Sulfur dioxide effects on plants exhibiting Crassulacean Acid Metabolism

The effects of SO(2) on species exhibiting Crassulacean Acid Metabolism (CAM) were determined with short term-high concentration 'acute' greenhouse exposures (0.6 to 3.0 microl liter(-1) (ppm) SO(2) for 2 and 8 h), and long term-low concentration 'chronic' field exposures (0.35 to 0.90 microl liter(-1) SO(2) for 32 to 79 h periodically over 7 to 13 days). In the acute greenhouse exposures, visible injury was observed on Opuntia basilaris Engelm. & Bigel., exposed to 2.0 microl liter(-1) SO(2), but no injury was observed on Ananas comosus (L.) Merr., Bryophyllum blossfeldiana Poelln., Bryophyllum pinnata (Lam.) Pers., or Bryophyllum tubiflora (Harv.) Hamet, exposed to up to 2.8 microl liter(-1) SO(2) for 8 h. Stomatal conductance during the exposures averaged 0.067+/-0.021mol(-2)s(-1) for Opuntia basilaris, 0.029+/-0.008mol(-2)s(-1) for Ananas comosus, and 0.029+/-0.008mol m(-2)s(-1) for Bryophyllum pinnata. Opuntia basilaris was injured early during the day, but not at night; with the injury appearing as a white necrotic banding across just fully expanded pads. Moderately injured pads would regreen beginning 1 to 2 weeks after exposure. In chronic field exposures, no visible injury from SO(2) was observed on Opuntia basilaris, Dudleya arizonica Rose or Agave deserti Engelm. plants, grown either with supplemental irrigation or natural rainfall. In addition, in the field SO(2) had no effect on CO(2) uptake, total sulfur content, transpiration, or tissue acidity in either the light or the dark, or in irrigated vs natural rainfall plots.     

Nitrate reductase and glutamine synthetase activity,internal N pools,and growth of<Emphasis Type="Italic"> Ulva lactuca</Emphasis>: responses to long and short-term N supply

Fast-growing macroalgae, including Ulva lactuca Linnaeus, respond rapidly to changes in nutrient conditions, particularly to short-term N supply. This ability to rapidly take up and assimilate N contributes to the increasing occurrence of macroalgal blooms in heavily N loaded coastal ecosystems. To determine whether long-term nutrient histories affect short-term responses in activity of N-assimilating enzymes, including nitrate reductase (NRA) and glutamine synthetase activity (GSA), internal N storage, and macroalgal growth, we conducted an in situ nitrate fertilization experiment between 7 and 22 July 2004, with fronds of U. lactuca collected from estuaries with high and low N loads in Waquoit Bay, Cape Cod, Massachusetts, USA (N 41° and W 70°). Initial NRA, GSA, % N, δ¹⁵N, and growth of U. lactuca fronds were higher in the site where nitrate was in high supply. Differences in NRA persisted even after short-term experimental enrichment. Differences in internal N pools, δ¹⁵N, and growth, in contrast, mirrored the changes of nutrient supply. The rate of turnover of the internal N content of U. lactuca was quite short (<2 d), and turnover of enzyme activity may have been even shorter. N isotopic fractionation by U. lactuca appeared to be of small magnitude, unlike the case of phytoplankton, and similar to that of vascular plants. δ¹⁵N was a better indicator of short-term response to external and internal nutrient supplies in U. lactuca than enzyme activity or N content, and may reliably detect rapid changes in N availability, source, and uptake and assimilation processes.     

Anaerobic respiration in the polychaete Euzonus (Thoracophelia) mucronata

The intertidal polychaete Euzonus mucronata (Treadwell) is found in great numbers within beach sands that undergo periodic anoxia. Short-term exposures (2 to 4 h) to anaerobicity are withstood through the use of a supply of oxyhemoglobin to support continued aerobic metabolism. Longer periods of environmental anoxia activate an anaerobic metabolism capable of sustaining life for up to 20 days, and characterized by the excretion of succinate and propionate. These two mechanisms appear to be adaptations to the variations in occurrence and duration of anoxia within the intertidal sands inhabited by E. mucronata.Supported by an NSF Graduate Fellowship, 1973–1974.     

Characteristics of biotic and abiotic removals of dissolved organic carbon in wastewater effluents using soil batch reactors.

Biodegradable dissolved organic carbon (BDOC) analyses and abiotic adsorption of dissolved organic carbon (DOC) from different wastewater effluent were conducted to evaluate biotic and abiotic removal mechanisms as a function of the initial DOC concentration and source of DOC using soil batch reactors. To obtain high DOC concentrations, a laboratory-scale reverse osmosis unit was used. It was found that BDOC fraction was independent of the initial DOC concentration and was dependent on the source of wastewater and/or the types of wastewater treatment. The BDOC fractions varied from 9 to 73%. Trickling filter effluent (Tucson, Arizona) showed the highest BDOC, ranging from 65 to 73% biodegradable, while wastewater treated by the soil aquifer treatment (SAT) (NW-4) was found to be most refractory, with DOC removals of 9 to 14%. For nitrified/denitrified tertiary effluent (Mesa, Arizona) and secondary effluent (Scottsdale, Arizona), 36 to 42% removal of DOC was observed during the BDOC test. The amount of BDOC in the wastewater depended not on the concentration of DOC, but on the effectiveness of pretreatment. Abiotic adsorption capacity of wastewater effluent varied from 6 to 18%. Molecular weight distribution analyses showed that more than 50% of DOC in the Scottsdale concentrate had a molecular weight of less than 1000 Da, and no significant change in distribution profiles occurred after approximately 12% abiotic adsorption with both soils with acclimated microorganisms (SAT soil) and soils without acclimated microorganisms (non-SAT soils). Hence, preferential adsorption was not observed and the presence of acclimated microbes did not influence adsorption.     

Parental care compromises feeding in the pumpkinseed (<Emphasis Type="Italic">Lepomis gibbosus</Emphasis>)

Providing parental care is potentially costly. Costs can arise through elevated energy expenditure or from an increased risk of mortality. A cost of parental care can also occur because a parent is compromised in their ability to forage. We used pumpkinseed Lepomis gibbosus, a fish with an alternative male mating strategy, to test whether parental males differed in their feeding in comparison with females and cuckolder males. To address this question, we examined the stomach contents of female, cuckolder male, and parental male pumpkinseed during the breeding season over an entire diel cycle. We showed that parental males had a lower total weight of food in their stomachs in comparison with females, while cuckolder males did not. Parental males also had a lower weight and number of chironomids in their stomachs. The temporal pattern of feeding of parental males diverged from that of females, and they had a lower probability of pupal chironomids in their stomachs, which implies spatial segregation in foraging. Parental males had a greater probability of conspecific eggs in their stomachs than females, while the probability of egg cannibalism did not differ between cuckolder males and females. Overall, these finding meet predictions in accordance with an assumption that parental care and territoriality can compromise feeding.     

Direct versus indirect methods of quantifying herbivore grazing impact on a coral reef

Two methods were used to assess the grazing impact of roving herbivorous fishes across a coral reef depth gradient within Pioneer Bay, Orpheus Island, Great Barrier Reef. The first technique employed was a method traditionally used to quantify herbivory on coral reefs via the (indirect) inference of herbivore impact from biomass estimates and reported feeding rates. The second method (one of a range of direct approaches) used remote underwater video cameras to film the daily feeding activity of roving herbivores in the absence of divers. Both techniques recorded similar patterns and relative levels of herbivore biomass across five reef zones at the study site. Indirect estimates of the grazing impact across the reef depth gradient of the three predominant species of herbivore broadly coincided with levels quantified directly by remote underwater video, indicating that, to a large extent, presence does correspond to function. However, the video data suggested that, for individual species in particular reef zones, the absolute level of impact may be less than that inferred from presence. In the case of the parrotfish Scarus rivulatus, the video recordings suggested that, at the reef crest, an average of 52% (±18 SE) of each m² area of reef would be grazed each month, compared with an area of 109% (±41 SE) suggested by inferring grazing activity from presence alone. Potential biases associated with remote video recorders may explain some of the discrepancy between values. Overall, the results suggest that, for some fish groups, the indirect method of inferring function from presence can provide a good indication of relative levels of herbivore impact across a coral reef. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.