Ecological energetics of a daphnia ambigua population

Based on population data, growth and development rate, and feeding and respiratory rates, energy budgets were constructed for a wild population of Daphnia ambigua Scourfield in a pond at The University of Kansas, Lawrence. The relationships between monthly efficiency of energy transfer and food or temperature were analyzed by multiple and partial correlation. Annual energy consumption, based on seston concentration, by D. ambigua population amounted to 410.1 kcal/m³. Of this, 8.4% was used in somatic growth (Pg) and egg production (Pr); 2.7% was lost as exuvia (Pex) and 17.1% was lost in respiration (R). The amount of energy consumed lost as ammonia excretion and faeces was 1.4 and 70.4%, respectively. The total annual energy flow (assimilation) was 115.6 kcal/ m³; annual assimilation efficiency (28.2%) was lower than values reported for other planktonic Crustacea. Annual net production efficiency was 39.3% (32.8%, excluding exuvia). The annual P/R ratio was 0.64 to 0.66. The mean daily P accounted for 9.3% of the mean daily gross primary production of phytoplankton. The mean daily assimilation accounted for 23.6% of gross primary production, or 56.2% of net primary production.     

Sex differences in digestive traits in sexually size-dimorphic birds: Insights from an assimilation efficiency experiment on Black-tailed Godwit

Digestive assimilation efficiency is considered a trait with important implications for animal ecology. However, practically all studies have ignored the importance of sex differences in food assimilation efficiency (AE). Here, we investigated sex differences in dietary and physiological parameters in the Black-tailed Godwit Limosa limosa limosa feeding on rice seeds, a species with sexual dimorphism in body size and body mass. Gross daily food intake, gross energy intake, gross energy output and metabolizable energy intake did not vary significantly between sexes, but godwit females showed lower faeces energy density and higher AE than males. Mass-specific AE was similar in males and females, and the difference in AE could be attributed to the females' greater body mass. We suggest that a differential AE could play a role in explaining sex differences in habitat or micro-habitat selection during the non-breeding season in bird species with sexual dimorphism in size. Finally, we addressed the question about assimilation efficiency accuracy in models that estimate prey acquisitions by declining shorebirds as the Black-tailed Godwit.     

Primary productivity and related parameters in three different types of inland waters in Sri Lanka

Gross and net primary production together with chlorophyll-a biomass were investigated with respect to depth and diurnal changes in three categories of inland waters (reservoirs, temporary ponds, brackish water lagoons) in Sri Lanka. Ten field sites, in both the dry and wet zones of the island, were investigated. Bimodal productivity profiles were recorded in two of the three reservoirs studied. The diel pattern of net photosynthetic rate varied between sites although peak photosynthetic efficiency occurred at solar noon. Surface photoinhibition was characteristic of the reservoirs and brackish water lagoons but not of the temporary ponds. Mean gross primary production was 3.02 g C m^–2 d^–1 but was higher in the temporary ponds than in the reservoirs. The gross primary production in the brackish water Koggala Lagoon at 0.08 g C m^–2 d^–1 is a record low for tropical lagoons and was 2.5 times less than the two other lagoons investigated. Variability in net primary production between sites was similar to the variation in gross production with a relatively low mean value for tropical inland waters of 0.495 C m^–2 d^–1. Mean maximum photosynthetic rate was 0.30 mg C m^–3 h^–1 but was lower in the reservoirs than in the temporary ponds and lagoons.     

Carbon budgets for a phytoplanktivorous fish fed three different unialgal populations

Summary The filter feeding blue tilapia, Tilapia aurea, was fed three different algae. Blue tilapia ingestion of two green algae, Chlamydomonas sp. and Ankistrodesmus falcatus and the filamentous blue-green alga, Anabaena flos-aquae, ranged from 21%–89% of the available cells. There were significant differences in the assimilation of algal carbon by the fish depending on the alga fed; A. flos-aquae was the easiest to assimilate (83%). The fish respired significantly less of the Chlamydomonas sp. ingested carbon (15%). The gross growth efficiency of fishes fed either green alga was not significantly different (22%–24%), but these efficiencies were significantly less than the gross growth efficiency of fish fed A. flos-aquae (46%). The carbon budgets for fish feeding on the green algae were similar to that constructed from the literature for a congener fed a mixed algae diet. However, the assimilation component of the budget for blue tilapia fed A. flos-aquae was 2 times greater than that of the literature budget.     

Measured and modeled interactive effects of potassium deficiency and water deficit on gross primary productivity and light‐use efficiency in Eucalyptus grandis plantations

Global climate change is expected to increase the length of drought periods in many tropical regions. Although large amounts of potassium (K) are applied in tropical crops and planted forests, little is known about the interaction between K nutrition and water deficit on the physiological mechanisms governing plant growth. A process‐based model (MAESPA) parameterized in a split‐plot experiment in Brazil was used to gain insight into the combined effects of K deficiency and water deficit on absorbed radiation (aPAR), gross primary productivity (GPP), and light‐use efficiency for carbon assimilation and stem biomass production (LUE_C and LUE_s) in Eucalyptus grandis plantations. The main‐plot factor was the water supply (undisturbed rainfall vs. 37% of throughfall excluded) and the subplot factor was the K supply (with or without 0.45 mol K m^?2 K addition). Mean GPP was 28% lower without K addition over the first 3 years after planting whether throughfall was partly excluded or not. K deficiency reduced aPAR by 20% and LUE_C by 10% over the whole period of growth. With K addition, throughfall exclusion decreased GPP by 25%, resulting from a 21% decrease in LUE_C at the end of the study period. The effect of the combination of K deficiency and water deficit was less severe than the sum of the effects of K deficiency and water deficit individually, leading to a reduction in stem biomass production, gross primary productivity and LUE similar to K deficiency on its own. The modeling approach showed that K nutrition and water deficit influenced absorbed radiation essentially through changes in leaf area index and tree height. The changes in gross primary productivity and light‐use efficiency were, however, driven by a more complex set of tree parameters, especially those controlling water uptake by roots and leaf photosynthetic capacities.     

Light and assimilation number in a small desert,recharged-groundwater pond

Summary Measurements of irradiance, chlorophyll a concentration, respiration, and net and gross photosynthesis were carried out in a small desert pond containing recharged-groundwater from the Flushing Meadows water reclamation project at Phoenix, Arizona. Over the 6-month period May–October, chl. a concentration averaged 119 mg m^-3; and gross primary productivity in terms of the mean daily carbon fixation rate was 8.29 g C m^-3, which is roughly equal to productive fish and farm ponds but less than many polluted eutrophic lakes and streams. Both net and gross assimilation numbers were found to be satisfactorily represented by pure sine waves that implied total inhibition of those two processes near an underwater irradiance value of 0.32 cal cm^-2 min^-1.The maximum value of the gross assimilation number at 0.16 cal cm^-2 min^-1 of 30 mg C hr^-1 per mg chl. a ranked with some of the highest values that have been found world-wide.Joint contribution of the Department of Zoology, Arizona State University, and the Agricultural Research Service, U.S. Department of Agriculture. Portions of this work were supported by the Grace Ellis Ford Fellowship, American Association of University Women, awarded to Joyce M. Foster on July 1, 1971.     

Limnological studies of and primary production in temple pond ecosystems

Three temple ponds with permanent blooms of blue green algae were highly productive. They all showed high alkalinity, hardness, electrical conductivity and pH. Organic carbon and nitrogen were highest in Sarvatheertham pond—60 to 79.6 mg./l. C and 4.10 to 7.60 mg./l. N. In Tamaraikulam it was 16.5 to 20.3 mg. C/l. and 1.03 to 1.32 mg. N/l. In Sarvatheertham, the gross production ranged from 2.85 to 20.72 g. O₂/m.²/d. Self shading by blanket algae of blue greens reduced productivity in Sarvatheertham, where a persistent thermal and biochemical stratification was noted. Very high organic carbon and nitrogen contents were noted in Sarvatheertham pond. The dry weight of plankton in this pond ranged from 430 to 900 mg./l. Productivity computed from diurnal changes in alkalinity and dissolved oxygen also revealed a high rate in Ayyankulam, Tamaraikulam and Sarvatheertham in descending order. Very wide fluctuations in pH, both diurnally and depth-wise, were recorded in Sarvatheertham and to a lesser extent in the other two ponds. Photosynthetic efficiency was 4.03% in Ayyankulam, 2.09% in Tamaraikulam and 1.56% in Sarvatheertham. By the diurnal oxygen curve method, a gross primary production of 97.5 g. O₂/m.²/d was recorded in Ayyankulam.     

滩涂池塘生态系统的光合能量利用及其影响因子

研究了江苏沿海滩涂不同养殖模式下初级生产力特征、能量利用率及其影响因子.结果表明,滩涂养殖水体浮游植物的初级生产力存在垂直分布、日变化和季节的动态变化,这种变化与太阳辐射强度有直接的关系.滩涂养殖水体净初级生产量平均值为(7.58±2.52) gO2/(m2 · d),只占毛产量的55.41%,太阳能转化为鲢、鳙鱼产量的生态效率为0.020%～0.029%,这些指标低于我国高产养殖塘,鱼塘生态系统结构有待进一步优化.浮游植物生物量、透明度、N/P值、Mg2+浓度等因素显著影响水体初级生产力的大小,多元逐步回归表明浮游植物叶绿素含量和到达水体表面的太阳辐射强度是初级生产力的最主要因子,其回归方程为:Pg =0.0785Cha+0.0577 Iλ0+1.346;n=22, FCha>F Iλ0>F0.1,而盐度、Na+、Cl-浓度影响不显著.     

Influence of an Atypical Summer on the Primary Productivity of Phytoplankton in Two Tropical Ponds

Primary productivity of phytoplankton was measured in two fish ponds at monthly intervals during two annual cycles, of which the second one included an unusual drought. The temporal course of variations in phytoplankton primary productivity was essentially similar in both annual cycles, exhibiting peaks and troughs during summer and winter, respectively. However, monthly mean values of gross and net primary productivity of phytoplankton during the second year were several times higher than during the first. The greatest difference between the two years of investigation was found in the summer peak of primary productivity. It is estimated that an increase of nitrogen or phosphate or the N/P ratio by one unit during the second year caused a 2 to 16-fold enhancement of the rates of primary productivity. The seasonal changes of photosynthetic efficiency correlated with the concentrations of phosphate.     

Some effects of light on the energetics of Daphnia pulex and implications for the significance of vertical migration

Energy budgets were computed from data obtained for Daphnia pulex cultured under nine light intensities, polarized light and four wavelength ranges. The percent assimilation of preadult animals is highest at intensities above 7 ft-c. Net efficiency of growth was highest (> 50%) and the net efficiency of respiration was lowest ( < 49%) at intensities less than 28 ft-c. The percent assimilation of adult animals was highest ( > 10%) at 110, 55 and 14 ft-c. Under the nine intensities the gross efficiencies of growth were less than 1 % and net efficiencies of growth varied from 3.9 to 7.3%. Gross efficiencies of respiration were highest above 7 ft-c. The net efficiency of respiration usually varied between 20 and 30% and the lowest was 9.8% at 1.7 ft-c. and the highest was 50.1% at 110 ft-c. Gross efficiency of reproduction varied from 2.6% at 3.5 ft-c to 12.6% at 14 ft-c and generally varied between 4 and 7.5%. Net efficiency of reproduction varied from 45.9% at 110 ft-c to 84.3% at 1.7 ft-c and usually varied from 62 to 75% at other light intensities. The ratio of energy of respiration to energy of growth and reproduction ranged from 12% to 1.7 ft-c to 105.3% at 110 ft-c. This ratio usually varied from 25 to 34% at 14 ft-c or less and exceeded 37% at intensities above 14 ft-c. The percent assimilation (3.5%), gross (2.0%), and net (56.3%) efficiencies of respiration of preadult animals raised under polarized light were higher than for those at a similar, nonpolarized, intensity. The net efficiency of growth (43.7%) was lower under polarized light. The percent assimilation, gross efficiencies of growth, reproduction and respiration, net efficiencies of growth and reproduction of adult animals under polarized light (6.6 ft-c) were lower than for those under 7 ft-c. For preadult animals assimilation efficiencies were lower in wavelength treatments than in white light or darkness. The gross efficiencies of growth and respiration were lowest under red wavelengths and the net efficiencies of growth were lowest and respiration highest under green wavelengths. For adult animals, the assimilation efficiencies were lower in the wavelength treatments than those obtained in other light treatments. While the gross efficiencies of growth, reproduction and respiration were generally lower, the net efficiencies of growth and reproduction were generally within the range of values for other light conditions. The net efficiencies of respiration, except for red wavelengths, were lower than those for other light conditions except at 1.7 ft-c. The ratio of energy of respiration to energy of growth and reproduction showed similar trends. The effects of wavelength are generally separable from the effects of light intensity.     

Influence of gizzard shad on phytoplankton size and primary productivity in mesocosms and earthen ponds in the southeastern U.S.

Gizzard shad (Dorosoma cepedianum), a filter feeding omnivore, can consume phytoplankton, zooplankton and detritus and is a common prey fish in U.S. water bodies. Because of their feeding habits and abundance, shad have the potential to affect primary productivity (and hence water quality) directly through phytoplankton grazing and indirectly through zooplankton grazing and nutrient recycling. To test the ability of shad to influence primary productivity, we conducted a 16-day enclosure study (in 2.36-m³ mesocosms) and a 3-year whole-pond manipulation in 2–5 ha earthen ponds. In the mesocosm experiment, shad reduced zooplankton density and indirectly enhanced chlorophyll a concentration, primary productivity, and photosynthetic efficiency (assimilation number). While shad did not affect total phytoplankton density in the mesocosms, the density of large phytoplankton was directly reduced with shad. Results from the pond study were not consistent as predicted. There were few changes in the zooplankton and phytoplankton communities in ponds with versus ponds without gizzard shad. One apparent difference from systems in which previous work had been conducted was the presence of high densities of a potential competitor (i.e., larval bluegill) in our ponds. We suggest that the presence of these extremely high larval bluegill densities (20–350 larval bluegill m^–3; 3–700 times higher density than that of larval gizzard shad) led to the lack of differences between ponds with versus ponds without gizzard shad. That is, the influence of gizzard shad on zooplankton or phytoplankton was less than the influence of abundant bluegill larvae. Differences in systems across regions must be incorporated into our understanding of factors affecting trophic interactions in aquatic systems if we are to be able to manage these systems for both water quality and fisheries.     

Ecophysiological studies of Sonoran Desert plants

Summary The gas exchange and water relations of two Sonoran Desert plants was measured throughout a 12-month period. Seasonal photosynthesis patterns of both plants followed the seasonal variation in plant water potential. Ambrosia deltoidea, a drought-deciduous shrub, is mainly winter-spring active since maximum photosynthesis rates of 38 mg CO₂ dm^-2 h^-1 were measured at this time. This plant is characterized by marked seasonal variations in plant water potential, and was deciduous for approximately 120 days when plant water potential was below-50 bars. Olneya tesota, a non-riparian microphyllous tree, is evergreen and photosynthetically active throughout the entire year, although demonstrating maximum photosynthesis rates of 12 mg CO₂ dm^-2 h^-1 in spring and summer. The deep-rooted tree species maintains a favorable year-round water balance since minimum plant water potentials were seldom below-33 bars. The two species maintain a relatively high water use efficiency throughout the year, despite the high evaporative gradient characteristic of the Sonoran Desert.The leaves are the major site for carbon assimilation, contributing 87 and 81% of the annual carbon gain for the shrub and tree species, respectively. Above-ground gross primary production throughout the 12-month period was estimated solely from the leaf ¹⁴CO₂ assimilation studies. This production estimate was compared to above-ground net primary production determined by the harvest method. For both plant species gross production was interpreted to exceed net production by nearly a three-fold difference. On a per plant basis gross production was estimated to be 1.14 and 7.42 kg dry wt plant^-1 yr^-1 for A. deltoidea and O. tesota. The large difference between net and gross production is probably related to year-round utilization of carbon.This research was supported by National Science Foundation Grant BMS 74-02671-A04 through the U.S./I.B.P. Desert Biome at Utah State University     

Forest growth along a rainfall gradient in Hawaii: Acacia koa stand structure,productivity, foliar nutrients,and water- and nutrient-use efficiencies

We tested whether variation in growth of native koa (Acacia koa) forest along a rainfall gradient was attributable to differences in leaf area index (LAI) or to differences in physiological performance per unit of leaf area. Koa stands were studied on western Kauai prior to Hurricane Iniki, and ranged from 500 to 1130 m elevation and from 850 to 1800 mm annual precipitation. Koa stands along the gradient had basal area ranging from 8 to 42 m²/ha, LAI ranging from 1.4 to 5.4, and wood increment ranging from 0.7 to 7.1 tonnes/ha/year. N, P, and K contents by weight of sun leaves (phyllodes) were negatively correlated with specific leaf mass (SLM, g m^-2) across sites; on a leaf area basis, N increased whereas P and K decreased with SLM. LAI, aboveground woody biomass increment, and production per unit leaf area (E) increased as phyllode ¹³C became more negative. The ¹³C data suggested that intrinsic water-use efficiency (ratio of assimilation to conductance) increased as water availability decreased. In five of the six sites, phyllode P contents increased as LAI increased, but biomass increment and E were not correlated with phyllode nutrient contents, suggesting that productivity was limited more by water than by nutrient availability. Because vapor pressure deficits increased with decreasing elevation, actual water-use efficiency (ratio of assimilation to transpiration) was lower at drier, low-elevation sites. There was a trade-off between intrinsic water-use efficiency and production per unit of canopy N or P across the gradient. In summary, koa responds to water limitation both by reducing stand LAI and by adjusting gas exchange, which results in increased intrinsic water-use efficiency but decreased E.     

Biodiversity of settled material in a sediment trap in the Gulf of Trieste (northern Adriatic Sea)

Phytoplankton succession and sinking rates were studied from January to December 2003 at a coastal station in the Gulf of Trieste (northern Adriatic Sea), 200 m offshore, in a relatively undisturbed area. A conical sediment trap, moored at 15 m depth (water depth 17 m), was used. The hypothesis if the presence of benthic and epiphytic diatoms can lead to an overestimation of the vertical fluxes was tested. To evaluate primary and secondary sedimentation contributions, planktonic, benthic and epiphytic diatoms were distinguished. Benthic species abundance varied throughout the year and it was related to resuspension that strongly influenced sinking rates. All over the year, diatoms were the prevailing class in the trap material accounting for 75.32% of the settled cells, while flagellates represented 24.11%. Dinophyceae and resting cells constituted minor components, accounting for 0.43% and 0.14%, respectively. The gross sedimentation rates ranged from 0.006 × 10⁸ cell m⁻² d⁻¹ in the second week of May to 6.30 × 10⁸ cell m⁻² d⁻¹ in the third week of January with a mean annual value of 1.09 ± 1.43 × 10⁸ cell m⁻² d⁻¹. To the primary sedimentation rate Pseudo-nitzschia seriata of the group “Nitzschia seriata complex” contributed for 49.77% followed by Chaetoceros spp. (23.88%). The major contributor to the secondary sedimentation rate was the diatom Paralia sulcata, accounting for 24.76%. Epiphytic diatoms contributed for 11.19% and 12.27% on annual average gross abundance and biomass, respectively, reaching even 72.04% of gross abundance and 56.06% of gross biomass in the second week of August. The correlation between temperature and the logarithm of the epiphytic biomass was statistically significant, with r = 0.66 and P < 0.001. Both in the cluster analysis and in the PCA four main groups were formed, where benthic and epiphytic species were separately gathered. Planktonic, benthic and epiphytic forms accounted for 50.78%, 36.95% and 12.27%, respectively, calculated on the annual average biomass. Therefore, vertical fluxes can be overestimated of 50% or more if benthic and epiphytic species are not rejected.     

The assimilation efficiency of Asellus aquaticus L. (Crustacea, Isopoda)

(1) Comparative studies of the ash-ratio and gravimetric methods of determining assimilation efficiency in Asellus aquaticus showed that the differential use of minerals by this species rendered the ash-ratio method unreliable. Results obtained by the gravimetric method were therefore employed in the analysis of further experiments. (2) The assimilation efficiencies estimated for A. aquaticus ranged between 26 and 44%, and varied according to population density and reproductive condition. (3) Individual winter males had a significantly lower assimilation efficiency (26%) than grouped animals (35%), but the assimilation efficiency of summer males (33%) did not differ significantly from that of winter males at the same density. It is concluded that density affects assimilation efficiency in A. aquaticus. (4) The assimilation efficiency of summer males (33 %) is significantly different from that of summer females (non-ovigerous, 41 %; ovigerous, 44%). A mean assimilation efficiency of 40% is proposed for the summer period whereas an overall annual mean of 30% is suggested. (5) Despite the various assimilation efficiencies reported within any one season consumption rate per unit weight is fairly constant (winter, 0·04–0·05 cal/24 h; summer, 0·36–0·38 cal/24 h) and it is suggested that the different assimilation rates are a mechanism whereby the additional energy and material requirements of females for breeding can be met without increasing food intake.     

宁夏陆地生态系统水分利用效率特征及其影响因子

生态系统水分利用效率(Water Use Efficiency, WUE)是表征生态系统碳水耦合程度的重要指标,能反映生态系统碳水循环规律及其相互作用关系。基于MODIS数据以及宁夏生态系统类型数据,分析2000—2017年宁夏不同生态系统WUE的变化特征,探讨了NPP和ET两种因子对WUE年际与年内变化的影响。结果表明:(1)全区陆地生态系统的年均WUE为1.03 g·C/kg·H_2O,值域在0.55—2.98 g·C/kg·H_2O之间,总体上呈现南北高、中部低的特征。(2)不同生态系统的WUE差异较大,由高到低为水体及湿地、森林、农田、草地、聚落、荒漠和其他生态系统,在同类生态系统中,植被生物量和盖度越高的亚类生态系统,其WUE也越高。(3)宁夏陆地生态系统WUE存在着每年0.0141 g·C/kg·H_2O的下降趋势,年内WUE呈典型的单峰形态,变化范围在0.02—2.16 g·C/kg·H_2O之间。(4)年际尺度上,宁夏陆地生态系统WUE与年蒸散(Evapotranspiration,ET)有极显著负相关性(P0.01),而与净初级生产力(Net Primary Production,NPP)没有相关性;年内尺度上,WUE变化与ET呈显著正相关(P0.05),与NPP呈极显著正相关(P0.01),这与植被的年内季节性生长过程有关。(5)根据ET强弱和WUE高低,可将宁夏陆地生态系统水分利用效率特征划分为4类,即低ET低WUE区、低ET高WUE区、高ET低WUE区和高ET高WUE区。宁夏的生态恢复工程在增强植被生产力的同时,也增强了区域水分消耗,致使陆地生态系统整体水分利用效率下降,这为宁夏未来水资源调控和生态重建提供了科学依据。     

Effect of inland water salinity on growth performance and nutritional physiology in growing milkfish, Chanos chanos (Forsskal): field and laboratory studies

To investigate the effect of inland groundwater salinity on growth performance, feed conversion efficiency, nutrient retention and intestinal enzyme activity in milkfish, two experiments were conducted. In the first experiment (Expt I), a 100‐day monoculture of Chanos chanos [mean body weight (BW): 2.2 g] at different salinities (0, 10, 15, 20 and 25‰) was carried out in ponds fertilized with cowdung (about 10 000 kg ha^?1 year^?1) and poultry droppings (about 3000 kg ha^?1 year^?1). The fish were fed a compounded supplementary diet (containing 40% protein) at 5% BW day^?1. Studies have revealed that growth increased with each increase in the salinity level; the highest values in weight gain and energy assimilated were observed in ponds maintained at 25‰ salinity [weight: 322.2 g and specific growth rate (SGR): 8.3]. Highest values of condition factor (0.7) and exponential value (n) of the length–weight relationship (LWR; n = 3.25) were also observed in ponds maintained at 25‰ salinity. Dissolved oxygen (DO), biological oxygen demand (BOD), pH and nutrient release remained at the optimal level during the culture period. High values of chlorophyll a, net primary productivity (NPP), phytoplankton and zooplankton population coincided with the highest values of alkalinity and turbidity in ponds maintained at 25‰ salinity. Multivariate analysis revealed a significant positive correlation of chlorides (r = 0.91), conductivity (r = 0.89) and hardness (r = 0.96) with fish growth. Productivity indicating parameters viz. NPP (r = 0.45), nitrate (r = 0.94) and o‐PO₄ (r = 0.52) also showed a significant positive correlation with fish weight gain. In the second experiment (Expt II), milkfish (mean BW: 3.7 g) fry were exposed to different levels of salinity (0.0, 10, 15, 20, 25 and 30‰), and maintained for 90 days in the laboratory. Significantly (P < 0.05) high growth (percentage increase in BW: 183.1 and SGR: 1.2), feed conversion efficiency (64.5%) and intestinal enzyme activity (protease 5.1, amylase 4.1 and cellulolytic 3.2) were observed in the group maintained at 25 ppt salinity in comparison with other groups similarly maintained at low or high salinity levels. Carcass composition, muscle and liver glycogen levels were also significantly (P < 0.05) affected by salinity changes. The significance of these findings is discussed in this paper.     

Model simulations of spatial distributions and daily totals of photosynthesis in Eucalyptus grandis canopies

Summary A simulation model for radiation absorption and photosynthesis was used to test the hypothesis that observed nonuniform distributions of nitrogen concentrations in young Eucalyptus grandis trees result in greater amounts of daily assimilation than in hypothetical trees with uniform N distributions. Simulations were performed for trees aged 6, 9, 12 and 16 months which had been grown in plantations under a factorial combination of two levels of fertilization and irrigation. Observed leaf N distribution patterns yielded daily assimilation rates which were only marginally greater (<5%) than for hypothetical trees with uniform distributions. Patterns of assimilation distribution in individual tree crowns closely resembled those for absorbed radiation, rather than for N. These conclusions were unaffected by three choices of alternative leaf area density distributions. The simulation model was also used to calculate hourly and daily rates of canopy assimilation to investigate the relative importance of radiation absorption and total canopy nitrogen on assimilation. Simulated hourly rates of carbon assimilation were often lightsaturated, whereas daily carbon gain was directly proportional to radiation absorbed by the tree crown and to total mass of N in the leaves. Leaf nitrogen concentrations determined photosynthetic capacity, whereas total leaf area determined the amount of radiation absorbed and thus the degree to which capacity was realized. Observed total leaf area and total crown N were closely correlated. The model predicted that nitrogen use efficiences (NUE, mol CO₂ mol^–1 N) were 60% higher for unfertilized than for fertilized trees at low levels of absorbed photosynthetically active radiation (PAR). Nitrogen use efficiency was dependent on fertilizer treatment and on the amount of absorbed PAR; NUE declined with increasing absorbed PAR, but decreased more rapidly for unfertilized than for fertilized trees. Annual primary productivity was linearly related to both radiation absorbed and to mass of N in the canopy.     

Studies on the primary production of the river Shatt Al-Arab at Basrah,Iraq

The study was conducted on the Shatt Al-Arab River at Basrah, Iraq from September 1976 to August 1977 at three stations located at the upstream, middle and lowest parts of Basrah city. There was a bimodal seasonal variation of chlorophyll-a, the concentration of which ranged between 0.52–3.25 mg/m³. The gross primary production ranged between 6.03–37.02 mgC/m³/hr and showed a unimodal seasonal variation with a maximum in August. From the concentration of chlorophyll-a and from measurement of primary productivity it was clear that the section of the river at the upstream end of Basrah city was poorest and that at the middle of the Basrah city below Ashar Channel was the richest. A positive corelation between primary productivity and chlorophyll-a.     

Patterns of stem photosynthesis in two invasive legumes (Spartium junceum,Cytisus scoparius) of the California coastal region

Stem assimilation of Spartium junceum and Cytisus scoparius was measured over diurnal cycles during four time periods of 1992 in California. Spartium junceum plants were growing at an inland, coastal mountain site while the C. scoparius plants were growing at a coastal bluff habitat. Both species had positive stem assimilation that resulted in approximately 200 mmol m ² day^-1 carbon dioxide accumulation. Daily carbon gain decreased from spring to fall for S. junceum due to a decrease in shoot water potential. Although C. scoparius had the same relationship between assimilation and shoot water potential as that of S. junceum, carbon gain and water potential did not decrease during the year for C. scoparius. The major limitation for carbon gain of C. scoparius was light intensity because the coastal site was characterized by lower temperature, higher humidity, and more fog than the inland site. Although these species grew in habitats that had a different vapor pressure and temperature, the assimilation response to vapor pressure was similar between the species. Water use efficiency was higher and intercellular carbon dioxide was lower for S. junceum compared to C. scoparius. Although the leaves of both species are ephemeral, the canopy has a constant positive carbon balance because of stem assimilation. The constant carbon gain throughout the year, from stem assimilation, may enhance the growth capacity of these invasive species in disturbed habitats.