Processing and macroinvertebrate colonization of detritus in an Alaskan subarctic stream

Monument Creek, a second-order Alaskan subarctic stream, experiences a severe thermal regime, with water temperatures of 0°C for six months. Leaching, long-term decomposition and macroinvertebrate colonization of 5 g leaf packs were studied using leaves of the major riparian tree species, alder Alnus tenuifolia Nutt., birch Betula papyrifera Marsh. and willow Salix alaxensis (Anderss.) Cov. subsp. alaxensis and Salix arbucolides Anders. var. glabra Anderss. The processing rates of birch (k = 0.0080) and willow (k = 0.0063) were moderate while alder was processed very rapidly (k = 0.0513). Leaching rates did not differ significantly among the three leaf species, and accounted for 10–15% of total weight loss. Densities and biovolume of colonizing insects increased from fall to winter. Shredders dominated insect biovolume by midwinter, but were a small fraction of total biovolume in leaf packs that had frozen over winter and were sampled following spring thaw. This may be a function of low food quality in spring and/or the timing of shredder life histories. Limited allochthonous input and constriction of the stream channel due to freezing, with resultant high shredder densities, may explain the relatively rapid detritus processing rates in Monument Creek, despite cold stream temperatures.     

Barley straw decomposition with varied levels of microbial grazing by Folsomia fimetaria (L.) (Collembola,Isotomidae)

Summary Folsomia fimetaria (L.) were added (0, 5, 10, 20 animals) to 0.100 g barley straw which had been inoculated 10 days (244 h) earlier with a natural soil microflora. Respiration (CO₂ evolution) was monitored continuously. Mass loss, fungal standing crop (total and FDA-active), bacterial and protozoan biomass were estimated 42 days (1,000 h) after microbial inoculation. The degree of surface cover by hyphae was surveyed at regular intervals. No significant differences (P>0.05) were found in respiration, mass loss or microbial biomass, but the density of surface hyphae were reduced by addition of Collembola. Fungal production was low, less than 5% of the estimated microbial production, and could not account for all collembolan growth during incubation. F. fimetaria appeared to consume mainly bacteria and protozoa, and had little impact on carbon mineralization.     

Symbiotic germination and development of myco-heterotrophic plants in nature: transfer of carbon from ectomycorrhizal Salix repens and Betula pendula to the orchid Corallorhiza trifida through shared hyphal connections

Seedlings of the myco-heterotrophic orchid Corallorhiza trifida which had been germinated in the field in mesh bags developed hyphal links and mycorrhizas with Betula pendula and Salix repens , but not with Pinus sylvestris , when transplanted into soil microcosms. The fungus connecting the myco-heterotroph to Betula and Salix formed endomycorrhiza in the orchid with typical pelotons, but formed ectomycorrhizas with the autotrophs. The orchid plants, when linked to Betula and Salix by fungal hyphae, gained 6–14% in weight over 25–28 wk. In microcosms supporting P. sylvestris , and in control microcosms which lacked autotrophs, the Corallorhiza plants lost 13% of their weight over the same period. In the course of the 28-wk experimental period new Corallorhiza seedlings, in addition to those added as part of the experiment, appeared in the microcosms containing Salix and Betula but not in the Pinus microcosms. Shoots of Betula and Salix plants grown in association with Corallorhiza were fed with ¹⁴CO₂, and the movement of the isotope was subsequently traced by a combination of digital autoradiography and tissue oxidation. Direct transfer of C from both autotrophs to the myco-heterotroph occurred in all cases where the associates had become connected by a shared fungal symbiont. Orchid seedlings lacking these hyphal connections, introduced to the microcosms as controls immediately before isotope feeding, failed to assimilate significant amounts of C. The results provide the first experimental confirmation that growth of Corallorhiza trifida can be sustained by supply of C received directly from an autotrophic partner through linked fungal mycelia.     

Effects of Riparian Plant Diversity Loss on Aquatic Microbial Decomposers Become More Pronounced with Increasing Time

We examined the potential long-term impacts of riparian plant diversity loss on diversity and activity of aquatic microbial decomposers. Microbial assemblages were obtained in a mixed-forest stream by immersion of mesh bags containing three leaf species (alder, oak and eucalyptus), commonly found in riparian corridors of Iberian streams. Simulation of species loss was done in microcosms by including a set of all leaf species, retrieved from the stream, and non-colonized leaves of three, two or one leaf species. Leaves were renewed every month throughout six months, and microbial inoculum was ensured by a set of colonized leaves from the previous month. Microbial diversity, leaf mass loss and fungal biomass were assessed at the second and sixth months after plant species loss. Molecular diversity of fungi and bacteria, as the total number of operational taxonomic units per leaf diversity treatment, decreased with leaf diversity loss. Fungal biomass tended to decrease linearly with leaf species loss on oak and eucalyptus, suggesting more pronounced effects of leaf diversity on lower quality leaves. Decomposition of alder and eucalyptus leaves was affected by leaf species identity, mainly after longer times following diversity loss. Leaf decomposition of alder decreased when mixed with eucalyptus, while decomposition of eucalyptus decreased in mixtures with oak. Results suggest that the effects of leaf diversity on microbial decomposers depended on leaf species number and also on which species were lost from the system, especially after longer times. This may have implications for the management of riparian forests to maintain stream ecosystem functioning.     

Higher temperature reduces the effects of litter quality on decomposition by aquatic fungi

1. We investigated the effects of riparian plant diversity (species number and identity) and temperature on microbially mediated leaf decomposition by assessing fungal biodiversity, fungal reproduction and leaf mass loss. 2. Leaves of five riparian plant species were first immersed in a stream to allow microbial colonisation and were then exposed, alone or in all possible combinations, at 16 or 24 °C in laboratory microcosms. 3. Fungal biodiversity was reduced by temperature but was not affected by litter diversity. Temperature altered fungal community composition with species of warmer climate, such as Lunulospora curvula, becoming dominant. 4. Fungal reproduction was affected by litter diversity, but not by temperature. Fungal reproduction in leaf mixtures did not differ or was lower than that expected from the weighted sum of fungal sporulation on individual leaf species. At the higher temperature, the negative effect of litter diversity on fungal reproduction decreased with the number of leaf species. 5. Leaf mass loss was affected by the identity of leaf mixtures (i.e. litter quality), but not by leaf species number. This was mainly explained by the negative correlation between leaf decomposition and initial lignin concentration of leaves. 6. At 24 °C, the negative effects of lignin on microbially mediated leaf decomposition diminished, suggesting that higher temperatures may weaken the effects of litter quality on plant litter decomposition in streams. 7. The reduction in the negative effects of lignin at the higher temperature resulted in an increased microbially mediated litter decomposition, which may favour invertebrate‐mediated litter decomposition leading to a depletion of litter stocks in streams.     

Spatial and temporal variation of microbial respiration rates in a blackwater stream

1. The extent of spatial and temporal variation of microbial respiration was determined in a first-order, sand-bottomed, blackwater stream on the coastal plain of south-eastern Virginia, U.S.A.
2. Annual mean respiration rates (as g O₂ m^–3 h^–1) differed significantly among substrata: leaf litter, 12.9; woody debris, 2.4; surface sediment, 0.8; hyporheic sediment, 0.4; water column, 0.003. Rates associated with wood were higher than those with leaves when expressed per unit surface area.
3. Highest respiration rates on leaves, wood and in the water column occurred during the summer, whereas rates in the sediments were greatest during the late autumn and winter. Water temperature, as well as particulate organic matter and nitrogen content of the substrata, was correlated positively with respiration rates.
4. A stepwise multiple regression showed that temperature and nitrogen content together explained 88% of the variation in respiration rates of leaves and wood. In contrast, particulate organic matter content and nitrogen content explained 89–90% of the variation in respiration in the sediments. Although water temperature was a significant factor in the sediment multiple regressions, its addition as an independent variable improved the regression models only slightly.
5. Annual mean respiration in the stream channel, based on the proportional amount of respiration occurring associated with each type of substratum during each month, was 1.1 kg O₂ m^–2 yr^–1. Seventy per cent of respiration in the stream occurred in the hyporheic zone, 8–13% occurred in the surface sediment, leaf litter or woody debris, and < 1% occurred in the water column. Approximately 16% of total detritus, or 40% of non-woody detritus, stored in the stream during the year was lost to microbial respiration.     

Does mixing litter of different qualities alter stream microbial diversity and functioning on individual litter species?

We examined effects of leaf litter quality and species mixing on microbial community diversity and litter processing in a forested headwater stream. Single- and mixed-species litter from dominant tree species ( Liriodendron tulipifera , Acer rubrum , Quercus prinus , Rhododendron maximum ) were incubated in a southern Appalachian headwater stream. Litter carbon-to-nitrogen ratios (C:N), mass loss, microbial respiration, and microbial community diversity were analyzed on individual litter species after incubation. Initial C:N varied widely among individual litter species, and these differences persisted throughout the 50-day incubation period. Litter C:N of the recalcitrant species R. maximum remained higher than that of all other litter species, and C:N of R. maximum and L. tulipifera increased when both species were present together in a mixture. Although mass loss of individual species was generally unaffected by mixing, microbial respiration was greater on A. rubrum and Q. prinus litter incubated with R. maximum compared to either species alone. Enhanced resource heterogeneity, which was experimentally achieved by litter mixing low- and higher-quality litter species, resulted in apparent shifts in microbial community diversity on individual litter species. Responses of bacterial and fungal community diversity to litter mixing varied among individual litter species. Our results suggest that changes in tree species composition in riparian forests and subsequent changes in litter resource heterogeneity could alter stream microbial community diversity and function. As bacteria and fungi are important decomposers of plant litter in aquatic ecosystems, resource-dependent changes in microbial communities could alter detrital processing dynamics in streams.     

Towards a budget of leaf litter decomposition in a first-order woodland stream

To construct a budget of carbon transformations occurring during leaf decomposition, alder leaves were placed in a woodland stream, later retrieved at weekly intervals, and rates of fungal and bacterial production, microbial respiration, and release of dissolved organic matter (DOM) and fine particulate organic matter (FPOM) were determined during short laboratory incubations. Carbon dioxide was the major decomposition product, explaining 17% of the microbially mediated leaf mass loss. DOM and FPOM were also important products (5 and 3% of total mass loss, respectively), whereas carbon flow to microbial biomass was low (2%). Fungal biomass in leaves always exceeded bacterial biomass (95–99% of total microbial biomass), but production of bacteria and fungi was similar, indicating that both types of microorganisms need to be considered when examining leaf decomposition in streams. Comparison of leaf mass loss in coarse and fine mesh bags revealed, in addition, that the shredder, Gammarus pulex, had a major impact on leaf decomposition in this study.     

Exothermic responses of dormant Salix stems during exposure to subzero temperatures

Differential thermal analysis (DTA) was used to determine the exothermic responses in dormant stems and excised lengths of stem of Salix dasyclados Wimmer subjected to artificial freezing treatments.
The presence of ice on the surfaces of intact stems restricted the mechanism of freezing avoidance to temperatures above –4°C. In contrast, excised lengths of stem started to freeze as soon as the ambient temperature fell below –2°C, demonstrating that extracellular ice formation takes place earlier if cut surfaces are present. Exposure of dormant excised lengths of stem to subfreezing temperatures for more than 8 weeks did not alter their nucleation temperature not their exothermic differential responses. Early extracellular crystallisation of freezable cellular water provides conditions that allow dormant Salix dasyclados stems or excised lengths of stem to survive extreme freezing stress.
Crystallisation of extracellular and cellular water took place in the cortex, and did not result in visual damage or reduced survival. This nucleation of extracellular water took place over the same temperature range whether the excised dormant lengths of stem were partly (bark only) or completely thawed. Exposure of dormant tissue to 20°C for up to 24 h did not alter the level of freezing tolerance, nor did it increase the susceptibility of excised lengths of stem to damage by extreme temperature fluctuations.     

Spatial and temporal variation of microbial respiration rates in a blackwater stream

1. The extent of spatial and temporal variation of microbial respiration was determined in a first-order, sand-bottomed, blackwater stream on the coastal plain of south-eastern Virginia, U.S.A.
2. Annual mean respiration rates (as g O₂ m^–3 h^–1) differed significantly among substrata: leaf litter, 12.9; woody debris, 2.4; surface sediment, 0.8; hyporheic sediment, 0.4; water column, 0.003. Rates associated with wood were higher than those with leaves when expressed per unit surface area.
3. Highest respiration rates on leaves, wood and in the water column occurred during the summer, whereas rates in the sediments were greatest during the late autumn and winter. Water temperature, as well as particulate organic matter and nitrogen content of the substrata, was correlated positively with respiration rates.
4. A stepwise multiple regression showed that temperature and nitrogen content together explained 88% of the variation in respiration rates of leaves and wood. In contrast, particulate organic matter content and nitrogen content explained 89–90% of the variation in respiration in the sediments. Although water temperature was a significant factor in the sediment multiple regressions, its addition as an independent variable improved the regression models only slightly.
5. Annual mean respiration in the stream channel, based on the proportional amount of respiration occurring associated with each type of substratum during each month, was 1.1 kg O₂ m^–2 yr^–1. Seventy per cent of respiration in the stream occurred in the hyporheic zone, 8–13% occurred in the surface sediment, leaf litter or woody debris, and < 1% occurred in the water column. Approximately 16% of total detritus, or 40% of non-woody detritus, stored in the stream during the year was lost to microbial respiration.     

Decomposition of Eucalyptus globulus leaves and three native leaf species (Alnus glutinosa, Castanea sativa and Quercus faginea) in a Portuguese low order stream

Leaf decomposition of the exotic evergreen Eucalyptus globulus (eucalyptus), and three native deciduous tree species, Alnus glutinosa (alder), Castanea sativa (chestnut) and Quercus faginea (oak), was compared in a second order stream in Central Portugal. Changes in dry weight, nitrogen and polyphenolic compounds and microbial colonization were periodically assessed for three months.Negative exponential curves fit the leaf weight loss with time for all leaf species. Mass loss rate was in the order alder (K = 0.0161) > chestnut (K = 0.0079) > eucalyptus (K = 0.0068) > oak (K = 0.0037). Microbial colonization followed the same pattern as breakdown rates. Evidence of fungal colonization was observed in alder after 3 days in the stream, whereas it took 21 days in oak leaves to have fungal colonization. Fungal diversity was leaf species-dependent and increased with time. In all cases, percent nitrogen per unit leaf weight increased, at least, at the initial stages of decay while soluble polyphenolics (expressed as percentage per unit leaf weight) decreased rapidly in the first month of leaves immersion.Intrinsic factors such as nitrogen and polyphenolic content may explain differences in leaf decomposition. The possible incorporation of eucalyptus litter into secondary production in a reasonable time span is suggested, although community balance and structure might be affected by differences in allochthonous patterns determined by eucalyptus monocultures.     

Effects of a 4 °C increase in temperature on partitioning of leaf area and dry mass, root respiration and carbohydrates

1. Plants of Bellis perennis, Dactylis glomerata and Poa annua were grown from seed in controlled-environment cabinets at either 16 or 20 °C; at the higher temperature all three species had increased total dry mass and leaf area when assessed on the basis of chronological time. On the basis of thermal time (summation of degree-days above 0 °C; days °C) temperature decreased the dry mass in P. annua.
2. Partitioning was assessed as a change in the allometric coefficients relating shoot and root dry mass, leaf and plant mass, leaf area and plant mass, and leaf area and leaf mass. Of the 12 relationships examined only three were affected by temperature: there was increased partitioning towards the shoot relative to the root in D. glomerata and increased partitioning towards leaf area rather than leaf mass in D. glomerata and B.perennis .
3. Root respiration was unaffected by temperature of growth in D. glomerata and P.annua but was lower in B. perennis grown at elevated temperature.
4. Root respiration acclimated to temperature in P. annua and B. perennis (i.e. when measured at the same temperature, respiration was higher in plants grown at 16 °C).
5. Root soluble carbohydrate concentration was unaffected by temperature of growth in any of the species. Feeding sucrose to the roots for a short period had no effect on the rate of respiration of B. perennis or D. glomerata but increased root respiration of P. annua .     

Seasonal variation in foliar carbon exchange in Pinus radiata and Populus deltoides: respiration acclimates fully to changes in temperature but photosynthesis does not

We investigated seasonal variation in dark respiration and photosynthesis by measuring gas exchange characteristics on Pinus radiata and Populus deltoides under field conditions each month for 1 year. The field site in the South Island of New Zealand is characterized by large day-to-day and seasonal changes in air temperature. The rate of foliar respiration at a base temperature of 10 °C ( R ₁₀) in both pine and poplar was found to be greater during autumn and winter and displayed a strong downward adjustment in warmer months. The sensitivity of instantaneous leaf respiration to a 10 °C increase in temperature ( Q ₁₀) was also greater during the winter period. The net effect of this strong acclimation was that the long-term temperature response of respiration was essentially flat over a wide range of ambient temperatures. Seasonal changes in photosynthesis were sensitive to temperature but largely independent of leaf nitrogen concentration or stomatal conductance. Over the range of day time growth temperatures (5–32 °C), we did not observe strong evidence of photosynthetic acclimation to temperature, and the long-term responses of photosynthetic parameters to ambient temperature were similar to previously published instantaneous responses. The ratio of foliar respiration to photosynthetic capacity ( R _d/ A _sat) was significantly greater in winter than in spring/summer. This indicates that there is little likelihood that respiration would be stimulated significantly in either of these species with moderate increases in temperature – in fact net carbon uptake was favoured at moderately higher temperatures. Model calculations demonstrate that failing to account for strong thermal acclimation of leaf respiration influences determinations of leaf carbon exchange significantly, especially for the evergreen conifer.     

Plant mitochondria electron partitioning is independent of short-term temperature changes

We tested the hypotheses that relative activity of the less efficient alternative oxidase (AOX) path changes with diurnal temperature changes, and thus changes carbon use efficiency with temperature. The activities of the alternative and cytochrome oxidase (COX) paths in plant tissues of three species were determined by measuring ¹⁸O/¹⁶O discrimination and total respiration from 17 to 36 °C. A new, more accurate method for calculating oxygen uptake rate from the mass spectrometry data was developed. Total carbon use efficiency was calculated from the ratio of respiratory heat and CO₂ rates measured from 10 to 35 °C. Oxygen isotope discrimination (22.9 ± 0.4‰) and AOX participation were invariant with temperature in leaf tissue of Cucurbita pepo , Nicotiana sativa and Vicia faba , thus falsifying the first part of the hypothesis. Stress responses of respiration at the temperature extremes limited the range for which carbon use efficiency could be accurately measured to 15–30 °C in N. sativa , to 10–25 °C in C. pepo and to 20–30 °C in V. faba . Carbon-use efficiency was invariant at these temperatures in these species, demonstrating that changes in other pathways that would vary carbon-use efficiency were also invariant with temperature.     

Leaf litter decomposition and microbial activity in nutrient-enriched and unaltered reaches of a headwater stream

SUMMARY 1. Decomposition of red maple ( Acer rubrum ) and rhododendron ( Rhododendron maximum ) leaves and activity of associated microorganisms were compared in two reaches of a headwater stream in Coweeta Hydrologic Laboratory, NC, U.S.A. The downstream reach was enriched with ammonium, nitrate, and phosphate whereas the upstream reach was not altered.
2. Decomposition rate, microbial respiration, fungal and bacterial biomass, and the sporulation rate of aquatic hyphomycetes associated with decomposing leaf material were significantly higher for both leaf types in the nutrient-enriched reach. Species richness and community structure of aquatic hyphomycetes also exhibited considerable changes with an increase in the number of fungal codominants in the nutrient-enriched reach.
3. Fungal biomass was one to two orders of magnitude greater than bacterial biomass in both reaches. Changes in microbial respiration rate corresponded to those in fungal biomass and sporulation, suggesting a primary role of fungi in leaf decomposition.
4. Nutrient enrichment increased microbial activity, the proportion of leaf carbon channelled through the microbial compartment and the decomposition rate of leaf litter.     

Characteristics of the spawning migrations of brown trout, Salmo trutta L., and rainbow trout, S. gairdneri Richardson, in Great Lake, Tasmania

Upstream spawning migrations of mature brown trout, S. trutta , and rainbow trout, S. gairdneri , were studied in Liawenee Canal, Great Lake from 1949 to 1985. Brown trout migrations normally occurred from early April to mid-May and rainbow trout from late August to early November. In 1983, 16 425 brown trout and 1338 rainbow trout passed through a fixed upstream diversion trap. Brown trout spawning migrations occurred predominantly over the temperature range 6–10° C, while rainbow trout migrated predominantly over the range 5–11° C. Migrations peaked at water temperatures of 7.6°C (males) and 7.8°C (females) for brown trout, and 8.3°C (males) and 9.6°C (females) for rainbow trout. Rainbow trout migrations occurred at high flow conditions and were positively correlated with canal flow increases, while brown trout migrated under low canal flow. Mean length, weight and condition of rainbow trout of both sexes decreased significantly during migrations. Female brown trout decreased in weight and condition but not in length; male brown trout did not change in condition despite decreases in both length and weight during migrations. Overall sex ratio was 2:1 (female:male) for both species, with the relative proportion of male fish decreasing as migrations progressed. Age composition changed during migrations; dominant age classes were 3 < 4 < 5 + years for both species. Comparison of length, weight, condition and age revealed minor changes during the 37-year period 1949–1985.     

Microbial Biomass,Respiration, and Decomposition of Hura crepitans L. (Euphorbiaceae) Leaves in a Tropical Stream1

The processing of leaves in temperate streams has been the subject of numerous studies but equivalent tropical ecosystems have received little attention. We investigated leaf breakdown of a tropical tree species (Hura crepitans, Euphorbiaceae), in a tropical stream using leaf bags (0.5 mm mesh) over a period of 24 days. We followed the loss of mass and the changes in adenosine triphosphate (ATP) concentrations and respiration rates associated with the decomposing leaves. The breakdown rate was fast (k=?0.0672/d, k_d=?0.0031/degree‐day), with 81 percent loss of the initial mass within 24 days. This high rate was probably related to the stable and high water temperature (22°C) favoring strong biological activity. Respiration rates increased until day 16 (1.1 mg O₂/h/g AFDM), but maximum ATP concentrations were attained at day 9 (725 nmol ATP/g AFDM) when leaf mass remaining was 52 percent. To determine the relative importance of fungi and bacteria during leaf decomposition, ATP concentrations, and respiration rates were determined in samples treated with antibiotics, after incubation in the stream. The results of the samples treated with the antifungal or the bacterial antibiotic suggest a higher contribution of the fungal community for total microbial biomass and a higher contribution of the bacterial community for microbial respiration rates, especially during the later stages of leaf decomposition. However, these results should be analyzed with caution since both antibacterial and antifungal agents did not totally eliminate microbial activity and biomass.     

Decomposition of Fire Exposed Eucalyptus Leaves in a Portuguese Lowland Stream

We compared fire exposed with normal abscised eucalyptus leaves incubated in a stream running through eucalyptus plantations in central Portugal, in terms of breakdown rates, microbial activity, diversity and macroinvertebrate abundance. Although leaves exposed to fire had lower nutritional value, mass loss was similar for both leaf types (k = 0.0089–0.0095 d^–1 for fire and k = 0.0084–0.00103 d^–1 for normal leaves). Fungal biomass was similar among treatments, whereas sporulation and microbial respiration were lower in fire exposed leaves. Both leaf types had similar aquatic hyphomycetes communities. Physical fragmentation was important in fire exposed leaves breakdown. Invertebrates colonized leaves in low numbers in both treatments. Alteration of leaf litter quality determined by fires in streams does not seem to determine changes in ecosystem functioning in a short term. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Allocation of carbon to growth, storage and respiration in the vegetative barley plant

Abstract. It is proposed that the growing plant can be divided into three compartments with reference to carbon: soluble, storage and structural. Experiments carried out at 10, 15, 20 and 30°C in the light followed changes in size of these compartments in barley plants 10–24 days old. The redistribution of ^I4C photo-assimilated by 10 day old plants was monitored simultaneously. The soluble and storage compartments are a higher percentage of plant weight at lower temperatures, and are turned over rapidly at all temperatures; they form the source of respired ¹⁴C. About 30% of the ¹⁴C fixed enters structural material; in the first 24 h after labelling, for each unit of ¹⁴C entering the structural compartment, between 0–9 (at 15°C) and 3.2 (at 30°C) units of ¹⁴C are lost by respiration. At 15°C in the dark, respiratory loss of ¹⁴C is initially from soluble and storage compartments; thereafter respiration of ^I4C occurs at the expense of structural material.     

Seasonal change in the respiration of the dobsonfly larva, Protohermes grandis(Megaloptera: Corydalidae)

SUMMARY 1. Seasonal change in the respiration of the dobsonfly larva, Protohermes grandis ,was studied by measuring the oxygen consumption rate (resting metabolism) bimonthly for 2 years. The respiratory rate of the larva was significantly lower during the summer season when the stream temperature rose to 30°C.
2. Summer depression of respiration was confirmed by measuring the rate of carbon dioxide evolution. The mean value of the respiratory quotient was estimated to be 0.76 ± 0.05 SE. The larva is believed to conserve energy by this reduction in respiratory rate,
3. In other seasons, however, the larva maintained a higher respiratory rate and remained active even in the winter when the stream temperature decreased near to 0°C. In fact, significant growth in weight occurred from mid-October to late March.
4. This acclimation to temperature may enable the efficient allocation of energy during the long larval period (3 years) in streams which have large annual fluctuations in temperature.