Effects of air pollutants on the photosynthetic capacity of young Norway spruce trees. Response of single needle age classes during and after different treatments with O3, SO2, or NO2

Summary Potted young Norway spruce trees were exposed to different concentrations of the air pollutants ozone, sulphur dioxide and nitrogen dioxide under completely controlled environmental conditions. After the treatment, the potted trees were kept outdoors. Measurements of the maximum photosynthetic capacity (A₂₅₀₀) were performed with current-year and 1-year-old needles during and after exposure of the trees. In trees fumigated with nitrogen oxides no damage was found at the concentrations used, and the trees' ability to fix carbon dioxide was increased. Using SO₂, a rapid and marked decrease in A₂₅₀₀ was obtained within the first days of the experiment. This decrease did not continue further, but was reversed upon cessation of the fumigation. However, a clear dose-dependent decrease in A₂₅₀₀ occurred when trees were fumigated continuously with an ozone concentration of 450 nl l^–1 or more. The effect of ozone was not reversible, but continued during post-culture of the trees.     

Evidence for NO-dependent vasodilation in the trout (Oncorhynchus mykiss ) coronary system

The effects of l-arginine, and its analogues N ^ω-nitro-l-arginine methyl ester and N ^ω-nitro-l-arginine on vascular resistance were investigated in the intact coronary system of an isolated non-working trout heart preparation. l-Arginine, at 10^–8 mol · l^–1induced a slight vasodilatory effect (max 10%). N ^ω-nitro-l-arginine methyl ester and N ^ω-Nitro-l-arginine in the range 10^–8–10^–4 mol · l^–1 caused dose-dependent increases in coronary resistance. The vasodilatory action of l-arginine was abolished when the preparation was pretreated with 10^–4 mol · l^–1 N ^ω-nitro-l-arginine or N ^ω-nitro-l-arginine methyl ester. Nitroprusside alone at 1 mmol · l^–1 induced a maximum vasodilation (30%) of the coronary system. Methylene blue a known inhibitor of guanylate cyclase, induced a strong vasoconstriction (already significant at 10^–5 mol · l^–1) and was able to overcome the vasodilative effect of nitroprusside. The endothelial nitric oxide agonists acetylcholine and serotonin, established in mammalian vessels, also mediate vasodilation in trout coronary system. In 50% of preparations, acetylcholine induced a biphasic response with vasodilation at low concentration (max 15% at 10^–8 mol · l^–1). Serotonin displayed a dose-response vasodilation in the range 10^–8–10^–4 mol · l^–1 (max 20%). These vasodilative effects were reduced or abolished by 10^–4 mol · l^–1 l-NA. These data support the existence of NO-mediated vasodilation mechanisms in the trout coronary system. Accepted: 1 July 1996     

Nutrition and the ozone sensitivity of birch (Betula pendula)

 Cuttings of a single birch clone (Betula pendula) were grown in field fumigation chambers throughout the growing season in either filtered air (control) or 90/40 nl O₃ l^–1 (day/night). Both regimes were split into plants under high and low nutrient supply (macro- and micronutrients). The stomatal density of leaves was increased by ozone but was lowered at high nutrition, while the inner air space was hardly affected by the treatments. Ozone induced macroscopic leaf injury regardless of nutrition, but leaf shedding was delayed in the low-fertilized plants, despite O₃ uptake being similar to that in high-fertilized plants. The leaf turn-over was enhanced in the O₃-exposed high-fertilized plants, but length growth and leaf formation of stems were not affected by ozone in either nutrient regime. Leaves of high-fertilized plants showed O₃-caused decline in photosynthetic capacity, water-use efficiency, apparent carbon uptake efficiency and quantum yield earlier as compared with low-fertilized plants, whereas chlorophyll fluorescence (F_V/F_M) and leaf nitrogen concentration were rather stable. CO₂ uptake rate and rubisco activity of young leaves compensated for the O₃ injury in the ageing leaves of the low-fertilized plants. In 8-week-old leaves, however, the O₃-induced decline in CO₂ uptake did not differ between the nutrient regimes and was associated with increased dark respiration rather than changed photorespiration. The balance between CO₂ supply and demand was lost, as was stomatal limitation on CO₂ uptake. High nutrition did not help leaves to maintain a high photosynthetic capacity and life span under O₃ stress. Received: 6 July 1996 / Accepted: 4 June 1997     

Insulin and glucagon immunoreactivity during high-intensity exercise under opiate blockade

Eight fit men [maximum oxygen consumption (O_2max) 64.6 (1.9) ml · kg⁻¹ · min⁻¹, aged 28.3 (1.7) years (SE in parentheses) were studied during two treadmill exercise trials to determine the effect of endogenous opioids on insulin and glucagon immunoreactivity during intense exercise (80% O_2max). A double-blind experimental design was used with subjects undertaking the two exercise trials in counterbalanced order. Exercise trials were 20 min in duration and were conducted 7 days apart. One exercise trial was undertaken following administration of naloxone (N; 1.2 mg; 3 ml) and the other after receiving a placebo (P; 0.9% NaCl saline; 3 ml). Prior to each experimental trial a flexible catheter was placed into an antecubital vein and baseline blood samples were collected. Immediately after, each subject received either a N or P bolus injection. Blood samples were also collected after 20 min of continuous exercise (running). Glucagon was higher (P < 0.05), while insulin was lower (P < 0.05), during exercise compared with pre-exercise values in both trials. However, glucagon was higher (P < 0.05) in the P than in the N exercise trial [141.4 (8.3) ng · l⁻¹ vs 127.2 (7.6) ng · l⁻¹]. There were no differences in insulin during exercise between the P and N trials [50.2 (4.3) pmol · l⁻¹ vs 43.8 (5) pmol · l⁻¹]. These data suggest that endogenous opioids may augment the glucagon response during intense exercise. Accepted: 15 June 1996     

Assimilation,allocation and utilization of carbon by 3-year-old Scots pine (Pinus sylvestris L .) trees during winter and early spring

 The photosynthetic capacity of frost-hardy and frost-sensitive needles of 3-year-old Scots pines and the allocation and utilization of assimilated carbon was examined during winter and early spring. The photosynthates of the whole trees were labelled by ¹⁴CO₂ fixation and after chase periods of from 7 days to 4 months under natural climatic conditions, the distribution of radiocarbon in the various tissues of the trees was determined. During winter maximal photosynthetic rates of 1-year-old needles were considerably lower than in summer when calculated on a leaf area basis. However, when related to the chlorophyll content these discrepancies disappeared. The decrease of the photosynthetic capacity upon frost-hardening could be attributed to a two- to three-fold reduction in the chlorophyll content of the needles. The pulse-chase experiments showed that photosynthesis during the cold season preferentially provides substrates for respiration. Half of the assimilated ¹⁴C was respired during the first week, and after chase periods of 3 – 4 months the trees contained not more than 10 – 20% of the radiocarbon. The carbon, which was exported by the needles, was translocated basipetally via the twigs and the stem to the roots. Whereas in the axial system incorporation of radiocarbon into storage compounds, like starch, and into cell wall material was almost negligible during the cold season, in the roots one-third of the radiocarbon was recovered from starch 2 months after the ¹⁴C-pulse. In contrast to the above-ground parts of the trees, where starch content was very low during winter, in the roots considerable amounts of starch, up to 450 μmol hexose units · g^– 1 DW, were found even during mid-winter. In early spring the radiocarbon in the cell wall-, lipid-, and starch-fraction accounted for more than 80% of the ¹⁴C recovered at that time from the axial system. Incorporation of minor quantities into the cell wall fraction of the roots during winter and early spring indicate continuous root growth during the cold period as well as in early spring. Whereas during winter the buds did not attract freshly assimilated carbon, in spring just before bud break substantial amounts of carbon were translocated from the needles into the buds. In contrast, remobilization of carbon, which had been assimilated during autumn of the previous year, and import into the sprouting buds could not be demonstrated. Received: 3 November 1995 / Accepted: 1 March 1996     

Volume changes in the forearm and lower limbs during 2 h of acute hypobaric hypoxia in nonacclimatized subjects

 To investigate the role of fluid shifts during the short-term adjustment to acute hypobaric hypoxia (AHH), the changes in lower limb (LV) and forearm volumes (FV) were measured using a strain-gauge plethysmograph technique in ten healthy volunteers exposed to different altitudes (450 m, 2500 m, 3500 m, 4500 m) in a hypobaric chamber. Arterial blood pressure, heart rate, arterial oxygen saturation (S _aO₂), endtidal gases, minute ventilation and urine flow were also determined. A control experiment was performed with an analogous protocol under normobaric normoxic conditions. The results showed mean decreases both in LV and FV of −0.52 (SD 0.39) ml · 100 ml⁻¹ and −0.65 (SD 0.32) ml · 100 ml⁻¹, respectively, in the hypoxia experiments [controls: LV −0.28 (SD 0.37), FV −0.41 (SD 0.47) ml · 100 ml⁻¹]. Descent to normoxia resulted in further small but not significant decreases in mean LV [−0.02 (SD 0.11) ml · 100 ml⁻¹], whereas mean FV tended to increase slightly [ + 0.02 (SD 0.14) ml · 100 ml⁻¹]; in the control experiments mean LV and FV decreased continuously during the corresponding times [−0.19 (SD 0.31), −0.18 (SD 0.10) ml · 100 ml⁻¹, respectively]. During the whole AHH, mean urine flow increased significantly from 0.84 (SD 0.41) ml · min⁻¹ to 3.29 (SD 1.43) ml · min⁻¹ in contrast to the control conditions. We concluded that peripheral fluid volume shifts form a part of the hypoxia-induced acute cardiovascular changes at high altitude. In contrast to the often reported formation of peripheral oedema after prolonged exposure to hypobaric hypoxia, the results provided no evidence for the development of peripheral oedema during acute induction to high altitude. However, the marked increase in interindividual variance in S _aO₂ and urine flow points to the appearance of the first differences in the short-term adjustment even after 2 h of acute hypobaric hypoxia. Accepted: 27 August 1996     

Atmospheric CO2 concentration, N availability, and water status affect patterns of ergastic substance deposition in longleaf pine (Pinus palustris Mill.) foliage

 Leaf chemistry alterations due to increasing atmospheric CO₂ will reflect plant physiological changes and impact ecosystem function. Longleaf pine was grown for 20 months at two levels of atmospheric CO₂ (720 and 365 μmol mol^–1), two levels of soil N (4 g m^–2 year^–1 and 40 g m^–2 year^–1), and two soil moisture levels (– 0.5 and – 1.5 MPa) in open top chambers. After 20 months of exposure, needles were collected and ergastic substances including starch grains and polyphenols were assessed using light microscopy, and calcium oxalate crystals were assessed using light microscopy, scanning electron microscopy, and transmission electron microscopy. Polyphenol content was also determined using the Folin-Denis assay and condensed tannins were estimated by precipitation with protein. Evaluation of phenolic content histochemically was compared to results obtained using the Folin-Denis assay. Total leaf polyphenol and condensed tannin content were increased by main effects of elevated CO₂, low soil N and well-watered conditions. Elevated CO₂ and low soil N decreased crystal deposition within needle phloem. Elevated CO₂ had no effect on the percentage of cells within the mesophyll, endodermis, or transfusion tissue which contained visible starch inclusions. With respect to starch accumulation in response to N stress, mesophyll > endodermis > transfusion tissue. The opposite was true in the case of starch accumulation in response to main effects of water stress: mesophyll < endodermis < transfusion tissue. These results indicate that N and water conditions significantly affect deposition of leaf ergastic substances in longleaf pine, and that normal variability in leaf tissue quality resulting from gradients in soil resources will be magnified under conditions of elevated CO₂. Received: 5 November 1996 / Accepted: 7 March 1997     

Responses of Photosynthesis,Carbohydrates and Antioxidants in Needles of Norway Spruce to Slow and Rapid Changes in Ozone

The goal of the present study was to examine the effects of slow and rapid changes of ozone (O₃) concentrations on the physiological behaviour of current-year needles of Norway spruce (Picea abies (L.) Karst.). For this purpose five-year-old spruce seedlings were exposed in growth chambers for 49 days to either charcoal-filtered air, slowly increasing O₃ concentrations from zero up to 100 nl I^?1 in weekly steps of 25 nl I^?1, or immediately to 100 nl I^?1 of O₃. During the investigation period gas exchange, carbohydrate and antioxidant contents of the current flush were measured. In needles which experienced slowly increasing O₃ concentrations, cumulative O₃ uptake was approximately 30 % lower than in needles continuously fumigated with 100 nl I^?1 of O₃. The higher 0₃ uptake in the permanent 100 nl I^?1 O₃ treatment caused a pronounced decline in net photosynthesis, in the efficiency of CO₂ uptake and in the starch content of the seedlings. Initially the ascorbate pool increased, but after 5 weeks of exposure ascorbate concentrations declined and were comparable to values obtained in charcoal-filtered controls, while the thiol contents were enhanced during fumigation with permanent 100 nl I-^?1 O₃. On the contrary, slowly increasing O₃ caused a significant increase in total needle ascorbate throughout the fumigation period, which probably prevented an O₃-induced decline in the photosynthetic machinery as photosynthesis was not affected although the thiol contents were not enhanced. Furthermore, starch content was slightly higher than in O₃-free controls. These results suggest that seedlings of Norway spruce have the possibility to acclimate to O₃ stress, as slowly increasing O₃ concentrations seemed to increase resistance and the seedlings were able to compensate.     

Needle CO2 exchange, structure and defense traits in relation to needle age in Pinus heldreichii Christ – a relict of Tertiary flora

 Pinus heldreichii Christ is a long-lived, slow-growing Tertiary relict from the Balkans. In this study we evaluated the physiological characteristics of eight needle-age classes of P. heldreichii grown at the Arboretum of the Institute of Dendrology in Kórnik, Poland. At the end of the growing season, current-year foliage had the highest rates of mass-based light-saturated net photosynthesis (A_sat) of 33.5 nmol CO₂· g^–1· s^–1. A_sat decreased with needle age, but older needle classes retained from approximately 62 to 26% of the current needles’ rate. The relationship between leaf N and chlorophyll a concentration among all needle-age classes was highly significant (r = 0.96, P = 0.0006). The variation in A_sat of 1- to 7-year-old needles was linearly related to needle N concentration (r = 0.98, P = 0.0001). Needle dark respiration rates among these needle age classes ranged from 0.8 to 2.2 nmol · g^–1· s^–1 and decreased with needle age and nitrogen concentration. Total phenols and glucose concentrations increased linearly with needle age. A similar pattern was observed in acid buffering capacity and the pH of tissue homogenates. The water content ranged from 62% for the current needles to 51% for the 6-year-old needles. Greater investment in leaf structural tissue and increased chemical defense is associated with higher structural cost of older needles and may reduce their photosynthetic activity. Significant declines in water and nitrogen content with needle age and an increase in content of phenolics is most likely a defense adaptation of P. heldreichii related to the species’ long-lived leaves. Received: 8 January 1997 / Accepted: 4 March 1997     

Light microscopic structure of needles of Scots pine (Pinus sylvestris L.) in relation to air pollution and needle element concentrations in S.E. Finland and the Karelian Isthmus, N.W. Russia

 The mesophyll structure of current and second year needles of mature Scots pines (Pinus sylvestris L.), growing on a survey line from the Karelian Isthmus (N.W. Leningrad region, Russia) to S.E. Finland, was studied at the light microscopic level in 1992 and 1994. The area is affected by sulphur dioxide and nitrogen oxide emissions from Russia (200  000–285 000 ton/year SO₂ and about 100  000 ton/year NO_X), Estonia (140  000–320  000 ton/year SO₂ and 30  000–50  000 ton/year NO_X) and Finland (6000–9000 ton/year SO₂ and 23 000–25 000 ton/year NO_X) and by unknown amounts of neutralizing compounds from Estonia. Mean concentrations of SO₂ were between 1.0 and 1.5 μg m^–3 and those of ozone between 52 and 61 μg m^–3 during growing seasons of 1991–1994. The concentrations tended to be lower in 1993/94 than in 1991/92. The results showed cellular changes related to exposure to sulphur dioxide, ozone and acid wet deposition. The percentage of cells with injuries related to acid deposition was higher in 1994 than in 1992, possibly due to higher reduction of neutralizing than of acidifying compounds in the main emission areas, while the percentage of cells with injuries related to sulphur dioxide correlated positively with needle sulphur concentrations and showed a declining trend between Karelian Isthmus and S.E. Finland in the needles sampled in 1992. These changes and those related to ozone were considerably less numerous in 1994 than in 1992, possibly on account of the lower concentrations of SO₂ and ozone in 1993/94 than in 1991/92, especially in early summer, the time of the most sensitive phase of needle growth. In addition, periods of lower wet deposition in summer 1992, and considerably lower temperatures in autumn/winter 1992 than in 1994 may have enhanced the injuries in the needles collected in October/December 1992, relative to those collected in 1994. The results of the microscopic work agreed well with the simultaneous chemical measurements, pointing to the usefulness of cellular analysis for diagnostic work in the field. Received: 26 September 1997 / Accepted: 24 November 1997     

Reduced performance of male and female athletes at 580 m altitude

This study examined the effect of mild hypobaria (MH) on the peak oxygen consumption (O_2peak) and performance of ten trained male athletes [ (SEM); O_2peak = 72.4 (2.2) ml · kg⁻¹ · min⁻¹] and ten trained female athletes [O_2peak = 60.8 (2.1) ml · kg⁻¹ · min⁻¹]. Subjects performed 5-min maximal work tests on a cycle ergometer within a hypobaric chamber at both normobaria (N, 99.33 kPa) and at MH (92.66 kPa), using a counter-balanced design. MH was equivalent to 580 m altitude. O_2peak at MH decreased significantly compared with N in both men [− 5.9 (0.9)%] and women [− 3.7 (1.0)%]. Performance (total kJ) at MH was also reduced significantly in men [− 3.6 (0.8)%] and women [− 3.8 (1.2)%]. Arterial oxyhaemoglobin saturation (S_aO₂) at O_2peak was significantly lower at MH compared with N in both men [90.1 (0.6)% versus 92.0 (0.6)%] and women [89.7 (3.1)% versus 92.1 (3.0)%]. While S_aO₂ at O_2peak was not different between men and women, it was concluded that relative, rather than absolute, O_2peak may be a more appropriate predictor of exercise-induced hypoxaemia. For men and women, it was calculated that 67–76% of the decrease in O_2peak could be accounted for by a decrease in O₂ delivery, which indicates that reduced O₂ tension at mild altitude (580 m) leads to impairment of exercise performance in a maximal work bout lasting ≈ 5 min. Accepted: 30 July 1996     

Walking performance and economy in chronic heart failure patients pre and post exercise training

The effect of a 3-week exercise programme on performance and economy of walking was analysed in 16 male patients with chronic heart failure [mean age 51.8 (SD 6.9) years, height 174.9 (SD 6.3) cm, body mass 75.3 (SD 11.5) kg, ejection fraction 20.8 (SD 5.0)%]. They were submitted to a cardiopulmonary exercise test on a cycle ergometer and a 6-min walking test on a treadmill before and after the period of exercise training. The training programme consisted of interval cycle (five times a week for 15 min), and treadmill ergometer training (three times a week for 10 min) at approximately 70% cycling peak oxygen uptake (O_2peak) and supplementary exercises (three times a week for 20 min). Compared to the pre values cycling O_2peak [11.9 (SD 2.9) vs 14.0 (SD 2.3) ml ·  kg^–1 · min^–1], maximal self paced walking speed [0.68 (SD 0.33) vs 1.16 (SD 0.30) m · s^–1], and net walking power [2.16 (SD 0.89) vs 2.73 (SD 0.91) W · kg^–1] had increased (P < 0.01) while net energy cost [3.31 (SD 0.66) vs 2.33 (SD 0.38) J · kg^–1 ·  m^–1] had decreased (P < 0.001) after the training period. Approximately 42% of the increase of walking speed resulted from a higher walking power output, whereas approximately 58% corresponded to a positive effect on walking economy. The improvement in walking economy was a function of an increase in walking velocity itself and a result of a more efficient walking technique. These results would indicate that in patients with marked exercise intolerance, adequate exercise training programmes could contribute to favourable metabolic changes with positive effects on the economy of motion. Accepted: 29 August 1996     

The relationship between plasma potassium concentration and muscle torque during recovery following intense exercise

The present study investigated the relationship between plasma potassium ion concentration ([K⁺]) and skeletal muscle torque during three different 15-min recovery periods after fatigue induced by four 30-s sprints. Four males and one female completed the multiple sprint exercise on three separate days; recovery was passive, i.e. no cycling exercise (PRec), active cycling at 30% peak oxygen consumption O_2peak (30% Rec) and active cycling at 60% O_2peak (60% Rec). Plasma [K⁺] was measured from blood sampled from an antecubital vein of subjects at rest and at 0, 3, 5, 10 and 15 min into each recovery. Isokinetic leg strength was measured at rest and at 1, 6, 11 and 16 min during each recovery. Following the exhaustive sprints, [K⁺] increased significantly from an average mean (SEM) resting value of 3.81 (0.07) mmol · l⁻¹ to 4.48 (0.19) mmol · l⁻¹ (P < 0.01). In all recovery conditions, plasma [K⁺] returned to resting levels within 3 min following the fourth sprint. However, in the two active recovery conditions plasma [K⁺] increased over the remainder of the recovery periods to 4.36 (0.12) mmol · l⁻¹ in the 30% Rec condition and 4.62 (0.12) mmol · l⁻¹ in the 60% Rec condition, the latter being significantly higher than the former (P < 0.01). The maximum torque measured following the sprints decreased significantly, on average, to 61.1 (8.36)% of peak levels (P < 0.01). After 15 min of recovery, maximum torque was highest in the 30% Rec condition at 92.13 (3.06)% of peak levels (P < 0.01), compared to 85.23 (3.64)% and 85.71 (0.82)% for the PRec and 60% Rec conditions, respectively. In contrast to the significant differences in plasma [K⁺] across all three recovery conditions, muscle torque recovery was significantly different in only the 30% Rec condition. In summary, recovery of peak levels of muscle torque following fatiguing exercise does not appear to follow changes in plasma [K⁺]. Accepted: 18 October 1996     

Will rising atmospheric CO2 affect leaf litter quality and in situ decomposition rates in native plant communities?

Though field data for naturally senesced leaf litter are rare, it is commonly assumed that rising atmospheric CO₂ concentrations will reduce leaf litter quality and decomposition rates in terrestrial ecosystems and that this will lead to decreased rates of nutrient cycling and increased carbon sequestration in native ecosystems. We generally found that the quality of␣naturally senesced leaf litter (i.e. concentrations of C, N and lignin; C:N, lignin:N) of a variety of native plant species produced in alpine, temperate and tropical communities maintained at elevated CO₂ (600–680 μl l⁻¹) was not significantly different from that produced in similar communities maintained at current ambient CO₂ concentrations (340–355 μl l⁻¹). When this litter was allowed to decompose in situ in a humid tropical forest in Panama (Cecropia peltata, Elettaria cardamomum, and Ficus benjamina, 130 days exposure) and in a lowland temperate calcareous grassland in Switzerland (Carex flacca and a graminoid species mixture; 261 days exposure), decomposition rates of litter produced under ambient and elevated CO₂ did not differ significantly. The one exception to this pattern occurred in the high alpine sedge, Carex curvula, growing in the Swiss Alps. Decomposition of litter produced in situ under elevated CO₂ was significantly slower than that of litter produced under ambient CO₂ (14% vs. 21% of the initial litter mass had decomposed over a 61-day exposure period, respectively). Overall, our results indicate that relatively little or no change in leaf litter quality can be expected in plant communities growing under soil fertilities common in many native ecosystems as atmospheric CO₂ concentrations continue to rise. Even in situations where small reductions in litter quality do occur, these may not necessarily lead to significantly slower rates of decomposition. Hence in many native species in situ litter decomposition rates, and the time course of decomposition, may remain relatively unaffected by rising CO₂. Received: 12 September 1996 / Accepted: 30 November 1996     

Exercise-induced oxyhemoglobin desaturation and pulmonary diffusing capacity during high-intensity exercise

The purpose of this investigation was to examine if exercise-induced arterial oxyhemoglobin desaturation selectively observed in highly trained endurance athletes could be related to differences in the pulmonary diffusing capacity (D _L) measured during exercise. The D _L of 24 male endurance athletes was measured using a 3-s breath-hold carbon monoxide procedure (to give D _LCO) at rest as well as during cycling at 60% and 90% of these previously determined O_2max. Oxyhemoglobin saturation (S _aO₂%) was monitored throughout both exercise protocols using an Ohmeda Biox II oximeter. Exercise-induced oxyhemoglobin desaturation (DS) (S _aO₂% < 91% at O_2max) was observed in 13 subjects [88.2 (0.6)%] but not in the other 11 nondesaturation subjects [NDS: 92.9 (0.4)%] (P ≤ 0.05), although O_2max was not significantly different between the groups [DS: 4.34 (0.65) l / min vs NDS: 4.1 (0.49) l / min]. At rest, no differences in either D _LCO [m1 CO · mmHg⁻¹ · min⁻¹: 41.7 (1.7) (DS) vs 41.1 (1.8) (NDS)], D _LCO / _A [8.2 (0.4) (DS) vs 7.3 (0.9) (NDS)], MVV [l / min: 196.0 (10.4) (DS) vs 182.0 (9.9) (NDS)] or FEV₁/FVC [86.3 (2.2) (DS) vs 82.9 (4.7) (NDS)] were found between groups (P ≥ 0.05). However, _E /O₂ at O_2max was lower in the DS group [33.0 (1.1)] compared to the NDS group [36.8 (1.5)] (P ≤ 0.05). Exercise D _LCO (m1 CO · mmHg⁻¹ · min⁻¹) was not different between groups at either 60% O_2max [DS: 55.1 (1.4) vs NDS: 57.2 (2.1)] or at 90% O_2max [DS: 61.0 (1.8) vs NDS: 61.4 (2.9)]. A significant relationship (r = 0.698) was calculated to occur between S _aO₂% and _E /O₂ during maximal exercise. The present findings indicate that the exercise-induced oxyhemoglobin desaturation seen during submaximal and near-maximal exercise is not related to differences in D _L, although during maximal exercise S _aO₂ may be limited by a relatively lower exercise ventilation. Accepted: 25 September 1996     

Assessing the impact of ozone on photosynthesis of European beech (Fergus sylvatica L.) in environmental chambers

An exposure — response study with proportionalto-ambient ozone levels was conducted in closed chambers on 3-year-old European beech (Fagus sylvatica L.) of montane origin. The fumigation started in April 1990 and lasted for a single growing season. Climate data and ozone concentrations monitored at an experimental station of the Institute for Applied Plant Biology, Schönenbuch, Switzerland were simulated in the exposure chambers 12 days later (1*O₃). To test exposure-response relations three additional treatments were applied, subambient (0.2*O₃) and two proportionally increased ozone treatments (1.5*O₃ and 2*O₃). The photosynthetic behaviour of the trees in August revealed the light reactions to be less affected than parameters which are related to the dark reactions of photosynthesis. Assimilation (A₃₅₀), apparent carboxylation efficiency (CE), and maximum photosynthetic capacity (A₂₅₀₀) were reduced with increasing ozone concentration. For the ozone response of CE and A₂₅₀₀ Critical Levels were calculated.     

Effect of circulatory occlusion on human muscle metabolism during exercise and recovery

To assess muscle metabolism and inorganic phosphate (P_i) peak splitting during exercise, 31-phosphorus nuclear magnetic resonance spectroscopy was performed during ramp incremental and submaximal step exercise with and without circulatory occlusion. Seven healthy men performed calf flexion in a superconducting magnet. There was no P_i splitting during ramp incremental exercise with the circulation present and phosphocreatine (PCr) decreased linearly by 0.07 (SEM 0.01) mmol · l⁻¹ · s⁻¹, while exercise with the circulation occluded caused the P_i peak to split into a high and a low pH peak. The rate of PCr decrease during exercise with the circulation occluded was 0.15 (SEM 0.03) mmol · l⁻¹ · s⁻¹ which with the efficiency of the adenosine 5′-triphosphate (ATP) hydrolysis reaction corresponded well to the mechanical energy. Both with and without occlusion of the circulation PCr decreased with some time lag which may reflect the consumption of residual oxygen. In submaximal step exercise PCr decreased exponentially at the onset of exercise with the circulation open whereas it decreased linearly by 0.15␣mmol · l⁻¹ · s⁻¹ when the circulation was occluded. After exercise, occlusion of the circulation was maintained for 1 min more and there was no PCr resynthesis. It is suggested that ATP synthesis was limited by the availability of oxygen. Accepted: 14 August 1996     

Winter production of CO2 and N2O from alpine tundra: environmental controls and relationship to inter-system C and N fluxes

Fluxes of CO₂ and N₂O were measured from both natural and experimentally augmented snowpacks during the winters of 1993 and 1994 on Niwot Ridge in the Colorado Front Range. Consistent snow cover insulated the soil surface from extreme air temperatures and allowed heterotrophic activity to continue through much of the winter. In contrast, soil remained frozen at sites with inconsistent snow cover and production did not begin until snowmelt. Fluxes were measured when soil temperatures under the snow ranged from –5°C to 0°C, but there was no significant relationship between flux for either gas and temperature within this range. While early developing snowpacks resulted in warmer minimum soil temperatures allowing production to continue for most of the winter, the highest CO₂ fluxes were recorded at sites which experienced a hard freeze before a consistent snowpack developed. Consequently, the seasonal flux of CO₂ –C from snow covered soils was related both to the severity of freeze and the duration of snow cover. Over-winter CO₂ –C loss ranged from 0.3 g C m⁻² season⁻¹ at sites characterized by inconsistent snow cover to 25.7 g C m⁻² season⁻¹ at sites that experienced a hard freeze followed by an extended period of snow cover. In contrast to the pattern observed with C loss, a hard freeze early in the winter did not result in greater N₂O–N loss. Both mean daily N₂O fluxes and the total over-winter N₂O–N loss were related to the length of time soils were covered by a consistent snowpack. Over-winter N₂O–N loss ranged from less 0.23 mg N m⁻² from the latest developing, short duration snowpacks to 16.90 mg N m⁻² from sites with early snow cover. These data suggest that over-winter heterotrophic activity in snow-covered soil has the potential to mineralize from less than 1% to greater than 25% of the carbon fixed in ANPP, while over-winter N₂O fluxes range from less than half to an order of magnitude higher than growing season fluxes. The variability in these fluxes suggests that small changes in climate which affect the timing of seasonal snow cover may have a large effect on C and N cycling in these environments. Received: 5 April 1996 / Accepted: 25 November 1996     

Adaptive responses of aglomerular toadfish to dilute sea water

Plasma and urine of toadfish (Opsanus tau) in sea water and 10% sea water were analyzed to assess responses of an aglomerular fish to hypoosmotic challenge. Following transfer to 10% sea water, plasma osmotic pressure decreased slowly from 318 to 241 mmol · kg H₂O⁻¹, over a period of 10–15 days. Urine osmotic pressure decreased in parallel from 299 to 207 mmol · kg H₂O⁻¹, leaving urine/plasma ratios of osmotic pressure essentially unchanged. In contrast, the volume and composition of urine changed rapidly following transfer to 10% sea water. Urine flow rate increased 110% from 3.0 to 6.3 μl · 100g⁻¹ · h⁻¹ and Na⁺ excretion increased 346%, while excretion of Mg²⁻ and SO₄ ²⁻ decreased 81% and 90%, respectively. Excretion rates for Cl⁻ were low in seawater toadfish and decreased further in 10% sea water. An unknown sulfur-containing anion, present in the urine of seawater toadfish, contributed significantly to the composition and ionic balance in urine of toadfish in 10% sea water. These results suggest that the inability to produce strongly dilute urine obliges toadfish to lose salt in order to excrete water, in hypoosmotic media. The decrease in plasma osmotic pressure may be both a strategy to reduce osmotic and ionic gradients in dilute media and a consequence of the kidney's inability to excrete water without salt. Accepted: 22 August 1996     

Kinetic studies on the reactions of Fusarium galactose oxidase with five different substrates in the presence of dioxygen

 Reactions (25  °C) of galactose oxidase, GOase_ox from Fusarium NRRL 2903 with five different primary-alcohol-containing substrates RCH₂OH:- D-galactose (I) and 2-deoxy-d-galactose (II) (monosaccharides); methyl-β-d-galactopyranoside (III) (glycoside);d-raffinose (IV) (trisaccharide); and dihydroxyacetone (V) have been studied in the presence of O₂. The GOase_ox state has a tyrosyl radical coordinated at a square-pyramidal Cu^II active site, and is a two-equivalent oxidant. Reactant concentrations were [GOase_ox] (0.8–10 μM), RCH₂OH (1.0–6.0 mM), and O₂ (0.14–0.29 mM), with I=0.100 M (NaCl). The reactions, monitored at 450 nm by stopped-flow spectrophotometry, terminated with depletion of the O₂. Each trace was fitted to the competing reactions GOase_ox+RCH₂ OH → GOase_redH₂+RCHO (k ₁), and GOase_redH₂+O₂→ GOase_ox+H₂O₂ (k ₂), with GOase_redH₂ written as the doubly protonated two-electron-reduced Cu^I product. It was necessary to avoid auto-redox interconversion of GOase_ox and GOase_semi . Information obtained at pH 7.5 indicates a 5 : 95 (ox : semi) "native" mix equilibration complete in ∼3 h. At pH >7.5, rate constants 10^–4 k ₁ / M^–1 s^–1 for the reactions of GOase_ox with (I) (1.19), (II) (1.07), (III) (1.29), (IV) (1.81), (V) (2.94) were determined. On decreasing the pH to 5.5, k ₁ values decreased by factors of up to a half, and acid dissociation pK _as in the range 6.6–6.9 were obtained. UV-Vis spectrophotometric studies on GOase_ox gave an independently determined pK _a of 6.7. No corresponding reactions of the Tyr495Phe variant were observed, and there are no similar UV-Vis absorbance changes for this variant. The pK _a is therefore assigned to protonation of Tyr-495 which is a ligand to the Cu. The rate constant k ₂ (1.01×10⁷ M^–1 s^–1) is independent of pH in the range 5.5–9.0 investigated, suggesting that H⁺ (or H-atoms) for the O₂ → H₂O₂ change are provided by the active site of GOase_red . The Cu^I of GOase_red is less extensively complexed, and a coordination number of three is likely. Received: 4 February 1997 / Accepted: 16 May 1997