Nodule gas exchange and water potential response to rapid imposition of water deficit

The permeability (P) of the gaseous diffusion barrier in the nodules of soybean [Glycine max (L.) Merr.] decreases when water deficits are extended over a 7 to 10 d period. The mechanism controlling P changes is unclear, but may result from the release of water to intercellular pathways, and an associated change in the nodule water potential. The purpose of these experiments was to impose water deficit treatments rapidly in order to determine the early sequence of the responses of nodule water potential and nodule gas exchange without the complications that arise from long-term water deficit treatments. A vertical, split-root system was used to separate nodule drying effects from plant water deficits by replacing humidified air that was passed over upper root nodules in well-watered plants with dry air, or by replacing the nutrient solution that surrounded lower roots with -1.0 MPa polyethylene glycol (PEG) solution, or by a combination of the dry air and PEG treatments. The PEG treatment caused large decreases in both the components of nodule water potential and nodule relative water content, but there was no indication that these factors had immediate, direct effects on either nitrogenase activity or P. After 7 h of the PEG treatment a significant decrease in nitrogenase activity was found but no decrease in P was detected. These results indicate that changes in nitrogenase activity in response to water deficits precede decreases in P. Exposure of nodules to dry air in well-watered plants had no significant effect on either nitrogenase activity or P during the 7 h treatment.     

Specificity of bacterial response to variation of isotopic composition of water

Culture growth of bacteria with different membrane lipid composition was studied in liquid media with different isotope content of water. The concentration of deuterium in water was varied from 0.01 to 90%. It was shown that large concentrations of deuterium cause the inhibition of all cultures except Deinococcus radiodurans, the most stable living cell. Two cultures, Methylobacterium organophilum and Hyphomonas jannaschiana, showed a pronounced activation at a deuterium concentration of 0.01%. At higher deuterium concentrations, the inhibition of culture growth was observed. The strains Renobacter vacuolatum, Arcocella aquatica NO502 and Caulobacter crescentus did not show any significant effect at low concentrations of deuterium.     

Species effects on ecosystem processes are modified by faunal responses to habitat composition

Heterogeneity is a well-recognized feature of natural environments, and the spatial distribution and movement of individual species is primarily driven by resource requirements. In laboratory experiments designed to explore how different species drive ecosystem processes, such as nutrient release, habitat heterogeneity is often seen as something which must be rigorously controlled for. Most small experimental systems are therefore spatially homogeneous, and the link between environmental heterogeneity and its effects on the redistribution of individuals and species, and on ecosystem processes, has not been fully explored. In this paper, we used a mesocosm system to investigate the relationship between habitat composition, species movement and sediment nutrient release for each of four functionally contrasting species of marine benthic invertebrate macrofauna. For each species, various habitat configurations were generated by selectively enriching patches of sediment with macroalgae, a natural source of spatial variability in intertidal mudflats. We found that the direction and extent of faunal movement between patches differs with species identity, density and habitat composition. Combinations of these factors lead to concomitant changes in nutrient release, such that habitat composition effects are modified by species identity (in the case of NH4-N) and by species density (in the case of PO4-P). It is clear that failure to accommodate natural patterns of spatial heterogeneity in such studies may result in an incomplete understanding of system behaviour. This will be particularly important for future experiments designed to explore the effects of species richness on ecosystem processes, where the complex interactions reported here for single species may be compounded when species are brought together in multi-species combinations.     

Developmental changes in tomato fruit composition in response to water deficit and salinity

Processing tomato ( Lycopersicon esculentum Mill. cv. UC82B) plants were subjected to moderate levels of water deficit and salinity (Na₂SO₄/CaCl₂) in sand culture. Fruit water content and the relative contributions of organic and inorganic constituents to fruit solute potential (_Ψ) and soluble solids content were determined throughout development. Fruit _Ψ averaged –0.63, –0.86 and –0.77 MPa in the control, salinity and water deficit plants, respectively. Reduced net water import and maintenance of solute accumulation, irrespective of water import, accounted for the reductions in _Ψ of stressed fruits. Mineral ions (Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻ and SO^2-₄) contributed –0.31 MPa to _Ψ in salinized fruit, compared with –0.19 MPa in control and water deficit treatments. Changes in net carbon accumulation were not observed among treatments, despite considerable differences in fruit K⁺ status. Starch accumulation in immature fruit was increased and hexose accumulation was decreased by both salinity and water deficit. Maximum starch levels were negatively correlated with total fruit _Ψ, but were independent of fruit K⁺. Organic acid levels were generally higher throughout development in salinized plants, relative to control plants, and correlated with increased inorganic cation rather than anion accumulation in these fruits.     

Fish diet composition in floodplain lagoons of an Australian dryland river in relation to an extended dry period following flooding

Floodplain rivers worldwide are threatened by loss of connectivity to their floodplains and hence reduced benefits from floodplain energy subsidies. Dryland rivers with ‘boom and bust’ ecological responses to flooding and extended dry periods may be particularly vulnerable. This paper describes variations in dietary composition of three fish species of contrasting trophic position in dryland floodplain lagoons with variable flood inundation and drying histories. The study species were Ambassis agassizii - a microphagic carnivore, Leiopotherapon unicolor - a carnivore/omnivore, and Nematalosa erebi - an algivore/detritivor. Despite the range of food items recorded in fish guts, each species fed mostly on relatively few food categories and few food items within each category. Most of the spatial (i.e. among lagoons) and temporal dietary variation was associated with different proportional contributions of these food items. Given the absence or low magnitude of flooding during the study period, temporal changes in diets of the three species are probably the result of successional changes in composition of invertebrate prey as the dry season progressed. The focus of each fish species on relatively few food categories and a few reliable food items within each category may be the most profitable foraging strategy when food resources are limiting in progressively drying floodplain lagoons.     

Microbial response to reinjection of produced water in an oil reservoir

The microbial response to produced water reinjection (PWRI) in a North Sea oil field was investigated by a combination of cultivation and culture-independent molecular phylogenetic techniques. Special emphasise was put on the relationship between sulphate-reducing bacteria (SRB) and nitrate-reducing bacteria (NRB), and results were used to evaluate the possibility of nitrate treatment as a souring management tool during PWRI. Samples were collected by reversing the flow of the injection water, which provided samples from around the injection area. The backflowed samples were compared to produced water from the same platform and to backflowed samples from a biocide-treated seawater injector, which was the previous injection water treatment of the PWRI well. Results showed that reinjection of produced water promoted growth of thermophilic SRB. Thermophilic fatty acid oxidising NRB and potential nitrate-reducing sulphide-oxidising bacteria were also found. The finding of thermophilic NRB makes nitrate treatment during PWRI possible, although higher nitrate concentration will be necessary to compensate for the increased SRB activity.     

Hydraulic properties of rice and the response of gas exchange to water stress

We investigated the role of xylem cavitation, plant hydraulic conductance, and root pressure in the response of rice (Oryza sativa) gas exchange to water stress. In the field (Philippines), the percentage loss of xylem conductivity (PLC) from cavitation exceeded 60% in leaves even in watered controls. The PLC versus leaf water potential relationship indicated diurnal refilling of cavitated xylem. The leaf water potential causing 50 PLC (P(50)) was -1.6 MPa and did not differ between upland versus lowland rice varieties. Greenhouse-grown varieties (Utah) were more resistant to cavitation with a 50 PLC of -1.9 MPa but also showed no difference between varieties. Six-day droughts caused concomitant reductions in leaf-specific photosynthetic rate, leaf diffusive conductance, and soil-leaf hydraulic conductance that were associated with cavitation-inducing water potentials and the disappearance of nightly root pressure. The return of root pressure after drought was associated with the complete recovery of leaf diffusive conductance, leaf-specific photosynthetic rate, and soil-leaf hydraulic conductance. Root pressure after the 6-d drought (61.2 +/- 8.8 kPa) was stimulated 7-fold compared with well-watered plants before drought (8.5 +/- 3.8 kPa). The results indicate: (a) that xylem cavitation plays a major role in the reduction of plant hydraulic conductance during drought, and (b) that rice can readily reverse cavitation, possibly aided by nocturnal root pressure.     

The structure of cynipid oak galls: patterns in the evolution of an extended phenotype

Galls are highly specialized plant tissues whose development is induced by another organism. The most complex and diverse galls are those induced on oak trees by gallwasps (Hymenoptera: Cynipidae: Cynipini), each species inducing a characteristic gall structure. Debate continues over the possible adaptive significance of gall structural traits; some protect the gall inducer from attack by natural enemies, although the adaptive significance of others remains undemonstrated. Several gall traits are shared by groups of oak gallwasp species. It remains unknown whether shared traits represent (i) limited divergence from a shared ancestral gall form, or (ii) multiple cases of independent evolution. Here we map gall character states onto a molecular phylogeny of the oak cynipid genus Andricus, and demonstrate three features of the evolution of gall structure: (i) closely related species generally induce galls of similar structure; (ii) despite this general pattern, closely related species can induce markedly different galls; and (iii) several gall traits (the presence of many larval chambers in a single gall structure, surface resins, surface spines and internal air spaces) of demonstrated or suggested adaptive value to the gallwasp have evolved repeatedly. We discuss these results in the light of existing hypotheses on the adaptive significance of gall structure.     

Species richness and composition assessment of spiders in a Mediterranean scrubland

Intensive fieldwork has been undertaken in Portugal in order to develop a standardized and optimized sampling protocol for Mediterranean spiders. The present study had the objectives of testing the use of semi-quantitative sampling for obtaining an exhaustive species richness assessment of spiders and testing the effects of day, time of day, collector and sampling method on the collected species richness and composition of a Mediterranean scrubland. The collecting summed 224 samples corresponding to one person-hour of effective fieldwork each. In total, 115 species were captured, of which 110 were recorded inside a delimited one-hectare plot, corresponding to more than 70% of the about 160 estimated species. Although no estimator reached the asymptote, the Michaelis-Menten curve behaviour indicates that the estimated richness should be accurate. Most different sampling approaches (day, time of day, collector and sampling method) were found to influence richness, abundance or composition of the samples to some extent, although sampling method had the strongest influence whereas “collector” showed no effect at all. The results support the idea that the only variables that need to be controlled in similar protocols are the sampling methods and the time of day when each method is executed. We conclude that populations in structurally simple habitats present narrower peaks of adult abundance, which implies higher percentages of juveniles in samples. Finally, results also indicate that habitats with a relatively simple structure like scrublands may require as much sampling effort, in order to reach similar proportions of captured species in relation to the estimated richness, as habitats that are much more complex.     

Benthic algal response to hyporheic-surface water exchange in an alluvial river

We studied the response of benthic algae to points of hyporheic-surface water exchange in the main channel of the Middle Fork Flathead River within the Nyack Flood Plain, Montana. We examined hyporheic exchange at 120 sites using piezometers and measuring vertical hydraulic gradient (VHG), hydraulic conductivity, and vertical discharge. We removed benthic algae from a single cobble at each site, and we used VHG to group sampling sites for statistical analysis. Algal cell density and chlorophyll a concentration were significantly higher at sites with hyporheic discharge (+VHG, upwelling) compared to both sites with hyporheic recharge (−VHG, downwelling) and sites with no hyporheic-surface water exchange (=VHG, neutral) (ANOVA, P < 0.05). The assemblages of algae at upwelling sites were also significantly different from downwelling and neutral exchange sites (ANOSIM, P < 0.05). Filamentous green algae Stigeoclonium sp. and Zygnema sp. and a chrysophyte, Hydrurus foetidus (Villars) Trevisan were abundant at upwelling sites, whereas an assemblage of diatoms Achnanthidium minutissimum (Kützing) Czarnecki, Cymbella excisa Kützing, Diatoma moniliformis Kützing, and Gomphonema olivaceoides Hustedt, were the most abundant taxa at downwelling and neutral exchange sites, occurring attached to, or in close association with the stalks of Didymosphenia geminata (Lyngbye) Schmidt. These data show that benthic algal communities are structured differently depending on the direction of hyporheic flux in the main channel of a large alluvial river, suggesting that hyporheic-surface exchange may influence the spatial distribution of main-channel benthic algae in rivers with hyporheic-surface water connectivity. Handling editor: J. Padisak     

Heritable variation in an extended phenotype: the case of a parasitoid manipulated by a virus

In host-symbiont interactions, the genes of both host and symbiont can influence phenotypic traits. In the context of a conflict of interest, fitness-related traits are subjected to opposing selective pressures in the genomes of the partners. In the Drosophila parasitoid Leptopilina boulardi, females usually avoid laying eggs into already parasitized larvae. However, when infected by the virus LbFV, they readily lay additional eggs into parasitized larvae. Inducing superparasitism allows the virus to colonize uninfected parasitoid lineages but is usually maladaptive for the parasitoid. We tested for the presence of resistance genes to this behavioural manipulation in the parasitoid genotype by sampling 30 lines from five populations with contrasting viral prevalence, after infecting them with a reference viral isolate. No geographical differentiation was observed although some genotypes underwent less manipulation than others, and these differences were heritable across generations. The viral titre was not correlated with these differences although fecundity differed between extreme lines.     

Synthesis of Bcl-2 in response to anthracycline treatment may contribute to an apoptosis-resistant phenotype in leukemic cell lines.

BACKGROUND: Some forms of chemoresistance in leukemia may start from failure of tumour cells to successfully undergo apoptosis and Bcl-2 may play a role in this defect. Therefore, we evaluated the Bcl-2 content and synthesis in relation with the apoptotic potential in leukemic cell lines after anthracycline treatment. METHODS: U937, HL60, and K562 cells and their drug resistant (DR) variants were treated with varying concentrations of Idarubicin (IDA). Apoptosis was evaluated by fluorescence microscopy after acridine orange staining. Bcl-2 and Bax content were evaluated either by flow cytometry after indirect immunolabelling or by Western blot. RESULTS: High Bcl-2 contents were not related to a poor ability to undergo apoptosis in U937, HL60, K562 and their DR variants. IDA induced a concentration-dependent increase in Bcl-2 content in all cell lines as long as they do not perform apoptosis. Enhanced Bcl-2 expression was inhibited by cycloheximide, actinomycin D, or antisense oligonucleotide directed against bcl-2 mRNA. Bcl-2 expression was also increased in the resistant U937 variant after serum deprivation or C2-ceramide treatment. The synthesis of Bcl-2 led to an increased Bcl-2/Bax ratio solely in the cells with an apoptosis-resistance phenotype. CONCLUSIONS: These data suggest that exposure to IDA induces Bcl-2 expression in leukemic cell lines, and that this mechanism could contribute to apoptosis resistance and participate in the acquisition of chemoresistance. They also confirm that the evolution of the Bcl-2/Bax ratio reflects apoptotic ability better than the steady state level of Bcl-2 expression.     

Soybean response to nodulation by bradyrhizobia differing in rhizobitoxine phenotype

Rhizobitoxine-producing (RT⁺) strains of Bradyrhizobium japonicum, differing in their abilities to induce foliar chlorosis with ‘Forrest’ soybean (Glycine max [L.] Merr.), were evaluated for effects on short term shoot productivity, nodulation, N₂ fixation, and nodule protein production under greenhouse conditions. Soybeans were singly inoculated with washed suspensions of (Group II) USDA strains 31, 46, 76, 94, 110, 123 or 130. Strains USDA 110 and USDA 123 (Group I/Ia) were included as RT-controls. The plants were cultured in the absence of combined N in horticultural-grade vermiculite for 49 days. Beginning 21 days after planting, plants were evaluated weekly for chlorophyll, leaf protein and biomass accumulation, nodular contents of leghemoglobin, soluble protein and RT, and total shoot N content. Rhizobitoxine was detected in nodules of all RT⁺ strains with the exception of USDA 31. However, only USDA 76 and USDA 94 produced both quantifiable concentrations of RT and symptoms of RT-induced chlorosis. Coincident with moderate to severe chlorosis were reductions in chlorophyll concentrations, shoot and nodule dry weight, leaf protein and total N₂ fixation. During extended periods of severe chlorosis, reductions in Lb and soluble nodular protein were observed. Based on carbon accumulation, all non-chlorotic treatments were statistically more productive than the chlorotic treatments. Similarly, non-chlorotic Group II treatments tended to fix less carbon relative to the RT-Group I/Ia controls, although these differences were not statistically significant. The results of this study suggest that, in the absence of discernable foliar chlorosis, the effect of RT⁺ (Group II) nodulation on short term soybean productivity is minimal. Published as Miscellaneous Paper No. 1439 of the Delaware Agricultural Experiment Station. Published as Miscellaneous Paper No. 1439 of the Delaware Agricultural Experiment Station.     

Evolutionary conditioning of response to changes in ionic composition of water in hydrobionts: An example of freshwater zooplankton

The situation in Karelian water bodies polluted with mining waste has been analyzed. As a result of technogenic wastewater discharge, the total ion content in lake waters has increased tens of times, and the concentration of potassium ions (the main component of wastewater), hundreds of times. Pollution tolerance of hydrobiont populations depends on the historically developed adaptation potential of species. The lowest tolerance to mineral pollution is characteristic of crustaceans representing mesolimnic families Polyphemidae, Sididae, Leptodoridae, Holopedidae, Diaptomidae, and Temoridae. Representatives of paleolimnic crustacean families Daphniidae, Bosminidae, and Cycopidae as well rotifer species (Rotatoria) of freshwater origin are highly tolerant of changes in the ionic composition of water.