PHOTOSYNTHETIC CHARACTERISTICS OF THE COCCOLITHOPHORID EMILIANIA HUXLEYI (PRYMNESIOPHYCEAE) EXPOSED TO ELEVATED CONCENTRATIONS OF DISSOLVED INORGANIC CARBON1

Light-saturated photosynthesis (P_max) of Emiliania huxleyi (Lohmann) Hay et Mohler is known to be carbonlimited at natural concentrations of dissolved inorganic carbon (DIC). In the present study, light-limited and light-saturated photosynthetic rates of E. huxleyi were studied at three concentrations of DIC (2.4, 7.4, and 12.4 mM) for high-calcite (C_in/C_tot=0.48) and low-calcite (C_in/C_tot=0.08) cells of the same strain. The photosynthetic efficiency (α) and the maximum quantum yield (θ_max)A increased by more than a factor of 2 from the lowest to the highest DIC level. P_max a, and θ_max were always higher for the high-calcite than for the low-calcite cells at identical DIC levels. This may indicate that the calcifcation process acts as an extra supplier of CO₂ for photosynthesis making the CO₂ shortage at natural DIC levels a little smaller for high-calcite than for low-calcite E. huxleyi. A dependency of θ_max on DIC has not previously been shown for marine phytoplankton. θ_max is a key parameter in recent biooptical models of phytoplankton productivity, and the results from the present study are therefore important for modeling the productivity of E. huxleyi.     

An attempt to predict long-term effects of atmospheric nitrogen deposition on the yield of Norway spruce stands (Picea abies (L.) Karst.) in southwestern Sweden

Long-term field experiments in Norway spruce stands on fertile sites (site indices 27–35 m) in southwestern Sweden were analysed with respect to volume increment. Three treatments were included (0=No fertilization, N = Fertilization with N, NP = Fertilization with N and P).Volume growth was monitored for 18 years in 10 blocks. No significant differences in annual volume increment between the treatments were detected. Volume increments in the N treatment were 97%, 99% and 107% as high as those in the 0 treatment for the periods 1–5, 6–10 and 11–15 years after the first fertilization. Corresponding values for the NP treatment were 104%, 108% and 110%, indicating that P has a small positive effect.The amount of N-fertilization would correspond to an annual N deposition of 20 kg ha^-1 during the next 30 years in southwestern Sweden. For this period, the results imply that this N deposition would not affect the growth of Norway spruce stands on fertile sites.     

Importance of seed Zn content for wheat growth on Zn-deficient soil

Eggplants (Solanum melongena L. cv. Bonica) were grown in a glasshouse during summer under natural light with one unbranched shoot or one shoot with 3 to 4 branches and with or without fruit in quartz sand buffered and not buffered with 0.5% CaCO₃ (w : v), respectively. Nutrient solutions supplied contained nitrate or ammonium as the sole nitrogen source. Compared with nutrient solutions containing nitrate (10 mM), solutions containing ammonium (10 mM) caused a decrease in net photosynthesis of eggplants during early stages of vegetative growth when grown in quartz sand not buffered with CaCO₃. The decrease was not observed before leaves showed interveinal chlorosis. In contrast, net photosynthesis after bloom at first increased more rapidly in eggplants supplied with ammonium than with nitrate nitrogen. However, even in this case, net photosynthesis decreased four weeks later when ammonium nutrition was continued. The decrease was accompanied by epinasty and interveinal chlorosis on the lower leaves and later by severe wilting, leaf drop, stem lesions, and hampered growth of stems, roots, and fruits. These symptoms appeared later on plants not bearing fruits than on plants bearing fruits. If nutrient solutions containing increasing concentrations of ammonium (0.5–30 mM) were supplied after the time of first fruit ripening, shoot growth and set of later flowers and fruits were promoted. In contrast, vegetative growth and reproduction was only slightly affected by increasing the concentration of nitrate in the nutrient solutions. In quartz sand buffered with CaCO₃ ammonium nutrition caused deleterious effects only under low light conditions (shade) and on young plants during rapid fruit growth. If eggplants were supplied with ammonium nitrogen before bloom, vegetative growth was promoted, and set of flowers and fruit occurred earlier than on plants supplied with nitrate. Furthermore, the number of flowers and fruit yield increased. These effects of ammonium nutrition were more pronounced when plants were grown with branched shoots than with unbranched shoots. The results indicate that vegetative and reproductive growth of eggplants may be manipulated without causing injury to the plants by supplying ammonium nitrogen as long as the age of the plants, carbohydrate reserves of the roots, quantity of ammonium nitrogen supplied, and pH of the growth medium are favourable. T W Rufty Section editor     

The K/Na and Ca/Na ratios and rapeseed yield,under soil salinity or sodicity

Rapeseed (Brassica napus) is a crop relatively tolerant to salt and sodium. Our objective was to study the interactions between Na, K and Ca and their relationship with its yield under the isolated effects of soil salinity or sodicity.Two experiments were carried out using pots filled with the Ah horizon of a Typic Natraquoll. There were three salinity levels (2.3 dS m^-1; 6.0 dS m^-1 and 10.0 dS m^-1) and three sodicity levels, expressed as sodium adsorption ratios (SAR: 12; 27 and 44). The soil was kept near field capacity.As soil salinity increased, the K/Na and Ca/Na ratios in the tissues decreased markedly but yields and aerial biomass production were not affected. As soil SAR value increased, the K/Na and Ca/Na ratios in plants and K-Na and Ca-Na selectivities decreased. Plants could not maintain their Ca concentration in soil with a high SAR. The grain yield and biomass production diminished significantly in the highest SAR treatment. Our results are consistent with those showing detrimental osmotic effects of salts in Brassica napus. Conversely, under sodicity, the K/Na and Ca/Na ratios in plant tissues decreased considerably, in accordance with grain and biomass production. These results show that the effects of sodicity are different from those of salinity.     

Growth kinetics of glucose-limited petunia hybrida cells in chemostat cultures: Determination of experimental values for growth and maintenance parameters

With glucose-limited continuous cultures of Petunia hybrida six steady states were obtained at specific growth rates varying from 0.0035 to 0.012 h(-1) (corresponding with culture residence times varying from 285 to 85 h). The macromolecular and the elemental biomass composition which were determined in four steady states showed no major differences over the range of growth rates examined. During all six steady states specific subtrate and oxygen consumption as well as biomass and extracellular product formation rates were monitored. Moreover the specific activities of the mitochondrial cytochrome and alternative pathway were determined and used to estimate specific adenosine triphosphate (ATP) production rates. Data thus obtained were used in the determination of maintenance and true growth yield parameters. For the maintenance on glucose and ATP values of 0.0070 C-mol/C-mol/h and 0.034 mol/C-mol/h were obtained, respectively. True yields of biomass on glucose and ATP were 0.50 C-mol/C-mol and 0.28 C-mol/mol, respectively. (c) 1995 John Wiley & Sons, Inc.     

Dynamics and distribution of microphytobenthic chlorophyll-a in the Western Scheldt estuary (SW Netherlands)

The temporal dynamics and spatial distribution of microphytobenthic chlorophyll-a in the layer 0–1 cm were determined in the Western Scheldt estuary over the period 1991–1992. Connections between the annually averaged benthic chlorophyll-a and station elevation and sediment composition (as a measure of the hydrodynamic energy caused by currents and waves) were also examined.Microphytobenthic chlorophyll-a showed one main peak in early summer and a smaller peak in autumn. The mean chlorophyll-a concentration of 113 mg Chl-a m^–2 in the upper centimeter is of the same order of magnitude as in other estuarine areas. The average annual primary production of the microphytobenthos has been estimated at 136 g C m^–2 y^–1 The primary production of sediment inhabiting microalgae is at least 17% of the total primary production in the estuary.Considerable differences in annually averaged chlorophyll-a emerges between the stations. These differences are related mainly to the interaction between station elevation and clay content of the sediment.     

GROWTH,DARK RESPIRATION AND PHOTOSYNTHETIC PARAMETERS OF THE COCCOLITHOPHORID EMILIANIA HUXLEYI (PRYMNESIOPHYCEAE) ACCLIMATED TO DIFFERENT DAY LENGTH-IRRADIANCE COMBINATIONS1

Growth, dark respiration rate, photosynthetic parameters, and chemical composition were determined for Emiliania huxleyi (Lohmann) Hay et Mohler acclimated to different combinations of day length (12, 18, 24 h) and irradiance (30, 100, 200, 800 μmol·m^?2·s^?1). Specific growth rate (μ, day^?1) and carbon-specific dark respiration rate (r^C_d, day^?1) were independent of day length, but increased significantly with increasing irradiance. The photosynthetic parameters depended on the initial acclimation day length and irradiance: Chlorophyll a-specific maximum photosynthetic rate (P_m^B) increased up to threefold with decreasing day length and twofold with increasing irradiance. The maximum light utilization coefficient (α^B) and maximum quantum yield (φ_m) increased up to threefold with decreasing day length. α^B increased almost four-fold with decreasing irradiance, whereas φ_m was independent of irradiance. Literature data for phytoplankton indicate that P_m^B consistently increases with increasing irradiance, and day length-irradiance responses of α^B and φ_m are species specific. Results from the present experiment and other studies indicate that if day length-irradiance variability in the photosynthetic parameters are neglected, this may cause an over- or underestimation up to a factor of two in the photosynthetic rate estimation based on these parameters.