scispace - formally typeset
Search or ask a question

Showing papers on "Productivity (ecology) published in 1997"


Journal ArticleDOI
TL;DR: A cruise to the Ross Sea polynya in November-December, 1994 to measure the contribution of phytoplankton during the austral spring to the annual productivity of the region was conducted by.
Abstract: Although satellite data of surface layer pigments have suggested that the daily productivity in the Ross Sea is among the largest found in any marine system, no modern oceanographic cruise has entered the Ross Sea polynya to quantitatively assess the austral spring productivity over time scales of days to weeks. We conducted a cruise to the Ross Sea polynya in November–December, 1994 to measure the contribution of phytoplankton during the austral spring to the annual productivity of the region and found markedly enhanced levels of phytoplankton biomass. Chlorophyll concentrations were greater than 3 µg l−1 in mid-November, a time when the polynya was covered by a thin (ca. 20–30 cm) layer of ice. Particulate matter concentrations increased through time, and by early December chlorophyll and particulate carbon concentrations exceeded 10 µg l−1 and 53 µmol l−1, respectively. Primary productivity also increased through time: the mean productivity in early December equaled 3.53 g C m−2 d−1, and maximum measured rates exceeded 6 g C m−2 d−1. Productivity based on nitrate disappearance averaged 1.52 g C m−2 d−1 (with a maximum rate of 2.49 g C m−2 d−1), suggesting that the bloom's new production was also substantial. The Ross Sea polynya is the most southerly location in the Antarctic where phytoplankton growth is initiated this early and which supports such high standing stocks by early December. Inclusion of this production in a carbon budget for the region suggests that this area supports an annual production of 200 g C m−2, the largest of any region in the Southern Ocean, and confirms its hyperproductive nature.

250 citations


Journal ArticleDOI
01 Jul 1997-Ecology
TL;DR: Differences in published cost-of-flight values support the hypothesis that energetic competition determines flock structure at the low-productivity end of the system, and Sooty Terns have the lowest flight costs and feed in waters of lowest productivity.
Abstract: The oceanic eastern tropical Pacific supports a speciose seabird community that feeds in flocks and depends for food on schools of tunas and dolphins, which force prey to the surface. We analyzed data collected throughout an area of 40 3 10 6 km 2 of open ocean over 10 years (1979-1988) during 1136 at-sea days, from 1750 feeding flocks comprising 51 688 birds of 49 species. A PCA identified three distinct flock types based on species composition: ''Sooty Tern Flocks'' ( n 5 941 flocks) with a large number of Sooty Terns (Sterna fuscata), ''Juan-Wedge Flocks'' ( n 5 402 flocks) with a large number of Juan Fernandez Petrels (Pterodroma externa) and Wedge-tailed Shearwaters (Puffinus pacificus ), and ''Booby Flocks'' ( n 5 407 flocks) with a large number of Red-footed and Masked Boobies (Sula sula and S. dactylatra, respectively). Flock types exhibited largely disjunct distributions that mirrored patterns in thermocline depth and surface water chlo- rophyll content. Sooty Tern Flocks occurred in areas with deepest thermocline (77.6 m) and lowest chlorophyll (0.14 mg/m 3 ), Juan-Wedge Flocks in areas of intermediate ther- mocline (68.8 m) and chlorophyll (0.16 mg/m 3 ), and Booby Flocks in areas of shallowest thermocline (62.5 m) and highest chlorophyll (0.17 mg/m 3 ). These differences were sta- tistically significant. As thermocline depth and surface water chlorophyll are reliable in- dicators of surface water productivity, we conclude that Sooty Tern Flocks foraged in waters of low productivity, Juan-Wedge Flocks in waters of intermediate productivity, and Booby Flocks in waters of highest productivity. Differences in published cost-of-flight values support the hypothesis that energetic con- straint determines flock structure at the low-productivity end of the system. Sooty Terns have the lowest flight costs (4.8 W) and feed in waters of lowest productivity. Flight costs are progressively higher for those species feeding in more productive waters (9.9 W for Wedge-tailed Shearwaters, 19.0 W for Red-footed Boobies). Differences in body size sup- port the hypothesis that interference competition determines flock structure at the high- productivity end of the system. The largest species, Masked Boobies (1987 g) and Red- footed Boobies (1003 g), feed in areas of highest productivity; progressively smaller species, Juan Fernandez Petrels (430 g) and Wedge-tailed Shearwaters (388 g), and Sooty Terns (180 g), feed in areas of decreasing productivity. We hypothesize that this community is largely structured by two factors, competition and energetic constraint, that operate at opposite ends of a productivity gradient. As productivity decreases (low prey abundance), flight proficiency is increasingly important because only species with relatively low flight costs will be able to transit between prey patches. As productivity increases (high prey abundance), competitive ability is increasingly important because competitive dominants will exclude other species from feeding flocks. Our hypothesis is in accordance with em- pirical data and theoretical models designed to explain factors structuring communities for a wide variety of habitats and taxa.

239 citations


Journal ArticleDOI
01 Mar 1997-Ecology
TL;DR: In this article, the authors measured groundwater table depths and aboveground productivity in floodplain forests of South Carolina and Louisiana and concluded that the subsidy-stress hypothesis does not adequately describe patterns of NPP across Southeastern U.S. floodplain forest.
Abstract: It has been hypothesized that periodically flooded forests have higher rates of aboveground net primary production than upland forests and near-continuously flooded forests, but a competing hypothesis holds that the benefits of periodic inputs of nutrients and water may be diminished by stresses associated with anaerobic soils or drought. To test these hypotheses, we measured groundwater table depths and aboveground productivity in floodplain forests of South Carolina and Louisiana. We established paired plots on locally dry, intermediate, and wet topographic positions across three hydrologic transects in each state. These plots encompassed upland hardwood, bottomland hardwood, and cypress swamp forests. Measurements of leaf litterfall, wood production, and groundwater table depth were made in 1987 and 1988. We then used mean growing-season water depth (MWD) to group the plots into three classes: wet (>0 cm), intermediate (0 to -60 cm), and dry ( 25% dead stems) the slope of this line was 5 times greater (-24 gm-2yr- -cm- ). We conclude that the subsidy-stress hypothesis does not adequately describe patterns of NPP across Southeastern U.S. floodplain forests. Conditions of periodic flooding and flowing water do not often lead to high rates of productivity compared with upland forests. However, extensive flooding is nearly always a significant stress on forest productivity, particularly when the flooding regime has been recently perturbed through levee construc- tion or impoundment. Our data support a more complex interaction between subsidy and stress factors.

239 citations


Journal ArticleDOI
TL;DR: This article showed that the local richness of Neotropical primates (platyrrhines) is influenced by both historical biogeography and productivity but not by tree species richness or seasonality, and that fragmentation of Amazonian rain forests in the Pleistocene, if it occurred, appears to have had a negligible influence on primate alpha species richness.
Abstract: The explanation of patterns in species richness ranks among the most important tasks of ecology. Current theories emphasize the interaction between historical and geographical factors affecting the size of the regional species pool and of locally acting processes such as competitive exclusion, disturbance, productivity, and seasonality. Local species richness, or alpha diversity, of plants and primary consumers has been claimed to peak in habitats of low and intermediate productivity, which, if true, has major implications for conservation. Here, by contrast, we show that local richness of Neotropical primates (platyrrhines) is influenced by both historical biogeography and productivity but not by tree species richness or seasonality. This pattern indicates that habitats with the highest plant productivity are also the richest for many important primary consumers. We show further that fragmentation of Amazonian rain forests in the Pleistocene, if it occurred, appears to have had a negligible influence on primate alpha species richness.

214 citations


Journal ArticleDOI
TL;DR: Differences between measured and simulated results were attributed to several factors including difficulties associated with measuring nighttime CO(2) fluxes and model assumptions of site homogeneity, however, comparisons between simulations and field data improved markedly at coarser time-scales.
Abstract: A process-based, general ecosystem model (BIOME-BGC) was used to simulate daily gross primary production, maintenance and heterotrophic respiration, net primary production and net ecosystem carbon exchange of boreal aspen, jack pine and black spruce stands. Model simulations of daily net carbon exchange of the ecosystem (NEE) explained 51.7% (SE = 1.32 g C m(-2) day(-1)) of the variance in daily NEE derived from stand eddy flux measurements of CO(2) during 1994. Differences between measured and simulated results were attributed to several factors including difficulties associated with measuring nighttime CO(2) fluxes and model assumptions of site homogeneity. However, comparisons between simulations and field data improved markedly at coarser time-scales. Model simulations explained 66.1% (SE = 0.97 g C m(-2) day(-1)) of the variance in measured NEE when 5-day means of daily results were compared. Annual simulations of aboveground net primary production ranged from 0.6-2.4 Mg C ha(-1) year(-1) and were concurrent with results derived from tree increment core measurements and allometric equations. Model simulations showed that all of the sites were net sinks (0.1-4.1 Mg C ha(-1) year(-1)) of atmospheric carbon for 1994. Older conifer stands showed narrow margins between uptake of carbon by net photosynthesis and carbon release through respiration. Younger stands were more productive than older stands, primarily because of lower maintenance respiration costs. However, all sites appeared to be less productive than temperate forests. Productivity simulations were strongly linked to stand morphology and site conditions. Old jack pine and aspen stands showed decreased productivity in response to simulated low soil water contents near the end of the 1994 growing season. Compared with the aspen stand, the jack pine stand appeared better adapted to conserve soil water through lower daily evapotranspiration losses but also exhibited a narrower margin between daily net photosynthesis and respiration. Stands subjected to water stress during the growing season may exist on the edge between being annual sources or sinks for atmospheric carbon.

188 citations


Journal ArticleDOI
TL;DR: In this paper, the relationship of the trophic orga- nization of a river-dominated Gulf of Mexico estuary with interannual trends of freshwater input and biological controlling features was investigated.
Abstract: A long-term (9.5 yr) study addressed the relationship of the trophic orga- nization of a river-dominated Gulf of Mexico estuary with interannual trends of freshwater input and biological controlling features. Alluvial river flow characteristics were evaluated with respect to seasonal and interannual changes in physical, chemical, and biological trends in the receiving estuary. Infaunal and epifaunal macroinvertebrates and fishes taken over the period of sampling in the Apalachicola Bay system were transformed into their trophic equivalents. The long-term trophic organization of the bay was then related to observed changes in the physical and chemical conditions in the receiving estuary with particular attention to long-term response to a 2-yr drought. Within limited natural bounds of fresh- water flow from the Apalachicola River, there was little change in the trophic organization of the receiving estuary over prolonged periods. The physical instability of the estuary was actually a major component in the continuation of a biologically stable estuarine system. However, when a specific threshold of freshwater reduction was reached during a prolonged natural drought, we suggest that the clarification of the normally turbid and highly colored river-estuarine system led to rapid changes in the pattern of primary production, which, in turn, were associated with major changes in the trophic structure of the system. Increased light penetration due to the cessation of river flow was an important factor in the temporal response of bay productivity and herbivore/omnivore abundance. There was a dichotomous response of the estuarine trophic organization, with herbivores and omnivores responsive to river-dominated physicochemical factors whereas the carnivores responded to biological factors. Trophic response time could be measured in months to years from the point of the initiation of low-flow conditions. The reduction of nutrient loading during the drought period was postulated as a major cause of the loss of productivity of the river-dominated estuary during and after the drought period. Recovery of such productivity with resumption of increased river flows was likewise a long-term event. Based on the observed trends in the bay, postulated permanent reductions of freshwater flows due to anthropogenous ac- tivities could lead to major reductions of biological productivity in the Apalachicola Bay system. The long-term data indicated that, with reduction of freshwater flow below a level specific for the receiving system, the physically controlled, highly productive river-estu- arine system would become a species-rich, biologically controlled bay with substantially reduced productivity.

181 citations


Journal ArticleDOI
TL;DR: A model that relates productivity to carbon flow by using enzyme activities as indicators and assuming an optimum resource allocation relationship among C-, N-, and P-acquiring enzymes was evaluated, but predictive power was low.
Abstract: Bacterial production is the entry point for detrital macronutrients into aquatic food webs. Many factors affect productivity, but the heterogeneity of detrital substrates and the diversity of microbial communities confound simple relationships between carbon supply and growth. WC tried to link the two by analyzing extracellular enzyme activities. Water samples were collected from three rivers and assayed for bacterial productivity and the activities of eight enzymes. Production varied among systems, peaking at 644, 170, and 68 pmol C liter-’ d-’ in the Ottawa (Ohio), Maumee (Ohio), and Hudson (New York) Rivers. V,,,,, values were generally correlated with productivity. The mean ratios of productivity per unit peptidase and esterase activity were similar among rivers, whereas carbohydrase and phosphatase ratios varied widely. The data were used to evaluate a model that relates productivity to carbon flow by using enzyme activities as indicators and assuming an optimum resource allocation relationship among C-, N-, and P-acquiring enzymes. The data supported the model, but predictive power was low. Bacterial productivity generally increased with inorganic nutrient availability, but high levels of productivity at any specific eutrophic state required sources of both saccharides and amino acids.

172 citations


Journal ArticleDOI
TL;DR: Eutrophication in the Everglades has resulted in a decrease in periphytonbiomass and its contribution to marsh primary productivity, and these changes may have important implications for efforts to manage this wetland in asustainable manner.
Abstract: We sampled periphyton in dominant habitats at oligotrophic and eutrophic sites in the northern Everglades during the wet and the dryseasons to determine the effects of nutrient enrichment on periphytonbiomass, taxonomic composition, productivity, and phosphorus storage. Arealbiomass was high (100–1600 g ash-free dry mass [AFDM]m−2) in oligotrophic sloughs and in stands of the emergentmacrophyte Eleocharis cellulosa, but was low in adjacent stands of sawgrass,Cladium jamaicense (7–52 g AFDM m−2). Epipelon biomasswas high throughout the year at oligotrophic sites whereas epiphyton andmetaphyton biomass varied seasonally and peaked during the wet season.Periphyton biomass was low (3–68 g AFDM m−2) and limitedto epiphyton and metaphyton in open-water habitats at eutrophic sites andwas undetectable in cattail stands (Typha domingensis) that covered morethan 90% of the marsh in these areas. Oligotrophic periphytonassemblages exhibited strong seasonal shifts in species composition and weredominated by cyanobacteria (e.g., Chroococcus turgidus, Scytonema hofmannii)during the wet season and diatoms (e.g. Amphora lineolata, Mastogloiasmithii) during the dry season. Eutrophic assemblages were dominated byCyanobacteria (e.g., Oscillatoria princeps) and green algae (e.g., Spirogyraspp.) and exhibited comparatively little seasonality. Biomass-specific grossprimary productivity (GPP) of periphyton assemblages in eutrophic openwaters was higher than for comparable slough assemblages, but areal GPP wassimilar in these eutrophic (0.9–9.1 g C m−2d−1) and oligotrophic (1.75–11.49 g C m−2d−1) habitats. On a habitat-weighted basis, areal periphytonGPP was 6- to 30-fold lower in eutrophic areas of the marsh due to extensiveTypha stands that were devoid of periphyton. Periphyton at eutrophic siteshad higher P content and uptake rates than the oligotrophic assemblage, butstored only 5% as much P because of the lower areal biomass.Eutrophication in the Everglades has resulted in a decrease in periphytonbiomass and its contribution to marsh primary productivity. These changesmay have important implications for efforts to manage this wetland in asustainable manner.

158 citations


Journal ArticleDOI
TL;DR: In this article, the authors test the relationship of deep sea benthic foraminiferal assemblage composition to the surface ocean productivity gradient in the low latitude Atlantic Ocean using 81 surface sediment samples from a water depth range between 2800 and 3500 m.

145 citations


Journal ArticleDOI
TL;DR: In this paper, an overview of the distribution of biomass and productivity at different trophic levels of the pelagic Barents Sea ecosystem is presented, with comments on year-to-year and horizontal variations.
Abstract: On the basis of results that largely have been derived from the Norwegian research programme Pro Mare (1984-1989), an overview of the distribution of biomass and productivity at different trophic levels of the pelagic Barents Sea ecosystem is presented, with comments on year-to-year and horizontal variations. Average biomasses for the whole Barents Sea and several years range from 2000 kg of carbon km −2 for each of Calanus spp. and phytoplankton stocks, down to 0.1 kg carbon km −2 for the polar bear population.Phytoplankton blooms that deplete the winter nutrients give rise locally to a “new” productivity of 40-50 g C m −2 . Areal differences, however, are pronounced in terms of annual productivity: the “new” fraction is more than twice as high in the southern (Atlantic) part of the Barents Sea as in the areas north of the oceanic Polar Front (90 vs. <40 g C m −2 yr −1 ), Wind-generated vertical mixing (in association with passing atmospheric depressions) and turbulence generated on and around banks in the southern part are crucial in accounting for this difference. In the northern half of the Barents Sea a pronounced upper layer stability caused by the supply of meltwater from seasonal ice retards mixing so that “new” production is small following the depletion of winter nutrients - high productivity is restricted to the 20-50 km wide ice edge bloom.Year-to-year variations in fish stocks are pronounced and have always been so - there exists no “ecological balance” in any meaningful sense. These variations are clearly related to the influx of Atlantic water to the Barents Sea (i.e. “warm” years are high-productive years) and, thus, ultimately to the same forcing factors that determine climate variations in coastal Europe. Thus, sound management may diminish the annual fluctuations in fish stock sizes but certainly cannot eradicate them.

124 citations


Journal ArticleDOI
01 Jun 1997-Ecology
TL;DR: The diversity of plant life forms in tropical forests affords the opportunity for assembly of plant combinations, both natural and managed, that make full use of resources and sustain high productivity.
Abstract: The diversity of plant life forms in tropical forests affords the opportunity for assembly of plant combinations, both natural and managed, that make full use of resources and sustain high productivity. The influence of combining life forms on productivity and resource use was evaluated using three fast-growing tree species (Hyeronima alchorneoides, Cedrela odorata, and Cordia alliodora); each species was grown alone and with two perennial, large-stature, self-supporting monocots (Euterpe oleracea and Heliconia imbricata). Aboveground net primary productivity was extremely high in all stands. The monocots did not contribute significantly to the productivity of the Hyeronima polycultures, which was 4.5–8.4 g·m−2·d−1 between 18 and 36 mo. In contrast, the monocots accounted for 57% of the productivity (9.7 g·m−2·d−1) of Cedrela polycultures and 67% of the productivity (6.8 g·m−2·d−1) of the Cordia polycultures, by age 3 yr. The leaf area and density of fine roots in the Cedrela and Cordia polycultures were ...

Journal ArticleDOI
TL;DR: In this paper, the 13C tracer was used to measure primary productivity in the East China Sea and its adjacent area during winter, summer and fall in 1993 and 1994, and the depth-integrated primary productivity was 2.7 times higher in the shelf area than the rates at the Kuroshio Current.
Abstract: Primary productivity in the East China Sea and its adjacent area was measured by the13C tracer method during winter, summer and fall in 1993 and 1994. The depth-integrated primary productivity in the Kuroshio Current ranged from 220 to 350 mgC m−2d−1, and showed little seasonal variability. High primary productivity (above 570 mgC m−2d−1) was measured at the center of the continental shelf throughout the observation period. The productivity at the station nearest to the Changjiang estuary exhibited a distinctive seasonal change from 68 to 1,500 mgC m−2d−1. Depth-integrated primary productivity was 2.7 times higher in the shelf area than the rates at the Kuroshio Current. High chlorophyll-a specific productivity (mgC mgChl.-a−2d−1) throughout the euphotic zone was mainly found in the shelf area rather than off-shelf area, probably due to higher nutrient availability and higher activity of phytoplankton at the subsurface layer in the shelf area.


Journal ArticleDOI
TL;DR: In this article, the authors measured monthly for two years in a subtidal meadow subjected to moderate tidal amplitude in the San Juan Islands, WA, USA, and measured major physical and chemical factors (e.g., nutrient concentrations, light, and temperature) concurrently.

Journal ArticleDOI
TL;DR: It is demonstrated that the dissolved carbon pathway from mesozooplankton to bacteria averaged 57% (26-78%) of the algal carbon filtered from suspension, while during the decline of a diatom spring bloom in a eutrophic, temperate lake a significant increase in bacterial biomass was observed.
Abstract: Experiments were designed to investigate whether processes related to zooplankton feeding have a positive effect on bacterial growth. Bacterial abundance and (3H)thymidine incorpor- ation rates were followed in grazer-free batch cultures originally containing either Sccnedesmus quadncauda or Rhodomonas lacustns as food sources, and Daphnia cucullala or Eudiaptomus graciloides as grazers. Compared with controls lacking either animals or algae, a significantly higher bacterial abundance and productivity occurred in cultures which contained both phyto- and zoo- plankton. The same experimental methodology was tested during the decline of a diatom spring bloom in a eutrophic, temperate lake. A significant increase in bacterial biomass was observed due to the grazing activity of in situ mesozooplankters during the clear-water phase. Our results demonstrated that the dissolved carbon pathway from mesozooplankton to bacteria averaged 57% (26-78%) of the algal carbon filtered from suspension.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the influence of light and nutrient on phytoplankton productivity in the Logan River and southern Moreton Bay, a large embayment on the east coast of Australia.
Abstract: Phytoplankton productivity and the factors that influence it were studied in the Logan River and southern Moreton Bay, a large embayment on the east coast of Australia. Phytoplankton productivity, dissolved and total nutrient concentrations, and turbidity were determined throughout high and low rainfall periods to characterize light and nutrient influences on productivity. Turbidity and nutrient concentrations were highest at upriver sites, but productivity was highest at the river mouth and within the river plume. Phytoplankton productivity peaked after rainfall events (>150 mg C m−3 h−1), commensurate with a decrease in dissolved nitrogen concentrations. Productivity responses to increased nutrient concentrations and light availability were determined in laboratory incubations. During summer, productivities at the bay sites were stimulated by nitrogen (N) enrichment, while productivities at upriver sites were stimulated by phosphorus (P) addition. Light stimulation of productivities was more pronounced at upriver sites than bay sites. The relative magnitude of nutrient and light stimulation of productivities indicate a predominance of light limitation upriver, significant N limitation within the Logan River plume, and little effect of light, N, or P at sites beyond the Logan River plume. Productivity decreased with seasonal decreases in temperature. Lower water temperatures in winter probably helped determine maximum rates of phytoplankton productivity. The combination of light and N limitation of productivity during summer, and temperature limitation during winter, account for low areal productivities (<0.6 g C m−2 d−1), compared with other rivers and estuaries worldwide.

Journal ArticleDOI
01 Mar 1997
TL;DR: The role of bacterioplankton in the Somali Current, the Gulf of Aden and the Red Sea was studied during the SW- (May-August 1992) and NE-monsoon (January-February 1993) as discussed by the authors.
Abstract: The role of bacterioplankton in the Somali Current, the Gulf of Aden and the Red Sea was studied during the SW- (May–August 1992) and NE-monsoon (January–February 1993). The diversity in physical and biological characteristics of the regions and seasons is reflected in a broad range of both phyto- and bacterioplankton production. During the SW-monsoon, the Somali current showed highest bacterial production (up to 849 mgC m−2 day−1) in regions with enrichment of the surface waters by upwelling of cold, nutrient-rich, deep water. In contrast, the Gulf of Aden and the Red Sea were most productive during the NE-monsoon (average 225 mgC m−2 day−1). Depth profiles of the upper 300 m in general showed a subsurface maximum in bacterial abundance and production at 20–70 m depth. Heterotrophic activity and primary production were closely correlated, indicating the dependence of bacterioplankton on local phytoplankton-derived organic carbon and their ability to adapt quickly to changes in the environment. The bacterial carbon demand in the upper 300 m of the water column was largely supplied by phytoplankton production in the euphotic zone. Bacterial production was 18 ± 7% (average ± S.D.) of primary production. Assuming an assimilation efficiency of 50% for marine bacteria, they consumed up to half of the carbon produced by the phytoplankton. Cycling of carbon within the euphotic zone appears to be achieved by intense grazing by (micro)zooplankton and subsequent remineralization.

Journal Article
TL;DR: In this article, the authors compare the performance of parcelles polyclonales and monoclonales compared to parcelle monoclanales and polyclons.
Abstract: Quatre clones de Populus furent cultives dans un dispositif comportant trois espacements (0,5, 1,0 et 1,5 m) et des parcelles monoclonales et polyclonales ou tous les clones etaient completement melanges. Apres trois ans, plusieurs traits des arbres pris individuellement ou des peuplements differaient selon le clone, l'espacement, la methode de deploiement et les interactions entre ces facteurs. Les differences dans la croissance et la forme de la tige entre les clones etaient plus importantes dans les parcelles polyclonales que monoclonales. Du point de vue de la performance, les differences entre les methodes de deploiement etaient plus fortes dans les plantations les plus denses. Les peuplements monoclonaux etaient plus uniformes quant a la dimension des arbres que les peuplements polyclonaux. Le rendement total epige de matiere ligneuse seche atteignait en moyenne 48,0 Mg.ha -1 avec l'espacement de 0,5 m et diminuait avec l'augmentation de l'espacement. Le rendement de certains clones differait de celui d'autres clones dans les parcelles monoclonales et polyclonales. En assumant qu'on a plante le meme nombre de plants pour les clones correspondants, le mode de deploiement n'a pas affecte la productivite; c'est-a-dire que, meme s'il y avait des differences de rendement entre les clones, le rendement moyen des quatres clones en parcelles monoclonales (44,3 Mg.ha -1 ) ne differait pas du rendement des parcelles polyclonales (43,1 Mg.ha -1 ). Les rendements comparatifs (rendement dans les parcelles polyclonales/rendement dans les parcelles monoclonales) differaient par contre beaucoup et les augmentations ou les diminutions de rendement comparatif differaient selon l'espacement et le clone. La production et les stocks etaient moins egalement repartis entre les clones dans le cas des deploiements polyclonaux que monoclonaux.

Journal ArticleDOI
TL;DR: It appears that herbivores will not affect how grasses respond to elevated CO 2 and grazing is related to evolutionary grazing history or to mode of photosynthesis, and increased atmospheric CO2 may not affect food quantity in these three grasslands.
Abstract: Three plant species from each of three grassland ecosystems were grown under elevated (700 mL/m 3 ) and ambient (350 mL/m 3 )C O 2 and were defoliated or left undefoliated to test whether species response to elevated CO 2 and grazing is related to evolutionary grazing history or to mode of photosynthesis. The three ecosystems represented a tropical grassland dominated by C4 species (the Serengeti of Africa), a temperate grassland dominated by a mixture of C3 and C4 species (Flooding Pampa of South America), and a northern temperate grassland dominated by C3 species (Yellowstone National Park of North America). Plants were grown in growth chambers under common conditions to compare relative responses to grazing and elevated CO2. Elevated CO2 caused an increase in total biomass and total productivity (biomass 1 clippings) only in Yellowstone species, and increases in growth occurred primarily in crowns and roots (storage organs). There were no significant CO 2 effects on biomass or productivity in Serengeti or Flooding Pampa species, and no CO2 effects on aboveground biomass or productivity (aboveground biomass 1 clippings) in species from any of the three ecosys- tems. Since aboveground plant parts are the portions that are available to grazing mammals, this suggests that increased atmospheric CO2 may not affect food quantity in these three grasslands. There was no interaction between CO2 and defoliation for any species; thus, it appears that herbivores will not affect how grasses respond to elevated CO 2 (at least under average nutrient conditions). Elevated CO2 caused a reduction in leaf percentage of N in species from Yellowstone and Flooding Pampa (especially the C3 species, Briza subaristata), but not in Serengeti species. Because the quantity of food was unaffected by the CO2 treatments and forage N was reduced, grazing mammals in Yellowstone (elk, Cervus ela- phus, and bison, Bison bison) and the Flooding Pampa (cattle) may be negatively affected. Responses to defoliation were fairly consistent among ecosystems in aboveground pro- ductivity, which did not differ between defoliated and undefoliated plants, and in leaf water potentials and percentage of N, both of which increased in response to defoliation. However, differences among ecosystems were found for crown and root biomass in response to defoliation: Serengeti species, on average, had higher crown and similar root biomasses after defoliation, whereas defoliated species from the other two ecosystems had reduced crown and root biomass. We suggest that the lower intensity and increased temporal variance in grazing pressure in Yellowstone vs. the Serengeti, selected for plants that shift allocation away from roots and crowns in order to compensate for aboveground herbivory.

Journal ArticleDOI
TL;DR: The high standing biomass, high productivity and a presumably rapid turnover of biomass via detrital pathways suggest that fucoid macroalgae are important contributors to the stock of organic compounds on these nearshore reefs.
Abstract: Recently, concerns about human disturbance on coral reef communities have focused attention on macroalgae of nearshore fringing coral reefs of the Great Barrier Reef, Australia (GBR). However, the scarcity of baseline information makes it difficult to establish whether nearshore reef communities in the central GBR are perturbed or in a 'natural' state. This study provides data on biomass and productivity of nearshore reef macroalgae to serve as background information for the detection of future community changes. Over a period of 15 months, we estimated: i) biomass of conspicuous macroalgae in transects at three nearshore fringing reefs and ii) in situ net growth rates and net production of Sargassum baccularia. In summer, biomass was significantly dominated by large Fucales, especially S. baccularia (up to 200 g ash free dry weight m~). Ephemeral algae (species of Padina, Hydroclathrus, Colpomenia, Chnoospora, Laurencia) were most abundant in austral spring (up to 40 g AFDW m~). Maximum growth rates of S. baccularia of 3-4% day\" (entire thalli) occurred during the summer, preceding the reproductive period. Subsequent shedding of lateral branches resulted in negative growth rates during autumn/winter. In situ growth of excised shoots showed seasonal patterns comparable to entire thalli, except that growth rates were always positive. Biomass specific net production of excised shoots was significantly higher from spring to autumn than during winter. Areal productivity of S. baccularia had a significant maximum of 3 g C m~ day\" in spring, a value comparable to the productivity of coral-reef epilithic algal communities or temperate kelp forests. The high standing biomass, high productivity and a presumably rapid turnover of biomass via detrital pathways suggest that fucoid macroalgae are important contributors to the stock of organic compounds on these nearshore reefs.

Journal ArticleDOI
TL;DR: The importance of protists as bacterivores in a coastal community and an offshore community of Lake Erie was compared during the summer of 1994 and Heterotrophic nanoflagellates were the most important protistan bactervores at the offshore site, while HNAN and ciliates were similarly dominant bacterivore at the coastal site.
Abstract: The importance of protists as bacterivores in a coastal community and an offshore community of Lake Erie was compared during the summer of 1994. Bacterial density, cell size, and empirical conversion factors for bacterial productivity were highly variable at both sites and greater at the coastal site (P < 0.01). Bacterial productivity at the coastal site was 25-50 times higher than at the offshore site. Bacterivory was estimated in situ by fluorescently labeled native bacteria. Per-cell grazing rate and filtering rate for each taxon were routinely determined. Heterotrophic nanoflagellates (HNAN) were the most important protistan bacterivores at the offshore site, while HNAN and ciliates were similarly dominant bacterivores at the coastal site. Mixotrophic bacterivory was important only at the offshore site where Dinobryon was the dominant bacterivore. Bacterial carbon flux through protists was higher at the coastal site by an order of magnitude. Offshore protists grazed virtually the entire bacterial prod...


Journal Article
TL;DR: A long-term study to analyze the response of estuarine fishes to seasonal and interannual variations of Apalachicola River flow and associated habitat changes of the receiving estuary suggests that the fish associations were strongly dependent on interannually patterns of Apachicola river flow but that such relationships were primarily caused by biological interactions as defined by specific predator/prey relationships.
Abstract: A long-term (13 year) study was carried out to analyze the response of estuarine fishes (numbers, biomass and trophic organization) to seasonal and interannual variations of Apalachicola River flow and associated habitat changes of the receiving estuary (East Bay, Apalachicola Bay system, Florida). Periodic peak floods and prolonged droughts were important events that led to altered patterns of individual fish distribution in terms of numerical abundance and biomass. There was considerable interannual variation in the temporal distribution of the dominant fish species over the study period. Individual estuarine fish species use the estuary as a nursery ground with species-specific ontogenetic feeding patterns that are defined by the complex productivity patterns of the system. In East Bay, there was a dichotomous response of the estuarine trophic organization with herbivores and omnivores (dominated by infaunal and epifaunal macroinvertebrates) directly responsive to river-associated physicochemical factors whereas the carnivores (dominated by the fishes) responded to biological factors such as predation and competition. Estuarine fish organization was indirectly responsive to changes of river flow through prey responses to state habitat and productivity variables associated with river flows. This suggests that the fish associations were strongly dependent on interannual patterns of Apalachicola River flow but that such relationships were primarily caused by biological interactions as defined by specific predator/prey relationships. A prolonged drought led to reduced fish species richness and trophic diversity; such habitat stress was related to enhanced instability of the biological components of the estuary as a function of changes in nutrient cycling. The food web was simplified while overall fish biomass and individual species populations were numerically reduced. The trophic response times of fish assemblages were measured in years from the point of the initiation of the drought. Changes in flow rates that exceeded specific natural levels of variance could be followed by identification of the subtle yet important changes in estuarine productivity and related changes of fish representation within the food web. The use of individual fish species as indicators of such responses is not consistent with the processes that define the long-term behavior of estuarine populations.

Journal ArticleDOI
TL;DR: The model suggests that biomass dynamics and productivity are more sensitive to the light extinction coefficient than to the initial biomass conditions for the model, and suggest that biomass losses due to respiration and exudation are comparable to those resulting from mortality and frond breakage.

Journal Article
TL;DR: In this paper, the authors examine the fluxes of siliceous microplankton such as radiolarians, silicoflagellates, and diatoms in order to interpret temporal production changes in the upper ocean.
Abstract: ⋅Plankton flux, ⋅radiolaria, ⋅diatoms, ⋅silicoflagellates, ⋅seasonality, ⋅productivity, ⋅subarctic Pacific, ⋅the Gulf of Alaska. Siliceous microplankton such as radiolarians, silicoflagellates, and diatoms were exam- ined for their fluxes in order to interpret temporal production changes in the upper ocean. The eastern subarctic Pacific was chosen as the study region for its high biological productivity as well as a large amplitude of seasonality. Automated time-series sediment traps were deployed at two different locations in the Gulf of Alaska during 1982-1986 and 1985-1986. Temporal fluxes of siliceous microplankton showed large seasonal and interannual productivity changes during the course of the four-year long and one-year long field experiments. Most significantly, a severe suppression in production of biota occurred during late 1983 and most of 1984, reflecting a drastic reduction in the mixing of upper water layers, and causing less nutrient supply. Temporal fluxes of Neodenticula seminae, a dominant pennate diatom contributing greater than 70% of diatom flux assemblages in valve number, paralleled with that of total mass, indicating that this taxon is a productivity indicator. Radiolarian diversity indices and nassellarian fluxes are anti- correlated. Their temporal changes also match with all other relevant productivity parameters examined. Temporal flux pattern of Ceratospyris borealis, a nassellarian ra- diolarian, resembles quite well with that of N. seminae, suggesting that this species is also a promising paleoproductivity indicator.

Journal ArticleDOI
01 Dec 1997-Oikos
TL;DR: Investigation ofrophic interactions on herbaceous communities in a limestone dale in Northern England concluded that herbivore pressure is high because productivity is insufficient to sustain a high intensity of 'top-down' control from carnivores.
Abstract: Trophic interactions were investigated on herbaceous communities in a limestone dale in Northern England. Manipulative experiments involved the application of molluscicides and foliar and soil insecticides along natural productivity gradients. The results supported the theories of Fretwell and Oksanen in which trophic dynamics are predicted to be dependent upon primary productivity. Furthermore, the results extend the Fretwell-Oksanen model by the inclusion of invertebrates, and the applicability of the model to the small, individual habitat scale. At very low productivity, the vegetation was dominated by slow-growing, unpalatable species and did not experience a detectable amount of herbivory. In circumstances of high productivity, 'top-down' control of herbivores by carnivores appeared to protect the resident fast-growing and relatively palatable perennials from herbivory. Vegetation of intermediate productivity responded strongly to the removal of herbivores; here we conclude that herbivore pressure is high because productivity is insufficient to sustain a high intensity of 'top-down' control from carnivores.

Journal ArticleDOI
TL;DR: It is concluded that a high pp is determined by the ability of a plant to distribute its P over a large leaf area, rather than by greater allocation of P to the leaves.
Abstract: summary The growth of the grass Brachypodium pinnatum (L.) Beauv. in Dutch nutrient-poor chalk grasslands increases with enhanced nitrogen supply, whereas other grass species also require an enhanced phosphorus supply for a similar response (e.g. Dactylis glomerata L.), or are competitively suppressed at any increase in nutrient supply (e.g. Briza media L.). We investigated whether this interspecific variation in response to N and P supply is caused by differences in P productivity (PP), i.e. the instantaneous rate of biomass production per unit of P present in the plant. We hypothesized that PP is highest in Brachypodium pinnatum, in contrast to N productivity which is known to be the highest in Dactylis glomerata. Phosphorus productivity and its components were studied using a growth analysis with four exponential P addition rates of 0.03, 0.06, 009 and 0.11/0.15 mg P mg−1P d−1. Although Brachypodium pinnatum allocated more P to its leaf blades, it had a lower P productivity at high N and low P supply than did Dactylis glomerata. This was associated with a higher productivity per unit leaf P in Dactylis glomerata. Across all species and treatments, leaf PP showed a distinct negative correlation with P concentration per leaf area, regardless whether the variation in area-based leaf P concentration was caused by variation in leaf thickness, leaf tissue mass density or mass-based P concentration. A possible explanation for this would be a positive correlation between leaf chlorophyll concentration and P concentration, leading at high concentrations to shading within the leaf and to a low photosynthetic rate per unit leaf P. We conclude that a high pp is determined by the ability of a plant to distribute its P over a large leaf area, rather than by greater allocation of P to the leaves. Interspecific relationships for P productivity are similar to those known for N productivity.


Journal ArticleDOI
TL;DR: In this paper, the authors determined the productivity of size-fractionated phytoplankton in the northern North Pacific and the Bering Sea in summer and winter.
Abstract: We determined the productivity (ug C ug~' Chi a h~') of size-fractionated phytoplankton in the northern North Pacific and the Bering Sea in summer and winter. Picoplankton ( lff"C; whereas picoplankton in the subarctic region were similar in productivity or less productive than larger sized plankton, where the in situ temperature was 20 (am) were noticeably less productive than nanoplankton ( 9-20°C), nutrient-rich water, whereas netplankton were nearly as productive as nanoplankton in cold ( 9-16°C) water, while productivity was nearly equal in cold ( 10 um) in warm (10-20°C), nutrient-poor water in summer, while productivity was nearly equal in cold (<10°C), nutrient-rich water in winter. In addition, the number of cyanobacterial cells, one of the main © Oxford University Press 907

Journal ArticleDOI
TL;DR: In this article, the maximum rate of carbon fixation of phytoplankton in Lake Dunstan and Lake Wakatipu (Frankton Arm) was investigated and the relationship of biomass and productivity vs light and nutrients differed between the lakes.
Abstract: Phytoplankton biomass and productivity at two sites in the newly impounded Lake Dunstan and, upriver, in Lake Wakatipu (Frankton Arm) showed ranges throughout 1 year of 0.2–2.0 mg chlorophyll a m−3 and 0.9–6.0 mg C m−3 h−1 (maximum rate of carbon fixation). Peaks in phytoplankton abundance occurred in spring and summer in both lakes, but relationships of biomass and productivity vs light and nutrients differed between the lakes. In Lake Dunstan, P‐vs‐I parameters indicated that phytoplankton were photo‐acclimated to prevailing light conditions. In the Frankton Arm, P‐vs‐I parameters indicated that phytoplankton were poorly adapted to light conditions. Phytoplankton biomass and productivity were only depressed at the shortest observed hydraulic residence times (< 3 days). Phytoplankton biomass and productivity in Lake Dunstan were predicted from dissolved and particulate nitrogen concentrations and mean mixed‐layer light intensity. Annual mean chlorophyll a level was predicted satisfactorily using...