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1.
Background and aim
Exotic plant species can alter the nitrogen cycle in invaded ecosystems. We assess the differences in nitrogen use strategies and litter production and dynamics among three native riparian trees (Fraxinus angustifolia, Populus alba and Ulmus minor) and three co-occurring exotics (Ailanthus altissima, Robinia pseudoacacia and Ulmus pumila), currently spreading throughout river banks in inner Spain. We aim to predict the ecological consequences of a replacement of the natives by the exotics.Methods
We compared the leaf lifespan, nitrogen resorption efficiency in leaves, nitrogen mean residence time, amount and timing of litter production and amount of nitrogen returned to soils between these native and exotic species.Results
We found differences among species in all the variables measured, but not between native or exotic origins. Species were ranked from the most to the least conservative nitrogen use strategy as follows: U. pumila was the most conservative species, followed by the three natives (with an intermediate strategy), A. altissima and finally by the nitrogen-fixer R. pseudoacacia. The studied exotic species would produce contrasting impacts on the nitrogen cycle upon invasion.Conclusions
On the basis of our results, we predict little impacts on the nitrogen cycle if U. pumila dominates the landscape. Despite being nitrogen-fixer R. pseudocacia would not increase soil nitrogen availability in the study area due to its low litter production and litter decomposition rates. In contrast, we predict an increase in nitrogen availability of soils upon A. altissima invasion, as this species produces a high amount of nitrogen rich and labile litter. This study offers a striking example of the contingencies involved in predicting the ecosystem impacts of exotic plant invasion. 相似文献2.
P. Castro-Díez N. González-Muñoz A. Alonso A. Gallardo L. Poorter 《Biological invasions》2009,11(8):1973-1986
We assess the hypothesis that rates of nitrogen transformations in the soil are altered upon replacement of native by exotic
trees, differing in litter properties. Ailanthus altissima and Robinia pseudoacacia, two common exotic trees naturalized in the Iberian Peninsula, were compared with the native trees Ulmus minor and Fraxinus angustifolia, respectively. Naturally senesced leaves of each species were collected and C:N ratio, N and lignin content assessed. We
prepared 64 litter bags per species and left them to decompose, below the canopy of the same species and below the canopy
of the paired species. Dry mass, N concentration and N pool of the remaining litter were assessed after 5 and 7 months. Soil
samples were collected three times during the experiment to assess soil moisture, organic matter, pH, potential mineralization
rates and mineral N pools. Mineral N availability was assessed three times in the field by using ion-exchange resin-impregnated
membranes. Ailanthus litter decomposed faster than Ulmus litter, probably due to the higher toughness of the latter. In spite of its high N content, Robinia litter decomposed slower than Fraxinus one, probably due to its high lignin content. In both cases, litter decomposition was faster below the exotic than the native
canopies. The release of N per unit of initial litter mass was higher under both invaded situations (Ailanthus below Ailanthus and Robinia below Robinia) than under the native ones. However, soils collected below native and exotic trees neither differed in potential N mineralization
rate nor in mineral N. This may be attributed to a quick plant uptake of released N and/or to a high organic matter accumulation
in the soil previous to invasion that can exert a tighter control on soil N transformations than the current exotic litter. 相似文献
3.
Ailanthus altissima and Robinia pseudoacacia are two aggressive exotic tree species invading riparian ecosystems in Central Spain. We explored their allelopathic potentials as a possible mechanism explaining their success in these ecosystems. Specifically, we aimed (1) to compare the phytotoxic effects of the exotic and native (Fraxinus angustifolia and Populus alba) trees on the fitness of several understory plants coexisting in riparian ecosystems, and (2) to assess the capacity of the riparian soil to modulate the phytotoxic effects. In laboratory bioassays, aqueous leaf litter extracts from the donor tree species at field-realistic concentrations were tested on different fitness indicators of 13 understory target species, using germination paper and soil as substrates in petri dishes. Using germination paper, we found species-specific effects between donor and target species, but the phytotoxicity of the exotic trees as a group was not greater than that of the natives. Nevertheless, the exotic R. pseudoacacia was the most effective donor species reducing the radicle growth of the target species. Over riparian soil substrate, the aqueous leaf litter extracts did not produce any phytotoxic effect on the target species, except in one case. Altogether, our results highlight the importance of using both a native control when assessing the phytotoxicity of nonnative plants and also the natural soil in the modulation of phytotoxic effects. Ignoring both factors in laboratory bioassays would have led to the overestimation of the phytotoxicity of the exotic species as a mechanism contributing to their invasion success. 相似文献
4.
Decomposing litter is regarded as the most important source of allelochemicals released into soil. In this study, a greenhouse experiment was designed to assess the net effect of differently aged leaf litter from exotic (Ailanthus altissima, Robinia pseudoacacia and Ulmus pumila) and native riverine trees (Populus alba, Populus nigra and Ulmus minor) on the germination and growth of three herb species (Trifolium repens, Dactylis glomerata and Chenopodium album). We also characterized the chemical composition of litter samples at different litter ages (0, 1, 2 and 3 months) based on phenolic compounds, fibers and ergosterol (as a measure of fungal biomass) contents. Overall, litter from both native and exotic species had a negative effect on shoot and root growth of target species, indicating that phytotoxic effects of litter predominate over positive effects. The inhibition effect of the exotic species was similar or even lower than that of the natives, which does not support the Novel Weapons Hypothesis. Among exotic trees, U. pumila showed the highest inhibition effect on the growth of the target species. T. repens was the most sensitive target species. The importance of litter age varied with both target and donor species. In general, D. glomerata was more inhibited by fresh litter, C. album by half-decomposed litter of U. pumila and R. pseudoacacia and by fresh litter of A. altissima and T. repens was more inhibited by fresh litter of A. altissima and P. alba and by highly decomposed litter of U. minor. The concentration of total phenolics and flavonoids decreased while acid detergent fiber, lignin and ergosterol increased with increasing litter age. Hydroxybenzoic and protocatechuic acids and the flavonoid quercetin were detected in all litter species and at most of the litter ages, while gallic, chlorogenic, vanillic, coumaric and rosmarinic acids were species-specific and they were only detected in fresh litter. Ergosterol concentration appeared as the strongest constrictor of inhibitory effects of litter on understory species. The results of this study contribute to the understanding of the net effect of fresh and decomposed litter from exotic and native trees on the growth of understory species. 相似文献
5.
Invasive exotic plants can persist and successfully spread within ecosystems and negatively affect the recruitment of native species. The exotic invasive Ailanthus altissima and the native Robinia pseudoacacia are frequently found in disturbed sites and exhibit similar growth and reproductive characteristics, yet each has distinct functional roles such as allelopathy and nitrogen fixation, respectively. A four-month full additive series in the greenhouse was used to analyze the intraspecific and interspecific interference between these two species. In the greenhouse experiment, the inverse of the mean total biomass (g) response per plant for each species was regressed on the density of each species and revealed that the performance of the plants was significantly reduced by interspecific interference and not by intraspecific interference (p < 0.05). Other biomass traits such as root dry weight, shoot dry weight, stem dry weight, and leaf dry weight were also negatively affected by interspecific interference. Competition indices such as Relative Yield Total and Relative Crowding Coefficient suggested that A. altissima was the better competitor in mixed plantings. Ailanthus altissima consistently produced a larger above ground and below ground relative yield while R. pseudoacacia generated a larger aboveground relative yield in high density mixed species pots. 相似文献
6.
Pilar Castro-Díez Natalia Fierro-Brunnenmeister Noelia González-Mu?oz Antonio Gallardo 《Plant and Soil》2012,350(1-2):179-191
Aims
We assessed the effects of native and exotic tree leaf litter on soil properties in two contrasting scenarios. The native Quercus robur and Pinus pinaster tree species coexist with the aliens Eucalyptus globulus and Acacia dealbata in acid soils of NW Spain. The native trees Fraxinus angustifolia and Ulmus minor coexist with the aliens Ailanthus altissima, Robinia pseudoacacia and Ulmus pumila in eutrophic basic riparian soils in Central Spain.Methods
Four plastic trays per species were filled with homogenized top-soil of the site and covered with leaf litter. Before and after 9?months of incubation, litter mass, soil pH, organic matter, mineral and total N were measured. Available mineral N (NO 3 ? -N and NH 4 + -N) was assessed every 2?months.Results
Soil biological activity was higher in the basic than in the acid soil. Litter of the exotic trees tended to decompose less than litter of native species, probably due to the presence of secondary metabolites in the former. Soil pH, mineral and total N responded differently to different litter types, irrespective of their exotic or native origin (acid soil), or was similar across litter treatments (basic riparian soil). The similar response of the basic soil to the addition of different litter types may be due to the low contrast of litter quality between the species. E. globulus litter inhibitied soil microbial activity much more than the rest of the studied litter types, leading to a drastic impoverishment of N in soils.Conclusion
Litter of exotic N-fixing trees (A. dealbata and R. pseudoacacia) did not increase soil N pools because of the inhibition of microbial activity by secondary compounds. Therefore, secondary metabolites of the litter played a major role explaining exotic litter impact on soil properties. 相似文献7.
S. Mark Nelson 《International Review of Hydrobiology》2011,96(1):72-89
Replacement of native macrophyte species with exotic or invasive ones affects the quality of detritus entering streams and can alter nutrient cycles and community structure in aquatic ecosystems. Decomposition of air‐dried native hardstem bulrush (Schoenoplectus acutus), invasive southern cattail (Typha domingensis), and exotic common reed (Phragmites australis) were studied in an urban stream (Las Vegas, Nevada, USA) using litter bags. Samples were analyzed for dry mass, lignin, nutrients, trace elements, and macroinvertebrates. Litter type and sediment deposited on plant material influenced material loss. Trace elements arsenic and selenium increased in plant material to concentrations considered marginal for ecosystem contamination by exposure day 76. Mercury increases were inconsistent across plant species and did not exceed limits. Bulrush decomposed faster, and tended to have higher selenium concentrations, than did invasive southern cattail and exotic common reed. Macroinvertebrate communities colonizing litter bags were similar across plant litter types, but differed from mesh‐only bags and samples collected with a kick‐net. Macroinvertebrate exclusion resulted in significantly lower loss rates, but functional feeding groups such as shredders were not associated with decomposition differences. The caddisfly, Smicridea, physically modified stem material and aided in processing, but microbes appeared most important in biological material breakdown. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
8.
Fang Wang Dunmei Lin Wei Li Pengpeng Dou Le Han Mingfen Huang Shenhua Qian Jingmei Yao 《Ecology and evolution》2020,10(17):9257-9270
Litter decomposition, a fundamental process of nutrient cycling and energy flow in freshwater ecosystems, is driven by a diverse array of decomposers. As an important component of the heterotrophic food web, meiofauna can provide a trophic link between leaf‐associated microbes (i.e., bacteria and fungi)/plant detritus and macroinvertebrates, though their contribution to litter decomposition is not well understood. To investigate the role of different decomposer communities in litter decomposition, especially meiofauna, we compared the litter decomposition of three leaf species with different lignin to nitrogen ratios in litter bags with different mesh sizes (0.05, 0.25, and 2 mm) in a forested stream, in China for 78 days. The meiofauna significantly enhanced the decomposition of leaves of high‐and medium‐ quality, while decreasing (negative effect) or increasing (positive effect) the fungal biomass and diversity. Macrofauna and meiofauna together contributed to the decomposition of low‐quality leaf species. The presence of meiofauna and macrofauna triggered different aspects of the microbial community, with their effects on litter decomposition varying as a function of leaf quality. This study reveals that the meiofauna increased the trophic complexity and modulated their interactions with microbes, highlighting the important yet underestimated role of meiofauna in detritus‐based ecosystems. 相似文献
9.
10.
Jeffrey H. Braatne S. Maeika P. Sullivan Erin Chamberlain 《International Review of Hydrobiology》2007,92(6):656-665
Japanese knotweed (Fallopia japonica Houtt. Ronse Decrane ) is a highly invasive exotic plant that forms monocultures in riparian areas, effectively reducing plant diversity. This change in riparian plant composition alters the allocthonous input of leaf litter into adjacent streams. A field experiment was completed to understand how leaf decomposition and macroinvertebrate colonisation associated with the incorporation of exotic leaf litter. Leaf packs of Japanese knotweed, native alder (Alnus incana L.), native cottonwood (Populus trichocarpa Torr . and Gray ), and two additional mixed pack types (alder and cottonwood; alder, cottonwood, and Japanese knotweed) were placed into a 50 m stream reach in Clear Creek, Idaho, and removed over a three‐month period. Leaf decomposition and macroinvertebrate assemblages were similar between leaf types, despite differences in nitrogen and phosphorus content. The diversity of leaf types within a given leaf pack also had no effect on leaf decomposition or macroinvertebrate dynamics. These findings suggest that allochthonous inputs of Japanese knotweed fulfill a detrital function similar to that of native leaf litter. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
11.
《Journal of Plant Interactions》2013,8(1):173-184
The allelopathic effect of A. altissima and the nitrogen fixing ability of R. pseudoacacia make the interaction between these two species important to community dynamics. A replacement series greenhouse experiment was used to investigate the type of interaction between seedlings of A. altissima and R. pseudoacacia at high and low soil nutrition states. Also, seeds of A. altissima from its native (China) and invasive ranges (USA) were used to compare the effect of the different seed sources on the interaction with R. pseudoacacia. Robinia pseudoacacia was the better competitor. The presence of A. altissima significantly inhibited nodulation of R. pseudoacacia roots. In summary, in low nutrient early succession sites, seedlings of R. pseudoacacia and A. altissima will coexist and R. pseudoacacia will be the better competitor. However, A. altissima can increase its competitive ability by inhibiting nitrogen fixation by R. pseudoacacia. Differences between the competitive ability of the Chinese and US seed lots of A. altissima did not support the rapid evolution theory for invasive species success. 相似文献
12.
Leaf‐Litter Mixtures Affect Breakdown and Macroinvertebrate Colonization Rates in a Stream Ecosystem
Manuela Abelho 《International Review of Hydrobiology》2009,94(4):436-451
Previous work in terrestrial and aquatic ecosystems has suggested that the relationship between breakdown rates of leaf litter and plant species richness may change unpredictability due to non‐additive effects mediated by the presence of key‐species. By using single‐ and mixed‐species leaf bags (7 possible combinations of three litter species differing in toughness; common alder [Alnus glutinosa ], sweet chestnut [Castanea sativa ], and Spanish oak [Quercus ilex ilex ]), I tested whether leaf species diversity, measured as richness and composition, affects breakdown dynamics and macroinvertebrate colonization (abundance, richness and composition) during 90 days incubation in a stream. Decomposition rates were additive, i.e., observed decomposition rates were not different from expected ones. However, decomposition rates of individual leaf species were affected by the mixture, i.e., there were species‐specific responses to mixing litter. The invertebrate communities colonizing the mixtures were not richer and more diverse in mixtures than in single‐species leaf bags. On the opposite, mixing leaf species had a negative, non‐additive effect on rates of shredder and taxa colonization and on macroinvertebrate diversity. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
13.
Lohengrin A. Cavieres Paulina Chacón Alejandro Peñaloza Marco Molina-Montenegro Mary T. K. Arroyo 《Plant Ecology》2007,190(1):13-22
Leaf litter accumulation can have either positive, negative or neutral effects on seed germination and seedling recruitment.
In montane woodlands of the Mediterranean zone of central Chile, large amounts of leaf litter accumulate beneath the crowns
of the summer semi-deciduous tree Kageneckia angustifolia and no regeneration of this or other plant species has been observed beneath this tree throughout the year. In a sample plot
of 5000 m2 we selected ten K. angustifolia trees and measured (1) leaf litter accumulation beneath and outside canopy; (2) the effects of time elapsed since burial
on viability of K. angustifolia seeds with and without a leaf litter cover; (3) field seed germination with presence or absence of leaf litter and (4) the
possible chemical effects of K. angustifolia leaf litter leachates on seed germination of its own seeds and of other two co-occurring native shrubs species (Guindilia trinervis and Solanum ligustrinum). Our results show that a considerable accumulation of leaf litter occurred beneath K. angustifolia, and litter negatively affected seed viability and germination of this species in the field. Under laboratory conditions,
K. angustifolia leaf litter leachates inhibited seed germination of its own seeds and of the two native shrub species. Chemical effects are
likely involved in the negative effects of leaf litter on the recruitment of K. angustifolia in the montane sclerophyllous woodland of central Chile. 相似文献
14.
Riparian vegetation typically provides substantial allochthonous material to aquatic ecosystems where micro-organisms can
play an important role in organic matter degradation which can support consumer biomass. We examined the effects of leaf litter
quality (e.g., leaf nutrients, lignin and cellulose content), leaf species mixing, and microbial community diversity on in-stream
breakdown rates of litter from dominant riparian trees (Melaleuca
argentea, M. leucadendra, and Nauclea
orientalis) in both a perennial and intermittent river in Australia’s wet-dry tropics. Leaf mass remaining after 82 days of in-stream
incubation was negatively correlated (P < 0.05) with initial leaf N and P content while initial lignin and cellulose content had no statistically significant effect.
Breakdown rates of incubated leaves of both Melaleuca and Nauclea were significantly higher in mixed litter bags compared with single species litter bags. Although it was expected that leaf
N content would decrease from initial levels during decomposition, we found either similar or slightly higher N content following
in-stream incubation suggesting microbial colonisation increased overall N content. Stable isotopes of δ13C and δ15N for the major sources and consumers in both rivers provide evidence that leaf litter was an important macroinvertebrate
food source in the perennial river where heavy shading may limit algal production. However, in the intermittent river where
riparian cover was low, benthic algae were the major organic carbon source for consumers. Our findings suggest that riparian
tree species influence rates of in-stream organic matter processing, microbial community composition, and aquatic food web
dynamics in tropical wet-dry streams. 相似文献
15.
JOSÉ F. GONÇALVES JR RENAN S. REZENDE NARLIANE M. MARTINS RENER S. GREGÓRIO 《Austral ecology》2012,37(7):807-815
The hypothesis of this study was that colonizers in decaying leaf litter prefer native species (Erythrina verna) to exotic ones (Eucalyptus camaldulensis and Protium heptaphyllum). Therefore, native species are expected to show higher breakdown rates, increased biomass, richness and density of invertebrate species, and increased biomass of decomposer fungi. Breakdown of leaf litter from these three species was assessed in an Atlantic Rain Forest stream. Four samples were collected during a period of 90 days and washed on a sieve to separate the invertebrates. Then, a series of leaf disks were cut to determine ash‐free dry mass and fungal biomass, and the remaining material was oven‐dried to determine the dry weight. Eucalyptus camaldulensis and E. verna showed higher breakdown rates than P. heptaphyllum, due to differences in leaf physical and chemical characteristics. The harder detritus (P. heptaphyllum) broke down more slowly than detritus with high concentrations of labile compounds (E. camaldulensis). The density of the invertebrates associated with detritus increased with time. There were no differences in density, taxonomic richness or biomass of invertebrates among the leaf types, which indicated that the invertebrates did not distinguish between exotic and native detritus. Fungal colonization varied among samples; E. camaldulensis showed the lowest ergosterol concentrations, mainly due to a high concentration of total phenolics. The detritus with the highest hardness value was colonized most slowly by fungi. These results showed that leaf breakdown in Atlantic Rain Forest streams could be affected either by changes in riparian vegetation, or by becoming more savanna‐like process due to climate change. 相似文献
16.
Yoshino Ando Shunsuke Utsumi Takayuki Ohgushi 《Entomologia Experimentalis et Applicata》2010,136(2):174-183
We compared community composition, density, and species richness of herbivorous insects on the introduced plant Solidago altissima L. (Asteraceae) and the related native species Solidago virgaurea L. in Japan. We found large differences in community composition on the two Solidago species. Five hemipteran sap feeders were found only on S. altissima. Two of them, the aphid Uroleucon nigrotuberculatum Olive (Hemiptera: Aphididae) and the scale insect Parasaissetia nigra Nietner (Hemiptera: Coccidae), were exotic species, accounting for 62% of the total individuals on S. altissima. These exotic sap feeders mostly determined the difference of community composition on the two plant species. In contrast, the herbivore community on S. virgaurea consisted predominately of five native insects: two lepidopteran leaf chewers and three dipteran leaf miners. Overall species richness did not differ between the plants because the increased species richness of sap feeders was offset by the decreased richness of leaf chewers and leaf miners on S. altissima. The overall density of herbivorous insects was higher on S. altissima than on S. virgaurea, because of the high density of the two exotic sap feeding species on S. altissima. We discuss the importance of analyzing community composition in terms of feeding guilds of insect herbivores for understanding how communities of insect herbivores are organized on introduced plants in novel habitats. 相似文献
17.
We investigated the influence of the exotic nitrogen-fixing black locust (Robinia pseudoacacia) on nitrogen cycling in a pitch pine (Pinus rigida) −scrub oak (Quercus ilicifolia, Q. prinoides) ecosystem. Within paired pine-oak and adjacent black locust stands that were the result of a 20-35 year-old invasion, we
evaluated soil nutrient contents, soil nitrogen transformation rates, and annual litterfall biomass and nitrogen concentrations.
In the A horizon, black locust soils had 1.3-3.2 times greater nitrogen concentration relative to soils within pine-oak stands.
Black locust soils also had elevated levels of P and Ca, net nitrification rates and total net N-mineralization rates. Net
nitrification rates were 25-120 times greater in black locust than in pine-oak stands. Elevated net N-mineralization rates
in black locust stands were associated with an abundance of high nitrogen, low lignin leaf litter, with 86 kg N ha–1 yr–1 in leaf litter returned compared with 19 kg N ha–1 yr–1 in pine-oak stands. This difference resulted from a two-fold greater litterfall mass combined with increased litter nitrogen
concentration in black locust stands (1.1% and 2.6% N for scrub oak and black locust litter, respectively). Thus, black locust
supplements soil nitrogen pools, increases nitrogen return in litterfall, and enhances soil nitrogen mineralization rates
when it invades nutrient poor, pine-oak ecosystems.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
18.
Gregory M. Crutsinger Melissa N. Habenicht Aimée T. Classen Jennifer A. Schweitzer Nathan J. Sanders 《Plant and Soil》2008,303(1-2):95-103
Plant–insect interactions can alter ecosystem processes, especially if the insects modify plant architecture, quality, or
the quantity of leaf litter inputs. In this study, we investigated the interactions between the rosette gall midge Rhopalomyia solidaginis and tall goldenrod, Solidago altissima, to quantify the degree to which the midge alters plant architecture and how the galls affect rates of litter decomposition
and nutrient release in an old-field ecosystem. R. solidaginis commonly leads to the formation of a distinct apical rosette gall on S. altissima and approximately 15% of the ramets in a S. altissima patch were galled (range: 3–34%). Aboveground biomass of galled ramets was 60% higher and the leaf area density was four
times greater on galled leaf tissue relative to the portions of the plant that were not affected by the gall. Overall decomposition
rate constants did not differ between galled and ungalled leaf litter. However, leaf-litter mass loss was lower in galled
litter relative to ungalled litter, which was likely driven by modest differences in initial litter chemistry; this effect
diminished after 12 weeks of decomposition in the field. The proportion of N remaining was always higher in galled litter
than in ungalled litter at each collection date indicating differential release of nitrogen in galled leaf litter. Several
studies have shown that plant–insect interactions on woody species can alter ecosystem processes by affecting the quality
or quantity of litter inputs. Our results illustrate how plant–insect interactions in an herbaceous species can affect ecosystem
processes by altering the quality and quantity of litter inputs. Given that S. altissima dominates fields and that R. solidaginis galls are highly abundant throughout eastern North America, these interactions are likely to be important for both the structure
and function of old-field ecosystems. 相似文献
19.
Leaf litter processing and energy flow through macroinvertebrates in a woodland pond (Switzerland) 总被引:9,自引:0,他引:9
B. Oertli 《Oecologia》1993,96(4):466-477
Energy generated by leaf litter processing and its flow through the associated macroinvertebrate community was quantified in a pond near Geneva (Switzerland). Annual density, biomass, and production on oak (Quercus robur) leaf litter were assessed for all macroinvertebrate taxa with emphasis on predators. Empirical energetic relations provided an energy budget for the macroinvertebrate community. On 1 m2 of pond bottom, the processing of 5641 kJ of oak leaf litter resulted in 8.5% of leachate (6 days), and after 1 year 32% of material remained; the other 59.5% was biologically (animal or microbial) converted, including 11.2% processed by shredders. The mean annual density of associated macroinvertebrates was 51374 individuals, mean biomass was 3.53 g (dry mass) and production was about 1451 kJ (or 65 g). Predator production was 170 kJ/m2, non-chironomid primary consumer production was 101 kJ/m2 (including 57 kJ from shredders) and chironomid primary consumer production was estimated at 1180 kJ/m2. Predators contributed to a high proportion of total biomass (39%) but to a smaller amount of production (12%) or density (6%). In this two-stepped food-chain mainly based on detritus, the transfer coefficient between first level (detritus + primary producers) and third level (secondary consumers) was high (2–2.5%) and indicated efficient conversion of energy. This high efficiency was partly related to the reutilization of fine particulate organic matter by the collectors. The production estimate measured on leaf litter was compared with two other predominant substrates (Typha latifolia stems and Chara sp.), and exhibited the highest value. This study shows how leaf litter can constitute a direct source for high secondary production and be an efficient energy source in freshwater ecosystems. It is also demonstrated that a woodland pond can support a high macroinvertebrate production as compared with other freshwater ecosystems. 相似文献
20.
SALLY HLADYZ MARK O. GESSNER PAUL S. GILLER JEUS POZO GUY WOODWARD 《Freshwater Biology》2009,54(5):957-970
1. Resource quality and stoichiometric imbalances in carbon : nutrient ratios between consumers and resources can influence key ecosystem processes. In many streams, this has important implications for food webs that are based largely upon the utilization of terrestrial leaf‐litter, which varies widely among litter types in its value as a food source for detritivores and as a substrate for microbial decomposers. 2. We measured breakdown rates and macroinvertebrate colonization of leaf‐litter from a range of native and exotic plants of differing resource quality and palatability to consumers [e.g. carbon : nitrogen : phosphorus (C : N : P) ratios, lignin and cellulose content], in a field experiment. We also measured C : N : P ratios of the principal leaf‐shredding invertebrates, which revealed strong stoichiometric imbalances across trophic levels: C : N and C : P ratios typically differed by at least one order of magnitude between consumers and resources, whereas N : P imbalances were less marked. Application of the threshold elemental ratio approach, which integrates animal bioenergetics and body elemental composition in examining nutrient deficiency between consumers and resources, revealed less marked C : P imbalances than those based on the simpler arithmetic differences described above. 3. Litter breakdown rates declined as nutrient imbalances widened and resource quality fell, but they were independent of whether resources were exotic or native. The principal drivers of total, microbial and invertebrate‐mediated breakdown rates were lignin : N, lignin : P and fungal biomass, respectively. However, multiple regression using orthogonal predictors yielded even more efficient models of litter breakdown, as consumers responded to more than one aspect of resource quality. For example, fungal biomass and litter C : N both influenced invertebrate‐mediated breakdown. 4. Large stoichiometric imbalances and changes in resource quality are likely to have serious consequences for stream ecosystem functioning, especially when riparian zones have been invaded by exotic plant species whose chemical composition differs markedly from that of the native flora. Consequently, the magnitude and direction of change in breakdown rates and, thus, resource depletion, will be driven to a large extent by the biochemical traits (rather than taxonomic identity per se) of the resident and invading flora. 相似文献