Gas exchange parameters, water relations and carbohydrate partitioning in leaves of field-grown Prunus domestica following fruit removal

The effect of fruit removal on gas exchange, water relations, chlorophyll and non-structural carbohydrate content of leaves from mature, field-grown plum trees ( Prunus domestica L. cv. Stanley) was determined over 2 consecutive growing seasons. Removal of fruits during stage II of fruit development decreased CO₂ assimilation rate within 24 h from 12.6 to 8.5 μmol m^-2 s^-1 in 1986, and from 12.1 to 10.2 μmol m^-2 s^-1 in 1987. Depression of net photosynthesis persisted for at least 5 days and was greatest in the early afternoon. Recovery of the CO₂ assimilation rate to pretreatment levels coincided in defruited trees with vegetative growth that was more than 5-fold that of fruiting trees in the first 6 weeks after fruit removal in 1986. Estimated photorespiration was similar in both fruiting and defruited trees. The stomatal contribution to the decrease of CO₂ assimilation rate, calculated from assimilation/intercellular CO₂ curves, ranged from 31 to 46%. Defruiting did not affect leaf water potential, but decreased leaf osmotic potential. Leaf levels of chlorophyll, fructose, glucose, sorbitol and sucrose were not affected by defruiting, whereas starch content increased up to 51% in leaves of defruited trees within 24 h after fruit removal. However, because of the small starch pool present in plum leaves (<1.9% dry weight) it is unlikely that starch accumulation was responsible for the observed decline in CO₂ assimilation rate after fruit removal. The decrease of CO₂ assimilation rate is discussed in relation to the hypothesis of assimilate demand regulating photosynthesis through a feedback mechanism.     

Leaf Gas Exchange Characteristics in Relation to Leaf Canopy Position of Myrica faya in its Native Environment (Tenerife, Canary Islands)

Abstract: Diurnal courses of gas exchange were measured throughout one year in fully expanded current-year leaves in the uppermost canopy (sun leaves, 18 m above ground) and in the lower canopy (shade leaves, 12 m above ground) of Myrica faya Ait., a dominant component of the Canarian laurel forest in Tenerife, Canary Islands, Spain.
M. faya showed large differences between sun and shade leaves in gas exchange characteristics (about 50 % of maximum carbon assimilation rate (A_max) reduction in shade leaves, but this reduction can be higher on specific days) that were modulated by strong light attenuation and high leaf area index (LAI) of the stand. This species presented low A_max, about 10 μmol m^-2 s^-1, high maximum transpiration (E, 8 mmol m^-2 s^-1) and stomatal conductance (g_s, 750 mmol m^-2 s^-1) and very low instantaneous water use efficiency (WUE, mean maximum 1.1 mmol mol^-1) and A/g_s (mean maximum 23.5 μmol mol^-1). M. faya responded to high air vapour pressure deficit (VPD), decreasing its g_s but maintaining relatively high values of A and E during the studied period. Stomatal response to VPD showed a higher sensitivity than its congeners, M. cerifera, and Laurus azorica, tree species co-occurring in the Canarian laurel forest. In general, all these gas exchange characteristics lead us to consider this species more similar to subtropical plants of humid regions than to species of the Mediterranean region.     

Two mutants of Arabidopsis thaliana that become chlorotic in atmospheres enriched with CO2

Abstract. Two nonallelic, nuclear recessive mutants of Arabidopsis thaliana (L.) Heynh. which become chlorotic when grown in an atmosphere enriched to 20000 cm³ CO₂ m^-3 have been isolated. For one of the mutants, chlorosis begins at the veins and gradually spreads to the interveinal regions. A minimum photon flux density of ca 50 μmol m^-2 s^-1 is required for this response. For the other mutant, the yellowing is independent of the light intensity and begins at the basal regions of the leaves and spreads to the tips. The injurious effects of CO₂ seem to be restricted to photosynthetic tissues, since root elongation and callus growth were not inhibited by a high atmospheric CO₂ concentration for either mutant. Neither mutant became chlorotic in a low O₂ atmosphere that suppressed photorespiration as effectively as the elevated CO₂ does. Thus, the mutations do not impose a requirement for photorespiration. The possibilities that the high CO₂-sensitive phenotypes are caused by an effect of CO₂ in stomata, on ethylene synthesis, or on mineral uptake are discussed but are considered unlikely.     

The interaction of high temperature and elevated CO2 on photosynthetic acclimation of single leaves of rice in situ

Rice ( Oryza sativa L. cv. IR72) was grown at three different CO₂ concentrations (ambient, ambient + 200 μmol mol⁻¹, ambient + 300 μmol mol⁻¹) at two different growth temperatures (ambient, ambient + 4°C) from sowing to maturity to determine longterm photosynthetic acclimation to elevated CO₂ with and without increasing temperature. Single leaves of rice showed a cooperative enhancement of photosynthetic rate with elevated CO₂ and temperature during tillering, relative to the elevated CO₂ condition alone. However, after flowering, the degree of photosynthetic stimulation by elevated CO₂ was reduced for the ambient + 4°C treatment. This increasing insensitivity to CO₂ appeared to be accompanied by a reduction in ribulose-1.5-bisphosphate carboxylase/oxygenase (Rubisco) activity and/or concentration as evidenced by the reduction in the assimilation (A) to internal CO₂ (C₁) response curve. The reproductive response (e.g. percent filled grains, panicle weight) was reduced at the higher growth temperature and presumably reflects a greater increase in floral sterility. Results indicate that while CO₂ and temperature could act synergistically at the biochemical level, the direct effect of temperature on floral development with a subsequent reduction in carbon utilization may change sink strength so as to limit photosynthetic stimulation by elevated CO₂ concentration.     

Irradiance-dependent senescence of isolated leaves

Isolated leaves from pea ( Pisum sativum L. cv. Alaska or the genotype L-1107), oat ( Avena sativa L. cv. Victory), and fuchsia ( Fuchsia triphylla L. cv. Koralle) were retained at irradiances between 0 and 130 μmol m^-2 s^-1 PAR (photosynthetic active radiation). Irradiance-dependent CO₂ fixation was measured when the leaves were excised, and time-dependent changes in light compensation point were determined. If the irradiance was below the light compensation point for CO₂ fixation, the respiratory quotient was low, indicating that lipids were respired. The isolated leaves senesced at these low light levels. At higher light intensities the decrease in chlorophyll level was not accompainied by diminished protein level, and the respiratory quotient was close to unity. Only an irradiance equal to or slightly above the light compensation point maintained a stable chlorophyll level for a long time. This suggested that depletion of reserves in darkness or at low levels of irradiance is important for the initiation of the senescence syndrome. At high levels of irradiance, the decrement in chlorophyll level may be caused by photooxidation. Only in leaves placed under an irradiance close to the compensation point, was CO₂ fixation able to prevent aging of the leaves.     

Effect of light and gibberellic acid on photosynthesis during leaf senescence of alstroemeria cut flowers.

The functioning of the photosynthetic apparatus during leaf senescence was investigated in alstroemeria cut flowers by a combination of gas-exchange measurements and analysis of in vivo chlorophyll fluorescence. Chlorophyll loss in leaves of alstroemeria cut flowers is delayed by light and by a treatment of the cut flowers with gibberellic acid (GA₃). The maximal photosynthesis of the leaves was approximately 6 μmol CO₂ m⁻² s⁻¹ at I 350 μmol m⁻² s⁻¹ (PAR) which is relatively low for intact C₃ leaves. Qualitatively the gas-exchange rates followed the decline in chlorophyll content for the various treatments, i.e. light and GA₃-treatment delayed the decline in photosynthetic rates. However, when chlorophyll loss could not yet be observed in the leaves, photosynthetic rates were already strongly decreased. In vivo fluorescence measurements revealed that the decrease in CO₂ uptake is (partly) due to a decreased electron flow through photosystem II. Furthermore, analysis of the fluorescence data showed a high nonphotochemical quenching under all experimental conditions, indicating that the consumption of reducing power in the Calvin cycle is very low. The chlorophyll, remaining after 9 days incubation of leaves with GA₃ in the dark should be considered as a 'cosmetic' pigment without any function in the supply of assimilates to the flowers.     

The role of temperature in determining the stimulation of CO2 assimilation at elevated carbon dioxide concentration in soybean seedlings

Soybean ( Glycine max cv. Clark) was grown at both ambient (ca 350 μmol mol⁻¹) and elevated (ca 700 μmol mol⁻¹) CO₂ concentration at 5 growth temperatures (constant day/night temperatures of 20, 25, 30, 35 and 40°C) for 17–22 days after sowing to determine the interaction between temperature and CO₂ concentration on photosynthesis (measured as A, the rate of CO₂ assimilation per unit leaf area) at both the single leaf and whole plant level. Single leaves of soybean demonstrated increasingly greater stimulation of A at elevated CO₂ as temperature increased from 25 to 35°C (i.e. optimal growth rates). At 40°C, primary leaves failed to develop and plants eventually died. In contrast, for both whole plant A and total biomass production, increasing temperature resulted in less stimulation by elevated CO₂ concentration. For whole plants, increased CO₂ stimulated leaf area more as growth temperature increased. Differences between the response of A to elevated CO₂ for single leaves and whole plants may be related to increased self-shading experienced by whole plants at elevated CO₂ as temperature increased. Results from the present study suggest that self-shading could limit the response of CO₂ assimilation rate and the growth response of soybean plants if temperature and CO₂ increase concurrently, and illustrate that light may be an important consideration in predicting the relative stimulation of photosynthesis by elevated CO₂ at the whole plant level.     

Effect of elevated CO2 on the stomatal distribution and leaf physiology of Alnus glutinosa

Variation in stomatal development and physiology of mature leaves from Alnus glutinosa plants grown under reference (current ambient, 360 μmol mol⁻¹ CO₂) and double ambient (720 μmol mol⁻¹ CO₂) carbon dioxide (CO₂) mole fractions is assessed in terms of relative plant growth, stomatal characters (i.e. stomatal index and density) and leaf photosynthetic characters. This is the first study to consider the effects of elevated CO₂ concentration on the distribution of stomata and epidermal cells across the whole leaf and to try to ascertain the cause of intraleaf variation. In general, a doubling of the atmospheric CO₂ concentration enhanced plant growth and significantly increased stomatal index. However, there was no significant change in relative stomatal density. Under elevated CO₂ concentration there was a significant decrease in stomatal conductance and an increase in assimilation rate. However, no significant differences were found for the maximum rate of carboxylation ( V _cmax) and the light saturated rate of electron transport ( J _max) between the control and elevated CO₂ treatment.     

Carbon Dioxide Exchange Between the Atmosphere and an Alpine Shrubland Meadow During the Growing Season on the Qinghai-Tibetan Plateau

Abstract: In the present study, we used the eddy covariance method to measure CO₂ exchange between the atmosphere and an alpine shrubland meadow ecosystem (37°36'N, 101°18'E; 3 250 m a.s.l.) on the Qinghai-Tibetan Plateau, China, during the growing season in 2003, from 20 April to 30 September. This meadow is dominated by formations of Potentilla fruticosa L. The soil is Mol-Cryic Cambisols. During the study period, the meadow was not grazed. The maximum rates of CO₂ uptake and release derived from the diurnal course of CO₂ flux were -9.38 and 5.02 μmol·m^-2·s^-1, respectively. The largest daily CO₂ uptake was 1.7 g C·m^-2·d^-1 on 14 July, which is less than half that of an alpine Kobresia meadow ecosystem at similar latitudes. Daily CO₂ uptake during the measurement period indicated that the alpine shrubland meadow ecosystem may behave as a sink of atmospheric CO₂ during the growing season. The daytime CO₂ uptake was correlated exponentially or linearly with the daily photo synthetic photon flux density each month. The daytime average water use efficiency of the ecosystem was 6.47 mg CO₂/g H₂O. The efficiency of the ecosystem increased with a decrease in vapor pressure deficit.
(Managing editor: Ya-Qin HAN)     

LIGHT-DEPENDENT GROWTH, DARK SURVIVAL, AND GLUCOSE UPTAKE BY CRYPTOPHYTES ISOLATED FROM A FRESHWATER CHEMOCLINE

Clones of Cryptomonas phaseolus Skuja , Cryptomonas rostratiformis ( Skuja ) Skuja in Huber-Pestalozi, and Cryptomonas undulata Gervais were isolated from the deep chlorophyll maximum near the oxic/anoxic boundary layer of the mesoeutrophic lake Schlachtensee, Germany. Different autecological features of these species were studied in batch culture experiments . Cryptomonas cf . ovata Ehrenberg and Chroomonas sp. that never dominated in the deep chlorophyll layer were also isolated from Schlachtensee to study their light-dependent growth in comparison to the deep-living species . Cryptomonas undulata, C. cf . ovata, and C. phaseolus had a very low light compensation point ( 5–7 μmol.m^-2.s^-1 ), whereas the growth rate of Chroomonas sp. and C. rostratiformis was positive above 16 and 24 μmol.m^-2.s^-1 . Cryptomonas phaseclus and Chroomonas sp. became photoinhibited above photon flux densities of 92 and 116 μmol.m^-2.s^-1 . Cryptomonas rostratiformis, C. cf . ovata, and C. undulata reached a maximum growth rate at a considerably higher photon flux density (198–250 μmol.m^-2.s^-1 ). Cryptomonas phaseolus grew fastest under light-limiting conditions . Chyptomonas phaseolus and C. undulata were best able to suruive prolonged periods of darkness . Cryptomonas phaseolus, C. rostratiformis, and C. undulata did not show any uptake of fluorescent latex beads. When labeled glucose was provided in naturally occurring concentrations, carbon uptake by C. phaseolus, C. rostratiformis, and C. undulata was negligibly small in comparison to cellular carbon content. I suggest that the adaptation to a low-light environment is an important preadaptation for the dominance of C. phaseolus and C. undulata near the freshwater chemocline .     

Modifications of the leaf surface structures of Quercus ilex L. in open, naturally CO2-enriched environments

Two Italian CO₂ springs allowed us to study the long-term effect of a 350–2600 μ mol mol^–1 increase in CO₂ concentrations on the surface structures of leaves of Quercus ilex L. Carbon dioxide increased the quantity of cuticular waxes, above an apparent threshold of 750 μ mol mol^–1 CO₂. Leaf wettability was not modified by CO₂ concentrations. Reduction in stomatal frequency was observable up to 750 μ mol mol^–1 CO₂, the slope being almost the same as that estimated for the increase in CO₂ concentration from pre-industrial times to the present. At higher concentrations, CO₂ seemed to exert no more impact on stomatal frequency.     

Development and accumulation of ABA in fluridone-treated and drought-stressed Vicia faba plants under different light conditions

The effects of fluridone on guard cell morphology, chloroplast ultrastructure and accumulation of drought stress-induced abscisic acid (ABA) were studied in Vicia faba L. plants grown under different light conditions. Drought stress was induced by allowing the leaves to lose 12% of their fresh weight. The appearance of defective and undeveloped stomata, and chloroplasts with a destroyed thylakoid membrane system was found in fluridone-treated plants grown at a photosynthetic photon flux (PPF) of 600 μmol m^-2 s^-1. Plants grown at a PPF of 40 μmol m^-2 s^-1 had diminished levels of ABA after imposition of dehydration. Fluridone treatment reduced the level of ABA in both unstressed and dehydrated leaves. Accumulation of ABA in the control plants was considerably reduced when they were exposed to dark periods of 24, 48 and 72 h just before imposition of the stress. Twenty-four hours after the dark treatment dehydration of the leaves resulted in a 3-fold decrease in the level of stress-induced ABA, and 72 h after dark treatment the amount of stress-induced ABA approximated the prestressed values. Fluridone-treated plants failed to accumulate ABA under water stress. In addition to functionally active chloroplasts, well-developed and functional stomata are required for drought stress to elicit a rise in ABA.     

Effects of manganese toxicity on photosynthesis of white birch (Betula platyphylla var. japonica) seedlings

The effects of manganese (Mn) toxicity on photosynthesis in white birch ( Betula platyphylla var. japonica ) leaves were examined by the measurement of gas exchange and chlorophyll fluorescence in hydroponically cultured plants. The net photosynthetic rate at saturating light and ambient CO₂ (C_a) of 35 Pa decreased with increasing leaf Mn concentrations. The carboxylation efficiency, derived from the difference in CO₂ assimilation rate at intercellular CO₂ pressures attained at C_a of 13 Pa and O Pa, decreased with greater leaf Mn accumulation. Net photosynthetic rate at saturating light and saturating CO₂ (5%) also declined with leaf Mn accumulation while the maximum quantum yield of O₂ evolution at saturating CO₂ was not affected. The maximum efficiency of PSII photochemistry (F_v/F_m) was little affected by Mn accumulation in white birch leaves over a wide range of leaf Mn concentrations (2–17 mg g₋₁ dry weight). When measured in the steady state of photosynthesis under ambient air at 430 μmol quanta m₋₂ s₋₁, the levels of photochemical quenching (qP) and the excitation capture efficiency of open PSII (F'^v/F'^m) declined with Mn accumulation in leaves. The present results suggest that excess Mn in leaves affects the activities of the CO² reduction cycle rather than the potential efficiency of photochemistry, leading to increases in Q_A reduction state and thermal energy dissipation, and a decrease in quantum yield of PSII in the steady state.     

Elevated pyruvate,orthophosphate dikinase (PPDK) activity alters carbon metabolism in C3 transgenic potatoes with a C4 maize PPDK gene

Changes in carbon metabolism and δ¹³C value of transgenic potato plants with a maize pyruvate,orthophosphate dikinase (PPDK; EC 2.7.9.1) gene are reported. PPDK catalyzes the formation of phospho enol pyruvate (PEP), the initial acceptor of CO₂ in the C₄ photosynthetic pathway. PPDK activities in the leases of transgenic potatoes were up to 5.4‐fold higher than those of control potato plants (wild‐type and treated control plants). In the transgenic potato plants, PPDK activity in leaves was negatively correlated with pyruvate content (r²= 0.81), and was positively correlated with malate content (r²= 0.88). A significant increase in the δ¹³C value was observed in the transgenic potato plants, suggesting a certain contribution of PEP carboxylase as the initial acceptor of atmospheric CO₂. These data suggest that elevated PPDK activity may alter carbon metabolism and lead to a partial operation of C₄‐type carbon metabolism. However, since parameters associated with CO₂ gas exchange were not affected, the altered carbon metabolism had only a small effect on the total photosynthetic characteristics of the transgenic plants.     

Direct and indirect effects of Cd2+ on photosynthesis in sugar beet (Beta vulgaris)

Sugar-beet plants ( Beta vulgaris L. cv. Monohill) were cultivated for 4 weeks in a complete nutrient solution. Indirect effects of cadmium were studied by adding 5, 10 or 20 μ M CdCl₂ to the culture medium while direct effects were determined by adding 1, 5, 20, 50 or 2 000 μ M CdCl₂ to the assay media. The photosynthetic properties were characterized by measurement of CO₂ fixation in intact plants, fluorescence emission by intact leaves and isolated chloroplasts, photosystem (PS) I and PSII mediated electron transport of isolated chloroplasts, and CO₂-dependent O₂ evolution by protoplasts. When directly applied to isolated leaves, protoplasts and chloroplasts. Cd²⁺ impeded CO₂ fixation without affecting the rates of electron transport of PSI or PSII or the rate of dark respiration. When Cd²⁺ was applied through the culture medium the capacity for, and the maximal quantum yield of CO₂ assimilation by intact plants both decreased. This was associated with: (1) decreased total as well as effective chlorophyll content (PSII antennae size), (2) decreased coupling of electron transport in isolated chloroplasts, (3) perturbed carbon reduction cycle as indicated by fluorescence measurements. Also, protoplasts isolated from leaves of Cd²⁺-cultivated plants showed an increased rate of dark respiration.     

Flooding, gas exchange and hydraulic root conductivity of highbush blueberry

Highbush blueberry plants ( Vaccinium corymbosum L. cv. Bluecrop) growing in containers were flooded in the laboratory for various durations to determine the effect of flooding on carbon assimilation, photosynthetic response to varying CO₂ and O₂ concentrations and apparent quantum yield as measured in an open flow gas analysis system. Hydraulic conductivity of the root was also measured using a pressure chamber. Root conductivity was lower and the effect of increasing CO₂ levels on carbon assimilation less for flooded than unflooded plants after short-(i-2 days), intermediate-(10–14 days) and long-term (35–40 days) flooding. A reduction in O₂ levels surrounding the leaves from 21 to 2% for unflooded plants increased carbon assimilation by 33% and carboxylation efficiency from 0.012 to 0.021 mol CO₂ fixed (mol CO₂)⁻¹. Carboxylation efficiency of flooded plants, however, was unaffected by a decrease in percentage O₂, averaging 0.005 mol CO₂ fixed (mol CO₂)⁻¹. Apparent quantum yield decreased from 2.2 × 10⁻¹ mol of CO₂ fixed (mol light)⁻¹ for unflooded plants to 2.0 × 10⁻³ and 9.0 × 10⁻⁴ for intermediate- and long-term flooding durations, respectively. Shortterm flooding reduced carbon assimilation via a decrease in stomatal conductance, while longer flooding durations also decreased the carboxylation efficiency of the leaf.     

Pea seedling growth and development regulated by cotyledons and modified by irradiance

Growth and development of hydroponically grown pea seedlings ( Pisum sativum L. cv. Alaska) were measured using stem and root length as well as number of leaves and lateral roots. The growth was dependent on the presence of cotyledons and was modulated by the irradiance. All plants were grown in a full nutrient solution. If grown at low irradiance (73 μmol m^-2s^-1) they depended more and for a longer time on the cotyledons than plants grown at high irradiance (220 μmol m^-2s^-1). Low irradiance caused stem elongation but decreased root length and number of lateral roots as compared to plants grown at high irradiance. The dark respiration of the leaves was measured as oxygen uptake. In plants grown at the low irradiance, excision of the cotyledons caused the rate of oxygen uptake to increase by a factor of three, and the increase was sensitive to cyanide. Decotyledonized plants showed a high respiration rate and a diminished leaf growth for their entire life cycle. CO₂ fixation also increased in decotyledonized pea seedlings grown at either irradiance. The mobilization of food reserves from the seeds was positively correlated to seed dry weight, but only if the plants were grown at 73 μmol m^-2s^-1. Increasing dry weight of the seed enhanced top growth, whereas root growth was depressed, so that top and root responds differently with regard to that part of growth which depends on mobilization of reserves from the seed.     

Inhibition of photosynthesis by freezing temperatures and high light levels in cold-acclimated seedlings of Scots pine (Pinus sylvestris). – II. Effects on chlorophyll fluorescence at room temperature and 77 K.

Shoots of cold-acclimated seedlings of Pinus sylvestris L. were exposed to a temperature of –7°C for 4 h, in darkness or at a photon flux density of 1 300 μmol m^-2s^-1. Before and after freezing, fluorescence kinetics of intact needles and isolated chloroplast membranes were measured at both room temperature and 77 K. Maximum and variable fluorescence yield of photosystem II both at room temperature and 77 K decreased strongly after freezing in light, whereas the initial fluorescence yield was little affected. Quenching of maximum and variable fluorescence of photosystem I at 77 K also occurred. The results show that freezing in light damages photosystem II, thereby increasing the radiationless decay at the reaction centres of photosystem II. This is a typical symptom of photoinhibition of photosynthesis. Freezing in darkness did not significantly reduce fluorescence yield of photosystem II or photosystem I. Moreover, electron transport capacity was not significantly affected. We therefore suggest that the inhibition of the CO₂ assimilation in pine seedlings by freezing alone does not involve thylakoid inactivation.     

Biomass Production and Carbohydrate Content of Arabidopsis thaliana at Atmospheric CO2 Concentrations from 390 to 1680 μl l-1

Abstract: The concentration dependency of the impact of elevated atmospheric CO₂ concentrations on Arabidopsis thaliana L. was studied. Plants were exposed to nearly ambient (390), 560, 810, 1240 and 1680 μl I^-1 CO₂ during the vegetative growth phase for 8 days. Shoot biomass production and dry matter content were increased upon exposure to elevated CO₂. Maximal increase in shoot fresh and dry weight was obtained at 560 μl I^-1 CU₂, which was due to a transient stimulation of the relative growth rate for up to 3 days. The shoot starch content increased with increasing CO₂ concentrations up to two-fold at 1680 μl I^-1 CO₂, whereas the contents of soluble sugars and phenolic compounds were hardly affected by elevated CO₂. The chlorophyll and carotenoid contents were not substantially affected at elevated CO₂ and the chlorophyll a/b ratio remained unaltered. There was no acclimation of photosynthesis at elevated CO₂; the photosynthetic capacity of leaves, which had completely developed at elevated CO₂ was similar to that of leaves developed in ambient air. The possible consequences of an elevated atmospheric CO₂ concentration to Arabidopsis thaliana in its natural habitat is discussed.     

Performance and Photosynthetic Ecophysiology of Three Photo-Types of Dioscorea zingiberensis under Differing Light Intensities

Abstract: The performance and photosynthetic ecophysiology of three photo-types of Dioscorea zingiberensis were studied. The three types are designated DzTL, DzTM and DzTH, according to their adaptation to low (LL), medium (ML) and high (HL) light intensities, respectively. Under LL (23 - 55 μmol m^-2 s^-1) and simulated natural light (SNL), DzTM grows well with increased longevity, and green leaves which are unspotted; while its leaves became small, light yellow and short-lived under HL (550 - 850 μmol m^-2 s^-1). In contrast, under LL the leaves of DzTH were very large, spotted, light yellow and short-lived; while they were small, green and long-lived under HL. Under HL, DzTH had a much higher chlorophyll content than DzTM. Under LL, DzTM and DzTL had a higher Chl content than DzTH. Among the three types, DzTM had the highest peroxidase activity. DzTL had a higher electron transport rate (ETR), maximal quantum yield (MQY) and effective quantum yield (EQY) than DzTH and DzTL under LL, while DzTH had higher ETR, MQY and EQY than the other two types under ML and HL. Therefore, three different photo-types can be characterized according to their adaptation to LL, ML and HL: DzTL, DzTM and DzTH, respectively.