Nmol CO2 Research Articles

Effects of leaf, shoot and fruit development on photosynthesis of lychee trees (Litchi chinensis).

Changes in gas exchange with leaf age and fruit growth were determined in lychee trees (Litchi chinensis Sonn.) growing in subtropical Queensland (27 degrees S). Leaves expanded in a sigmoid pattern over 50 days during spring, with net CO2 assimilation (A) increasing from -4.1 +/- 0.9 to 8.3 +/- 0.5 micromol m-2 s-1 as the leaves changed from soft and red, to soft and light green, to hard and dark green. Over the same period, dark respiration (Rd) decreased from 5.0 +/- 0.8 to 2.0 +/- 0.1 micromol CO2 m-2 s-1. Net CO2 assimilation was above zero about 30 days after leaf emergence or when the leaves were half fully expanded. Chlorophyll concentrations increased from 0.7 +/- 0.2 mg g-1 in young red leaves to 10.3 +/- 0.7 mg g-1 in dark green leaves, along with stomatal conductance (gs, from 0.16 +/- 0.09 to 0.47 +/- 0.17 mol H2O m-2 s-1). Fruit growth was sigmoidal, with maximum values of fresh mass (29 g), dry mass (6 g) and fruit surface area (39 cm2) occurring 97 to 115 days after fruit set. Fruit CO2 exchange in the light (Rl) and dark (Rd) decreased from fruit set to fruit maturity, whether expressed on a surface area (10 to 3 micromol CO2 m-2 s-1 and 20 to 3 micromol CO2 m-2 s-1, respectively) or on a dry mass basis (24 to 2 nmol CO2 g-1 s-1 and 33 to 2 nmol CO2 g-1 s-1, respectively). Photosynthesis never exceeded respiration, however, the difference between Rl and Rd was greatest in young green fruit (4 to 8 micromol CO2 m-2 s-1). About 90% of the carbon required for fruit growth was accounted for in the dry matter of the fruit, with the remainder required for respiration. Fruit photosynthesis contributed about 3% of the total carbon requirement of the fruit over the season. Fruit growth was mainly dependent on CO2 assimilation in recently expanded dark green leaves.

Stem growth and respiration in loblolly pine plantations differing in soil resource availability.

Stem respiration and growth in 10-year-old loblolly pine (Pinus taeda L.) plantations were measured monthly during the third year of fertilization and irrigation treatments to determine whether soil resource availability differentially altered growth and respiration in stem tissue. Fertilized trees had significantly greater stem biomass, stem nitrogen concentration ([N]) and growth rate than unfertilized trees. Stem respiration (Rt) was significantly greater in fertilized trees when expressed on a per unit surface area (Rt,a, micromol CO2 m-2 s-1), sapwood volume (Rt,v, micromol CO2 m-3 s-1), or mass (Rt,w, nmol CO2 g-1 s-1) basis; however, there was no difference between treatments when expressed as a function of stem N content (Rt,n, micromol CO2 (mol N)-1 s-1). Irrigation had no significant effect on Rt or annual stem growth. Daily total respiration (Rd, mol CO2 m-2 day-1) and stem diameter growth both had a seasonal bimodal pattern with peaks in early spring and midsummer. Stem [N] declined significantly during the growing season. Stem growth rate and [N] explained 75% of the seasonal variation in temperature-normalized Rt,a. The mature tissue method was used to partition total stem respiration (Rt) into maintenance (Rm) and growth (Rg) components. There was a linear correlation between winter Rt,v, a measure of basal Rm, and sapwood N content; however, Rt,v per unit N was greater in January before diameter growth started than in the following December after growth ceased, indicating that Rt,v declined as stem diameter increased. Consequently, estimates of annual maintenance respiration (RM) based on January data were 44% higher than estimates based on December data. Growth respiration was correlated with stem growth rate (r2 = 0.55). The growth respiration coefficient (rg)-the slope of the relationship between Rg and stem growth rate-was 0.24. Respiration accounted for 37% of annual stem carbon budget. Stem carbon-use efficiency (CUE)-the ratio of stem growth to stem growth plus respiration-averaged 0.63 and was unaffected by fertilization.

Size-fractionated Carboxylase Activities During a 32 h Cycle at 30 m Depth in the North-western Mediterranean Sea After an Episodic Wind Event

Using size-fractionation filtration (1 μm), we associated carboxylase activities (Rubisco, β-carboxy-lases) and chlorophyll measurements with cell enumeration by flow cytometry at a permanent site of the central Ligurian Sea in the north-western Mediterranean Sea (73°25 1 N-7°51 'E). The analyses were carried out over a day/night cycle (at 30 m depth) following a strong wind event, during the transition period from spring mesotrophic to summer oligotrophic conditions. The highest values of Rubisco activity and β-carboxylase activity per chlorophyll a (Chl a) for >1 μm cells were observed during the light period of the cycle, reaching 18.9 and 4.3 nmol CO 2 (μg Chl a) -1 h -1 , respectively. This higher activity is assumed to be correlated with a dominance of nanoflagellates in the phytoplankton community Such phytoplankton species generally had higher β-carboxylase activity, expressed as a percentage of Rubisco activity (the βC/R ratio), than diatoms. Using flow cytometry analysis to enumerate those cells < 1 μm in size, we followed the values of Rubisco activity and pigment content expressed per cell, for picophytoplankton cells. The photoautotrophic activity, measured as the in vitro Rubisco activity for small picoeukaryote cells, was higher than for cyanobacteria cells with lower apparent cell size. These results suggested an optimum of CO 2 assimilation reached by the pico- and nano-phytoplankton in accordance with the cell size and growth rates from previous observations in the literature.

Metabolic differences between attached and free-living marine bacteria: inadequacy of liquid cultures for describing in situ bacterial activity

Marinobacter sp. strain CAB was cultivated with or without porous glass beads as solid support. Two substrates were used: the hydrophilic sodium lactate and a hydrophobic C 18-isoprenoid ketone (6,10,14-trimethylpentadecan-2-one (TMP)). The substrate adsorption onto the beads was measured. Bacterial adhesion was determined by a direct count technique and amounted to 70% of total cells. In the immobilised cell cultures (ICC), generation times were 1.5 and 1.8 times shorter than in the planktonic cultures (FCC) with sodium lactate and with TMP, respectively. In ICC, the growth yields were lower (15.3 FCC×10 9 and 0.8 ICC×10 9 bacteria mg −1 of sodium lactate; 50 FCC×10 9 and 35 ICC×10 9 bacteria mg −1 of TMP). The mineralisation of substrates was estimated after mass spectrometric determination of the CO 2 production rates of both free and immobilised cell cultures. The results indicated a higher specific CO 2 production rate in the ICC with sodium lactate (3.1 FCC±0.2 and 3.5 ICC±0.3 nmol CO 2 mg −1 protein min −1) but not in the ICC with TMP (1.9 FCC±0.7 and 0.5 ICC±0.3 nmol CO 2 mg −1 protein min −1). The affinities for the two substrates were lower in the presence of the solid support ( K m,ICC=18.2±0.2 μM and 37.1±2.0 μM, for sodium lactate and TMP, respectively) than without support ( K m,FCC=8.5±1.5 μM and 8.4±1.2 μM, for sodium lactate and TMP, respectively). Moreover, the presence of a solid support showed a lower inhibition by the TMP ( K i,FCC=3.8±1.0 μM and K i,ICC=12.2±2.5 μM) which may explain why the immobilised cell cultures degraded hydrophobic TMP more efficiently than the planktonic cultures.

Ontogenetic patterns of leaf CO2 exchange, morphology and chemistry in Betula pendula trees

In order to explore ontogenetic variation in leaf-level physiological traits of Betula pendula trees, we measured changes in mass- (Amass) and area-based (Aarea) net photosynthesis under light-saturated conditions, mass- (RSmass) and area-based (RSarea) leaf respiration, relative growth rate, leaf mass per area (LMA), total nonstructural carbohydrates (TNC), and macro- and micronutrient concentrations. Expanding leaves maintained high rates of Aarea, but due to high growth respiration rates, net CO2 fixation occurred only at irradiances >200 µmol photons m–2 s–1. We found that full structural leaf development is not a necessary prerequisite for maintaining positive CO2 balance in young birch leaves. Maximum rates of Aarea were realized in late June and early July, whereas the highest values of Amass occurred in May and steadily declined thereafter. The maintenance respiration rate averaged ≈8 nmol CO2 g–1 s–1, whereas growth respiration varied between 0 and 65 nmol CO2 g–1 s–1. After reaching its lowest point in mid-June, leaf respiration increased gradually until the end of the growing season. Mass and area-based dark respiration were significantly positively correlated with LMA at stages of leaf maturity, and senescence. Concentrations of P and K decreased during leaf development and stabilized or increased during maturity, and concentrations of immobile elements such as Ca, Mn and B increased throughout the growing season. Identification of interrelations between leaf development, CO2 exchange, TNC and leaf nutrients allowed us to define factors related to ontogenetic variation in leaf-level physiological traits and can be helpful in establishing periods appropriate for sampling birch leaves for diagnostic purposes such as assessment of plant and site productivity or effects of biotic or abiotic factors.

A new gas chromatograph‐isotope ratio mass spectrometry technique for high‐precision, N2O‐free analysis of δ13C and δ18O in atmospheric CO2 from small air samples

A new gas Chromatograph‐isotope ratio mass spectrometry (GC‐IRMS) technique for the first N2O‐free, high‐precision (&lt;0.05‰) isotopic analysis of δ13C and δ18O in atmospheric CO2 from small air samples has been developed. On‐line GC separation of CO2 and N2O from a whole air sample is combined with IRMS under elevated ion source pressures. A specialized open split interface is an integral part of the inlet system and ensures a continuous flow of either sample gas or pure helium to the IRMS. The analysis, including all flushing, uses a total amount of 45 mL of an air sample collected at ambient pressure. Of this, three 0.5 mL aliquots are injected onto the GC column, each providing ∼0.8 nmol CO2 in the IRMS source. At this sample size, δ13C precision obtained is at the theoretical shot noise limit. For typical ambient air samples collected in the Southern Hemisphere, demonstrated precisions for δ13C, δ18O, and the CO2 mixing ratio (all measured simultaneously) are 0.02‰, 0.04‰, and 0.4 ppm, parts per million (ppm) respectively. Since these data are achieved from small air samples without contamination by atmospheric N2O or the use of cryogen, the technique will be a valuable tool in global carbon cycle research.

Costs and Benefits of Carnivory in Plants: Insights from the Photosynthetic Performance of Four Carnivorous Plants in a Subarctic Environment

We measured photosynthetic performance in four subarctic carnivorous plants, Pinguicula alpina, P. villosa, P. vulgaris and Drosera rotundifolia, in order to test if there is a cost of combining photosynthetic and trapping devices into the same organ (leaves). We compared these data with published results on photosynthetic rates in subarctic non-carnivorous plants. In P. vulgaris, an experiment of prey addition and removal further tested the existence of a short-term benefit of increased nutrient gain from prey in terms of photosynthetic efficiency. Leaf area-based photosynthetic rates (P a ) ranged 2.0-3.0 μmol CO 2 m -2 s -1 , dry mass-based photosynthetic rates (P w ) 42--69 nmol CO 2 g - 1s -1 , and photosynthetic nitrogen use efficiency (PNUE) 29-45 μmol CO 2 mol N - 1 s 1 . In general, P a and P w of carnivorous plants increased with leaf nitrogen content. When each species was analysed separately, those relationships were weak (P. alpina and P. villosa) or non-significant (P. vulgaris and D. rotundifolia). The photosynthetic rate of carnivorous plants was lower than that of other subarctic growth forms. In addition, P w for a given leaf nitrogen content was significantly lower in carnivorous plants than in non-carnivorous ones. No change in P a , P w or PNUE occurred as a result of prey capture manipulation, but treatments differed only slightly in nutrient content. P w and PNUE showed a trend to be higher in reproductive P. alpina plants as compared to vegetative ones. In P. vulgaris, however, an increased leaf respiration was found in reproductive plants.

Limitation of carbon assimilation of intertidal Zostera noltii and Z. marina by desiccation at low tide

Carbon dioxide assimilation of emersed Zostera noltii leaves was measured by infrared gas analysis to determine its dependence on leaf water content and the duration of air exposure in the tidal flats of the German Wadden Sea (south east North Sea). After 5 h of exposure to air during low tide, leaves of Z. noltii had lost up to 50% of their water content. The degree of leaf water loss rapidly increased with the distance from the water line and, thus, was a function of the duration of exposure. A decrease in leaf water content by about 30% (from 340–390 to 190–250% DW) resulted in a reversible reduction in light-saturated net photosynthesis rate ( A max) of Z. noltii by more than 50% (24–31 nmol CO 2 g DW −1 s −1 vs. 6–14 nmol g DW −1 s −1). Similarly, laboratory experiments with artificially dried leaves showed a decrease of A max by about 40% for a water content reduction from 400 to 270% DW. Drying experiments with leaves of the co-occurring species Z. marina showed a rapid reduction of A max from 30 nmol CO 2 g DW −1 s −1 (at 500% leaf water content) to zero or even negative CO 2 fluxes (at 180% water content). These results indicate that photosynthesis is more sensitive to desiccation in Z. marina than in Z. noltii under a given leaf water content. The two intertidal Zostera species use low tide periods for rapid assimilation of atmospheric CO 2 as long as their leaf water status is favourable, but desiccation can significantly reduce carbon gain at low tides. We conclude that the presence of seagrasses in the tidal flats of the Wadden Sea is primarily restricted by desiccation at the upper limit.

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 Kornik, Poland. At the end of the growing season, current-year foliage had the highest rates of mass-based light-saturated net photosynthesis (Asat) of 33.5 nmol CO2· g–1· s–1. Asat 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 Asat 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.

Carbon efflux rates of fine roots of three tree species decline shortly after excision

Fine roots (diameter ≦2 mm) of Acer rubrum, Quercus rubra and Pinus strobus were used to determine whether respiration rates (measured as CO 2 efflux rates) remain sufficiently stable for the 1 min to 10 h interval after excision to allow reliable measurements to be taken. Roots of five individuals of each species were excavated from the upper 10 cm of the soil. From each tree, two samples of roots (dry weights between 0.21 and 1.18 g) were excised and immediately subjected to one of two treatments. The attached soil was removed mechanically with (wet treatment) or without (dry treatment) the further removal of soil by submersion in and rinsing with water. Within 1 min of excision, roots were placed in a gas exchange system and their respiration was measured. The measurements were repeated 5, 15, 30 min and 1, 2 ( Acer and Pinus), 3 ( Quercus), 6 and 10 h after excision. For all species, carbon efflux rates showed a marked decline over time, dropping significantly ( p ≤ 0.05) over 5 min for Acer and Pinus and over 15 min for Quercus (by 37, 52 and 33%, respectively). The initial rates (12.9, 9.2 and 8.7 nmol CO 2 g −1 s −1 at 25 °C for Acer, Quercus and Pinus, respectively) declined to a minimum (4.2, 2.9 and 4.4 nmol CO 2 g −1 s −1) in 30 ( Pinus) or 60 ( Acer and Quercus) min then levelled off ( Acer and Quercus) or started to increase ( Pinus). Possible mechanisms causing the decline are discussed.

Ornithine decarboxylase activity is associated with proliferation but not with T3-induced differentiation of Caco-2 cells.

Ornithine decarboxylase (ODC) activity and polyamine (putrescine, spermidine, spermine) concentrations were measured in parallel in enterocyte-like Caco-2 cells maintained under various culture conditions. ODC activity was maximal at the beginning of the exponential growth phase, decreasing dramatically thereafter to a negligible level at confluency (day 9). Kinetic studies performed on day 3 revealed the presence of a single enzyme with a Km around 200 microM and a Vmax of about 2 nmol CO2 released/h/mg protein. Similar values were obtained in both serum-supplemented and transferrin/selenium (TS)-defined culture media, indicating that ODC kinetic parameters are not affected by any factors present in serum. Polyamine concentrations were maximal on day 5. By day 9, they returned to initial levels and remained at these fairly high values until day 21. Since we have previously shown (Jumarie and Malo, 1994, in Vitro Cell. Dev. Biol., 30A:753-760) that triiodothyronine (T3) stimulates differentiation but not proliferation of Caco-2 cells maintained in TS-defined medium, we investigated if it induces differentiation by a polyamine-dependent mechanism. Short- and long-term measurements revealed similar ODC activity and polyamine levels whether T3 was present or not in the culture medium. These results clearly demonstrate that polyamine synthesis is more likely to be associated with Caco-2 cell proliferation, and that the T3 effect on Caco-2 cell differentiation does not involve polyamine biosynthesis. Moreover, our data show that ODC activity is not solely regulated by intracellular polyamine concentration.

Growth and maintenance respiratory costs of cucumber fruits as affected by temperature, and ontogeny and size of the fruits

The rates of dry weight increase and respiration of fruits were measured throughout fruit ontogeny at 20, 25 and 30°C in cucumber (Cucumis sativus L. cv. Corona). By maintaining one or five fruits per plant, which strongly affected fruit dry weight but not ontogeny, the effects of fruit size and ontogeny on respiration could be studied separately. The respiration rate per fruit followed a sigmoid curve during fruit ontogeny, while the specific respiration rate (respiration rate per unit dry weight) declined with time after anthesis. The specific respiration rate was almost linearly related to the relative growth rate. The specific respiratory costs for both growth and maintenance were highest in young fruits, but were not affected by fruit size. The average specific respiratory costs for growth and maintenance at 25°C were 3.3–3.9 mmol CO2 g−1 and 4.0 nmol CO2 g−1 s−1, respectively. An increase in temperature had no effect on the specific respiratory costs for growth, while the costs for maintenance increased with a Q10 of about 2. The costs for growth agreed reasonably well with theoretical estimates based on the chemical composition of the fruits but not with estimates based on only the carbon and ash content. The respiratory losses as a fraction of the total carbon requirement of a fruit changed during fruit ontogeny, but were independent of temperature and were similar for slow‐ and fast‐growing fruits. The cumulative respiratory losses accounted for 13–15% of the total carbon requirement.

High soil carbon dioxide concentrations inhibit root respiration of Douglas fir.

Total and basal respiration (Rt and Rb , respectively) of intact and undisturbed roots of one-year-old Douglas fir seedlings, Pseudotsuga menziesii var. glauca [Beissn] Franco, were measured at experimentally varied soil carbon dioxide concentrations ([CO2 ]). Use of specially designed root boxes and a CO2 gas-flow compensating system designed around an infrared gas analyzer (IRGA) allowed controlled delivery of CO2 to roots and simultaneous measurements of CO2 released by roots. Root respiration rate responded to each inlet [CO2 ], independent of whether the previous concentration had been higher or lower, within two to three hours (paired t test = 0.041, P= 0.622, and n= 13). Total and basal respiration rates decreased exponentially as soil [CO2 ] rose from 130 ppm, well below atmospheric [CO2 ], to 7015 ppm, a concentration not uncommon in field soils. Analyses of variance (ANOVA) showed that the effects of soil [CO2 ] on rates of total and basal root respiration were statistically significant. Root respiration rates decreased by 4 to 5 nmol CO2 g-1 dry weight of roots s-1 for every doubling of [CO2 ] according to the following equations: ln(R1 ) (nmol CO2 g-1 s-1 ) = 5.24-0.30*ln[CO2 ] with r= 0.78, P < 0.0001, and n= 70; and ln(Rb ) (nmol CO2 g-1 s-1 ) = 6.29-0.52 * ln[CO2 ] with r= 0.82, P < 0.0001, and n= 35. The sensitivity of root respiration to [CO2 ] suggests that some previous laboratory measurements of root respiration at atmospheric [CO2 ], which is 3 to 10-fold lower than [CO2 ] in field soils, overestimated root respiration in the field. Further, the potential importance of soil [CO2 ] indicates that it should be accounted for in models of below-ground carbon budgets.

Root respiration and its importance for the carbon balance of beech saplings (Fagus sylvatica L.) in a montane beech forest

Root respiration of 10-year-old beech saplings (Fagus sylvatica L.) grown in the understorey (UND) and in a natural gap (GAP) of a mature beech forest in the Solling mountains, FRG, was investigated from April until December, 1990. Respiration rates of fine, medium and coarse roots were measured in situ by a PC-controlled cuvette system. Fine root respiration rates were in the range of 0.5–9.8 nmol CO2 gDW−1 s−1 at both sites, but respiration rates of UND saplings were higher, compared to those of GAP saplings. The dependence of respiratory activity on soil temperature proved to be highly significant (p<0.001) for both plots, following a quasi-Arrhenius type curve. Fine root respiration rates of UND saplings were highly significantly, negatively correlated with the water content of the attached organic material, whereas respiration rates of GAP saplings did not show such a correlation. Further, a significant correlation (p<0.01) between mycorrhizal biomass and respiration rate was detected at the UND site, but not at the GAP site. Medium and coarse root respiration rates were very similar and no significant differences between the two sites were detected. Maximum respiration rates of 3.1 nmol CO2 gDW−1 s−1 were reached in the middle of July. Due to low light intensities in the under storey, daily net CO2 assimilation rates of UND saplings were much smaller than those of GAP saplings. At both sites, net CO2 assimilation rates varied more than respiration rates and thus the carbon balance of beech saplings was more affected by the rate of carbon fixation than by the rate of respiratory carbon loss.

Adaptation of a strain of Spirulina platensis to grow in cobalt- and iodine-enriched media.

Cobalt- and iodide-enriched (adapted, tolerant) strains of the protein-rich cyanobacterium, Spirulina platensis, were produced by repeated sub-culturing in increasing concentrations of the two trace elements. The strains enriched with cobalt and iodide showed higher uptake of these elements than the controls. The LD50 values for the parent and cobalt-adapted strains were 95 and 231 mumol l-1 CO2+, respectively. Likewise, the LD50 values for parent and iodide-adapted strains were 12 and 42 mmol l-1 I-. The carotenoid:chlorophyll a ratio of the parent strains increased after cobalt addition. The cobalt-adapted strain showed a much higher ratio than the cobalt-grown parent (sensitive) cells which remained unchanged after cobalt addition. Intracellular CO2+ uptake by the cells was concentration-dependent and followed Michaelis-Menten kinetics with saturation in uptake occurring in the parent and adapted strains at 126 and 189 mumol l-1 Co2+, respectively. At saturating concentrations, the maximum CO2+ uptake was 39.73 and 158.43 nmol CO2+ mg-1 protein, respectively for the parent and adapted strains. The adapted strain also showed greater cobalt adsorption. The Km of intracellular CO2+ uptake was lower in the case of adapted cells as compared with the parent, whereas Vmax showed an opposite trend. Thus, the adapted cells appear to be more efficient than the parent strain in intracellular uptake of cobalt. Differences between kinetic constants of both the strains suggest that the strains may be physiologically different. Likewise, iodide uptake was significantly higher in iodide-adapted cells than in controls.

Carbohydrate requirements for dark respiration by peach vegetative organs.

The specific respiration rate at 20 degrees C (R(20)) of peach leaves and stems declined rapidly from a high value in the early spring (22.5 nmol CO(2) g(dw) (-1) s(-1)) to relatively constant rates by July (3.1 nmol CO(2) g(dw) (-1) s(-1)). Leaf R(20) declined more rapidly than current-year stem R(20), but leaf and current-year stem R(20)s were similar by July. The R(20) of current-year stems in July was approximately 2.5 times greater than that of one-year-old stems (1.3 nmol CO(2) g(dw) (-1) s(-1)), and about 30 times greater than that of the trunk R(20) (0.1 nmol CO(2) g(dw) (-1) s(-1)). The Q(10)s of leaves and stems were approximately 2 for a temperature increase between 20 and 30. The Q(10)s above 30 were 2.03 for leaves but only 1.61 for stems. Leaves and current-year stems accounted for 2 and 17% of the aboveground vegetative biomass in April and August, respectively, but accounted for 59-80% of total daily (24 h) respiration. Although trunk biomass accounted for 91 and 77% of aboveground vegetative biomass, in April and August, respectively, trunk respiration accounted for only 8-15% of daily aboveground respiration. Before harvest, during a period when fruit growth was source-limited, daily fruit respiration exceeded respiration by all aboveground vegetative organs.

Seasonal CO2 exchange patterns of developing peach (Prunus persica) fruits in response to temperature, light and CO2 concentration

CO2 exchange rates per unit dry weight, measured in the field on attached fruits of the late‐maturing Cal Red peach cultivar, at 1200 μmol photons m−2S−1 and in dark, and photosynthetic rates, calculated by the difference between the rates of CO2 evolution in light and dark, declined over the growing season. Calculated photosynthetic rates per fruit increased over the season with increasing fruit dry matter, but declined in maturing fruits apparently coinciding with the loss of chlorophyll. Slight net fruit photosynthetic rates ranging from 0. 087 ± 0. 06 to 0. 003 ± 0. 05 nmol CO2 (g dry weight)−1 S−1 were measured in midseason under optimal temperature (15 and 20°C) and light (1200 μmol photons m−2 S−1) conditions. Calculated fruit photosynthetic rates per unit dry weight increased with increasing temperatures and photon flux densities during fruit development. Dark respiration rates per unit dry weight doubled within a temperature interval of 10°C; the mean seasonal O10 value was 2. 03 between 20 and 30°C. The highest photosynthetic rates were measured at 35°C throughout the growing season. Since dark respiration rates increased at high temperatures to a greater extent than CO2 exchange rates in light, fruit photosynthesis was apparently stimulated by high internal CO2 concentrations via CO2 refixation. At 15°C, fruit photosynthetic rates tended to be saturated at about 600 μmol photons m−2 S−1. Young peach fruits responded to increasing ambient CO2 concentrations with decreasing net CO2 exchange rates in light, but more mature fruits did not respond to increases in ambient CO2. Fruit CO2 exchange rates in the dark remained fairly constant, apparently uninfluenced by ambient CO2 concentrations during the entire growing season. Calculated fruit photosynthetic rates clearly revealed the difference in CO2 response of young and mature peach fruits. Photosynthetic rates of younger peach fruits apparently approached saturation at 370 μl CO21−2. In CO2 free air, fruit photosynthesis was dependent on CO2 refixation since CO2 uptake by the fruits from the external atmosphere was not possible. The difference in photosynthetic rates between fruits in CO2‐free air and 370 μl CO2 1−1 indicated that young peach fruits were apparently able to take up CO2 from the external atmosphere. CO2 uptake by peach fruits contributed between 28 and 16% to the fruit photosynthetic rate early in the season, whereas photosynthesis in maturing fruits was supplied entirely by CO2 refixation.

Whole-plant CO2 exchange of seedlings of two Pinus sylvestris L. provenances grown under simulated photoperiodic conditions of 50� and 60� N

Seedlings of Scots pine (Pinus sylvestris L.) from Russia (59°58′N) and Poland (53°34′N) were grown for 4 months in controlled environment chambers, simulating the photoperiod conditions of 50° and 60° N. The Russian population grown at 50° N showed earlier height growth cessation than the Polish population. Photoperiodic conditions of 60° N increased proportional allocation of dry mass to shoots and lowered allocation to roots in the Russian population, which also had greater allocation to roots than the Polish population in both treatments. Total non-structural carbohydrate concentrations in roots and secondary needles of both populations were significantly higher at the end of the 4 month growing season at 50° compared to 60° N. Net photosynthesis rates were similar for both provenances and both treatments. The rate of transpiration was higher and water-use efficiency lower for plants grown in long-day conditions of 60° N. The mean respiration rate of roots ranged between 30 and 36 nmol CO2 · g-1 dry mass · s-1 and was 2–4 times higher than values observed for needles. Root respiration rates were greater in the Polish than the Russian population. Despite this, the greater allocation to root dry mass of the Russian population resulted in greater root respiratory cost as a proportion of daily carbon gain. Overall, root respiration accounted for between 18 to 34% of the total daily net carbon assimilation of these populations. Root and total respiration as a proportion of net daily carbon assimilation were greater at 50° than 60°N. Mean net integrated CO2 gains were 2.2–2.5 mmol CO2 · day-1 for seedlings from Russia compared to 3 mmol CO2 · day-1 for Poland.

Carbon dioxide exchange of developing avocado (Persea americana Mill.) fruit.

Net efflux of CO(2) from attached avocado (Persea americana Mill.) fruit was measured periodically from three weeks after anthesis to fruit maturity. Net CO(2) exchange was determined in daylight (light respiration, R(l)) at a photosynthetic photon flux (PPF) greater than 600 micromol m(-1) s(-1), and in the dark (dark respiration, R(d)). Dark respiration and R(l) were highest during the early cell division stage of fruit growth (about 25 and 22 nmol CO(2) g(dw) (-1) s(-1), respectively) and decreased gradually until fruit maturity to about 1 and 0.5 nmol CO(2) nmol CO(2) g(dw) (-1) s(-1), respectively. Fruit photosynthesis, calculated from the difference between R(d) and R(l), ranged from 0.5 to 3.1 nmol CO(2) g(dw) (-1) s(-1). Net rate of CO(2) assimilation on a fruit dry weight basis was highest during the early stages of fruit growth and reached the lowest rate at fruit maturity. Net rate of CO(2) assimilation of fruit exposed to light was 0.4 to 2.5% of that for fully expanded leaves. Although the relative amount of carbon assimilated by the fruit was small compared with the total amount of carbon assimilated by the leaves, the data indicate that avocado fruit contribute to their own carbon requirement by means of CO(2) assimilated in the light.

Carbon dioxide efflux from roots of calamodin and apple.

The specific rate of CO(2) efflux (respiration) from roots of intact fruiting calamodin plants (Citrus madurensis Lour.) showed no diel trend, and did not respond significantly to short-term (2 day) changes in shoot irradiance. Mean root respiration rate was about 8.4 nmol CO(2) g(-1) s(-1) at 20 degrees C, and increased with temperature with a Q(10) of about 2. In calamodin plants, the proportion of total root length that was white averaged 6.0 mm m(-1). Respiration of roots of apple plants (Malus domestica Borkh.), planted in spring as rootstocks and grown at high irradiance and N supply, declined from about 5.3 to 2.8 nmol CO(2) g(-1) s(-1) between 46 and 138 days after bud burst. At 50% irradiance, root respiration was reduced more than 25% at 46 and 92 days after bud burst, but was not significantly affected later in the season. Reducing shoot irradiance reduced the proportion of total root length that was white, e.g., from 217 to 146 mm m(-1) at 46 days after bud burst. For plants previously grown at low irradiance, increasing shoot irradiance for 6 days increased the rate of root respiration by 5 to 10%. For plants previously grown at high irradiance, reducing shoot irradiance for 6 days reduced root respiration by about 20% early in the season, but had no significant effect later in the season. For plants grown with low-N supply (5% of the high-N), root respiration was reduced early in the season, but was not significantly affected later. Reducing the N supply increased slightly the proportion of total root length that was white. For plants previously grown with low-N, increasing the N supply for 6 days reduced further the rate of root respiration. For plants previously grown with high-N, reducing the N supply for 6 days did not significantly affect the rate of root respiration. Specific respiration rates of root systems excised from mature trees growing outdoors peaked in June, at about 2.4 nmol CO(2) g(-1) s(-1), and then declined for the remainder of the growing season.