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Showing papers on "Productivity (ecology) published in 2008"


Journal ArticleDOI
TL;DR: In this article, the authors review 72 published articles to elucidate characteristics of biomass allocation and productivity of mangrove forests and also introduce recent progress on the study of MANGEO to solve the site and species-specific problems.

688 citations


Journal ArticleDOI
24 Jul 2008-Nature
TL;DR: It is shown that parasites have substantial biomass in these ecosystems and that the annual production of free-swimming trematode transmission stages was greater than the combined biomass of all quantified parasites and was also greater than bird biomass.
Abstract: Parasites can have strong impacts but are thought to contribute little biomass to ecosystems. We quantified the biomass of free-living and parasitic species in three estuaries on the Pacific coast of California and Baja California. Here we show that parasites have substantial biomass in these ecosystems. We found that parasite biomass exceeded that of top predators. The biomass of trematodes was particularly high, being comparable to that of the abundant birds, fishes, burrowing shrimps and polychaetes. Trophically transmitted parasites and parasitic castrators subsumed more biomass than did other parasitic functional groups. The extended phenotype biomass controlled by parasitic castrators sometimes exceeded that of their uninfected hosts. The annual production of free-swimming trematode transmission stages was greater than the combined biomass of all quantified parasites and was also greater than bird biomass. This biomass and productivity of parasites implies a profound role for infectious processes in these estuaries.

555 citations


Journal ArticleDOI
TL;DR: In this paper, seasonal variations in daily net ecosystem productivity and two main components of this productivity, daily total ecosystem respiration (REd) and daily gross ecosystem productivity (GEPd), were estimated over 2 years at a flux tower site in French Guiana, South America (5 °16'54"N, 52 °54'44"W).
Abstract: The lack of information on the ways seasonal drought modifies the CO2 exchange between Neotropical rainforest ecosystems and the atmosphere and the resulting carbon balance hinders our ability to precisely predict how these ecosystems will respond as global environmental changes force them to face increasingly contrasting conditions in the future. To address this issue, seasonal variations in daily net ecosystem productivity (NEPd) and two main components of this productivity, daily total ecosystem respiration (REd) and daily gross ecosystem productivity (GEPd), were estimated over 2 years at a flux tower site in French Guiana, South America (5 °16'54"N, 52 °54'44"W). We compared seasonal variations between wet and dry periods and between dry periods of contrasting levels of intensity (i.e. mild vs. severe) during equivalent 93-day periods. During the wet periods, the ecosystem was almost in balance with the atmosphere (storage of 9.0 g C m?2). Seasonal dry periods, regardless of their severity, are associated with higher incident radiation and lower REd combined with reduced soil respiration associated with low soil water availability. During the mild dry period, as is normally the case in this region, the amount of carbon stored in the ecosystem was 32.7 g C m?2. Severe drought conditions resulted in even lower REd, whereas the photosynthetic activity was only moderately reduced and no change in canopy structure was observed. Thus, the severe dry period was characterized by greater carbon storage (64.6 g C m?2), emphasizing that environmental conditions, such as during a severe drought, modify the CO2 exchange between Neotropical rainforest ecosystems and the atmosphere and potentially the resulting carbon balance

219 citations


Journal ArticleDOI
TL;DR: In this paper, the response of vegetation distribution, carbon, and fire to three scenarios of future climate change was simulated for California using the MC1 Dynamic General Vegetation Model, and the results showed that, under all three scenarios, Alpine/subalpine forest cover declined, and increases in the productivity of evergreen hardwoods led to the displacement of Evergreen Conifer Forest by Mixed Evergreen Forest.
Abstract: The response of vegetation distribution, carbon, and fire to three scenarios of future climate change was simulated for California using the MC1 Dynamic General Vegetation Model. Under all three scenarios, Alpine/Subalpine Forest cover declined, and increases in the productivity of evergreen hardwoods led to the displacement of Evergreen Conifer Forest by Mixed Evergreen Forest. Grassland expanded, largely at the expense of Woodland and Shrubland, even under the cooler and less dry climate scenario where increased woody plant production was offset by increased wildfire. Increases in net primary productivity under the cooler and less dry scenario contributed to a simulated carbon sink of about 321 teragrams for California by the end of the century. Declines in net primary productivity under the two warmer and drier scenarios contributed to a net loss of carbon ranging from about 76 to 129 teragrams. Total annual area burned in California increased under all three scenarios, ranging from 9-15% above the historical norm by the end of the century. Annual biomass consumption by fire by the end of the century was about 18% greater than the historical norm under the more productive cooler and less dry scenario. Under the warmer and drier scenarios, simulated biomass consumption was initially greater, but then at, or below, the historical norm by the end of the century.

209 citations


Journal ArticleDOI
TL;DR: A novel approach to food web studies by combining the two established methods of stable isotope analysis and fatty acid (FA) analysis is investigated, determined the C isotopic composition of individual diatom FA and traced these biomarkers in consumers, and demonstrated the potential value of compound-specific isotopeAnalysis of marine lipids to trace C flow through marine food webs.
Abstract: Global warming and the loss of sea ice threaten to alter patterns of productivity in arctic marine ecosystems because of a likely decline in primary productivity by sea ice algae. Estimates of the contribution of ice algae to total primary production range widely, from just 3 to >50%, and the importance of ice algae to higher trophic levels remains unknown. To help answer this question, we investigated a novel approach to food web studies by combining the two established methods of stable isotope analysis and fatty acid (FA) analysis--we determined the C isotopic composition of individual diatom FA and traced these biomarkers in consumers. Samples were collected near Barrow, Alaska and included ice algae, pelagic phytoplankton, zooplankton, fish, seabirds, pinnipeds and cetaceans. Ice algae and pelagic phytoplankton had distinctive overall FA signatures and clear differences in delta(13)C for two specific diatom FA biomarkers: 16:4n-1 (-24.0+/-2.4 and -30.7+/-0.8 per thousand, respectively) and 20:5n-3 (-18.3+/-2.0 and -26.9+/-0.7 per thousand, respectively). Nearly all delta(13)C values of these two FA in consumers fell between the two stable isotopic end members. A mass balance equation indicated that FA material derived from ice algae, compared to pelagic diatoms, averaged 71% (44-107%) in consumers based on delta(13)C values of 16:4n-1, but only 24% (0-61%) based on 20:5n-3. Our estimates derived from 16:4n-1, which is produced only by diatoms, probably best represented the contribution of ice algae relative to pelagic diatoms. However, many types of algae produce 20:5n-3, so the lower value derived from it likely represented a more realistic estimate of the proportion of ice algae material relative to all other types of phytoplankton. These preliminary results demonstrate the potential value of compound-specific isotope analysis of marine lipids to trace C flow through marine food webs and provide a foundation for future work.

195 citations


Journal ArticleDOI
TL;DR: The increase in above-ground biomass for both trees and lianas is consistent with the hypothesis of a shift in the functioning of Amazonian rain forests driven by environmental changes, although alternative hypotheses such as a recovery from past disturbances cannot be ruled out at the site, as suggested by the observed decrease in stem density.
Abstract: The dynamics of tropical forest woody plants was studied at the Nouragues Field Station, central French Guiana. Stem density, basal area, above-ground biomass and above-ground net primary productivity, including the contribution of litterfall, were estimated from two large permanent census plots of 12 and 10 ha, established on contrasting soil types, and censused twice, first in 1992?1994, then again in 2000?2002. Mean stem density was 512 stems ha?1 and basal area, 30m2 ha?1. Stem mortality rate ranged between 1.51% and 2.06% y?1. In both plots, stem density decreased over the study period. Using a correlation between wood density and wood hardness directly measured by a Pilodyn wood tester,we found that the mean wood densitywas 0.63 g cm?3, 12% smaller than the mean of wood density estimated from the literature values for the species occurring in our plot. Above-ground biomass ranged from 356 to 398Mgha?1 (oven-dry mass), and it increased over the census period. Leaf biomass was 6.47Mg ha?1. Our total estimate of aboveground net primary productivity was 8.81 MgC ha?1 y?1 (in carbon units), not accounting for loss to herbivory, branchfalls, or biogenic volatile organic compounds, whichmay altogether account for an additional 1MgC ha?1 y?1. Coarse wood productivity (stem growth plus recruitment) contributed to 4.16 MgC ha?1 y?1. Litterfall contributed to 4.65MgC ha?1 y?1 with 3.16 MgC ha?1 y?1 due to leaves, 1.10 MgC ha?1 y?1 to twigs, and 0.39MgC ha?1 y?1 to fruits and flowers. The increase in above-ground biomass for both trees and lianas is consistentwith the hypothesis of a shift in the functioning of Amazonian rain forests driven by environmental changes, although alternative hypotheses such as a recovery from past disturbances cannot be ruled out at our site, as suggested by the observed decrease in stem density. Key Words: above-ground biomass, carbon, French Guiana, net primary productivity, tropical forest

158 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used the phytoplankton biomass (binned at 7-day intervals), PAR and cloud cover data from SeaWiFS, ice concentrations data from SSM/I and AMSR-E, and sea surface temperature data from AVHRR, in combination with a vertically integrated model to estimate primary productivity throughout the Southern Ocean (south of 60"s).
Abstract: Sea ice in the Southern Ocean is a major controlling factor on phytoplankton productivity and growth, but the relationship is modified by regional differences in atmospheric and oceanographic conditions We used the phytoplankton biomass (binned at 7-day intervals), PAR and cloud cover data from SeaWiFS, ice concentrations data from SSM/I and AMSR-E, and sea-surface temperature data from AVHRR, in combination with a vertically integrated model to estimate primary productivity throughout the Southern Ocean (south of 60"s) We also selected six areas within the Southern Ocean and analyzed the variability of the primary productivity and trends through time, as well as the relationship of sea ice to productivity We found substantial interannual variability in productivity from 1997 - 2005 in all regions of the Southern Ocean, and this variability appeared to be driven in large part by ice dynamics The most productive regions of Antarctic waters were the continental shelves, which showed the earliest growth, the maximum biomass, and the greatest areal specific productivity In contrast, no large, sustained blooms occurred in waters of greater depth (> 1,000 m) We suggest that this is due to the slightly greater mixed layer depths found in waters off the continental shelf, and that the interactive effects of iron and irradiance (that is, increased iron requirements in low irradiance environments) result in the limitation of phytoplankton biomass over large regions of the Southern Ocean

157 citations


Journal ArticleDOI
TL;DR: On average, increasing species richness in perennial herbaceous polycultures increased productivity and weed suppression, but well-adapted species produced high biomass yield regardless of richness.
Abstract: Species diversity can increase natural grasslands productivity but the effect of diversity in agricultural systems is not well understood. Our objective was to measure the effects of species composition, species richness, and harvest management on crop and weed biomass in perennial herbaceous polycultures. In 2003, 49 combinations of seven species (legumes, C 3 and C 4 grasses) including all monocultures and selected two to six species polycultures were sown in small plots at two Iowa, USA, locations in a replicated field design. Plots were split in half and managed with either one or three harvests in each of 2004 and 2005. Biomass increased log-linearly with species richness in all location-management environments and the response was not different between managements. Polycultures outyielded monocultures on average by 73%. The most productive species in monoculture for each management best explained the variation in biomass productivity. The biomass of plots containing this species did not increase with richness in most environments but biomass of plots without this species increased log-linearly in all cases. Weed biomass decreased exponentially with richness in all environments. On average, increasing species richness in perennial herbaceous polycultures increased productivity and weed suppression, but well-adapted species produced high biomass yield regardless of richness.

156 citations


Book ChapterDOI
01 Jan 2008
TL;DR: In this article, Boyer et al. showed that low water availability limits the productivity of many natural ecosystems, particularly in dry climates (Fig. 3.1) and that losses in crop yield due to water stress exceed losses due to all other biotic and environmental factors combined.
Abstract: Although water is the most abundant molecule on the Earth’s surface, the availability of water is the factor that most strongly restricts terrestrial plant production on a global scale. Low water availability limits the productivity of many natural ecosystems, particularly in dry climates (Fig. 3.1). In addition, losses in crop yield due to water stress exceed losses due to all other biotic and environmental factors combined (Boyer 1985). Regions where rainfall is abundant and fairly evenly distributed over the growing season, such as in the wet tropics, have lush vegetation. Where summer droughts are frequent and severe, forests are replaced by grasslands, as in the Asian steppes and North American prairies. Further decrease in rainfall results in semidesert, with scattered shrubs, and finally deserts. Even the effects of temperature are partly exerted through water relations because rates of evaporation and transpiration are correlated with temperature. Thus, if we want to explain natural patterns of productivity or to increase productivity of agriculture or forestry, it is crucial that we understand the controls over plant water relations and the consequences for plant growth of an inadequate water supply.

155 citations


Journal ArticleDOI
TL;DR: Artificial synchrony of arrival (sowing) of PFTs may induce assembly routes favouring faster-establishing taxa, with consequences for ecosystem functioning (e.g. productivity).
Abstract: 'Who comes first' is decisive for plant community assembly and ecosystem properties. Early arrival or faster initial development of a species leads to space occupancy both above and below ground and contributes to species success. However, regular disturbance (e.g. biomass removal) might permit later-arriving or slower-developing species to catch up. Here, artificial communities of grassland species belonging to the plant functional types (PFTs) herb, grass and legume were used to test the effect of stepwise arrival (sowing) of PFTs. Dramatic effects were found as a result of a 3 wk arrival difference on composition and above-ground biomass that persisted over four harvests and two seasons. Priority effects, such as unequal germination time (arrival), and thus differences in community age structure, had lasting effects on PFT biomass contribution and associated ecosystem functioning. These effects were robust against above-ground disturbance. Benefits of earlier root formation outweighed above-ground species interaction. Earlier space occupancy and bigger reserve pools are the likely causes. Natural populations commonly exhibit age diversity and asynchrony of development among taxa. In experiments, artificial synchrony of arrival (sowing) may thus induce assembly routes favouring faster-establishing taxa, with consequences for ecosystem functioning (e.g. productivity). Founder effects, such as those observed here, could be even greater in communities of slow-growing species or forests, given their longer generation time and minor disturbance.

153 citations


Journal ArticleDOI
TL;DR: In this article, the authors quantified aboveground plant biomass and net primary productivity (ANPP) for 4 years after a 1999 wildfire in a well-drained (dry) site, and also across a dry and a moderately well-drain (mesic) chronosequence of sites that varied in time since fire (2 to ∼116 years).
Abstract: Plant biomass accumulation and productivity are important determinants of ecosystem carbon (C) balance during post-fire succession. In boreal black spruce (Picea mariana) forests near Delta Junction, Alaska, we quantified aboveground plant biomass and net primary productivity (ANPP) for 4 years after a 1999 wildfire in a well-drained (dry) site, and also across a dry and a moderately well-drained (mesic) chronosequence of sites that varied in time since fire (2 to ∼116 years). Four years after fire, total biomass at the 1999 burn site had increased exponentially to 160 ± 21 g m−2 (mean ± 1SE) and vascular ANPP had recovered to 138 ± 32 g m−2 y−1, which was not different than that of a nearby unburned stand (160 ± 48 g m−2 y−1) that had similar pre-fire stand structure and understory composition. Production in the young site was dominated by re-sprouting graminoids, whereas production in the unburned site was dominated by black spruce. On the dry and mesic chronosequences, total biomass pools, including overstory and understory vascular and non-vascular plants, and lichens, increased logarithmically (dry) or linearly (mesic) with increasing site age, reaching a maximum of 2469 ± 180 (dry) and 4008 ± 233 g m−2 (mesic) in mature stands. Biomass differences were primarily due to higher tree density in the mesic sites because mass per tree was similar between sites. ANPP of vascular and non-vascular plants increased linearly over time in the mesic chronosequence to 335 ± 68 g m−2 y−1 in the mature site, but in the dry chronosequence it peaked at 410 ± 43 g m−2 y−1 in a 15-year-old stand dominated by deciduous trees and shrubs. Key factors regulating biomass accumulation and production in these ecosystems appear to be the abundance and composition of re-sprouting species early in succession, the abundance of deciduous trees and shrubs in intermediate aged stands, and the density of black spruce across all stand ages. A better understanding of the controls over these factors will help predict how changes in climate and fire regime will affect the carbon balance of Interior Alaska.

Journal ArticleDOI
TL;DR: In this article, the authors analyzed riverine dissolved organic matter and nutrient loads in three adjacent coastal watersheds along the Gulf of Alaska and found that different levels of glacial coverage can alter the timing and magnitude of fresh water, dissolved organic material and nutrient yields.
Abstract: Dissolved organic matter and nutrients from high-latitude coastal watersheds stimulate microbial activity and primary productivity in near-shore ecosystems. A survey of southeast Alaskan watersheds suggests that the extent of glacial coverage may control the release of these nutrients to rivers and ultimately the oceans. The delivery of fresh water, carbon, nitrogen and phosphorous from high-latitude regional watersheds is important to the ecology and nutrient balance of coastal marine ecosystems in the Northern1 and Southern2 hemispheres. Bioavailable dissolved organic matter from rivers can support microbes in near-shore environments, and may also stimulate primary production3,4. Recent studies suggest that impacts of climate change, such as thawing permafrost, may affect nutrient yields in large northern rivers5. Here we analyse riverine dissolved organic matter and nutrient loads in three adjacent coastal watersheds along the Gulf of Alaska. We find that different levels of glacial coverage can alter the timing and magnitude of fresh water, dissolved organic matter and nutrient yields. Our results suggest that a lower extent of glacial coverage within a watershed can lead to higher amounts of dissolved organic matter, but decreased phosphorous yields. Moreover, an abundance of early successional plant species following deglaciation can increase riverine nitrogen levels. We conclude that changes in riverine yields of dissolved organic matter and nutrients due to reductions in glacier extent in coastal watersheds may affect the productivity and function of near-shore coastal ecosystems.

Journal ArticleDOI
TL;DR: Bacterial predation resistance increases in nutrient-rich waters with high protozoan predation, and Quantile regression analysis indicated that the selection pressures on edible bacteria were increasing along the productivity gradient.
Abstract: Top-down control of lower trophic levels, e.g., bacteria, has been suggested to increase along aquatic productivity gradients. The response by the bacterial community may be to become more predation resistant in highly productive environments. To test this hypothesis, samples were taken from 20 aquatic systems along a productivity gradient (dissolved organic carbon from 7 to 71 mg/L), during late summer. The results showed that the biomass of bacteria, phytoplankton, and ciliates increased along the gradient (r2 = 0.532, 0.426, and 0.758, P < 0.01, respectively). However, the organisms did not increase equally, and the ratio of protozoan to bacterial biomass showed a 100-fold increase along the gradient. Ciliates dominated the protozoan biomass in the more nutrient-rich waters. The edibility of colony-forming bacteria was tested using a ciliate predator, Tetrahymena pyriformis. Bacterial edibility was found to decrease with increases in nutrient richness and ciliate biomass in the aquatic systems (r2 = 0.358, P < 0.01; r2 = 0.242, P < 0.05, respectively). Quantile regression analysis indicated that the selection pressures on edible bacteria were increasing along the productivity gradient. Thus, inedible forms of bacteria were selected for in the transition from oligotrophic to eutrophic conditions. Isolated bacteria were distributed among the alpha-, beta-, and gamma- Proteobacteria and the Actinobacteria and Firmicutes taxa. We conclude that bacterial predation resistance increases in nutrient-rich waters with high protozoan predation.

Journal ArticleDOI
TL;DR: In this paper, the authors examined the zooplankton community near the Pribilof Islands and on the middle shelf of the southeastern Bering Sea in summer of 1999 and 2004 to document differences and similarities in species composition, abundance and biomass by region and year.
Abstract: The southeastern Bering Sea sustains one of the largest fisheries in the United States, as well as wildlife resources that support valuable tourist and subsistence economies. The fish and wildlife populations in turn are sustained by a food web linking primary producers to apex predators through the zooplankton community. Recent shifts in climate toward warmer conditions may threaten these resources by altering productivity and trophic relationships in the ecosystem on the southeastern Bering Sea shelf. We examined the zooplankton community near the Pribilof Islands and on the middle shelf of the southeastern Bering Sea in summer of 1999 and 2004 to document differences and similarities in species composition, abundance and biomass by region and year. Between August 1999 and August 2004, the summer zooplankton community of the middle shelf shifted from large to small species. Significant declines were observed in the biomass of large scyphozoans (Chrysaora melanaster), large copepods (Calanus marshallae), arrow worms (Sagitta elegans) and euphausiids (Thysanoessa raschii, T. inermis) between 1999 and 2004. In contrast, significantly higher densities of the small copepods (Pseudocalanus spp., Oithona similis) and small hydromedusae (Euphysa flammea) were observed in 2004 relative to 1999. Stomach analyses of young-of-the-year (age 0) pollock (Theragra chalcogramma) from the middle shelf indicated a dietary shift from large to small copepods in 2004 relative to 1999. The shift in the zooplankton community was accompanied by a 3-fold increase in water-column stability in 2004 relative to 1999, primarily due to warmer water above the thermocline, with a mean temperature of 7.3 °C in 1999 and 12.6 °C in 2004. The elevated water-column stability and warmer conditions may have influenced the zooplankton composition by lowering summer primary production and selecting for species more tolerant of a warm, oligotrophic environment. A time series of temperature from the middle shelf indicates that the warmer conditions in 2004 are part of a trend rather than an expression of interannual variability. These results suggest that if climate on the Bering Sea shelf continues to warm, the zooplankton community may shift from large to small taxa which could strongly impact apex predators and the economies they support.

Journal ArticleDOI
TL;DR: In this paper, the initial effects of warming on the CO2 balance of a lichen-rich dwarf shrub tundra, a widespread but little studied ecosystem type in the Arctic, was assessed.
Abstract: The aim of this study was to assess initial effects of warming on the CO2 balance of a lichen-rich dwarf shrub tundra, a widespread but little studied ecosystem type in the Arctic. We analyzed whole ecosystem carbon exchange rates as well as nutrient dynamics, microbial and plant community composition and biomass after 2 years of experimental temperature increase. Plant biomass increased significantly with warming, mainly due to the strong response of lichens, the dominant plant group within this ecosystem. Experimental warming also increased soil nitrogen pools and nitrogen turnover rates. Major changes in soil microbial and plant composition, however, were not detected. Although experimental warming increased gross ecosystem productivity, the higher plant biomass did not compensate for the much greater increase in C losses. Ecosystem respiration and net ecosystem CO2 losses were significantly higher in warmed plots compared to control ones. We suggest that this was due to increased soil respiration, since soil carbon pools were lower in warmed soils, at least in the upper horizons. Our study thus supports the general hypothesis that tundra ecosystems turn from a carbon sink to a carbon source when temperatures increase in the short-term. Since lichens, which produce low quality litter, increased their biomass significantly with warming in this specific ecosystem type, CO2 losses may slow down in the long-term.

Journal ArticleDOI
TL;DR: A mechanism, the fertility effect, by which increased plant species diversity may increase community productivity over time by increasing the supply of nutrients via both greater inputs and greater retention is suggested.
Abstract: Most explanations for the positive effect of plant species diversity on productivity have focused on the efficiency of resource use, implicitly assuming that resource supply is constant. To test this assumption, we grew seedlings of Echinacea purpurea in soil collected beneath 10-year-old, experimental plant communities containing one, two, four, eight, or 16 native grassland species. The results of this greenhouse bioassay challenge the assumption of constant resource supply; we found that bioassay seedlings grown in soil collected from experimental communities containing 16 plant species produced 70% more biomass than seedlings grown in soil collected beneath monocultures. This increase was likely attributable to greater soil N availability, which had increased in higher diversity communities over the 10-year-duration of the experiment. In a distinction akin to the selection/complementarity partition commonly made in studies of diversity and productivity, we further determined whether the additive effects of functional groups or the interactive effects of functional groups explained the increase in fertility with diversity. The increase in bioassay seedling biomass with diversity was largely explained by a concomitant increase in N-fixer, C4 grass, forb, and C3 grass biomass with diversity, suggesting that the additive effects of these four functional groups at higher diversity contributed to enhance N availability and retention. Nevertheless, diversity still explained a significant amount of the residual variation in bioassay seedling biomass after functional group biomass was included in a multiple regression, suggesting that interactions also increased fertility in diverse communities. Our results suggest a mechanism, the fertility effect, by which increased plant species diversity may increase community productivity over time by increasing the supply of nutrients via both greater inputs and greater retention.

Book ChapterDOI
01 Jan 2008
TL;DR: A review of available literature suggests that rates of in-stream primary production in tropical regions are typically at least an order of magnitude greater than comparable temperate systems as mentioned in this paper, which is in contrast to many wellstudied north temperate latitude streams in deciduous forest ecosystems, which are thought to depend mainly upon terrestrial leaf litter and detritus-based food webs.
Abstract: Net primary production is a fundamental ecological process that reflects the amount of carbon synthesized within an ecosystem, which is ultimately available to consumers. Although current ecosystem models of streams and rivers have placed variable emphasis on the importance of instream primary production to aquatic food webs, recent research indicates that aquatic algae are a significant contributor to food webs in tropical rivers and streams. This is in contrast to many well-studied north temperate latitude streams in deciduous forest ecosystems, which are thought to depend mainly upon terrestrial leaf litter and detritus-based food webs. A review of available literature suggests that rates of in-stream primary production in tropical regions are typically at least an order of magnitude greater than comparable temperate systems. Although nutrient status can significantly modify rates, the ultimate driver of aquatic primary production is light availability. Rates of benthic gross primary productivity in tropical streams range from 100 to 200mgCm-2 d-1 under shaded conditions to much higher values associated with open canopies. Light inputs to the channel can be controlled by stream orientation, with east-west channels receiving much more light compared to those orientated north-south. Rates of production for large tropical rivers are similar to those for streams, although factors that regulate production are different and hence they respond differently to human impact. Values for rivers range from 10 to 200mgCm-2 d-1 to more than 1000mgCm-2 d-1. Production is often limited by turbidity, which tends to be at a maximum after high flow events. In polluted tropical rivers, productivity responds to nutrient enrichment and can attain rates of 6000mgCm-2 d-1. The highest rates of production in tropical river systems typically occur in floodplains subject to seasonal inundation, where aquatic vascular plants dominate total productivity. These macrophytes (herbaceous vascular plants that can be primarily terrestrial or aquatic) can proliferate in situ or be transported from upstream. Rooted aquatic plants with emergent or floating leaves respond to the rising water level, sometimes elongating their stems at a rate of 20cmd-1, and many terrestrial plants tolerate prolonged submergence. These ecosystems can attain very high rates of primary production that rival those of intensively managed agro-ecosystems. Floodplain forest can also be a productive component of these ecosystems. Both attached algae (periphyton) and phytoplankton contribute substantially to algal production in floodplain waters. Floodplains are important for fodder and for nursery habitat for fish, which re-invade main channels when floods recede. Tropical rivers may flow into coastal mangrove ecosystems, where rates of productivity are variable and often dependent of methodologies of measurement. Rates of mangrove production range from 1300mgCm-2 d-1 in the T鲭inos Lagoon, Mexico to 1900-2700mgCm-2 d-1 in the Fly River estuary (Papua New Guinea). However, rates of phytoplankton growth within mangrove forests are low, probably controlled by shading and turbidity, and are comparable to those of tropical streams. As pressures for water resource development intensify, tropical fluvial ecosystems are coming under increasing pressure. It is important to understand how these ecosystems function and to ensure problems of developing water resources in temperate regions are not repeated in the tropics.

Journal ArticleDOI
TL;DR: The results support the idea that environmental factors could act as hidden sources of variability in biodiversity experiments and quantified the relative importance of environmental heterogeneity and diversity on tree growth and mortality in a tropical tree plantation.
Abstract: Summary 1. Over 5000 trees were grown in plots of differing diversity levels (1, 3 and 6 species) in a plantation established in Panama. Four and five years after establishment, we analysed parameters related to the productivity of this tropical plantation (tree survival, height and biomass as well as plot basal area) to test for the presence of biodiversity effects. The relative importance of environmental heterogeneity (such as soil, topography, and drainage) and biodiversity on tree growth and mortality was determined using partial redundancy analysis. 2. Hierarchical clustering revealed nine different soil clusters based on soil quality and drainage. By chance, the six-species plots were apparently established on more variable soils then on the other diversity levels. We found little evidence for spatial autocorrelation between subplots, with the exception of four subplots located on a ridge that extends on the North‐South axis of the plantation and corresponds to a zone of higher productivity. 3. The redundancy analysis indicated that environmental heterogeneity and biodiversity together explained around 50% of the variation in subplot productivity and tree mortality. Environment explained 35‐57% of the variation in productivity and mortality, respectively, whereas diversity explained an additional 23‐30%. 4. Our simulation model revealed a significant positive effect of biodiversity on growth but no effect of biodiversity on mortality. The standardized effect sizes that we used to detect over- or under-yielding or no effect in comparison with monoculture were highly variable and the variability was largely explained by traits related to site topography. 5. Synthesis . In our tropical tree plantation, we detected biodiversity effects at a scale relevant to conservation and quantified the relative importance of environmental heterogeneity and diversity on tree growth and mortality. Our results support the idea that environmental factors could act as hidden sources of variability in biodiversity experiments. Environmental and spatial heterogeneity induced variable responses to biodiversity and amplified the differences between three- and six-species plots. Species identity explained more variation in productivity than did the species diversity. One species, Cedrela odorata , was associated with increased productivity.

Journal ArticleDOI
TL;DR: Analysis of five additional FTCs in winter for the above- and below-ground productivity of experimental grassland communities and soil enzymatic activity over the following growing season shows changes in productivity resulting in an increased shoot-to-root ratio and shifts in timing are capable of altering ecosystem stability and ecosystem services, such as productivity and nutrient retention.
Abstract: Ongoing global warming will increase the frequency of soil freeze-thaw cycles (FTCs) in cool-temperate and other high-latitude regions. The spatial relevance of seasonally frozen ground amounts to c. 55% of the total land area of the northern hemisphere. Evidence suggests that FTCs contribute to nutrient dynamics. Knowledge of their effects on plant communities is scarce, although plants may be the decisive factor in controlling ecosystem functions such as nutrient retention. Here, the effects are analysed of five additional FTCs in winter for the above- and below-ground productivity of experimental grassland communities and soil enzymatic activity over the following growing season. Freeze-thaw cycles increased the above-ground productivity but reduced root length over the whole subsequent growing season. In summer, no changes in soil enzymatic activities representing the carbon, nitrogen and phosphorus cycles were observed in the FTC-manipulated plots, except for an increased cellobiohydrolase activity. Changes in productivity resulting in an increased shoot-to-root ratio and shifts in timing are capable of altering ecosystem stability and ecosystem services, such as productivity and nutrient retention.

Journal ArticleDOI
TL;DR: The main source of interannual phytoplankton variability in the Delta during 1996-2005, including the upward trend, appears to have been freshwater flow variability and its effect on particle residence time as discussed by the authors.
Abstract: Several pelagic fish populations in the upper San Francisco Estuary have recently declined to historically low abundances, prompting an interest in the status of their food supply. Previous studies have indicated that the primary food supply for metazoans in the Delta is phytoplankton productivity, and the long-term decrease in phytoplankton over the last few decades may very well play a role in the long-term decline of pelagic fish abundance. Regional phytoplankton biomass trends during 1996–2005, however, are positive in the Delta and neutral in Suisun Bay, the two major sub-regions of the upper estuary. The trend in Delta primary productivity is also positive. Changes in phytoplankton biomass and production during the last decade are therefore unlikely to be the cause of these more recent metazoan declines. The main source of interannual phytoplankton variability in the Delta during 1996–2005, including the upward trend, appears to have been freshwater flow variability and its effect on particle residence time. This conclusion is supported by trend analyses; the concurrence of these time trends at widely-separated stations; empirical models at the annual and monthly time scales; particle residence time estimates; and experience from other estuaries. A significant temperature increase was also noticed, at least partially independent of flow changes, but its net effect on the phytoplankton community is unknown because of differential effects on growth and loss processes. Phytoplankton biomass in Suisun Bay, in contrast to the Delta, did not increase during 1996–2005. Consistent with this observation, Suisun Bay phytoplankton exhibited relatively low responsiveness to flow variability. This behavior differs from earlier chlorophyll-flow relationships reported in the literature. The reason appears to be the invasion of Suisun Bay by a clam—Corbula amurensis—in 1986, which has since maintained the phytoplankton community mostly at low levels by vigorous filter-feeding. In the past, flows into Suisun Bay generally diluted the higher phytoplankton concentrations within the bay; now they bring in higher phytoplankton concentrations from upstream. The supply of phytoplankton carbon to Suisun Bay has always been dominated by allochthonous sources, at least for mean flow conditions. Now this dominance must be even more pronounced.

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TL;DR: In this article, the authors carried out measurements in a semiarid Pinus halepensis (Aleppo pine) forest of aboveground respiration rates of foliage, R f, and stem, R t over 3 years.
Abstract: Predictions of warming and drying in the Mediterranean and other regions require quantifying of such effects on ecosystem carbon dynamics and respiration. Long-term effects can only be obtained from forests in which seasonal drought is a regular feature. We carried out measurements in a semiarid Pinus halepensis (Aleppo pine) forest of aboveground respiration rates of foliage, R f , and stem, R t over 3 years. Component respiration combined with ongoing biometric, net CO 2 flux [net ecosystem productivity (NEP)] and soil respiration measurements were scaled to the ecosystem level to estimate gross and net primary productivity (GPP, NPP) and carbon-use efficiency (CUE = NPP/ GPP) using 6 years data. GPP, NPP and NEP were, on average, 880, 350 and 211 g Cm -2 yr -1 , respectively. The above ground respiration made up half of total ecosystem respiration but CUE remained high at 0.4. Large seasonal variations in both R f and R t were not consistently correlated with seasonal temperature trends. Seasonal adjustments of respiration were observed in both the normalized rate (R 20 ) and short-term temperature sensitivity (Q 10 ), resulting in low respiration rates during the hot, dry period. R f in fully developed needles was highest over winter-spring, and foliage R 20 was correlated with photosynthesis over the year. Needle growth occurred over summer, with respiration rates in developing needles higher than the fully developed foliage at most times. R t showed a distinct seasonal maximum in May irrespective of year, which was not correlated to the winter stem growth, but could be associated with phenological drivers such as carbohydrate re-mobilization and cambial activity. We show that in a semiarid pine forest photosynthesis and stem growth peak in (wet) winter and leaf growth in (dry) summer, and associated adjustments of component respiration, dominated by those in R 20 , minimize annual respiratory losses. This is likely a key for maintaining high CUE and ecosystem productivity similar to much wetter sites, and could lead to different predictions of the effect of warming and drying climate on productivity of pine forests than based on short-term droughts.

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TL;DR: In this article, the productivity of hilly grassland of the Xilin River Basin as affected by slope aspect (North versus South), aboveground green biomass (AGB) and species composition were studied at four hill sites in 2005.


Journal Article
TL;DR: An Ecopath-Ecosim ecosystem model under development for coastal areas of the Gulf of Mexico simulates responses of 63 biomass pools to changes in fisheries and primary productivity and makes one highly counterintuitive policy prediction about impacts of management efforts aimed at reducing by-catch in the shrimp trawl fishery.
Abstract: An Ecopath-Ecosim ecosystem model under development for coastal areas of the Gulf of Mexico simulates responses of 63 biomass pools to changes in fisheries and primary productivity. Ten key species are represented by detailed, multistanza population-dynamics models (31 of the biomass pools) that attempt to account explicitly for possible changes in recruitment rates due to changes in by-catch rates and trophic interactions. Over a 1950-2004 historical reference period, the model shows good simulated agreement with time-series patterns estimated from stock assessment and relative abundance index data for many of the species, and in particular it offers an explanation for apparent nonstationarity in natural mortality rates of menhaden (declining apparent M over time). It makes one highly counterintuitive policy prediction about impacts of management efforts aimed at reducing by-catch in the shrimp trawl fishery, namely that by-catch reduction may cause negative impacts on productivity of several valued species [menhaden, Brevoortia patronus Goode, 1878; red drum, Sciaenops ocellatus (Linnaeus, 1766); red snapper, Lutjanus campechanus (Poey, 1860)] by allowing recovery of some benthic predators such as catfishes [Arius felis (Linnaeus, 1766), Bagre marinus (Mitchill, 1815)] that have been reduced by trawling but are also potentially important predators on juveniles of the valued species. Recognition of this policy implication would have been impossible without explicit, multistanza representation of juvenile life histories and trophic interactions, because the predicted changes in predation regimes represent only very small overall biomass fluxes.

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TL;DR: This paper examined the molecular biodiversity within all three microbial domains (Bacteria, Archaea, and Eukaryota) and the heterotrophic productivity in Lake Mackenzie, a stamukhi lake in the western Canadian Arctic, and made comparative measurements in the freshwater (Mackenzie River) and marine source waters.
Abstract: Stamukhi lakes are vast but little-explored Arctic ecosystems. They occur throughout winter, spring, and early summer near large river inflows along the Arctic coastline, and are the result of freshwater retention behind the thick barrier of rubble ice (stamukhi) that forms at the outer limit of land-fast sea ice. We examined the molecular biodiversity within all three microbial domains (Bacteria, Archaea, and Eukaryota) and the heterotrophic productivity in Lake Mackenzie, a stamukhi lake in the western Canadian Arctic, and made comparative measurements in the freshwater (Mackenzie River) and marine (Beaufort Sea) source waters. Bacterial and eukaryotic communities in the stamukhi lake differed in composition and diversity from both marine and riverine environments, whereas the archaeal communities were similar in the lake and river. Bacteria 16S ribosomal RNA sequences from the lake were mostly within freshwater clusters of Betaproteobacteria and Bacteroidetes and the Archaea were within the Lake Dagow sediment and Rice cluster-V clusters of Euryarchaeota. The eukaryotes were mainly ciliates from the subclass Choreotrichia, and there was a notable lack of flagellates. Heterotrophic production rates in the lake were lower than in the river and more similar to those in the sea, despite much higher bacterial concentrations than in either. The lake samples had markedly higher ratios of 3H leucine to 3H thymidine incorporation than in the river and sea, implying some physiological stress. Lake Mackenzie is an active microbial ecosystem with distinct physical and microbiological properties. This circumpolar ecosystem type, vulnerable to the ongoing effects of climate change, likely plays a key functional role in processing riverine inputs to the Arctic Ocean.

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TL;DR: Information on these highly abundant but often overlooked faunal groups is essential for estimates of overall abundance, biomass, species richness and productivity in the benthos, and as such has important implications for several areas of aquatic research, e.g. for those dealing with trophic dynamics.
Abstract: SUMMARY 1. The ciliate and metazoan meiofaunal assemblages of two contrasting lowland streams in south-east England were examined over the period of a year, using a high taxonomic resolution. Monthly samples were taken from an oligotrophic, acid stream (Lone Oak) and a circumneutral, nutrient-rich stream (Pant) between March 2003 and February 2004. 2. We assessed the relative importance of ciliates and rotifers within the small-sized benthic assemblage with respect to their abundance, biomass and species richness. In addition, we examined the influence of abiotic and biotic parameters and season on the assemblage composition at two levels of taxonomic resolution (species and groups). 3. Ciliates dominated the assemblages numerically, with maximum densities of over 900 000 and 6 000 000 ind. m )2 in Lone Oak and Pant respectively. Rotifers and nematodes dominated meiofaunal densities, although their contribution to total meiofaunal biomass (maxima of 71.9 mgC m )2 in Lone Oak and of 646.8 mgC m )2 in the Pant) was low and rotifer biomass equalled that of ciliates. 4. Although the two streams differed in terms of total abundance of ciliates and meiofauna and shared only 7% of species, the relative proportion of groups was similar. Sediment grain size distribution (the percentile representing the 0.5–1 mm fraction) was correlated with assemblage structure at the species level, revealing the tight coupling between these small organisms and their physical environment. Seasonal changes in the relative abundance of groups followed similar patterns in both streams, and were correlated with the abundance of cyclopoid copepods and temperature. 5. Information on these highly abundant but often overlooked faunal groups is essential for estimates of overall abundance, biomass, species richness and productivity in the benthos, and as such has important implications for several areas of aquatic research, e.g. for those dealing with trophic dynamics.

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TL;DR: The results corroborate the predictions of the EEH, implying that the endotherm community and the vegetation of the North European tundra behaves dynamically as if each trophic level consisted of a single population, in spite of local co‐occurrence of >20 plant species representing different major taxonomic groups, growth forms, and defensive strategies.
Abstract: According to the exploitation ecosystems hypothesis (EEH), productive terrestrial ecosystems are characterized by community‐level trophic cascades, whereas unproductive ecosystems harbor food‐limited grazers, which regulate community‐level plant biomass. We tested this hypothesis along arctic‐alpine productivity gradients at the Joatka field base, Finnmark, Norway. In unproductive habitats, mammalian predators were absent and plant biomass was constant, whereas herbivore biomass varied, reflecting the productivity of the habitat. In productive habitats, predatory mammals were persistently present and plant biomass varied in space, but herbivore biomass did not. Plant biomass of productive tundra scrublands declined by 40% when vegetation blocks were transferred to predation‐free islands. Corresponding transfer to herbivore‐free islands triggered an increase in plant biomass. Fertilization of an unproductive tundra heath resulted in a fourfold increase in rodent density and a corresponding increa...

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TL;DR: In this paper, the authors show that a climate-induced decline of an invertebrate species in a low-diversity ecosystem could contribute to significant changes in carbon (C) cycling.
Abstract: Low-diversity ecosystems cover large portions of the Earth's land surface, yet studies of climate change on ecosystem functioning typically focus on temperate ecosystems, where diversity is high and the effects of individual species on ecosystem functioning are difficult to determine. We show that a climate-induced decline of an invertebrate species in a low-diversity ecosystem could contribute to significant changes in carbon (C) cycling. Recent climate variability in the McMurdo Dry Valleys of Antarctica is associated with changes in hydrology, biological productivity, and community composition of terrestrial and aquatic ecosystems. One of the greatest changes documented in the dry valleys is a 65% decrease in the abundance of the dominant soil invertebrate (Scottnema lindsayae, Nematoda) between 1993 and 2005, illustrating sensitivity of biota in this ecosystem to small changes in temperature. Globally, such declines are expected to have significant influences over ecosystem processes such as C cycling. To determine the implications of this climate-induced decline in nematode abundance on soil C cycling we followed the fate of a 13C tracer added to soils in Taylor Valley, Antarctica. Carbon assimilation by the dry valley nematode community contributed significantly to soil C cycling (2–7% of the heterotrophic C flux). Thus, the influence of a climate-induced decline in abundance of a dominant species may have a significant effect on ecosystem functioning in a low-diversity ecosystem.

Journal ArticleDOI
TL;DR: The results suggest that N and P co-limitation in the bacterial community results in increased competition between the heterotrophic and autotrophic components of the surface communities in the Central North Atlantic Ocean, and potentially impacts the cycling of organic matter by the bacterioplankton.
Abstract: Bacterial productivity and biomass are thought to be limited by dissolved organic carbon (DOC) in much of the world’s oceans. However, the mixed layer of oligotrophic oceans is often depleted in dissolved inorganic nitrogen and phosphate, raising the possibility that macronutrients may also limit heterotrophic bacterial growth. We used nutrient bioassay experiments to determine whether inorganic nutrients (N, P, Fe) and/or DOC could limit bacterial productivity and biomass in the central North Atlantic during the spring of 2004 (Mar–Apr). We observed that both heterotrophic bacterial productivity and biomass were co-limited by N and P in the oligotrophic North Atlantic, and additions of labile DOC (glucose) provided no stimulation unless N and P were also added. Flow cytometry results indicated that only a small subset of large cells high in nucleic acid content were responsible for the increased productivity in the combined NP amendments. In contrast, nutrient additions elicited no net change on the dominant component of the bacterial population, composed of small cells with relatively low nucleic acid content. In the combined NP treatments the relative increase in bacterial production was greater than that measured when phytoplankton productivity was relieved of nitrogen limitation. These results suggest that N and P co-limitation in the bacterial community results in increased competition between the heterotrophic and autotrophic components of the surface communities in the Central North Atlantic Ocean, and potentially impacts the cycling of organic matter by the bacterioplankton.

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TL;DR: In this article, the authors examined the dependence of bacterial productivity and respiration on primary productivity in a shallow tropical ecosystem (Cochin Estuary), and found that the degree of dependence of BP (6.3-199.7μg C-L −1 ǫd −1 ) and BR(6.6-430.4μg cǫ d −1ǫ ) on PP (2.1-608.0μgcǫ) was extremely weak, and that the CO 2 supersaturation caused by increased bacterial respiration (
Abstract: Bacterial productivity (BP) and respiration (BR) were examined in relation to primary productivity (PP) for the first time in a shallow tropical ecosystem (Cochin Estuary), India. The degree of dependence of BP (6.3–199.7 μg C L −1 d −1 ) and BR (6.6–430.4 μg C L −1 d −1 ) on PP (2.1–608.0 μg C L −1 d −1 ) was found to be extremely weak. The BP/PP (0.05–8.5) and PP/BR (0.02–7.9) ratios widely varied in the estuary depending on the season and location. There was a seasonal shift in net pelagic production from autotrophy to heterotrophy due to terrestrial organic matter input through rivers which enhanced the bacterial heterotrophic activity and very high pCO 2 (106–6001 μatm) levels. The heterotrophic zones were characterized by low PP but high bacterial production and respiration leading to oxygen undersaturation and exceptionally high pCO 2 . We propose that the CO 2 supersaturation caused by increased bacterial respiration (in excess of PP) was a result of bacterial degradation of allochthonous organic matter. This indicates that sources other than planktonic compartment need to be explored to understand the C-cycling in this estuary. These results are of particular relevance to tropical ecosystems in general, where the bulk of world's river discharges occur.