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Showing papers on "Productivity (ecology) published in 2001"


Journal ArticleDOI
TL;DR: In this article, the authors presented CO2 flux data from 18 forest ecosystems, studied in the European Union funded EUROFLUX project, and observed a significant correlation was observed between annual soil respiration (SR) and gross primary productivity (GPP) among the relatively undisturbed forests.
Abstract: Summary This paper presents CO2 flux data from 18 forest ecosystems, studied in the European Union funded EUROFLUX project. Overall, mean annual gross primary productivity (GPP, the total amount of carbon (C) fixed during photosynthesis) of these forests was 1380 ± 330 gC m−2 y−1 (mean ±SD). On average, 80% of GPP was respired by autotrophs and heterotrophs and released back into the atmosphere (total ecosystem respiration, TER = 1100 ± 260 gC m−2 y−1). Mean annual soil respiration (SR) was 760 ± 340 gC m−2 y−1 (55% of GPP and 69% of TER). Among the investigated forests, large differences were observed in annual SR and TER that were not correlated with mean annual temperature. However, a significant correlation was observed between annual SR and TER and GPP among the relatively undisturbed forests. On the assumption that (i) root respiration is constrained by the allocation of photosynthates to the roots, which is coupled to productivity, and that (ii) the largest fraction of heterotrophic soil respiration originates from decomposition of young organic matter (leaves, fine roots), whose availability also depends on primary productivity, it is hypothesized that differences in SR among forests are likely to depend more on productivity than on temperature. At sites where soil disturbance has occurred (e.g. ploughing, drainage), soil espiration was a larger component of the ecosystem C budget and deviated from the relationship between annual SR (and TER) and GPP observed among the less-disturbed forests. At one particular forest, carbon losses from the soil were so large, that in some years the site became a net source of carbon to the atmosphere. Excluding the disturbed sites from the present analysis reduced mean SR to 660 ± 290 gC m−2 y−1, representing 49% of GPP and 63% of TER in the relatively undisturbed forest ecosystems.

958 citations


Journal ArticleDOI
TL;DR: Positive interactions may be an important but previously underemphasized mechanism linking high diversity to high productivity under stressful environmental conditions.
Abstract: If environmental stress provides conditions under which positive relationships between plant species richness and productivity become apparent, then species that seem functionally redundant under constant conditions may add to community functioning under variable conditions. Using naturally co-occurring mosses and liverworts, we constructed bryophyte communities to test relationships between species diversity (1, 2, 4, 8, 16, 24, or 32 species) and productivity under constant conditions and when exposed to experimental drought. We found no relationship between species richness and biomass under constant conditions. However, when communities were exposed to experimental drought, biomass increased with species richness. Responses of individual species demonstrated that facilitative interactions rather than sampling effects or niche complementarity best explained results—survivorship increased for almost all species, and those species least resistant to drought in monoculture had the greatest increase in biomass. Positive interactions may be an important but previously underemphasized mechanism linking high diversity to high productivity under stressful environmental conditions.

377 citations


Journal ArticleDOI
TL;DR: It is estimated that the conventional WP-2 net with a 200 μm mesh may capture <10% of conventional mesozooplankton numbers, whilst underestimating biomass by one-third and leading to an underestimate of secondary production by two-thirds, which has serious implications for estimates of zooplankington-mediated fluxes and for the modelling of ecosystem dynamics.
Abstract: Oithona has been described as the most ubiquitous and abundant copepod in the world's oceans. Most of our knowledge of zooplankton abundance and distribution is derived from net samples whose mesh size is often 200 μm or greater, and researchers have commented on losses of smaller organisms such as Oithona and Oncaea, as well as juvenile forms of larger copepods, from these nets. We review the literature on this subject over the last 50 years, and note that such nets remain in common use for estimating the abundance, biomass and productivity of mesozooplankton. We show that an important fraction of mesozooplankton between 200 and 800 μm in length is significantly under-represented in many current and historical data sets. A 5 year study of the abundance and size distribution of zooplankton biomass on the Atlantic Meridional Transect has produced a very large data set covering a wide range of ecosystem types across the Atlantic Ocean, from subtropical oligotrophic to areas of upwelling and vernal blooming. We use these data to derive estimates of mesh selection effects for commonly used nets on measures of zooplankton abundance, biomass and secondary production, and compare these estimates to those derived from the literature. We estimate that the conventional WP-2 net with a 200 μm mesh may capture <10% of conventional mesozooplankton numbers, whilst underestimating biomass by one-third and leading to an underestimate of secondary production by two-thirds. This has serious implications for estimates of zooplankton-mediated fluxes and for the modelling of ecosystem dynamics.

367 citations


Journal ArticleDOI
TL;DR: In this article, the average concentrations of chlorophyll a and the estimated rates of primary production in the surface waters of the North Pacific Subtropical Gyre (NPSG) off Hawaii have more than doubled while the concentrations of dissolved silicate and phosphate have decreased during the past three decades.
Abstract: Oceanic productivity, fishery yields and the net marine sequestration of atmospheric greenhouse gases are all controlled by the structure and function of planktonic communities. Detailed paleoceanographic studies have documented abrupt changes in these processes over timescales ranging from centuries to millennia. Most of these major shifts in oceanic productivity and biodiversity are attributable to changes in Earth's climate, manifested through large-scale ocean–atmosphere interactions. By comparison, contemporary biodiversity and plankton community dynamics are generally considered to be “static”, in part due to the lack of a suitable time frame of reference, and the absence of oceanic data to document ecosystem change over relatively short timescales (decades to centuries). Here we show that the average concentrations of chlorophyll a (chl a) and the estimated rates of primary production in the surface waters of the North Pacific Subtropical Gyre (NPSG) off Hawaii have more than doubled while the concentrations of dissolved silicate and phosphate have decreased during the past three decades. These changes are accompanied by an increase in the concentration of chl b, suggesting a shift in phytoplankton community structure. We hypothesize that these observed ecosystem trends and other related biogeochemical processes in the upper portion of the NPSG are manifestations of plankton community succession in response to climate variations. The hypothesized photosynthetic population “domain shift” toward an ecosystem dominated by prokaryotes has altered nutrient flux pathways and affected food web structure, new and export production processes, and fishery yields. Further stratification of the surface ocean resulting from global warming could lead to even more enhanced selection pressures and additional changes in biogeochemical dynamics.

338 citations


Journal ArticleDOI
28 Sep 2001-Science
TL;DR: Late Pleistocene changes in oceanic primary productivity along the equator in the Indian and Pacific oceans are revealed by quantitative changes in nanoplankton communities preserved in nine deep-sea cores, suggesting an important role for equatorial biological productivity in modifying atmospheric CO2.
Abstract: Late Pleistocene changes in oceanic primary productivity along the equator in the Indian and Pacific oceans are revealed by quantitative changes in nanoplankton communities preserved in nine deep-sea cores. We show that variations in equatorial productivity are primarily caused by glacial-interglacial variability and by precession-controlled changes in the east-west thermocline slope of the Indo-Pacific. The precession-controlled variations in productivity are linked to processes similar to the Southern Oscillation phenomenon, and they precede changes in the oxygen isotopic ratio, which indicates that they are not the result of ice sheet fluctuations. The 30,000-year spectral peak in the tropical Indo-Pacific Ocean productivity records is also present in the Antarctica atmospheric CO2 record, suggesting an important role for equatorial biological productivity in modifying atmospheric CO2.

286 citations


Journal ArticleDOI
TL;DR: It is found that the equatorial upwelling causes an increase in phytoplankton biomass and productivity without altering the typical size structure found in less productive regions such as the subtropical gyres.
Abstract: A total of 94 vertical profiles of size-fractionated chlorophyll a concentration and primary production rate were obtained along a meridional transect from the United Kingdom to the Falkland Islands (50° N to 50° S) during 4 cruises carried out in April and October 1996 and in April and October 1997. This data set allowed us to characterize the patterns of phytoplankton size-structure and pro- ductivity in temperate, oligotrophic, upwelling and equatorial regions. On average, picophytoplank- ton (0.2 to 2 µm) accounted for 56 and 71% of the total integrated carbon (C) fixation and autotrophic biomass, respectively. Enhanced biomass and productivity contributions by nano- and microplankton took place in the temperate regions and in the upwelling area off Mauritania. Small ( 2 µm) phytoplankton accounted for a proportion of total biomass that was similar to their shares of productivity. In the oligotrophic and equatorial regions, in contrast, large phytoplankton tended to account for a fraction of the total pro- duction that was significantly higher than their share of the biomass. We found that the equatorial upwelling causes an increase in phytoplankton biomass and productivity without altering the typical size structure found in less productive regions such as the subtropical gyres. In the oligotrophic ocean, significant changes in C fixation rates take place without accompanying variations in the magnitude of the phytoplankton standing stocks or the size structure of the microbial community.

257 citations


Journal ArticleDOI
01 Jun 2001-Oikos
TL;DR: The results provide clear evidence that effects of mycorrhizal fungal diversity on productivity are context dependent and may be positive, negative or neutral depending on the situation considered.
Abstract: While there has been much recent interest about the relationships between plant diversity and plant productivity, much remains unknown about how the diversity of mycorrhizal fungi affects plant productivity. We investigated the effects of ectomycorrhizal fungal community composition and diversity on the productivity and growth characteristics of seedlings of two tree species (Pinus sylvetris and Betula pendula) as well as their interactions with each other. This involved setting up a mycorrhizal fungal diversity gradient from one to eight species using a design previously demonstrated to be able to separate diversity effects from compositional effects. We found that the eight mycorrhizal fungal species differed in their effects on seedling productivity and that the nature of effects was determined by the fertility of the substrate. Fungal species richness effects were also important in affecting seedling productivity over and above what could be explained by “sampling effect” but only in some situations. For B. pendula in a low fertility substrate there were clear positive causative effects between fungal species richness and productivity with the eight species treatment having over double the productivity of any of the eight monoculture treatments; no diversity effects were, however, detected in a high fertility substrate. For P. sylvestris in a high fertility substrate there were significant negative effects of fungal diversity on productivity while in a low fertility substrate no effects were apparent. The possible mechanistic bases for these results are discussed. The growth of P. sylvestris relative to that of B. pendula when grown in combination was unaffected by mycorrhizal treatments. Our results provide clear evidence that effects of mycorrhizal fungal diversity on productivity are context dependent and may be positive, negative or neutral depending on the situation considered.

246 citations


Journal ArticleDOI
TL;DR: In this paper, the authors described the seasonal progression of productivity and its regulation on a section which ran from the coast of Oman to about 1000 kilometres offshore in the central Arabian Sea at 65°E.
Abstract: The annual cycle of monsoon-driven variability in primary productivity was studied in 1995 during the Arabian Sea Expedition as part of the United States Joint Global Ocean Flux Studies (US JGOFS). This paper describes the seasonal progression of productivity and its regulation on a section which ran from the coast of Oman to about 1000 km offshore in the central Arabian Sea at 65°E. During the SW Monsoon (June–mid-September), the coolest water and highest nutrient concentrations were close to the coast, although they extended offshore to about 800 km; during the January NE Monsoon, deep convective mixing provided nutrients to the mixed layer in the region 400 – 1000 km offshore. As expected, the SW Monsoon was the most productive season (123±9 mmol C m−2 d−1) along the southern US JGOFS section from the coast to 1000 km offshore, but productivity in the NE Monsoon was surprisingly high (112±7 mmol C m−2 d−1). There was no onshore/offshore gradient in primary productivity from 150 to 1000 km off the Omani coast in 1995, and there was no evidence of light limitation of either primary productivity or photosynthetic performance (PoptB) from deep convective mixing during the NE Monsoon, deep wind mixing during the SW Monsoon or offshore Ekman downwelling during the SW Monsoon. Productivity during the Spring Intermonsoon (86±6 mmol C m−2 d−1) was much higher than in oligotrophic regions such as the tropical Pacific Ocean (29±2 mmol C m−2 d−1) or the North Pacific gyre region (32±8 mmol C m−2 d−1). The 1995 annual mean productivity (111±11 mmol C m−2 d−1) along this section from the Omani coast to the central Arabian Sea was about equal to the spring bloom maximum (107±23 mmol C m−2 d−1) during the 1989 North Atlantic Bloom Experiment (NABE) and the equatorial, 1°N–1°S wave guide maximum (95±6 mmol C m−2 d−1) in the Pacific Ocean during the 1992 EqPac study. The 1995 SW Monsoon primary productivity was similar to the mean value observed in the same region in 1994 by the Arabesque Expedition (127±14 mmol C m−2 d−1) and in 1964 by the ANTON BRUUN Expedition (115±27 mmol C m−2 d−1). During the 1995 SW Monsoon, strong, narrow and meandering current filaments extended from the region of coastal upwelling to about 700 km offshore; these filaments had levels of biomass, primary productivity, chlorophyll-specific productivity and diatom abundance that were elevated relative to other locations during the SW Monsoon. The SW Monsoon was the most productive period, but SW Monsoon primary productivity values were lower than predicted because efficient grazing by mesozooplankton kept diatoms from accumulating the biomass necessary for achieving the high levels of primary productivity characteristic of other coastal upwelling regions. The high rates of chlorophyll-specific productivity (PoptB>10 mmol C mg Chl−1 d−1) observed in the 1995 SW Monsoon, together with the observed dust flux and iron concentrations, indicate that the Arabian Sea was more iron replete than the equatorial Pacific Ocean or the Southern Ocean.

225 citations


Journal ArticleDOI
TL;DR: In this article, the impact of grazing and nutrient supply on epilithic periphyton was investigated in factorial field experiments in four seasons at three Swedish sites of different productivity and herbivore composition ( Lake Limmaren, Lake Erken, and Vaddo ¨, a low salinity coastal site).
Abstract: The impact of grazing and nutrient supply on epilithic periphyton was investigated in factorial field experiments in four seasons at three Swedish sites of different productivity and herbivore composition (Lake Limmaren, Lake Erken, and Vaddo ¨, a low salinity coastal site). Nutrient supply was enhanced by a granulose fertilizer containing nitrogen (N) and phosphorus (P), and grazer density was manipulated by exclusion cages. Algal biomass was increased by nutrient enrichment and reduced by grazer presence, but effects were highly variable between sites and seasons. Generally, grazers had stronger effects on algal biomass than nutrient enrichment, but there was no overriding effect of either grazing or nutrients. This indicated a simultaneous top-down and bottom-up control of algal biomass. Taxonomic composition of the periphyton was more affected by grazer presence than by nutrients. Internal nutrient ratios of the algae indicated N limitation at two of the sites. At all sites, the content of N and P in the periphytic assemblage was enhanced by the experimental nutrient enrichment, resulting in decreased C : N and C : P ratios. The presence of herbivores also increased periphytic nutrient content (decreased N : P and C : P ratios) in some experiments, suggesting an increase in algal P due to excretion. The effect strength of grazers and nutrients on periphyton was affected by different abiotic characteristics such as light availability, nutrient concen- trations, and temperature. However, single environmental characteristics were not sufficient to explain the relative importance of grazing and nutrients.

216 citations


Journal ArticleDOI
TL;DR: The authors' rapid visual surveys proved useful for quantifying seagrass abundance, and the data presented in this paper serve as a benchmark against which future change in the system can be quantified.
Abstract: We document the distribution and abundance of seagrasses, as well as the intra-annual temporal patterns in the abundance of seagrasses and the productivity of the nearshore dominant seagrass (Thalassia testudinum) in the south Florida region. At least one species of seagrass was present at 80.8% of 874 randomly chosen mapping sites, delimiting 12,800 km2 of seagrass beds in the 17,000-km2 survey area. Halophila decipiens had the greatest range in the study area; it was found to occur over 7,500 km2. The range of T. testudinum was almost as extensive (6,400 km2), followed by Syringodium filiforme (4,400 km2), Halodule wrightii (3,000 km2) and Halophila engelmanni (50 km2 ). The seasonal maxima of standing crop was about 32% higher than the yearly mean. The productivity of T. testudinum was both temporally and spatially variable. Yearly mean areal productivity averaged 0.70 g m−2day−1, with a range of 0.05–3.29 g m−2 day−1. Specific productivity ranged between 3.2 and 34.2 mg g−1 day−1, with a mean of 18.3 mg g−1 day−1. Annual peaks in specific productivity occurred in August, and minima in February. Integrating the standing crop for the study area gives an estimate of 1.4 × 1011 g T. testudinum and 3.6 × 1010 g S. filiforme, which translate to a yearly production of 9.4 × 1011 g T. testudinum leaves and 2.4 × 1011 g S. filiforme leaves. We assessed the efficacy of rapid visual surveys for estimating abundance of seagrasses in south Florida by comparing these results to measures of leaf biomass for T. testudinum and S. filiforme. Our rapid visual surveys proved useful for quantifying seagrass abundance, and the data presented in this paper serve as a benchmark against which future change in the system can be quantified.

186 citations


Journal ArticleDOI
TL;DR: Time-series observations at a nominally fixed location in the northern Arabian Sea (21°N, 64°E) during the Northeast Monsoon (winter, February) of l997 showed the prevalence of cold sea-surface temperatures (SST) and deep mixed layers resulting from winter cooling and convection.
Abstract: Time-series observations at a nominally fixed location in the northern Arabian Sea (21°N, 64°E) during the Northeast Monsoon (winter, February) of l997 showed the prevalence of cold sea-surface temperatures (SST) and deep mixed layers resulting from winter cooling and convection The covariation of nitrate concentrations in the surface layers and concentrations of chlorophyll a and primary production in the euphotic zone with mixed-layer depth (MLD) and wind suggests that carbon fixation was controlled primarily by physical forcing Cooler waters during winter 1997 relative to winter 1995 were associated with deeper MLDs, higher nitrate concentrations, elevated primary productivity, and higher chlorophyll a concentrations, leading to the inference that even a 1°C decrease in SST could lead to significantly higher primary productivity Satellite data on sea surface temperature (advanced very high-resolution radiometer; AVHRR) and TOPEX/POSElDON altimeter data suggest that this interannual variation is of basin-wide spatial scale After the termination of winter cooling and subsequent warming during the Spring Intermonsoon, the Arabian Sea has low primary production During the latter period, micro-organisms, ie heterotrophic bacteria and microzooplankton)-proliferate, a feeding mode through the microbial loop that appears to be inherent to mesozooplankton for sustaining their biomass throughout the year in this region

Journal ArticleDOI
TL;DR: Dissolved organic carbon production by microbial populations was measured at 19 stations in the Atlantic Ocean to quantify the fraction of photoassimilated carbon that flows through the dissolved organic pool at basin scale and to assess the relationship between the percentage of DOC production, phytoplankton size structure, and rates of net community production.
Abstract: Dissolved organic carbon (DOC) production by microbial populations was measured at 19 stations in the Atlantic Ocean to quantify the fraction of photoassimilated carbon that flows through the dissolved organic pool at basin scale and to assess the relationship between the percentage of DOC production, phytoplankton size structure, and rates of net community production. Experiments were conducted during four cruises carried out between May 1998 and October 1999, covering three upwelling regions: Benguela (SW Africa), Mauritania (NW Africa) and NW Spain, and the oligotrophic North Atlantic subtropical gyre between 308N and 368N. Photic zone integrated particulate organic carbon (POC) production rates ranged from 10 to 1,178 mg C m 22 h 21 , thus covering a wide productivity spectrum. The percentage of DOC production with respect to total integrated primary production ranged from 4 to 42%, being larger in oligotrophic, picoplankton-dominated waters, where a balanced metabolism of the microbial community was observed, than in productive, net autotrophic waters, where large-sized cells formed the bulk of the phytoplankton biomass. A highly significant relationship was calculated between DOC and POC production rates in upwelling conditions. By contrast, the relationship between these variables in oligotrophic environments was weak, which suggests that different processes could be controlling the release of dissolved organic matter in productive and unproductive waters. Dissolved organic matter (DOM) is one of the least understood pools of marine matter and represents a major reservoir of organic carbon in the ocean. A large fraction of the dissolved organic carbon (DOC) present in the ocean ultimately derives from primary producers. However, a great deal of controversy still exists on the ecological significance and the ultimate control of DOC production in the ocean. The magnitude of DOC-related fluxes remains still largely uncertain, especially in oligotrophic regions. The high rates of DOC uptake by heterotrophic bacteria in relation to primary production recently measured in unproductive waters (e.g., Hansell et al. 1995; del Giorgio et al. 1997), largely justifies the growing biogeochemical interest of measuring and modeling DOC production in planktonic ecosystems. Initially, the radioactive carbon method for primary production estimation was modified for the measurement of direct excretion of dissolved organic compounds from algal cells. More recently, it has been recognized that several processes, besides direct excretion from intact algal cells, are 1

Journal ArticleDOI
TL;DR: In this article, a method of measuring above-ground plant biomass and production that can be applied consistently among vegetation types and that generates seasonal, spatially-explicit results is presented.

Journal ArticleDOI
TL;DR: In this article, plant species richness and foliage production were studied with respect to N and P additions in three alpine communities varying in snowpack depth and duration, and the effects were also measured in conjunction with a snowpack enhancement experiment.
Abstract: The extent to which nutrient limitation affects species composition, abundance, and productivity of the alpine tundra is an ongoing area of ecological inquiry. At Niwot Ridge in the Front Range of Colorado, plant species richness and foliage production were studied with respect to N and P additions in three alpine communities varying in snowpack depth and duration. These effects were also measured in conjunction with a snowpack enhancement experiment. Measurements of plant responses were made 4 yr following the initiation of the manipulations. The addition of either N or P enhanced plant foliage productivity (P = 0.05 and P = 0.03, respectively). Nitrogen additions had a negative effect on the species richness censused in 1-m2 plots (P 0.60). Snowpack did not affect foliage productivity (P = 0.20), but species richness was negatively affected (P < 0.001). Snowpack also appeared to mediate species-specific responses to N and P additions. In the alpine, the relationship between species diversity and plant productivity is mediated by species-specific traits. After 4 yr, the increased production by plant species sensitive to P additions did not reduce species richness. This suggests that production-induced competitive exclusion is not a generalization that can be used to explain the decline in species richness. Moreover, the reduction in species richness due to N addition occurred across all of the tundra communities studied here.

Journal ArticleDOI
01 Feb 2001-Oikos
TL;DR: This paper employs a simple model in which the dynamics of species richness are a function of aboveground community biomass and environmentally controlled gradients in species pools, and leads to two main predictions about the role of biomass regulation.
Abstract: Considerable debate has developed over the importance of community biomass and species pools in the regulation of community diversity. Attempts to explain patterns of plant diversity as a function of community biomass or productivity have been only partially successful and, in general, have explained only a fraction of the observed variation in diversity. At the same time, studies that have focused on the importance of species pools have led some to conclude that diversity is primarily regulated in the short term by the size of the species pool rather than by biotic interactions. In this paper, I explore how community biomass and species pools may work in combination to regulate diversity in herbaceous plant communities. To address this problem, I employ a simple model in which the dynamics of species richness are a function of aboveground community biomass and environmentally controlled gradients in species pools. Model results lead to two main predictions about the role of biomass regulation: (1) Seasonal dynamics of richness will tend to follow a regular oscillation, with richness rising to peak values during the early to middle portion of the growing season and then declining during the latter part of the season. (2) Seasonal dieback of aboveground tissues facilitates the long-term maintenance of high levels of richness in the community. The persistence of aboveground tissues and accumulation of litter are especially important in limiting the number of species through the suppression of recruitment. Model results also lead to two main predictions about the role of species pools: (1) The height and position of peak richness relative to community biomass will be influenced by the rate at which the species pool increases as available soil resources increase. (2) Variations in nonresource environmental factors (e.g. soil pH or soil salinity) have the potential to regulate species pools in a way that is uncorrelated with aboveground biomass. Under extreme conditions, such nonresource effects can create a unimodal envelope of biomass–richness values. Available evidence from the literature provides partial support for these predictions, though additional data are needed to provide more convincing tests.

Journal ArticleDOI
TL;DR: In this paper, measurements of both wet and dry deposition of dissolved inorganic nitrogen (DIN) have been performed at a remote coastal area in the island of Crete (Finokalia) during a 3-year period (1996-1999).
Abstract: To assess the importance of the atmospheric deposition of nitrogen (N) on the productivity of the eastern Mediterranean Sea, measurements of both wet and dry deposition of dissolved inorganic nitrogen (DIN) have been performed at a remote coastal area in the island of Crete (Finokalia) during a 3-year period (1996–1999). The estimation of dry deposition of DIN is based on measurements of both gaseous (HNO3 and NH3) and particulate phase (NO3− and NH4+) nitrogen compounds. The results of the wet and dry deposition obtained at Finokalia have been compared with data of particulate organic nitrogen (PON) obtained during two yearly (1994–1995 and 1997–1998) surveys (CINCS and MATER) in the Cretan Sea by using sediment traps deployed at 200 and 500 m depths. Our results show that the atmospheric deposition of DIN can account for up to 370% of the measured PON in the sediment traps, indicating that atmospheric pathway alone can sufficiently account for the measured new nitrogen production. On the basis of the primary productivity induced by the imported DIN and the productivity of the southeastern Mediterranean derived from in situ measurements a mean f ratio of 0.24 is calculated indicating that from the N point of view, the eastern Mediterranean can no longer be considered as among the most oligotrophic seas of the world. Other elements, most probably phosphorus (P), can account for the oligotrophic character of the eastern Mediterranean Sea. To our knowledge this is the first attempt to understand the role of the atmospheric input of nitrogen on the productivity of the eastern Mediterranean Sea.

Journal ArticleDOI
TL;DR: The hypothesis that increased productivity corresponding with higher species richness results in increased litter production, higher standing litter pools and a negative feedback on productivity is supported, because of an increased standing nitrogen pool in the litter.
Abstract: We examined the impact of biodiversity on litter decomposition in an experiment that manipulated plant species richness. Using biomass originating from the experimental species richness gradient and from a species used as a common substrate, we measured rates of decomposition in litterbags in two locations: in situ in the experiment plots and in an adjacent common garden. This allowed us to separate the effects of litter quality and decomposition location on decomposition. We found that plant species richness had a significant, but minor negative effect on the quality (nitrogen concentration) of the biomass. Neither litter type nor location had a consistent effect on the rate of carbon and nitrogen loss over a 1-year period. Thus, the increased productivity and corresponding lower soil available nitrogen levels observed in high diversity plots do not lead to faster litter decomposition or faster nitrogen turnover. This supports the hypothesis that increased productivity corresponding with higher species richness results in increased litter production, higher standing litter pools and a negative feedback on productivity, because of an increased standing nitrogen pool in the litter.

Journal ArticleDOI
TL;DR: The zooplankton community of the central North Pacific has been sampled at Stn. ALOHA since 1994 as part of routine data collection for the Hawaii Ocean Time-series (HOT) Program.
Abstract: The zooplankton community of the central North Pacific has been sampled at Stn. ALOHA since 1994 as part of routine data collections for the Hawaii Ocean Time-series (HOT) Program. Typically, three day and three night tows are collected in the upper 150 m on each cruise with a 1-m, 200-μm mesh net. Size-fractioned carbon and dry weight biomass have been determined for each sample, and one day and one night sample per cruise have been enumerated microscopically through 1996. The accumulated data show statistically significant seasonal signals, with peak biomass and abundance during the summer months for the total community and for smaller size fractions (0.2–0.5, 0.5–1, 1–2 mm). Interannual variability is seen as significantly higher nighttime biomass during summer 1996, which is also related to the enhancement of small size fractions. Comparisons of the present composition of the community to the results of classic studies at the CLIMAX site show remarkable similarities in the species sampled and their abundance ranges. Nonetheless, biomass estimates, corrected for relative capture efficiencies of the different net systems, suggest that there may have been an increase of about a factor of two in zooplankton standing stocks over the past two decades. This hypothesis raises issues about the comparability of the two sites, but the increase, if real, would be consistent with the observed decadal-scale increase in phytoplankton chlorophyll a . The small harpacticoid copepod, Macrosetella gracilis , demonstrates a strong summer maximum consistent with the increased abundance of nitrogen-fixing Trichodesmium spp. during mid-summer months, as described in recent studies at Stn. ALOHA. Accordingly, nitrogen fixation could provide the source of new nutrients to support higher productivity, larger phytoplankton, and enhanced zooplankton standing stocks in the summer, when the upper water column is most stratified and isolated from nutrient influxes from below.

Journal ArticleDOI
TL;DR: Results demonstrate that iron addition to this high-nitrate, low-chlorophyll region affects both autotrophic and heterotrophic microorganisms and that bacterial carbon demand can be potentially met by the fivefold increase in photosynthetic productivity in the mixed layer.
Abstract: The response of the heterotrophic bacterial community to iron addition was determined during the mesoscale iron-enrichment experiment conducted in the eastern equatorial Pacific during May-June 1995 (IronEx II). Bacterial abundance and 3 H-leucine incorporation rates were measured for samples collected from the middle of the mixed layer (15 m) over the course of the iron-induced phytoplankton bloom and its decline. Bacterial abundance and productivity increased 1.7- and threefold, respectively, compared to un-enriched waters. Specific growth rates of heterotrophic bacteria increased three- to fourfold. These results demonstrate that iron addition to this high-nitrate, low-chlorophyll region affects both autotrophic and heterotrophic microorganisms and that bacterial carbon demand can be potentially met by the fivefold increase in photosynthetic productivity in the mixed layer.

Journal ArticleDOI
TL;DR: In this paper, the authors compared multiple indexes of productivity, nutrient circulation, and hydroperiod among three communities on the Flint River floodplain, Georgia, that differed in terms of inundation frequency and hypothesized that the wettest community would have the lowest total net primary production (NPP) values because of saturated soil conditions.
Abstract: Floodplain forest ecosystems are highly valuable to society because of their potential for water quality improvement and vegetation productivity, among many other functions. Previous studies have indicated that hydrology influences productivity but that the relationship between hydroperiod and productivity is a complex one. Consequently, we compared multiple indexes of productivity, nutrient circulation, and hydroperiod among three communities on the Flint River floodplain, Georgia, that differed in terms of inundation frequency. We hypothesized that (a) the wettest community would have the lowest total net primary production (NPP) values because of saturated soil conditions; (b) as wetness increases, nutrient circulation in litterfall would decrease because of the hypothesized lower productivity in the wetter community; and (c) as wetness increases, internal translocation would become more efficient. The study site was partitioned into three wetness types—somewhat poorly drained (SPD), intermediate (I) and poorly drained (PD). We found that belowground biomass was greatest on the SPD, litterfall was similar for all three sites, and that woody biomass current annual increment (CAI) was greatest in the PD community. However, when the three variables were totaled for each site, the PD had the greatest NPP, thus disproving hypothesis (a). For hypothesis (b), we observed that P content in litterfall, although not significant, followed the predicted trend; nitrogen (N) content displayed the opposite pattern (PD > I > SPD). As wetness increased, internal translocation became more efficient for phosphorus (support for hypothesis [c]), but the SPD community was more efficient at retranslocating N (contradiction of hypothesis [c]).

Journal ArticleDOI
TL;DR: Productivity ‘hotspots’ utilized by gazelles during critical periods in their life cycle should be first priority for conservation and the impact of livestock grazing on these areas should be evaluated.

Journal ArticleDOI
TL;DR: This study showed that the direct effect of nutrient enrichment by mussel biodeposition produced the greatest positive response in productivity of T. testudinum in the seagrass meadows of St. Joseph Bay, Florida.
Abstract: A field experiment utilizing mussel mimics and sediment nutrient enrichment was con- ducted to examine the effect of the mussel Modilous americanus on meadows of the seagrass Tha- lassia testudinum. The experimental design tested the separate factors of increased habitat structure and increased nutrient enrichment resulting from the presence of the mussels. Nutrient enrichment had a significantly positive effect on sediment porewater nutrient concentrations and a significantly negative effect on leaf tissue C:N, C:P and N:P ratios. Increased habitat structure had a significantly positive effect on epiphytic grazer densities and a significantly negative effect on epiphytic biomass. In addition, calculated % light reduction by epiphytes was significantly reduced by structure and significantly increased by nutrient enrichment. This study showed that the direct effect of nutrient enrichment by mussel biodeposition produced the greatest positive response in productivity of T. testudinum in the seagrass meadows of St. Joseph Bay, Florida. In other systems experiencing eutrophication, however, it is possible that increased habitat complexity may have the greater effect on seagrass productivity.

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TL;DR: In this paper, the early Oligocene period of rapid climate change (across Oxygen isotope shift Oi-1) productivity showed major changes in the region around Australia (DSDP Site 592 off New Zealand, ODP Site 763 off NW Australia).

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TL;DR: In this paper, the authors monitored standing crop and dugong activity over 14 months in a subtidal community dominated by the tropical seagrass Halodule uninervis and the green alga Penicillus nodulosus in a small cove in subtropical Shark Bay, Western Australia.

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01 Sep 2001-Oikos
TL;DR: A framework to explain the relationship between species richness and productivity in terrestrial plant communities is developed and suggests the existence of a selection effect that involves species that are highly productive in mixtures, rather than in monoculture.
Abstract: Several researchers have hypothesized that, through various mechanisms, loss of species and functional group richness from a plant community will affect the magnitude and interannual variability of productivity. To test this hypothesis, I conducted a microcosm study of California grassland communities that differed in species richness. I grew cohorts of microcosms that simulated undisturbed grassland (in one year) and gopher-disturbed grassland (in two consecutive years). As the number of species per functional group decreased from 4 to 1, biomass production remained constant in all three cohorts. As species richness decreased from 16 to 1 (or 8 to 1, in either case including a drop in functional group richness), productivity declined in one of the cohorts. In this cohort, productivity of one polyculture marginally exceeded that of the most productive monoculture. Resource complementarity and a type of selection effect may have each contributed to the observed diversity-productivity relationships. Results suggest the existence of a selection effect that involves species that are highly productive in mixtures, rather than in monoculture. Over two seasons, species and functional group richness did not affect the interannual variability of biomass production. Comparisons of interannual changes in the productivity of monocultures and polycultures suggested that, in some polycultures, increased water availability might have relieved interspecific competition more than intraspecific competition. Based on results from this experiment and other manipulative experiments, I develop a framework to explain the relationship between species richness and productivity in terrestrial plant communities. The framework highlights the importance of environmental variation in shaping the diversity/productivity relationship.

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TL;DR: In this article, surface layer data are used to address two questions concerning the in#uence of the monsoon cycle on bacterial dynamics: (1) Is there a bacterial bloom in the SW Monsoon? and (2) Is bacterial production low during the oligotrophic Spring Intermonsoon? An extensive comparison of epi#uorescence microscopy and #ow cytometry, unprecedented at this scale, detected essentially the same heterotrophic bacterial populations and distributions, with some between-cruise di!erences.
Abstract: Heterotrophic bacterial abundance and productivity were measured during "ve and four cruises, respectively, in the northwest Arabian Sea as part of the US JGOFS Process Study, which provided a new view of seasonal bacterial dynamics in that part of the basin in#uenced by monsoonal forcing. In this paper, surface layer data are used to address two questions concerning the in#uence of the monsoon cycle on bacterial dynamics: (1) Is there a bacterial bloom in the SW Monsoon? and (2) Is bacterial production low during the oligotrophic Spring Intermonsoon? An extensive comparison of epi#uorescence microscopy and #ow cytometry, unprecedented at this scale, detected essentially the same heterotrophic bacterial populations and distributions, with some between-cruise di!erences. Use of the two methods allowed us to extend our observations in space and time. Bacterial productivity, both in the surface layer and integrated over the euphotic zone, was elevated less than 2-fold during the Southwest Monsoon. Levels of bacterial abundance and production were low during the Northeast Monsoon, then increased in March during the Spring Intermonsoon. There was some stimulation of abundance or production inshore in response to coastal upwelling. In general, the basin was enriched in bacterial biomass '510 cells l throughout the year, relative to other tropical regimes, presumably in response to overall high PP and DOC levels. Seasonally uniformDOC levels may be regulated in part by intense bacterial utilization rates, but also re #ect seasonal consistency in PP. 2001 Elsevier Science Ltd. All rights reserved.

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TL;DR: The median density of shorebirds during their non-breeding season on the coast of South America was significantly greater in coastal zones with high primary productivity than in zones with moderate and low primary productivity.
Abstract: -The median density of shorebirds during their non-breeding season on the coast of South America was significantly greater in coastal zones with high primary productivity than in zones with moderate and low primary productivity. A world-wide review showed that sites harboring large numbers of wintering and migratory shorebirds corresponded significantly with regions of high coastal zone productivity. We suggest that the spacing of rich intertidal foraging habitats along the world's coastlines has been an important feature in the evolution of long distance migration by shorebirds. Received 16 November 2000, accepted 20 December 2000.

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TL;DR: In this article, the effects of slash-and-burn of a tropical dry forest (TDF) and pasture establishment on fine root (≤1mm) biomass and productivity were examined.

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TL;DR: Evidence was found that several features of E. marinus population dynamics were dependent on environmental factors resulting from the particular estuary hydraulic regime, including female morphologically recognisable at smaller sizes than males, but males became larger than females.
Abstract: The population density of Echinogammarus marinus in the Mondego estuary changed throughout the year, with a maximum during spring. The lowest densities were found in the north arm of the estuary, and the highest ones in the inner areas of the south arm. Higher densities appeared associated with the presence of muddy deposits under Fucus vesiculosus (Phaeophyta) and also with the presence of green macroalgae biomass over the sediments. Females were morphologically recognisable at smaller sizes than males, but males became larger than females. Fecundity increases with the size of females and is influenced by temperature and salinity. Sexual activity and recruitment take place continuously throughout the year, although it almost ceases by the end of winter. Present results are in opposition to the hypothesis of discontinuous recruitment presented in a previous study. Productivity (ash free dry weight- AFDW) was estimated at 1.74 to 2.45 g·m–2·year–1 in the north arm of the estuary corresponding to an annual turnover ratio ( P / B ) of 4.14 to 6.18. In the south arm, productivity was estimated at 1.96 to 2.74 g AFDW·m–2·year–1 in the middle section ( P / B of 4.68 to 6.56), and at 3.85 to 5.38 g AFDW·m–2·year–1 in the innermost sampling area ( P / B of 4.54 to 6.36). Differences in productivity appeared to depend only on population density, while annual P / B ratios were similar over the estuary. Evidence was found that several features of E. marinus population dynamics were dependent on environmental factors resulting from the particular estuary hydraulic regime.

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TL;DR: The magnitude of the winter–spring bloom in Massachusetts Bay from 1995 to 1999 was significantly correlated with winter water temperature and zooplankton abundance over the bloom period (typically February–April), and potential factors influencing the occurrence of a spring bloom were investigated.
Abstract: The seasonal productivity cycle and factors controlling annual variation in the timing and magnitude of the winter–spring bloom were examined for several locations (range: 42°20.35′–42°26.63′N; 70°44.19′–70°56.52′W) in Boston Harbor and Massachusetts Bay, USA, from 1995 to 1999, and compared with earlier published data (1992–1994). Primary productivity (mg C m−2 day−1) in Massachusetts Bay from 1995 to 1999 was generally characterized by a well-developed winter–spring bloom of several weeks duration, high but variable production during the summer, and a prominent fall bloom. The bulk of production (mg C m−3 day−1) typically occurred in the upper 15 m of the water column. At a nearby Boston Harbor station a gradual pattern of increasing areal production from winter through summer was more typical, with the bulk of production restricted to the upper 5 m. Annual productivity in Massachusetts Bay and Boston Harbor ranged from a low of 160 g C m−2 year−1 to a high of 787 g C m−2 year−1 from 1992 to 1999. Mean annual productivity was higher (mean=525 g C m−2 year−1) and more variable near the harbor entrance than in western Massachusetts Bay. At the harbor station productivity varied more than 3.5-fold (CV=40%) over an 8 year sampling period. Average annual productivity (305–419 g C m−2 year−1) and variability around the means (CV=25–27%) were lower at both the outer nearfield and central nearfield regions of Massachusetts Bay. Annual productivity in 1998 was unusually low at all three sites ( 0.05) among years (1995–1999). The mean photic depth during the bloom period was significantly deeper (P < 0.05) in 1998, signifying greater light availability with depth. Nutrients were also in abundance during the winter–spring of 1998 with stratified conditions not observed until May. In general, the magnitude of the winter–spring bloom in Massachusetts Bay from 1995 to 1999 was significantly correlated with winter water temperature (r2=0.78) and zooplankton abundance (r2=0.74) over the bloom period (typically February–April). The absence of the 1998 bloom was associated with higher than average water temperature and elevated levels of zooplankton abundance just prior to, and during, the peak winter–spring bloom period.