The effect of CaCl<Subscript>2</Subscript> on calcium content,photosynthesis, and chlorophyll fluorescence of tung tree seedlings under drought conditions

The study investigated the effects of different CaCl₂ concentrations (2, 5, and 10 mM) on photosynthetic enzymatic activities, photosynthesis, and chlorophyll fluorescence of tung tree seedlings under drought conditions. Plants were sprayed with either CaCl₂ or distilled water until run-off. Irrigation was then withheld to induce drought stress. The strength of drought stress was evaluated by relative leaf water content and soil water content, which was 27.3 and 9.5% on day 0 and day 12, respectively. Drought stress decreased activities of ribulose-1,5-bisphosphate carboxylase/oxygenase and phosphoenolpyruvate carboxylase, chlorophyll (a+b) content, net photosynthetic rate, stomatal conductance, transpiration rate, electron transport rate, the maximal quantum yield of PSII photochemistry, and effective quantum yield of PSII in tung tree seedlings. The CaCl₂ pretreatments alleviated the negative effect of drought stress to some degree on all the parameters mentioned above.     

Physiological and biochemical responses of photomorphogenic tomato mutants (cv. Micro-Tom) under water withholding

In addition to mediating photomorphogenesis, phytochromes are responsible for many abiotic stress responses, acting upon biochemical and molecular mechanisms of cell signaling. In this work, we measured the physiological and biochemical responses of phytochrome-mutant plants under water stress. In tomato (Solanum lycopersicum L.), the aurea mutant (au) is phytochrome-deficient and the high-pigment-1 mutant (hp1) has exaggerated light responses. We examined the effects of water withholding on water potential, leaf gas exchange, chlorophyll fluorescence, chloroplast pigment content and antioxidant enzyme activity in au and hp1 and their wild-type cultivar Micro-Tom (MT). Initial fluorescence and potential quantum efficiency of photosystem II (PSII) photochemistry were not affected by the treatment, but effective quantum yield of PSII, electron transport rate decreased and non-photochemical quenching increased significantly in MT. Under water withholding conditions, MT had higher malondialdehyde concentration than the mutants, but au had higher activities of catalase and ascorbate peroxidase compared to the other genotypes. The tolerance of mutants to the effects of water withholding may be explained by the higher activity of antioxidant enzymes in au and by a higher concentration of antioxidant compounds, such as carotenoids, in hp1.     

Osmotic stress affects physiological responses and growth characteristics of three pistachio cultivars

Pistachio (Pistacia vera L.) has a high tolerance to drought and soil salinity. Although adult pistachio trees are well known to be drought tolerant, the studies on physiological adaptation of pistachio cultivars to drought are limited. Therefore, three pistachio cultivars, i.e., Akbari, Kaleghochi, and Ohadi were subjected to three osmotic drought stress treatments: control (?0.1 MPa), moderate (?0.75 MPa) and severe drought (?1.5 MPa) stress using PEG 6000 for a 14-day period. All drought stress treatments decreased net photosynthesis (P _n), stomatal conductance (g _s), intercellular CO₂ concentration (C _i), and transpiration rate (E), but Ohadi maintained better its photosynthetic capacity compared to Akbari and Kaleghochi. Maximum quantum yield of PSII photochemistry (F _v /F _m), effective PSII quantum yield (ΦPSII) and photochemical quenching (qP) were also reduced. The chlorophyll fluorescence parameters indicated that Akbari was more susceptible to the applied drought stress. Drought stress levels decreased chlorophyll pigments, fresh weight, stem elongation, leaf nitrogen content (N), leaf water potential and increased water use efficiency (WUE). Proline increased strongly under drought stress for Akbari. After 2 weeks of stress a recovery of 2 weeks was applied. This period was insufficient to fully restore the negative effects of the applied stress on the studied cultivars. Based on the reduction of photosynthesis and the increase of the proline content Akbari seems more sensitive to the applied drought stress.     

The effect of galling aphids feeding on photosynthesis photochemistry of elm trees (<Emphasis Type="Italic">Ulmus</Emphasis> sp.)

Changes of chlorophyll (Chl) a fluorescence and photosynthetic pigment contents were analysed in galled leaves (visibly damaged and undamaged parts) and intact leaves. The values of minimal fluorescence of the dark-adapted state, maximal quantum yield of PSII photochemistry, effective quantum yield of PSII photochemical conversion, and photochemical quenching coefficient decreased in Ulmus pumila L. leaves galled by Tetraneura ulmi (L.) and in U. glabra Huds. galled by Eriosoma ulmi (L.). Colopha compressa (Koch.) feeding affected these parameters only in damaged parts of U. laevis Pall. galled leaves. The increasing number of T. ulmi galls progressively decreased photosynthetic performance. In gall tissues of all analysed aphid species, the lowest photosynthetic pigment content was found, indicating that the photosynthetic capacity must have been low in galls. Significant reduction of Chl and carotenoid contents were observed in damaged and undamaged portions of galled leaves only in the case of T. ulmi feeding.     

The effect of methanol on photosynthetic parameters of bean (Phaseolus vulgaris L.) under water deficit

Water availability is the main factor limiting crop growth and productivity in dry regions. This study was carried out in order to determine the effect of spraying methanol solution on the photosynthetic characteristics of bean plants. The main aim of our experiment was to improve plant performance under stress caused by water shortage. Two factors were involved: water-deficit stress, such as severe stress (25% of field capacity), mild stress (75% of field capacity), and no stress (100% of field capacity), and application of methanol solution spray at four concentrations: control (without spraying), 10, 20, and 30%. Methanol was applied three times at different growth stages (seedling, flowering, and podding stage) in 10-d intervals. The treatment with 20% methanol at the seedling stage resulted in increased net photosynthesis (P_N), intercellular CO₂ concentration (C_i), and decreased transpiration rate (E) under no stress and mild stress conditions. Under severe stress, 10 and 20%-methanol treatments resulted in increased C_i, maximal quantum yield of PSII photochemistry, and decreased E. At the flowering stage, methanol treatments resulted in decreased E and increased C_i under mild and severe stress. At the podding stage, 10 and 20%-methanol treatments resulted in increased P_N, C_i, and total chlorophyll content under mild stress. In conclusion, we suggested that foliar application of methanol had a positive role in enhancing photosynthetic performance.     

Effects of drought stress on growth and chlorophyll fluorescence of Lycium ruthenicum Murr. seedlings

The present study aimed to determine effects of drought stress on Lycium ruthenicum Murr. seedlings. Our results showed that mild drought stress was beneficial to growth of L. ruthenicum seedlings. Their height, basal diameter, crown, leaf number, stem dry mass, leaf and root dry mass increased gradually when the soil water content declined from 34.7 to 21.2%. However, with further decrease of the soil water content, the growth of L. ruthenicum seedlings was limited. After 28 d of treatment, the seedlings were apparently vulnerable to drought stress, which resulted in significant leaf shedding and slow growth. However, growth was restored after rehydration. Drought treatments led to a decrease in contents of chlorophyll (Chl) a, b, and Chl (a+b) and increase in the Chl a/b ratio. After rewatering, the Chl content recovered to the content of the control plants. Under drought stress, minimal fluorescence and nonphotochemical quenching coefficient increased, thereby indicating that L. ruthenicum seedlings could protect PSII reaction centres from damage. Maximum fluorescence, maximum quantum yield, actual quantum yield of PSII photochemistry, and photochemical quenching decreased, which suggested that drought stress impacted the openness of PSII reaction centres. A comparison of these responses might help identify the drought tolerance mechanisms of L. ruthenicum. This could be the reference for the planting location and irrigation arrangements during the growing period of L. ruthenicum.     

Effect of vermicompost fertilizer on photosynthetic characteristics of chickpea (Cicer arietinum L.) under drought stress

Water availability is an important factor for plant growth in arid environments. In recent decades, vermicompost (VC) fertilizer has been used in agriculture as a safe and effective fertilizer with high water-holding capacity. The aim of the present study was to characterize effects of VC fertilizer on photosynthetic activity of chickpea (Cicer arietinum L. cv. Karaj) under drought conditions at three different growth stages. Tests were carried out with four volumetric ratios of VC to soil, i.e., 0:100, 10:90, 20:80, and 30:70, and three levels of drought stress, i.e., no stress (NS), moderate drought (MS), and severe drought (SS) (100, 75, and 25% of field capacity, respectively). Evaluations were performed at the seedling, flowering, and podding stage. We found that the VC treatment under NS conditions significantly increased total chlorophyll content [Chl (a+b)], intercellular CO₂ concentration (C_i), net photosynthetic rate (P_N), transpiration rate (E), and maximal quantum yield of PSII photochemistry (F_v/F_m) at all three stages. The VC addition of 10 and 20% significantly enhanced the Chl content and F_v/F_m under MS and F_v/F_m, C_i, and P_N under SS at the flowering stage. In conclusion, our results proved a positive effect of the VC fertilizer on photosynthesis of chickpea under NS conditions, but it was not found under MS and SS.     

Photosynthetic and antioxidative upregulation in drought-stressed sesame (<Emphasis Type="Italic">Sesamum indicum</Emphasis> L.) subjected to foliar-applied salicylic acid

Insufficient attention has been paid to the physiological responses of sesame to drought and it is unclear if exogenous plant growth regulators are beneficial to drought-stressed sesame. Thus, a field study was conducted on seven Sesamum indicum genotypes affected by two levels of irrigation (60 and 80% depletions in available soil water) and by foliar-applied salicylic acid (SA; 0 and 0.6 mM). Water deficit led to depressions in net photosynthetic rate, stomatal conductance, leaf area index, chlorophyll a, b, and total chlorophyll contents, maximum quantum efficiency of PSII, and plant dry matter and seed yield, despite increases in carotenoid concentration, superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase activities. SA was found beneficial in ameliorating the depressions in all of the above characteristics, indicating that it could be applied for lessening the harmful effects of the drought stress.     

Photosynthetic characteristics and effects of exogenous glycine of Chorispora bungeana under drought stress

We investigated the photosynthetic characteristics of Chorispora bungeana under conditions of drought stress caused by different concentrations of polyethylene glycol-6000 (PEG; 0, 5, 20, and 40%) and various concentrations of exogenous glycine (0, 5, 10, and 20 mM) with 20% PEG. We showed that moderate and severe drought stress of PEG reduced the chlorophyll (Chl) content (both Chl a and b), maximal quantum yield of PSII photochemistry (F_v/F_m), actual photochemical efficiency of PSII in light (Y_II), and quantum yield of regulated energy dissipation (Y_NPQ), while Chl a/b and quantum yield of nonregulated energy dissipation (Y_NO) increased. The low and moderate drought stress increased Mg²⁺ and Fe³⁺ contents, while a decrease in Mg²⁺ and Fe³⁺ was found under severe drought stress. Compared to sole PEG stress, the addition of exogenous 10 mM glycine increased Chl, Mg²⁺ and Fe³⁺ contents, F_v/F_m, Y_II, and Y_NPQ, and reduced Y_NO. On the contrary, 20 mM glycine showed an opposite effect, except for Y_NO. Our results proved that Chl contents and fluorescence parameters are reliable indicators for drought tolerance of C. bungeana. We suggest that a proper glycine content can relieve the effect of drought stress on C. bungeana.     

The influence of antimycin A on pigment composition and functional activity of photosynthetic apparatus in <Emphasis Type="Italic">Triticum aestivum</Emphasis> L. under high temperature

The purpose of the current investigation was to evaluate the influence of antimycin A (AA) as an activator of the alternative respiratory pathway (AP) on photosynthetic pigment composition and functional activity of the photosynthetic apparatus of wheat seedlings (Triticum aestivum L.) under exposure to high temperature as well as their acclimation. Our results indicated that a significant decrease (44–74%) of photosynthetic pigment contents was caused by a long-term exposure to high temperature (42°C), while the short-term exposure resulted in 20–46% decline. However, a combined effect of AA and long-term high temperature reduced the total pigment contents by 28–41%. Our results demonstrated that the reduction of the chlorophyll a/b ratio was less significant under the combined effect of AA and high temperature than that under the stressful condition without AA. We observed that short-term and long-term high temperature modified PSII functionality of the first leaves in wheat seedlings, which was manifested by the low maximal quantum yield of PSII photochemistry, maximum fluorescence yield in the dark-adapted state, and by high minimum fluorescence yield in the dark-adapted state. The quantum yield of PSII photochemistry decreased rapidly by 16–24% under the combination of AA and high temperature. Overall, these results suggest that the activation of the alternative pathway, induced by AA, contributed to the stabilization of the photosynthetic apparatus in wheat seedlings under high temperature.     

AM1 is a potential ABA substitute for drought tolerance as revealed by physiological and ultra-structural responses of oilseed rape

Abscisic acid (ABA) is an important signaling molecule for plants under drought tolerance. However, ABA itself has many limitations to be used in agriculture practically. Recently, AM1 (ABA-mimicking ligand) has been found to replace ABA. In this study, we have investigated AM1’s potential role for drought tolerance by growing two contrasting rapeseed (Brassica napus L.) genotypes: Qinyou 8 (drought sensitive) and Q2 (drought resistant) with exogenous ABA or AM1 application under well-watered and drought-stressed conditions. Results demonstrate that drought stress has hampered plant growth (relative height growth rate, plant biomass, leaf area), plant water status (leaf relative water content, root moisture content, leaf water potential), photosynthetic gas exchange attributes like net photosynthesis rate (Pn), stomatal conductance (Gs), intercellular CO₂ concentration (Ci), transpiration rate (E); chlorophyll fluorescence parameters like photosynthetic efficiency (Fv/Fm), effective quantum yield of PSII (Φ _PSII ), photochemical quenching coefficient (qL), electron transport rate (ETR) and chlorophyll content, especially for Qinyou 8 significantly compared to well-watered plants. Whereas increased root/shoot ratio (R/S), water use efficiency (WUE) and non-photochemical quenching (NPQ) was recorded in both genotypes under drought stress. On the other hand, exogenous ABA or AM1 treatment has regulated all the above parameters in a rational way to avoid drought stress. Chloroplast transmission electron microscope images, especially for Qinyou8, have revealed that oxidative stress induced by drought has blurred the grana thylakoids, increased the size or number of plastoglobules due to lipid peroxidation, and the presence of starch granules depict weak capacity to convert them into simple sugars for osmotic adjustment. However, intact grana thylakoid, few plastoglobules with no or very few starch granules were observed in the chloroplast from ABA- or AM1-treated plants under drought. More importantly, AM1-treated plants under drought stress have responded in an extremely similar way like ABA-treated ones. Finally, it is suggested that AM1 is a potential ABA substitute for plant drought tolerance.     

Effects of melatonin on photosynthetic performance and antioxidants in melon during cold and recovery

Melatonin (MT), a tryptophan derivative, plays an important role in the function and survival of organisms. To better understand the role of MT in cold tolerance, the melon (Cucumis melo L.) were sprayed with various concentrations of MT (0, 50, 100, 200 or 400 μM), exposed to cold stress (day/night temperature of 12/6 °C) for 7 d, and then returned to optimal conditions (28/18 °C) for 7-d recovery. The foliar application of MT (especially 200 μM) significantly alleviated cold-induced growth suppression, and MT-treated plants recovered more quickly than untreated plants. Further, MT-treated plants had higher chlorophyll content, photosynthetic rate, stomatal conductance, as well as maximal quantum yield of photosystem (PS) II photochemistry, and efficiency of excitation energy capture of open PS II centres under cold stress than untreated plants. Furthermore, exogenous MT significantly reduced malondialdehyde content and markedly increased the activities of antioxidant enzymes superoxide dismutase (SOD), guaiacol peroxidase (POD), and catalase (CAT) under cold stress. MT also increased expression of antioxidant genes CmSOD, CmPOD, and CmCAT under cold stress. The results indicate that MT pretreatment alleviated the detrimental effects of cold stress and accelerateds the recovery mainly by enhancing photosynthesis and antioxidant capacity in melon leaves.     

Exogenous proline induces soluble sugar accumulation and alleviates drought stress effects on photosystem II functioning of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> leaves

The effects of exogenous applied proline (Pro), on photosystem II (PSII) photochemistry of drought stressed (DS) 4-week old Arabidopsis thaliana plants, was studied by using chlorophyll (chl) fluorescence imaging. The maximum quantum yield of PSII photochemistry (F _v /F _m) in DS plants decreased significantly to 77% of that of the control value, suggesting that DS plants could not maintain PSII function, possibly due to accelerated photoinhibition of PSII. Free Pro and total soluble sugars (SS) increased, in response to DS. Exogenous foliar application of Pro by spraying, led to a remarkable increase in the accumulation of Pro and surprisingly also of SS. Both of them served to scavenge reactive oxygen species (ROS), as it was evident by the decreased lipid peroxidation level measured as malondialdehyde (MDA). DS plants sprayed with Pro showed a tolerance to photoinhibition, this indicated by F _v/F _m being close to values typical of healthy leaves by maintaining more than 98% of PSII function. Also the higher quantum efficiency of PSII photochemistry (Φ _PSΙΙ ) and the decreased excitation pressure (1 ? q _p ) recorded for stressed leaves with Pro, lead us to conclude that Pro appears to be involved in the protection of chloroplast structures by quenching ROS. The enhanced dissipation of excess light energy of PSII, in part accounts for the observed increased resistance to DS in A. thaliana leaves with Pro. Our data pointed out that Pro signalling interacts with SS signaling pathway and provided a new insight in Pro metabolism.     

Induction of water deficit tolerance in wheat due to exogenous application of plant growth regulators: membrane stability,water relations and photosynthesis

Our experiment was carried out in order to explore effects of plant growth regulators (PGR; thidiazuron, paclobutrazol, and ascorbic acid) on physiological traits of wheat genotypes under water surplus and deficit conditions. Study revealed that relative water content, membrane stability index, chlorophyll content, photosynthetic rate (P_N), and maximal quantum yield of PSII improved with PGRs application across the genotypes both under irrigation and water stress. The response of HD 2733 genotype was more positive toward PGRs treatment as compared to other genotypes under water stress. Higher P_N and chlorophyll contents were observed in HD 2987 followed by C 306 genotype under water-stress conditions. Moreover, Rubisco small subunit (SSU) expression was lower in wheat genotypes under water stress as compared to irrigated conditions. Application of PGRs led to upregulation of SSU under water stress, while no significant change was found in Rubisco level and activity under irrigated condition in dependence on PGRs treatments. Yield-related traits showed also significant reduction under water-stress conditions, while application of PGRs enhanced the yield and its components. Results indicated that the PGRs exhibited a positive interaction and synergetic effect on water stressed wheat plants in terms of photosynthetic machinery and yield.     

Effect of day/night temperature difference on chlorophyll content,photosynthesis and fluorescence parameters of tomato at fruit stage

In order to investigate the effect of day/night temperature difference (DIF) on photosynthetic characteristics of tomato plants (Solanum lycopersicum, cv. Jinguan 5) at fruit stage, an experiment was carried out in climate chambers. Five day/night temperature regimes (16/34, 19/31, 25/25, 31/19, and 34/16°C) with respective DIFs of -18, -12, 0, +12, and +18 were used and measured at mean daily temperature of 25°C. The results showed that chlorophyll (Chl) a, Chl b, net photosynthetic rate (P_N), stomatal conductance (g_s), maximum quantum yield of PSII photochemistry (F_v/F_m), effective quantum yield of PSII photochemistry (?_PSII), and photochemical quenching (qp) significantly increased under positive DIF, while they decreased with negative DIF. In contrast, the Chl a/b ratio and nonphotochemical quenching (NPQ) decreased under positive DIF, while increased with negative DIF. Chl a, Chl b, P_N, g_s, F_v/F_m, ?_PSII, and qp were larger under +12 DIF than those at +18 DIF, while Chl a/b and NPQ showed an opposite trend.     

Effect of high light intensity on the photosynthetic apparatus of two hybrid lines of <Emphasis Type="Italic">Paulownia</Emphasis> grown on soils with different salinity

The objective of this investigation was to evaluate the simultaneous action of light stress and salinity. Pulse amplitude modulated chlorophyll fluorescence, P₇₀₀ redox state, and pigment analysis were used to assess the impact of high light intensity on Paulownia tomentosa × fortunei and Paulownia elongata × elongata grown on soils with different salinity. It was found that light stress reduced the amount of pigments and the efficiency of photochemical energy conversion, inhibited the maximum and the effective quantum yields of PSII photochemistry, decreased photochemical quenching and photosynthetic rate. Data also showed influence on the primary quinone acceptor (Q_A) reoxidation, which led to the restriction of the electron flow from Q_A to plastoquinone and stimulation of the cyclic electron flow. The possible reasons for the increased effects of the light stress under conditions of high salt concentration in soil for Paulownia tomentosa × fortunei are discussed.     

Lanthanum improves salt tolerance of maize seedlings

In this study, the effects of lanthanum were investigated on contents of pigments, chlorophyll (Chl) fluorescence, antioxidative enzymes, and biomass of maize seedlings under salt stress. The results showed that salt stress significantly decreased the contents of Chl and carotenoids, maximum photochemical efficiency of PSII (F_v/F_m), photochemical quenching (q_P), and quantum efficiency of PSII photochemistry (Φ_PSII), net photosynthetic rate (P_N), and biomass. Salt stress increased nonphotochemical quenching (q_N), the activities of ascorbate peroxidase, catalase, superoxide dismutase, glutathione peroxidase, and the contents of malondialdehyde and hydrogen peroxide compared with control. Pretreatment with lanthanum prior to salt stress significantly enhanced the contents of Chl and carotenoids, F_v/F_m, q_P, q_N, Φ_PSII, P_N, biomass, and activities of the above antioxidant enzymes compared with the salt-stressed plants. Pretreatment with lanthanum also significantly reduced the contents of malondialdehyde and hydrogen peroxide induced by salt stress. Our results suggested that lanthanum can improve salt tolerance of maize seedlings by enhancing the function of photosynthetic apparatus and antioxidant capacity.     

Effects of water stress on photosynthesis and nitrogen metabolism in vegetative and reproductive shoots of <Emphasis Type="Italic">Leymus chinensis</Emphasis>

In Leymus chinensis, mild water stress (soil moisture 60–65 % of field capacity) had no significant effects on nitrogen metabolism, photosynthesis, and chlorophyll fluorescence. Severe water stress (35–40 %) significantly decreased the activities of nitrate reductase, glutamine synthetase, and glutamate dehydrogenase, net photosynthetic rate, stomatal conductance, transpiration rate, maximal efficiency of photosystem 2 photochemistry (F_v/F_m), actual quantum yield, and photochemical quenching, but increased the endopeptidase activity and malondialdehyde contents. The adverse effects on photosynthesis and N metabolism were markedly greater in reproductive shoots than in vegetative shoots.     

Effect of ammonium/nitrate ratio on pak choi (<Emphasis Type="Italic">Brassica chinensis</Emphasis> L.) photosynthetic capacity and biomass accumulation under low light intensity and water deficit

We conducted a hydroponic experiment in order to study effects of the ammonium/nitrate ratio (0:15, 5:10, 7.5:7.5, and 10:5) on photosynthetic characteristics and biomass accumulation in Brassica chinensis under low light intensity and water stress. Results showed that net photosynthetic rate, transpiration rate, intrinsic water-use efficiency, stomatal conductance, intercellular CO₂ concentration, effective quantum yield of PSII photochemistry, electron transport rate, and nonphotochemical quenching were lower in the treatment (low light intensity and water deficit) than those in the control, whereas stomatal limitation increased. Minimum fluorescence, maximal quantum yield of PSII photochemistry, and photochemical quenching were largely unchanged. Pigment contents first increased and then decreased as the ammonium/nitrate ratios were altered, with significant differences between treatment and control observed at all ratios except for 10:5. Biomass first increased slightly and then decreased both in treated and control plants. Results suggest that economic losses caused by extreme conditions can be minimized by a proper adjustment of the ammonium/nitrate ratio.     

Photosynthetic and physiological responses of foxtail millet (<Emphasis Type="Italic">Setaria italica</Emphasis> L.) to low-light stress during grain-filling stage

Two foxtail millet (Setaria italica L.) varieties were subjected to different shading intensity treatments during a grain-filling stage in a field experiment in order to clarify physiological mechanisms of low-light effects on the yield. Our results showed that the grain fresh mass per panicle, yield, photosynthetic pigment contents, net photosynthetic rate, stomatal conductance, effective quantum yield of PSII photochemistry, and electron transport rate decreased with the increase of shading intensity, whereas the intercellular CO₂ concentration increased in both varieties. In addition, shading changed a double-peak diurnal variation of photosynthesis to a one-peak curve. In conclusion, the lower yield of foxtail millet was caused mainly by a reduction of grain mass assimilated, a decline in chlorophyll content, and the low photosynthetic rate due to low light during the grain-filling stage. Reduced light energy absorption and conversion, restricted electron transfer, and reduced stomatal conductance might cause the decrease in photosynthesis.