Frond development and phenology of Thelypteris limbosperma, Athyrium distentifolium, and Matteuccia struthiopteris in Western Norway

Odland, A. 1995. Frond development and phenology of Thelypteris limbosperma, Athyrium distentifolium, and Matteuccia struthiopteris in Western Norway. — Nord. J. Bot. 15: 225–236. Copenhagen. ISSN 0107–055X. The pattern of growth and phenology of Thelypteris limbosperma, Athyrium distentifolium, and Matteuccia struthiopteris fronds has been investigated, with particular emphasis on height increments of the sporophytes and the development of fertile fronds. In order to study both interspecific and intraspecific differences, fern stands along altitudinal gradients have been monitored. To investigate the initiation of fertility, fronds representing different developmental stages have been sampled. Climatic data have been collected with a data-logger during the study periods. The ferns show significant differences in growth pattern and phenology. Matteuccia struthiopteris has a growth curve that is best described as monomolecular, characterised by high growth rates during the early developmental stage, while the development of Thelypteris limbosperma and Athyrium distentifolium follow a logistic growth curve. The species need different periods of time to develop their fronds. The main frond elongation does not start before soil temperature has reached 7 C. After that, the growth is mainly controlled by air temperature. Within the interval when mean maximum temperatures are 8–20 C, all three ferns showed increased growth rates with increasing air temperatures, but the increase was greatest in M. struthiopteris. At higher temperatures, the growth rate of M. struthiopteris and T. limbosperma decreased. Athyrium distentifolium is characterised by producing sori at an early developmental stage. Fertile Matteuccia strurhiopteris fronds are developed at a much later developmental stage. Thelypteris limbosperma needs a longer period of time to produce mature fronds than the other species. The investigation indicates that plant growth and development are determined by both internal and external factors. It is concluded that growth rate, phenology, and the ability of ferns to produce mature fronds reveal close similarities with their response to environmental variables, and hence with their broad-scale geographical distributional patterns.     

Ammonia-nitrogen excretion in Daphnia pulex

Ammonia-nitrogen excretion rates were measured in natural summer and cultured populations of Daphnia pulex from Silver Lake, Clay County, Minnesota, USA during 1973. The mean rate of ammonia-nitrogen excretion for the summer populations was 0.20 µg N animal^–1 day^–1 or 5.11 µg N mg^–1 dry body weight day^–1 (N = 80) measured at 15°, 20°, and 25°C. These rates appear to be temperature and weight dependent, but they are probably affected by factors other than temperature and dry body weight. Ammonia-nitrogen excretion rates of Daphnia pulex cultured on Chlamydomonas reinhardi yielded the following relationship with temperature: Log₁₀E = (0.061) T 1.773, where E is µg N animal^–1 day^–1 and T is temperature °C. The ammonia-nitrogen excretion on a mg^–1 dry body weight day^–1 basis was related to temperature according to the following similar expression Log₁₀E = (0.043) T + 0.153, where E is µg N mg^–1 dry body weight day^–1, and T is temperature °C. The length-weight relationship of Daphnia pulex for the summer populations (N = 1583) was log₁₀W = (0.526) Log₁₀L + 1.357, where W is weight in µg and L is length in mm.     

Rotifer distribution in relation to temperature and oxygen content

Lunzer Obersee, a small lake located at an altitude of 1100 m above sea level, was investigated from July 1985 to October 1987. The rotifer community consists of 7 dominant species, 7 subdominant species and 34 species which occasionally occurred in the plankton. The dominant species show rather different demands in relation to temperature and oxygen content; e.g.: Filinia hofmanni was found at a wide range of oxygen concentrations (0.6–13.3 mg O₂l^–1) and low temperatures (4–6 °O, living in the upper water layers (1–7 m) during spring and in the deeper, anoxic zone in summer. In contrast, Asplanchna priodonta was found at rather high oxygen contents (> 9 mg O₂ l^–1), ), and showed a wide range of temperature tolerance (4–15 °C).On the basis of field data the temperature and oxygen requirements of several species are described and discussed.     

Evaporative cooling and endothermy in the 13-year periodical cicada,Magicicada tredecem (Homoptera: Cicadidae)

Summary The thermobiology of a cicada, Magicicada tredecem, from a warm, high humidity environment was investigated. Thoracic temperature (T_th) of M. tredecem in the field was strongly dependent on, and consistently higher than, ambient temperature (T_am), averaging 33.0±0.19°C on warm sunny days (T_am=28–29°C, rh=60–75%). Laboratory studies documented cuticle water fluxes high enough ( 5mg · cm^–2 · h^–1 in dry air at 40°C) to result in a significant degree of passive evaporative cooling, but the ability of M. tredecem to actively facilitate evaporative water loss during thermal stress is comparatively limited: water loss rates (WLR) of live M. tredecem at 40°C (dry air) were only 35–45% greater than those of dead cicadas. The limited ability of M. tredecem to facilitate transcuticular WLR is associated with limited surface distribution of the cuticular ducts through which water is actively extruded during evaporative cooling. In the laboratory, active extrusion of water had no appreciable effect on T_th, demonstrating that evaporative cooling was due largely to passive water flux through the highly permeable cuticle. The location of the abdominal pore tracts is such that extrusion of water through the ducts may preferentially cool the heart and perhaps other abdominal tissues. Long-term climatological data indicate that M. tredecem rarely encounters T_am levels high enough (i.e., above its apparent T_th setpoint of 34–35°C) to require evaporative cooling. Inactive M. tredecem can endothermically increase T_th. An hypothesis is proposed to account for the diversity of body temperature setpoints in cicadas.Abbreviations rh relative humidity - SOT standard operating temperature - T _am ambient temperature - T _b body temperature - T _sp body temperature setpoint - T _th thoracic temperature - TWF transcuticular water flux - WLR water loss rate     

A synecological investigation of Matteuccia struthiopteris — dominanted stands in Western Norway

This investigation is based on phytosociological and ecological analyses of stands dominated by M. struthiopteris within its main distributional area in Western Norway. The distribution and floristical composition of such stands are related to different environmental parameters such as regional climate, soil and topography. The data are analysed by numerical methods, of which two-way indicator species analysis (TWINSPAN), canonical correspondence analysis (CCA), and simple discriminant functions (DISCRIM) are the most useful. Few stands occur in areas where the mean July temperature is below 12.0 °C, and where the mean January temperature is higher than 0 °C. The soil is rich in metal cations, with a base saturation mostly higher than 50% in the B-layer. Based on a TWINSPAN classification of the 230 investigated stands, 9 different groups (types) are distinguished. Many stands have a tree layer of Alnus incana, while stands with a canopy of Betula pubescens, Fraxinus excelsior and Ulmus glabra are considered to be marginal sites for M. struthiopteris. The types described are interpreted as belonging to the Pruno padi-Alnetum incanae, Alno incanae-Fraxinetum excelsioris and Alno incanae-Ulmetum glabrae associations within the Alno-Ulmion alliance. The floristic composition of the quadrats is highly correlated with the altitude/temperature gradient. The other important factor is interpreted to be soil moisture. Soil richness is poorly correlated with the floristic composition of the different stands. Several stands represent a regeneration stage after cessation in cultivation, while others appear to have been very little influenced by human activity.     

Freeze or dehydrate: only two options for the survival of subzero temperatures in the arctic enchytraeid<Emphasis Type="Italic"> Fridericia ratzeli</Emphasis>

Hygrophilic soil animals, like enchytraeids, overwintering in frozen soil are unlikely to base their cold tolerance on supercooling of body fluids. It seems more likely that they will either freeze due to inoculative freezing, or dehydrate and adjust their body fluid melting point to ambient temperature as has been shown for earthworm cocoons and Collembola. In the present study we tested this hypothesis by exposing field-collected adult Fridericia ratzeli from Disko, West Greenland, to freezing temperatures under various moisture regimes. When cooled at –1 °C min^–1 under dry conditions F. ratzeli had a mean temperature of crystallisation (T_c) of –5.8 °C. However, when exposed to temperatures above standard T_c for 22 h, at –4 °C, most individuals (90%, n= 30) remained unfrozen. Slow cooling from –1 °C to –6 °C in vials where the air was in equilibrium with the vapour pressure of ice resulted in freezing in about 65% of the individuals. These individuals maintained a normal body water content of 2.7–3.0 mg mg^–1 dry weight and had body fluid melting points of about –0.5 °C with little or no change due to freezing. About 35% of the individuals dehydrated drastically to below 1.1 mg mg^–1 dry weight at –6 °C, and consequently had lowered their body fluid melting point to ca. –6 °C at this time. Survival was high in both frozen and dehydrated animals at –6 °C, about 60%. Approximately 25% of the animals (both frozen and dehydrated individuals) had elevated glucose concentrations, but the mean glucose concentration was not increased to any great extent in any group due to cold exposure. The desiccating potential of ice was simulated using aqueous NaCl solutions at 0 °C. Water loss and survival in this experiment were in good agreement with results from freezing experiments. The influence of soil moisture on survival and tendency to dehydrate was also evaluated. However, soil moisture ranging between 0.74 g g^–1 and 1.15 g g^–1 dry soil did not result in any significant differences in survival or frequency of dehydrated animals even though the apparent wetness and structure of the soil was clearly different in these moisture contents.Abbreviations DW dry weight - FW fresh weight - MP melting point - RH relative humidity - Tc crystallisation temperatures - WC water contentCommunicated by I.D. Hume     

Ecological studies of Chloroflexis,a gliding photosynthetic bacterium

Summary Chloroflexis, a gliding, filamentous, photosynthetic bacterium, is present in the stratified algal-bacterial mats which occur in the 50°–70°C temperature range of alkaline hot spring effluents. The organism is in association with the alga in the upper, algal layer, and also forms thick, orange mats beneath the algal layer. Natural populations of Chloroflexis from these mats demonstrated light-stimulated uptake of some ¹⁴C-labelled organic compounds. Photosynthetic ¹⁴CO₂ fixation by natural samples of Chloroflexis was investigated with respect to temperature, light intensity and mat depth. Bacterial photosynthesis was determined in samples in which algae were present by use of the inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). Bacterial photosynthesis was maximal at depths down to about 3 mm and then decreased rapidly to very low levels at greater depths. The greatest amounts of bacteriochlorophyll pigments were also concentrated in the top 3–4 mm of the mat. The optimum light intensity for bacterial photosynthesis (about 400 ft-c) was considerably lower than the normal summer light intensity at the surface of the mat (5000-8000 ft-c).The temperature optima for photosynthesis by the bacterial component of natural mat samples from several sites of different temperatures in a hot spring thermal gradient were determined. Temperature optima approximated the environmental temperatures, indicative of the occurrence of strains of Chloroflexis adapted to different temperatures. Although bacterial standing crop was greatest in the temperature range 50°–55°C, maximum photosynthetic efficiency was observed at about 45°C. Sulfide was stimulatory to photosynthetic ¹⁴CO₂ fixation by naturally occurring populations of Chloroflexis under field conditions. These data are consistent with the hypothesis that Chloroflexis may utilize sulfide as an electron donor for photosynthetic CO₂ reduction. However, it is also likely that Chloroflexis grows photoheterotrophically in these mats, obtaining organic compounds from algal excretory products.     

Photosynthetic performance of transplanted ecotypes ofEcklonia cava(Laminariales, Phaeophyta)

Young sporophytes of short-stipe ecotype ofEcklonia cavafrom a warmer locality (Tei, Kochi Pref., southern Japan) and those of long-stipe ecotype from a cooler locality (Nabeta, Shizuoka Pref., central Japan) were transplanted in 1995 to artificial reefs immersed at the habitat of long-stipe ecotype in Nabeta Bay, Shizuoka Pref., central Japan. The characteristics of photosynthesis and respiration of bladelets of the transplanted sporophytes of the two ecotypes were compared in winter and summer 1997; the results were assessed per unit area, per unit chlorophyllacontent and per unit dry weight. In photosynthesis-light curves at 10–29 °C, light saturation occurred at 200–400 mol photon m^–2s^–1in sporophytes from both Tei and Nabeta. The maximum photosynthetic rate (P _max) at 10–29 °C and the light-saturation index (I _k) at 25–29 °C in sporophytes from both localities were generally higher in winter than in summer.P _maxat 25–29 °C (per unit area and chlorophylla) were higher in sporophytes from Tei than those from Nabeta in both seasons. The optimum temperature for photosynthesis was 25 °C in winter and 27 °C in summer at high light intensities of 100–400 mol photon m^–2s^–1. However, at lower light intensities of 12.5–50 mol photon m^–2s^–1, it was 20 °C in winter and 25–27 °C in summer for sporophytes from both locations. Dark respiration increased with temperature rise in the range of 10–29 °C in sporophytes from both locations in summer and winter. The sporophytes transplanted from Tei (warmer area) showed higher photosynthetic activities than those from Nabeta (cooler area) at warmer temperatures even under the same environmental conditions. This indicates that these physiological ecotypes have arisen from genetic differentiation.     

城市湖泊湿地温湿效应——以武汉市为例

选择武汉城市三环内主城区14块湖泊湿地为研究对象,采用小尺度定量测定的方法,研究城市湖泊湿地与温湿效应间的关系。结果表明:(1)城市湿地温度值与面积指数、距离指数呈显著负相关,与景观形状指数呈显著正相关(P0.05);湿度值与面积指数、距离指数、环境类型指数呈显著正相关,与景观形状指数呈显著负相关(P0.05)。其中面积指数的贡献值最大。(2)14块湖泊湿地的降温增湿效应排序为湖泊11—14湖泊6—10湖泊1—5。当湖泊湿地面积为9.2—12.2 hm2时,其降温增湿效应明显;当湖泊湿地面积为308.4hm2左右时,降温效应显著且趋于稳定,湖泊湿地面积为67.6hm2左右时,增湿效应显著且趋于稳定(P0.05)。当湖泊湿地面积达到临界值之后,多斑块离散型(Dispersive)湖泊湿地布局对整个城市环境的降温增湿效应更为显著。     

Rapid atrazine mineralisation in soil slurry and moist soil by inoculation of an atrazine-degrading Pseudomonas sp. strain

The evaluation of pesticide-mineralising microorganisms to clean-up contaminated soils was studied with the widely applied and easily detectable compound atrazine, which is rapidly mineralised by several microorganisms including the Pseudomonas sp. strain Yaya 6. The rate of atrazine removal was proportional to the water content of the soil and the amount of bacteria added to the soil. In soil slurry, 6 mg atrazine kg soil⁻¹ was eliminated within 1 day after application of 0.3 g dry weight inoculant biomass kg soil⁻¹ and within 5 days when 0.003 g kg soil⁻¹ was used. In partially saturated soil (60% of the maximal water-holding capacity) 15 mg atrazine kg soil⁻¹ was eliminated within 2 days by 1 g biomass kg soil⁻¹ and within 25 days when 0.01 g biomass kg soil⁻¹ was used. In unsaturated soil, about 60% [U-ring-¹⁴C]atrazine was converted to ¹⁴CO₂ within 14 days. Atrazine was very efficiently removed by the inoculant biomass, not only in soil that was freshly contaminated but also in soil aged with atrazine for up to 260 days. The bacteria exposed to atrazine in unsaturated sterile soil were still active after a starvation period of 240 days: 15 mg newly added atrazine kg soil⁻¹ was eliminated within 5 days. Received: 31 October 1997 / Received revision: 16 January 1998 / Accepted: 18 January 1998     

Optimisation of reaction conditions for production ofS-(−)-2-hydroxypropiophenone byAcinetobacter calcoaceticus

Summary Whole cells and cell-free extracts ofAcinetobacter calcoaceticus containing benzoylformate decarboxylase efficiently condensed benzoylformate and acetaldehyde to produce the acyloin compoundS-(–)-2-hydroxypropiophenone. Optimal concentrations of acetaldehyde cosubstrate for this reaction were found to be 1600 and 800 mM when whole cells and cell-free extracts were used respectively as biocatalysts. In both cases, optimal benzoylformate concentration was 100 mM. Temperature and pH optima for the biotransformation reaction were 30°C and 6.0 respectively. Under optimised conditions, maximum production of 2-hydroxypropiophenone, amounting to 8.4 g L^–1, occurred after a 2-h incubation. Product formation equivalent to 6.95 g in 1 h corresponded to a productivity of 267 mg acyloin per g dry cells per h.     

Drinking rates and Na+ effluxes in response to temperature change in two species of marine flatfish: dab,Limanda limanda and plaice,Pleuronectes platessa

The relationship between fish mass and drinking rate in two species of flatfish, dab and plaice, weighing between 1 and 150 g was investigated. Both plaice and dab showed increased drinking rates with increasing fish mass, although — when calculated on a weight-specific basis — the increase was negligible. Fish were acclimated to winter and summer temperatures of 9 and 14°C, respectively. In winter both species were acutely transferred to 5, 14 and 21°C and in summer to 5, 9, 21 and 25°C. Drinking rates, Na⁺ efflux and body ion content were measured. Dab showed lower drinking rates than plaice (e.g. the weight-specific drinking rates of summer-and winter-acclimated dab were 0.12±0.01 and 0.06±0.006 ml·h^-1·100 g^-1, respectively, compared to that of plaice which were 0.25±0.02 ml·h^-1·100 g^-1 in summer and 0.17±0.02 ml·h^-1·100g^-1 in winter). Summer dab exhibited decreased weight-specific drinking rates at 5, 9 and 25°C, while winter dab increased drinking at 21°C. Winter plaice also showed increased drinking at 21°C and a decrease at 5°C, but in contrast summer plaice did not increase drinking at either 21 or 25°C but showed a decrease at 5 and 9°C. Winter dab and plaice showed similar Na⁺ efflux rates but summer dab showed higher efflux at all temperatures except 5°C. The data indicates that (a) the osmoregulatory function of plaice is much weaker than that of dab at higher temperatures (>20°C) and (b) mass has a greater effect on drinking and Na⁺ efflux rates than temperature; although when calculated on a weight-specific basis neither drinking nor efflux showed any variation with fish mass suggesting that these functions occur at similar intensities across the entire weight range.Abbreviations ANOVA analysis of variance - ⁵¹Cr-EDTA ⁵¹chromium ethylenediaminetetra-acetic acid - SW sea water     

Bioremediation (Natural Attenuation and Biostimulation) of Diesel-Oil-Contaminated Soil in an Alpine Glacier Skiing Area

We investigated the feasibility of bioremediation as a treatment option for a chronically diesel-oil-polluted soil in an alpine glacier area at an altitude of 2,875 m above sea level. To examine the efficiencies of natural attenuation and biostimulation, we used field-incubated lysimeters (mesocosms) with unfertilized and fertilized (N-P-K) soil. For three summer seasons (July 1997 to September 1999), we monitored changes in hydrocarbon concentrations in soil and soil leachate and the accompanying changes in soil microbial counts and activity. A significant reduction in the diesel oil level could be achieved. At the end of the third summer season (after 780 days), the initial level of contamination (2,612 ± 70 μg of hydrocarbons g [dry weight] of soil⁻¹) was reduced by (50 ± 4)% and (70 ± 2)% in the unfertilized and fertilized soil, respectively. Nonetheless, the residual levels of contamination (1,296 ± 110 and 774 ± 52 μg of hydrocarbons g [dry weight] of soil⁻¹ in the unfertilized and fertilized soil, respectively) were still high. Most of the hydrocarbon loss occurred during the first summer season ([42 ± 6]% loss) in the fertilized soil and during the second summer season ([41 ± 4]% loss) in the unfertilized soil. In the fertilized soil, all biological parameters (microbial numbers, soil respiration, catalase and lipase activities) were significantly enhanced and correlated significantly with each other, as well as with the residual hydrocarbon concentration, pointing to the importance of biodegradation. The effect of biostimulation of the indigenous soil microorganisms declined with time. The microbial activities in the unfertilized soil fluctuated around background levels during the whole study.     

Influence of root temperature on growth of Pinus sylvestris,Fagus sylvatica,Tilia cordata and Quercus robur

One-year-old tree seedlings were incubated in a greenhouse from April to July, under natural daylight conditions, with their root systems at constant temperatures of 5, 10, 15, 20, 25, 30 and 35 °C and with the above ground parts kept at a constant air temperature of 18–20 °C. The course of height growth, total mass increment, root, shoot and leaf weight as well as leaf areas were measured. The results indicate that clear differences exist in the optimal root zone temperatures for various growth parameters in different tree species. Pinus sylvestris had a maximal height increment at about 5–10 °C and maximal total mass increment at 15 °C root temperature. In contrast, the optimum for Quercus robur was at 25 °C. Tilia cordata and Fagus sylvatica had their optima for most growth parameters at 20 °C. The root temperature apparently indirectly influenced photosynthesis (dry weight accumulation) and respiration loss. From the observed symptoms and indications in the literature it seems probable that a change in hormone levels is involved as the main factor in the described effects. Variation of root temperature had only an insignificant effect on bud burst and the time at which the shoots sprouted. Apparently species of northern origin seem to have lower root temperature optima than those of more southern origin. This is to be verified by investigation of other tree species.     

Transient changes in transpiration, and stem and soil CO2 efflux in longleaf pine (Pinus palustris Mill.) following fire-induced leaf area reduction

In 20-year-old longleaf pine, we examined short-term effects of reduced live leaf area (A _L) via canopy scorching on sap flow (Q; kg H₂O h⁻¹), transpiration per unit leaf area (E _L; mm day⁻¹), stem CO₂ efflux (R _stem; μmol m⁻² s⁻¹) and soil CO₂ efflux (R _soil; μmol m⁻² s⁻¹) over a 2-week period during early summer. R _stem and Q were measured at two positions (1.3-m or BH, and base of live crown—BLC), and R _soil was measured using 15 open-system chambers on each plot. E _L before and after treatment was estimated using Q measured at BLC with estimates of A _L before and after scorching. We expected Q to decrease in scorched trees compared with controls resulting from reduced A _L. We expected R _stem at BLC and BH and R _soil to decrease following scorching due to reduced leaf area, which would decrease carbon supply to the stem and roots. Scorching reduced A _L by 77%. Prior to scorching, Q at BH was similar between scorch and control trees. Following scorching, Q was not different between control and scorch trees; however, E _L increased immediately following scorching by 3.5-fold compared to control trees. Changes in E _L in scorched trees corresponded well with changes in VPD (D), whereas control trees appeared more decoupled over the 5-day period following treatment. By the end of the study, R _stem decreased to 15–25% in scorched trees at both stem positions compared to control trees. Last, we found that scorching resulted in a delayed and temporary increase in R _soil rather than a decrease. No change in Q and increased E _L following scorching indicates a substantial adjustment in stomatal conductance in scorched trees. Divergence in R _stem between scorch and control trees suggests a gradual decline in stem carbohydrates following scorching. The absence of a strong R _soil response is likely due to non-limiting supplies of root starch during early summer.     

Gas exchange characteristics and temperature relations of two desert annuals: A comparison of a winter-active and a summer-active species

Summary The gas exchange characteristics of two C₃ desert annuals with contrasting phenologies, Geraea canescens T. & G. (winter-active) and Dicoria canescens T. & G. (summer-active), both Asteraceae, were determined for plants grown under a moderate (25°/15° C, day/night temperature) and a high (40°/27° C) growth temperature regime. Both species had high photosynthetic capacities; maximum net photosynthetic rates were 38 and 48 mol CO₂ m^-2 s^-1 for Geraea and Dicoria, respectively, and were not influenced by growth temperature regime. However, the temperature optima of net photosynthesis shifted from 26° C for Geraea and from 28° C for Dicoria when grown under the moderate temperature regime to 31° C for both species when grown under the high temperature regime. Although the shifts in temperature optima were smaller than those observed for many desert perennials, both species showed substantial increases in photosynthetic rates at high temperatures when grown at 40°/27° C. In general, the gas exchange characteristics of Geraea and Dicoria were very similar to each other and to those reported for other C₃ desert annuals. Geraea and Dicoria experienced different seasonal patterns of change in several environmental variables. For Geraea, maximum daily air temperature (T _a) increased from 24° to 41° C over its growing season while Dicoria experienced maximum T _a at midseason (45° C). At points during their respective growing seasons when midday T _a ranged between 35° and 40° C, leaf temperatures (T ₁) of both species were below T _a and, therefore, were closer to the photosynthetic temperature optima measured in the laboratory. Leaf conductances to water vapor (g ₁) and water potentials () were high at these times, but later in their growing seasons Dicoria maintained high g ₁ and while Geraea showed large decreases in these quantities. The ability of Dicoria to successfully growth through the hot, dry summers of the California deserts may be related to its ability to acquire the available water in locally mesic habitats.     

Respiration, nutrient excretion and filtration rate of tropical freshwater mussels and their contribution to production and energy flow in Lake Kariba, Zimbabwe

The productivity and ecological role of benthos in man-made Lake Kariba was assessed through the use of P/B-ratios and by measuring the metabolism (respiration, N and P excretion) of the most abundant mussel species (Aspatharia wahlbergi, Corbicula africana and Caelatura mossambicensis) in laboratory experiments. For A. wahlbergi also filtration rate was estimated.The annual production of benthos for the populated 0–12 m interval was estimated at 11.0 g m ^–2 yr^–1 (shellfree dry weight) of which mussels contributed for 8.81 g (80%), snails 2.16 g (20%) and insects 0.03 g (0.3%) respectively. The most important mussel species in the lake were Caelatura mossambicensis (4.97 g m^–2 yr^–1) and Corbicula africana (3.33 g). The dominant snail species was Melanoides tuberculata (1.63 g). For the total lake, also including deeper unpopulated bottoms, the annual production of benthos was 2.70 g m^–2 yr^–1 (shell-free dry weight).Respiration and excretion varied with temperature displaying a bell-shaped relationship. Metabolic rates in Aspatharia wahlbergi increased about 5× between 16.5 °C and the maximum at 34.0 °C and then decreased again at 39.0 °C, when the mussels showed signs of severe stress. Metabolism in Corbicula africana had a lower optimum with fairly constant activity between 18.6 and 29.2 °C, rapidly decreasing above this temperature.The average respiration, nutrient excretion and water filtration rates for mussels in Lake Kariba at 25.2 °C were estimated to about 0.6 mg O₂ 85 µg NH₄–N, 1.5 µg PO₄–P and 0.51 water filtered h^–1 g^–1 shellfree dry weight. This gives that a volume corresponding to about the total epilimnion of the lake is filtered by the mussels annually. Further, mussels can be estimated to remineralise % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaGymaiaac+% cacaaI0aaaaa!3A2B!\[1/4\] of the total load of phosphate, and 8 times the total load of nitrogen every year. The population needs 3.5 × 10⁴ tons of organic carbon for its maintainance, which indicates that about 5% of the annual phytoplankton production is channeled through mussels. We conclude that the mussels, rather than being an important food source for fish, seem to play a large role in the nutrient dynamics of Lake Kariba.     

Production of constitutive, thermostable, hyper active exo-pectinase from Bacillus GK-8

Summary A new alkalophilic Bacillus GK-8 overproduced three thermostable extracellular pectinases. The temperature optima was 60°C for all the three enzymes which retained full activity for 2 h. They had pH optima 5.4, 7.0 and 10.4 and were designated as PI, PII and PIII respectively. The half life at 80°C of PI, PII and PIII was 18 min., 12 min. and 12 min., respectively. The enzyme activity was stimulated by Mg²⁺, Ca²⁺, Zn²⁺, Co²⁺ and Mn²⁺ ions.     

INFLUENCE OF IRRADIATION,SOIL WATER POTENTIAL,AND LEAF TEMPERATURE ON LEAF MORPHOLOGY OF A DESERT BROADLEAF,ENCELIA FARINOSA GRAY (COMPOSITAE)

Laboratory experiments were performed to evaluate observed seasonal changes in leaf morphology of the desert perennial shrub, Encelia farinosa Gray. Plants were grown under low or high conditions of photosynthetically active irradiation, soil water potential (Ψ^soil), and leaf temperature (8 different experimental regimes). The relative growth rate, leaf water vapor conductance, leaf water potential, and leaf length were all greater for the high Ψ^soil regimes, the largest leaves occurring at low irradiation. High irradiation during growth led to thicker leaves with a higher internal to external leaf area ratio (A^mes/A); low Ψ^soil tended to increase A^mes/A somewhat. High irradiation also led to decreased absorptance to solar irradiation caused by increased pubescence. High leaf temperature during development resulted in slightly smaller, thicker leaves with higher A^mes/A. Thus, irradiation appeared to have its major influence on leaf thickness, A^mes/A, and absorptance, with a secondary effect on leaf length; Ψ^soil affected primarily leaf length, growth rate, and water status, and secondarily A^mes/A. Results are discussed with regard to recent ecophysiological studies on the observed seasonal changes in leaf morphology of E. farinosa.     

Microhabitat,water relations,and photosynthesis of a desert fern,Notholaena parryi

Summary Interrelationships between morphology, microhabitat, water relations, and photosynthesis of a xeric fern, Notholaena parryi D.C. Eat. (Pteridaceae), were examined in the western Colorado desert. In its typical microhabitat rock outcroppings protected N. parryi from direct sunlight and moderated the diurnal variations in air temperature. For example, frond temperature at noon in late winter was 15.3° C, which was 7.3° C cooler than an energy budget simulation predicting frond temperature at an exposed site. The lowest soil water potential leading to daytime stomatal opening was about-1.5 MPa (-15 bars). Rainfall runoff that was channeled to the periphery of the rocks caused ^soil near the fern roots to rise above-1.5 MPa even after light rainfalls, and it remained above-1.5 MPa longer after rainfall than in non-rocky sites.The water potential gradient along the stipe necessary to support the observed rates of transpiration was about-10 MPa m^-1; such a large gradient reflected the small conducting area in the xylem. The water vapor conductance decreased as the frond temperature was raised, an effect that became proportionally greater as the soil dried out. The daytime water-use efficiency (mass CO₂ fixed/mass water transpired) was 0.0058 for a spring day. Individual fronds reached 90% of light saturation for photosynthesis at only 100 Einsteins m^-2 s^-1, a photosynthetically active radiation similar to that from the diffuse sunlight incident on the generally north-facing microhabitat of the fern. Below 50 E m^-2 s^-1 the quantum requirement was 13 Einsteins absorbed/mole CO₂ fixed. The ratio of chlorophyll to P700 was 552, indicating a fairly large photosynthetic unit that is characteristic of plants adapted to shaded habitats. The temperature optimum for net photosynthesis shifted from 13° C in midwinter (mean daily air temperature of 11° C) to 19° C in early fall (air temperature of 23° C).