Showing papers on "Productivity (ecology) published in 2003"
TL;DR: There is evidence that climate warming is diminishing productivity in Lake Tanganyika, East Africa, and the impact of regional effects of global climate change on aquatic ecosystem functions and services can be larger than that of local anthropogenic activity or overfishing.
Abstract: Although the effects of climate warming on the chemical and physical properties of lakes have been documented, biotic and ecosystem-scale responses to climate change have been only estimated or predicted by manipulations and models. Here we present evidence that climate warming is diminishing productivity in Lake Tanganyika, East Africa. This lake has historically supported a highly productive pelagic fishery that currently provides 25-40% of the animal protein supply for the populations of the surrounding countries. In parallel with regional warming patterns since the beginning of the twentieth century, a rise in surface-water temperature has increased the stability of the water column. A regional decrease in wind velocity has contributed to reduced mixing, decreasing deep-water nutrient upwelling and entrainment into surface waters. Carbon isotope records in sediment cores suggest that primary productivity may have decreased by about 20%, implying a roughly 30% decrease in fish yields. Our study provides evidence that the impact of regional effects of global climate change on aquatic ecosystem functions and services can be larger than that of local anthropogenic activity or overfishing.
642 citations
TL;DR: In this article, the authors used biological measurements to estimate carbon storage in vegetation and soil pools, net primary productivity, and net ecosystem productivity to examine variation with stand age in ponderosa pine forests.
Abstract: Forest development following stand-replacing disturbance influences a variety of ecosystem processes including carbon exchange with the atmosphere. On a series of ponderosa pine (Pinius ponderosa var. Laws.) stands ranging from 9 to> 300 years in central Oregon, USA, we used biological measurements to estimate carbon storage in vegetation and soil pools, net primary productivity (NPP) and net ecosystem productivity (NEP) to examine variation with stand age. Measurements were made on plots representing four age classes with three replications: initiation (I, 9–23 years), young (Y, 56–89 years), mature (M, 95–106 years), and old (O, 190–316 years) stands typical of the forest type in the region. Net ecosystem productivity was lowest in the I stands (−124 g C m−2 yr−1), moderate in Y stands (118 g C m−2 yr−1), highest in M stands (170 g C m−2 yr−1), and low in the O stands (35 g C m−2 yr−1). Net primary productivity followed similar trends, but did not decline as much in the O stands. The ratio of fine root to foliage carbon was highest in the I stands, which is likely necessary for establishment in the semiarid environment, where forests are subject to drought during the growing season (300–800 mm precipitation per year). Carbon storage in live mass was the highest in the O stands (mean 17.6 kg C m−2). Total ecosystem carbon storage and the fraction of ecosystem carbon in aboveground wood mass increased rapidly until 150–200 years, and did not decline in older stands. Forest inventory data on 950 ponderosa pine plots in Oregon show that the greatest proportion of plots exist in stands ∼ 100 years old, indicating that a majority of stands are approaching maximum carbon storage and net carbon uptake. Our data suggests that NEP averages ∼ 70 g C m−2 year−1 for ponderosa pine forests in Oregon. About 85% of the total carbon storage in biomass on the survey plots exists in stands greater than 100 years, which has implications for managing forests for carbon sequestration. To investigate variation in carbon storage and fluxes with disturbance, simulation with process models requires a dynamic parameterization for biomass allocation that depends on stand age, and should include a representation of competition between multiple plant functional types for space, water, and nutrients.
384 citations
TL;DR: Richness of threatened species was higher in P (co)-limited sites than in N-limited sites, suggesting that increased P availabilities in wetlands may be particularly important in causing disappearance of threatenedspecies in western Europe.
Abstract: We evaluated whether the kind of nutrient limitation (N, P, or K) may affect species richness–productivity patterns and subsequently may explain variation in species richness and in richness of threatened species. We present a data set from previous studies in wetlands in Poland, Belgium, and The Netherlands and examine species richness–productivity patterns for vascular plants in all 150 sites together as well as for N-, P-, and K-limited sites separately. The kind of nutrient limitation was assessed by N:P, N:K, and K:P ratios in the vegetation. Critical values for these ratios were derived from a literature review of fertilization experiments. The kind of nutrient limitation influenced species richness–productivity patterns in our 150 sites through large differences in productivity. P (co)-limitation occurred only at low productivity, K (co)-limitation up to intermediate productivity, and N limitation along the entire productivity gradient. There was a decreasing trend in species richness with increasing productivity for K (co)-limited sites, whereas for both the N-limited sites and P (co)-limited sites a sort of “filled hump-shaped curve” was observed. The species richness–productivity relationship for threatened species was restricted to a much narrower productivity range than that for all species. Richness of threatened species was higher in P (co)-limited sites than in N-limited sites, suggesting that increased P availabilities in wetlands may be particularly important in causing disappearance of threatened species in western Europe. The role of nutrient limitation in species richness–productivity relationships not only reveals mechanisms that may explain variation in species richness and occurrence of threatened species, but it also may be important for nature management practice.
360 citations
TL;DR: It is shown, for the first time, that bacterial diversity varies along a gradient of primary productivity and thus make an important step towards understanding processes responsible for the maintenance of bacterial biodiversity.
Abstract: Primary productivity is a key determinant of biodiversity patterns in plants and animals but has not previously been shown to affect bacterial diversity. We examined the relationship between productivity and bacterial richness in aquatic mesocosms designed to mimic small ponds. We observed that productivity could influence the composition and richness of bacterial communities. We showed that, even within the same system, different bacterial taxonomic groups could exhibit different responses to changes in productivity. The richness of members of the Cytophaga-Flavobacteria-Bacteroides group exhibited a significant hump-shaped relationship with productivity, as is often observed for plant and animal richness in aquatic systems. In contrast, we observed a significant U-shaped relationship between richness and productivity for a-proteobacteria and no discernable relationship for b-proteobacteria. We show, for the first time, that bacterial diversity varies along a gradient of primary productivity and thus make an important step towards understanding processes responsible for the maintenance of bacterial biodiversity.
293 citations
TL;DR: In this paper, a chronosequence of 1- to 28-yr-old, constructed Spartina alterniflora marshes were measured along a chrono-quence to identify trajectories and rates of ecosystem development of wetland structure and function.
Abstract: Ecological attributes were measured along a chronosequence of 1- to 28-yr- old, constructed Spartina alterniflora marshes to identify trajectories and rates of ecosystem development of wetland structure and function. Attributes related to biological productivity and diversity (Spartina, epiphytic and sediment algae, benthic invertebrates), soil devel- opment (sediment deposition, organic C, N, P, organic matter quality), and microbial pro- cesses (C mineralization) were compared among eight constructed marshes and eight paired natural reference marshes. Most ecological attributes developed in a predictable manner over time, and most achieved equivalence to natural marshes 5-15 yr after marsh construc- tion. An exception was soil organic C and N pools (0-30 cm) that, after 28 yr, were significantly lower in constructed marshes. Development of habitat structure (Spartina stem height and density) and biodiversity (algae and invertebrates) developed concurrently with functional characteristics such as biomass, chlorophylla, and invertebrate density. Processes related to hydrology, sediment deposition and soil C and N accumulation, developed almost instantaneously with the establishment of Spartina, and young (1- to 3-yr-old), constructed marshes trapped sediment and sequestered N at higher rates than comparable reference marshes. Development of heterotrophic activity (C mineralization, invertebrate density) was strongly linked to surface (0-10 cm) soil organic C content. Ecosystem development of constructed (and natural) salt marshes depended on a minimum of 100 g N/m 2 (0.05- 0.1% N) to support emergent vegetation and 1000 g C/m 2 (0.5-1% C) to sustain the het-
291 citations
TL;DR: A system of forested lake islands in the boreal zone of Sweden for which fire frequency increases with increasing island size is studied, finding that large islands supported higher plant productivity and litter decomposition rates than did smaller ones, and, with increasing time since fire, litter decomposing rates were suppressed sooner than was ecosystem productivity.
Abstract: Boreal forest soils play an important role in the global carbon cycle by functioning as a large terrestrial carbon sink or source, and the alteration of fire regime through global change phenomena may influence this role. We studied a system of forested lake islands in the boreal zone of Sweden for which fire frequency increases with increasing island size. Large islands supported higher plant productivity and litter decomposition rates than did smaller ones, and, with increasing time since fire, litter decomposition rates were suppressed sooner than was ecosystem productivity. This contributes to greater carbon storage with increasing time since fire; for every century without a major fire, an additional 0.5 kilograms per square meter of carbon becomes stored in the humus.
285 citations
TL;DR: Heterogeneity in soil nutrients created by cattle management practices within a geologically homogeneous savanna is used to examine relationships among soil nitrogen and phosphorus, above- ground net primary production (ANPP), grass nutrient content, and a mixed community of native and domestic herbivores on central Kenyan rangeland.
Abstract: Small-scale fertilization experiments have shown that soil nutrients limit plant productivity in many semiarid grasslands and savannas, but linkages among nutrients, grasses, and grazers are rarely studied in an ecosystem context. We used hectare-scale heterogeneity in soil nutrients created by cattle management practices within a geologically homogeneous savanna to examine relationships among soil nitrogen and phosphorus, above- ground net primary production (ANPP), grass nutrient content, and a mixed community of native and domestic herbivores on central Kenyan rangeland. Increasing soil N and P content was consistently associated with increasing plant productivity and rainfall use efficiency in wet, dry, and drought years. A fertilization experiment and analyses of grass N:P ratios across sites indicated that N is the primary limiting nutrient on nutrient-rich glades, whereas N and P co-limit productivity on nutrient-poor bushland sites. Variation in ANPP among patches within the landscape was linearly correlated with consumption rates of large her- bivores. Grazing pressure was consistently high ( .60% of ANPP) at all but one site in a dry year (1999), and was greater in nutrient-rich glades (73 6 4% of ANPP) than in nutrient- poor bushland sites (43 6 7% of ANPP) in a wet year (2001). Grasses of nutrient-rich sites contained sufficient P concentrations to meet requirements for pregnant and lactating un- gulates, whereas grasses in nutrient-poor swards were P deficient. Even though native and domestic herbivores selectively used and intensively grazed nutrient-rich sites, productivity on these sites remained high throughout the study. Analyses of nitrogen budgets for nutrient- rich and nutrient-poor sites showed that large herbivores themselves caused a net N input to the former and a net N loss from the latter. Thus, large herbivores not only respond to heterogeneity in soil and plant nutrients across the landscape, but also play a role in maintaining the N-enriched status of highly productive and intensively grazed sites.
258 citations
TL;DR: The results show that the effects of resource availability on productivity and diversity are similar in young and mature grasslands, and that manipulation of a limiting nutrient during grassland establishment can influence floristic composition, with conse- quences for long-term patterns of diversity in restored ecosystems.
Abstract: In native tallgrass prairie, soil depth and nitrogen (N) availability strongly influence aboveground net primary productivity (ANPP) and plant species composition. We manipulated these factors in a newly restored grassland to determine if these resources similarly constrain productivity and diversity during the initial three years of grassland establishment. Four types of experimental plots with six treatment combinations of deep and shallow soil at reduced-, ambient-, and enriched-N availability formed the basis of this study. The soil responses to the experimental treatments were examined over three years, and patterns in diversity and productivity were examined in year 3. The soil depth treatment did not significantly affect soil carbon (C) and N pools or ANPP and diversity. A pulse amendment of C added to the soil prior to planting increased soil microbial biomass and decreased potential net N mineralization rates to effectively reduce N availability throughout the study. Nitrogen availability declined over time in nonamended soils as a result of plant establishment, but adding fertilizer N alleviated the increasing immobilization potential of the soil. The level of ANPP was lowest and diversity highest in the reduced-N treatment, whereas the enriched-N treatment resulted in high productivity, but low diversity. As a result, diversity was inversely correlated with productivity in these newly established com- munities. The same mechanism invoked to explain decreased diversity under nutrient en- richment in old-field ecosystems and native grasslands (e.g., reduced light availability with increased production) was supported in the restored prairie by the positive relationship between ANPP and intercepted light, and a strong correlation between light availability and diversity. The effects of nutrient availability on plant community composition (diversity and richness) were due primarily to the responses of prairie species, as the productivity of early successional, nonprairie species was less than 1% of total ANPP after three years of establishment. These results show that the effects of resource availability on productivity and diversity are similar in young and mature grasslands, and that manipulation of a limiting nutrient during grassland establishment can influence floristic composition, with conse- quences for long-term patterns of diversity in restored ecosystems.
206 citations
TL;DR: The hypothesis that plant species diversity may have idiosyncratic effects on soil communities, even though studies on a longer term could reveal time lags in the response to changes in composition and biomass production of plant communities, is supported.
Abstract: We examined the relationship between plant species diversity, productivity and the development of the soil community during early secondary succession on former arable land across Europe. We tested the hypothesis that increasing the initial plant species diversity enhances the biomass production and consequently stimulates soil microbial biomass and abundance of soil invertebrates. We performed five identical field experiments on abandoned arable land in five European countries (CZ, NL, SE, SP and UK) which allowed us to test our hypothesis in a range of climate, soil and other environmental factors that varied between the experimental sites. The initial plant diversity was altered by sowing seed mixtures of mid-successional grassland species with two or five grass species, one or five legumes and one or five forbs. The results of low and high sown diversity treatments were compared with plots that were naturally colonized by species present in the seed bank. In three out of the five field sites, there was no correlation between plant species number and plant biomass production, one site had a positive and the other a negative relation. Treatments with a high diversity seed mixture had a higher biomass than the naturally colonized plots. However, there was no significant difference between high and low sown diversity plots at four out of five sites. The three-year study did not give any evidence of a general bottom-up effect from increased plant biomass on biomass of bacteria, saprophytic fungi or abundance of microarthropods. The biomass of arbuscular mycorrhizal was negatively related to plant biomass. The abundance of nematodes increased after abandonment and was related to plant biomass at four sites. Our results support the hypothesis that plant species diversity may have idiosyncratic effects on soil communities, even though studies on a longer term could reveal time lags in the response to changes in composition and biomass production of plant communities.
203 citations
TL;DR: It is hypothesize that low N supply and plant productivity, and hence low litter C supply to saprotrophs is associated with a high plant C supplyTo mycorrhizal fungi, while the reverse occurs under high N supply, and should mean that effects of N availability onC supply to these functional groups of microbes acts in opposing directions.
Abstract: Soil microorganisms are considered C-limited, while plant productivity is frequently N-limited. Large stores of organic C in boreal forest soils are attributed to negative effects of low temperature, soil acidity and plant residue recalcitrance upon microbial activity. We examined microbial activity, biomass and community composition along a natural 90-m-long soil N supply gradient, where plant species composition varies profoundly, forest productivity three-fold and soil pH by three units. There was, however, no significant variation in soil respiration in the field across the gradient. Neither did microbial biomass C determined by fumigation-extraction vary, while other estimates of activity and biomass showed a weak increase with increasing N supply and soil pH. Simultaneously, a phospholipid fatty acid attributed mainly to mycorrhizal fungi declined drastically, while bacterial biomass increased. We hypothesize that low N supply and plant productivity, and hence low litter C supply to saprotrophs is associated with a high plant C supply to mycorrhizal fungi, while the reverse occurs under high N supply. This should mean that effects of N availability on C supply to these functional groups of microbes acts in opposing directions. (Less)
197 citations
TL;DR: Evidence is provided that niche complementarity can strongly increase productivity in grasslands, although the communities contained only grasses and forbs.
Abstract: We investigated the effect of species richness on productivity in randomly assembled grassland communities without legumes. Aboveground biomass increased with increasing species richness and different measures of complementarity showed strong increases with plant species richness. Increasing productivity could not be attributed to a relative increase of highly productive species. Instead, the increase appeared to be caused by the increased performance of several low-productive species. Our results provide evidence that niche complementarity can strongly increase productivity in grasslands, although the communities contained only grasses and forbs.
Abstract: Intermittent saline intrusions are a common feature of many coastal lakes and wetlands. These ecosystems are often important sites of biodiversity, biological productivity, and ecosystem ser- vices such as the removal of sediment, nutrients, and contaminants from inflowing rivers. Predicted effects of global climate change, including sea level rise, are likely to intensify saline intrusions into such ecosystems. Analyses of taxonomic diversity and abundance of zooplankton at different salini- ties in Lake Waihola, South Island, New Zealand, are supported by results of laboratory studies of salinity tolerances of 3 crustacean taxa Gladioferens pectinatus, Boeckella hamata and Daphnia carinata obtained from the lake. The field and laboratory analyses show that severe perturbations of zooplankton community structure and abundance are caused by even minor saline intrusions into Lake Waihola that raise the salinity to >1.2 psu. Our analyses of Lake Waihola, and data from brack- ish ecosystems around the world, show that even relatively small increases in salinity levels can drive such systems to a state of depleted biodiversity and abundance, altering ecosystem functioning.
TL;DR: In this paper, spatial patterns of forest structure and growth following 50 years of development were associated with variations in the soil environment across the tidal gradient, and most measurements of forest biomass and productivity were inversely related to salinity.
Abstract: The objective of this study was to quantify spatial patterns in above- and belowground biomass, primary productivity, and growth efficiency along a tidal gradient in a 4700-ha mangrove forest in the Dominican Republic. We tested the hypothesis that spatial patterns of forest structure and growth following 50 years of development were associated with variations in the soil environment across the tidal gradient. Twenty-three plots were monitored from 1994 to 1998. Aboveground biomass and biomass accumulation were estimated by applying allometric regression equations derived from dimension analysis of trees harvested at our study site. Soil porewater salinity ranged from 5 to 38 g kg -1 across the tidal gradient, and most measurements of forest biomass and productivity were inversely related to salinity. Mean standing biomass (233 ± 16.0 Mg ha -1 ; range, 123.5-383.5), biomass increment (9.7 ± 1.0 Mg . ha -1 y -1 ; range, 3.7-18.1), annual litterfall rates (11.4 Mg . ha -1 yr -1 ; range, 10.2-12.8), leaf area index (LAI) (4.4 m 2 . m -2 ; range, 2.9-5.6), aboveground net primary productivity (ANPP) (19.7 Mg . ha -1 y -1 ; range, 15.6-25.0), and growth efficiency (1.6±0.2 kg . ha -1 y -1 ; range, 1.0-3.6) all showed an inverse linear relationship with salinity. Fine-root biomass (≤ 2 mm) (9.7 ± 1.2 Mg . ha -1 ; range, 2.7-13.8) showed a weak tendency to increase with salinity, and the ratio of root to aboveground biomass increased strongly with salinity. Our results suggest that physiological stresses associated with salinity, or with some combination of salinity and other covarying soil factors, control forest structure and growth along the tidal gradient. The higher allocation of carbon to belowground resources in more saline sites apparently contributed to reductions in ANPP along the tidal gradient.
TL;DR: Factorially excluding foliar fungal pathogens and insect herbivores from an intact grassland ecosystem identifies pathogens as potential regulators of ecosystem processes and promotes the incorporation of pathogens into trophic theory.
Abstract: Current theories of trophic regulation of ecosystem net primary production and plant biomass incorporate herbivores, but not plant pathogens. Obstacles to the incorporation of pathogens include a lack of data on pathogen effects on primary production, especially outside agricultural and forest ecosystems, and an apparent inability to quantify pathogen biomass. Here, I report the results of an experiment factorially excluding foliar fungal pathogens and insect herbivores from an intact grassland ecosystem. At peak in control plots, 8.9% of community leaf area was infected by pathogens. Disease reduction treatment dramatically increased root production and biomass by increasing leaf longevity and photosynthetic capacity. In contrast, herbivory reduction had no detectable effects at the ecosystem or leaf scale. Additionally, biomass of foliar fungal pathogens in the ecosystem was comparable with that of insect herbivores. These results identify pathogens as potential regulators of ecosystem processes and promote the incorporation of pathogens into trophic theory.
TL;DR: The lake has high conservation value because of three bird species in particular – lesser flamingo, Cape teal and black-necked grebe – and is ecologically simple, with only one species dominating the phytoplankton – the cyanobacterium `spirulina', Arthrospira fusiformis.
Abstract: Lake Bogoria, in the Rift Valley of Kenya is an extreme saline lake (conductivity 40–80 mS cm-1, alkalinity 1500 m equ 1-1). It is hydrologically more stable than the other, endorheic lakes in Kenya, because it is deep — maximum depth at present just over 10 m in an area of 3000 ha — and so does not have periods when it is dry. It is ecologically simple, with only one species dominating the phytoplankton — the cyanobacterium ‘spirulina’, Arthrospira fusiformis. Its biomass and productivity were very high — biomass between 38 and 365 μg 1-1 chlorophyll ‘a’ and 3.4–21 x 103 coils ml-1 and net production between 0.24 and 1 gm C m3 h, the latter in a narrow zone of less than a metre. There were no macro-zooplankton in the plankton and the only grazer of A. fusiformis was the lesser flamingo, Phoeniconaias minor, which occurred irregularly in very high concentrations (in excess of 1 x 106). Detritivory in the benthos was effected by a single chironomid species, Paratendipes sp., at a maximum density of 4 x 104 m-2. The mean daily emergence of adult chironomids was estimated to be 1 x 103 m-2, the maximum 3. There was no littoral plant community within the lake but 44 dicotyledonous and 31 monocotyledonous plant species in the drawn-down zone and adjacent to it. A diverse draw-down terrestrial invertebrate fauna, only superficially described here, processed the flamingo feathers and carcasses, with other detritus such as chironomid pupal exuviae and decaying A. fusiformis scum. About 50 bird species depended upon the chironomids, either as they emerged through the water column as flying adults or later on the shoreline as floating pupal exuvia and dead adults. The lake has high conservation value because of three bird species in particular — lesser flamingo, Cape teal and black-necked grebe. The former provides real economic value in a region otherwise impoverished, because of the spectacle of tens of thousands of flamingos set against the landscape of hot springs and fumaroles at the lake edge, which draws 15 000 visitors per annum. P. minor has experienced three periods during the past ten years when major mortalities have occurred, the last of which killed 700 birds day-1. This could have involved as many as 200 000 birds (about 1/5th of the maximum population at this lake) if mortality was at a constant rate for the nine months it was observed. Causes of mortality have been suggested as avian tuberculosis, poisoning from cyanobacterial toxins or from heavy metal contamination at Lake Nakuru, but it is still not yet clear what contribution each makes to the problem.
TL;DR: The optimization of the operation, under the climatic conditions of southern Spain, of an experimental plant for β-carotene production by Dunaliella has been pursued and the operating conditions established as being most appropriate for efficient mass production of β- carotene rich D. salina have validated this location.
Abstract: The optimization of the operation, under the climatic conditions of southern Spain, of an experimental plant for β-carotene production by Dunaliella has been pursued. The effects of mixing, culture depth, cell density and dilution cycles on β-carotene and biomass productivity were studied under a semicontinuous culture regime in open tanks outdoors. Using 3 m2-surface containers, the highest productivity values, for both β-carotene and biomass, were recorded with a flow rate of 0.55 m s−1; 10 cm depth; 0.7 − 0.9 × 106cell ml−1, population density; and dilution cycles of two days. An average annual productivity of 1.65 g (dry wt) m−2 d−1 was estimated for Dunaliella biomass, being that for β-carotene of about 0.1 g m−2 d−1. Under these optimized conditions, experiments have been carried out at the Cadiz Bay with 20 m2-surface tanks during a whole-year cycle. The results obtained have validated this location and the operating conditions established as being most appropriate for efficient mass production of β-carotene rich D. salina.
TL;DR: Phytoplankton Productivity provides, in one book, cutting edge reviews and key facts on the subject, making it a vital information source for marine and freshwater biologists, oceanographers, ecologists, environmental scientists and plant scientists.
Abstract: Description: This landmark publication takes the 50th anniversary of the publication of the seminal paper by the Danish scientist, Einer Steemann Nielsen, as an occasion to assess the development, present state and future of the major aspects in freshwater and marine plankton productivity. Each chapter of this important work has been written by internationally–acknowledged experts in the subject, and the whole has been carefully drawn together and edited to provide a book that is an essential tool and reference for all aquatic scientists. The book takes ascending temporal and spatial size scale as its framework – covering molecular to geological scales. Chapters include reviews of physiology and biochemistry, measurement of phytoplankton productivity, the supply and uptake of nutrients, variability in processes and production, the evolution of the carbon cycle, and ecosystems. The subject is set in context with a chapter covering the work of Steemann Nielsen, whose work inspired the last 50 years of aquatic productivity studies. Historical aspects are discussed together with thought–provoking assessments of modern technological approaches and where future research emphasis should be focussed. Phytoplankton Productivity provides, in one book, cutting edge reviews and key facts on the subject, making it a vital information source for marine and freshwater biologists, oceanographers, ecologists, environmental scientists and plant scientists. Copies should also be available in libraries of any research establishment and university as a reference for students, wherever these subjects are studied and taught.
TL;DR: It is suggested that seedling emergence does not relate linearly to time since grazing and that seed availability does not limit productivity and diversity in these subhumid grasslands.
Abstract: Recent studies indicate that plant species richness and primary productivity of grasslands may be limited by seed availability. However, it is not known how widespread this limitation is, whether it is affected by disturbance, or which mechanisms underlie any disturbance effect. We tested for seed limitation and explored the role of litter accumulation in explaining effects of recent grazing history on seedling establishment, species diversity (richness and evenness), and plant productivity in a subhumid grassland ecosystem in Texas, USA. We added seeds and removed litter in a factorial treatment arrangement (seeds added, litter removed, seeds added and litter removed, and control (no seeds added nor litter removed)) within each of five fields: currently grazed, no grazing for 1-2, 2-3, or 6-7 yr, and an unplowed prairie remnant. Seeds from each of 20 native species were added to replicated 1-m 2 plots in each field during each of two growing seasons. Adding seeds increased seedling emergence in all fields, but this increase was much greater when litter was removed, especially in ungrazed fields. Counter to our expectations, seedling emergence increased with time since grazing when litter was removed and was greatest in fields not grazed for 1-3 yr when litter was present. As expected, light availability at the soil surface decreased with time since grazing. However, soil water availability to 15 cm depth increased with time since grazing, suggesting that limits on seedling emergence changed from water to light with time since grazing. Aboveground productivity during the second year of the study was significantly reduced following seed additions in the four fields along the grazing gradient, primarily because of a decrease in the productivity of C4 grasses. Species diversity decreased with time since grazing. Seed additions slightly increased species richness but decreased species evenness in fields located along the grazing gradient, resulting in no net effect on diversity. In the more species-rich prairie remnant, seed additions had no effect on aboveground productivity or species richness or evenness. These results suggest that seedling emergence does not relate linearly to time since grazing and that seed availability does not limit productivity and diversity in these subhumid grasslands.
TL;DR: Sanya Bay encompasses a high diversity of natural habitats, ranging from coral reefs, rocky and sandy shores and mudflats to mangroves, and is rich in natural resources and biodiversity with 235 species of phytoplankton and 129 species of zooplanks identified in the survey.
TL;DR: In this paper, living (Rose Bengal stained) benthic foraminifera were collected with a multicorer from six stations between 2°N and 12°S off West Africa.
Abstract: Living (Rose Bengal stained) benthic foraminifera were collected with a multicorer from six stations between 2°N and 12°S off West Africa. The foraminiferal communities in the investigated area reflect the direct influence of different productivity regimes, and are characterized by spatially and seasonally varying upwelling activity. At five stations, foraminiferal abundance coincides well with the gradient of surface productivity. However, at one station off the Congo River, the influence of strong fresh water discharge is documented. Although this station lies directly in the center of an upwelling area, foraminiferal standing stocks are surprisingly low. It is suggested that the Congo discharge may induce a fractionation of the organic matter into small and light particles of low nutritional content, by contrast to the relatively fast-sinking aggregates found in the centers of high productivity areas. Quality and quantity of the organic matter seem to influence the distribution of microhabitats as well. The flux of organic carbon to the sea-floor controls the sequence of degradation of organic matter in sediment and the position of different redox fronts. The vertical foraminiferal stratification within sediment closely parallels the distribution of oxygen and nitrate in porewater, and reflects different nutritive strategies and adaptation to different types of organic matter. The epifauna and shallow infauna colonize oxygenated sediments where labile organic matter is available. The intermediate infauna ( M. barleeanum ) is linked to the zone of nitrate reduction in sediments where epifaunal and shallow infaunal species are not competitive anymore, and must feed on bacterial biomass or on metabolizable nutritious particles produced by bacterial degradation of more refractory organic matter. The deep infauna shows its maximum distribution in anoxic sediments, where no easily metabolizable organic matter is available.
01 Jan 2003
TL;DR: In this article, the effect of changing ice cover on the food web structure and production in Disko Bay, Western Greenland, is analysed through application of a dynamical model for the planktonic food web.
Abstract: A rise in global temperatures could potentially lead to less ice in the Arctic, including a reduction in the ice-covered period. The consequence of a changing ice cover on the food web structure and production in Disko Bay, Western Greenland, is analysed through application of a dynamical model for the planktonic food web. The model is successfully calibrated and tested for sensitivity, using a detailed data set for 1996–1997. Model scenarios are (1) extended ice cover and (2) no ice. These scenarios are compared to model runs with measured ice cover in two normal years. In the extended ice scenario, assuming unchanged copepod behaviour, copepods are starving or feeding in the ice/water interface from the time they ascend to the surface layer from over-wintering depths until the ice break-up in June. The total annual primary production reaches the same level as it does in the average year, but copepod ingestion and, as a consequence, vertical carbon export is reduced by app. 40%. In the ice-free situation, an early diatom bloom is initiated by stratification of the water in March, before the copepods ascend. The diatom bloom is grazed upon by protozooplankton, which reach a high biomass before the copepods ascend in April. Annual primary production increases by 52% while copepod ingestion and vertical loss of carbon is reduced by 57%. This study illustrates how a change in the ice cover in Arctic areas can potentially create a mismatch between spring primary production and copepod grazers. The result may be a planktonic food web dominated by protozooplankton, resulting in lower export of organic material out of the photic zone despite increased primary productivity, or alternatively lead to changes in species composition or behaviour.
TL;DR: Decadal-scale variations of ecosystem productivity in the Bohai Sea are described by using the survey data of 1959–60, 1982–83, 1992–93 and 1998–99 to indicate that a large variation in ecosystem productivity is one of the important characteristics of coastal ecosystem dynamics.
Abstract: Decadal-scale variations of ecosystem productivity in the Bohai Sea are described by using the survey data of 1959–60, 1982–83, 1992–93 and 1998–99. Indices including chlorophyll a concentration, primary production, phytoplankton abundance, zooplankton biomass and fishery biomass were used to describe the ecosystem productivity at different trophic levels. During the past four decades, the productivity and community structure of the Bohai Sea ecosystem has been highly variable. Primary productivity and fish productivity decreased from 1959 to 1998, such that phytoplankton abundance in 1992 and 1998 was about 38% of that in 1959 and 1982, fishery biomass in 1998 was particularly low, which was only about 5% of that in 1959. Zooplankton secondary productivity also showed a decreasing trend from 1959 to 1992, but reached high levels in 1998, about three times as much as 1959 and 1982, and four times as much as 1992. These results indicate that a large variation in ecosystem productivity is one of the important characteristics of coastal ecosystem dynamics. Therefore, it is impossible to apply a single theory to explain the causes of variations in the Bohai Sea ecosystem as the changes in productivity are likely to be forced and/or modulated by multiple mechanisms.
TL;DR: The results suggest that in non-acidic tundra carbon sequestration in plant biomass will not increase substantially under increased soil nutrient conditions because of the lack of overstory shrub species.
Abstract: In arctic Alaska, researchers have manipulated air temperature, light availability, and soil nutrient availability in several tundra communities over the past two decades. These communities responded quite differently to the same manipulations, and species responded individualistically within communities and among sites. For example, moist acidic tundra is primarily nitrogen (N)-limited, whereas wet sedge tundra is primarily phosphorus (P)-limited, and the magnitude of growth responses varies across sites within communities. Here we report results of four years of manipulated nutrients (N and/or P) and/or air temperature in an understudied, diverse plant community, moist non-acidic tussock tundra, in northern Alaska. Our goals were to determine which factors limit above-ground net primary productivity (ANPP) and biomass, how community composition changes may affect ecosystem attributes, and to compare these results with those from other communities to determine their generality.
Although relative abundance of functional groups shifted in several treatments, the only significant change in community-level ANPP and biomass occurred in plots that received both N and P, driven by an increase in graminoid biomass and production resulting from a positive effect of adding N. There was no difference in community biomass among any other treatments; however, some growth forms and individual species did respond. After four years no one species has come to dominate the treatment plots and species richness has not changed. These results are similar to studies in dry heath, wet sedge, and moist acidic tundra where community biomass had the greatest response to both N and P and warming results were more subtle. Unlike in moist acidic tundra where shrub biomass increased markedly with fertilization, our results suggest that in non-acidic tundra carbon sequestration in plant biomass will not increase substantially under increased soil nutrient conditions because of the lack of overstory shrub species.
TL;DR: In this article, a new independent indicator, Sr/Ca in coccolith carbonate, was used to investigate the biotic response in the most complete PETM deep sea record which was recovered at ODP Site 690 in the Weddell Sea.
Abstract: [1] A major perturbation of the global carbon cycle ∼55 million years ago, believed to result from release of 1000–2000 Gt of C from methane hydrates, correlates with an intense but transient greenhouse warming event known as the Paleocene Eocene Thermal Maximum (PETM). The rapid (105 years) recovery of global temperatures reflects important negative feedbacks in the climate system and carbon cycle. Enhanced marine productivity may be one important feedback, but indicators for productivity changes have yielded conflicting results. Here we use a new independent indicator, Sr/Ca in coccolith carbonate, which covaries with the productivity of coccolithophorid algae, to investigate the biotic response in the most complete PETM deep sea record which was recovered at ODP Site 690 in the Weddell Sea. In the dominant coccolithophorid genus Toweius a large (40%) Sr/Ca increase immediately after the gas hydrate release signals a dramatic productivity increase. Productivity levels remained high for 60,000 years but decreased to pre-event levels by 120,000 years after the gas hydrate release. Productivity levels during the PETM are higher than observed at any other time in our ∼400,000 year record. Other coccolithophorid genera Chiasmolithus and Discoaster show a brief modest (25% Sr/Ca increase) increase in productivity that lags behind the methane event by 50,000 years and is within the range of productivity variation elsewhere in the record. The timing of the Toweius productivity increase agrees well with Os isotope records of globally increased weathering intensity, which may have provided higher nutrient fluxes to stimulate algal productivity. If this type of productivity response occurred globally, it would also be consistent with the timing of C drawdown that may have returned temperatures to near pre-event levels.
TL;DR: In this paper, the structure, biomass, and productivity of two Taxodiaceae-dominated forests that grew north of the Arctic Circle (paleolatitude 75-80°N) were investigated.
Abstract: Abundant fossil plant remains are preserved in the high-latitude middle Eocene deposits of the Buchanan Lake Formation on Axel Heiberg Island, Nunavut Territory, Canada. Intact leaf litter, logs, and stumps preserved in situ as mummified remains offer an opportunity to determine the structure, biomass, and productivity of two Taxodiaceae-dominated forests that grew north of the Arctic Circle (paleolatitude 75–80°N). We excavated fossil tree trunks and treetops to develop equations that describe the height, structure, and mass of the aboveground components of Eocene-age Metasequoia trees. We combined those data with surveys of in situ stumps to determine the structure, biomass, and productivity of two fossil forests, “N” and “HR.” We calculated a canopy height of 40 ± 3 m for the N forest and 25 m ± 2 m for the HR forest. Buried knots in dissected logs and abundant branch-free bole wood indicate that these were tall, closed-canopy forests. Stem tapers indicate that the overstory was of uniform hei...
TL;DR: It is suggested that past studies of plant productivity in Western Atlantic marshes, by not accounting for the confounding effects of grazing, are likely to have significantly underestimated plant growth and overestimated the relative importance of bottom-up factors in regulating marsh primary production.
Abstract: Quantifying primary productivity and understanding the factors that control plant growth are primary goals of ecosystem ecology. Although some methods have been very successful in providing accurate measurements of plant growth and elucidating the importance of both physical and biological factors in regulating primary production (e.g. terrestrial systems: Smith 1996; marine communities: Bertness et al. 2001), many techniques are still hampered by methodological biases that greatly affect productivity estimates and overall experimental results. For example, a recent review of tropical seagrass systems suggests that past experiments investigating seagrass productivity may have been compromised because they did not control for the confounding effects of grazing (i.e. monitoring and/or excluding fish and invertebrate grazers – Valentine and Heck 1999). The authors argue that the probable consequences of not accounting for herbivore effects are: (1) inaccurate estimates of both net and gross primary production and (2) an intellectual bias concerning the relative roles of bottom-up (i.e. nutrients and nutrient regulating factors) and top-down (e.g. herbivory) forces in controlling seagrass growth. In this paper, we argue that these conclusions also apply broadly to salt marshes along the East Coast of both North and South America. Specifically, we suggest that past studies of plant productivity in Western Atlantic marshes, by not accounting for the confounding effects of grazing (i.e. excluding herbivorous crabs and snails), are likely to have significantly underestimated plant growth and overestimated the relative importance of bottom-up factors in regulating marsh primary production. We contend that current methods of measuring marsh grass growth must be amended to include grazer exclusions in carefully controlled field experiments. Only then will we be able to obtain accurate measurements of marsh plant productivity and assess the relative importance of top-down effects in controlling marsh grass growth.
TL;DR: In this article, the effects of experimental burial using two types of sediment: (1) sand (6 and 0.2% silt-clay and organic matter con- tent, respectively); and (2) silt (27 and 3.3%) were assessed.
Abstract: Mortality and productivity of Zostera marina L. were assessed to examine the effects of experimental burial using 2 types of sediment: (1) sand (6 and 0.2% silt-clay and organic matter con- tent, respectively); and (2) silt (27 and 3.3% silt-clay and organic matter content, respectively). Z. marina was buried to 0, 25, 50, 75 and 100% of its average aboveground height (16 cm) in an exist- ing eelgrass bed using 2 types of sediment characterized as either silty or sandy. Increasing percent- ages of plant burial significantly increased mortality and decreased productivity. Survival and pro- ductivity of eelgrass were substantially reduced when only 25% of the plant height was buried. Plants buried 75% or more of their height were characterized by survival and productivity measures of 0. No statistically significant differences in plant mortality or productivity were found between the 2 sediment types in this experiment. Changes in morphology of the plants were detected in measures of leaf length and surface area in a short duration (12 d) trial of the experiment, apparently in response to senescence, but etiolation was not observed. Results of this experiment indicate Z. marina can only tolerate rapid sedimentation events that cover less than half of its photosynthetic surfaces. Furthermore, the lowest levels of burial treatments (25% of plant height) resulted in mor- tality greater than 50%, indicating that even this small level of rapid sedimentation is significantly detrimental to Z. marina.
TL;DR: In this article, Nongin Thai mini-watersheds are defined as geographical components of rainfed lowland rice culture in Northeast Thailand, and constitute distinct units in understanding environmental constraints for lo...
Abstract: Mini-watersheds called Nongin Thai are geographical components of rainfed lowland rice culture in Northeast Thailand, and constitute distinct units in understanding environmental constraints for lo...
TL;DR: It is hypothesized that the Phanerozoic record of fossil diversity is a function of a secular increase in nutrient availability and productivity (food, energy), and cyclic changes in sea level and habitat area due to supercontinent assembly and rifting as mentioned in this paper.
Abstract: It is hypothesized that the Phanerozoic record of fossil diversity is a function of a secular increase in nutrient availability and productivity (food, energy), and cyclic changes in sea level and habitat area due to supercontinent assembly and rifting. Both variables may have affected biodiversity through the combined variable of {productivity × area}. {Productivity × area} remained relatively constant after the Cambro-Ordovician until the end of the Permian, as did the traditional curve for biodiversity. During assembly of Pangea, decreasing sea level and habitat area were counteracted by increasing nutrient inputs due to uplift and the spread of vascular plants and enhanced continental weathering. As Pangea underwent its final assembly, interior drainage increased, so that by the end of the Permian both habitat area and nutrient runoff decreased. Following the end-Permian extinctions, the traditional curve of diversity began to increase, habitat area, nutrient levels and productivity all increased. Despite the confounding factors of differential preservation and sampling bias toward the present, the fossil record reflects a real response by the marine biosphere to tectonism, sea level, paleoceanographic regime and climate, and the spread of terrestrial floras, and their influence on habitat area, nutrient inputs, and productivity through time.
TL;DR: In this paper, the authors monitored Silicates, nitrates, phosphates, chlorophyll a, and primary productivity at low and high tide between September 1985 and September 1986.
Abstract: Resumen en: Silicates, nitrates, phosphates, chlorophyll a and primary productivity were monitored at low and high tide between September 1985 and September 1986, a...