High Nutrient Conditions Research Articles

Resistance and tolerance in Populus tremuloides: genetic variation, costs, and environmental dependency

Plants defend themselves against herbivores via resistance, which reduces damage, and tolerance, which minimizes the negative effects of damage. Theory predicts the existence of tradeoffs between defense and growth, as well as between resistance and tolerance, that could maintain the genetic variation for resistance and tolerance often observed in plant populations. We examined resistance and tolerance among aspen (Populus tremuloides) trees grown under divergent soil nutrient regimes. This common garden experiment revealed substantial genetic variation for resistance and tolerance under both low- and high-nutrient conditions. Costs of resistance exist, particularly under high-nutrient conditions where allocation to resistance chemicals competes directly with growth for limited carbon resources. We found no significant costs of tolerance, however, under either nutrient condition. Despite genetic variation for both resistance and tolerance, we found no evidence for a tradeoff between these two defense traits suggesting that resistance and tolerance are complementary, rather than mutually exclusive, defenses in aspen.

Seasonal and spatial variation in the sources and fluxes of long chain diols and mid-chain hydroxy methyl alkanoates in the Arabian Sea

Long chain 1,14-diols and 12-hydroxy methyl alkanoates may be useful indicators for high-nutrient conditions as their inferred sources, diatoms belonging to the genus Proboscia, are often abundant in upwelling regions. In order to test this hypothesis, the lipids of three different Proboscia species in culture were determined and the fluxes of different long chain diol isomers and mid-chain hydroxy methyl alkanoates in the Arabian Sea were studied. The culture studies showed that long chain 1,14-diols and 12-hydroxy methyl alkanoates are indeed major lipids in Proboscia indica, Proboscia inermis and Proboscia alata. Time-series sediment trap data from the Arabian Sea showed increased fluxes of long chain 1,14-diols and 12-hydroxy methyl alkanoates in periods of upwelling and low fluxes for the rest of the year. High fluxes were found primarily at stations in the upwelling area close to the coast, whereas at a station located 590 km off the coast of Oman fluxes were substantially lower. These results show that long chain 1,14-diols and 12-hydroxy methyl alkanoates can be used as proxies for upwelling conditions. Flux patterns of 1,15-diols did not, however, resemble those of 1,14-diols: 1,15-diols reached maximum flux earlier than 1,14-diols, annual flux of 1,15-diols was much lower than 1,14-diols and upwelling did not seem to affect 1,15-diol flux values. This agrees with the idea that the Eustigmatophytes rather than Proboscia spp. should be considered as the major source of 1,15-diols.

Biological and chemical characteristics of high-chlorophyll, low-temperature water observed near the Sulu Archipelago

Abstract According to ocean-color remote sensing data, a low phytoplankton biomass exists in the central parts of the Sulu and Celebes seas, whereas higher concentrations of chlorophyll a are observed in the waters near the Sulu Archipelago, which separates these water bodies. These high-chlorophyll a waters have lower temperatures than those of surrounding waters, indicating vertical mixing of nutrient-rich subsurface water that is attributable to the topographical features of the Sulu Ridge. Differences in photosynthetic parameters, primary productivity and the phytoplankton community structure between the high-chlorophyll area near the Sulu Archipelago and the oligotrophic basin area in the Philippine, Sulu and Celebes seas were investigated in November 2002 during the R.V. Hakuho-Maru KH-02-4 cruise. Entrainment of subsurface water and vertical mixing by intense tidal flow from the Sulu Archipelago to the Celebes Sea created a low-temperature, high-nutrient condition at the southeastern edge of the Sulu Ridge. Chlorophyll a concentrations greater than 2 μg l−1 were observed at stations 5–15 km offshore at the edge of the Sulu Ridge. This high-chlorophyll tongue in the Celebes Sea showed high primary productivity: it was 1.6–18 times higher than those measured in oligotrophic central basin regions of the Philippine, Sulu, and Celebes seas. Microscopic observation of these high-chlorophyll waters showed the dominance of chain-forming large centric diatoms. Extension of high-chlorophyll waters was not observed at the Sulu Sea side, where the surface water salinity was lower than in the Celebes Sea and consequently prevented intrusion of the Celebes Sea water into the surface layer. Occasional extensions of productive, chlorophyll-rich surface water from the archipelagic zone to the surrounding basin area seems to be an important factor causing spatiotemporal variability in the phytoplankton biomass in the southern Sulu Sea and the western Celebes Sea.

Hypereutrophication in Ngau Mei Hoi Bay, Hong Kong

Abstract Investigations into eutrophication of Ngau Mei Hoi Bay, Hong Kong, were carried out in July and December 1996. The results show that Ngau Mei Hoi Bay can be classified as hypereutrophic. During summer phytoplankton blooms (average chlorophyll a = 33.96 μg L−1), high oxygen saturation (up to 145.3%), high pH (7.8–8.4), and nutrient depletion (mean NO3+NO2 = 0.89 μg L−1) at the surface in association with hypoxic (dissolved oxygen concentration was down to 0.9 mg L−1), low pH (down to 4.9), and high nutrient (mean NO3+NO2 = 96.28 μg L−1) conditions at the bottom layer were observed. This typical phenomenon of eutrophication resulted from nutrient enrichment by anthropogenic activities, water column stratification formed by spreading of the Pearl River plume at the surface, and outer shelf water intrusion at the bottom. The perniciousness of the hypereutrophication and future monitoring needs for environmental management are also discussed.

Assessing the impact of nutrient enrichment in estuaries: Susceptibility to eutrophication

The main aim of this study was to develop a generic tool for assessing risks and impacts of nutrient enrichment in estuaries. A simple model was developed to predict the magnitude of primary production by phytoplankton in different estuaries from nutrient input (total available nitrogen and/or phosphorus) and to determine likely trophic status. In the model, primary production is strongly influenced by water residence times and relative light regimes. The model indicates that estuaries with low and moderate light levels are the least likely to show a biological response to nutrient inputs. Estuaries with a good light regime are likely to be sensitive to nutrient enrichment, and to show similar responses, mediated only by site-specific geomorphological features. Nixon’s scale was used to describe the relative trophic status of estuaries, and to set nutrient and chlorophyll thresholds for assessing trophic status. Estuaries identified as being eutrophic may not show any signs of eutrophication. Additional attributes need to be considered to assess negative impacts. Here, likely detriment to the oxygen regime was considered, but is most applicable to areas of restricted exchange. Factors which limit phytoplankton growth under high nutrient conditions (water residence times and/or light availability) may favour the growth of other primary producers, such as macrophytes, which may have a negative impact on other biological communities. The assessment tool was developed for estuaries in England and Wales, based on a simple 3-category typology determined by geomorphology and relative light levels. Nixon’s scale needs to be validated for estuaries in England and Wales, once more data are available on light levels and primary production.

Surface-water chemistry and fertility variations in the tropical Atlantic across the Paleocene/Eocene Thermal Maximum as evidenced by calcareous nannoplankton from ODP Leg 207, Hole 1259B

Calcareous nannoplankton assemblages at Ocean Drilling Program (ODP) Site 1259 on Demerara Rise (western equatorial Atlantic) underwent an abrupt and fundamental turnover across the Paleocene/Eocene Thermal Maximum (PETM) ~55.5 m.y. ago. The PETM is marked by a dissolution interval barren or nearly-barren of nannofossils due to the rapid acidification of the world oceans. Toweius, Fasciculithus, and Chiasmolithus sharply decrease at the onset, whereas Chiasmolithus, Markalius cf. M. apertus, and Neochiasmolithus thrive immediately after the event, which also signals the successive first appearances of Discoaster araneus, Rhomboaster, and Tribrachiatus. The environmental indications of these changes were further investigated by correspondence analysis on quantitative nannofossil counts. The PETM event has been attributed to CO 2-forced greenhouse effects. At Site 1259, the elevated pCO 2 and subsequent lowered surface-water pH values at the onset of the PETM caused intensive carbonate dissolution, producing the nannofossil-barren interval. The chemically stressed habitats may well have also induced the evolution of ephemeral nannofossil “excursion taxa”, such as Rhomboaster and malformed discoasters ( D. araneus and Discoaster anartios). Based on its sudden increase, Markalius cf. M. apertus is considered to have been a local opportunistic species that took advantage of the surface-water changes. At the same time, a presumably higher runoff from continental areas fertilized the western equatorial Atlantic as indicated by an increase in the abundance of r-mode specialists preferring high-nutrient conditions, such as Chiasmolithus, Coccolithus pelagicus, and Hornibrookina arca. Contrasts between the results of this study and previous work at ODP Site 690 in the Southern Ocean, the New Jersey continental margin, and the central paleoequatorial Pacific further demonstrate that the response to the PETM can be influenced by local differences in geologic setting and oceanographic conditions.

Fitness Benefits of Systemic Acquired Resistance During Hyaloperonospora parasitica Infection in Arabidopsis thaliana

We investigated the fitness benefits of systemic acquired resistance (SAR) in Arabidopsis thaliana using a mutational and transformational genetic approach. Genetic lines were designed to differ in the genes determining resistance signaling in a common genetic background. Two mutant lines (cpr1 and cpr5) constitutively activate SAR at different points in SAR signaling, and one mutant line (npr1) has impaired SAR. The transgenic line (NPR1-H) has enhanced resistance when SAR is activated, but SAR is still inducible similarly to wild type. The fitness benefits were also investigated under two nutrient levels to test theories that preventing pathogen damage and realized resistance benefits may be affected by nutrient availability. Under low-nutrient conditions and treatment with the pathogenic oomycete, Hyaloperonospora parasitica, wild type had a higher fitness than the mutant that could not activate SAR, demonstrating that normal inducible SAR is beneficial in these conditions; this result, however, was not found under high-nutrient conditions. The mutants with constitutive SAR all failed to show a fitness benefit in comparison to wild type under a H. parasitica pathogen treatment, suggesting that SAR is induced to prevent an excessive fitness cost.

Resistance and Tolerance of Terminalia sericea Trees to Simulated Herbivore Damage Under Different Soil Nutrient and Moisture Conditions

Resource availability, degree of herbivore damage, genetic variability, and their interactions influence the allocation of investment by plants to resistance and tolerance traits. We evaluated the independent and interactive effects of soil nutrients and moisture, and simulated the effects of herbivore damage on condensed tannins (resistance) and growth/regrowth (tolerance) traits of Terminalia sericea, a deciduous tree in the Kalahari desert that constitutes a major component of livestock diet. We used a completely crossed randomized-block design experiment to examine the effects of nutrients, water availability, and herbivore damage on regrowth and resistance traits of T. sericea seedlings. Plant height, number of branches, internode length, leaf area, leaf mass for each seedling, combined weight of stems and twigs, and root mass were recorded. Condensed tannin concentrations were 22.5 and 21.5% higher under low nutrients and low soil moisture than under high nutrient and high water treatment levels. Tannin concentrations did not differ significantly between control and experimental seedlings 2 mo after simulated herbivore damage. Tannin concentrations correlated more strongly with growth traits under low- than under high-nutrient conditions. No trade-offs were detected among individual growth traits, nor between growth traits and condensed tannins. T. sericea appeared to invest more in both resistance and regrowth traits when grown under low-nutrient conditions. Investment in the resistance trait (condensed tannin) under high-nutrient conditions was minimal and, to a lesser degree, correlated with plant growth. These results suggest that T. sericea displays both resistance and tolerance strategies, and that the degree to which each is expressed is resource-dependent.

Shoot Development and Extension of Quercus serrata Saplings in Response to Insect Damage and Nutrient Conditions

Plants have the ability to compensate for damage caused by herbivores. This is important to plant growth, because a plant cannot always avoid damage, even if it has developed defence mechanisms against herbivores. In previous work, we elucidated the herbivory-induced compensatory response of Quercus (at both the individual shoot and whole sapling levels) in both low- and high-nutrient conditions throughout one growing season. In this study, we determine how the compensatory growth of Quercus serrata saplings is achieved at different nutrient levels. Quercus serrata saplings were grown under controlled conditions. Length, number of leaves and percentage of leaf area lost on all extension units (EUs) were measured. Both the probability of flushing and the length of subsequent EUs significantly increased with an increase in the length of the parent EU. The probability of flushing increased with an increase in leaf damage of the parent EU, but the length of subsequent EUs decreased. This indicates that EU growth is fundamentally regulated at the individual EU level. The probabilities of a second and third flush were significantly higher in plants in high-nutrient soil than those in low-nutrient soil. The subsequent EUs of damaged saplings were also significantly longer at high-nutrient conditions. An increase in the probability of flushes in response to herbivore damage is important for damaged saplings to produce new EUs; further, shortening the length of EUs helps to effectively reproduce foliage lost by herbivory. The probability of flushing also varied according to soil nutrient levels, suggesting that the compensatory growth of individual EUs in response to local damage levels is affected by the nutrients available to the whole sapling.

Ecology of Dictyosphaerium pulchellum Wood (Chlorophyta, Chlorococcales) in a shallow, acid, forest lake

This study relates to the ecology of Dictyosphaerium pulchellum Wood in Delamere Lake in Cheshire, UK. Dictyosphaerium pulchellum is a cosmopolitan, green colonial phytoplankton species that occasionally forms dense, monospecific populations in lakes. Delamere Lake is a small, shallow, acid lake (mean pH, 4.5) with very high phytoplankton biomass (annual mean chlorophyll a, 290 μg l−1) and devoid of any significant cladoceran population, the efficient grazers of phytoplankton. A predominantly unicellular form of D. pulchellum was the dominant species in Lake Delamere, and it comprised on average ca. 80% (maximum >99%) of the lake phytoplankton biovolume. Laboratory and lake experiments were conducted on this species showed that its pH tolerance varied between 2.4 and 10.7, and its optimum tolerance range between 3.3 and 8.5 depending on other environmental variables. Low pH was not responsible for the unicellular habit of this alga, but a very high nutrient regime could be an important factor. Bioassays revealed that in Delamere Lake this species was limited by nitrogen, but nitrogen did not hamper high growth in the lake. Dictyosphaerium pulchellum can persist at low light levels, tolerate CO2-deficiency and can grow in polyhumic water with water colour around 300 mg Pt l−1, but probably not in darker waters. The dominance of D. pulchellum in Delamere Lake is apparently due to a combination of several factors: its ability to tolerate both low pH and high turbidity, exploit high nutrient conditions, absence of effective grazing pressure by zooplankton and being a superior competitor.

Biofilm Formation and Sloughing inSerratia marcescensAre Controlled by Quorum Sensing and Nutrient Cues

We describe here a role for quorum sensing in the detachment, or sloughing, of Serratia marcescens filamentous biofilms, and we show that nutrient conditions affect the biofilm morphotype. Under reduced carbon or nitrogen conditions, S. marcescens formed a classical biofilm consisting of microcolonies. The filamentous biofilm could be converted to a microcolony-type biofilm by switching the medium after establishment of the biofilm. Similarly, when initially grown as a microcolony biofilm, S. marcescens could be converted back to a filamentous biofilm by increasing the nutrient composition. Under high-nutrient conditions, an N-acyl homoserine lactone quorum-sensing mutant formed biofilms that were indistinguishable from the wild-type biofilms. Similarly, other quorum-sensing-dependent behaviors, such as swarming motility, could be rendered quorum sensing independent by manipulating the growth medium. Quorum sensing was also found to be involved in the sloughing of the filamentous biofilm. The biofilm formed by the bacterium consistently sloughed from the substratum after approximately 75 to 80 h of development. The quorum-sensing mutant, when supplemented with exogenous signal, formed a wild-type filamentous biofilm and sloughed at the same time as the wild type, and this was independent of surfactant production. When we removed the signal from the quorum-sensing mutant prior to the time of sloughing, the biofilm did not undergo significant detachment. Together, the data suggest that biofilm formation by S. marcescens is a dynamic process that is controlled by both nutrient cues and the quorum-sensing system.

Resource Level Affects Relative Performance of the Two Motility Systems of Myxococcus xanthus

The adventurous (A) and social (S) motility systems of the microbial predator Myxococcus xanthus show differential swarming performance on distinct surface types. Under standard laboratory conditions, A-motility performs well on hard agar but poorly on soft agar, whereas the inverse pattern is shown by S-motility. These properties may allow M. xanthus to swarm effectively across a greater diversity of natural surfaces than would be possible with one motility system alone. Nonetheless, the range of ecological conditions under which dual motility enhances effective swarming across distinct surfaces and how ecological parameters affect the complementarity of A-motility and S-motility remain unclear. Here we have examined the role of nutrient concentration in determining swarming patterns driven by dual motility on distinct agar surfaces, as well as the relative contributions of A-motility and S-motility to these patterns. Swarm expansion rates of dually motile (A+S+), solely A-motile (A+S-), and solely S-motile (A-S+) strains were compared on hard and soft agar across a wide range of casitone concentrations. At low casitone concentrations (0-0.1%), swarming on soft agar driven by S-motility is very poor, and is significantly slower than swarming on hard agar driven by A-motility. This reverses at high casitone concentration (1-3.2%) such that swarming on soft agar is much faster than swarming on hard agar. This pattern greatly constrained the ability of M. xanthus to encounter patches of prey bacteria on a soft agar surface when nutrient levels between the patches were low. The swarming patterns of a strain that is unable to produce extracellular fibrils indicate that these appendages are responsible for the elevated swarming of S-motility at high resource levels. Together, these data suggest that large contributions by S-motility to predatory swarming in natural soils may be limited to soft, wet, high-nutrient conditions that may be uncommon. Several likely benefits of S-motility to the M. xanthus life cycle are discussed, including synergistic interactions with A-motility across a wide variety of conditions.

Genotype × environment interactions, stoichiometric food quality effects, and clonal coexistence in Daphnia pulex

The role of stoichiometric food quality in influencing genotype coexistence and competitive interactions between clones of the freshwater microcrustacean, Daphnia pulex, was examined in controlled laboratory microcosm experiments. Two genetically distinct clones of D. pulex, which show variation in their ribosomal rDNA structure, as well as differences in a number of previously characterized growth-rate-related features (i.e., life-history features), were allowed to compete in two different arenas: (1) batch cultures differing in algal food quality (i.e., high vs. low carbon:phosphorus (C:P ratio) in the green alga, Scenedesmus acutus); (2) continuous flow microcosms receiving different light levels (i.e., photosynthetically active radiation) that affected algal C:P ratios. In experiment 1, a clear genotype x environment interaction was determined with clone 1 out-competing clone 2 under high nutrient (i.e., low food C:P) conditions, while the exact opposite pattern was observed under low nutrient (i.e., high C:P) conditions. In experiment 2, clone 1 dominated over clone 2 under high light (higher C:P) conditions, but clonal coexistence was observed under low light (low C:P) conditions. These results indicate that food (nutrient) quality effects (hitherto an often overlooked factor) may play a role in microevolutionary (genotypic) responses to changing stoichiometric conditions in natural populations.

Effects of solar ultraviolet radiation on the periphyton community in lotic systems: comparison of attached algae and bacteria during their development

The effects of solar ultraviolet radiation (UVR) on the development of a periphyton community were studied in an outdoor artificial stream apparatus. Algal biomass, species composition, and bacterial cell density were measured under full sunlight and non-UVR (photosynthetically active radiation [PAR]-only) conditions. Attachment of algae was detected on days 6–9. Although the chlorophyll-a concentration under non-UVR conditions was 2–4 times that under full sunlight (PAR + UVR) throughout the experiment, neither net algal growth rate nor species composition differed significantly between the two light conditions. The relative carotenoid pigment contents of attached algae in the PAR + UVR condition were 1.1–1.3 times those in the non-UVR condition. Rates of increase of bacterial cell densities under the PAR + UVR condition were depressed by solar UVR for the first few days, although there were no apparent differences in the rates of increase between the light conditions later in the experiment. The small effect of UVR on the development of this periphyton community may be attributable to low UV flux at this study site and to the experimental conditions under which the algae were kept: a high physiological state with high nutrient conditions. Attached bacteria and algae that colonize substrata first are likely to be sensitive to solar UVR, and the negative effects of UVR are mitigated by the development of a periphyton community.

Morphological variation in the deep ocean-dwelling coccolithophore Florisphaera profunda (Haptophyta)

Detailed analysis of the morphology of Florisphaera profunda from plankton samples collected at three sites in the Atlantic and Pacific Oceans reveals wide variation in this deep ocean-dwelling coccolithophore. In addition to the two varieties described previously, we found a third distinctive form, Florisphaera profunda var. rhinocera var. nov. All three varieties occur at each of the sampling sites. The analysis of monthly samples from different levels in the lower photic zone (LPZ) (100–200 m) at the Hawaii Ocean Time series station suggests that the varieties have similar distributions, which are correlated to primary productivity and the availability of light. The analysis of coccolith and coccosphere size in F. profunda reveals the existence of several size modes in Florisphaera profunda var. profunda and F. profunda var. elongata. The biological significance of these modes, or morphotypes is not known. However, their co-occurrence in single samples from different oceanic areas suggests that they are not ecophenotypes. In the light of recent molecular genetic analyses of intraspecific groups within commonly occurring coccolithophores, the varieties and size morphotypes of F. profunda are of significant interest for the study of marine phytoplankton biodiversity. Coccolithophores inhabiting the LPZ may be adapted to the low light, high nutrient conditions of this layer and hold great potential as a means to reconstruct past oceanographic conditions such as the position of the nutricline. However, coccolithophore biodiversity in the LPZ is poorly documented and the number of species may be much higher than previously thought.

TROPHIC DIATOM INDICES (TDI) AND THE DEVELOPMENT OF SITE-SPECIFIC NUTRIENT CRITERIA

In 2004 a four year study performed for NJDEP by the Patrick Center for Environmental Research showed that trophic diatom inference models could be used effectively to assess late-summer nutrient concentrations and benthic algal responses specific to different physiographic provinces in the state. Diatoms are widely recognized and used as indicators of river and stream water quality because benthic diatom species composition responds directly to nutrients and can be a more stable indicator of tropic state than measurements of nutrient concentrations or algal biomass (e.g., chlorophyll a). Objectives of the study were to: 1) develop New Jersey specific field and lab protocols for characterizing eutrophication (nutrient concentrations) in streams using attached periphyton algae, 2) assess the relationships between stressors (i.e., total phosphorus/nitrogen) and overt signs of eutrophication (e.g., algae), and 3) develop biological metrics as potential biocriteria (e.g., diatom community structure and trophic diatom indices - TDI). We chose weighted average inference modeling as our approach because it incorporated the most accurate method for quantifying species response to nutrients. We used nutrient concentrations inferred from the models in two ways: 1) directly, by using the inferred diatom values as estimates of the nutrient concentrations prevailing at the site during the time the algal assemblages were developing, and 2) indirectly, by rescaling the inferred concentrations from 0-100 to create trophic diatom indices (TDI) more easily interpretable by non-specialists. In the current study in 2004 we performed a pilot study to test the TDIs above and below two Sewage Treatment Plant (STP) facilities in New Jersey to evaluate their usefulness as a stressor-response model necessary to generate site-specific biocriteria for nutrients. We conclude that the TP and TN diatom inference models and indices are promising tools to monitor and infer nutrient conditions but that further study is necessary to adequately evaluate their effectiveness for routine use as part of a regulatory program. Diatom community composition differed among sites, and the differences can be explained by variation in nutrient concentrations. Diatom indices indicated relatively high nutrient conditions at all sampling sites, and between-site differences were consistent with measured values. Both the diatom indicators of enrichment and the measured nutrient concentrations showed a marked increase below one STP, but not below the other. This may be because the discharge from one plant was much greater than the other, one-time sampling did not

Experimental evidence for the effects of additional water, nutrients and physical disturbance on invasive plants in low fertility Hawkesbury Sandstone soils, Sydney, Australia

Summary The environmental conditions of a site are thought to influence its invasibility by exotic plants. We tested the effects of physical disturbance, water and nutrient addition on growth and survival of a total of 28 plant species from urban bushland remnants on low fertility Hawkesbury Sandstone soils in Sydney, Australia. Species were classified as native (to Australia, including the local community) or exotic (from outside Australia) and as non‐invasive or invasive. In a glasshouse experiment the treatments were control (natural soil), added water, added nutrients and added water and nutrients. We found significant differences in response of the plant types to additional nutrients but not to water. Under additional nutrients, exotic invasive species had better survival than all other plant types. There were strong biomass responses to added nutrients for all plant types except native non‐invasives. In contrast, the survival and growth of all plant types were similar under control and additional water treatments. In a field experiment the factors were site (high and low nutrient soils) and physical disturbance but survival differed between plant types only in relation to site. Exotic species had much better survival than native species at the high nutrient site only. Exotic invasive species had the strongest biomass responses to the high nutrient site while native and exotic non‐invasive species showed relatively smaller growth responses. Differences between invasive and non‐invasive plants were not consistent between exotic and native species. Exotic invasives had greater survival than exotic non‐invasives under high nutrient conditions in both experiments, and only exotic invasives showed consistently strong biomass responses to nutrient addition. For native species, there were no differences between invasives and non‐invasives in survival in high nutrient conditions in the glasshouse or field; however, only invasive species showed a positive growth response to high nutrient conditions. This study provides clear evidence that the success of exotic invasive species in this low fertility vegetation community is facilitated by the addition of nutrients. It would appear that on relatively infertile (particularly phosphorus‐limited) sites, invasive species cannot take advantage of additional resources provided by physical disturbance or water addition due to overwhelming nutrient‐limitation. We suggest that a combination of the environmental conditions (nutrient‐enrichment) and invading species having traits that allow high survival and faster growth in response to nutrients, may allow successful invasion in Hawkesbury Sandstone communities.

Escherichia coli growth under modeled reduced gravity

Bacteria exhibit varying responses to modeled reduced gravity that can be simulated by clino-rotation. When Escherichia coli was subjected to different rotation speeds during clino-rotation, significant differences between modeled reduced gravity and normal gravity controls were observed only at higher speeds (30-50 rpm). There was no apparent affect of removing samples on the results obtained. When E. coli was grown in minimal medium (at 40 rpm), cell size was not affected by modeled reduced gravity and there were few differences in cell numbers. However, in higher nutrient conditions (i.e., dilute nutrient broth), total cell numbers were higher and cells were smaller under reduced gravity compared to normal gravity controls. Overall, the responses to modeled reduced gravity varied with nutrient conditions; larger surface to volume ratios may help compensate for the zone of nutrient depletion around the cells under modeled reduced gravity.

The effect of breeding on allometry and phenotypic plasticity in four varieties of oat ( Avena sativa L.)

New directions in crop improvement via alteration of plant responsiveness to variation in growth conditions are being actively debated. It appears, however, that little is known about the impact of previous breeding on the phenotypic plasticity of plants, which results from correlated responses to selection on high yield. We used four oat ( Avena sativa) varieties, originating from 1930, 1952, 1980 and 1999, to examine the effects of long-term breeding on the patterns of autecological phenotypic responses to variation in light and nutrient supply. The modern variety showed the least plasticity in stem elongation in response to variation in light conditions. As a by-product of decreased sensitivity to light availability, the modern oat variety appeared to be more susceptible to low light levels compared to other varieties. The patterns of plastic response in leaf area and root biomass were similar in all varieties. Changes in allocation to panicles in response to resource variation were completely attributable to passive plasticity, i.e. the proportion of biomass invested into reproduction varied as a function of total plant size. Interestingly, variation in specific leaf mass, the trait considered to be important in adaptive shade-avoidance responses, was only partially attributable to ontogenetic plasticity (environmentally induced adjustments of ontogeny). Our results support the idea that it can be more advantageous in the breeding of crop plants to select for a fixed pattern of allocation to different tissues, dependent on developmental stage, than to select for the ability to adjust the whole ontogeny to particular environmental conditions. Uniform high-nutrient conditions and completely predictable changes in light environment during ontogeny are common for crop plants, and are known to enhance genetic differentiation, not plasticity. Obviously, it is not possible to lose ontogenetic plasticity, as such, entirely: plants will have to adjust their development in response to stressful conditions if the allocational pattern of underdeveloped plants is not consistent with optimal foraging behaviour. On the other hand, the similar patterns of plastic responses in the studied varieties imply that further development of more plastic varieties can be precluded by homogenizing selection on optimal reaction norm (greater plasticity can be associated with excessively high costs and can outweigh possible advantages).

Flood tolerance in wetland angiosperms: a comparison of invasive and noninvasive species

We assessed the biomass production, biomass allocation patterns, height growth, and root airspace of seventeen wetland plant taxa, including two potentially invasive species, grown under high nutrient conditions and subjected to four hydrologic regimes: constant drawdown, cyclic flooding and drawdown, cyclic flooding and drought, and constant flooding for the duration of the experiment (∼10 weeks). We found that: (1) the potentially invasive reed canary grass ( Phalaris arundinacea) and broadleaf cattail ( Typha latifolia) responded to treatments similarly; both outgrew the other perennial species in all four hydrologic regimes; (2) Phalaris had the highest levels of root airspace of all the taxa; (3) the grasses and graminoids nearly always tolerated flooding better than the broadleaf forbs, perhaps in part due to greater quantities of root airspace; and (4) the species that were most sensitive to flooding are typically found in drier, groundwater-fed, and more nutrient-poor environments. We hypothesize that Phalaris and Typha, which are both tall and productive, should be competitive dominants under a variety of hydrologic conditions, at least where nutrients are abundant, as in urban and agricultural landscapes. Eight of the noninvasive taxa tolerated flooding but produced less biomass and/or were shorter or shorter-lived than Phalaris and Typha. Among the five taxa that were most sensitive to flooding were slow-growing habitat specialists; such species will likely experience declines in areas that become impounded or experience greater volumes of runoff.