Phytoplankton Primary Productivity and Population Efficiency Studies in a Prairie-Parkland Lake Near Edmonton,Alberta, Canada

The standing crop and primary productivity of a small eutrophic, prairie-parkland lake were measured. In general, both standing crops and primary productivity were large, 29.4 and 73.09 mg chlorophyll a m⁻³ and m⁻² and 78.71 and 196.77 mg C hr ⁻¹m⁻³ and m⁻² respectively. Productivity decreased with increasing depth, therefore, decreasing light intensity. Relations between productivity and chlorophyll a content, productivity and light intensity, phytoplankton productivity efficiency and light intensity, productivity and water temperature were investigated, as was the photosynthetic index. Experiments designed to determine the photosynthetic capacity of the phytoplankton distinguished between actively growing and senescent populations. The latter were present during the winter ice cover.     

Seasonality of standing crop of a Sargassum (Fucales,Phaeophyta) bed in Bolinao,Pangasinan, Philippines

The seasonality of standing crop of a Sargassum bed was investigated by conducting monthly sampling from February 1988 to July 1989. Environmental parameters of water movement, salinity, number of daytime minus tides, and water temperature were also measured. An intra-annual pattern of variation in standing crop of Sargassum crassifolium, S. cristaefolium, S. oligocystum, and S. polycystum was observed. Standing crop was generally lowest in February, March, April, or May, and highest in November through January. Sargassum accounted for about 35 to 85% of the monthly algal standing crop of the bed, and the observed variation in overall standing crop of the bed generally reflected the standing crop of Sargassum. The seasonality of the standing crops of the associated algal divisions also followed an annual cycle, but their maximum and minimum standing crops did not coincide with those of Sargassum. Individually, as well as collectively, the standing crops of the Sargassum spp. were poorly correlated with the environmental factors observed.     

PRODUCTIVITY OF PODOSTEMUM CERATOPHYLLUM IN THE NEW RIVER,VIRGINIA

Productivity of Podostemum ceratophyllum, the dominant aquatic macrophyte in the New River, was measured at four sites representing soft- and hardwater reaches of the river. Available dissolved inorganic carbon (DIC) was 4–5 times greater in the hardwater reach. The difference in available DIC was reflected in standing crop and productivity of P. ceratophyllum. Maximum standing crops of P. ceratophyllum at the two hardwater sites (Sites 1 and 2) were 244.8 ± 30.7 g ash-free dry wt (AFDW) m^−-2 and 193.8 ± 18.7 g AFDW m^−-2 compared to 128.5 ± 14.9 g AFDW m^−-2 and 101.3 ± 6.9 g AFDW m^−-2 for the softwater sites (Sites 3 and 4). Productivity, based on differences in standing crops, was: Site 1, 1.08 ± 0.12 g C m^−-2 d^−-1; Site 2, 0.86 ± 0.08 g Cm^−-2d^−-1; Site 3,0.58 ± 0.06 g C m^−-2 d^−-1; Site 4,0.45 ± 0.03 g C m^−-2 d^−-1. Corresponding values for productivity as ¹⁴C uptake were: 2.77 ± 0.44 g C m^−-2 d^−-1; 2.10 ± 0.45 g C m^−-2 d^−-1; 0.34 ± 0.04 g C m^−-2 d^−-1; 0.28 ± 0.03 g C m^−-2 d^−-1. Productivity/biomass (P/B) based on ¹⁴C uptake and standing crop revealed that P. ceratophyllum productivity was inhibited at the softwater sites perhaps due to carbon limitation. Because of its abundance and its high productivity, P. ceratophyllum is hypothesized to contribute significantly to the New River organic matter budget.     

PERIODICITY OF EPIPELIC UNICELLULAR VOLVOCALES (CHLOROPHYCEAE) IN A SHALLOW ACID POOL1

The occurrence, periodicity and growth of twenty species of unicellular Volvocales on sediments in an acidic pool are described. Minimum populations were recorded in winter, but during the rest of the year standing crops fluctuated rapidly. The greatest species diversity and primary productivity occurred in late spring-early summer and in autumn, when maximum numbers of Chlamydomonas spp. and Chloromonas spp. increased exponentially on the sediments. The chlamydomonads were more numerous in the epipelon than other major algal components such as diatoms, euglenoids, bluegreen algae and desmids. Growth of the chlamydomonad population occurred after the period of maximum diatom standing crop. Evidence shows that rates of primary production were greater in late spring and late summer when species diversity and standing crop or apparent growth rates of unicellular Volvocales were high. Thus these algae which are normally neglected may be more important in primary productivity than previously believed since they grow during periods when larger algae are scarce. Analysis of the data using the multivariate technique of Reciprocal Averaging confirmed seasonal periodicity in this community of epipelic flagellates. It also identified species with distinctive ecological requirements. A relationship between the bicarbonate-alkalinity of the overlying water and the chlamydomonad population was demonstrated by ordination analysis.     

Nectar dispersion patterns in three Australian plant species

Standing crops of floral nectar were measured from three species of plants: Dampiera stricta, Goodenia bellidifolia and Aotus ericoides. The amount of nectar in nearest neighbour blossoms in nine of the 10 samples were significantly correlated with one another suggesting that patches of high and low reward quality exist in these species. The patterns further suggest that the pollinators of these species employ arearestricted searching behaviour. The range of variability in standing crops for all three species was quite high. The nature of that variability suggests that A. ericoides is less variable in its rate of nectar production than are the other two species and, therefore, that it has the potential to be more tightly co-evolved with its pollinators.     

Primary productivity,phytoplankton and limiting nutrient factors in labrador lakes

The primary productivity of some lakes and reservoirs in western Labrador was measured by the ¹⁴C method in order to determine the range of productivities and the effects of impoundment. No primary productivity data previously existed for this part of Canada. Both the primary productivity and standing crops of phytoplankton were found to be low in a newly impounded lake but later rose to levels greater than in surrounding natural lakes. In nutrient enrichment experiments, carbon was never found to be limiting but phosphorus stimulated primary productivity when added alone or in combination with nitrogen.     

Hyperthermal effluent Effects on heleoplanktonic Cladocera and the influence of submerged macrophytes

In July and August, 1974, measurements were made of the standing crops of Cladocera in the littoral zone of Par Pond (Savannah River Plant, Aiken, South Carolina, U.S.A.), which receives hyperthermal effluent from a nuclear reactor. Crops of Ceriodaphnia spp. and Diaphanosoma brachyurum were greater in the heated than in the ambient area, while Bosmina longirostris maintained higher standing crops in the ambient area than in the area receiving hyperthermal effluent. In August, 1974, exclosures were placed in the effluent-affected area to test the hypothesis that the high density of rooted aquatic macrophytes in the effluent-affected area influences the standing crop of these Cladocera. The effects of changes in reactor effluent temperature were also determined in the exclosure experiments. The results of the exclosure study support two generalizations: 1) the presence of dense rooted vegetation allows higher standing crops of Ceriodaphnia spp. and D. brachyurum; and 2) lower temperatures than those usually found at the heated station would favor B. longirostris standing crops, while the higher effluent temperatures favor Ceriodaphnia spp. and D. brachyurum.     

Towards a dynamic photosynthesis model to guide yield improvement in C4 crops

The most productive C4 food and biofuel crops, such as Saccharum officinarum (sugarcane), Sorghum bicolor (sorghum) and Zea mays (maize), all use NADP-ME-type C4 photosynthesis. Despite high productivities, these crops fall well short of the theoretical maximum solar conversion efficiency of 6%. Understanding the basis of these inefficiencies is key for bioengineering and breeding strategies to increase the sustainable productivity of these major C4 crops. Photosynthesis is studied predominantly at steady state in saturating light. In field stands of these crops light is continually changing, and often with rapid fluctuations. Although light may change in a second, the adjustment of photosynthesis may take many minutes, leading to inefficiencies. We measured the rates of CO₂ uptake and stomatal conductance of maize, sorghum and sugarcane under fluctuating light regimes. The gas exchange results were combined with a new dynamic photosynthesis model to infer the limiting factors under non-steady-state conditions. The dynamic photosynthesis model was developed from an existing C4 metabolic model for maize and extended to include: (i) post-translational regulation of key photosynthetic enzymes and their temperature responses; (ii) dynamic stomatal conductance; and (iii) leaf energy balance. Testing the model outputs against measured rates of leaf CO₂ uptake and stomatal conductance in the three C4 crops indicated that Rubisco activase, the pyruvate phosphate dikinase regulatory protein and stomatal conductance are the major limitations to the efficiency of NADP-ME-type C4 photosynthesis during dark-to-high light transitions. We propose that the level of influence of these limiting factors make them targets for bioengineering the improved photosynthetic efficiency of these key crops.     

Temporal changes in periphyton standing crop during an unusually dry winter in streams of the Western Cascades,Oregon

The effects of light and discharge on standing crops of periphyton in adjacent shaded and open reaches of first to fourth order streams were examined during winter in three streams of the Western Cascades, Oregon. Standing crops were measured in terms of chlorophylla and periphyton biomass at each site on 8 occasions. Open sites supported higher standing crops of periphyton than shaded sites and increases in standing crop were shown to be related to light input at each site. Biomass increased throughout winter until scouring associated with an unusually late winter freshet reduced periphyton standing crops to their lowest observed levels. It is concluded that periphyton levels are affected by a combination of factors of which light levels, and the periodicity of storm events are of major importance.     

Benthic algal biomass and productivity in high subarctic streams,Alaska

Year-round measurements of the standing crop of epilithic algae (as chlorophyll a concentration) in two streams — one second and one fourth order (map scale 1:63 360) — in interior Alaska (64°–65° N) were only about one tenth that reported from streams of temperate North America. Cell densities in these streams, however, were similar to those in comparable temperate streams. Year-round domination of the benthic flora by very tiny diatoms (Achnanthes spp.) may explain the apparent disparity between low chlorophyll a content and nearly average cell densities. Chlorophyll a standing crop in a more alkaline groundwater-fed stream, however, was higher and within the range of similarly sized temperate streams. Maximum chlorophyll a standing crop varied positively with alkalinity in 5 clear-water streams where standing crop was measured on natural or artificial substrates. Seasonal mean concentrations of sestonic chlorophyll a (used as estimates of benthic algal chlorophyll a standing crop) varied directly and significantly with alkalinity among ten clear-water streams; and, with total phosphorus among 8 of 10 clear-water and 5 brown-water streams studied. During the summer, when there is little darkness, gross primary productivity (as estimated by the diurnal dissolved-oxygen method) was similar to that of northern temperate streams. Gross primary productivity was also seen to vary directly with alkalinity in 5 clear-water streams of this region.U.S. Fish and Wildlife Service     

Assessing Targets for the Restoration of Herbaceous Vegetation in Ponderosa Pine Forests

A restoration project is considered a success when the initial target is met, but many targets are plausible. We evaluated the success of a restoration project in its 11th year since treatment in a southwestern ponderosa pine–bunchgrass community and the appropriateness of several targets. We measured the responses of (1) total standing crop; (2) standing crop of five functional groups (C₃ and C₄ graminoids, leguminous forbs, and nonleguminous perennial and annual forbs); (3) graminoid community composition; and (4) standing crop of five common graminoid species (Festuca arizonica, Muhlenbergia montana, Elymus elymoides, Carex geophila, and Poa fendleriana). Targets were quantified in remnant grass patches, which provided the standards for these targets, and were assessed in three other forest patch types (pre‐settlement tree patches, post‐settlement tree patches, and patches where all post‐settlement trees were removed). Patches where all post‐settlement trees were removed reached target levels for total standing crop, C₃ and C₄ graminoid standing crop, graminoid community composition, and M. montana, E. elymoides, and C. geophila standing crops. Standing crop of legumes and of F. arizonica did not increase over time in any patch type. Targets were not met in pre‐settlement patches or in patches where some post‐settlement trees were left standing, suggesting that it is unrealistic to expect equal responses across all patch types. If increasing herbaceous standing crop is a major goal, practitioners should create gaps within the pine forest canopy.     

Agroecology of Tropical Underground Crops for Small-Scale Agriculture

The important tropical root and tuberous crops cassava (Manihot esculenta), sweet potato (Ipomoea batatas), yams (Dioscorea spp.), and the aroids (especially Xanthosoma and Colocasia spp.) represent an important source of relatively inexpensive carbohydrates to large sectors of the population in tropical areas. One or more tropical root crops are normally a staple in rural communities and are typically grown on small-scale subsistence farms. The current status of the agroecology research on these crops, including productivity under polyculture systems, resource (water, nutrients, light, space) utilization, tolerance to environmental stress, pest dynamics response to habitat manipulation, and alternative cultural practices, is reviewed in this paper as they relate to the performance of these crops in small-scale tropical agricultural systems. The development of technological recommendations to improve the productivity of tropical root crops in the tropics is dependent on an understanding of important underlying agroecological principles. The objective of background ecophysiological work is to develop crop-specific technological packages appropriate to low-input subsistence farming, and to match specific crops with a cropping system that will result in adequate yields and in ecological and socioeconomical sustainability. Because of the close relationship between crops and humans in small-scale farms of the tropics, it is imperative that agroecology research be holistic, multidisciplinary, and cognizant of the many socioeconomic and cultural factors that will determine whether improved technologies will be adopted in any given location.     

A case of thermal pollution limited primary productivity in a southwestern U.S.A. Reservoir

North Lake, a small (330 ha. surface area) southwestern U.S.A. cooling water reservoir was found to contain less phytoplankton production (104.0 mg C m⁻³ day⁻¹), lower annual mean total organic carbon (3.7 mg l⁻¹) and phytoplankton standing crops (0.9 ml m⁻³) than other local area reservoirs. Concentrations of inorganic P and N were at or below test detection limits during the study year 1973–1974.In situ ¹⁴C non-filtration primary productivity techniques demonstrated significant (≃13 percent) stimulation of planktonic primary productivity due to power plant entrainment. Optical counts showed no destruction of entrained phytoplankters. Populations of Cyanophyta were never dominant, although they frequently bloom in most other local reservoirs. Thermal loading at North Lake is thought to ultimately depress phytoplankton primary production and standing crop by causing nutrient limitation.     

ALGAE OF TWO SOMERSETSHIRE POOLS STANDING CROPS OF PHYTOPLANKTON AND EPIPELIC ALGAE AS MEASURED BY CELL NUMBERS AND CHLOROPHYLL A

Standing crops measured as cell numbers and as chlorophyll a content of phytoplankton and epipelic algal communities (those free-living on sediment surfaces) in 2 small water bodies of contrasted nutrient status were measured for 27 months. Mean yearly crops, on an areal basis, of phytoplankton were 4–13.4 times greater than those of epipelic algae in the nutrient-rich pool, but were only 0.65–1.8 times as great in the nutrient-poor pool, which, however, was shallower than the rich pool. The role of cells < 5 μ, in diameter in the composition of standing crops was minor. Effects of phytoplankton in limiting growth of epipelic algae by light attenuation are shown. Compilation of available data shows a direct relationship between epipelic algal crops in various water bodies and nutrient-status of the ambient water, similar to that already established for phytoplankton.     

Morpho-Physiological Aspects of Productivity and Quality in Squash and Pumpkins (Cucurbita spp.)

Squash and pumpkins are important horticultural crops worldwide, but there has been relatively little research to systematically describe yield components and improve productivity in this species. This review outlines some of the basic growth-analysis techniques for describing different aspects of productivity and attempts to summarize investigations on physiological, morphological, and ecological aspects of productivity and the relationship of these factors to eating quality in the three most important domesticated species of Cucurbita—C. pepo, C. maxima, and C. moschata. The emphasis of this review is on components of yield that can be modified either by selective breeding or through use of cultural techniques. Increasing economic crop yield while also balancing the needs to maintain and improve culinary qualities of the edible product will also be discussed. The bush phenotype is being increasingly exploited in new cultivar development. Advantages and disadvantages of using bush genotypes in cultivar development are addressed. In addition, because of increasing use of Cucurbita seeds for vegetable oils, snackseeds, and pharmaceutical purposes, physiological components of seed yield are also discussed.     

Ecological effects of seaweed harvesting in the Gulf of California and Pacific Ocean off Baja California and California

The ecological effects of harvesting were investigated for two species, the giant kelp Macrocystis pyrifera and Eucheuma uncinatum, by using harvest records and aerial surveys that show yield changes and by using studies of recruitment, survivorship and community interactions. There were no ecological effects found for M. pyrifera harvested with contemporary methods, and there are no recommendations for changing current management practices for this species. It is recommended that E. uncinatum, which on occasion produces commercially significant standing crops, not be harvested unless special precautions are taken to leave some plants for regeneration of the harvested populations.     

Nutrient enrichment experiments in three central Florida lakes of different trophic states

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.     

Biological nitrogen fixation: An efficient source of nitrogen for sustainable agricultural production?

A fundamental shift has taken place in agricultural research and world food production. In the past, the principal driving force was to increase the yield potential of food crops and to maximize productivity. Today, the drive for productivity is increasingly combined with a desire for sustainability. For farming systems to remain productive, and to be sustainable in the long-term, it will be necessary to replenish the reserves of nutrients which are removed or lost from the soil. In the case of nitrogen (N), inputs into agricultural systems may be in the form of N-fertilizer, or be derived from atmospheric N₂ via biological N₂ fixation (BNF).Although BNF has long been a component of many farming systems throughout the world, its importance as a primary source of N for agriculture has diminished in recent decades as increasing amounts of fertilizer-N are used for the production of food and cash crops. However, international emphasis on environmentally sustainable development with the use of renewable resources is likely to focus attention on the potential role of BNF in supplying N for agriculture. This paper documents inputs of N via symbiotic N₂ fixation measured in experimental plots and in farmers' fields in tropical and temperate regions. It considers contributions of fixed N from legumes (crop, pasture, green manures and trees), Casuarina, and Azolla, and compares the relative utilization of N derived from these sources with fertilizer N.     

Observations on standing crops of epipelic and epipsammic algal communities in Shear Water,Wilts

Methods of estimating the standing crops of epipsammic diatoms have been evaluated and compared with those used for epipelic algal crops.

Good correlations between chlorophyll a content and cell counts were obtained for epipelic populations, but because of the presence of large numbers of decaying cells, inseparable from living cells, such correlation was not obtained with epipsammic algae, even after correction of the pigment estimates for the presence of pheophytin a. The standing crop of epipsammic algae was at all times greater than that of epipelic algae at the same sampling station, and this was attributed to the differential effects of sediment disturbance by burrowing animals and water movements.     

Phytoplankton biomass and primary productivity of of Lake Leake and Tooms Lake,Tasmania

Phytoplankton biomass and primary productivity were studied in two lakes in eastern Tasmania. Low standing crops (7–746 and 42–180 mm³m⁻³ for Lake Leake and Tooms Lake respectively) and low primary productivity (approx. 9 g C m⁻² yr⁻¹ for both lakes) indicate extreme oligotrophy. During a period when biomass remained constant in Lake Leake the hourly assimilation rate in constant light conditions varied seasonally, indicating physiological adjustment by the algae (“light adaptation”). The relationships between plankton biomass and carbon assimilation are discussed.