The effect of night temperature upon the vegetative and reproductive developments in lycopersicon esculentum

The tomato is one of the most sensitive plants, and yet one of the most tolerant and one of the most readily influenced by its en-vironment. It thrives under a wide range of conditions, but the crop is not well adapted to regions where monthly mean temperatures are 80° F or higher, The influence of temperature during the period preceding fruit-ing of tomatoes has been studied for some time. Various observations suggested that low temperature following establishment in the field might be responsible for rough fruits, poor fruit-set of the. first clusters, poor pollination and other common low temperature effects. With the work of Went, Wittwer and others it seemed that some of these effects might not, in fact, occur but that other effects did take place. Low temperature during seedling stage, provided it did not fall below 50° F seemed to encourage the development of flowers, and did not diminish fruit set. With these bits of information, it seemed desirable to study the effect of low night temperature, beginning at 45° F, after the plants were set in the field. From the information which was at hand it became the object of this experiment to study the fruiting behavior of tomatoes through the flowering, fruit-setting and fruit development of the first three clusters. If the idea that lower temperatures at night encourages more flowering and do not discourage fruit setting, could be extended to clusters beyond the first, perhaps a means of increasing total crop productions would be available. For field tomatoes a choice of loca-tion having a long growing season with relatively cool nights might have special value

Randomized lasso links microbial taxa with aquatic functional groups inferred from flow cytometry

High-nucleic-acid (HNA) and low-nucleic-acid (LNA) bacteria are two operational groups identified by flow cytometry (FCM) in aquatic systems. A number of reports have shown that HNA cell density correlates strongly with heterotrophic production, while LNA cell density does not. However, which taxa are specifically associated with these groups, and by extension, productivity has remained elusive. Here, we addressed this knowledge gap by using a machine learning-based variable selection approach that integrated FCM and 16S rRNA gene sequencing data collected from 14 freshwater lakes spanning a broad range in physicochemical conditions. There was a strong association between bacterial heterotrophic production and HNA absolute cell abundances (R-2 = 0.65), but not with the more abundant LNA cells. This solidifies findings, mainly from marine systems, that HNA and LNA bacteria could be considered separate functional groups, the former contributing a disproportionately large share of carbon cycling. Taxa selected by the models could predict HNA and LNA absolute cell abundances at all taxonomic levels. Selected operational taxonomic units (OTUs) ranged from low to high relative abundance and were mostly lake system specific (89.5% to 99.2%). A subset of selected OTUs was associated with both LNA and HNA groups (12.5% to 33.3%), suggesting either phenotypic plasticity or within-OTU genetic and physiological heterogeneity. These findings may lead to the identification of system-specific putative ecological indicators for heterotrophic productivity. Generally, our approach allows for the association of OTUs with specific functional groups in diverse ecosystems in order to improve our understanding of (microbial) biodiversity-ecosystem functioning relationships. IMPORTANCE A major goal in microbial ecology is to understand how microbial community structure influences ecosystem functioning. Various methods to directly associate bacterial taxa to functional groups in the environment are being developed. In this study, we applied machine learning methods to relate taxonomic data obtained from marker gene surveys to functional groups identified by flow cytometry. This allowed us to identify the taxa that are associated with heterotrophic productivity in freshwater lakes and indicated that the key contributors were highly system specific, regularly rare members of the community, and that some could possibly switch between being low and high contributors. Our approach provides a promising framework to identify taxa that contribute to ecosystem functioning and can be further developed to explore microbial contributions beyond heterotrophic production

Constraints on the utility of MnO2 cartridge method for the extraction of radionuclides: A case study using \u3csup\u3e234\u3c/sup\u3eTh

Large volume (102–103 L) seawater samples are routinely processed to investigate the partitioning of particle reactive radionuclides and Ra between solution and size-fractionated suspended particulate matter. One of the most frequently used methods to preconcentrate these nuclides from such large volumes involves extraction onto three filter cartridges (a prefilter for particulate species and two MnO2-coated filters for dissolved species) connected in series. This method assumes that the extraction efficiency is uniform for both MnO2-coated cartridges, that no dissolved species are removed by the prefilter, and that any adsorbed radionuclides are not desorbed from the MnO2-coated cartridges during filtration. In this study, we utilized 234Th-spiked coastal seawater and deionized water to address the removal of dissolved Th onto prefilters and MnO2-coated filter cartridges. Experimental results provide the first data that indicate (1) a small fraction of dissolved Th (\u3c6%) can be removed by the prefilter cartridge; (2) a small fraction of dissolved Th (\u3c5%) retained by the MnO2 surface can also be desorbed, which undermines the assumption of uniform extraction efficiency for Th; and (3) the absolute and relative extraction efficiencies can vary widely. These experiments provide insight on the variability of the extraction efficiency of MnO2-coated filter cartridges by comparing the relative and absolute efficiencies and recommend the use of a constant efficiency on the combined activity from two filter cartridges connected in series for future studies of dissolved 234Th and other radionuclides in natural waters using sequential filtration/extraction methods

Intense winter heterotrophic production stimulated by benthic resuspension

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109851/1/lno20004571672.pd

Versatile Photophysiology of Compositionally Similar Cyanobacterial Mat Communities Inhabiting Submerged Sinkholes of Lake Huron

Recently discovered submerged sinkholes in Lake Huron are high-sulfur, lowoxygen extreme environments for microbial life. In order to understand the relationship between the physical environment, photophysiology and community composition, we measured the physical conditions, photophysiological indices, and genetic diversity at 3 microbial mat sites bathed in high conductivity groundwater under a natural light gradient during 2012 and 2013. A strong seasonal trend prevailed at all sites, characterized by decreased photosynthetic yield (Fv’/Fm’; 0.25 to 0.40) during the summer (April to August) and increased yield (0.70 to 0.75) during the winter (November to March). Chlorophyll a content varied seasonally in a similar manner to photo - synthetic yield. All sites were dominated by \u3e80% abundance of one cyanobacterial group, most closely related to Phormidium sp. Phycobilins (phycocyanin and phycoerythrin) were consistently higher in concentration than chlorophyll. Photosynthetic yield was statistically indistinguishable between sites, suggesting that these mat communities are able to acclimate across a wide range of photosynthetically active radiation (PAR). Interestingly, these cyanobacteria carried out oxygenic photosynthesis in the presence of in vitro H2S, further suggestive of their versatile photophysiologies under variable redox conditions. Collectively, our study provides insight into the adaptive capabilities of cyanobacteria by revealing how they photophysiologically respond to changes in light climate and redox conditions, and are thereby able to inhabit a wide range of physico-chemical environments. Such versatile physiologies may have enabled their ancestors to thrive across a range of habitats on early Earth

Possible link between Earth's rotation rate and oxygenation

The biotic and abiotic controls on major shifts in atmospheric oxygen and the persistence of low-oxygen periods over a majority of Earth’s history remain under debate. Explanations of Earth’s stepwise pattern of oxygenation have mostly neglected the effect of changing diel illumination dynamics linked to daylength, which has increased through geological time due to Earth’s rotational deceleration caused by tidal friction. Here we used microsensor measurements and dynamic modelling of interfacial solute fluxes in cyanobacterial mats to investigate the effect of changing daylength on Precambrian benthic ecosystems. Simulated increases in daylength across Earth’s historical range boosted the diel benthic oxygen export, even when the gross photosynthetic production remained constant. This fundamental relationship between net productivity and daylength emerges from the interaction of diffusive mass transfer and diel illumination dynamics, and is amplified by metabolic regulation and microbial behaviour. We found that the resultant daylength-driven surplus organic carbon burial could have shaped the increase in atmospheric oxygen that occurred during the Great and Neoproterozoic Oxidation Events. Our suggested mechanism, which links the coinciding increases in daylength and atmospheric oxygen via enhanced net productivity, reveals a possible contribution of planetary mechanics to the evolution of Earth’s biology and geochemistry

From Bacteria to Fish: Ecological Consequences of Seasonal Hypoxia in a Great Lakes Estuary

The occurrence of bottom-water hypoxia is increasing in bodies of water around the world. Hypoxia is of concern due to the way it negatively impacts lakes and estuaries at the whole ecosystem level. During 2015, we examined the influence of hypoxia on the Muskegon Lake ecosystem by collecting surface- and bottom-water nutrient samples, bacterial abundance counts, benthic fish community information, and performing profiles of chlorophyll and phycocyanin as proxies for phytoplankton and cyanobacterial growth, respectively. Several significant changes occurred in the bottom waters of the Muskegon Lake ecosystem as a result of hypoxia. Lake-wide concentrations of soluble reactive phosphorus (SRP) and total phosphorus increased with decreasing dissolved oxygen (DO). Bacterial abundance was significantly lower when DO was less than 2.2 mg L-1. Whereas there were no drastic changes in surface chlorophyll a concentration through the season, phycocyanin increased threefold during and following a series of major wind-mixing events. Phycocyanin remained elevated for over 1.5 months despite several strong wind events, suggesting that high SRP concentrations in the bottom waters may have mixed into the surface waters, sustaining the bloom. The fish assemblage in the hypolimnion also changed in association with hypoxia. Overall fish abundance, number of species, and maximum length all decreased in catch as a function of bottom DO concentrations. The link between hypoxia and wind events appears to serve as a positive feedback loop by continuing internal loading and cyanobacterial blooms in the lake, while simultaneously eroding habitat quality for benthic fish

Year-Round Measures of Planktonic Metabolism Reveal Net Autotrophy in Surface Waters of a Great Lakes Estuary

During 2009 and 2010, we quantified monthly changes in plankton metabolism and environmental variables in the surface waters of Muskegon Lake, a Great Lakes estuary connected to Lake Michigan. Muskegon Lake’s mean (±SE) annual gross plankton primary production (GPP) and respiration (R) rates were 46 ± 9 and 23 ± 4 mg C l−1 yr−1, respectively. GPP:R ratios of 0.6 to +4.8 with a yearly mean of 2.0 ± 0.3 indicated that the surface water of Muskegon Lake was net autotrophic during all but the winter months under ice cover, when it was in a near carbon balance to slightly heterotrophic state. Approximately 5% of GPP and 12% of R occurred during the winter months, highlighting winter’s potential role in nutrient regeneration. An overall positive annual net community production (NCP) rate of 28 ± 6 mg C l−1 yr−1 makes Muskegon Lake’s surface waters a net sink for carbon on an annual basis. Annual heterotrophic bacterial production (BP) rates were 5 ± 3 mg C l−1 yr−1, suggesting a substantial fraction of GPP was likely processed through the microbial food web (2 to 76%). A stepwise multiple linear regression model revealed the plausible drivers of GPP (temperature [T], photosynthetically active radiation [PAR], total phosphorus [TP], dissolved oxygen [DO], chlorophyll a [chl a]), NCP (T, PAR, TP), R (T, DO, ammonium [NH3], soluble reactive phosphorous [SRP], dissolved organic carbon [DOC]) and GPP:R (T, PAR, SRP, DOC). Year-round measurements inform us of the strong seasonality in the carbon cycle of temperate lakes

Production and Fate of Transparent Exopolymer Particles in the Ocean

The production and fate of transparent exopolymer particles (TEP) have been investigated in various oceanic regions (tropical, temperate, and polar), from the sea surface microlayer (SML) to the deep ocean. Accumulation of TEP within the mixed layer was observed even in the absence of phytoplankton blooms, indicating abiotic processes are important in TEP production. The abiotic TEP aggregation rates measured in the tropical and temperate North Pacific and the Arctic Ocean averaged between 8 and 12 μmol C L-1 d-1. Depth profiles from under sea ice in the Arctic revealed the highest TEP concentrations, potentially released by sympagic algal activity at the bottom of the sea ice. The aggregation rates in the SML, the interfacial layer between the ocean and atmosphere, were generally enhanced over those in the bulk surface waters by factors of 2 to 30. This finding further strengthens a developing consensus on the gelatinous nature of the SML, which will also affect microbial life, light penetration, and surface wave properties. We present a conceptual model implying that abiotic aggregation is an important factor for TEP production in the ocean, in particular in sea surface microlayers, while consumption by zooplankton and protists recycle TEP, providing a new pool of dissolved precursor material. Overall, TEP is recycled within the water column through heterotrophic grazing and degradation, providing a new pool of TEP precursor materials, while enhanced aggregation rates of TEP in the SML indicates the importance of this thin surface film in the marine carbon cycle

Seeking Sunlight: Rapid Phototactic Motility of Filamentous Mat-Forming Cyanobacteria Optimize Photosynthesis and Enhance Carbon Burial in Lake Huron’s Submerged Sinkholes

We studied the motility of filamentous mat-forming cyanobacteria consisting primarily ofOscillatoria-like cells growing under low-light, low-oxygen, and high-sulfur conditions in Lake Huron’s submerged sinkholes using in situ observations, in vitro measurements and time-lapse microscopy. Gliding movement of the cyanobacterial trichomes (100–10,000 μm long filaments, composed of cells ~10 μm wide and ~3 μm tall) revealed individual as well as group-coordinated motility. When placed in a petri dish and dispersed in ground water from the sinkhole, filaments re-aggregated into defined colonies within minutes, then dispersed again. Speed of individual filaments increased with temperature from ~50 μm min-1 or ~15 body lengths min-1 at 10∘C to ~215 μm min-1 or ~70 body lengths min-1 at 35∘C – rates that are rapid relative to non-flagellated/ciliated microbes. Filaments exhibited precise and coordinated positive phototaxis toward pinpoints of light and congregated under the light of foil cutouts. Such light-responsive clusters showed an increase in photosynthetic yield – suggesting phototactic motility aids in light acquisition as well as photosynthesis. Once light source was removed, filaments slowly spread out evenly and re-aggregated, demonstrating coordinated movement through inter-filament communication regardless of light. Pebbles and pieces of broken shells placed upon intact mat were quickly covered by vertically motile filaments within hours and became fully buried in the anoxic sediments over 3–4 diurnal cycles – likely facilitating the preservation of falling debris. Coordinated horizontal and vertical filament motility optimize mat cohesion and dynamics, photosynthetic efficiency and sedimentary carbon burial in modern-day sinkhole habitats that resemble the shallow seas in Earth’s early history. Analogous cyanobacterial motility may have played a key role in the oxygenation of the planet by optimizing photosynthesis while favoring carbon burial