Carbon Dioxide and Water Vapour Exchange of Leaves on Field-Grown Citrus Trees

Carbon dioxide and water vapour exchange rates were measuredon attached leaves of field-grown citrus trees. The exchangerates were measured continuously during several weeks in thespring of two successive years. These data confirmed the ratherlow rates of maximum CO₂ exchange (6–11 µmol m^–2s^–1) by citrus leaves. However, the maximum rate was maintainedthrough the midday period on only about half the days. On theother days, characterized by high temperatures and high atmosphericwater vapour pressure deficits, pronounced midday depressionsin CO₂ exchange rates were observed. Since midday transpirationremained stable at a constant rate even with increasing vapourpressure deficit, these results indicate that stomatal closurewas occurring. In fact, the data suggest tfiat specific, maximumtranspiration rates were associated with differing rootstocks.Thus, the rate of water supply to the leaves may be an importantfactor in determining the maximum transpiration rate, and therebymediating control of stomatal conductance and the resultantmidday depression in CO² exchange rates.     

Simulating Daily and Half-Hourly Fluxes of Forest Carbon Dioxide and Water Vapor Exchange with a Simple Model of Light and Water Use

For the large-scale application of simple, aggregated models, it is important to be able to link the values of model parameters to easily measurable ecosystem characteristics. However, the aggregation of model inputs and outputs over time and space can hamper this linkage. In this paper, two temporal versions of the same simple carbon dioxide (CO₂) and water exchange model, based on the concepts of water- and light-use efficiencies, were used to simulate the half-hourly and daily CO₂ and water exchange of a Douglas fir forest (Pseudotsuga menziesii (Mirb.) Franco) in the Netherlands for 2 years, before and after a thinning. We tested the performance of the models and the interpretability of changes in optimized parameter values, due to the thinning, in terms of ecosystem functioning. The performance of the half-hourly model was satisfactory, whereas the performance of the daily model was high for water exchange but clearly lower for CO₂ exchange. A comparison of the model parameters before and after the thinning showed that the coefficients of the half-hourly model could be separated into more physiologically determined and stand-determined characteristics, but this separation was not clear for the daily model. These results show that if the temporal resolution of the model is high enough, the effects of a major ecosystem manipulation, such as thinning, can be detected and interpreted using eddy flux data and a very simple biophysical model. The model parameters have an unambiguous interpretation and can be inferred from basic ecosystem observables, such as leaf area index (LAI) and aboveground biomass. A sensitivity analysis found strong correlations between parameter sets with similar model performance. For any comparison of the parameter values of different studies, ranges of parameter values and their correlations should be presented rather than one optimized value. Received 2 May 2001; accepted 15 February 2002.     

Precise Measurements of Carbon Dioxide Exchange by Illuminated Leaves near the Compensation Point

The results of precise measurements of rates of carbon dioxideassimilation at low external concentrations of carbon dioxideand of rates of carbon dioxide output into virtually carbondioxide-freeair show that linear extrapolations of the carbon dioxide intakecurve plotted against the external concentrations of carbondioxide give an exaggerated estimate of the rate of carbon dioxideoutput from illuminated leaves into carbon dioxide-free air. The shape of the exchange curve suggests that the rate of endogenousproduction of carbon dioxide changes at external concentrationsin the region of the carbon dioxide compensation point ().     

Enzyme Activities Associated with Carbon Dioxide Exchange in Illuminated Leaves of Hordeum vulgare L.: IV. The Effect of Light Intensity on the Carbon Dioxide Compensation Point

The carbon dioxide compensation point () was found to vary whenmeasured at increasing light intensities, in plants grown ata constant illumination. This response varied with the physiologicalage of the leaf. The also varied when measured at a constantillumination, with plants grown at different light intensities.The activity of the enzymes RuDP carboxylase, nitrate reductase,glycollate oxidase, and catalase was found to be influencedby the light intensity at which the plants were grown. A goodcorrelation was obtained between the measured and the ratioof nitrate reductase: RuDP carboxylase activities, suggestingthat nitrate reductase may be used as an indirect measure ofphotorespiration in plants receiving nitrate as the sole nitrogensource.     

The Effect of Sea Water on Carbon Dioxide Exchange by the Halophyte Limonium californicum (Boiss.) Heller

Plants of Limonium californicum, a perennial halophyte, maintainhigh levels of photosynthetic activity for long periods subsequentto flooding of their roots with sea water. Possible mechanismsfor this are discussed.     

Apparatus for the Simultaneous Measurement of Water Vapour and Carbon Dioxide Exchanges of Single Leaves

Equipment is described which delivers air with concentrationsof CO₂ and water vapour closely controlled in the ranges 0 to2500 ppm and 5 to 15 mb respectively, at flow rates of up to10 1 min^-1, to each four leaf chambers. The leaf temperatureis controlled to ±0.5 °C and, with a light intensityof 0.3 cal cm^-2 min^-1 visible radiation (0.4 to 0.7 µm)leaf temperature can be maintained at 17.5 °C.The apparatusused to measure the concentration differences between the watervapour and CO₂ entering and leaving the leaf chamber (used tocalculate transpiration, photosynthetic, and respiration rates)is described in detail.Results of tests, which show the necessityfor mounting a fan within the leaf chamber, are reported.Typicallight- and CO₂-response curves are given for kale leaves (Brassicaoleracca var. acephala) and an attempt is made to quantify theerrors in the measurement of photosynthesis and transpiration.     

Simultaneous Measurement of Oxygen, Carbon Dioxide, and Water Vapour Exchange in Intact Plants

A low flow of air is passed through a temperature-controlledplant chamber in order to obtain relatively large (300–500µl-1) differences in [O₂] between influx and efflux streams.These differences are measured with a stabilized O₂ electrodesystem incorporating elements of gas conditioning electroniczero suppression and signal amplification. Changes in [O₂] of400 µl l-1 can be detected at full scale recorder deflectionagainst a background concentration of 21% O₂. The concentrationsof CO₂ and H₂O within the chamber are held constant by con-trolled-flowCO₂-scrubbing and dehumidifying loops. Carbon dioxide, H₂O,and O₂ fluxes are measured and leaf diffusion resistance andinternal [CO₂] are calculated in essentially ‘real time’.     

Enzyme Activities Associated with Carbon Dioxide Exchange in Illuminated Leaves of Hordeum vulgare L.: II. Effects of External Concentrations of Carbon Dioxide and Oxygen

Plants grown in a high carbon dioxide environment (< 1 percent) were found to have increased levels of RuDP carboxylase,and suppressed activities of catalase, glycollate oxidase, andnitrate reductase, enzymes all associated with the peroxisome.Similarly, plants grown in low oxygen concentrations showedsuppressed activities of the peroxisomal enzymes. However, underthese conditions RuDP carboxylase activity was also suppressed.These results further suggest that nitrate reductase activityis associated with photorespiration.     

Carbon Dioxide Efflux from Leaves in Light and Darkness

Efflux of carbon dioxide in light and darkness was measured at low ambient CO₂ concentrations in leaves of Rumex acetosa. Light carbon dioxide production (photo-respiration) was found to depend on irradiance and to differ from dark production as to the response to temperature and ambient concentrations of O₂ and CO₂. These observations support previously made suggestions that photorespiration follows a different metabolic pathway to dark respiration.     

Enzyme Activities Associated with Carbon Dioxide Exchange in Illuminated Leaves of Hordeum vulgare L.: III. Effects of Concentration and Form of Nitrogen Supplied on Carbon Dioxide Compensation Point

Increasing the nitrate concentration in the nutrient media wasfound not to influence the carbon dioxide compensation point(). However, a higher value of was obtained in the presenceof ammonia nitrogen in the nutrient media. Increasing the nitrateconcentration in the media gave a higher activity of RuDP carboxylase,nitrate reductase, glycollate oxidase, and catalase. Similarlythe plants grown in ammonia nitrogen showed higher activitiesof RuDP carboxylase and catalase, and a considerably higherglycollate oxidase activity.     

Modelling and Measuring Transpiration from Scots Pine with Increased Temperature and Carbon Dioxide Enrichment

Starting in 1996, individual trees of Scots pine (Pinus sylvestrisL.) aged 30 years, were grown in closed-top chambers and exposedto either normal ambient conditions (CON), elevated CO₂(approx.700 µmol mol^-1; Elev. C), elevated temperature (approx.2 °C and approx. 6 °C above the outside ambient temperatureduring the ‘growing season’ and ‘off season’,respectively; Elev. T) or a combination of elevated CO₂and warmertemperature (Elev. CT). Sap flow was monitored simultaneouslyby the constant-power heat balance method in a total of 16 trees,four for each treatment, over a 32 d period in summer 1998 (afterthe completion of needle expansion and branch elongation). Toquantify the contributions of crown and physical environmentalvariables to total crown transpiration, a ‘sun/shade model’was developed and used to partition the changes in transpirationto different sources. The results of the sap flow measurementsindicate that (1) total daily sap flow (E_tree.d) varied from0.15–3.41 kg per tree; (2) the treatment effect on E_tree.ddependedgreatly on the weather conditions; (3) the cumulative E_tree.dforthe 32 d dropped significantly by 22% relative to CON (P =0.038)under Elev. C and increased significantly by 21% (P =0.043)and 16% (P =0.048) under Elev. T and Elev. CT, respectively.In general, the modelled transpiration gave good agreement withthe sap flow results. The model computations showed that, ona typical sunny day in summer, the effect of treatment on crownstomatal conductance was responsible for approx. 80% of thechange inE_tree.d , while the increase in needle area and theeffect on total radiation absorption contributed only a smallpercentage. Furthermore, sunlit needles were responsible forover 60% of change in transpiration. The effect of the treatmentson E_tree.dwas larger at high temperature and vapour pressuredeficit but was not sensitive to incident daily radiation. Copyright2000 Annals of Botany Company Transpiration model, sap flow, CO₂and temperature elevation, environment-controlled chamber, Pinus sylvestris L.     

Oscillatory Transpiration and CO2 Exchange of Citrus Leaves at the CO2 Compensation Concentration

CO₂ and H₂O vapor exchange were measured by enclosing citrus (Citrus sinensis cv. Sour Orange) leaves in a temperature controlled transparent leaf chamber. Introduction of dry air into the closed circuit gas flow caused cyclic oscillation in CO₂ and H₂O vapor exchange. It is suggested that oscillation in the CO₂ exchange at the CO₂ compensation concentration is due to oscillation in non-stomatal resistance to CO₂. Three types of oscillation were observed: 3–6 min (peak to peak) in young leaves, 30 min in mature leaves, and 160 min in old leaves.     

Carbon Dioxide Exchange Between an Old-growth Forest and the Atmosphere

Eddy-covariance and biometeorological methods show significant net annual carbon uptake in an old-growth Douglas-fir forest in southwestern Washington, USA. These results contrast with previous assumptions that old-growth forest ecosystems are in carbon equilibrium. The basis for differences between conventional biomass-based carbon sequestration estimates and the biometeorologic estimates are discussed. Annual net ecosystem exchange was comparable to younger ecosystems at the same latitude, as quantified in the AmeriFlux program. Net ecosystem carbon uptake was significantly correlated with photosynthetically active radiation and air temperature, as well as soil moisture and precipitation. Optimum ecosystem photosynthesis occurred at relatively cool temperatures (5°–10°C). Understory and soil carbon exchange always represented a source of carbon to the atmosphere, with a strong seasonal cycle in source strength. Understory and soil carbon exchange showed a Q₁₀ temperature dependence and represented a substantial portion of the ecosystem carbon budget. The period of main carbon uptake and the period of soil and ecosystem respiration are out of phase, however, and driven by different climatic boundary conditions. The period of strongest ecosystem carbon uptake coincides with the lowest observed values of soil and ecosystem respiration. Despite the substantial contribution of soil, the overall strength of the photosynthetic sink resulted in the net annual uptake. The net uptake estimates here included two correction methods, one for advection and the other for low levels of turbulence.     

Carbon Dioxide Exchange and Acidity Levels in Detached Pineapple, Ananas comosus (L.), Merr., Leaves during the Day at Various Temperatures, Oxygen and Carbon Dioxide Concentrations

The effects of temperature, O₂, and CO₂ on titratable acid content and on CO₂ exchange were measured in detached pineapple (Ananas comosus) leaves during the daily 15-hour light period. Comparative measurements were made in air and in CO₂-free air. Increasing the leaf temperature from 20 to 35 C decreased the total CO₂ uptake in air and slightly increased the total CO₂ released into CO₂-free air. Between 25 and 35 C, the activation energy for daily acid loss was near 12 kcal mol⁻¹, but at lower temperatures the activation energy was much greater.     

The Effect of Several Pollutants on the Transpiration of Rice Plants

The purpose of this paper is to show how the change of transpiration destroys water balance in rice plants. The inhibition of, transpiration was pronounced under the following two conditions: 1) The amount of pollutants accumulated in the roots, stems and leaves of the plant was very large; 2) Any one of the organs, that is, its root, stem or leaf, showed visible injury. The later was the direct cause of the declination of transpiration. Because the absorption and transport of wate were inhibited. With the decline of transpiration, photosynthesis also declined rapidly. Owing to this, the plant grow slowly, with its stem and leaf sparse. Thus the plant phenological period became abnormal and the biomass and production of rice decreased. According to inhibition level of the plan transpiration, the toxicity of the pollutants and the plant resistance could be distinguished.     

Effect of Water Stress on Transpiration in Birch Seedlings

Transpiration of birch seedlings in the field is largely controlled by the amount of available water in the soil. This is in contrast with the situation found in CO₂ exchange, where distinct interaction between temperature and drought was observed in our previous studies. The present study indicates that no similar relationships exist as far as transpiration is concerned, and in agreement with our previous preliminary studies, separate control mechanisms thus seem to affect transpiration on the one hand and photosynthesis on the other under natural conditions.