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141.
142.
Laminaria longicrucis De la Pylaie took up exogenous nitrate under both summer and winter conditions. During July and August no NO3- was detected in the ambient water or in algal tissues although it was present in both in February. Discs (2.3 cm diam.) of thin blade tissue were incubated with NO3- at four temperatures, with and without illumination. Similar values Jor NO3- uptake were found for both summer and winter collected plants when measured in light at 0 C. An apparent K of 4–6 μM was recorded for both types of plants; the Vmax ranged from 7 to 10 μmol h-1 g-1 dry wt measured in ca. 1800 μW cm-2 of cool-white fluorescent light. Uptake rates at 5 C were 66%, and at 0 C 30% of those for controls run at 15 C. The alga scavenged NO3- from solutions <0.5 μM. Ammonia did not inhibit NO3- uptake. Antibiotic pretreatment reduced NO3- uptake by a maximum of 12%. Nitrite uptake was inhibited in proportion to the concentration of NO3- in the medium. 相似文献
143.
A High cephamycin C producing strain of Nocardia lactam-durans was used to study cell growth and antibiotics production in defined media. Batch fermentations in shake flasks and stirred tanks showed that antibiotic production occurred during cell growth and the production rate rapidly decline as the growth slowed. Glutamate served as a primary substrate during this phase. Later, ammonia was utilized along with a remainder of the glucose. Rapid antibiotic production occurred in this phase. Increased glutamate promoted higher growth, a rise in ammonium ion concentration, and a marked reduction in antibiotic titers. An increase of the glucose concentration along with the glutamate concentration balanced to the medium; no ammonium ion rise occurred and a peak specific antibiotic titer comparable to the control medium was obtained. In a phosphate-limited medium, cell growth equivalent to the control medium and increased antibiotic titers were obtained. In these experiments, adjustment of Na(+) and K(+) ion concentration equal to that in the control medium was found to be important. Based on carbon and nitrogen balances, the activity of the key nitrogen metabolism enzymes, and the published literature, a two-stage model of regulation is suggested. 相似文献
144.
Nutrient enrichment experiments in three central Florida lakes of different trophic states 总被引:1,自引:1,他引:0
Seasonal nutrient enrichment experiments (short-term bioassays) were conducted in three Florida lakes of different trophic
states to determine the effects of addition of various nutrient combinations upon chlorophyll a and phytoplankton standing crops. Nutrient enriched surface water samples with crustacean zooplankton removed were incubated
in situ in clear polyethylene bags for 3 to 6 days. The 25 factorial design employed two levels (ambient and enriched) of each of five nutrients [NH4
+, PO
inf4
sup3−
, Fe− -EDTA, SiO
inf3
sup2−
and a cation (Ca2+ or K+) or trace elements]. Ammonium produced significant increases in chlorophyll a and phytoplankton standing crops in all experiments. Phosphate produced similar results in the mesotrophic lake, but the
eutrophic lakes had both positive and nonsignificant responses which varied seasonally between lakes. Iron increased chlorophyll
a in most experiments but affected total phytoplankton standing crop only during the summer and fall. Silicon had negative
effects in some experiments. Cations and trace elements produced marked differences between lakes for chlorophyll a, but total phytoplankton standing crop showed few significant responses. Synergistic responses to two- and three-factor interactions
were observed in all lakes. Differences in the responses of phytoplankton taxonomic divisions to enrichment may be responsible
for much of the between lake variation in chlorophyll a and total phytoplankton volume responses. Nutrient limitations in these lakes are discussed and related to limnological factors
and predictive models. 相似文献
145.
Bledius (Elbidus) bicornis (Germ.) and B. (Eucerotobledius) furcatus (Oliv.) (Coleoptera: Staphylinidae) are the most important burrowing species in the emergent areas and shores in the athalassic
lake of Fuente de Piedra (Málaga, S. of Spain).
A first estimate of the importance of these organisms in this system is presented. These insects kick out sediment during
their burrowing activity, which accumulates on the surface near the burrows as tumuli which can be easily eroded. The lake
perimeter (17 km) is densely colonized (usual densities from 1700 to 2500 ind m−2). The amount of granulated material that can be potentially kicked out was 46.22 g dry wt m−2 day−1. At the same time, the material that constitutes the tumuli shows different characteristics from the compact ground below
the surface. Thus, it is relatively enriched with organic matter (6.15 g per square meter), soluble phosphate (406.5 μg m−2) and ammonium (4856 μg m−2), whereas it lacks nitrate. Results of a transect from uninhabited areas to zones of maximum population density also show
a similarity between the higher ground level of ammonium and phosphate concentrations and population density. 相似文献
146.
An enclosure experiment was conducted to assess the effects of a zooplankton elimination on the structure of a phytoplankton community. Phytoplankton biomass and production were higher in grazer-free enclosures, while the productivity per unit biovolume was lower. Exclusion of zooplankton favoured the majority of algal species, especially chrysophyceans (Dinobryon spp.) and the diatom Rhizosolenia, while mucilagineous green-algae were disfavoured. Middle sized algae (ESD 15–50 µm) and those with the largest Surface Area/Volume ratio were proportionally most favoured by the elimination of grazers.These differences in phytoplankton community structure are discussed in relation to effects of direct selective grazing and nutrient recycling by zooplankton. Some differences, as the immediate positive response of Dinobryon and Rhizosolenia, are probably caused by grazing release, while others, e.g. the response of mucilagineous species, might be caused by changed competitive relationships between the algae. 相似文献
147.
R. De Philippis C. Sili G. Tassinato M. Vincenzini R. Materassi 《Bioresource technology》1991,38(2-3)
Batch cultures of Cyanospira capsulata, a heterocystous cyanobacterium possessing a thick polysaccharidic capsule, were characterized by increasing viscosity owing to the continuous release of a soluble polysaccharide (EPS) into the culture medium. Both capsulated trichomes and solubilized EPS contributed to the flow properties of whole cultures. A typical pseudoplastic behaviour, the more marked the more aged were the cultures, was evidenced.The production of EPS was investigated under different growth conditions by changing some nutritional and physical parameters known to affect the synthesis of exopolysaccharides in algae and cyanobacteria. Among the factors tested (Ca2+, Mg2+ or PO4−4 deficiencies, salinity and pH) only Mg2+ shortage caused a significant enhancement of the EPS production. Under continuous illumination in open ponds, the EPS productivity of batch cultures on standard mineral medium was about 5·8 g m−2 day−1, whereas under Mg2+ deficiency with a consequent increase of the cultures' viscosity 相似文献
148.
149.
茶园冬季乔木落叶的分解和矿质元素释放 总被引:1,自引:0,他引:1
在我国南方存在着一种传统植茶方式——茶林复合生态系统,近年来人们已逐步认识到它在维持土壤肥力,抗御自然灾害和保证茶叶内质特性等方面的作用,然而对冬季乔木落叶分解和矿质元素释放的作用尚无报道。本文是对安徽省黄山市休宁县茶树-乌桕复合园和茶树-板栗复合园的冬季乔木落叶分解的研究,为全面认识茶林复合生态系统的性质提供依据。 相似文献
150.
The degradation of plant material was studied in order to obtain degradation coefficients and nutrient release kinetics of the vegetation that will be submerged during the filling of the future Parana Medio man-made lake. A group of 13 plant species representative of the whole vegetation of the area were chosen.The plant samples (submerged at 2.5–4 m in the Setubal lagoon), were periodically analyzed during 97 days. The experimental data were fitted to an exponential decomposition model. The plants were classified according to their velocities of degradation into three groups: fast (K>0.01), mean (0.01>K>0.005) and slow (K<0.005). The curves of release of P, N, Ca, Mg, Na and K in function of time are presented and discussed. 相似文献