Ryosuke Endo

Selection of microalgae suitable for culturing with digestate from methane fermentation

The effects of digestate on the growth rates of Euglena gracilis, Chlorella vulgaris, and Dunaliella tertiolecta were investigated to select suitable microalgae for culturing with digestate from methane fermentation. Microalgae were cultured in an aqueous solution containing digestate at concentrations of 5%, 10%, 13%, 20%, 40%, 50%, and 100%, and Cramer–Myers (CM) solution as a control, at photosynthetic photon flux densities (PPFDs) of 75–150 μmol m−2 s−1 with continuous illumination at 30°C. The number of cells was monitored daily, and specific growth rates (μ) were calculated as cellular multiplication rates. The maximum μ values of these species were greater in appropriate concentrations of digestate than in CM medium. The maximum μ values were 0.047 h−1 in 10% digestate for E. gracilis, 0.065 h−1 in 20% digestate for C. vulgaris, and 0.052 h−1 in 50% digestate for D. tertiolecta at a PPFD of 150 μmol m−2 s−1. The μ of D. tertiolecta were 2.5 and 1.1 times higher than those of E. gracilis and C. vulgaris, respectively, in 50% digestate. These results demonstrated that these species could be cultured at high growth rates with diluted methane fermentation sludge and that, among these species, Dunaliella sp. was suitable for culturing at higher concentration of digestate under relatively low-level light conditions.

High-light-like photosynthetic responses of Cucumis sativus leaves acclimated to fluorescent illumination with a high red:far-red ratio: interaction between light quality and quantity

This study evaluated the photosynthetic responses of Cucumis sativus leaves acclimated to illumination from three-band white fluorescent lamps with a high red:far-red (R:FR) ratio (R:FR = 10.5) and the photosynthetic responses of leaves acclimated to metal-halide lamps that provided a spectrum similar to that of natural light (R:FR = 1.2) at acclimation photosynthetic photon flux density (PPFD) of 100 to 700 μmol m−2 s−1. The maximum gross photosynthetic rate (PG) of the fluorescent-acclimated leaves was approximately 1.4 times that of the metal-halide-acclimated leaves at all acclimation PPFDs. The ratio of quantum efficiency of photosystem II (ΦPSII) of the fluorescent-acclimated leaves to that of the metal-halide-acclimated leaves tended to increase with increasing acclimation PPFD, whereas the corresponding ratios for the leaf mass per unit area tended to decrease with increasing acclimation PPFD. These results suggest that the greater maximum PG of the fluorescent-acclimated leaves resulted from an interaction between the acclimation light quality and quantity, which was mainly caused by the greater leaf biomass for photosynthesis per area at low acclimation PPFDs and by the higher ΦPSII as a result of changes in characteristics and distribution of chloroplasts, or a combination of these factors at high acclimation PPFDs.

The photosynthetic parameters of cucumber as affected by irradiances with different red:far-red ratios

We compared photosynthetic performance between cucumber (Cucumis sativus L.) leaves acclimated to saturating irradiances with high red: far red (R:FR = 10) and normal R:FR (= 1.4) ratios. The net photosynthetic rate (PN) and stomatal conductance (gs) of the leaves acclimated to high R:FR were greater than those of the leaves acclimated to normal R:FR; the greater gs partly explains the greater PN. The greater gs of the high-R:FR-leaves probably resulted from a higher stomatal density and/or a greater size. PN of the high R:FR leaves was still greater than that of the normal R:FR leaves at the same intercellular CO2 concentration (ci). This indicates that non-stomatal factors also increased the photosynthetic capacity of the high R:FR leaves. The maximum Rubisco carboxylase activity estimated from a PN-ci curve analysis was also greater in the high R:FR leaves, however, the intrinsic water-use efficiency (WUEi = PN/gs) of the high R:FR leaves was lower than that of the normal R:FR leaves.

A comparative study on growth and morphology of wasabi plantlets under the influence of the micro-environment in shoot and root zones during photoautotrophic and photomixotrophic micropropagation

The growth of wasabi (Wasabia japonica Matsumura) plantlets under different micro-environments inside culture vessels in photoautotrophic micropropagation (PA) and photomixotrophic micropropagation (PM) conditions were compared. After 28 days of culture, dry weight, relative growth rate, leaf area, and leaf chlorophyll contents of plantlets in PA were greater than those in PM. The number of leaves did not differ significantly between PA and PM conditions. PA promoted root growth and development with a greater number of roots, root length, root diameter, root fresh weight, root dry weight, and root xylem vessel system. Dissolved oxygen concentration in PA culture medium sharply decreased after 7 days of culture and then recovered. In PM culture medium, no significant fluctuation of dissolved oxygen concentration was apparent. The net photosynthetic rates of plantlets in PA were much higher than those in PM and increased with culture time. In contrast, the net photosynthetic rates of wasabi plantlets in PM kept a low and constant value during the culture period. With the presence of gas exchange membranes attached to the vessel lids, the detected vapor pressure deficit was higher in PA than in PM conditions. Higher stomatal density and larger stomatal aperture on the abaxial and adaxial surfaces of the leaves in PM medium promoted leaf water loss following ex vitro conditions. Thus, PA is applicable for producing healthy wasabi transplants.

Atmospheric Humidity Influences Oviposition Rate of Tetranychus urticae (Acari: Tetranychidae) Through Morphological Responses of Host Cucumis sativus Leaves.

Abstract We investigated the effects of morphology of host cucumber, Cucumis sativus L., leaves acclimatized to different atmospheric humidity levels on oviposition by adult females of the twospotted spider mite, Tetranychus urticae Koch. Cucumber seedlings were grown at a vapor pressure deficit (VPD) of 0.4, 1.9, or 3.0 kPa at 28°C (90%, 50%, or 20% relative humidity, respectively) in growth chambers until the second true leaves had expanded. Adult females of T. urticae were released on the adaxial surfaces of leaf squares cut from first and second true leaves in each treatment group, and held in the same humidity condition. Eggs were counted 2 d after release. The lower acclimatization humidity (higher VPD) increased trichome (leaf hair) density of the host leaves and oviposition rate, but the relationship between the trichome and oviposition differed between leaf positions. The leaf mass per area (LMA) was greater in first true leaves than in second true leaves, but was not influenced by VPD. A linear regression model with oviposition rate as the dependent variable and trichome density and LMA as independent variables showed that both variables influenced the oviposition rate approximately equally. We conclude that oviposition was accelerated under low humidity (high VPD) conditions indirectly probably through an increase in the trichome density of host leaves.

Effects of the interaction between vapor-pressure deficit and salinity on growth and photosynthesis of Cucumis sativus seedlings under different CO2 concentrations

We studied growth and photosynthesis of cucumber (Cucumis sativus) seedlings under two vapor-pressure deficit levels (VPD; 0.4 and 3.0 kPa), two salinity levels (0 mM and 34 mM NaCl), and two CO2 concentrations ([CO2]; 400 and 1,000 μmol mol–1). Relative growth rate (RGR) decreased with increasing VPD, but the causal factor differed between salinity levels and CO2 concentrations. Under ambient [CO2], RGR decreased with increasing VPD at low salinity mainly due to decreased leaf area ratio (LAR), and decreased net assimilation rate (NAR) at high salinity. The decrease in intercellular [CO2] (Ci) with decreasing stomatal conductance caused by high VPD did not significantly limit net photosynthetic rate (PN) at low salinity, but PN was potentially limited by Ci at high salinity. At high [CO2], high VPD reduced LAR, but did not affect NAR. This is because the decrease in Ci occurred where slope of PN–Ci curve was almost flat.

Growth performances and changes of macronutrient ion concentrations in the culture medium when Euglena gracilis was cultured with nitrified digestate

ABSTRACT We investigated the possibility of using Euglena gracilis to convert digestate from methane fermentation of organic wastes into a medium for soilless crop culture. The growth of E. gracilis cultured with aqueous solutions containing filtrate of raw digestate at 1–30% (v/v) and nitrified digestate at 10–100% (v/v) was examined. Concentrations of plant macronutrient ions in nitrified digestate before and after culturing E. gracilis were also examined. Specific growth rates in aqueous solutions containing filtrate of raw digestate at 1–10% and nitrified digestate at 10–100% showed no significant differences, respectively (0.781 ± 0.031 d−1 and 0.925 ± 0.033 d−1, mean ± standard error). The rates in the filtrate of nitrified digestate were significantly higher than those in the filtrate of raw digestate. Moreover, there were no significant differences between the concentrations of plant macronutrient ions other than in the filtrate of nitrified digestate before and after culturing E. gracilis. The concentration of decreased significantly by 10.5% of the initial concentration. As a result, the constituent ratio of plant macronutrient ions other than magnesium in the solution after culturing E. gracilis was similar to that in a standard nutrient solution for soilless culture.

Possibility of co-culturing Euglena gracilis and Lactuca sativa L. with biogas digestate

ABSTRACT The goal of this study was to establish a system for co-culturing microalgae and crop plants with biogas digestate. We examined growth performances of E. gracilis and L. sativa co-cultured using a commercial liquid fertilizer designed for soilless culture supplemented with vitamins and ammonium. This solution simulated the filtrate of nitrified biogas digestate derived from the organic fraction of municipal solid waste but was supplemented with insufficient plant nutrients (Mg, Fe and Mn). The specific growth rate of the co-cultured E. gracilis was 0.761 ± 0.081 d−1 (mean ± SE), which was the same rate that E. gracilis achieved when grown as a sole culture. There were no significant differences between L. sativa cultured with E. gracilis until the stationary growth phase of E. gracilis was reached and those cultured alone relative to biomass, RGRs (relative growth rates), or relative to SPAD values of leaves. These results suggest that E. gracilis and L. sativa could be co-cultured with the biogas digestate after being nitrified and filtered. In addition, considering concentrations of plant macronutrients in the residual solution after the co-culturing E. gracilis and L. sativa, it could be re-used as the nutrient solution for co-culturing E. gracilis and L. sativa. GRAPHICAL ABSTRACT