Effect of Salicylic Acid Formulations on Induced Plant Defense against Cassava Anthracnose Disease

This study was to investigate defense mechanisms on cassava induced by salicylic acid formulation (SA) against anthracnose disease. Our results indicated that the SA could reduce anthracnose severity in cassava plants up to 33.3% under the greenhouse condition. The β-1,3-glucanase and chitinase enzyme activities were significantly increased at 24 hours after inoculation (HAI) and decrease at 48 HAI after Colletotrichum gloeosporioides challenge inoculation, respectively, for cassava treated with SA formulation. Synchrotron radiation–based Fourier-transform infrared microspectroscopy spectra revealed changes of the C=H stretching vibration (3,000–2,800 cm⁻¹), pectin (1,740–1,700 cm⁻¹), amide I protein (1,700–1,600 cm⁻¹), amide II protein (1,600–1,500 cm⁻¹), lignin (1,515 cm⁻¹) as well as mainly C–O–C of polysaccharides (1,300–1,100 cm⁻¹) in the leaf epidermal and mesophyll tissues treated with SA formulations, compared to those treated with fungicide carbendazim and distilled water after the challenged inoculation with C. gloeosporioides. The results indicate that biochemical changes in cassava leaf treated with SA played an important role in the enhancement of structural and chemical defense mechanisms leading to reduced anthracnose severity.     

Induction of SerpinB2 and Th1/Th2 Modulation by SerpinB2 during Lentiviral Infections In Vivo

SerpinB2, also known as plasminogen activator inhibitor type 2, is a major product of activated monocytes/macrophages and is often strongly induced during infection and inflammation; however, its physiological function remains somewhat elusive. Herein we show that SerpinB2 is induced in peripheral blood mononuclear cells following infection of pigtail macaques with CCR5-utilizing (macrophage-tropic) SIV_mac239, but not the rapidly pathogenic CXCR4-utilizing (T cell-tropic) SHIV_mn229. To investigate the role of SerpinB2 in lentiviral infections, SerpinB2^−/− mice were infected with EcoHIV, a chimeric HIV in which HIV gp120 has been replaced with gp80 from ecotropic murine leukemia virus. EcoHIV infected SerpinB2^−/− mice produced significantly lower anti-gag IgG1 antibody titres than infected SerpinB2^+/+ mice, and showed slightly delayed clearance of EcoHIV. Analyses of published microarray studies showed significantly higher levels of SerpinB2 mRNA in monocytes from HIV-1 infected patients when compared with uninfected controls, as well as a significant negative correlation between SerpinB2 and T-bet mRNA levels in peripheral blood mononuclear cells. These data illustrate that SerpinB2 can be induced by lentiviral infection in vivo and support the emerging notion that a physiological role of SerpinB2 is modulation of Th1/Th2 responses.     

Lysophosphatidylinositol-Acyltransferase-1 (LPIAT1) Is Required to Maintain Physiological Levels of PtdIns and PtdInsP2 in the Mouse

We disrupted the gene encoding lysophosphatidylinositol-acyltransferase-1 (LPIAT1) in the mouse with the aim of understanding its role in determining cellular phosphoinositide content. LPIAT1^−/− mice were born at lower than Mendelian ratios and exhibited a severe developmental brain defect. We compared the phospholipid content of livers and brains from LPIAT1^−/− and LPIAT1^+/+ littermates by LC-ESI/MS. In accord with previous studies, the most abundant molecular species of each phosphoinositide class (PtdIns, PtdInsP, PtdInsP₂ and PtdInsP₃) possessed a C38∶4 complement of fatty-acyl esters (C18∶0 and C20∶4 are usually assigned to the sn-1 and sn-2 positions, respectively). LPIAT1^−/− liver and brain contained relatively less of the C38∶4 species of PtdIns, PtdInsP and PtdInsP₂ (dropping from 95–97% to 75–85% of the total species measured for each lipid class) and relatively more of the less abundant species (PtdInsP₃ less abundant species were below our quantification levels). The increases in the less abundant PtdIns and PtdInsP₂ species did not compensate for the loss in C38∶4 species, resulting in a 26–44% reduction in total PtdIns and PtdInsP₂ levels in both brain and liver. LPIAT1^−/− brain and liver also contained increased levels of C18∶0 lyso-PtdIns (300% and 525% respectively) indicating a defect in the reacylation of this molecule. LPIAT1^−/− brain additionally contained significantly reduced C38∶4 PC and PE levels (by 47% and 55% respectively), possibly contributing to the phenotype in this organ. The levels of all other molecular species of PC, PE, PS and PA measured in the brain and liver were very similar between LPIAT1^−/− and LPIAT1^+/+ samples. These results suggest LPIAT1 activity plays a non-redundant role in maintaining physiological levels of PtdIns within an active deacylation/reacylation cycle in mouse tissues. They also suggest that this pathway must act in concert with other, as yet unidentified, mechanisms to achieve the enrichment observed in C38∶4 molecular species of phosphoinositides.     

Diffusion of Single Cardiac Ryanodine Receptors in Lipid Bilayers Is Decreased by Annexin 12

Diffusion of cardiac ryanodine receptors (RyR2) in lipid bilayers was characterized. RyR2 location was monitored by imaging fluo-3 fluorescence due to Ca²⁺ flux through RyR2 channels or fluorescence from RyR2 conjugated with Alexa 488 or containing green fluorescent protein. Single channel currents were recorded to ensure that functional channels were studied. RyR2 exhibited an apparent diffusion coefficient (D_RyR) of 1.2 × 10⁻⁸ cm² s⁻¹ and a mean path length of 5.0 μm. Optimal use of optical methods for analysis of RyR2 channel function requires that RyR2 diffusion be limited. Therefore, we tested the effect of annexin 12, which interacts with anionic phospholipids in a Ca²⁺-dependent manner. Addition of annexin 12 (0.25–4.0 μM) to the trans side of bilayers containing an 80:20 ratio of phosphatidylethanolamine/phosphatidylserine decreased RyR2 diffusion in a concentration-dependent manner. Annexin 12 (2 μM) decreased the apparent D_RyR 683-fold from 1.2–10⁻⁸ to 1.8 × 10⁻¹¹ cm² s⁻¹ and the mean path length 10-fold from 5.0 to 0.5 μm without obvious changes in the conductance of the native bilayer or in activation of RyR2 channels by Ca²⁺ or suramin. Thus, annexin 12 may provide a useful tool for optimizing optical analysis of RyR2 channels in lipid bilayers.     

Influence of Acidic pH on Hydrogen and Acetate Production by an Electrosynthetic Microbiome

Production of hydrogen and organic compounds by an electrosynthetic microbiome using electrodes and carbon dioxide as sole electron donor and carbon source, respectively, was examined after exposure to acidic pH (∼5). Hydrogen production by biocathodes poised at −600 mV vs. SHE increased>100-fold and acetate production ceased at acidic pH, but ∼5–15 mM (catholyte volume)/day acetate and>1,000 mM/day hydrogen were attained at pH ∼6.5 following repeated exposure to acidic pH. Cyclic voltammetry revealed a 250 mV decrease in hydrogen overpotential and a maximum current density of 12.2 mA/cm² at −765 mV (0.065 mA/cm² sterile control at −800 mV) by the Acetobacterium-dominated community. Supplying −800 mV to the microbiome after repeated exposure to acidic pH resulted in up to 2.6 kg/m³/day hydrogen (≈2.6 gallons gasoline equivalent), 0.7 kg/m³/day formate, and 3.1 kg/m³/day acetate ( = 4.7 kg CO₂ captured).     

Global trends and uncertainties in terrestrial denitrification and N2O emissions

Soil nitrogen (N) budgets are used in a global, distributed flow-path model with 0.5° × 0.5° resolution, representing denitrification and N₂O emissions from soils, groundwater and riparian zones for the period 1900–2000 and scenarios for the period 2000–2050 based on the Millennium Ecosystem Assessment. Total agricultural and natural N inputs from N fertilizers, animal manure, biological N₂ fixation and atmospheric N deposition increased from 155 to 345 Tg N yr⁻¹ (Tg = teragram; 1 Tg = 10¹² g) between 1900 and 2000. Depending on the scenario, inputs are estimated to further increase to 408–510 Tg N yr⁻¹ by 2050. In the period 1900–2000, the soil N budget surplus (inputs minus withdrawal by plants) increased from 118 to 202 Tg yr⁻¹, and this may remain stable or further increase to 275 Tg yr⁻¹ by 2050, depending on the scenario. N₂ production from denitrification increased from 52 to 96 Tg yr⁻¹ between 1900 and 2000, and N₂O–N emissions from 10 to 12 Tg N yr⁻¹. The scenarios foresee a further increase to 142 Tg N₂–N and 16 Tg N₂O–N yr⁻¹ by 2050. Our results indicate that riparian buffer zones are an important source of N₂O contributing an estimated 0.9 Tg N₂O–N yr⁻¹ in 2000. Soils are key sites for denitrification and are much more important than groundwater and riparian zones in controlling the N flow to rivers and the oceans.     

Effects of phosphorus deficiency on the photosynthesis and respiration of leaves of sugar beet

Phosphorus deficiency was induced in sugar beet plants (Beta vulgaris L. var. F5855441), cultured hydroponically under standardized environmental conditions, by removal of phosphorus from the nutrient supply at the ten leaf stage 28 days after germination. CO₂ and water vapor exchange rates of individual attached leaves were determined at intervals after P cutoff. Leaves grown with an adequate nutrient supply attained net rates of photosynthetic CO₂ fixation of 125 ng CO₂ cm⁻² sec⁻¹ at saturating irradiance, 25 C, and an ambient CO₂ concentration of about 250 μl l⁻¹. After P cutoff, leaf phosphorus concentrations decreased as did net rates of photosynthetic CO₂ uptake, photorespiratory evolution of CO₂ into CO₂-free air, and dark respiration, so that 30 days after cutoff these rates were about one-third of the control rates. The decrease in photosynthetic rates during the first 15 days after cutoff was associated with increased mesophyll resistance (r_m) which increased from 2.4 to 4.9 sec cm⁻¹, while from 15 to 30 days there was an increase in leaf (mainly stomatal) diffusion resistance (r_l′) from 0.3 to 0.9 sec cm⁻¹, as well as further increases in r_m to 8.5 sec cm⁻¹. Leaf diffusion resistance (r_l′) was increased greatly by low P at low but not at high irradiance, r_l′ for plants at low P reaching values as high as 9 sec cm⁻¹.     

Sediment Nitrification, Denitrification, and Nitrous Oxide Production in a Deep Arctic Lake

We used a combination of ¹⁵N tracer methods and a C₂H₂ blockage technique to determine the role of sediment nitrification and denitrification in a deep oligotrophic arctic lake. Inorganic nitrogen concentrations ranged between 40 and 600 nmol · cm⁻³, increasing with depth below the sediment-water interface. Nitrate concentrations were at least 10 times lower, and nitrate was only detectable within the top 0 to 6 cm of sediment. Eh and pH profiles showed an oxidized surface zone underlain by more reduced conditions. The lake water never became anoxic. Sediment Eh values ranged from −7 to 484 mV, decreasing with depth, whereas pH ranged from 6.0 to 7.3, usually increasing with depth. The average nitrification rate (49 ng of N · cm⁻³ · day⁻¹) was similar to the average denitrification rate (44 ng of N · cm⁻³ · day⁻¹). In situ N₂O production from nitrification and denitrification ranged from 0 to 25 ng of N · cm⁻³ · day⁻¹. Denitrification appears to depend on the supply of nitrate by nitrification, such that the two processes are coupled functionally in this sediment system. However, the low rates result in only a small nitrogen loss.     

Dilation of the Human Immunodeficiency Virus–1 Envelope Glycoprotein Fusion Pore Revealed by the Inhibitory Action of a Synthetic Peptide from gp41

We have monitored fusion between cell pairs consisting of a single human immunodeficiency virus–1 (HIV-1) envelope glycoprotein–expressing cell and a CD4⁺ target cell, which had been labeled with both a fluorescent lipid in the membrane and a fluorescent solute in the cytosol. We developed a new three-color assay to keep track of the cell into which fluorescent lipids and/or solutes are redistributed. Lipid and solute redistribution occur as a result of opening a lipid-permissive fusion pore and a solute-permissive fusion pore (FP_S), respectively. A synthetic peptide (DP178) corresponding to residues 643–678 of the HIV-1_LAI gp120-gp41 sequence (Wild, C.T., D.C. Shugars, T.K. Greenwell, C.B. McDanal, and T.J. Matthews. 1994. Proc. Natl. Acad. Sci. USA. 91:12676–12680) completely inhibited FP_S at 50 ng/ml, whereas at that concentration there was 20–30% fusion activity measured by the lipid redistribution. The differences detected in lipid mixing versus contents mixing are maintained up to 6 h of coculture of gp120-41–expressing cells with target cells, indicating that DP178 can “clamp” the fusion complex in the lipid mixing intermediate for very long time periods. A peptide from the NH₂-terminal of gp41, DP107, inhibited HIV-1_LAI gp120-gp41–mediated cell fusion at higher concentrations, but with no differences between lipid and aqueous dye redistribution at the different inhibitor concentrations. The inhibition of solute redistribution by DP178 was complete when the peptide was added to the fusion reaction mixture during the first 15 min of coculture. We have analyzed the inhibition data in terms of a fusion pore dilation model that incorporates the recently determined high resolution structure of the gp41 core.     

Effects of Catchment and Riparian Landscape Setting on Water Chemistry and Seasonal Evolution of Water Quality in the Upper Han River Basin,China

Six-year (2005–2010) evolution of water chemistry (Cl⁻, NO₃ ⁻, SO₄ ²⁻, HCO₃ ⁻, Na⁺, K⁺, Ca²⁺ and Mg²⁺) and their interactions with morphological properties (i.e., slope and area), land cover, and hydrological seasonality were examined to identify controlling factors and processes governing patterns of stream water quality in the upper Han River, China. Correlation analysis and stepwise multiple regression models revealed significant correlations between ions (i.e., Cl⁻, SO₄ ²⁻, Na⁺ and K⁺) and land cover (i.e., vegetation and bare land) over the entire catchment in both high- and low-flow periods, and in the buffer zone the correlation was much more stronger in the low-flow period. Catchment with steeper slope (>15°) was negatively correlated with major ions, largely due to multicollinearity of basin characteristics. Land cover within the buffer zone explained slightly less of major elements than at catchment scale in the rainy season, whereas in the dry season, land cover along the river networks in particular this within 100 m riparian zone much better explained major elements rather than this over the entire catchment. Anthropogenic land uses (i.e., urban and agriculture) however could not explain water chemical variables, albeit EC, TDS, anthropogenic markers (Cl⁻, NO₃ ⁻, SO₄ ²), Na⁺, K⁺ and Ca²⁺ significantly increased during 2005–2010, which was corroborated by principal component analyses (PCA) that indicated anthropogenic inputs. Observations demonstrated much higher solute concentrations in the industrial-polluted river. Our results suggested that seasonal evolution of water quality in combined with spatial analysis at multiple scales should be a vital part of identifying the controls on spatio-temporal patterns of water quality.     

Discriminating Hepatocellular Carcinoma in Rats Using a High-Tc SQUID Detected Nuclear Resonance Spectrometer in a Magnetic Shielding Box

In this study, we report the spin-lattice relaxation rate of hepatocellular carcinoma (HCC) and normal liver tissue in rats using a high-T_c superconducting quantum interference device (SQUID) based nuclear magnetic resonance (NMR) spectrometer. The resonance spectrometer used for discriminating liver tumors in rats via the difference in longitudinal relaxation time in low magnetic fields was set up in a compact and portable magnetic shielding box. The frequency-domain NMR signals of HCC tissues and normal liver tissues were analyzed to study their respective longitudinal relaxation rate T₁ ⁻¹. The T₁ ⁻¹ of liver tissues for ten normal rats and ten cancerous rats were investigated respectively. The averaged T₁ ⁻¹ value of normal liver tissue was (6.41±0.66) s⁻¹, and the averaged T₁ ⁻¹ value of cancerous tissue was (3.38±0.15) s⁻¹. The ratio of T₁ ⁻¹ for normal liver tissues and cancerous liver tissues of the rats investigated is estimated to be 1.9. Since this significant statistical difference, the T₁ ⁻¹ value can be used to distinguish the HCC tissues from normal liver tissues. This method of examining liver and tumor tissues has the advantages of being convenient, easy to operate, and stable.     

Nitrogen loss by anaerobic oxidation of ammonium in rice rhizosphere

Anaerobic oxidation of ammonium (anammox) is recognized as an important process for nitrogen (N) cycling, yet its role in agricultural ecosystems, which are intensively fertilized, remains unclear. In this study, we investigated the presence, activity, functional gene abundance and role of anammox bacteria in rhizosphere and non-rhizosphere paddy soils using catalyzed reporter deposition–fluorescence in situ hybridization, isotope-tracing technique, quantitative PCR assay and 16S rRNA gene clone libraries. Results showed that rhizosphere anammox contributed to 31–41% N₂ production with activities of 0.33–0.64 nmol N₂ g⁻¹ soil h⁻¹, whereas the non-rhizosphere anammox bacteria contributed to only 2–3% N₂ production with lower activities of 0.08–0.26 nmol N₂ g⁻¹ soil h⁻¹. Higher anammox bacterial cells were observed (0.75–1.4 × 10⁷ copies g⁻¹ soil) in the rhizosphere, which were twofold higher compared with the non-rhizosphere soil (3.7–5.9 × 10⁶ copies g⁻¹ soil). Phylogenetic analysis of the anammox bacterial 16S rRNA genes indicated that two genera of ‘Candidatus Kuenenia'' and ‘Candidatus Brocadia'' and the family of Planctomycetaceae were identified. We suggest the rhizosphere provides a favorable niche for anammox bacteria, which are important to N cycling, but were previously largely overlooked.     

Inhibition of PbGP43 Expression May Suggest that gp43 is a Virulence Factor in Paracoccidioides brasiliensis

Glycoprotein gp43 is an immunodominant diagnostic antigen for paracoccidioidomycosis caused by Paracoccidioides brasiliensis. It is abundantly secreted in isolates such as Pb339. It is structurally related to beta-1,3-exoglucanases, however inactive. Its function in fungal biology is unknown, but it elicits humoral, innate and protective cellular immune responses; it binds to extracellular matrix-associated proteins. In this study we applied an antisense RNA (aRNA) technology and Agrobacterium tumefaciens-mediated transformation to generate mitotically stable PbGP43 mutants (PbGP43 aRNA) derived from wild type Pb339 to study its role in P. brasiliensis biology and during infection. Control PbEV was transformed with empty vector. Growth curve, cell vitality and morphology of PbGP43 aRNA mutants were indistinguishable from those of controls. PbGP43 expression was reduced 80–85% in mutants 1 and 2, as determined by real time PCR, correlating with a massive decrease in gp43 expression. This was shown by immunoblotting of culture supernatants revealed with anti-gp43 mouse monoclonal and rabbit polyclonal antibodies, and also by affinity-ligand assays of extracellular molecules with laminin and fibronectin. In vitro, there was significantly increased TNF-α production and reduced yeast recovery when PbGP43 aRNA1 was exposed to IFN-γ-stimulated macrophages, suggesting reduced binding/uptake and/or increased killing. In vivo, fungal burden in lungs of BALB/c mice infected with silenced mutant was negligible and associated with decreased lung ΙΛ−10 and IL-6. Therefore, our results correlated low gp43 expression with lower pathogenicity in mice, but that will be definitely proven when PbGP43 knockouts become available. This is the first study of gp43 using genetically modified P. brasiliensis.     

Deletion of IL-33R (ST2) Abrogates Resistance to EAE in BALB/C Mice by Enhancing Polarization of APC to Inflammatory Phenotype

The administration of interleukin 33 and deletion of IL-33 receptor, ST2 molecule, affects the induction of autoimmunity in different experimental models of human autoimmune diseases. The aim of this study was to analyze the effect of ST2 deletion on the induction of experimental autoimmune encephalomyelitis (EAE) in resistant BALB/c mice. Mice were immunized with MOG_35–55 peptide or disease was induced by passive transfer of encephalitogenic singenic cells and EAE was clinically and histologically evaluated. Expression of intracellular inflammatory cytokines, markers of activation and chemokine receptors on lymphoid tissue and CNS infiltrating mononuclear cells was analyzed by flow cytometry. We report here that deletion of ST2^−/− molecule abrogates resistance of BALB/c mice to EAE induction based on clinical and histopathological findings. Brain and spinal cord infiltrates of ST2^−/− mice had significantly higher number of CD4⁺ T lymphocytes containing inflammatory cytokines compared to BALB/c WT mice. Adoptive transfer of ST2^−/− primed lymphocytes induced clinical signs of the disease in ST2^−/− as well as in WT mice. MOG_35–55 restimulated ST2^−/− CD4⁺ cells as well as ex vivo analyzed lymph node cells had higher expression of T-bet and IL-17, IFN-γ, TNF-α and GM-CSF in comparison with WT CD4⁺ cells. ST2^−/− mice had higher percentages of CD4⁺ cells expressing chemokine receptors important for migration to CNS in comparison with WT CD4⁺ cells. Draining lymph nodes of ST2^−/− mice contained higher percentage of CD11c⁺CD11b⁺CD8⁻ cells containing inflammatory cytokines IL-6 and IL-12 with higher expression of activation markers. Transfer of ST2^−/− but not WT dendritic cells induced EAE in MOG_35–55 immunized WT mice. Our results indicate that ST2 deficiency attenuates inherent resistance of BALB/c mice to EAE induction by enhancing differentiation of proinflammatory antigen presenting cells and consecutive differentiation of encephalitogenic T cells in the draining lymph node rather than affecting their action in the target tissue.     

Recovery of Spores from Thermophilic Dairy Bacilli and Effects of Their Surface Characteristics on Attachment to Different Surfaces

Spores from four Geobacillus spp. were isolated from a milk powder manufacturing line in New Zealand. Liquid sporulation media produced spore yields of ~10⁷ spores ml⁻¹; spores were purified using a two-phase system created with polyethylene glycol 4000 and 3 M phosphate buffer. The zeta potentials of the spores from the four isolates ranged from −10 to −20 mV at neutral pH, with an isoelectric point between pH 3 and 4. Through contact angle measurements, spores were found to be hydrophilic and had relative hydrophobicity values of 10 to 40%, as measured by the microbial adhesion to hexadecane assay. The most hydrophilic spore isolate with the smallest negative charge attached in the highest numbers to Thermanox and stainless steel (1 × 10⁴ spores cm⁻²), with fewer spores attaching to glass (3 × 10³ spores cm⁻²). However, spores produced by the other three strains attached in similar numbers (P > 0.05) to all substrata (~1 × 10³ spores cm⁻²), indicating that there was no simple relationship between individual physicochemical interactions and spore adherence. Therefore, surface modifications which limit the attachment of one strain may not be effective for all stains, and control regimens need to be devised with reference to the characteristics of the particular strains of concern.     

WSX-1 Signalling Inhibits CD4+ T Cell Migration to the Liver during Malaria Infection by Repressing Chemokine-Independent Pathways

IL-27 is an important and non-redundant regulator of effector T cell accumulation in non-lymphoid tissues during infection. Using malaria as a model systemic pro-inflammatory infection, we demonstrate that the aberrant accumulation of CD4⁺ T cells in the liver of infected IL27R^−/− (WSX-1^−/−) mice is a result of differences in cellular recruitment, rather than changes in T cell proliferation or cell death. We show that IL-27 both inhibits the migratory capacity of infection-derived CD4⁺ T cells towards infection-derived liver cells, but also suppresses the production of soluble liver-derived mediator(s) that direct CD4⁺ T cell movement towards the inflamed tissue. Although CCL4 and CCL5 expression was higher in livers of infected WSX-1^−/− mice than infected WT mice, and hepatic CD4⁺ T cells from WSX-1^−/− mice expressed higher levels of CCR5 than cells from WT mice, migration of CD4⁺ T cells to the liver of WSX-1^−/− mice during infection was not controlled by chemokine (R) signalling. However, anti-IL-12p40 treatment reduced migration of CD4⁺ T cells towards infection-derived liver cells, primarily by abrogating the hepatotropic migratory capacity of T cells, rather than diminishing soluble tissue-derived migratory signals. These results indicate that IL-27R signalling restricts CD4⁺ T cell accumulation within the liver during infection primarily by suppressing T cell chemotaxis, which may be linked to its capacity to repress Th1 differentiation, as well as by inhibiting the production of soluble, tissue-derived chemotaxins.     

Initial Effects of the Mount St. Helens Eruption on Nitrogen Cycle and Related Chemical Processes in Ryan Lake

Ryan Lake, a 1.6-hectare basin lake near the periphery of the tree blowdown area in the blast zone 19 km north of Mount St. Helens, was studied from August to October 1980 to determine the microbial and chemical response of the lake to the eruption. Nutrient enrichment through the addition of fresh volcanic material and the organic debris from the surrounding conifer forest stimulated intense microbial activity. Concentrations of such nutrients as phosphorus, sulfur, manganese, iron, and dissolved organic carbon were markedly elevated. Nitrogen cycle activity was especially important to the lake ecosystem in regulating biogeochemical cycling owing to the limiting abundance of nitrogen compounds. Nitrogen fixation, both aerobic and anaerobic, was active from aerobic benthic and planktonic cyanobacteria with rates up to 210 nmol of N₂ cm⁻¹ h⁻¹ and 667 nmol of N₂ liter⁻¹ h⁻¹, respectively, and from anaerobic bacteria with rates reaching 220 nmol of N₂ liter⁻¹ h⁻¹. Nitrification was limited to the aerobic epilimnion and littoral zones where rates were 43 and 261 nmol of NO₂ liter⁻¹ day⁻¹, respectively. Potential denitrification rates were as high as 30 μmol of N₂O liter⁻¹ day⁻¹ in the anaerobic hypolimnion. Total bacterial numbers ranged from 1 × 10⁶ to 3 × 10⁸ ml⁻¹ with the number of viable sulfur-metal-oxidizing bacteria reaching 2 × 10⁶ ml⁻¹ in the hypolimnion. A general scenario for the microbial cycling of nitrogen, carbon, sulfur, and metals is presented for volcanically impacted lakes. The important role of nitrogen as these lakes recover from the cataclysmic eruption and proceed back towards their prior status as oligotrophic alpine lakes is emphasized.     

Estimation of Sediment Denitrification Rates at In Situ Nitrate Concentrations

The denitrification rates in a marine sediment, estimated by using ¹⁵N-nitrate, V_max, K_m, and sediment nitrate concentrations, were 12.5 and 2.0 nmol of N₂-N cm⁻³ day⁻¹ at 0 to 1 and 1 to 3 cm, respectively, at 12°C. The total rate was 165 nmol of N₂-N m⁻² day⁻¹.     

Effects of Light, Carbon Dioxide, and Temperature on Photosynthesis, Oxygen Inhibition of Photosynthesis, and Transpiration in Solanum tuberosum

Individual leaves of potato (Solanum tuberosum L. W729R), a C₃ plant, were subjected to various irradiances (400-700 nm), CO₂ levels, and temperatures in a controlled-environment chamber. As irradiance increased, stomatal and mesophyll resistance exerted a strong and some-what paralleled regulation of photosynthesis as both showed a similar decrease reaching a minimum at about 85 neinsteins·cm⁻²·sec⁻¹ (about ½ of full sunlight). Also, there was a proportional hyperbolic increase in transpiration and photosynthesis with increasing irradiance up to 85 neinsteins·cm⁻²·sec⁻¹. These results contrast with many C₃ plants that have a near full opening of stomata at much less light than is required for saturation of photosynthesis.