Diurnal CO2 Exchange Research Articles

Photosynthetic characteristics of the invasive weed Chromolaena odorata and other co‐occurring species in KwaZulu‐Natal

AbstractIn this study, we tested the hypothesis that photosynthetic characteristics contributed to the success and spread of the invasive, C3 perennial weed, Chromolaena odorata (L.) R. M. King & H. Rob. Measurements of gas exchange, chlorophyll fluorescence and water relations parameters were taken in summer and winter, as well as in sun and shade plants. Typically, diurnal CO2 exchange increased from dawn to a mid‐morning maximum between 10:00 h and 11:00 h, and thereafter decreased gradually for the rest of the day. Light response curves indicated saturation of CO2 uptake and electron transport rate (ETR) through Photosystem II (PSII) at a photosynthetic photon flux density (PPFD) ≥1800 μmol m−2 s−1. Maximal CO2 exchange was 15.64 ± 0.87 (±SE) in summer and 13.15 ± 0.26 μmol m−2 s−1 in winter. Leaf conductance (g), CO2 uptake (A) and transpiration (E) followed trends similar to those for PPFD. Leaf water potential (Ψ) and water use efficiency (WUE) declined from the predawn maximum values to a minimum at midday and thereafter recovered at dusk. Diurnal trends in actual quantum yield (ΦPSII) and maximum quantum yield (Fv/Fm) decreased from dawn to a minimum at midday, followed by complete recovery at dusk. The relationship between A and g, and A and ETR was linear. Trends in A, ΦPSII and ETR through PSII were tightly coupled to those of incident PPFD. Efficient light utilisation is achieved through modifying plastic traits such as leaf size, specific leaf area and chlorophyll content. Chromolaena is a facultative shade‐tolerant weed that exhibits superior light utilisation to maximise carbon gain, while efficient photoprotective mechanisms minimise photoinhibition and photodamage to the photosystems. These adaptive architectural and physiological strategies may probably confer competitive advantage over other species.

A photosynthesis continuous monitoring system for CAM plants

Diurnal CO2 exchanges in crassulacean acid metabolism (CAM) plants are significantly different from those in C3 and C4 plants. The instantaneous short-time CO2 exchange of a single leaf measured by commercial portable photosynthesis measuring systems with a small leaf chamber cannot reflect the plant photosynthetic capacity for CAM plants because of the CO2 fixation property. Therefore, a photosynthesis continuous monitoring system with two canopy cuvettes was developed for measuring diurnal net CO2 exchange rates for CAM plants. To evaluate stability and applicability of the photosynthesis continuous monitoring system, continuous measurement of net CO2 exchange rates of plants with different photosynthetic pathways were conducted. An obligate CAM plant (Kalanchoe daigremontiana), four facultative CAM plants (Dendrobium officinale, D. chrysotoxum, D. nobile, and D. primulinum), a C3 plant (Strawberry, Fragaria ananassa), and a C4 plant (Corn, Zea mays) were selected as model plants. K. daigremontiana had a significant CO2 absorption during the dark period and its net CO2 exchange rates fluctuated around 0 μmol/(m2•s) during the photoperiod in a growth chamber. Net CO2 exchange rates of F. ananassa and Z. mays in a greenhouse gradually increased after sunrise, reaching a maximum at about 12:00, and then gradually decreased to negative values during the night time. It is interesting to observe that D. officinale in the greenhouse and growth chamber absorbed CO2 during both day and night times. The photosynthetic pathways of D. chrysotoxum, D. nobile, and D. primulinum were also well distinguished by this photosynthesis continuous monitoring system. The results showed that the photosynthesis continuous monitoring system is capable for quantitative evaluation of diurnal net CO2 exchange characteristics not only in the CAM plants but also in small size C3 and C4 plants with low net photosynthetic rates for long-time and high-accuracy measurements. Keywords: diurnal net CO2 exchanges, infrared CO2 analyzer, mass airflow meter, net photosynthetic rate, photosynthetic pathway DOI: 10.25165/j.ijabe.20191203.4885 Citation: Cheng Y S, He D X. A photosynthesis continuous monitoring system for CAM plants. Int J Agric & Biol Eng, 2019; 12(3): 141–146.

Photosynthesis continuous monitoring system for CAM plants

Diurnal CO2 exchanges in crassulacean acid metabolism (CAM) plants are significantly different from those in C3 and C4 plants. The instantaneous short-time CO2 exchange of a single leaf measured by commercial portable photosynthesis measuring systems with a small leaf chamber cannot reflect the plant photosynthetic capacity for CAM plants because of the CO2 fixation property. Therefore, a photosynthesis continuous monitoring system with two canopy cuvettes was developed for measuring diurnal net CO2 exchange rates for CAM plants. To evaluate stability and applicability of the photosynthesis continuous monitoring system, continuous measurement of net CO2 exchange rates of plants with different photosynthetic pathways were conducted. An obligate CAM plant (Kalanchoe daigremontiana), four facultative CAM plants (Dendrobium officinale, D. chrysotoxum, D. nobile, and D. primulinum), a C3 plant (Strawberry, Fragaria ananassa), and a C4 plant (Corn, Zea mays) were selected as model plants. K. daigremontiana had a significant CO2 absorption during the dark period and its net CO2 exchange rates fluctuated around 0 μmol/(m2•s) during the photoperiod in a growth chamber. Net CO2 exchange rates of F. ananassa and Z. mays in a greenhouse gradually increased after sunrise, reaching a maximum at about 12:00, and then gradually decreased to negative values during the night time. It is interesting to observe that D. officinale in the greenhouse and growth chamber absorbed CO2 during both day and night times. The photosynthetic pathways of D. chrysotoxum, D. nobile, and D. primulinum were also well distinguished by this photosynthesis continuous monitoring system. The results showed that the photosynthesis continuous monitoring system is capable for quantitative evaluation of diurnal net CO2 exchange characteristics not only in the CAM plants but also in small size C3 and C4 plants with low net photosynthetic rates for long-time and high-accuracy measurements. Keywords: diurnal net CO2 exchanges, infrared CO2 analyzer, mass airflow meter, net photosynthetic rate, photosynthetic pathway DOI: 10.25165/j.ijabe.20191203.4885 Citation: Cheng Y S, He D X. A photosynthesis continuous monitoring system for CAM plants. Int J Agric & Biol Eng, 2019; 12(3): 141–146.

Productivity and CO2 Exchange of Great Plains Ecoregions. I. Shortgrass Steppe: Flux Tower Estimates

The shortgrass steppe (SGS) occupies the southwestern part of the Great Plains. Half of the land is cultivated, but significant areas remain under natural vegetation. Despite previous studies of the SGS carbon cycle, not all aspects have been completely addressed, including gross productivity, ecosystem respiration, and ecophysiological parameters. Our analysis of 1998−2007 flux tower measurements at five Bowen ratio–energy balance (BREB) and three eddy covariance (EC) sites characterized seasonal and interannual variability of gross photosynthesis and ecosystem respiration. Identification of the nonrectangular hyperbolic equation for the diurnal CO2 exchange, with vapor pressure deficit (VPD) limitation and exponential temperature response, quantified quantum yield α, photosynthetic capacity Amax, and respiration rate rd with variation ranges (19 <α < 51 mmol mol−1, 0.48 <Amax < 2.1 mg CO2 m−2 s−1, 0.15 <rd < 0.49 mg CO2 m−2 s−1). Gross photosynthesis varied from 1 100 to 2 700 g CO2 m−2 yr−1, respiration from 900 to 3,000 g CO2 m−2 yr−1, and net ecosystem production from −900 to +700 g CO2 m−2 yr−1, indicating that SGS may switch from a sink to a source depending on weather. Comparison of the 2004−2006 measurements at two BREB and two parallel EC flux towers located at comparable SGS sites showed moderately higher photosynthesis, lower respiration, and higher net production at the BREB than EC sites. However, the difference was not related only to methodologies, as the normalized difference vegetation index at the BREB sites was higher than at the EC sites. Overall magnitudes and seasonal patterns at the BREB and the EC sites during the 3-yr period were similar, with trajectories within the ± 1.5 standard deviation around the mean of the four sites and mostly reflecting the effects of meteorology.

Diurnal CO2 exchange variation in evergreen leaves of the tropical tree, durian (Durio zibethinus Murray)

Diurnal variation of in situ CO2 exchange was investigated during the stage where young and old leaves co-exist in three shoots of tropical evergreen trees of Durio zibethinus Murray growing in an experimental field of Universiti Putra Malaysia. The quantitative proportion of young to old leaves and specific leaf area differed among the three samples. The dark respiration rates in the nighttime and daytime were related exponentially to air temperature. The Q10 ranged between 1.72 and 1.78 for the nighttime dark respiration, and 2.16 and 4.07 for the daytime dark respiration. The relationship between net photosynthetic rate and photosynthetic photon flux density was graphed using a hyperbolic function, where as the specific leaf area decreased the asymptotic rates tended to decrease. CO2 exchange per day was effected by leaf age. The total dark respiration (sum of nighttime and daytime dark respiration) was high and net photosynthesis was low in the shoot where the proportion of young leaves was high. The photosynthetic efficiency of different aged-leaves, which was defined as the ratio of net photosynthesis to dark respiration, ranged from 32 to 152%. Photosynthetic efficiency was low in the shoot with a high proportion of young leaf area, because of low net photosynthesis and high dark respiration. Characteristics of leaf photosynthesis were discussed with respect to leaf physiology and phenology.

C 3 Photosynthesis in the Gametophyte of the Epiphytic CAM Fern Pyrrosia longifolia (Polypodiaceae)

Sporophytes of some epiphytic species in the fern genus Pyrrosia exhibit Crassulacean acid metabolism (CAM), generally considered to be a derived physiological response to xeric habitats. Because these species alternate between independent sporophytic and gametophytic generations yet only the sporophyte has been characterized physiologically, experiments were conducted to determine the photosynthetic pathways present in mature sporophytes, immature sporophytes, and gametophytes of Pyrrosia longifolia. Diurnal CO2 exchange and malic acid fluctuations demonstrated that although the mature sporophytes exhibited CAM, only C3 photosynthesis occurred in the gametophytes and young sporophytes. Consideration of the above results and those from previous studies, as well as the life cycle of ferns, indicates that the induction of CAM probably occurs at a certain developmental stage of the sporophyte and/or following exposure to stress. Elucidation of the precise mechanisms underlying this C3-CAM transition awaits further research.

C3 photosynthesis in the gametophyte of the epiphytic CAM fern Pyrrosia longifolia (Polypodiaceae)

Sporophytes of some epiphytic species in the fern genus Pyrrosia exhibit Crassulacean acid metabolism (CAM), generally considered to be a derived physiological response to xeric habitats. Because these species alternate between independent sporophytic and gametophytic generations yet only the sporophyte has been characterized physiologically, experiments were conducted to determine the photosynthetic pathways present in mature sporophytes, immature sporophytes, and gametophytes of Pyrrosia longifolia. Diurnal CO2 exchange and malic acid fluctuations demonstrated that although the mature sporophytes exhibited CAM, only C3 photosynthesis occurred in the gametophytes and young sporophytes. Consideration of the above results and those from previous studies, as well as the life cycle of ferns, indicates that the induction of CAM probably occurs at a certain developmental stage of the sporophyte and/or following exposure to stress. Elucidation of the precise mechanisms underlying this C3‐CAM transition awaits further research.

Effects of Water Stress on Gas Exchange Characteristics in Crassulacean Acid Metabolism Plant, Dendrobium Ekapol cv. Panda.

デンドロビウム (Dendrobium Ekapol cv. Panda)を用い, 水ストレスが個葉のガス交換に及ぼす影響を調べた. Crassulacean Acid Metabolism型CO2交換は, 水ストレスを与えると速やかに変化し, まず明期の後半に生じるCO2吸収が減少した. 次いで暗期と明期始めのCO2吸収も減少したが, 葉の水ポテンシャルが-0.6MPa以下でも正のCO2交換速度を維持した. 各PhaseのCO2収支量は, 水ポテンシャルが-0.38MPa以下に低下すると急激に減少し, デンドロビウムのCO2交換速度が低下する水ポテンシャルの閾値は-0.38MPa付近にあるものと考えられた. ホスホエノールピルビン酸カルボキシラーゼの活性は, 水ストレスを与えると増加し, CO2吸収の減少と対応しなかった. 一方, 水ストレス条件下の葉の拡散伝導度とCO2吸収速度との間には, いずれのPhaseにおいても高い正の相関関係が認められ, 本研究で認められた水ストレス下のCO2吸収は, 主に気孔を含むガス拡散系により律速されていると考えた.

Upland tundra in the foothills of the Brooks Range, Alaska: Diurnal CO2 exchange patterns of characteristic lichen species

Summary CO2 exchange, water content, and microclimate conditions were observed for seven characteristic lichen species in their natural habitat within upland tundra communities of northern Alaska. Diurnal courses of lichen gas exchange response were recorded over five-day periods during the arctic summer and fall (from July to early September 1988 and 1989). Water availability is the environmental factor of foremost importance in determining rates of primary production. Water sources were rain, fog, and dew fall, as well as high air humidity, which alone could reactivate most of the green algal species after desiccation. Despite high variability in environmental conditions, certain patterns in the diurnal course of thallus hydration occurred repeatedly, so that five different weather types were defined within which gas exchange performance was predictable. Even short periods of favourable hydration were used by lichens for positive net photosynthesis (NP). There was no indication of adverse consequences of “resaturation respiration”. Even after a dry period of 3 days, sudden rehydration resulted in carbon gain without delay. For short periods of time, the combinations of water content, temperature and light imposed on the lichens enables high rates of NP. Individual species differed greatly in their maximal NP rate, which correlated with chlorophyll and nitrogen content. At favourable times in the field, observed NP rates approached the maximum capacity found in laboratory experiments at natural ambient CO2. Often with sufficient hydration, carbon gain was limited by light. CO2 exchange became negative even during daylight hours due to the effects of fog and clouds with light below compensation levels. Reduced but still positive rates of NP were observed with snow and with frozen lichens. In order to draw general conclusions about activity over the summer season, the time was calculated for a characteristic set of sampling days during which thalli were inactivated due to dehydration (no CO2 exchange measurable), during which they photosynthetically fixed CO2, and during which CO2 was released. The thalli were inactivated on the average 42.5 % of the time. Species-specific differences with respect to the total period of dehydration were surprisingly small (from 39.0% forStereocaulon alpinum to 45.5 % for Cetraria cucullata). Thus, growth-form specific morphology and anatomy of the samples, which were exposed side-by-side at the same site did not result in large differences in active phases. On the other hand, differences in physiological traits between species result in varying division of active phases with respect to positive and negative NP. For example, Dactylina arctica photosynthesized 1.36 times longer than Peltigera malacea. Other traits tend to offset the negative effect of long periods with respiratory CO2 release. As a result, the cyanobacterial lichen Peltigera malacea with the shortest total period of positive NP was, nevertheless, the most productive species due to its high photosynthetic capacity. Our field observations strengthen the viewpoint that studies of lichen physiological differentiation are essential for understanding species autecology and that approaches based on interpretation of morphological attributes may sometimes be exaggerated in their importance.

ファレノプシスにおけるＣＡＭ型光合成への葉齢・花序・水分・温度・光条件の影響

Effects of some factors on CAM (Crassulacean acid metabolism) photosynthesis in Phalaenopsis were investigated by measuring diurnal CO2 exchange patterns. Following results were obtained.1. The diurnal CO2 uptake pattern of Phalaenopsis leaves is nearly typical of CAM photosynthesis. Leaf age had no influence on CAM photosynthesis; the youngest leaf absorbed slightly more CO2 during the day and less at the night than did mature leaves. Although the third and forth leaves were shaded by the upper leaves, they fixed CO2 via CAM photosynthesis at rates similar to the upper two leaves fully exposed to light.2. Formation of inflorescence did not influence the diurnal pattern of CO2 uptake of CAM photosynthesis. But the plants without inflorescence had lower activities in CO2 uptake via CAM photosynthesis than those with inflorescence.3. When the day and night temperature were kept constant, 20°C was the optimum for the night time CO2 uptake. Although the day time CO2 uptake decreased as temperature increased, total CO2 uptake during 24 hr was maximized at 20°C. Higher day and lower night temperatures (25°15°C) were more favorable than a constant 20°C with respect to CO2 assimilation of CAM photosynthesis at night or during the entire day. Low day time temperature of 10°C depressed CO2 uptake rates at night and promotes during the day so that the Phalaenopsis leaves approximated those of plants with C3-photosynthetic system.4. The day and night time CO2 uptake increased with higher light intensity up to 130μE/m2/sec. Above 130μE/m2/sec the capacity of leaves to assimilate CO2 at night was saturated and that during the day became lower. Therefore, CAM photosynthesis in Phalaenopsis has a lower light saturating point than other plants.5. Under our growing conditions, withholding water for 10 days resulted in a severe water stress which significantly depressed CO2 uptake both day and night.

Energy utilization and carbon metabolism in mediterranean scurb vegetation of Chile and California : I. Methods: A transportable cuvette field photosynthesis and data acquisition system and representative results for Ceanothus greggii.

A transportable system for field and laboratory measurement of plant CO2 exchange and transpiration is described. A computer based data acquisition system which controls data-logging has been successfully proven in mediterranean zones of central Chile and southern California and in the taiga of central Alaska. Six Peltier-effect cooled acrylic plastic chambers are utilized in an open infrared gas analysis system for continuous monitoring of CO2 exchange. Chamber air temperatures automatically track ambient air temperatures or can be preset to maintain a constant temperature. Use of Peltier-effect cooling modules and electric cartridge heaters result in light-weight chambers and heat exchange units with low power requirements. No refrigeration or liquid coolant is required under most operating conditions. A unique sampling method using natural illumination and six chambers allows highly replicated determinations of the temperature and light dependence of photosynthesis and/or respiration to be made over the course of a 6-d sampling period. Measurements are made continuously 24 h/day. Diurnal CO2 exchange patterns are determined from one chamber that tracks the ambient air temperature. The other five chambers have air temperatures fixed at distinct levels over a 35° C range. Each day the chambers are changed to another temperature level according to a randomized sampling pattern. All the data are pooled at the end of the 6-d run to construct the light and temperature response surfaces of CO2 exchange typical of the individuals sampled. Simultaneous determinations of conductance, leaf temperature, air temperature, and light are made.