The chl a specific absorption coefficients [ a * ( ), m 2 и mg chl a Ϫ 1 ] were examined in chemostat culture of the Prymnesiophyceae Isochrysis galbana (Parke) under a 12:12-h light:dark cycle at low light (75 mol photons и m Ϫ 2 и s Ϫ 1 ) and high light (500 mol photons и m Ϫ 2 и s Ϫ 1 ) conditions. Other associated measurements such as pigment composition, cell density, and diameter as the measure of cell size were also made at the two light regimes every 2 h for 2 days to confirm the periodicity. A distinct diel variability was observed for the a * ( ) with maxima near dawn and minima near dusk. The magnitude of diel variation in a * (440) was 15% at low light and 22% at high light. Pronounced diel patterns were observed for cell size with minima near dawn and maxima near dusk. The magnitude of diel variation in cell size was 9.3% at low light and 21% at high light. The absorption efficiency factors [ Q a (440)] were determined by reconstruction using intracellular concentrations of pigments and cell size. The Q a (440) also showed a distinct diel variability, with minima near dawn and maxima near dusk. The diel variation in a * ( ) and Q a ( ) was primarily caused by changes in cell size due to growth, although there was some influence from diel variations in the intracellular pigment concentrations. The results presented here indicated that diel variation in a * ( ) was an important component of the optical characterization of phytoplankton.

Soybean rust (SBR), caused by Phakopsora pachyrhizi (Sydow & Sydow), has become a serious issue in Brazil. As Brazil is one of the largest soybean-producing and exporting countries in the world, a considerable decrease in soybean production due to SBR would have a significant impact on the global soybean market. SBR-resistant cultivars have been developed to prevent a decrease in soybean production. This study was conducted to evaluate the effect of SBR-resistant cultivars on soybean production and the soybean market in Brazil using a supply and demand model. This model consists of functions of yield, cultivated area, exports, and stock changes of soybean and soybean products, demand for soybean products, and price linkages. Five scenarios were simulated to evaluate the economic impact of adopting SBR-resistant cultivars as follows: One without SBR infection, two with serious production losses due to SBR in the south and southeast regions and all the states of Brazil, and two with the adoption of SBR-resistant cultivars in the south and south-east regions and all the states of Brazil. Our simulations suggest that adopting SBR-resistant cultivars reduces the cost of controlling SBR by approximately half and is essential for sustainable soybean production and a stable global soybean market.

Dependency of carbon cell quota (C) on cell volume (V) was studied for the Prymnesiophyte Isochrysis galbana. Changes in the cell volume and carbon quota during cell divisions were examined at 25°C in a continuous culture with an enriched f/2 medium under a 12/12 h light/dark cycle at an irradiance of 45, 150, and 365 μmol m 2 sec 1 . Carbon quota estimates followed the relation log C=b log V+log a, where b is the slope and log a is the intercept of the relationship. Significant relationships between carbon quota and cell volume during cell divisions were obtained at the three irradiances tested. The value of the slope and the intercept ranged from 0.59 to 0.98 and from 0.22 to 0.64, respectively, however, they were not significantly different between the three irradiances. The relationship between carbon quota to cell volume during cell divisions also corresponded well to previously published carbon quota to cell volume relationship values within the size range of nanophytoplankton ranging from 2 to 20 μm, even though the irradiances used in the experiments differed from those studied previously. Due to the close similarity in cell size and division manner between the majority of nanophytoplankton communities and I. galbana, the results of the present study can be applied to natural assemblages of nanophytoplankton to estimate their carbon biomass in the euphotic layer regardless of sampling time on a given day.

We investigated the diel variation in motility under different irradiance of the prymnesiophyte Isochrysis galbana Parke. The effectiveness of nutrient uptake by motility relative to molecular diffusion in seawater is quantified by the Sherwood number Sh, which is a function of cell size (µm) and motility rate (µm s −1). We calculated Sh for the prymnesiophyte I. galbana by determining its cellular equivalent spherical diameter (ESD, µm) and motility rate (numbers of ESD s −1). Nutrient-enriched batch cultures were grown at 25°C in 12:12h light:dark cycles at light-limiting or light-saturated irradiances for 48 h. Observed motilities and Sh values were within the range of previously reported values and indicated a significant relationship between motility and Sh with ESD. Diel variations in motility and Sh showed maxima at the middle of the light period and minima at the middle of the dark period under both light conditions. Diel patterns of motility and Sh might be related to those of photosynthesis due to the supply of energy of motility.

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