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1.
Samples of eelgrass, Zostera marina L., were collected monthly from December 1974 through December 1975 in a shallow embayment near Beaufort, N.C., and separated into green leaves, dead leaves, and leaf detrital material. Each component was analysed for dry weight, organic matter, inorganic and organic carbon, nitrogen and amino compounds.The standing crop of green and dead blades reached a maximum in April through June, while detrital matter had peaks in December, April and July–September. Inorganic carbon in the three grass fractions showed seasonal variations similar to those observed for epiphytic biomass in previous years, and represented 14, 24, and 30% of the total carbon associated with the green and dead leaves and detrital fragments, respectively. Organic carbon represented a decreasing proportion of the dry weight of these three fractions on a dry weight basis while there was a significant increase in organic carbon on an ash-free dry weight basis in the detrital fragments relative to the head dead blades. During senescence there was a loss of nitrogen from the leaves and an increase in the nitrogen content of the organic matter of the detritus relative to the dead leaves. The latter suggests that there was microbial growth on the detritus and subsequent nitrogen immobilization from the surrounding medium. There were significant decreases of lysine, histidine, arginine, glycine, tyrosine, and glucosamine in the dead leaves relative to the detritus. The glucosamine, derived from N-acetyl-glucosamine, a product of murein which is a component of microbial cell walls, had a seasonal distribution similar to that of the epiphytic community and available inorganic nitrogen in the surrounding water. The relative proportions of N-acetyl-glucosamine, nitrogen and organic carbon were all higher in the fall and winter.  相似文献   

2.
Biological invasions modify the quality and supply of detrital subsidies to aquatic and terrestrial ecosystems. Where the invader has very different traits to native species, major changes in associated consumer communities may result, as a consequence of differences in their nutritional value and effects on the sedimentary habitat. We assessed how the replacement of seagrasses with the invasive alga Caulerpa taxifolia in modified Australian estuaries influences invertebrate communities of mudflats that are subsidized by detritus from submerged aquatic vegetation. Two months after experimental enrichment of sediments with high (60?g dry weight per 0.25?m2 plot) or low (30?g dry weight) quantities of either non-native C. taxifolia or native Posidonia australis or Zostera capricorni detritus, there were positive effects of detrital addition on invertebrate abundance that occurred irrespective of the resource added. By 4?months after addition, however, detritus from invasive C. taxifolia had produced effects on benthic communities that could not be replicated by detritus from either of the native seagrasses. Plots receiving the high loading of C. taxifolia detritus contained fewer invertebrates than plots of the other treatments, perhaps due to the induction of sediment hypoxia. The pattern, however, reversed at low detrital loading, with the plots receiving 30?g of C. taxifolia containing more invertebrates and more taxa than the other plots, presumably due to the greater resource availability for detritivores. Our results demonstrate that replacement of native seagrass with invasive algal detritus can have large impacts on sediment-dwelling communities.  相似文献   

3.
Resource nutrient content and identity are common bottom–up controls on organismal growth and nutritional regulation. One framework to study these factors, ecological stoichiometry theory, predicts that elevated resource nitrogen (N) and phosphorus (P) contents enhance organism growth by alleviating constraints on N and P acquisition. However, the regulatory mechanisms underlying this response – including whether responses depend on resource identity – remain poorly understood. In this study, we tested roles of detrital N and P contents and identity (leaf species) in constraining growth of aquatic invertebrate detritivores. We synthesized results from seven detritivore species fed wide nutrient gradients of oak and maple detritus in the laboratory. Across detritivore taxa, we used a meta‐analytic approach quantifying effects of detrital leaf species and N and P contents on growth, consumption, and N‐ and P‐specific assimilation and growth efficiencies. Detritivore growth rates increased on higher‐N and P detritus and on oak compared to maple detritus. Notably, the mechanisms of improved growth differed between the responses to detrital nutrients versus leaf species, with the former driven by greater consumption rates despite lower assimilation efficiencies on higher‐nutrient detritus, and the latter driven by improved N and P assimilation and N growth efficiencies on oak detritus. These findings suggest animal nutrient acquisition changes flexibly in response to resource changes, altering the fate of detrital N and P throughout regulation. We affirm resource identity and nutrients as important bottom–up controls, but suggest these factors act through separate pathways to affect organism growth and thereby change detrital ecosystems under anthropogenic forest compositional change and nutrient enrichment.  相似文献   

4.
Yang LH 《Oecologia》2006,147(3):522-532
Detritivore communities influence the decomposition of detrital resources in virtually all natural systems. Conversely, detrital resources can also have considerable bottom-up effects on detritivore communities. While many investigations have examined detritivory and decomposition processes, few have considered interactions between detritivores and detritus as concurrent processes in the same system, or in the context of natural detrital pulses. In many systems, resource pulses contribute substantial detrital inputs to belowground systems. These detrital pulses may influence interactions between the detritivore community and detrital decomposition. I conducted field experiments to investigate interactions between detrital resource pulses of periodical cicada (Magicicada spp.) carcasses and scavenging detritivorous macroarthropods. Cicada litterfall pulses influenced several broad groups in the macroarthropod community, including relatively specialized necrophilous taxa and relatively generalized detritivores, omnivores and predators. Conversely, detritivore activity increased the rate of cicada carcass decomposition by 4,082% compared to caged control carcasses. These results suggest that interactions between pulses of cicada detritus and the detritivore community influence both the persistence of ephemeral detrital resources, and the distribution, abundance and behavior of detritivore populations.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.  相似文献   

5.
Detritivory is the dominant trophic paradigm in most terrestrial, aquatic, and marine ecosystems, yet accurate measurement of consumer trophic position within detrital (=“brown”) food webs has remained unresolved. Measurement of detritivore trophic position is complicated by the fact that detritus is suffused with microbes, creating a detrital complex of living and nonliving biomass. Given that microbes and metazoans are trophic analogues of each other, animals feeding on detrital complexes are ingesting other detritivores (microbes), which should elevate metazoan trophic position and should be rampant within brown food webs. We tested these hypotheses using isotopic (15N) analyses of amino acids extracted from wild and laboratory‐cultured consumers. Vertebrate (fish) and invertebrate detritivores (beetles and moths) were reared on detritus, with and without microbial colonization. In the field, detritivorous animal specimens were collected and analyzed to compare trophic identities among laboratory‐reared and free‐roaming detritivores. When colonized by bacteria or fungi, the trophic positions of detrital complexes increased significantly over time. The magnitude of trophic inflation was mediated by the extent of microbial consumption of detrital substrates. When detrital complexes were fed to vertebrate and invertebrate animals, the consumers registered similar degrees of trophic inflation, albeit one trophic level higher than their diets. The wild‐collected detritivore fauna in our study exhibited significantly elevated trophic positions. Our findings suggest that the trophic positions of detrital complexes rise predictably as microbes convert nonliving organic matter into living microbial biomass. Animals consuming such detrital complexes exhibit similar trophic inflation, directly attributable to the assimilation of microbe‐derived amino acids. Our data demonstrate that detritivorous microbes elevate metazoan trophic position, suggesting that detritivory among animals is, functionally, omnivory. By quantifying the impacts of microbivory on the trophic positions of detritivorous animals and then tracking how these effects propagate “up” food chains, we reveal the degree to which microbes influence consumer groups within trophic hierarchies. The trophic inflation observed among our field‐collected fauna further suggests that microbial proteins represent an immense contribution to metazoan biomass. Collectively, these findings provide an empirical basis to interpret detritivore trophic identity, and further illuminate the magnitude of microbial contributions to food webs.  相似文献   

6.
7.
The deposit-feeding prosobranch Hydrobia ventrosa (Montagu) was fed 14C-labelled food for a short period. As food, sterile detritus (homogenously 14C-labelled, dried barley hay), detritus with attached bacteria, and pure bacteria were used. The distribution of the ingested 14C was followed for a 24-h period. It was found that the assimilation efficiencies of sterile hay, hay with bacteria, and pure bacteria were 34, 56, and 70 %, respectively. This indicates a significance of bacteria for deposit-feeders. There is a considerable loss of dissolved organic material, in part due to leakage from faecal pellets (13 % of the ingested C in the case of a pure bacterial meal and 7 % of the ingested C in the case of sterile hay). The animals also excrete about 30 % of the assimilated carbon. Excretion of mucus constitutes about 9 % of the assimilated carbon. The fraction of assimilated carbon respired depends on the nature of the food. For sterile hay, hay with bacteria, and pure bacteria the percentage respired was 53, 30, and 38 %, respectively. Growth efficiency is, therefore, higher when protein-rich bacteria are included in the diet.  相似文献   

8.
Omnivores can impact ecosystems via opposing direct or indirect effects. For example, omnivores that feed on herbivores and plants could either increase plant biomass due to the removal of herbivores or decrease plant biomass due to direct consumption. Thus, empirical quantification of the relative importance of direct and indirect impacts of omnivores is needed, especially the impacts of invasive omnivores. Here we investigated how an invasive omnivore (signal crayfish, Pacifastacus leniusculus) impacts stream ecosystems. First, we performed a large-scale experiment to examine the short-term (three month) direct and indirect impacts of crayfish on a stream food web. Second, we performed a comparative study of un-invaded areas and areas invaded 90 years ago to examine whether patterns from the experiment scaled up to longer time frames. In the experiment, crayfish increased leaf litter breakdown rate, decreased the abundance and biomass of other benthic invertebrates, and increased algal production. Thus, crayfish controlled detritus via direct consumption and likely drove a trophic cascade through predation on grazers. Consistent with the experiment, the comparative study also found that benthic invertebrate biomass decreased with crayfish. However, contrary to the experiment, crayfish presence was not significantly associated with higher leaf litter breakdown in the comparative study. We posit that during invasion, generalist crayfish replace the more specialized native detritivores (caddisflies), thereby leading to little long-term change in net detrital breakdown. A feeding experiment revealed that these native detritivores and the crayfish were both effective consumers of detritus. Thus, the impacts of omnivores represent a temporally-shifting interplay between direct and indirect effects that can control basal resources.  相似文献   

9.
Several studies have investigated the effect of nematodes on microbial degradation of macrophyte detritus, but little is known about the potential effect of bacterivorous nematodes on productivity of macrofaunal detritivores. We investigated the influence of the bacterivorous nematode Rhabditis (Pellioditis) mediterranea on the incorporation rate of isotopically-labelled macroalgal detritus by the amphipod Paramoera chevreuxi in a laboratory microcosm. The fatty acid composition of amphipods, nematodes, and macroalgal detritus was characterized to help determine the pathway of detritus incorporation by amphipods. The potential importance of R. mediterranea as a source of highly unsaturated fatty acids (HUFAs) to higher trophic levels was also investigated.We found no clear evidence for an effect of nematodes on the incorporation rate of fresh macroalgal detritus by amphipods, although there was some indication that the type of detritus (i.e. the green Chaetomorpha sp. vs the red Polysiphonia sp.) is important in determining the nature and extent of the relationship between nematodes and macrofaunal detritivores. Fatty acid data indicated that nematodes did not contribute significantly to the diet of amphipods when detritus was present, and there was no evidence that nematodes affected the pathway of detritus incorporation by amphipods. Amphipods incorporated Chaetomorpha sp. detritus about 10 times faster than Polysiphonia sp. detritus despite the higher C/N ratio and lower HUFA content of the former. This suggests that other factors, such as the presence of grazer deterrent compounds, are important in determining the palatability of macroalgal detritus. Amphipods fed exclusively on nematodes retained high HUFA levels but suffered high mortality. The burrowing behaviour of nematodes is suggested as the most likely factor limiting their availability to predators.Results suggest a limited interaction between amphipods and bacterivorous nematodes in detrital food webs. Further experiments are needed to test the wider applicability of these findings to different nematode and macrofaunal taxa, and for different types of detritus.  相似文献   

10.
Food webs of many ecosystems are sustained by organic matter from other habitats. Human activities and climatic change are increasingly modifying the quality and supply of these resources, yet for most ecosystems it is unknown how the taxonomic composition of organic matter influences community composition. Along the coastline of Sydney, Australia, the once abundant habitat-forming macroalga, Phyllospora comosa, is now locally extinct. Shallow reefs are now primarily occupied by Sargassum sp. and, to a lesser extent, the kelp Ecklonia radiata. We experimentally manipulated the supply of P. comosa, Sargassum sp. and E. radiata to estuarine sediments to assess responses by macroinvertebrate communities to: (1) changing the identity of the dominant detrital resource; and (2) varying the ratio of input of different macrophytes. Estuarine sediments dosed with P. comosa supported greater abundances of macroinvertebrates than sediments receiving Sargassum sp. or the kelp E. radiata. Whereas plots receiving Sargassum sp. or E. radiata had fewer macroinvertebrates than controls, plots receiving a moderate (120 g dry weight per m2) loading of P. comosa had more. Mixtures of detritus dominated by P. comosa supported similar macroinvertebrate communities to monocultures of the alga. Communities in sediments receiving detritus comprised of less than one-third P. comosa were, however, distinctly different. Our study provides evidence that the ecological ramifications of species decline can extend to spatially removed ecosystems, subsidised by allochthonous materials. Even prior to extinction of detrital sources, small changes in their provision of organic matter may alter the structure of subsidised communities.  相似文献   

11.
Approximately one-third of organic seston in western Lake Erie was estimated to be living algae; the remainder was mainly detritus. The amount of detrital carbon was least in summer and maximal in autumn. Allochthonous organic matter, particularly municipal and industrial wastes, and resuspended sediments were considered to be major sources of detritus.  相似文献   

12.
A shallow turbid man-made impoundment was studied intensively for five years. The carbon (C) budget indicated a well balanced system, where phytoplankton productivity and respiratory losses accounted for the major inputs and outputs. The carbon content was dominated by dissolved organic carbon, followed by detritus > fish > phytoplankton > bacteria > zooplankton > zoobenthos.From an analysis of a matrix flow model, three dominant components of C-flow in the system were identified, i.e. dissolved inorganic carbon (DIC), particulate organic carbon (POC) and fish. Phytoplankton and detritus were the important components of POC. The largest flow of C was through the largest pool, dissolved inorganic carbon (DIC), whilst the second largest flow was through the fifth largest pool, the phytoplankton. Phytoplankton was very important in determining the structure of the system, and variations in phytoplankton primary productivity influenced the entire system. This also applied to the input of organic material from macrophytes, but not to variations in the inflow and outflow of water from the impoundment.The input of detrital material from a littoral macrophyte community also markedly influenced the system. DOC was identified as a carbon buffer in the system, and differential flow occurred through this component upon variations in phytoplankton productivity.  相似文献   

13.
Summary Carbohydrate, lipid, and protein compositions are stoichiometrically related to organic CHN (carbon, hydrogen, nitrogen) contents. Elemental CHN analyses of total biomass and ash, therefore, provide a basis for the calculation of proximate biochemical composition and bomb caloric value. The classical nitrogen to protein conversion factor (6.25) should be replaced by 5.8±0.13. A linear relation exists between the mass fraction of non-protein carbon and the carbohydrate and lipid content. Residual water in dry organic matter can be estimated with the additional information derived from hydrogen measurements.The stoichiometric CHN method and direct biochemical analysis agreed within 10% of ash-free dry biomass (for muscle, liver and fat tissue of silver carp; gut contents composed of detritus and algae; commercial fish food). The detrital material, however, had to be corrected for non-protein nitrogen.A linear relationship between bomb caloric value and organic carbon fractions was derived on the basis of thermodynamic and stoichiometric principles, in agreement with experimental data published for bacteria, algae, protozoa and invertebrates. The highly automatic stoichiometric CHN method for the separation of nutrient contents in biomass extends existing ecophysiological concepts for the construction of balanced carbon and nitrogen, as well as biochemical and energy budgets. Offprint requests to: Institut für Zoologie, Abt. Zoophysiologie, Universität Innsbruck, Peter-Mayr-Str. 1A, A-6020 Innsbruck, Austria  相似文献   

14.
Changes of caloric values and energy-rich organic compounds were studied in the detritus derived from mangrove Kandelia candel (L.) Druce leaf litter during the various in situ seasonal decomposition in Jiulong River Estuary, Fujian, China. The results showed that the caloric values varied little among the seasonal fallen leaves being a mean of 19.63 kJ/g dry wt or 21.55 kJ/g AF dry wt, the caloric values of detritus increased remarkably after decomposition but they more rapidly in summer and autumn than in winter and spring. The change was well in agreement with the degree of decomposition, being increased in the early decomposition period and slightly decreased in the later, with a peak at about the half-time of decomposition (50% weight loss). The maximum was averagely 17.67% of dry weight and 14.35 % of ash-free dry; weight basis over the initial values. The dissipation of total energy was somewhat slower than the loss of dry matter. As decomposition proceeds the energy of detritus was more and more contributed by raw protein, raw fat, raw fibers rather than by N-free extract. Therefore it is suggested that detritus at half-time of decomposition should be more important to marine detritivores from the viewpoint of energy supplement.  相似文献   

15.
A minimal food web model was constructed comprising one grazing and one detritus food chain coupled by nutrient cycling and generalist carnivores to investigate how prey preference by carnivores may affect the strength of trophic cascades across a gradient of nutrient enrichment. The equilibrium or mean abundance of each food web component and the magnitude of the carnivore effect on lower trophic levels were calculated for different values of the prey preference and nutrient input parameters. Our model predicts that nutrient enrichment increases the mean abundances of carnivores, autotrophs and detritus, but the magnitude of this effect is dependent on the prey preference term. On the other hand, herbivores and detritivores are relatively unaffected by enrichment but are strongly affected by carnivore preference. Carnivores have a negative effect on herbivores and a positive effect on autotrophs and detritus, whereas the effect on detritivores can be both positive and negative. At high preference for herbivores, carnivores have a positive effect on detritivores, because the positive effect of increased detritus availability due to reduced herbivore grazing outweighs the negative effect of predation. At high preference for detritivores, the balance is changed in the other direction. We argue that in systems where authochtonous primary production is the major source of detritus, herbivores can control the rates of detritus production and have indirect effects on detritivores, which may feed back into effects on herbivores through their shared enemies. This positive feedback is probably one mechanism affecting the resilience of alternative stable states in shallow lakes. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Author Contributions  J.L.A. conceived the model and the study, J.R. wrote the Matlab programs and ran the simulations and J.L.A. wrote most of the paper.  相似文献   

16.
《Aquatic Botany》1987,27(1):97-119
Bacteria growing on and in close association with the rhizome detritus of two seagrasses, Zostera marina L. and Thalassia testudinum Banks ex König, were examined using epifluorescence and scanning electron microscopy. The microbial community consisted of a diverse assemblage of bacteria dominated in biomass by large rod-shaped and filamentous cells. The large size of cells and the occurrence of measurable acetylene reduction activity suggested that a healthy, growing population of bacteria was associated with the rhizome detritus. Bacteria carbon biomass ranged betwee 5.2×10−5 and 1.7×10−3 g C gdw−1 of rhizome detritus. Depending on cell doubling times, bacterial metabolism could account for a substantial portion of the turnover of rhizome detritus. Estimates of potential microbial production, nitrogen fixation and the physico-chemical nature of rhizome detritus are discussed and we propose hypotheses for the disposition of this detrital organic matter.  相似文献   

17.
1. Explaining resource–diversity relationships is a long‐standing goal in ecology, and there is currently little consensus as to the relative contributions of neutral versus a variety of proposed niche‐related mechanisms. 2. The resource–diversity relationship of insect detritivores was examined in a survey of 25 small, parallel streams flowing into the Bay of Fundy in eastern Canada, with the objective of determining whether neutral processes (sampling effects) could account for the observed patterns. 3. Detritivore taxonomic richness showed a positive, but decelerating relationship with quantity of detritus. Richness also increased with catchment area and with stream permanence. 4. Species distribution patterns were significantly nested, and low resource streams (little detritus) tended to have species with large ranges (i.e. found in many or most streams). 5. Sampling effects could explain only part of the positive relationship between richness and detrital resources, but accounted for the species richness–area relationship. 6. Two mechanisms that could potentially increase niche space as resource abundance increased were rejected: there was no evidence that riparian forest diversity or beta diversity increased with detrital resources. 7. Two niche‐related mechanisms were consistent with existing data, but will require further testing. First, flood disturbance may decrease species richness by eliminating species that require benign habitat, and lowering detritus retention, producing a positive correlation between detritivore richness and resources. Second, large wood in streams located in older riparian forest may increase habitat heterogeneity (number of niches) and the retention of organic matter, again leading to a positive relationship between detritivore diversity and detrital resources. 8. It was concluded that the positive ‘productivity–diversity’ relationship for stream detritivores was most likely produced in part by sampling effects, but also by ecological processes (disturbance and succession) that simultaneously influence resource level and niche availability.  相似文献   

18.
In temperate forested streams, fruit from riparian trees is generally a minor and seasonal component of the allo‐chthonous detritus. In contrast, riparian fruit input to tropical streams is often high and continuous. Detrital fruit is abundant in some forested Hawaiian streams compared to other forms of riparian detritus, and rates of leaf litter processing by macroscopic invertebrates are very low. These observations suggested that fruit is an important food resource for detritivores. A microcosm system was used to measure the rates at which two common detrital fruits, guava and mango, were processed by two common detritivores, the prawn Macrobrachium lar and the gastropod Tarebia granifera. Comparisons of fruit weight loss rates normalized by detritivore weight indicated that M, lar processed guavas at significantly higher rates than T. granifera, differences in rates of mango processing by M. lar and T. granifera were not significant. Microcosms containing both M. lar and T. granifera were used to test for interactions between the invertebrates that affected rates of mango processing. No interspecific interactions were detected. A field study was conducted in Kaiwiki Stream, Island of Hawaii, to determine rates of detrital fruit input and export. Detrital fruit was supplied to the study area year‐round, with peaks corresponding to summer and autumn fruiting seasons. Guavas and mangos accounted for 85 percent of the fruit biomass entering the stream and 92 percent of the fruit exported from the stream. Mean daily export rates of guava were 7 percent of input, and export rates of mango were 5 percent of input. These measurements suggested that most of the fruit entering the stream is retained and comprises a substantial food resource for detritivores. Comparisons of the biomass‐specific rates at which M. lar and T. granifera processed mangos and guavas with the rates at which mangos and guavas entered Kaiwiki Stream suggested that these invertebrates can process most of the detrital fruit in the stream.  相似文献   

19.
Nutrient cycles in both terrestrial and many freshwater habitats are fueled by terrestrial detritus. However, direct comparisons of decomposition processes in these environments are scarce. Aiming at shedding light on similarities and differences in these processes in different habitats, we studied decomposition of low-quality versus high-quality detritus through the action of shredders versus grazers in aquatic versus terrestrial microcosms under controlled climatic conditions. Decomposition processes were most strongly affected by whether they took place in the terrestrial or the aquatic environment: Leaching resulted in a rapid mass loss of detritus in the aquatic environment, and detritus traits became less pronounced over time. Thus, breakdown was mediated through dissolved organic matter (DOM) in water but through particulate organic matter (POM) on land. Litter mass loss and the promoting effects of detritivores on mass loss also depended on the environment, but shredders always had a greater effect than grazers. Both litter and detritivore diversity were overall of little relevance for litter mass loss, but more so in the aquatic than the terrestrial environment. By contrast, the influence of detritivores on microbes was stronger in water than on land, but effects depended on the litter type. The type of both litter and detritivores, however, was less significant in the aquatic than in the terrestrial environment, possibly due to leaching and abiotic processing of litter during early decomposition, resulting in diminishing differences between litter types. We conclude that the habitat type shapes the dynamics of leaf litter decomposition. Heavy leaching (in the aquatic environment) shortens initial decomposition phases and dislocates the degradation of easily accessible compounds in the form of DOM from the leaves into the water column. Consequently, initial interspecific differences in litter quality diminish, and both functional differences in, and diversity of, both litter and detritivores become less important than in the terrestrial environment.  相似文献   

20.
Previous studies of Pyramid Lake, Nevada, led to the hypothesis that detritus could be an important food source for zooplankton because abundance of palatable algal species did not seem to be enough to support the zooplankton community throughout the year. Furthermore, a large portion of the annual primary productivity was attributed to a nonpalatable blue-green alga, Nodularia spumigena. We felt this alga became important to the Pyramid Lake aquatic community upon death, as edible detritus and a source of new nitrogen. Changes in pelagic detritus concentrations and microbial standing crops were monitored to determine the availability of these potential foods. Epilimnetic particulate organic carbon (POC) was primarily living phytoplankton. During holomixis and following spring primary production, hypolimnetic POC was 60–97% detrital, but these profundal POC concentrations were low (ca 650 µg l-1). Detritus-bacteria aggregates were observed only following the September cyanophyte bloom. Although pelagic detritus availability for zooplankton was low, bacterial populations were sufficient to be at least a supplemental food source. Bacteria numbers ranged from 0.50 106 to 24.7 106 ml-1 and increased in response to photosynthetic peaks. Microbial diversity, contribution to POC, and particle association were notable after July. The percentage of living carbon (assessed with ATP measurements) attributable to bacteria was highest in late summer and fall hypolimnetic samples. Patterns of change in organic phosphorus and nitrogen, the presence of a nitrogen-fixing cyanophyte, the N:P ratio, and results of other research demonstrated that non-nitrogen-fixing algae of Pyramid Lake are limited by inorganic nitrogen. The importance of N. spumigena to the aquatic community appeared to be as a source of new nitrogen, rather than as a forage; its mineralization is critical for the growth of palatable diatoms and green algae following winter mixing.  相似文献   

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