Three-dimensional computer models of electrospray ionization sources were constructed in COMSOL Multiphysics to solve the static electric fields using finite element methods. The magnitude of the electric field strength for onset of electrospray and optimum signal was calculated under various conditions. The modification of the electric field distribution in the ion source by an atmospheric pressure ion lens was also investigated by plotting the equipotential surfaces, electric field lines and trajectories of charged droplets. Both the calculated and the experimental results demonstrate that the changes in the ion signal detected by the mass spectrometer are attributable to the focusing effect of the ion lens when appropriate voltages are applied on the sprayer and ion lens. The optimum signal was found by setting the sprayer voltage from 3000 to 5000 V while scanning the ion lens voltage. The calculated strengths of the electric field at the sprayer tip for optimum signals are similar although the applied voltages at the sprayer and ion lens are significantly different.

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Bioavailability of nitrogen (N) and phosphorus (P) is known to affect marine phytoplankton physiology, thus influencing their primary productivity; and it's of general interest to see how the N or/and P additions affect the differently cell-sized phytoplankton assemblages. Data from the northern South China Sea showed that P addition increased up to 6 times of total chl a content within 24 h in the estuarine water; and N+P addition increased more than 20 times of chl a within 144 h in the pelagic water. The P addition powered 18.0% and 149% increase in the carbon fixation of larger (>3 μm) and smaller (<3 μm) cell assemblies from the estuarine water, respectively; while the limited effects were observed between them in the pelagic water. Additions of N and P interactively increased the carbon fixation of both cell-sized assemblies in the pelagic water, but only small cell-sized fraction in the estuarine water. Moreover, the estuarine phytoplankton cells appeared to respond faster to the nutrient additions than the pelagic ones, and the smaller cells respond to a greater extent than their larger counterparts in the estuarine water but not in the pelagic water.

Zoosporic fungi play an important role in aquatic environments, but their diversity, especially that of parasitic fungi of phytoplankton, has still not been fully revealed. We conducted monthly analyses of the community structure of zoosporic fungi at a pelagic site in Lake Biwa, Japan, from May to December 2016. Metabarcoding analysis, targeted to a large subunit region of ribosomal DNA in the nano-size fraction of particles (2-20 µm), was carried out on the samples. We also counted large phytoplankton and chytrid sporangia attached to the hosts. We detected 3 zoosporic fungal phyla (Blastocladiomycota, Chytridiomycota and Cryptomycota) within 107 operational taxonomic units (OTUs), in which Chytridiomycota was the most diverse and abundant phylum. Few fungal OTUs overlapped between months, and specific communities were detected in each month. These results showed that diverse zoosporic fungi with high temporal variability inhabited the lake. Five large phytoplankton species were found to be infected by chytrids: Staurastrum dorsidentiferum, S. rotula, Closterium aciculare, Asterionella formosa and Aulacoseira granulata. Some chytrids were detected by metabarcoding analysis: Zygophlyctis asterionellae infecting A. formosa, Staurastromyces oculus infecting S. dorsidentiferum and Pendulichytrium sphaericum infecting A. granulata. One OTU detected in association with infected C. aciculare by microscopic counting might have been an obligate parasitic chytrid of C. aciculare. The results indicated that a combination of metabarcoding and microscopic analysis revealed more information on zoosporic fungi, including those that are parasitic.