Ciliates as engineers of phototrophic biofilms

1. Phototrophic biofilms consist of a matrix of phototrophs, non‐photosynthetic bacteria and extracellular polymeric substances (EPS) which is spatially structured. Despite widespread exploitation of algae and bacteria within phototrophic biofilms, for example by protozoans, the ‘engineering’ effects of these ciliates on the spatial heterogeneity of phototrophic biofilms are poorly studied. 2. We studied the potential engineering effects of two ciliates, Urostyla sp. and Paramecium bursaria, on the spatial heterogeneity of synthetic multispecies biofilms. Biomass of phototrophic organisms, EPS and bacteria was analysed three dimensionally using confocal laser scanning microscopy. Spatial heterogeneity and cover of the phototrophs, bacteria and EPS were determined at several depths within the biofilm. 3. Ciliate species did not interfere with the overall development of phototrophic microorganisms, because the thickness of the biofilm was equal whether the ciliates were present or not, even though their abundance did affect spatial heterogeneity of biofilm components. When Urostyla was present, it reduced aggregation in EPS and bacteria and increased EPS biovolume. This implies a local facilitating effect of ciliates on photosynthetic activity. Biofilms to which Paramecium was added did not differ from controls in terms of phototrophs, EPS cover and biovolume. Nevertheless, ciliates affected the spatial heterogeneity of these components as phototrophs and EPS became more evenly distributed. 4. This study shows that ecosystem engineering by organisms does not only occur at large spatial scales, as in grasslands and estuaries, but also plays a role at the microscopic scale of biofilms. This effect on spatial heterogeneity was not driven by substantial exploitation of biofilm components, but via the subtle engineering effects of ciliates.     

Yield of wheat across a subambient carbon dioxide gradient

Yields and yield components of two cultivars of day-neutral spring wheat ( Triticum aestivum L.) were assessed along a gradient of daytime carbon dioxide (CO₂) concentrations from about 200 to near 350 μmol CO₂ (mol air)^–1 in a 38 m-long controlled environment chamber. The range in CO₂ concentration studied approximates that of Earth's atmosphere since the last ice age. This 75% rise in CO₂ concentration increased grain yields more than 200% under well-watered conditions and by 80–150% when wheat was grown without additions of water during the last half of the 100-day growing season. The 27% increase in CO₂ from the pre-industrial level of 150 years ago (275 μmol mol^–1) to near the current concentration (350 μmol mol^–1) increased grain yields of 'Yaqui 54' and 'Seri M82' spring wheats by 55% and 53%, respectively, under well-watered conditions. Yield increased because of greater numbers of grains per spike, rather than heavier grains or numbers of spikes per plant. Water use increased little with CO₂ concentration, resulting in improved water use efficiency as CO₂ rose. Data suggest that rising CO₂ concentration contributed to the substantial increase in average wheat yields in the U.S. during recent decades.     

Characterization of Populations of Promastigotes of Leishmania donovani1

Promastigotes of Leismania donovani cultured for either 3 or 10 days in vitro and inoculated intracardially into golden hamsters with an equal number of organisms from either population showed a 7-fold difference in infectivity when compared at both 10 to 16 days post-infection. Reproducible histochemical staining for the promastigote enzymes glucose-6-phosphate dehydrogenase (G6PDH) and peptidase after polyacrylamide gel electrophoresis showed two isoelectric variants of G6PDH (Bands 1 and 2) that displayed a 45% decrease (Band 1) and a 60% increase (Band 2) in total activity when 3- and 10-day-old promastigores were compared. Peptidase activity, present in a single band, increased 7-fold in 10-day-old promastigotes. A decrease in the lectin-induced agglutination of promastigotes by castor bean agglutinin (RCA₆₀), specific for D-galactose and N-acetyl-D-galactosamine, was seen when 3- and 10-day-old promastigotes are compared. Antisera raised against sonicated 10-day-old promastigotes showed a unique precipitin band between the antiserum and sonicated 10-day-old promastigotes not found between the antiserum and sonicated 3-day-old promastigotes.     

An examination of the importance of ethanol in causing injury to flooded plants

Abstract. We have examined the widely held theory that ethanol toxicity is a prime cause of the injury and death of plants in soil flooded with water. The tests were made on peas ( Pisum sativum L.) at the early flowering or fruiting stages, when they are known to be severely injured by flooding.
Supplying ethanol in aerobic or anaerobic nutrient solution at similar concentrations to those we found in flooded soil (up to 3.9 mol m⁻³) or in the xylem sap of flooded pea plants (up to 2.1 mol m⁻³) caused no injury. One hundred times these concentrations gave little extra effect and failed to simulate flooding injury. Isolated leaf protoplasts and detached leaves were also resistant to damage by ethanol at these concentrations.
Other published measurements of ethanol concentrations in flooded plants are similar to or less than those we report for pea plants. Exceptions include root nodules and germinating pea seeds. Reports by others of responses to applied ethanol in a wide variety of circumstances confirm that in flooded plants the amounts are probably too small to explain the observed injury. Alternative mechanisms are discussed.     

Sensitivity of Siberian larch forests to climate change

The Northern Hemisphere's boreal forests, particularly the Siberian boreal forest, may have a strong effect on Earth's climate through changes in dominant vegetation and associated regional surface albedo. We show that warmer climate will likely convert Siberia's deciduous larch (Larix spp.) to evergreen conifer forests, and thus decrease regional surface albedo. The dynamic vegetation model, FAREAST, simulates Russian boreal forest composition and was used to explore the feedback between climate change and forest composition at continental, regional, and local scales. FAREAST was used to simulate the impact of changes in temperature and precipitation on total and genus‐level biomass at sites across Siberia and the Russian Far East (RFE), and for six high‐ and low‐diversity regions. Model runs with and without European Larch (Larix decidua) included in the available species pool were compared to assess the potential for this species, which is adapted to warmer climate conditions, to mitigate the effects of climate change, especially the shift to evergreen dominance. At the continental scale, when temperature is increased, larch‐dominated sites become vulnerable to early replacement by evergreen conifers. At the regional and local scales, the diverse Amur region of the RFE does not show a strong response to climate change, but the low‐diversity regions in central and southern Siberia have an abrupt vegetation shift from larch‐dominated forest to evergreen‐conifer forest in response to increased temperatures. The introduction of L. decidua prevents the collapse of larch in these low‐diversity areas and thus mitigates the response to warming. Using contemporary MODIS albedo measurements, we determined that a conversion from larch to evergreen stands in low‐diversity regions of southern Siberia would generate a local positive radiative forcing of 5.1±2.6 W m^?2. This radiative heating would reinforce the warming projected to occur in the area under climate change.     

The Effects of Root Pruning on the Water Relations of Helianthus annuus L.

Four-week-old Helianthus annuus plants, grown in both soil andliquid culture, were root pruned at the point of root attachmentto the stem. Transpiration, leaf water potential and leaf conductivitywere monitored for several days after pruning. Pruning loweredtranspiration and leaf conductivity in amounts proportionalto the amount of pruning. In some experiments pruning causeda slight lowering of leaf water potential, while in others nopruning effect could be found. The effects of pruning varieddepending upon culture conditions, with greater effects beingfound in soil and unaerated liquid culture than in aerated liquidculture. Soil water potential did not appear to have a stronginfluence on the magnitude of the pruning effect. The effectsof root pruning are less than would be predicted by an Ohm'sLaw analysis of flow; possible reasons for this are discussed.     

Fine Structure of an Unidentified Protozoon in the Epithelium of Rainbow Trout Exposed to Water with Myxosoma cerebralis*

SYNOPSIS. An intracellular protozoon was discovered in the epithelium of young rainbow trout (Salmo gairdneri) exposed for as short a time as 1 hr to water known to contain infective stages of Myxosoma cerebralis. Light- and electron-microscopic examination of this tissue revealed what appeared to be a proliferative stage (presumptive schizont) of a sporozoon; other possible stages in the life cycle were also observed. The relationship of this unidentified protozoon to M. cerebralis remains unresolved.