Photosynthetic Photon Flux Conditions Research Articles

Photo-protection and photo-inhibition during light induction in Barbula indica and Conocephalum conicum under different light gradients.

The objectives of this study were to measure the chlorophyll fluorescence (ChlF) parameters of Barbula indica (Hook.) Spreng and Conocephalum conicum (L.) Dumort subjected to various light intensities (LI) as a reflection of their adaptability to their habitats. The electron transport rate (ETR) of all plants under 500μmolm-2s-1 photosynthetic photon flux density (PPFD) was significantly higher than other LI treatments, implying that these plants could be grown under a specific and optimal light intensity adapted to 500 PPFD conditions. As LI increased from 50 to 2,000 PPFD, we observed in all plants increased non-photochemical quenching (NPQ) and photo-inhibitory quenching (qI) and decreased photosystem II efficiency (ΦPSII), potential quantum efficiency of PSII (Fv/Fm), actual PSII efficiency (ΔF/Fm'%), and Fv/Fm%. In addition, energy-dependent quenching (qE), the light protection system (qE + qZ + qT), and qI increased as ΦPSII decreased and photo-inhibition% increased under 1000, 1500, and 2000 PPFD conditions, suggesting that these plants had higher photo-protective ability under high LI treatments to maintain higher photosynthetic system performance. B. indica plants remained photochemically active and maintained higher qE under 300, 500, and 1000 PPFD, whereas C. conicum qZ + qT exhibited higher photo-protection under 500, 1000, and 1500 PPFD conditions. These ChlF indices can be used for predicting photosynthetic responses to light induction in different bryophytes and provide a theoretical basis for ecological monitoring.

Evaluation of the enhancement of photosynthetic rate in a komatsuna (Brassica rapa L. var. perviridis) canopy with upward lighting using an optical simulation in a plant factory with artificial light.

In a plant factory with artificial light (PFAL), upward lighting is expected to prevent senescence and decrease in the photosynthetic capacity of the lower leaves in the canopy. Upward lighting may also increase the photosynthetic rate of a canopy by improving its photosynthetic photon flux density (PPFD) distribution. However, the net photosynthetic rate (Pn) of leaves is lower when the abaxial surface is irradiated than that when the adaxial surface is irradiated. The aim of this study was to estimate the PPFD in a PFAL and the Pn of plants using three-dimensional plant models and optical simulation. First, we measured the Pn of komatsuna (Brassica rapa L. var. perviridis) leaves under different conditions of the proportion (pad ) of PPFD on the adaxial surface to total PPFD on both surfaces and developed an equation for the light response curve of photosynthesis considering pad . When PPFD was low, except when it was 30 and 70 µmol m-2 s-1, Pn increased as pad increased, because the absorptance also increased with pad . Under high PPFD conditions, Pn was maximized at 67-83% of pad because the light would be distributed more efficiently for photosynthesis. Next, using optical simulation and the developed equation, we estimated the photosynthetic rate of a komatsuna canopy (CPn) under downward and upward lighting. The CPn increased by 1.08-1.13 times by combining downward and upward lighting due to the increase in the photosynthetic photon flux (PPF) of light incident on the canopy and the decrease in the spatial variation of PPFD on the leaves in the canopy. As the depreciation of lamps for upward lighting accounts for 7.5-9.0% of the production cost in a PFAL, even if the depreciation of lamps for upward lighting increased, enhancement of CPn by upward lighting would be cost-effective. We performed optical simulations under 220 conditions and evaluated them using CPn as an index. Moreover, we provided the proportion of PPF of upward lighting that improved CPn and discussed the reason for this improvement. The result shows that optical simulation is useful for evaluating the lighting design in a PFAL and analyzing the effects of the lighting design on the light environment and photosynthesis.

Photosynthetic responses of Eulophia dentata, Bletilla formosana, and Saccharum spontaneum under various photosynthetic photon flux density conditions

This study aimed to determine the photosynthetic performance and differences in chlorophyll fluorescence (ChlF) parameters between Eulophia dentata and its companion species Bletilla formosana and Saccharum spontaneum when subjected to different photosynthetic photon flux density (PPFDs). Leaf surfaces were then illuminated with 50, 100 (low PPFDs), 300, 500, 800 (moderate PPFDs); 1,000; 1,500; and 2,000 (high PPFDs) μmol m-2.s-1, and the ChlF parameters were measured during the whole process. Increasing nonphotochemical quenching of ChlF and decreasing potential quantum efficiency of PSII, actual quantum efficiency of PSII, and quantum efficiency ratio of PSII in dark recovery from 0-60 min were observed in all leaves. A significant and negative relationship was detected between energy-dependent quenching (qE) and photoinhibition percent in three species under specific PPFD conditions, whereas a significant and positive relationship was detected between photoinhibitory quenching (qI) and photoinhibition percent. The qE and qI can be easily measured in the field and provide useful ecological indexes for E. dentata species restoration, habitat creation, and monitoring.

Estimating Light Acclimation Parameters of Cucumber Leaves Using Time-Weighted Averages of Daily Photosynthetic Photon Flux Density.

Leaves acclimate to day-to-day fluctuating levels of photosynthetic photon flux density (PPFD) by adjusting their morphological and physiological parameters. Accurate estimation of these parameters under day-to-day fluctuating PPFD conditions benefits crop growth modeling and light environment management in greenhouses, although it remains challenging. We quantified the relationships between day-to-day PPFD changes over 6 days and light acclimation parameters for cucumber seedling leaves, including leaf mass per area (LMA), chlorophyll (Chl) a/b ratio, maximum net photosynthetic rate (Pnmax), maximum rate of ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (Vcmax), and maximum rate of electron transport (Jmax). The last two parameters reflect the capacity of the photosynthetic partial reactions. We built linear regression models of these parameters based on average or time-weighted averages of daily PPFDs. For time-weighted averages of daily PPFDs, the influence of daily PPFD was given a specific weight. We employed three types of functions to calculate this weight, including linear, quadratic, and sigmoid derivative types. We then determined the trend of weights that estimated each parameter most accurately. Moreover, we introduced saturating functions to calibrate the average or time-weighted averages of daily PPFDs, considering that light acclimation parameters are usually saturated under high PPFDs. We found that time-weighted average PPFDs, in which recent PPFD levels had larger weights than earlier levels, better estimated LMA than average PPFDs. This suggests that recent PPFDs contribute more to LMA than earlier PPFDs. Except for the Chl a/b ratio, the average PPFDs estimated Pnmax, Vcmax, and Jmax with acceptable accuracy. In contrast, time-weighted averages of daily PPFDs did not improve the estimation accuracy of these four parameters, possibly due to their low response rates and plasticity. Calibrating functions generally improved estimation of Chl a/b ratio, Vcmax, and Jmax because of their saturating tendencies under high PPFDs. Our findings provide a reasonable approach to quantifying the extent to which the leaves acclimate to day-to-day fluctuating PPFDs, especially the extent of LMA.

Characteristics of isoprene emission from moso bamboo leaves in a forest in central Taiwan

The expansion of moso bamboo (Phyllostachys edulis) may potentially impact regional isoprene emissions. Modeling based on field measurements is an effective approach for assessing the potential impact of the moso bamboo expansion. The G93 algorithm is one of the most widely used models, however no studies have tested the applicability of the algorithm for moso bamboo isoprene emission. This study was undertaken to establish a model for reproducing moso bamboo isoprene emission fluxes. To this aim, this study examined 1) the isoprene emission ability of moso bamboo, and 2) its responses to environmental factors such as leaf temperature and light. We also tested 3) the reproducibility of the G93 algorithm for moso bamboo isoprene emission fluxes. This study used a chamber method with a modified photosynthesis system and carbon absorbents to quantify isoprene emitted from bamboo leaves in central Taiwan under the humid subtropical climate. First, we screened isoprene emission from 12 bamboo species, and the results confirmed that moso bamboo exhibited significant isoprene emission potential. Second, we measured isoprene emission fluxes from moso bamboo leaves with light controls every month from summer to spring. The isoprene emission fluxes increased with photosynthetic photon flux density (PPFD); under sufficient PPFD conditions, the seasonal changes in the isoprene emission fluxes were regulated by leaf temperature, and low isoprene emission fluxes were found in low leaf temperature conditions. Thirdly, overestimations were observed in the G93 algorithm with the original parameters in periods with leaf temperatures <23 °C. Using the G93 algorithm with site-specific parameters could improve the overestimation in the low-temperature period. This study suggests the necessity of parameterization in the G93 algorithm to reproduce the suppression of isoprene emission fluxes from moso bamboo leaves in the low-temperature period.

Effect of temporally heterogeneous light on photosynthetic light use efficiency, plant acclimation and growth in Abatia parviflora.

Individual leaves have a unique instantaneous photosynthetic photon flux density (PPFD) at which net photosynthetic light use efficiency (ϵL, the ratio between net photosynthesis and PPFD) is maximised (PPFDϵmax). When PPFD is above or below PPFDϵmax, efficiency declines. Thus, we hypothesised that heterogeneous PPFD conditions should increase the amount of time leaves photosynthesise at a PPFD different than PPFDϵmax and result in reduced growth. To date, this prediction has not been rigorously tested. Here, we exposed seedlings of Abatia parviflora Ruiz & Pav to light regimes of equal total daily irradiance but with three different daily time courses of PPFD: constant PPFD (No_H), low heterogeneity (Low_H) and high heterogeneity (High_H). Mean ϵL, leaf daily photosynthesis and plant growth were all significantly higher in No_H and Low_H plants than in High_H plants, supporting our hypothesis. In addition, mean ϵL was positively related to final plant biomass. Unexpectedly, High_H plants had more etiolated stems and more horizontal leaves than No_H and Low_H plants, possibly due to exposure to low PPFD in the morning and afternoon. In conclusion, PPFD heterogeneity had an important effect on average ϵL, photosynthesis and growth, but also on allocation and plant morphology.

Growth and Accumulation of Secondary Metabolites in Perilla as Affected by Photosynthetic Photon Flux Density and Electrical Conductivity of the Nutrient Solution.

The global demand for medicinal plants is increasing. The quality of plants grown outdoors, however, is difficult to control. Myriad environmental factors influence plant growth and directly impact biosynthetic pathways, thus affecting the secondary metabolism of bioactive compounds. Plant factories use artificial lighting to increase the quality of medicinal plants and stabilize production. Photosynthetic photon flux density (PPFD) and electrical conductivity (EC) of nutrient solutions are two important factors that substantially influence perilla (Perilla frutescens, Labiatae) plant growth and quality. To identify suitable levels of PPFD and EC for perilla plants grown in a plant factory, the growth, photosynthesis, and accumulation of secondary metabolites in red and green perilla plants were measured at PPFD values of 100, 200, and 300 μmol m-2 s-1 in nutrient solutions with EC values of 1.0, 2.0, and 3.0 dS m-1. The results showed significant interactive effects between PPFD and EC for both the fresh and dry weights of green perilla, but not for red perilla. The fresh and dry weights of shoots and leafy areas were affected more by EC than by PPFD in green perilla, whereas they were affected more by PPFD than by EC in red perilla. Leaf net photosynthetic rates were increased as PPFD increased in both perilla varieties, regardless of EC. The perillaldehyde concentration (mg g-1) in red perilla was unaffected by the treatments, but accumulation in plants (mg per plant) was significantly enhanced as the weight of dry leaves increased. Perillaldehyde concentrations in green perilla showed significant differences between combinations of the highest PPFD with the highest EC and the lowest PPFD with the lowest EC. Rosmarinic acid concentration (mg g-1) was increased in a combination of low EC and high PPFD conditions. Optimal cultivation conditions of red and green perilla in plant factory will be discussed in terms of plant growth and contents of medicinal ingredients.

Under slow flow conditions, daily rates of canopy photosynthesis of marine macrophytes were insensitive to model choice and flow‐rate

SummaryWater motion drives the flux of suspended and dissolved material (e.g., nutrients, gametes, and dissolved oxygen) to and from macrophyte canopies, and is one of the most important mechanisms that can regulate the growth, survival, and persistence of marine macrophytes populations. At small spatial scales (e.g., lamina or leaves and individuals), increasing flow‐rates have been demonstrated to enhance physiological processes, especially photosynthesis rates, and we expected a similar response at the canopy scale. We conducted seven experiments over 25 days using a pair of open‐air flow‐chambers under natural light, temperature, and seawater conditions. In the four marine macrophyte (Sargassum piluliferum, S. siliquastrum, S. thunbergii, and Zostera marina) canopies examined, an increase in flow‐rate did not enhance photosynthesis rates. The odds that daily gross photosynthesis rates increase with a decrease in flow‐rates was 1.77 to 1. We also examined if two non‐linear equations and one linear equation, often used to describe the relationship between photosynthesis to photosynthetic photon flux density (PPFD), biased estimates of the daily rates of photosynthesis and respiration. It was revealed that the functional form of the equation strongly influenced photosynthesis and respiration rate estimates at short time scales (i.e., minutes), however, daily rates were insensitive to the type of equation used to model the relationship between photosynthesis and PPFD. We suggest that the predominance of photosynthesis rates occurring in under‐saturating PPFD conditions (&gt; 40 % of daylight hours) may be one of the reasons for this insensitivity.

당귀의 광합성 특성과 수경재배 방식에 따른 생장 분석

The aim of this study was to investigate which hydroponic system is the optimum for growth and photosynthetic characteristics of Angelica gigas during experiment. Angelica gigas ‘Manchu’ were sowed and managed under a growth room chamber. The environmental conditions (temperature 22℃/18℃ (day/night), relative humidity 50-70%, photosynthetic photon flux density (PPFD) 120±6 μmol m -2 s -1 ) were maintained for 3 weeks. Forty eight seedlings with 4-5 leaves were transplanted in deep flow technique (DFT), substrate, and spray culture systems [culture bed: 800 (L) x 800 (W) x 400 mm(H)] under 150±5 μmol m -2 s -1 PPFD provided with fluorescence lamps and cultivated for 11 weeks. At the end of the experiment, fresh and dry weights, leaf lenghth and width, SPAD, root fresh, and dry weights, and root volume of Anglica gigas were measured. Photosynthetic rate of Anglica gigas were measured with portable photosynthesis systems to investigate optimum PPFD, CO₂ concentration, and air temperature conditions. Fresh and dry weights of Anglica gigas grown in substrate were significantly greater than DFT-treated, but there were not significant with spray treatment. Leaf photosynthesis of Anglica gigas showed the tendency to sharply increase as PPFD was increased from 50 to 200 μmol m -2 s -1 . Though CO₂ saturation point was around 1000-1200 μmol mol-1, increase in air temperature from 16 to 26℃ did not quite affect photosynthesis of Anglica gigas. In conclusion, Anglica gigas may be optimally cultivated with a spray culture system as air temperature, PPFD, and CO₂ concentration for environment are controlled at 20±3℃, 150 μmol m -2 s -1 , and around 1000 μmol mol -1 for mass production.

Effects of photosynthetic photon flux and carbon dioxide concentration on the photosynthesis and growth of grafted pepper transplants during healing and acclimatization

In the production of grafted transplants, healing and acclimatization are the most critical processes for survival. We investigated the influence of the photosynthetic photon flux (PPF) and the carbon dioxide (CO2) concentration during healing and acclimatization on the photosynthetic characteristics and growth of grafted pepper transplants to determine the optimum environmental conditions for healing and acclimatization in a healing chamber with artificial lighting source. Grafted pepper transplants were healed and acclimatized under two levels of CO2 (374 or 1,013 μmol·mol−1) and four levels of PPF (dark, 50, 98 or 147 μmol·m−2·s−1) for six days. The CO2 exchange rates of the grafted pepper transplants significantly increased with increasing PPF during healing and acclimatization. The CO2 exchange rates were higher under elevated CO2 concentrations than ambient CO2 concentration. The effect of CO2 enrichment was greater in low light intensity. The CO2 exchange rates at 50, 98 or 147 μmol·m−2·s−1 under elevated CO2 concentrations were 511, 261, and 172%, respectively, compared to the ambient CO2 concentrations. The increase of photosynthesis led to an improvement in growth. The SPAD value, dry weight and leaf area were greater under higher PPF and CO2 concentrations. PPF also influenced the anatomical structures of the leaves, and the palisade and spongy tissue cells of the leaves irradiated with higher PPF were aligned more densely, with more chloroplasts and small empty space. When compared to the tunnel in the greenhouse with natural light, healing and acclimatization under high CO2 (1,000 μmol·mol−1) and PPF (150 μmol·m−2·s−1) conditions in the healing chamber promoted the growth and graft union formation of grafted pepper transplants. The results suggested that high-quality grafted pepper seedlings could be achieved by healing and acclimatization in a healing chamber where optimal conditions such as high PPF and CO2 were maintained within the range evaluated in this experiment.

Photosynthetic characteristics of Cymbidium ‘Red Fire’ and ‘Yokihi’ at different developmental stages

Photosynthetic characteristics of two Cymbidium hybrids, ‘Red Fire’ and ‘Yokihi’, were investigated at different developmental stages. The net CO2 assimilation rate (An) as a function of incident photosynthetic photon flux (PPF), intercellular CO2 concentration (Ci), and relative humidity (RH) in a leaf chamber head was determined in a greenhouse with 1- and 2-year-old plant leaves. The maximum net CO2 assimilation rate (Anmax) in response to PPF of 1-year-old ‘Red Fire’ was 6.11 μmol·CO2·m−2·s−1 at 700 μmol·m−2 ·s−1 PPF, whereas it was 4.9 μmol·CO2·m−2·s−1 at 500 μmol·m−2·s−1 PPF in ‘Yokihi’. Under low light intensity (below 250 μmol·m−2 ·s−1 PPF), An was more pronounced in ‘Yokihi’ than in ‘Red Fire’. In 2-year-old Cymbidium, however, the maximum An was less than 2 μmol·CO2·m−2·s−1 in both cultivars at the same CO2 condition of 600 μmol·CO2·mol−1 air. The An increased in the leaves of 2-year-old plant under an elevated CO2 condition up to 1,500 μmol·CO2·mol−1 air with increasing PPF up to about 800 μmol·m−2·s−1. The An increased with increasing Ci and showed the highest value when Ci was over 1,000 and 2,000 μmol·mol −1 air in ‘Red Fire’ and ‘Yokihi’, respectively. The carboxylation efficiency of ‘Red Fire’ and ‘Yokihi’ were 0.044 and 0.036 μmol·CO2·m−2·s−1, respectively, while An of ‘Yokihi’ was higher than that of ‘Red Fire’ at above 1,000 μmol·mol−1 air Ci. The An tended to increase with RH, increasing from 15 to 70% in both hybrids. The Anmax of ‘Yokihi’ was observed at over 70% of RH, whereas 45% of RH was sufficient enough to show Anmax in ‘Red Fire’. The results shows that the photosynthetic characteristics of Cymbidium ‘Red Fire’ and ‘Yokihi’ can be increased by controlling the PPF, CO2, and RH conditions and the optimal conditions for maximum photosynthetic efficiency vary by cultivar, developmental stage, and greenhouse conditions.

Using combined measurements of gas exchange and chlorophyll fluorescence to investigate the photosynthetic light responses of plant species adapted to different light regimes

One broad-leaved pioneer tree, Alnus formosana, two broad-leaved understory shrubs, Ardisia crenata and Ardisia cornudentata, and four ferns with different light adaptation capabilities (ranked from high to low, Pyrrosia lingus, Asplenium antiquum, Diplazium donianum, Archangiopteris somai) were used to elucidate the light responses of photosynthetic rate and electron transport rate (ETR). Pot-grown materials received up to 3 levels of light intensity, i.e., 100%, 50% and 10% sunlight. Both gas exchange and chlorophyll (Chl) fluorescence were measured simultaneously by an equipment under constant temperature and 7 levels (0-2,000 μmol m-2 s-1) of photosynthetic photon flux density (PPFD). Plants adapted to-or acclimated to high light always had higher light-saturation point and maximal photosynthetic rate. Even materials had a broad range of photosynthetic capacity [maximal photosynthetic rate ranging from 2 to 23 μmol(CO2) m-2 s-1], the ratio of ETR to gross photosynthetic rate (P G) was close for A. formosana and the 4 fern species when measured under constant temperature, but the PPFD varied. In addition, P. lingus and A. formosana grown under 100% sunlight and measured at different seasonal temperatures (15, 20, 25, and 30°C) showed increased ETR/P G ratio with increasing temperature and could be fitted by first- and second-order equations, respectively. With this equation, estimated and measured P G were closely correlated (r 2 = 0.916 and r 2 = 0.964 for P. lingus and A. formosana, respectively, p<0.001). These equations contain only the 2 easily obtained dynamic indicators, ETR and leaf temperature. Therefore, for some species with near ETR/P G ratio in differential levels of PPFD, these equations could be used to simulate dynamic variation of leaf scale photosynthetic rate under different temperature and PPFD conditions.

Midday depression of leaf CO2 exchange within the crown of Dipterocarpus sublamellatus in a lowland dipterocarp forest in Peninsular Malaysia

We observed diurnal and seasonal patterns of leaf-scale gas exchange within the crown of a Dipterocarpus sublamellatus Foxw. tree growing in a lowland dipterocarp forest at Pasoh, Peninsular Malaysia. Observations were carried out nine times over 6 years, from September 2002 to December 2007. Observation periods included both wet and mild-dry periods, and natural and saturated photosynthetic photon flux density (PPFD) light conditions. In situ measurements of the diurnal change in net photosynthetic rate and in stomatal conductance were carried out on canopy leaves of a 40-m-tall D. sublamellatus tree, which was accessed from a canopy corridor. A diurnal change in electron transport rate was observed under saturated PPFD conditions. The maximum net assimilation rate was approximately 10 micromol m(-2) s(-1). There was a clear inhibition of the net assimilation rate coupled with stomatal closure after late morning and this inhibition occurred year-round. Although the electron transport rate decreased alongside this inhibition, it sometimes followed on. Numerical analysis showed that the main factor in the inhibition of the net assimilation rate was patchy bimodal stomatal closure, which occurred in both mild-dry and wet periods. The midday depression occurred year-round, though there are fluctuations in soil moisture during the mild-dry and wet periods. The magnitude of the inhibition was not related to soil water content but was related to vapor pressure deficit (VPD): that is, whether the days were sunny and hot or cloudy and cool. On cloudy, cool days in the wet period, the net photosynthesis was only moderately inhibited, but it still decreased in the afternoon and was coupled with patchy stomatal closure, even in quite moderate VPD, leaf temperature and PPFD conditions. Our results suggest that patchy stomatal closure signaled by the increase in VPD, in transpiration and by circadian rhythms, was the key factor in constraining midday leaf gas exchange of the D. sublamellatus canopy leaves.

Acclimation of Plant Populations to Shade: Photosynthesis, Respiration, and Carbon Use Efficiency

Cloudy days cause an abrupt reduction in daily photosynthetic photon flux (PPF), but we have a poor understanding of how plants acclimate to this change. We used a unique 10-chamber, steady-state, gas-exchange system to continuously measure daily photosynthesis and night respiration of populations of a starch accumulator [tomato (Lycopersicon esculentum Mill. cv. Micro-Tina)] and a sucrose accumulator [lettuce (Lactuca sativa L. cv. Grand Rapids)] over 42 days. All measurements were done at elevated CO2 (1200 μmol·mol-1) to avoid any CO2 limitations and included both shoots and roots. We integrated photosynthesis and respiration measurements separately to determine daily net carbon gain and carbon use efficiency (CUE) as the ratio of daily net C gain to total day-time C fixed over the 42-day period. After 16 to 20 days of growth in constant PPF, plants in some chambers were subjected to an abrupt PPF reduction to simulate shade or a series of cloudy days. The immediate effect and the long term acclimation rate were assessed from canopy quantum yield and carbon use efficiency. The effect of shade on carbon use efficiency and acclimation was much slower than predicted by widely used growth models. It took 12 days for tomato populations to recover their original CUE and lettuce CUE never completely acclimated. Tomatoes, the starch accumulator, acclimated to low light more rapidly than lettuce, the sucrose accumulator. Plant growth models should be modified to include the photosynthesis/respiration imbalance and resulting inefficiency of carbon gain associated with changing PPF conditions on cloudy days.

VENTILATION AND LIGHT INTENSITY DURING IN VITRO CULTURE AFFECT RELATIVE GROWTH RATE AND PHOTOSYNTHATE PARTITIONING OF CALADIUM PLANTLETS AFTER TRANSPLANTING TO EX VITRO

Caladium bicolor 'Candidum' plantlets were cultured on medium containing 2% sucrose and 0.8% agar in vitro under different conditions of ventilation and photosynthetic photon flux density (PPFD) and then transplanted to an ex vitro environment. During in vitro culture, the plantlets were fed with 13 CO 2 . Dry weight of plantlets cultured in the high-ventilated vessel was no greater than that cultured in a low-ventilated vessel, however, after transplanting, the relative growth rate of the plantlets cultured in the high-ventilated vessel was greater than that cultured in a low-ventilated vessel. Culturing in the low-ventilated vessel increased partitioning of 13 C to a stem during in vitro culture and in the long term after transplanting. Culturing under low PPFD did not affect the distribution ratio of 13C in plant parts, but after acclimatization, the 13C atom % excess in the whole plant cultured under low PPFD was lower than that cultured under high PPFD, indicating that the photosynthates obtained under low PPFD conditions were less re-translocated to new tissues and organs. The results indicate that the ventilation condition and light intensity during in vitro culture affect the translocation of photosynthates not only during the culture but also in the long term after transplanting to ex vitro.

Interacting effects of photosynthetic photon flux density and temperature on canopy CO 2 exchange rate of spring wheat under different CO 2-concentrations

Summary The objective of the present study was to quantify the interaction between photosynthetic photon flux density (PPFD) and temperature on canopy CO 2 exchange race (CCER) of wheat at ambient and elevated CO 2 -concentrations. Spring wheat ( Triticum aestivum L. cv. Minaret) was grown from emergence to maturity in open-top chambers under ambient (360 ppm) and elevated CO 2 -concentrations (680 ppm). CCER was measured using a specifically designed open system consisting of two canopy chambers (ca. 1.26 m 3 each) and a monitoring unit. Air temperature and light intensity were measured directly above the canopy. CCER was measured from the first node stage until anthesis when leaf area index ranged between 2–3. PPFD ranged from 0 — ca. 1,100 μmolm −2 s −1 and temperature from 7.5°–39°C. CCER increased with increasing temperature and PPFD and was light-satured at 800 μmol m −2 s −1 under ambient CO 2 -concentration. CO 2 -enrichment stimulated CCER by up to 50% bui there was no complete light saturation. Under high PPFD conditions (> 600 μmolm −2 s −1 ) and at low temperatures ( 30 °C) and low PPFD conditions ( −2 s −1 ) the positive CO 2 -effect on CCER was reduced nearly to zero. Thus, temperature optima of the stimulation of CCER by elevated CO 2 -concentrations were found. The optimum temperature of CCER increased with increasing light intensity and was shifted by the CO 2 -enrichment to higher temperatures by ca. 0.5 °C (at low PPFD) — 2 °C (at high PPFD). The results were compared with the predicitions from recent mechanistic models of CCER.

閉鎖型苗生産システムにおける電気エネルギ消費量削減のための光合成有効光量子束調節

Sweetpotato plants were grown for 15 d under stepwise photosynthetic photon flux (PPF) and two levels of constant PPF conditions. In stepwise PPF condition, the PPFs were set at 100, 200 and 300μmol m-2 s-10-4, 5-9 and 10-14 d after planting, respectively. PPFs of 200 and 300μmol m-2 s-1 were chosen as the constant PPF conditions. Under same integrated PPF (PPF×photoperiod×experimental period), dry weight per plant 14 d after planting was 1.1 times higher in stepwise PPF condition than in constant PPF condition. The increase in dry weight per electric energy consumption of lamps was 1.1 times higher in stepwise PPF condition than in constant PPF conditions. Therefore, stepwise PPF control is a useful method for reducing electric energy consumption and increasing electric energy utilization efficiency (chemical energy contained in plants/electric energy consumption of the system) of the closed-type transplant production system.

Diurnal changes in leaf gas exchange and chlorophyll fluorescence in tropical tree species with contrasting light requirements

Interspecific ecophysiological differences in response to different light environments are important to consider in regeneration behavior and forest dynamics. The diurnal changes in leaf gas exchange and chlorophyll fluorescence of two dipterocarps, Shorea leprosula (a high light‐requiring) and Neobalanocarpus heimii (a low light‐requiring), and a pioneer tree species (Macaranga gigantea) growing in open and gap sites were examined. In the open site, the maximum net photosynthetic rate (Pn), photosystem II (PSII) quantum yield (Δ; F/Fm′), and relative electron transport rate (r‐ETR) through PSII at a given photosynthetic photon flux density (PPFD) was higher in S. leprosula and M. gigantea than in N. heimii, while non‐photochemical quenching (NPQ) at a given PPFD was higher in N. heimii. The maximum values of net photosynthetic rate (Pn) in M. gigantea and S. leprosula was higher in the open site (8–11 μmol m−2 s−1) than in the gap site (5 μmol m−2 s−1), whereas that in N. heimii was lower in the open site (2 μmol m−2 s−1) than in the gap site (4 μmol m−2 s−1), indicating that N. heimii was less favorable to the open site. These data provide evidence to support the hypothesis that ecophysiological characteristics link with plant’s regeneration behavior and successional status. Although Pn and stomatal conductance decreased at midday in M. gigantea and S. leprosula in the open site, both r‐ETR and leaf temperature remained unchanged. This indicates that stomatal closure rather than reduced photochemical capacity limited Pn in the daytime. Conversely, there was reduced r‐ETR under high PPFD conditions in N. heimii in the open site, indicating reduced photochemical capacity. In the gap site, Pn increased in all leaves in the morning before exposure to direct sunlight, suggesting a relatively high use of diffuse light in the morning.

In situ Comparison of Daily Photosynthetic Activity Patterns of Saxicolous Lichens and Mosses in Sierra de Guadarrama, Central Spain

In situ Comparison of Daily Photosynthetic Activity Patterns of Saxicolous Lichens and Mosses in Sierra de Guadarrama, Central Spain

Interacting Effects of Photoperiod and Photosynthetic Photon Flux on Net Carbon Assimilation and Starch Accumulation in Potato Leaves

The effect of photoperiod (PP) on net carbon assimilation rate (Anet) and starch accumulation in newly mature canopy leaves of 'Norland' potato (Solanum tuberosum L.) was determined under high (412 varies as mol m-2s-1) and low (263 varies as mol m-2s-1) photosynthetic photon flux (PPF) conditions. The Anet decreased from 13.9 to 11.6 and 9.3 micromoles m-2s-1, and leaf starch increased from 70 to 129 and 118 mg g-1 drymass (DM) as photoperiod (PP) was increased from 12/12 to 18/6, and 24/0, respectively. Longer PP had a greater effect with high PPF conditions than with low PPF treatments, with high PPF showing greater decline in Anet. Photoperiod did not affect either the CO2 compensation point (50 micromoles mol-1) or CO2 saturation point (1100-1200 micromoles mol-1) for Anet. These results show an apparent limit to the amount of starch that can be stored (approximately 15% DM) in potato leaves. An apparent feedback mechanism exists for regulating Anet under high PPF, high CO2, and long PP, but there was no correlation between Anet and starch concentration in individual leaves. This suggests that maximum Anet cannot be sustained with elevated CO2 conditions under long PP (> or = 12 hours) and high PPF conditions. If a physiological limit exists for the fixation and transport of carbon,then increasing photoperiod and light intensity under high CO2 conditions is not the most appropriate means to maximize the yield of potatoes.