Influence of light and temperature on photosynthesis and respiration by Pithophora oedogonia (Mont.) Wittr. (chlorophyceae)

Rates of net photosynthesis and respiration were determined for Pithophora oedogonia (Mont.) Wittr. acclimatized to 56 combinations of light (7–1200 μE m^?2 s^?1) and temperature (5–35°C). Conditions for maximum net photosynthesis were estimated to be 26°C and 970 μE m^?2 s^?1. The rate of net photosyntheses varied considerably with temperature, with the maximum measured value (9.67 mg O₂ h^?1 g dry wt.^?1) occurring at 25°C. Respiration rate increased with temperature and the light received just prior to measurement. The maximum respiration rate (7.05 mg O₂ g^?1 h^?1) occurred at 30°C and 1200 μE m^?2 s^?1. Exposure of Pithophora to light levels of 600 or 1200 μE m^?2 s^?1 prior to determination of the respiration rate resulted in significantly elevated levels of oxygen consumption at temperatures ≥ 15°C. The relationship between light, temperature and photosynthesis and respiration were summarized as three-dimensional response surfaces.     

EFFECTS OF LIGHT AND TEMPERATURE ON NET PHOTOSYNTHESIS AND DARK RESPIRATION OF GAMETOPHYTES AND EMBRYONIC SPOROPHYTES OF MACROCYSTIS PYRIFERA1

The rates of net photosynthesis as a function of irradiance and temperature were determined for gametophytes and embryonic sporophytes of the kelp, Macrocystis pyrifera (L.) C. Ag. Gametophytes exhibited higher net photosynthetic rates based on oxygen and pH measurements than their derived embryonic sporophytes, but reached light saturation at comparable irradiance levels. The net photosynthesis of gametophytes reached a maximum of 66.4 mg O₂ g dry wt^?1 h^?1 (86.5 mg CO₂ g dry wt^?1 h^?1), a value approximately seven times the rate reported previously for the adult sporophyte blades. Gametophytes were light saturated at 70 μE m^?2 s^?1 and exhibited a significant decline in photosynthetic performance at irradiances 140 μE m^?1 s^?1. Embryonic sporophytes revealed a maximum photosynthetic capacity of 20.6 mg O₂ g dry wt^?1 h^?1 (25.3 mg CO₂ g dry wt^?1 h^?1), a rate about twice that reported for adult sporophyte blades. Embryonic sporophytes also became light saturated at 70 μE m^?2 s^?1, but unlike their parental gametophytes, failed to exhibit lesser photosynthetic rates at the highest irradiance levels studied; light compensation occurred at 2.8 μE m^?2 s^?1. Light-saturated net photosynthetic rates of gametophytes and embryonic sporophytes varied significantly with temperature. Gametophytes exhibited maximal photosynthesis at 15° to 20° C, whereas embryonic sporophytes maintained comparable rates between 10° and 20° C. Both gametophytes and embryonic sporophytes declined in photosynthetic capacity at 30° C. Dark respiration of gametophytes was uniform from 10° to 25° C, but increased six-fold at 30° C; the rates for embryonic sporophytes were comparable over the entire range of temperatures examined. The broader light and temperature tolerances of the embryonic sporophytes suggest that this stage in the life history of M. pyrifera is well suited for the subtidal benthic environment and for the conditions in the upper levels of the water column.     

CARBON ALLOCATION IN MACROCYSTIS PYRIFERA (PHAEOPHYTA): INTRINSIC VARIABILITY IN PHOTOSYNTHESIS AND RESPIRATION1

Measurements of net photosynthesis (PS, O₂ evolution), dark respiration (R, O₂ consumption), and light and dark carbon fixation (¹⁴C) were conducted on whole blades, isolated blade discs, sporophylls, apical scimitars and representative portions of stipe and holdfast of the giant kelp Macrocystis pyrifera L.C. Ag. On a dry weight basis, highest net PS rates were observed in apical scimitar segments and whole blades (3.81 and 3.07 mgC · g dry wt^?1· h^?1, respectively), followed by sporophylls (1.42 mgC·g dry wt^?1· h^?1) and stipe segments (0.15 mgC·g dry wt^?1· h^?1). No PS capacity was observed in holdfast material. Respiration rates showed similar ranking ranging from 1.22 mgC·g dry wt^?1·h^?1 for apical scimitar to 0.18–0.22 mgC·g dry wt^?1· h^?1 for holdfast material. Considerable within blade variability in both PS and R was also found. Steepest PS and R gradients on both an areal and weight basis were found within immature blades followed by senescent and mature blade material. Highest net PS rates were associated with the blade tips ranging from 3.08 (mature blades) to 10.3 mgC·dry wt^?1·h^?1 (immature blades). Highest rates of R generally occurred towards the basal portions of blades and ranged from 1.03–1.80 mgC·g dry wt^?1·h^?1 for immature blades. The variability within and between blades was high, with coefficients of variation approaching 50%. The observed patterns can be related to the decreasing proportionment of photosynthetic tissue and increasing proportionment of structural tissue as occurs from the blade tip to the blade base. Rates of light carbon fixation (LCF) revealed longitudinal profiles similar to oxygen measurements for the different blade types, with the absolute rates being slightly lower. Patterns of dark carbon fixation (DCF) were less easily interpreted. Highest rates of DCF (0.04–0.06 mgC·g dry wt^?1·h^?1) occurred at the basal portions of immature and senescent blades. Longitudinal profiles of total chlorophyll (a + c) on both an areal and weight basis were very similar to the profiles of PS. Normalized to chlorophyll a, PS displayed an unusual longitudinal profile in immature tissue; however, such profiles for mature and senescent tissues were similar to those for PS on an areal basis. It was demonstrated that it is difficult, if not impossible, to select single tissue discs that are representative of whole blades. The metabolic longitudinal profiles reveal a characteristic developmental pattern; the previous working definitions of immature, mature, and senescent blades, based on morphology and frond position thus have a physiological basis.     

PHOTOSYNTHESIS AND RESPIRATION OF THE CONCHOCELIS STAGE OF ALASKAN PORPHYRA (BANGIALES,RHODOPHYTA) SPECIES IN RESPONSE TO ENVIRONMENTAL VARIABLES1

Photosynthesis and respiration of three Alaskan Porphyra species, P. abbottiae V. Krishnam., P. pseudolinearis Ueda species complex (identified as P. “pseudolinearis” below), and P. torta V. Krishnam., were investigated under a range of environmental parameters. Photosynthesis versus irradiance (P–I) curves revealed that maximal photosynthesis (P_max), irradiance at maximal photosynthesis (I_max), and compensation irradiance (I_c) varied with salinity, temperature, and species. The P_max of Porphyra abbottiae conchocelis varied between 83 and 240 μmol O₂ · g dwt^?1 · h^?1 (where dwt indicates dry weight) at 30–140 μmol photons · m^?2 · s^?1 (I_max) depending on temperature. Higher irradiances resulted in photoinhibition. Maximal photosynthesis of the conchocelis of P. abbottiae occurred at 11°C, 60 μmol photons · m^?2·s^?1, and 30 psu (practical salinity units). The conchocelis of P. “pseudolinearis” and P. torta had similar P_max values but higher I_max values than those of P. abbottiae. The P_max of P. “pseudolinearis” conchocelis was 200–240 μmol O₂ · g dwt^?1 · h^?1 and for P. torta was 90–240 μmol O₂ · g dwt^?1 · h^?1. Maximal photosynthesis for P. “pseudolinearis” occurred at 7°C and 250 μmol photons · m^?2 · s^?1 at 30 psu, but P_max did not change much with temperature. Maximal photosynthesis for P. torta occurred at 15°C, 200 μmol photons · m^?2 · s^?1, and 30 psu. Photosynthesis rates for all species declined at salinities <25 or >35 psu. Estimated compensation irradiances (I_c) were relatively low (3–5 μmol · photons · m^?2 · s^?1) for intertidal macrophytes. Porphyra conchocelis had lower respiration rates at 7°C than at 11°C or 15°C. All three species exhibited minimal respiration rates at salinities between 25 and 35 psu.     

PHOTOSYNTHESIS,DARK RESPIRATION AND DESICCATION RESISTANCE OF THE INTERTIDAL SEAWEEDS HESPEROPHYCUS HARVEYANUS AND PELVETIA FASTIGIATA F. GRACILIS12

Rates of net photosynthesis and dark respiration were determined under submersed and emerged conditions for Hesperophycus harveyanus S. & G. and Pelvetia fastigiata f. gracilis (Decne.) S. & G. Both species exhibited submersed photosynthesis-light relationships and dark respiration rates similar to those established for other closely related intertidal, fucoids. Maximal net photosynthesis of H. harveyanus (0.21 mmol O₂ g dry wt.^-1· h^-1; 0.18 mmol CO₂ g dry wt.^-1· h^-1) was similar to that of P. fastigiata f. gracilis (0.17 mmol. O₂ g dry wt.^-1· h^-1; 0.14 mmol CO₂ g dry wt. ^-1· h^-1). Light saturation occurred between 150 and 250 μE · m^-2· s^-1 for H. harveyanus and between 75 and 150 μE · m^-2· s^-1 for P. fastigiata f. gracilis; photon flux densities required for compensation were 6.4 and 9.2 μE · m^-2· s^-1, respectively. Photoinhibition was not observed for either species. The light-saturated, submersed net photosynthetic performances of both species varied significantly with temperature. Greatest photosynthetic rates were obtained at 23° C for H. harveyanus and at 18° C for P. fastigiata f. gracilis. Under emersed conditions, the maximal net photosynthetic rate and the photon flux densities required for saturation were greater for H. harveyanus (0.08 mmol CO₂ g dry wt.^-1· h^-1; 260 to 700 μE · m^-2· s^-1) than for P. fastigiata f. gracilis (0.02 mmol CO₂g dry wt.^-1· h^-1; 72 to 125 μE · m^-2· s^-1). However, for both species, emersed photosynthetic rates were much lower (14–44%) than those obtained under submersed conditions. Desiccation negatively influenced emersed photosynthesis, of both species, but H. harveyanus thalli contained more water when fully hydrated and lost water more slowly during dehydration, thus suggesting greater photosynthetic potential during field conditions of emersion.     

Nitrogen addition reduces soil respiration in a mature tropical forest in southern China

Response of soil respiration (CO₂ emission) to simulated nitrogen (N) deposition in a mature tropical forest in southern China was studied from October 2005 to September 2006. The objective was to test the hypothesis that N addition would reduce soil respiration in N saturated tropical forests. Static chamber and gas chromatography techniques were used to quantify the soil respiration, following four‐levels of N treatments (Control, no N addition; Low‐N, 5 g N m^?2 yr^?1; Medium‐N, 10 g N m^?2 yr^?1; and High‐N, 15 g N m^?2 yr^?1 experimental inputs), which had been applied for 26 months before and continued throughout the respiration measurement period. Results showed that soil respiration exhibited a strong seasonal pattern, with the highest rates found in the warm and wet growing season (April–September) and the lowest rates in the dry dormant season (December–February). Soil respiration rates showed a significant positive exponential relationship with soil temperature, whereas soil moisture only affect soil respiration at dry conditions in the dormant season. Annual accumulative soil respiration was 601±30 g CO₂‐C m^?2 yr^?1 in the Controls. Annual mean soil respiration rate in the Control, Low‐N and Medium‐N treatments (69±3, 72±3 and 63±1 mg CO₂‐C m^?2 h^?1, respectively) did not differ significantly, whereas it was 14% lower in the High‐N treatment (58±3 mg CO₂‐C m^?2 h^?1) compared with the Control treatment, also the temperature sensitivity of respiration, Q₁₀ was reduced from 2.6 in the Control with 2.2 in the High‐N treatment. The decrease in soil respiration occurred in the warm and wet growing season and were correlated with a decrease in soil microbial activities and in fine root biomass in the N‐treated plots. Our results suggest that response of soil respiration to atmospheric N deposition in tropical forests is a decline, but it may vary depending on the rate of N deposition.     

PRODUCTIVITY OF THE FILAMENTOUS ALGA PITHOPHORA OEDOGONIA (CHLOROPHYTA) IN SURREY LAKE,INDIANA1

Biomass, akinete numbers, net photosynthesis, and respiration of Pithophora oedogonia were monitored over two growing seasons in shallow Surrey Lake, Indiana. Low rates of photosynthesis occurred from late fall to early spring and increased to maximum levels in late spring to summer (29–39 mgO₂·g^?1 dry wt·h^?1). Areal biomass increased following the rise in photosynthesis and peaked in autumn (163–206g dry wt·m^?2). Photosynthetic rates were directly correlated with temperature, nitrogen, and phosphorus over the entire annual cycle and during the growing season. Differences in photosynthetic activity and biomass between the two growing seasons (1980 and 1981) were apparently related to higher, early spring temperatures and higher levels of NO₃-N and PO₄-P in 1981. Laboratory investigations of temperature and light effects on Pithophora photosynthesis and respiration indicated that these processes were severely inhibited below 15°C. The highest P_max value occurred at 35°C (0.602 μmol O₂·mg^?1 chl a·min^?1). Rates of dark respiration did not increase above 25°C thus contributing to a favorable balance of photosynthetic production to respiratory utilization at high temperatures. Light was most efficiently utilized at 15°C as indicated by minimum values of I_k(47 μE·m^?2·s^?1) and I_c (6 μE·m^?2·s^?1). Comparison of P. oedogonia and Cladophora glomerata indicated that the former was more tolerant of temperatures above 30°C. Pithophora's tolerance of high temperature and efficient use of low light intensity appear to be adaptive to conditions found within the dense, floating algal mats and the shallow littoral areas inhabited by this filamentous alga.     

Effect of irradiance and temperature on the photosynthesis of a cultivated red alga,Pyropia tenera (= Porphyra tenera), at the southern limit of distribution in Japan

The effect of irradiance and temperature on the photosynthesis of the red alga, Pyropia tenera, was determined for maricultured gametophytes and sporophytes collected from a region that is known as one of the southern limits of its distribution in Japan. Macroscopic gametophytes were examined using both pulse‐amplitude modulated fluorometry and/or dissolved oxygen sensors. A model of the net photosynthesis–irradiance (P‐E) relationship of the gametophytes at 12°C revealed that the net photosynthetic rate quickly increased at irradiances below the estimated saturation irradiance of 46 μmol photons m^?2 s^?1, and the compensation irradiance was 9 μmol photons m^?2 s^?1. Gross photosynthesis and dark respiration for the gametophytes were also determined over a range of temperatures (8–34°C), revealing that the gross photosynthetic rates of 46.3 μmol O₂ mg_chl‐a^?1 min^?1 was highest at 9.3 (95% Bayesian credible interval (BCI): 2.3–14.5)°C, and the dark respiration rate increased at a rate of 0.93 μmol O₂ mg_chl‐a^?1 min^?1°C^?1. The measured dark respiration rates ranged from ?0.06 μmol O₂ mg_chl‐a^?1 min^?1 at 6°C to ?25.2 μmol O₂ mg_chl‐a^?1 min^?1 at 34°C. The highest value of the maximum quantum yield (Fv/Fm) for the gametophytes occurred at 22.4 (BCI: 21.5–23.3) °C and was 0.48 (BCI: 0.475–0.486), although those of the sporophyte occurred at 12.9 (BCI: 7.4–15.1) °C and was 0.52 (BCI: 0.506–0.544). This species may be considered well‐adapted to the current range of seawater temperatures in this region. However, since the gametophytes have such a low temperature requirement, they are most likely close to their tolerable temperatures in the natural environment.     

Photosynthesis of Marine Macroalgae from Antarctica: Light and Temperature Requirements

The photosynthetic performance of macroalgae isolated in Antarctica was studied in the laboratory. Species investigated were the brown algae Himantothallus grandifolius, Desmarestia anceps, Ascoseira mirabilis, the red algae Palmaria decipiens, Iridaea cordata, Gigartina skottsbergii, and the green algae Enteromorpha bulbosa, Acrosiphonia arcta, Ulothrix subflaccida and U. implexa. Unialgal cultures of the brown and red algae were maintained at 0°C, the green algae were cultivated at 10°C. I_K values were between 18 and 53 μmol m^?2 s^?1 characteristic or low light adapted algae. Only the two Ulothrix species showed higher I_K values between 70 and 74 μmol m^?2 s^?1. Photosynthesis compensated dark respiration at very low photon fluence rates between 1.6 and 10.6 μmol m^?2 s^?1. Values of α were high: between 0.4 and 1.1 μmol O₂ g^?1 FW h^?1 (μmol m^?2 s^?1)^?1 in the brown and red algae and between 2.1 and 4.9 μmol O₂ g^?1 FW h^?1 (μmol m^?2 s^?1)^?1 in the green algal species. At 0°C P_max values of the brown and red algae ranged from 6.8 to 19.1 μmol O₂ g^?1 FW h^?1 and were similarly high or higher than those of comparable Arctic-cold temperate species. Optimum temperatures for photosynthesis were 5 to 10°C in A. mirabilis, 10°C in H. grandifolius, 15°C in G. skottsbergii and 20°C or higher in D. anceps and I. cordata. P: R ratios strongly decreased in most brown and red algae with increasing temperatures due to different Q₁₀ values for photosynthesis (1.4 to 2.5) and dark respiration (2.5 to 4.1). These features indicate considerable physiological adaptation to the prevailing low light conditions and temperatures of Antarctic waters. In this respect the lower depth distribution limits and the northern distribution boundaries of these species partly depend on the physiological properties described here.     

COMPARISON OF DEVELOPMENT AND PHOTOSYNTHETIC GROWTH FOR FILAMENT CLUMPS AND REGENERATED MICROPLANTLET CULTURES OF AGARDHIELLA SUBULATA (RHODOPHYTA, GIGARTINALES)

Two axenic, in vitro liquid suspension cultures were established for Agardhiella subulata (C. Agardh) Kraft et Wynne, and their growth characteristics were compared. This study illustrated how reliable routes for the development of suspension cultures of macrophytic red algae of terete thallus morphology can be achieved for biotechnology applications. Undifferentiated filament clumps of 2–8 mm diameter were established by induction of callus-like tissue from thallus explants, and lightly branched microplantlets of 2–10 mm length were established by regeneration of filament clumps. The filament clumps were susceptible to regeneration. Adventitious shoot formation was reliably induced from 40% to 70% of the filament clumps by gentle mixing at 100 rev min^?1 on an orbital shaker. The specific growth rate of the microplantlets was higher than the filament clumps in nonagitated well plate culture (4%–6% per day for microplantlets vs. 2%–3% per day for filament clumps) at 24° C and 8–36 μmol photons·m^?2·s^?1 irradiance (10:14 h LD cycle) when grown on ASP12 artificial seawater medium at pH 8.6–8.9 with 20%–25% per day medium replacement. Oxygen evolution rate vs. irradiance measurements showed that relative to the filament clumps, microplantlets had a higher maximum specific oxygen evolution rate (P_o,max= 0.181 ± 0.035 vs. 0.130 ± 0.023 mmol O₂·g^?1 dry cell mass·h^?1), but comparable respiration rate (Q_o= 0.040 ± 0.013 vs. 0.033 ± 0.017 mmol O₂·g^?1 dry cell mass·h^?1), compensation point (I_c= 3.8 ± 2.4 vs. 5.7 ± 1.2 μmol photons·m^?2·s^?1), and light intensity at 63.2% of saturation (I_k= 17.5 ± 3.9 vs. 14.9 ± 2.6 μmol photons·m^?2·s^?1). The microplantlet culture was more suitable for suspension culture development than the filament clump culture because it was morphologically stable and exhibited higher growth rates.     

Utilization of metabolic scope in relation to feeding and activity by individual and grouped zebrafish, Brachydanio rerio (Hamilton-Buchanan)

Metabolic scope and its utilization in relation to feeding and activity were measured in individual and grouped zebrafish (weight range, 430–551 mg) at 24° C by respirometry. Mean maximum metabolic rate, induced by swimming to exhaustion, R_max(i), was 1223 (s.d. , 157) mg O₂, kg^?1 h^?1 for individuals. Standard metabolic rate, R_s. was 364 mg O₂ kg^?1 h^?1, as estimated by extrapolating to zero activity from measurements of unfed, spontaneously active individuals. Mean routine metabolic rate, R_rout, of individuals was 421 (s.d. , 58) mg O₂, kg_-1 h_-1. The mean voluntary maximum metabolic rate, R_max(v), following transfer of minimally exercised fish to the respirometer, was 1110 (s.d. , 83) mg O₂ kg ^?1 h^?1 for groups of six fish, and was not significantly different from the value measured for individuals, 1066 (s.d. , 122) mg O₂, kg^?1 h^?1. Grouped fish acclimated to the respirometer more slowly than individual fish and exhibited significantly higher R_rout, apparently a result of greater social interaction and activity in groups. Mean R_rout for groups was 560 (s.d. , 78) mg O₂, kg^?1 h^?1. While groups of zebrafish fed a ration of 5% wet body weight day^?1 exhibited consistently higher metabolic rates than fish fed rations of 2.5% wet body weight day^?1 the high ration group still used only a maximum of 77% of the metabolic scope. Zebrafish of the size studied do not appear to demonstrate a high degree of conflict in utilization of metabolic scope by different respiratory components. The metabolic rates measured for zebrafish are among the highest yet measured for fish of similar size and at similar temperatures.     

Heart rate as an indicator of metabolic rate and activity in adult Atlantic salmon, Salmo salar

Telemetered heart rate (f_H) was examined as an indicator of activity and oxygen consumption rate (VO₂) in adult, cultivated, Atlantic salmon, Salmo salar L. Heart rate was measured during sustained swimming in a flume for six fish at 10° C [mean weight, 1114 g; mean fork length (f. l.), 50·6 cm] and seven fish at 15° C (mean weight, 1119 g; mean f. l., 50·7 cm) at speeds of up to 2·2 body lengths/s. Semi–logarithmic relationships between heart rate and swimming speed were obtained at both temperatures. Spontaneously swimming fish in still water exhibited characteristic heart rate increases associated with activity. Heart rate and Vo₂ were monitored simultaneously in a 575–1 circular respirometer for six fish (three male, three female) at 4° C (mean weight, 1804 g; mean F. L., 62· cm) and six fish (three male, three female) at 10° C (mean weight, 2045 g; mean f. l., 63·2 cm) during spontaneous but unquantified activity. Linear regressions were obtained by transforming data for both f_H and Vo₂ to log values. At each temperature, slopes of the regressions between f_H and Vo₂ for individual fishes were not significantly different, but in some cases elevations were. All differences in elevation were between male and female fish. There were no significant differences in regression slope or elevation for fish of the same sex at the two temperatures and so regressions were calculated for the sexes, pooling data from 4 and 10° C. There was no significant difference in the mean ± S. D. Vo₂ between the sexes at 4° C (male, 66·0 ± 59·6 mgO₂ kg^?1 h^?1; female, 88·0 ± 60·1 mgO₂ kg^?1 h^?1) or 10° C (male, 166·2 ± 115·4 mgO₂ kg^?1 h^?1; female, 169·2 ± 111–1 mgO₂ kg^?1h^?1). Resting Vo₂ (x?± s. d.) at 4°C was 36·7 ± 8.4 mgO₂ kg^?1 h^?1, and 10° C was 72·8 ± 11·9 mgO₂ kg^?1 h^?1. Maximum Vo₂ (x?± S. D.) at 4° C was 250·6 ± 40·2 mgO₂ kg^?1 h^?1, and at 10° C was 423·6 ± 25·2 mgO₂ kg^?1 h^?1. Heart rate appears to be a useful indicator of metabolic rate over the temperature range examined, for the cultivated fish studied, but it is possible that the relationship for wild fish may differ.     

LIGHT AND TEMPERATURE AS FACTORS REGULATING SEASONAL GROWTH AND DISTRIBUTION OF ULOTHRIX ZONATA (ULVOPHYCEAE)1

Ulothrix zonata (Weber and Mohr) Kütz. is an unbranched filamentous green alga found in rocky littoral areas of many northern lakes. Field observations of its seasonal and spatial distribution indicated that it should have a low temperature and a high irradiance optimum for net photosynthesis, and at temperatures above 10°C it should show an increasingly unfavorable energy balance. Measurements of net photosynthesis and respiration were made at 56 combinations of light and temperature. Optimum conditions were 5°C and 1100 μE·m^?2·s^?1 at which net photosynthesis was 16.8 mg O₂·g^?1·h^?1. As temperature increased above 5° C optimum irradiance decreased to 125 μE·m^?2·s^?1 at 30°C. Respiration rates increased with both temperature and prior irradiance. Light-enhanced respiration rates were significantly greater than dark respiration rates following irradiance exposures of 125 μE·m^?2·s^?1 or greater. Polynomials were fitted to the data to generate response surfaces. Polynomial equations represent statistical models which can accurately predict photosynthesis and respiration for inclusion in ecosystem models.     

Interactions of tropospheric CO2 and O3 enrichments and moisture variations on microbial biomass and respiration in soil

Soil microbial biomass C (C_mic) is a sensitive indicator of trends in organic matter dynamics in terrestrial ecosystems. This study was conducted to determine the effects of tropospheric CO₂ or O₃ enrichments and moisture variations on total soil organic C (C_org), mineralizable C fraction (C_Min), C_mic, maintenance respiratory (qCO₂) or C_mic death (qD) quotients, and their relationship with basal respiration (BR) rates and field respiration (FR) fluxes in wheat‐soybean agroecosystems. Wheat (Triticum aestivum L.) and soybean (Glycine max. L. Merr) plants were grown to maturity in 3‐m dia open‐top field chambers and exposed to charcoal‐filtered (CF) air at 350 μL CO₂ L^?1; CF air + 150 μL CO₂ L^?1; nonfiltered (NF) air + 35 nL O₃ L^?1; and NF air + 35 nL O₃ L^?1 + 150 μL CO₂ L^?1 at optimum (? 0.05 MPa) and restricted soil moisture (? 1.0 ± 0.05 MPa) regimes. The + 150 μL CO₂ L^?1 additions were 18 h d^?1 and the + 35 nL O₃ L^?1 treatments were 7 h d^?1 from April until late October. While C_org did not vary consistently, C_Min, C_mic and C_mic fractions increased in soils under tropospheric CO₂ enrichment (500 μL CO₂ L^?1) and decreased under high O₃ exposures (55 ± 6 nL O₃ L^?1 for wheat; 60 ± 5 nL O₃ L^?1 for soybean) compared to the CF treatments (25 ± 5 nL O₃ L^?1). The qCO₂ or qD quotients of C_mic were also significantly decreased in soils under high CO₂ but increased under high O₃ exposures compared to the CF control. The BR rates did not vary consistently but they were higher in well‐watered soils. The FR fluxes were lower under high O₃ exposures compared to soils under the CF control. An increase in C_mic or C_mic fractions and decrease in qCO₂ or qD observed under high CO₂ treatment suggest that these soils were acting as C sinks whereas, reductions in C_mic or C_mic fractions and increase in qCO₂ or qD in soils under elevated tropospheric O₃ exposures suggest the soils were serving as a source of CO₂.     

Evidence of temperature‐independent metabolic rates in diurnal Namib Desert tenebrionid beetles

To investigate whether the sensitivity to environmental temperature varies between nocturnal and diurnal species of tenebrionid beetle, the metabolic rates of three diurnal species (Onymacris plana Peringuey, Onymacris rugatipennis Haag and Physadesmia globosa Haag) and three nocturnal species (Epiphysa arenicola Penrith, Gonopus sp. and Stips sp.) of beetles from the Namib Desert are measured over a range of temperatures (15–40 °C) that are experienced by these beetles in their natural habitat. The diurnal species O. plana, O. rugatipennis and P. globosa exhibit temperature‐independent metabolic rates (mean Q₁₀ = 1.2) within temperature ranges that are ecologically relevant for diurnal desert beetles (30–40 °C). Onymacris plana, in particular, has a 20–40 °C rate–temperature slope (0.007 log₁₀ mL O₂ h^?1 g^?1 °C^?1; Q₁₀ = 1.1) that is less than half that of the other five beetle species (0.022–0.063 log₁₀ mL O₂ h^?1 g^?1 °C^?1; Q₁₀ ranges from 1.3–1.9), suggesting that O. plana is more metabolically independent of temperature than the other nocturnal and diurnal tenebrionids being investigated. Animals with metabolic rates that are decoupled from body temperature (or ambient temperature) may have an ecological advantage that allows them to exploit thermal and spatial niches during extreme temperature conditions.     

Studies on nitrate reductase activity in Laminariadigitata (Huds.) Lamour. I. Longitudinal and transverse profiles of nitrate reductase activity within the thallus

The distribution of the enzyme nitrate reductase (NR) within the thallus of the brown alga Laminaria digitata (Huds.) Lamour is described for plants sampled from the east coast of Scotland in May and June when growth rates are at a maximum. Highest NR activities (≈ 0.2 μmol NO₃^? reduced·g^?1 wet wt·h^?1) occurred in the mature blade. NR activities declined towards the basal meristematic region of the blade. Activities in the stipe and holdfast were also low, being between 0.05 and 0.07 μmol NO₃^? reduced·g^?1 wet wt·h^?1. The activities of the enzyme glutamine synthetase (GS), which is important in the assimilation of NH₄⁺, showed a similar distribution within the blade to those of NR.The transverse profile of NR activity in the stipe exhibited a decline from the outer to the inner tissues. Maximum activities (0.13 μmol NO₃^? reduced·g^?1 wet wt·h^?1) occurred in the meristoderm, while those of the cortex and medulla were 0.04 and 0.01 μmol NO₃^? reduced·g^?1 wet wt·h^?1 respectively.These data indicate that most of the NO₃^? assimilation occurs in the mature blade rather than in the meristematic tissue where there is a high nitrogen demand for growth. The data are consistent with the maintenance of meristematic growth by the internal transport of organic nitrogen from the mature blade.     

Community Structure,Geochemical Characteristics and Mineralogy of a Hypersaline Microbial Mat,Cabo Rojo,PR

Seasonal variations in precipitation changed the community composition and microbial activity in a hypersaline, tropical microbial mat, in Cabo Rojo, PR. Using a combination of dissection, light, and transmission electron microscopy, terminal restriction fragment length polymorphism (T-RFLP), in situ microelectrode studies, and ³⁵ S isotope incubations, we documented the major differences between wet and dry seasons. During the wet season (precipitation 177 mm), cyanobacterial (green layer) and anoxyphototrophic (pink layer) communities, as well as the black FeS layer were well-developed, and T-RFLP patterns indicated a diverse community. The rate of oxygenic photosynthesis was 49 μ M min ^{? 1} . Aerobic respiration was 29 μ M min ^{? 1} , and sulfate reduction was 264 nmol cm ^{? 3} h ^{? 1} . During the dry season (precipitation 51 mm), cyanobacteria and anoxyphototrophs were less diverse and abundant, and T-RFLP patterns were less complex. The O ₂ production rate was reduced to 9 μ M min ^{? 1} , as was O ₂ consumption (7 μ M min ^{? 1} ) and sulfate reduction (26 nmol cm ^{? 3} h ^{? 1} ). Aragonite, calcite, halite, and quartz were the predominant minerals. Seasonal differences were found in the green and pink layers for both halite and quartz. Gypsum was not observed, likely due to a sample handling artifact. The fluctuations in community composition and metabolic activity, principally reflected in fluctuations in binding and trapping potential of the uppermost mat community, might be responsible for the observed differences in mineralogy.     

Respiration,worker body size,tempo and activity in whole colonies of ants

Ants are social, and their metabolism should be measured on at least two levels: (i) the individual workers and brood of which the colony is composed and (ii) the colony in its entirety. Whole colony respiration, tempo (size‐free running speed in body lengths per second) and whole colony activity were simultaneously measured for 15 species of ants in four subfamilies, and these data are related to average worker and whole‐colony weight, activity, percentage brood and percentage fat. Across all 15 species, whole colony respiration rate (μL CO₂ h^?1) is linearly related to whole colony live weight (log–log slope = 1.0). Colonies composed of large workers respire less than colonies composed of an equal live weight of small workers, and colonies with high tempos respire more than lower tempo colonies of equal weight. The tempos and respiration rates of smaller ants tend to be higher, and a higher tempo exacts a cost in higher respiration independent of the effect of small body size. Individual worker respiration (μL CO₂ h^?1) scales to worker live weight with an exponent of 0.76. Whole colony specific respiration rate (μL CO₂ g^?1 h^?1) is unrelated to colony live weight. The regressions of respiration rates against colony and worker dry weight, lean weight and metabolic weight have similar slopes to those of live weight but different intercepts. Respiration is not related to worker percentage fat, percentage brood or activity. Ant ecology, tempo, body size, polymorphism and colony size are discussed in relation to respiration.     

Seasonal Growth and Photosynthetic Performance of the Antarctic Macroalga Desmarestia menziesii (Phaeophyceae) Cultivated under Fluctuating Antarctic Daylengths

Growth, photosynthesis, dark respiration and pigment contents were monitored in adult sporophytes of the Antarctic brown alga Desmarestia menziesii J. Agardh grown under fluctuating Antarctic daylength conditions. Growth rates were closely coupled to daylength variations with values varying from 0.05% d^?1 in winter condition (July-August) to 0.5% d^?1 in early summer (December). Photosynthetic pigments had maximum values of 1.8 mg g^?1 FW (chlorophyll a), 0.4 mg g^?1 FW (chlorophyll c) and 0.9 mg g^?1 FW (fucoxanthin) in summer. These changes were also closely related to individual size and biomass of the plants. Net photosynthesis (P_max), on a fresh weight basis, showed a clear seasonal pattern with highest rates of 25μmol O₂ g^?1 FW h^?1 in October and minima close to 9μmol O₂ g^?1 FW h^?1 in April. Dark respiration was high in spring (13μmol O₂ g^?1 FW h^?1) approximately coinciding with growth peaks. Likewise, photosynthetic efficiency (α) and the initial saturating light point of photosynthesis (l_k) increased significantly in spring [1.3 μimol O₂ g^?1 FW h^?1 (μmol m^?2 s^?1)^?1 and 26μmol photons m^?2 s^?1, respectively]. In the case of α, no significant differences between fresh weight and Chl a based rates were found. The results of the present study are the first that demonstrate seasonality of physiological parameters in D. menziesii sporophytes and confirm also that phenology and physiology of macroalgae can be simulated in the laboratory. On the other hand this study adds new elements to the explanation of the life strategy of D. menziesii, in particular that algal growth and photosynthesis occur under a programmed seasonal pattern.     

Growth of Ecklonia cava (Laminariales, Phaeophyta) sporophytes transplanted to a locality with different temperature conditions

Transplanting experiments were carried out to determine whether the small type sporophytes with short stipe of Ecklonia cava Kjellman (Laminariales, Phaeophyta) growing in a locality with warm temperatures, change into larger type with a long stipe when transplanted to a locality with cooler temperatures. Juvenile E. cava sporophytes, having a stipe shorter than 5 cm long were collected from Tei in Tosa Bay (southern Japan) (seawater temperature 15–29°C) and transplanted to Nabeta Bay (central Japan) (seawater temperature 13–25°C), where larger type E. cava sporophytes characterized by long stipe (ca 1 m) grow. They were attached to artificial reefs at the sea bottom (9 m depth) in Nabeta Bay to monitor their growth. For comparison, juvenile E. cava sporophytes of almost similar size growing in Nabeta Bay were also transplanted in the same way to the same experimental site. Observations of growth of sporophytes from Tei and Nabeta were carried out monthly for 2 years from November 1995 to October 1997. The transplanted Tei and Nabeta sporophytes showed an increase in stipe length and diameter from winter to spring, whereas almost no increase was observed during summer and autumn. At the end of the study period, the stipe of Nabeta sporophytes reached 25.6 cm in length and 17.0 mm in diameter, whereas that of Tei sporophytes reached 11.1 cm in length and 11.2 mm in diameter. The primary blade length was 16.0 cm in Nabeta sporophytes, whereas it was 5.5 cm in Tei sporophytes. Thus, Tei sporophytes still remained smaller than Nabeta sporophytes even under the same environmental conditions.