EFFECT OF TREE CANOPY REMOVAL BY GYPSY MOTH LARVAE ON THE MACROALGAE OF A RHODE ISLAND HEADWATER STREAM1

A spring-fed, headwater stream in central Rhode Island was examined during the period from June to October, 1979 to 1982. In the first two summers, a dense riparian canopy reduced the light penetration at the stream surface to a range of 5 to 18% of incident radiation. The lotic macroalgal community during this period was limited to 1 to 4 species covering < 1 to 35% of the stream bottom. However, in June and July, 1981, the surrounding leaf canopy was removed by a massive gypsy moth larval outbreak. Light penetration to the stream during this summer increased to 73% by early July, thereby resulting in a rise in water temperatures by 3.7°C. Even though there was a partial regrowth of leaves in late July and August of 1981, macroalgal cover values continued to rise to an early August peak of 80%. During the third summer, 88% of the macroalgal abundance could be attributed to illumination and water temperature. The filamentous diatom Funotia pectinalis ( O.F. Müll.) Rabh. was the predominant species in the midsummer of all four years, accounting for at least 60% of the total cover. In 1981. an important taxon was the desmid Hyalotheca dissiliens (S. Smith) Bréb., a species which was not seen in other years. A less severe gypsy moth defoliation occurred in 1982 but did not produce significant differences in light, temperature or macroalgal cover from 1979 and 1980. The results indicate that light and temperature can be limiting during the summer in spring-fed, headwater streams and that seed populations of some species are present in undetect-able levels during these periods of suboptimal growth conditions. In addition, it appears that stream macroalgal communities can be quite resilient, recovering rapidly following a major perturbation .     

Photosynthesis,water use and growth of a C4 grass stand at high CO2 concentration

Leaf photosynthesis rate of the C₄ species Paspalum plicatulum Michx was virtually CO₂-saturated at normal atmospheric CO₂ concentration but transpiration decreased as CO₂ was increased above normal concentrations thereby increasing transpiration efficiency. To test whether this leaf response led growth to be CO₂-sensitive when water supply was restricted, plants were grown in sealed pots of soil as miniature swards. Water was supplied either daily to maintain a constant water table, or at three growth restricting levels on a 5-day drying cycle. Plants were either in a cabinet with normal air (340 mol (CO₂) mol^-1 (air)) or with 250 mol mol^-1 enrichment. Harvesting was by several cycles of defoliation.With abundant water supply high CO₂ concentration did not cause increased growth, but it did not cause an increase in growth over a wide range of growth-limiting water supplies either. Only when water supply was less than 30–50% of the amount used by the stand with a water-table was there evidence that dry weight growth was enhanced by high CO₂. In addition, with successive regrowth, the enhancing effect under a regime of minimal water allocations, became attenuated. Examination of leaf gas exchange, growth and water use data showed that in the long term stomatal conductance responses were of little significance in matching plant water use to low water allocation; regulation of leaf area was the mechanism through which consumption matched supply. Since high CO₂ effects operate principally via stomatal conductance in C₄ species, we postulate that for this species higher CO₂ concentrations expected globally in future will not have much effect on long term growth.     

QSAR modeling and transmission electron microscopy stereology of altered mitochondrial ultrastructure of white blood cells in patients diagnosed as schizophrenic and treated with antipsychotic drugs.

Treatment of patients diagnosed as schizophrenic with antipsychotic drugs (neuroleptics) is known to cause occasional unexplained depletion of white blood cells, especially neutrophil granulocytes. It has been known for many years that neuroleptics can interfere with the mitochondrial respiratory chain in vitro. Because there has been a growing interest recently in mitochondrial targeting of drugs, and since a quantitative structure-activity relationship (QSAR) model that predicts mitochondrial accumulation of neuroleptics has been published, we investigated the effects of neuroleptics on white blood cell mitochondria. Venous blood samples were collected from both patients undergoing treatment with neuroleptics and healthy volunteers. The samples were processed for transmission electron microscopy. The resulting images of white blood cells were analyzed using stereology to compare quantitatively mitochondrial morphology in the patient and control groups. We found that in patients, but not in controls, there was swelling of mitochondria and fragmentation of the mitochondrial cristae. There also were fewer mitochondria in patients than in controls, although due to the swelling of the organelles, the volume density of mitochondria in the two groups was not significantly different. Such changes are typical of a toxic insult. Consequently, it seems plausible that, since schizophrenia is not a disease considered to affect white blood cells per se, these changes probably are due to the medication.     

Mapping the zebrafish brain methylome using reduced representation bisulfite sequencing

Reduced representation bisulfite sequencing (RRBS) has been used to profile DNA methylation patterns in mammalian genomes such as human, mouse and rat. The methylome of the zebrafish, an important animal model, has not yet been characterized at base-pair resolution using RRBS. Therefore, we evaluated the technique of RRBS in this model organism by generating four single-nucleotide resolution DNA methylomes of adult zebrafish brain. We performed several simulations to show the distribution of fragments and enrichment of CpGs in different in silico reduced representation genomes of zebrafish. Four RRBS brain libraries generated 98 million sequenced reads and had higher frequencies of multiple mapping than equivalent human RRBS libraries. The zebrafish methylome indicates there is higher global DNA methylation in the zebrafish genome compared with its equivalent human methylome. This observation was confirmed by RRBS of zebrafish liver. High coverage CpG dinucleotides are enriched in CpG island shores more than in the CpG island core. We found that 45% of the mapped CpGs reside in gene bodies, and 7% in gene promoters. This analysis provides a roadmap for generating reproducible base-pair level methylomes for zebrafish using RRBS and our results provide the first evidence that RRBS is a suitable technique for global methylation analysis in zebrafish.     

Very high productivity of the C4 aquatic grass Echinochloa polystachya in the Amazon floodplain confirmed by net ecosystem CO2 flux measurements

Fluxes of CO₂ and H₂O vapour from dense stands of the C4 emergent macrophyte grass Echinochloa polystachya were measured by eddy covariance in both the low water (LW) and high water (HW, flooded) phases of the annual Amazon river cycle at Manaus, Brazil. Typical clear-sky midday CO₂ uptake rates by the vegetation stand (including detritus, sediment or water surface) were 30 and 35 µmol CO₂ (ground) m^-2 s^-1 in the LW and HW periods, respectively. A rectangular hyperbola model fitted the responses of "instantaneous" (20- or 30-min average) net CO₂ exchange rates to incident photosynthetic photon flux densities (PFD) well. Stand evaporation rates were linearly related to PFD. The major difference in CO₂ uptake rates between the two periods was the larger respiration flux during LW due to the CO₂ efflux from sediment, roots and litter. Integrated 20- or 30-min fluxes were used to derive relationships between daily CO₂ and H₂O vapour fluxes and incident radiation. The daily CO₂ fluxes were almost linearly related to incident radiation, but there was evidence of saturation at the highest daily radiation totals. Annual productivity estimated from the daily model in 1996-1997 agreed closely with that previously estimated for 1985-1986 from a leaf-scale photosynthetic model, but were some 15% less than those derived at that time from biomass harvests. Both CO₂ uptake and water use efficiency were comparable with those found in fertilised maize fields in warm temperate conditions.     

The ‘shock period’: dynamics of phytoplankton during the spring–summer transition of a stratifying English lake

The spring to summer transition in a productive English lake is considered with respect to phytoplankton and its environmental conditions. Salient environmental changes include the onset of temperature/density stratification that is usually accompanied by a clear-water phase associated with a maximum of grazing Daphnia and a minimum of phytoplankton in the 0â€5 m zone. Below this zone, as thermal stratification progresses, a deep maximum of phytoplankton can develop under strong thermal/density gradients and enhanced light penetration. Examples are resolved by estimations of chlorophyll-a , beam attenuance in situ and cell counts. Attributed origins are by sedimentation of diatoms, migration of flagellates, and depth-adjusted buoyancy of a gas-vacuolate cyanophyte. The transition period involves a decline of spring-associated diatom populations and a rise of summer-associated species. The generally low algal abundance within the transition phase has at least four origins †prior nutrient (Si) depletion, sedimentation, grazing, and low inoculum levels of successor species. It can be augmented by the re-growth of species abundant in spring, by early extensions of normally summer species, by seasonally characteristic colonial chrysophytes, and by other phytoflagellates of small size that are seasonally less specific (opportunistic) and probably critical for Daphnia grazing with consequent generation of the clear-water phase.