Corresponding author. Email: connie.lovejoy@bio.ulaval.ca ABSTRACT: Colored permafrost thaw ponds (thermokarst ponds), are abundant freshwater ecosystems in the subarctic. The ponds can emit significant levels of greenhouse gases, which are drivers of climate change, but little is known of their microbial communities. The ponds are vertically stratified for most of the year with suboxic to anoxic hypolimnia, suggesting varied habitats despite their shallow depths (1 to 4 m). Pelagic bacterial communities in 4 contrasting ponds near the coast of Hudson Bay, Quebec, Canada, were investigated by cloning and sequencing the 16S rRNA gene from environmental DNA. Surface and bottom water libraries yielded a total of 109 operational taxonomical units (defined as 97% sequence similarity) from 261 clones. The majority of clones had their closest matches to other environmental clones originating from freshwater environments, especially lakes. Proteobacteria accounted for the majority of sequences (33%), followed by Bacteroidetes (19%), Actinobacteria (13%), Chlorobi (10%), Verrucomicrobia (8%), and Cyanobacteria (7%). There were large differences in the assemblages inhabiting the different ponds and water layers. Bacteroidetes were predominant at the surface, while Chlorobi were found in bottom waters. Sequences with best matches to known methanotrophic bacteria represented up to 20% of all sequences. Methanotrophs included Methylobacter psychrophilus, Crenothrix polyspora, and Methylocystis parvus as closest matches. Ordination analysis clearly separated surface and bottom waters, where relatively large quantities of organic matter, low light availability, cool temperatures, and suboxic conditions selected for the distinct communities. The separation of surface waters of different ponds showed that bacterial communities could differ between superficially similar environments. This study illustrates the high diversity in bacterial assemblages occurring in ponds separated by a few meters, and thus, the potentially complex response of thaw pond systems to climate change. KEY WORDS: Bacterial community composition · 16S rRNA clone libraries · Thermokarst lakes Full text in pdf format PreviousNextCite this article as: Rossi PG, Laurion I, Lovejoy C (2013) Distribution and identity of Bacteria in subarctic permafrost thaw ponds. Aquat Microb Ecol 69:231-245. https://doi.org/10.3354/ame01634 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 69, No. 3. Online publication date: July 04, 2013 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2013 Inter-Research.

Global distribution of root climbers is positively associated with precipitation and negatively associated with seasonality

Abstract:Root climbers constitute a distinctive group within climbing plants and some evidence suggests that they are associated with high precipitation and low light availability at local scales, which is in contrast with general patterns of liana distribution in the tropics. The influence of precipitation and seasonality on the occurrence of root climbers was evaluated both globally and in the tropics. The presence/absence of root climbers was recorded in 174 sites of Alwyn H. Gentry Forest Transect Data Set. The effects of mean annual precipitation and dry-season length (and temperature) on their occurrence were analysed using logistic regressions. Root climbers were significantly more frequent in sites with greater precipitation and reduced seasonality. Increasing temperature reduced root-climber occurrence in tropical sites, but this effect was marginally significant at a global scale. Dry and open habitats appear unsuitable for root climbers. This can be explained by the susceptibility to desiccation of adventitious roots and/or the low acclimation ability of these climbers to high irradiance.

Factors Controlling Phytoplankton Biomass in a Subtropical Coastal Lagoon: Relative Scales of Influence

Patterns in phytoplankton biomass are essential to understanding estuarine ecosystem structure and function and are the net result of various gain and loss processes. In this study, patterns in phytoplankton biomass were explored in relation to a suite of potentially regulating factors in a well-flushed, subtropical lagoon, the Matanzas River Estuary (MRE) in northeast Florida. We examined temporal variability in water temperature, light availability, nutrient concentrations, phytoplankton productivity, and phytoplankton standing stock over 8 years (2003–2010) and explored relationships among variables through correlation analysis. Laboratory experiments in the spring and summer of 2009 quantified phytoplankton growth rates, nutrient limitation potential, and zooplankton grazing rates. The potential influence of oyster grazing was also examined by scaling up population metrics and filtration rate estimates. Results indicated that phytoplankton biomass in the study area was relatively low mainly due to a combination of low temperature and light availability in the winter and consistent tidal water exchange and bivalve grazing throughout the year. Relatively low levels of phytoplankton standing stock and small inter-annual variability within the MRE reflect a balance between gain and loss processes which provide a degree of resilience of the system to natural and anthropogenic influences.

Environmental influences on growth and defence responses of the invasive shrub, Lonicera maackii, to simulated and real herbivory in the juvenile stage

Tolerance and defence against herbivory are among the many mechanisms attributed to the success of invasive plants in their novel ranges. Because tolerance and defence against herbivory differ with the ontogeny of a plant, the effects of herbivore damage on plant fitness vary with ontogenetic stage and are compounded throughout a plant's lifetime. Environmental stresses such as light and nutrient limitations can further influence the response of the plant. Much is known about the response of plants in the seedling and reproductive adult stages, but less attention has been given to the pre-reproductive juvenile stage. Juvenile plants of the North American invasive Lonicera maackii were exposed to simulated herbivory under high and low light and nitrogen availability and growth, allocation patterns and foliar defensive chemistry were measured. In a second experiment, complete nutrient availability and damage type (generalist caterpillar or simulated) were manipulated. Juvenile plants receiving 50 % defoliation had lower total biomass and a higher root^:^shoot ratio than controls for all treatment combinations except low nitrogen/low light. Low light and defoliation increased root^:^shoot ratio. Light, fertilization and defoliation had little impact on foliar defensive chemistry. In the second experiment, there was a reduction in total biomass when caterpillar damage was applied. The root^:^shoot ratio increased under low soil fertility and was not affected by defoliation. Stem-diameter growth rates and specific leaf area did not vary by damage type or fertilization. Foliar protein increased through time, and more strongly in defoliated plants than in controls, while peroxidase activity and total flavonoids decreased with time. Overall, resource limitations were more influential than damage in the growth of juvenile L. maackii plants. The findings illustrate that even when resources are limited, the tolerance and defence against herbivory of a woody invasive plant in the juvenile stage may contribute to the establishment and persistence of some species in a variety of habitats.