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1.
Benthic invertebrates, litter decomposition, andlitterbag invertebrates were examined in streamsdraining pine monoculture and undisturbed hardwoodcatchments at the Coweeta Hydrologic Laboratory in thesouthern Appalachian Mountains, USA. Bimonthlybenthic samples were collected from a stream draininga pine catchment at Coweeta during 1992, and comparedto previously collected (1989–1990) benthic data froma stream draining an adjacent hardwood catchment. Litter decomposition and litterbag invertebrates wereexamined by placing litterbags filled with pine ormaple litter in streams draining pine catchments andhardwood catchments during 1992–1993 and 1993–1994. Total benthic invertebrate abundance and biomass inthe pine stream was ca. 57% and 74% that of thehardwood stream, respectively. Shredder biomass wasalso lower in the pine stream but, as a result ofhigher Leuctra spp. abundance, shredderabundance was higher in the pine stream than thehardwood stream. Decomposition rates of both pine andred maple litter were significantly faster in pinestreams than adjacent hardwood streams (p<0.05). Total shredder abundance, biomass, and production weresimilar in maple bags from pine and hardwood streams. However, trichopteran shredder abundance and biomass,and production of some trichopteran taxa such asLepidostoma spp., were significantly higher in maplelitterbags from pine streams than hardwood streams(p<0.05). In contrast, plecopteran shredders(mainly Tallaperla sp.) were more important inmaple litterbags from hardwood streams. Shredderswere well represented in pine litterbags from pinestreams, but low shredder values were obtained frompine litterbags in hardwood streams. Resultssuggest conversion of hardwood forest to pinemonoculture influences taxonomic composition of streaminvertebrates and litter decomposition dynamics. Although the impact of this landscape-leveldisturbance on invertebrate shredder communitiesappeared somewhat subtle, significant differences indecomposition dynamics indicate vital ecosystem-levelprocesses are altered in streams draining pinecatchments. 相似文献
2.
Respiration and annual fungal production associated with decomposing leaf litter in two streams 总被引:5,自引:0,他引:5
1. We compared fungal biomass, production and microbial respiration associated with decomposing leaves in one softwater stream (Payne Creek) and one hardwater stream (Lindsey Spring Branch). 2. Both streams received similar annual leaf litter fall (478–492 g m?2), but Lindsey Spring Branch had higher average monthly standing crop of leaf litter (69 ± 24 g m?2; mean ± SE) than Payne Creek (39 ± 9 g m?2). 3. Leaves sampled from Lindsey Spring Branch contained a higher mean concentration of fungal biomass (71 ± 11 mg g?1) than those from Payne Creek (54 ± 8 mg g?1). Maximum spore concentrations in the water of Lindsay Spring Branch were also higher than those in Payne Creek. These results agreed with litterbag studies of red maple (Acer rubrum) leaves, which decomposed faster (decay rate of 0.014 versus 0.004 day?1), exhibited higher maximum fungal biomass and had higher rates of fungal sporulation in Lindsey Spring Branch than in Payne Creek. 4. Rates of fungal production and respiration per g leaf were similar in the two streams, although rates of fungal production and respiration per square metre were higher in Lindsey Spring Branch than in Payne Creek because of the differences in leaf litter standing crop. 5. Annual fungal production was 16 ± 6 g m?2 (mean ± 95% CI) in Payne Creek and 46 ± 25 g m?2 in Lindsey Spring Branch. Measurements were taken through the autumn of 2 years to obtain an indication of inter‐year variability. Fungal production during October to January of the 2 years varied between 3 and 6 g m?2 in Payne Creek and 7–27 g m?2 in Lindsey Spring Branch. 6. Partial organic matter budgets constructed for both streams indicated that 3 ± 1% of leaf litter fall went into fungal production and 7 ± 2% was lost as respiration in Payne Creek. In Lindsey Spring Branch, fungal production accounted for 10 ± 5% of leaf litter fall and microbial respiration for 13 ± 9%. 相似文献
3.
Leaf litter breakdown in a Mediterranean stream characterised by travertine precipitation 总被引:4,自引:0,他引:4
1. Breakdown of four leaf species ( Platanus orientalis , Populus nigra , Salix atrocinerea , Rubus ulmifolius ) was studied in a Mediterranean second-order stream characterised by abundant travertine precipitation, a history of fire in its catchment, and a recently revegetated alluvial corridor.
2. Compared to breakdown rates reported in the literature for congeneric species, breakdown of the four species was slow (k = 0.0024–0.0069 day−1 for the tree species, and 0.0103 and 0.0111 day−1 for Rubus ), in spite of high water temperatures, indicating that the travertine layer that quickly covered submerged leaves impeded decomposer activity and physical fragmentation losses.
3. Breakdown rates nevertheless differed between leaf species in a predictable manner, suggesting that the observed mass loss was largely due to biological processes.
4. The observed tendency towards increasing leaf nitrogen and phosphorus concentrations during breakdown suggests that microorganisms were actively involved in leaf breakdown; however, this interpretation must be viewed with caution because of potentially confounding effects by nutrients contained in the travertine layer.
5. Leaf breakdown of the three indigenous species was faster than that of the exotic species P. orientalis . Due to the recalcitrance of its leaves, the frequent use of Platanus in revegetation schemes following the destruction of indigenous vegetation by fire, exacerbates the negative effect of travertine precipitation on leaf breakdown and, by extension, energy flow in Mediterranean karst streams. 相似文献
2. Compared to breakdown rates reported in the literature for congeneric species, breakdown of the four species was slow (k = 0.0024–0.0069 day
3. Breakdown rates nevertheless differed between leaf species in a predictable manner, suggesting that the observed mass loss was largely due to biological processes.
4. The observed tendency towards increasing leaf nitrogen and phosphorus concentrations during breakdown suggests that microorganisms were actively involved in leaf breakdown; however, this interpretation must be viewed with caution because of potentially confounding effects by nutrients contained in the travertine layer.
5. Leaf breakdown of the three indigenous species was faster than that of the exotic species P. orientalis . Due to the recalcitrance of its leaves, the frequent use of Platanus in revegetation schemes following the destruction of indigenous vegetation by fire, exacerbates the negative effect of travertine precipitation on leaf breakdown and, by extension, energy flow in Mediterranean karst streams. 相似文献
4.
Summary 1. Heterotrophic microorganisms are crucial for mineralising leaf litter and rendering it more palatable to leaf‐shredding invertebrates. A substantial part of leaf litter entering running waters may be buried in the streambed and thus be exposed to the constraining conditions prevailing in the hyporheic zone. The fate of this buried organic matter and particularly the role of microbial conditioning in this habitat remain largely unexplored. 2. The aim of this study was to determine how the location of leaf litter within the streambed (i.e. at the surface or buried), as well as the leaf litter burial history, may affect the leaf‐associated aquatic hyphomycete communities and therefore leaf consumption by invertebrate detritivores. We tested the hypotheses that (i) burial of leaf litter would result in lower decomposition rates associated with changes in microbial assemblages compared with leaf litter at the surface and (ii) altered microbial conditioning of buried leaf litter would lead to decreased quality and palatability to their consumers, translating into lower growth rates of detritivores. 3. These hypotheses were tested experimentally in a second‐order stream where leaf‐associated microbial communities, as well as leaf litter decomposition rates, elemental composition and toughness, were compared across controlled treatments differing by their location within the streambed. We examined the effects of the diverse conditioning treatments on decaying leaf palatability to consumers through feeding trials on three shredder taxa including a freshwater amphipod, of which we also determined the growth rate. 4. Microbial leaf litter decomposition, fungal biomass and sporulation rates were reduced when leaf litter was buried in the hyporheic zone. While the total species richness of fungal assemblages was similar among treatments, the composition of fungal assemblages was affected by leaf litter burial in sediment. 5. Leaf litter burial markedly affected the food quality (especially P content) of leaf material, probably due to the changes in microbial conditioning. Leaf litter palatability to shredders was highest for leaves exposed at the sediment surface and tended to be negatively related to leaf litter toughness and C/P ratio. In addition, burial of leaf litter led to lower amphipod growth rates, which were positively correlated with leaf litter P content. 6. These results emphasise the importance of leaf colonisation by aquatic fungi in the hyporheic zone of headwater streams, where fungal conditioning of leaf litter appears particularly critical for nutrient and energy transfer to higher trophic levels. 相似文献
5.
Copper and zinc mixtures induce shifts in microbial communities and reduce leaf litter decomposition in streams 总被引:1,自引:0,他引:1
SOFIA DUARTE CLÁUDIA PASCOAL ARTUR ALVES ANTÓNIO CORREIA FERNANDA CÁSSIO 《Freshwater Biology》2008,53(1):91-101
1. To assess the impact of metal mixtures on microbial decomposition of leaf litter, we exposed leaves previously immersed in a stream to environmentally realistic concentrations of copper (Cu) and zinc (Zn) (three levels), alone and in all possible combinations. The response of the microbial community was monitored after 10, 25 and 40 days of metal exposure by examining leaf mass loss, fungal and bacterial biomass, fungal reproduction and fungal and bacterial diversity.
2. Analysis of microbial diversity, assessed by denaturing gradient gel electrophoresis and identification of fungal spores, indicated that metal exposure altered the structure of fungal and bacterial communities on decomposing leaves.
3. Exposure to metal mixtures or to the highest Cu concentration significantly reduced leaf decomposition rates and fungal reproduction, but not fungal biomass. Bacterial biomass was strongly inhibited by all metal treatments.
4. The effects of Cu and Zn mixtures on microbial decomposition of leaf litter were mostly additive, because observed effects did not differ from those expected as the sum of single metal effects. However, antagonistic effects on bacterial biomass were found in all metal combinations and on fungal reproduction in metal combinations with the highest Cu concentrations, particularly at longer exposure times. 相似文献
2. Analysis of microbial diversity, assessed by denaturing gradient gel electrophoresis and identification of fungal spores, indicated that metal exposure altered the structure of fungal and bacterial communities on decomposing leaves.
3. Exposure to metal mixtures or to the highest Cu concentration significantly reduced leaf decomposition rates and fungal reproduction, but not fungal biomass. Bacterial biomass was strongly inhibited by all metal treatments.
4. The effects of Cu and Zn mixtures on microbial decomposition of leaf litter were mostly additive, because observed effects did not differ from those expected as the sum of single metal effects. However, antagonistic effects on bacterial biomass were found in all metal combinations and on fungal reproduction in metal combinations with the highest Cu concentrations, particularly at longer exposure times. 相似文献
6.
1. Faecal pellets of Gammarus (shredders) and Simulium larvae (suspension feeders) are bound by exopolymers. Immediately after egestion, Gammarus pellets are covered by a peritrophic membrane that breaks up within hours, although pellets remain intact because of internal binding materials. 2. Although they expand soon after egestion, the faecal pellets of Gammarus and Simulium remain intact for more than 30 days. Their internal structure is altered and the main agents of this change are bacteria that have survived passage through the gut (and become bound within pellets). 3. When disrupted physically, freshly egested (1‐ to 2‐day old) Simulium faecal pellets break up into relatively large pieces whereas freshly egested Gammarus faecal pellets break apart into much smaller pieces. Disruption of 30‐day old Simulium faecal pellets results in similar sized pieces to those from freshly egested pellets, but disruption of 30‐day old Gammarus pellets produces pieces that are two orders of magnitude larger than those resulting from disruption of freshly egested pellets. 4. Faecal pellets of Gammarus and Simulium are eaten by stream invertebrates and are sites of microbial breakdown. Faecal pellets are a source of organic matter for benthic invertebrates, bacteria and, indirectly, for plants. 相似文献
7.
Leaf litter breakdown rates in boreal streams: does shredder species richness matter? 总被引:5,自引:0,他引:5
1. Leaf litter breakdown rates were assessed in 23 boreal streams of varying size (first–seventh order) in central and northern Sweden. 2. Shredders were most abundant in small streams, while shredder species richness showed a hump-shaped relationship with stream order, with most species in fourth order streams. 3. In a partial least-squares regression analysis, year, water temperature, shredder species richness and shredder abundance were those factors correlating most strongly with leaf breakdown rates. Shredder species richness was more strongly correlated with leaf litter breakdown rates than shredder abundance, and shredder biomass showed no such correlation. 4. These data suggest that shredder species richness is an important variable in terms of leaf litter dynamics in streams. 相似文献
8.
- 1 The rate of microbial respiration on fine‐grained stream sediments was measured at 371 first to fourth‐order streams in the Central Appalachian region (Maryland, Pennsylvania, Virginia, and West Virginia), Southern Rocky Mountains (Colorado), and California's Central Valley in 1994 and 1995.
- 2 Study streams were randomly selected from the United States Environmental Protection Agency's (USEPA) River Reach File (RF3) using the sample design developed by USEPA's Environmental Monitoring and Assessment Program (EMAP).
- 3 Respiration rate ranged from 0 to 0.621 g O2 g‐1 AFDM h‐1 in Central Appalachian streams, 0‐0.254 g O2 g‐1 AFDM h‐1 in Rocky Mountain streams, and 0‐0.436 g O2 g‐1 AFDM h‐1 in Central Valley streams.
- 4 Respiration was significantly lower in Southern Rocky Mountain streams and in cold water streams (< 15 °C) of the Central Appalachians.
- 5 Within a defined index period, respiration was not significantly different between years, and was significantly correlated with stream temperature and chemistry (DOC, total N, total P, K, Cl, and alkalinity).
- 6 The uniformity of respiration estimates among the three study regions suggests that sediment microbial respiration may be collected at any number of scales above the site‐level for reliable prediction of respiration patterns at larger spatial scales.
9.
10.
SALLY A. ENTREKIN JENNIFER L. TANK EMMA J. ROSI-MARSHALL TIMOTHY J. HOELLEIN GARY A. LAMBERTI 《Freshwater Biology》2009,54(8):1741-1758
1. We measured responses in macroinvertebrate secondary production after large wood additions to three forested headwater streams in the Upper Peninsula of Michigan. These streams had fine‐grained sediments and low retention capacity due to low amounts of in‐channel wood from a legacy of past logging. We predicted that wood addition would increase macroinvertebrate secondary production by increasing exposed coarse substrate and retention of organic matter. 2. Large wood (25 logs) was added haphazardly to a 100‐m reach in each stream, and a 100‐m upstream reach served as control; each reach was sampled monthly, 1 year before and 2 years after wood addition (i.e. BACI design). Macroinvertebrate secondary production was measured 1 year after wood addition in two habitat types: inorganic sediments of the main channel and debris accumulations of leaf litter and small wood. 3. Overall macroinvertebrate production did not change significantly because each stream responded differently to wood addition. Production increased by 22% in the main‐channel of one stream, and showed insignificant changes in the other two streams compared to values before wood addition. Changes in main‐channel macroinvertebrate production were related to small changes in substrate composition, which probably affected habitat and periphyton abundance. Macroinvertebrate production was much greater in debris accumulations than in the main‐channel, indicating the potential for increased retention of leaf litter to increase overall macroinvertebrate production, especially in autumn. 4. Surrounding land use, substrate composition, temperature and method of log placement are variables that interact to influence the response of stream biota to wood additions. In most studies, wood additions occur in altered catchments, are rarely monitored, and secondary production is not a common metric. Our results suggest that the time required for measurable changes in geomorphology, organic matter retention, or invertebrate production is likely to take years to achieve, so monitoring should span more than 5 years, and ecosystem metrics, such as macroinvertebrate secondary production, should be incorporated into restoration monitoring programs. 相似文献
11.
Wayne Linklater 《Hydrobiologia》1995,306(3):241-250
Breakdown of leaves from three native riparian tree species, and their colonisation by shredding and collecting insect larvae, were investigated in three streams on Banks Peninsula, New Zealand. Leaves were introduced in baskets at the time of leaf fall. Breakdown rates of leaves were faster than previously recorded in New Zealand streams and were comparable to those of many northern hemisphere deciduous species. Shredder and total detritivore densities and biomass in leaf baskets were also greater than previously found in New Zealand streams. Peaks of shredder biomass on red beech and mahoe leaves were found when only about 20% of leaf biomass remained. No shredder peak was recorded on fuchsia leaves, and no collector peaks occurred in any of the streams. Relative shredder and collector biomass (per g DW leaf) in leaf baskets did not exceed or was smaller than in leaf litter accumulations of mixed origin and conditioning throughout the streams during leaf breakdown although absolute shredder and collector biomass (per m2 stream bottom) was occasionally larger in baskets than in the rest of the stream. These findings support contentions that spatial and temporal relationships between detrital inputs and detritivore biomass and life histories are weak in New Zealand streams. 相似文献
12.
Life histories, production dynamics and resource utilisation of mayflies (Ephemeroptera) in two tropical Asian forest streams 总被引:7,自引:0,他引:7
SUMMARY 1. A 2‐year study of the life histories, production dynamics and resource utilisation of five mayfly species was undertaken in two forest streams in Hong Kong [Tai Po Kau Forest Stream (TPKFS) and Shing Mun River (SMR)]. Afronurus sp. and Cinygmina sp. (Heptageniidae), Procloeon sp. and Baetiella pseudofrequenta (Baetidae), and Choroterpes sp. (Leptophlebiidae) were abundant in both streams and contributed more than 50% of the total mayfly populations. 2. All species had asynchronous larval development with recruitment occurring throughout the year. Mean annual production (all mayflies combined) was 3.1 and 2.0 g dry weight m?2 year?1 in SMR and TPKFS, respectively – the higher value at SMR reflecting greater mayfly densities – with more than 70% of production occurring during the wet season. Mayfly production varied between years, decreasing by 5% in TPKFS and 43% in SMR during 1996–97, reflecting lower densities of heptageniids relative to 1995–96. Annual biomass turnover rates (P/B) were high in both sites ranging from 27.2 to 94.6 in TPKFS (Cinygmina sp. and Procloeon sp.) and from 31.8 to 109.8 in SMR (Cinygmina sp. and B. pseudofrequenta). 3. Patterns of daily production in both streams showed that Afronurus sp., Cinygmina sp. and Choroterpes sp. were most productive during the wet season, while Procloeon sp. maintained high production levels throughout the year. The highest daily production of B. pseudofrequenta occurred during the wet season in TPKFS, but in the dry season at SMR. Temporal overlap in production and hence resource utilisation in both streams, calculated using the proportional similarity index (PS), ranged from 0.39 to 0.81. It was highest (0.63–0.81) between pairs of species of Heptageniidae and Baetidae, and lowest between Choroterpes sp. and other mayflies (0.39–0.61). No clear temporal segregation was observed among any species. However, when using the fraction of production attributable to each food, lower PS values were obtained for all species in both sites. In SMR, trophic segregation may have occurred between the two species pairs Procloeon sp.–Cinygmina sp. and Procloeon sp.–Choroterpes sp. (PS=0.17 and 0.03, respectively). 4. A combination of production data and information on the stable isotope signature of mayflies revealed that, during both the wet and dry seasons, more than 50% of total mayfly production in TPKFS was derived from autochthonous foods. In SMR, 68% of production was supported by allochthonous foods during the wet season, and 72% by autochthonous sources in the dry season. Considering that more than 70% of the total production occurred in the wet season, the trophic basis of mayfly production in SMR is mostly allochthonous (58%) while in TPKFS it is mainly of autochthonous origin (66%). The year‐round importance of autochthonous foods in shaded streams such as TPKFS is surprising, but the wet season contribution of allochthonous foods (especially in SMR) may have resulted from depletion of algal biomass during spates. 相似文献
13.
Sara G. Baer Edward R. Siler Susan L. Eggert J. Bruce Wallace 《Freshwater Biology》2001,46(3):347-365
1. Macroinvertebrate colonization dynamics were examined on artificial substrata in a stream with terrestrial litter inputs excluded, downstream of the litter-exclusion treatment, and in a reference stream. 2. Short-term examination of the rates of organic matter accrual and invertebrate colonization demonstrated significantly lower accumulation of leaf detritus and invertebrates in the litter-excluded reach and a short distance downstream of that reach. 3. All major fractions of organic matter and invertebrates declined on artificial substrata during the 3-year litter exclusion. Further, secondary production on artificial substrata in the litter-excluded reach decreased from 6.2 to 1.5 g AFDM m−2 year−1 from pretreatment to the third year of litter exclusion, respectively. 4. Downstream, fine particulate organic matter on artificial substrata decreased during litter exclusion, and there was a significant reduction in colonization of collector-filterers. Total secondary production downstream of the litter exclusion declined >70%, demonstrating that downstream colonization dynamics are linked to upstream detritus inputs and processing by stream invertebrates. 相似文献
14.
1. Large-scale invasions of riparian trees can alter the quantity and quality of allochthonous inputs of leaf litter to streams and thus have the potential to alter stream organic matter dynamics. Non-native saltcedar ( Tamarix sp.) and Russian olive ( Elaeagnus angustifolia ) are now among the most common trees in riparian zones in western North America, yet their impacts on energy flow in streams are virtually unknown.
2. We conducted a laboratory feeding experiment to compare the growth of the aquatic crane fly Tipula (Diptera: Tipulidae) on leaf litter from native cottonwood ( Populus ) and non-native Tamarix and Elaeagnus . Tipula showed positive growth on leaf litter of all three species; however, after 7 weeks, larvae fed Tamarix leaves averaged 1.7 and 2.5 times the mass of those fed Elaeagnus and Populus , respectively. Tipula survival was highest on Populus , intermediate on Tamarix and lowest on Elaeagnus .
3. High Tipula growth on Tamarix probably reflects a combination of leaf chemistry and morphology. Conditioned Tamarix leaf litter had intermediate carbon : nitrogen values (33 : 1) compared to Populus (40 : 1) and Elaeagnus (26 : 1), and it had intermediate proportions of structural carbon (42%) compared to Elaeagnus (57%) and Populus (35%). Tamarix leaves are also relatively small and possibly more easily ingested by Tipula than either Elaeagnus or Populus .
4. Field surveys of streams in the western U.S.A. revealed that Tamarix and Elaeagnus leaf packs were rare compared to native Populus , probably due to the elongate shape and small size of the non-native leaves. Thus we conclude that, in general, the impact of non-native riparian invasion on aquatic shredders will depend not only on leaf decomposition rate and palatability but also on rates of leaf litter input to the stream coupled with streambed retention and subsequent availability to consumers. 相似文献
2. We conducted a laboratory feeding experiment to compare the growth of the aquatic crane fly Tipula (Diptera: Tipulidae) on leaf litter from native cottonwood ( Populus ) and non-native Tamarix and Elaeagnus . Tipula showed positive growth on leaf litter of all three species; however, after 7 weeks, larvae fed Tamarix leaves averaged 1.7 and 2.5 times the mass of those fed Elaeagnus and Populus , respectively. Tipula survival was highest on Populus , intermediate on Tamarix and lowest on Elaeagnus .
3. High Tipula growth on Tamarix probably reflects a combination of leaf chemistry and morphology. Conditioned Tamarix leaf litter had intermediate carbon : nitrogen values (33 : 1) compared to Populus (40 : 1) and Elaeagnus (26 : 1), and it had intermediate proportions of structural carbon (42%) compared to Elaeagnus (57%) and Populus (35%). Tamarix leaves are also relatively small and possibly more easily ingested by Tipula than either Elaeagnus or Populus .
4. Field surveys of streams in the western U.S.A. revealed that Tamarix and Elaeagnus leaf packs were rare compared to native Populus , probably due to the elongate shape and small size of the non-native leaves. Thus we conclude that, in general, the impact of non-native riparian invasion on aquatic shredders will depend not only on leaf decomposition rate and palatability but also on rates of leaf litter input to the stream coupled with streambed retention and subsequent availability to consumers. 相似文献
15.
This paper describes a portable chamber that measures net primary production of stream periphyton using a 14C uptake method. The unique feature is that substrates are moved through water at a velocity of 20 cm s −1 rather than moving water over substrates. The chamber consists of a plexiglass cylinder that is 9 cm in height and 15 cm in diameter. On the top of the cylinder is a DC gearmotor powered by a 12 volt, deep cycle, marine battery. The motor turns a shaft that rotates a 13.3 cm plexiglass plate at a velocity of 20 cm s −1 . Small tiles (3.2 cm × 3.2 cm × 0.5 cm) that have natural algal assemblages are mounted on the rotating plate. After adding 500 ml of filtered stream water and 185 kBq (5 μCi) NaH14CO3 to the chamber, the chambers are placed along a stream margin for 5 h. Measurements of 14C uptake by algae on the tiles provide estimates of net primary production (NPP). To assess the sensitivity and practicality of the chamber, algal primary production was measured in open and closed canopy sections of Kingsley Creek, Randallsville, New York. In autumn, primary production was higher in the open than closed canopy section and NPP was lower in spring in both sections probably because of scouring of algae due to snowmelt. 相似文献
16.
Composition of speciose leaf litter alters stream detritivore growth, feeding activity and leaf breakdown 总被引:3,自引:0,他引:3
Leaf litter derived from riparian trees can control secondary production of detritivores in forested streams. Species-rich assemblages of leaf litter reflect riparian plant species richness and represent a heterogeneous resource for stream consumers. Such variation in resource quality may alter consumer growth and thus the feedback on leaf breakdown rate via changes in feeding activity. To assess the consequences of this type of resource heterogeneity on both consumer growth and subsequent litter breakdown, we performed a laboratory experiment where we offered a leaf-shredding stream detritivore (the stonefly Tallaperla maria, Peltoperlidae) ten treatments of either single- or mixed-species leaf litter. We measured consumer growth rate, breakdown rate and feeding activity both with and without consumers for each treatment and showed that all three variables responded to speciose leaf litter. However, the number of leaf species was not responsible for these results, but leaf species composition explained the apparent non-additive effects. T. maria growth responded both positively and negatively to litter composition, and growth on mixed-litter could not always be predicted by averaging estimates of growth in single-species treatments. Furthermore, breakdown and feeding rates in mixed litter treatments could not always be predicted from estimates of single-species rates. Given that species richness and composition of senesced leaves in streams reflects riparian plant species richness, in-stream secondary production of detritivores and organic matter dynamics may be related to species loss of trees in the riparian zone. Loss of key species may be more critical to maintaining such processes than species richness per se. 相似文献
17.
1. Agriculture causes high sediment, nutrient and light input to streams, which may affect rates of ecosystem processes, such as organic matter decay. In the southern Appalachians, socioeconomic trends over the past 50 years have caused widespread abandonment of farmland with subsequent reforestation. Physical and chemical properties of streams in these reforested areas may be returning to pre‐agriculture levels thereby creating the potential for recovery of ecosystem processes. 2. We examined wood breakdown and microbial activity on wood substrata in streams with different historical and current agricultural activity in their catchments. We analysed historical (1950) and recent (1998) forested land cover from large areas of the southern Appalachians and categorized streams based on percent forested land cover in these two time periods. Categories included a gradient of current agriculture from forested to heavily agricultural and reforestation from agriculture due to land abandonment. We compared microbial respiration on wood veneer substrata and breakdown of wood veneers among these land‐use categories. We also compared temperature, sediment accumulation and nitrogen and phosphorus concentrations. 3. Streams with current agriculture had higher concentrations of dissolved inorganic nitrogen than forested streams. Despite reforestation from agriculture, nitrogen concentrations were also elevated in streams with agricultural histories relative to forested streams. Temperature was also higher in agricultural streams but appeared to recover from historical agriculture through reforestation and stream shading. 4. Wood breakdown rates ranged from 0.0015 to 0.0076 day?1 and were similar to other studies using wood veneers to determine breakdown rate. Microbial respiration increased with incubation time in streams up to approximately 150 days, after which it remained constant. Neither wood breakdown nor microbial respiration was significantly different among land‐use categories, despite the observed physical and chemical differences in streams based on land‐use. Wood breakdown rates could be predicted by microbial respiration indicating microbial control of wood breakdown in these streams. Both breakdown and microbial respiration were negatively correlated with the amount of inorganic sediment accumulated on wood veneers. 5. Higher nutrients and temperature led us to expect faster breakdown and higher microbial respiration in agricultural streams, but sediment in these streams may be limiting microbial activity and breakdown of organic material resulting in little net effect of agriculture on wood breakdown. Wood may not be desirable as a tool for functional assessment of stream integrity due to its unpredictable response to agriculture. 相似文献
18.
Evaluation of methods for estimating macroinvertebrate species richness using individual stones in tropical streams 总被引:2,自引:0,他引:2
1. The most straightforward way to assess diversity in a site is the species count. However, a relatively large sample is needed for a reliable result because of the presence of many rare species in rich assemblages. The use of richness estimation methods is suggested by many authors as a solution for this problem in many cases.
2. We examined the performance of 13 methods for estimating richness of stream macroinvertebrates inhabiting riffles both at local (stream) and regional (catchment) scales. The evaluation was based on (1) the smallest sub-sample size needed to estimate total richness in the sample, (2) constancy of this size, (3) lack of erratic behaviour in curve shape and (4) similarity in curve shape through different data sets. Samples were from three single stream sites (local) and three from several streams within the same catchment basin (regional). All collections were made from protected forest areas in south-east Brazil.
3. All estimation methods were dependent on sub-sample size, producing higher estimates when using larger sub-sample sizes. The Stout and Vandermeer method estimated total richness in the samples with the smallest sub-sample size, but showed some erratic behaviour at small sub-sample sizes, and the estimated curves were not similar among the six samples. The Bootstrap method was the best estimator in relation to constancy of sub-sample sizes, but needed an unacceptably large sub-sample to estimate total richness in the samples. The second order Jackknife method was the second best estimator both for minimum sub-sample size and constancy of this size and we suggest its use in future studies of diversity in tropical streams. Despite the inferior performance of several other methods, some produced acceptable results. Comments are made on the utility of using these estimators for predicting species richness in an area and for comparative purposes in diversity studies. 相似文献
2. We examined the performance of 13 methods for estimating richness of stream macroinvertebrates inhabiting riffles both at local (stream) and regional (catchment) scales. The evaluation was based on (1) the smallest sub-sample size needed to estimate total richness in the sample, (2) constancy of this size, (3) lack of erratic behaviour in curve shape and (4) similarity in curve shape through different data sets. Samples were from three single stream sites (local) and three from several streams within the same catchment basin (regional). All collections were made from protected forest areas in south-east Brazil.
3. All estimation methods were dependent on sub-sample size, producing higher estimates when using larger sub-sample sizes. The Stout and Vandermeer method estimated total richness in the samples with the smallest sub-sample size, but showed some erratic behaviour at small sub-sample sizes, and the estimated curves were not similar among the six samples. The Bootstrap method was the best estimator in relation to constancy of sub-sample sizes, but needed an unacceptably large sub-sample to estimate total richness in the samples. The second order Jackknife method was the second best estimator both for minimum sub-sample size and constancy of this size and we suggest its use in future studies of diversity in tropical streams. Despite the inferior performance of several other methods, some produced acceptable results. Comments are made on the utility of using these estimators for predicting species richness in an area and for comparative purposes in diversity studies. 相似文献
19.
Effect of pH on microbial degradation of leaf litter in seven streams of the English Lake District 总被引:6,自引:0,他引:6
A. -C. Chamier 《Oecologia》1987,71(4):491-500
Summary Rates of degradation of alder, oak and grass leaf packs with associated microbial populations were measured in seven streams pH 6.8–4.9. Streams were chosen from upland and lowland sites of the same river for contrasts in pH, water chemistry and riparian vegetation. The most important factor governing rates of degradation is the physical and chemical nature of the leaf material. At pH 6.8 rates of degradation, k, and microbial colonization were higher than at pH
5.5: k on alder x6; on oak x2; on grass x2. At lowland sites, pH 6.8, higher decay rates were associated with high levels of microbial colonization including c.14 spp of aquatic hyphomycete fungi—regardless of riparian vegetation. Decay rates were similar at upland sites, pH 6.8 and 6.6, involving high levels of colonization by fewer fungal species and fewer bacteria—regardless of riparian vegetation-though grass was barely degraded at upland sites of any pH. At pH
5.5, slow decay rates were associated with low levels of microbial colonization and few fungal species. Largest microbial populations at low pH associated with riparian trees did not lead to markedly increased decay rates. Factors of water chemistry at low pH appear to inhibit microbial metabolism. The implications of these findings for stream invertebrates active in the winter is discussed. 相似文献
20.
We examined microbial colonization, exoenzyme activity, and processing of leaves of yellow poplar (Liriodendron tulipifera), red maple (Acer rubrum), and white oak (Quercus alba) in three streams on the Allegheny Plateau of West Virginia, United States. Leaf packs were placed in streams that varied in their underlying bedrock geology, and therefore in their sensitivity to the high level of acidic precipitation that occurs in this region. The mean pH of the streams was 4.3 in the South Fork of Red Run (SFR), 6.2 in Wilson Hollow Run (WHR), and 7.7 in the North Fork of Hickman Slide Run (HSR). Through time, the patterns of microbial biomass and exoenzyme activity were generally similar among leaf species, but the magnitude of microbial biomass and exoenzyme activity differed among leaf species. Pectinase activity was greatest in HSR, the most alkaline stream, whereas the activity of exocellulase and xylanase was greatest in WHR and SFR, the intermediate and acidic streams. This variation in the activity of different exoenzymes was consistent with published pH optima for these exoenzymes. Variation in processing rates, both among leaf species and among streams, seems to be related to the level of microbial exoenzyme activity on the leaf detritus. 相似文献