Chain Correlation between Variables of Gas Exchange and Yield Potential in Different Winter Wheat Cultivars

Variables of gas exchange of flag leaves and grain yield potentials of five representative winter wheat (Triticum aestivum L.) cultivars varied greatly across different development stages under the same management and irrigation. The cultivars with high yield potential had higher net photosynthetic rate (P _N), PPFD (photosynthetic photon flux density) saturated photosynthetic rate (P _sat), stomatal conductance (g _s), and maximum apparent quantum yield of CO₂ fixation (_m,app) than those with low grain yield, but their dark respiration rate (R _D) and compensation irradiance (I _c) were remarkably lower. Compared with overall increase of yield potential of 71 % from low yield cultivars to high yield ones, P _N, P _sat, _m,app, and g _s were 13, 19, 57, and 32 % higher, respectively; but R _D and I _c decreased by 19 and 76 %, respectively. Such difference was evidently large during anthesis stage (e.g., P _N by 33 %), which indicated that this period could be the best for assisting further selection for better cultivars. However, transpiration rate (E) and water use efficiency (WUE) differed only little. At different development stages, especially at anthesis, P _N and P _sat were positively correlated with _m,app, g _s, and yield potential, and negatively correlated with R _D and I _c. Thus the high-yield-potential winter wheat cultivars possess many better characters in photosynthesis and associated parameters than the low-yield cultivars.     

Clonal Differences in Photosynthesis in Hevea Brasiliensis Müll. Arg.

The objective of the present investigation was to examine the extent of variations in single leaf net photosynthetic rate (P_N) and its relative dependence on stomatal conductance (g_s) and the mesophyll capacity to fix carbon in 12 clones of the natural rubber plant. There were significant variations in P_N measured at low and saturating photon flux density (PFD); the extent of variation was larger at low than at saturating PFD. The compensation irradiance (CI) and apparent quantum yield of CO₂ assimilation (φ_c) calculated from the P_N/PFD response curves showed significant variations among the clones. P_N at low irradiance was positively correlated with φ_c. Thus a clone with large P_N at low irradiance, high φ_c, and low CI may tolerate shade better and thus produce a high tree stand per hectare. A strong positive correlation existed between P_N saturated with radiant energy (P_sat) and carboxylation efficiency (CE) estimated from the response curves of P_N on intercellular CO₂ concentration (C_i), but g_s showed a poor correlation with P_sat High CO₂ compensation concentration (Γ) led to low CE in Hevea clones. A clone with large P_sat, high CE, low g_s, and low Γ is the one in which photosynthesis is more dependent on the mesophyll factors than stomata. Such a clone may produce relatively high biomass and maintain high water use efficiency. This revised version was published online in September 2006 with corrections to the Cover Date.     

Interrelationships Between Nitrogen Supply and Photosynthetic Parameters in Vicia faba L.

We determined for Vicia faba L the influence of nitrogen uptake and accumulation on the values of photon saturated net photosynthetic rate (P _Nmax), quantum yield efficiency (), intercellular CO₂ concentration (C _i), and carboxylation efficiency (C _e). As leaf nitrogen content (N_L) increased, the converged onto a maximum asymptotic value of 0.0664±0.0049 mol(CO₂) mol(quantum)^–1. Also, as N_L increased the C _i value fell to an asymptotic minimum of 115.80±1.59 mol mol^–1, and C _e converged onto a maximum asymptotic value of 1.645±0.054 mol(CO₂) m^–2 s^–1 Pa^–1 and declined to zero at a N_L-intercept equal to 0.596±0.096 g(N) m^–2. fell to zero for an N_L-intercept of 0.660±0.052 g(N) m^–2. As N_L increased, the value of P _Nmax converged onto a maximum asymptotic value of 33.400±2.563 mol(CO₂) m^–2 s^–1. P _N fell to zero for an N_L-intercept of 0.710±0.035 g(N) m^–2. Under variable daily meteorological conditions the values for N_L, specific leaf area (_L), root mass fraction (R_f), P _Nmax, and remained constant for a given N supply. A monotonic decline in the steady-state value of R_f occurred with increasing N supply. _L increased with increasing N supply or with increasing N_L.     

Leaf gas exchange capacity in relation to leaf position on the stem in field grown teak (Tectona grandis L.f.)

Leaf gas exchange patterns in relation to leaf positions on stems were studied in field grown forest tree, teak (Tectona grandis L.f.) during first year growth under intensive culture plantation. Net photosynthetic rates (PN) were low in immature leaves (1-2 from shoot apices), increased basipetally on shoot, peaked in leaves (3rd or 4th leaves from shoot apices) which had recently reached full expansion, and thereafter declined in lower crown leaves. High PN found in fully expanded young leaves was associated with increased dark respiration rate (RD) and high radiation saturation as well as compensating irradiance for PN when compared to those of aged leaves. Intercellular CO2 concentrations (Ci) determined at ambient CO2 concentration and saturating irradiance were apparently low for leaves exhibiting high PN when compared to those of aged leaves. Differences in stomatal conductance (gs) and the rate of transpiration (E) were not apparent between leaves after full expansion. The relationship of PN with Ci recorded for leaves at different positions on stems and under natural ambient CO2 concentrations showed a linear decrease in PN with marked increasing Ci and suggested that increase in mesophyll limitations could cause decline in PN during aging of teak leaves after full expansion. Highly significant positive linear correlation was found between PN and Ci determined at below ambient CO2 concentrations and saturating irradiance for both fully expanded young and aged leaves. The estimate of linear relationship between PN and Ci, often considered as carboxylation efficiency, was higher for fully expanded young leaves characterised by high PN than for aged leaves exhibiting low PN. Hence, the increase in mesophyll limitations or decrease in carboxylation efficiency could explain gradual reduction in photosynthetic potential with leaf age after maturation in teak. This revised version was published online in June 2006 with corrections to the Cover Date.     

Determinant of photosynthetic capacity in rice leaves under ambient air conditions

At the grain-filling stage, net photosynthetic rate (P _N), stomatal conductance (g _s), and ribulose-1,5-bisphosphate carboxylation efficiency (CE) were correlated in order to find the determinant of photosynthetic capacity in rice leaves. For a flag leaf, P _N in leaf middle region was higher than in its upper region, and leaf basal region had the lowest P _N value. The differences in g _s and CE were similar. P _N, g _s, and CE gradually declined from upper to basal leaves, showing a leaf position gradient. The correlation coefficient between P _N and CE was much higher than that between P _N and g _s in both cases, and P _N was negatively correlated with intercellular CO₂ concentration (C _i). Hence the carboxylation activity or activated amount of ribulose-1,5-bisphosphate carboxylase/oxygenase rather than g_s was the determinant of the photosynthetic capacity in rice leaves. In addition, in flag leaves of different tillers P _N was positively correlated with g _s, but negatively correlated with C _i. Thus g _s is not the determinant of the photosynthetic capacity in rice leaves.The study was supported by the State Key Basic Research and Development Plan (No.G1998010100).     

Photosynthetic Response of Carrots to Varying Irradiances

Response to irradiance of leaf net photosynthetic rates (P _N) of four carrot cultivars: Cascade, Caro Choice (CC), Oranza, and Red Core Chantenay (RCC) were examined in a controlled environment. Gas exchange measurements were conducted at photosynthetic active radiation (PAR) from 100 to 1 000 μmol m⁻² s⁻¹ at 20 °C and 350 μmol (CO₂) mol⁻¹(air). The values of P _N were fitted to a rectangular hyperbolic nonlinear regression model. P _N for all cultivars increased similarly with increasing PAR but Cascade and Oranza generally had higher P _N than CC. None of the cultivars reached saturation at 1 000 μmol m⁻² s⁻¹. The predicted P _N at saturation (P _Nmax) for Cascade, CC, Oranza, and RCC were 19.78, 16.40, 19.79, and 18.11 μmol (CO₂) m⁻² s⁻¹, respectively. The compensation irradiance (I _c) occurred at 54 μmol m⁻² s⁻¹ for Cascade, 36 μmol m⁻² s⁻¹ for CC, 45 μmol m⁻² s⁻¹ for Oranza, and 25 μmol m⁻² s⁻¹ for RCC. The quantum yield among the cultivars ranged between 0.057–0.033 mol(CO₂) mol⁻¹(PAR) and did not differ. Dark respiration varied from 2.66 μmol m⁻² s⁻¹ for Cascade to 0.85 μmol m⁻² s⁻¹ for RCC. As P _N increased with PAR, intercellular CO₂ decreased in a non-linear manner. Increasing PAR increased stomatal conductance and transpiration rate to a peak between 600 and 800 μmol m⁻² s⁻¹ followed by a steep decline resulting in sharp increases in water use efficiency. This revised version was published online in August 2006 with corrections to the Cover Date.     

Photosynthetic Response of Vigna radiata to Pre-Sowing Seed Treatment with 28-Homobrassinolide

Surface sterilised seeds of mungbean (Vigna radiata L. Wilczek cv. T-44) were soaked in 0, 10⁻⁸, 10⁻⁶, or 10⁻⁴ M aqueous solution of 28-homobrassinolide (HBR) for 4, 8, or 12 h. The treated seeds were grown in sandy loam soil filled in earthen pots and sampled at 30, 40, and 50 d. Net photosynthetic rate, leaf chlorophyll content, carbonic anhydrase activity (E.C. 4.2.1.1), carboxylation efficiency, stomatal conductance, and seed yield at harvest were enhanced by the HBR treatment. The best combination was the pre-sowing seed treatment with 10⁻⁶ M HBR for 8 h. This revised version was published online in August 2006 with corrections to the Cover Date.     

Diurnal and Seasonal Changes in Photosynthetic Characteristics in Different Olive (Olea europaea L.) Cultivars

Diurnal and seasonal changes in photosynthetic characteristics, leaf area dry mass (ADM), and reducing sugar and total chlorophyll (Chl) contents of leaves of Frantoio, Leccino, and Maurino olive cultivars were investigated in Central Italy. Leaf net photosynthetic rate (P _N) per unit leaf area changed during the growing season and during the day, but the cultivar did not significantly influence the changes. In both young and one-year-old leaves the highest P _N values were observed in October, while the lowest values were recorded in August and December; during the day the highest P _N values were generally found in the morning. The pattern of photosynthetic response to photosynthetic photon flux density (PPFD) of leaves was similar in the three genotypes. Sub-stomatal CO₂ concentration (C _I) tended to increase when P _N decreased. The increase in C _I was accompanied by a stomatal conductance to water vapor (g _S) decrease. In general, P _N and dark respiration rate (R _D) were correlated. Transpiration rate (E), with no differences between the cultivars, increased from April to July, decreased greatly in August, then increased in October and finally decreased again in December. Leaf water content increased from April to June, remained high until mid July, decreased significantly in August, remaining constant until December with no differences associated with the cultivar. In both young and one-year-old leaves, the leaf water content per unit leaf area was slightly greater in Frantoio than in the other two cultivars. The one-year-old leaves had a higher Chl content than the young ones. The cultivar did not substantially influence the leaf reducing sugar content which decreased from April to August, when it reached the lowest level, then increased rapidly until October. During the day the reducing sugar content did not change significantly. The leaf ADM was slightly higher in Frantoio than in the other cultivars and one-year-old leaves had higher values than the young ones. Leaf ADM decreased from April to June and then tended to increase until December. During the day there were no substantial variations.     

Activity of 1-Aminocyclopropane Carboxylic Acid Synthase in Two Mustard (Brassica juncea L.) Cultivars Differing in Photosynthetic Capacity

The pattern of activity of 1-aminocyclopropane carboxylic acid synthase (ACS) was similar to photosynthetic and growth traits observed at 30, 45, and 60 d after sowing in mustard (Brassica juncea L.) cultivars Varuna and RH 30 differing in photosynthetic capacity. Higher activity of ACS and therefore ethylene release in Varuna than RH 30 increased stomatal conductance, intercellular CO₂ concentration, carboxylation rate (carbonic anhydrase and intrinsic water use efficiency), and thus net photosynthetic rate (P _N) and leaf and plant dry masses (DM) at all sampling times. Moreover, Varuna also had larger leaf area which contributed to higher P _N and DM. A positive correlation between ACS activity and P _N and leaf area was found in both the cultivars. Thus ACS activity may affect P _N through ethylene-induced changes on foliar gas exchange and leaf growth.     

Photosynthetic responses of Populus przewalski subjected to drought stress

Cuttings of P. przewalski were exposed to two different watering regimes which were watered to 100 and 25 % of field capacity (WW and WS, respectively). Drought stress not only significantly decreased net photosynthetic rate (P _N), transpiration rate (E), stomatal conductance (g _s), efficiency of photosystem 2 (PS2) (F_v/F_m and yield), and increased intrinsic water use efficiency (WUE_i) under controlled optimal conditions, but also altered the diurnal changes of gas exchange, chlorophyll fluorescence, and WUE_i. On the other hand, WS also affected the P _N-photosynthetically active radiation (PAR) response curve. Under drought stress, P _N peak appeared earlier (at about 10:30 of local time) than under WW condition (at about 12:30). At midday, there was a depression in P _N for WS plants, but not for WW plants, and it could be caused by the whole microclimate, especially high temperature, low relative humidity, and high PAR. There were stomatal and non-stomatal limitations to photosynthesis. Stomatal limitation dominated in the morning, and low P _N at midday was caused by both stomatal and non-stomatal limitations, whereas non-stomatal limitation dominated in the afternoon. In addition, drought stress also increased compensation irradiance and dark respiration rate, and decreased saturation irradiance and maximum net photosynthetic rate. Thus drought stress decreased plant assimilation and increased dissimilation through affected gas exchange, the diurnal pattern of gas exchange, and photosynthesis-PAR response curve, thereby reducing plant growth and productivity.     

Physiological Basis of the Difference in Net Photosynthetic Rate of Leaves between Two Maize Strains

Significant differences in net photosynthetic rate (P _N) of leaves between two maize (Zea mays L.) strains (Shuang 105 and 40×44) grown in the field were observed. At several growth stages, P _N of 40×44 was higher than that of Shuang 105 (from 10.3 to 32.5 %). Moreover, the strain 40×44 had a higher plant height, larger leaf area, lower chlorophyll content, and higher photochemical efficiency of photosystem 2 (PS2) (F_v/F_m and F/F_m) than strain Shuang 105. Shuang 105, which showed lower P _N, had lower stomatal conductances (g _s) but slightly higher intercellular CO₂ concentrations (C _i) than those of 40×44. Hence the differences in P _N between the two strains did not result from the difference in g _s, but probably from that in light reaction system.     

Photosynthetic Gas Exchange and Chlorophyll a Fluorescence of Three Wild Soybean Species in Response to NaCl Treatments

Responses of photosynthetic gas exchange and chlorophyll (Chl) a fluorescence of three wild soybeans, Glycine soja, G. tomentella, and G. tabacina occurring in different habitats of Taiwan, to four NaCl treatments, 0S, LS, MS, and HS (i.e. 0, 17, 51, and 85 mM NaCl) were compared. In G. soja following exposure to NaCl treatment for one month, the photon saturated photosynthetic rate (P _N), the ratio of variable to maximum fluorescence (F_v/F_m), the quantum yield of photosystem 2 (_PS2), and the electron transport rate (ETR) decreased dramatically. These reductions increased with increasing concentration of NaCl treatment. Plants of MS and HS treatments did not survive after extending the treatment to two months. Reductions in P _N, _PS2, and ETR (but not in F_v/F_m) were found in G. tabacina after two months of exposure to MS and HS treatments, but the reduction was not as severe as that in G. soja. In G. tomentella, significant reductions in P _N and g _s were found only in HS plants after two months of treatment, but no significant differences in F_v/F_m, _PS2, and ETR were found among plants of the four treatments. Thus the three wild soybeans in Taiwan have differentiated in their photosynthetic susceptibility to salinity, G. tomentella being the least susceptible, G. soja the most sensitive, and G. tabacina the intermediate. Different mechanisms are attributed to the inhibition effect of salinity on photosynthesis of the three species.     

Photosynthesis Parameters in Two Cultivars of Mulberry Differing in Salt Tolerance

Three-month-old mulberry (Morus alba L.) cultivars (salt tolerant cv. S1 and salt sensitive cv. ATP) were subjected to different concentrations of NaCl for 12 d. Leaf area, dry mass accumulation, total chlorophyll (Chl) content, net CO₂ assimilation rate (P _N), stomatal conductance (g _s), and transpiration rate (E) declined, and intercellular CO₂ concentration (C _i) increased. The changes in these parameters were dependent on stress severity and duration, and differed between the two cultivars. The tolerant cultivar showed a lesser reduction in P _N and g _s coupled with a better C _i and water use efficiency (WUE) than the sensitive cultivar. This revised version was published online in June 2006 with corrections to the Cover Date.     

Responses of Rice Cultivars to the Elevated CO2

The effect of CO₂ concentration elevated to 575 – 620 µmol mol^–1 on growth, tillering, grain yield, net photosynthetic rate, dark respiration rate, stomatal conductance, sugar content and protein profile of two rice (Oryza sativa L.) cultivars Pusa Basmati-1 and Pusa-677 at flowering stage was studied using open top chambers. The cultivar Pusa Basmati-1 responded more markedly for most of the growth and physiological parameters compared to Pusa-677. The increase in grain yield in Pusa Basmati-1 attributed largely to increased grain number. The increased net photosynthetic rate and greater accumulation of sugar contributed significantly to the accelerated development of leaves and tillers in both the cultivars. The reduction in the low molecular mass proteins including Rubisco and increase in high molecular mass photosystem 2 proteins was observed in both the cultivars. Additional sugars may possibly help in balancing the profile of photosynthetic proteins and sustain greater growth and productivity in rice cultivars.     

Photosynthetic responses of apricot (<Emphasis Type="Italic">Prunus armeniaca</Emphasis> L.) to photosynthetic photon flux density,leaf temperature,and CO<Subscript>2</Subscript> concentration

Two cultivars (Katy and Erhuacao) of apricot (Prunus armeniaca L.) were evaluated under open-field and solar-heated greenhouse conditions in northwest China, to determine the effect of photosynthetic photon flux density (PPFD), leaf temperature, and CO₂ concentration on the net photosynthetic rate (P _N). In greenhouse, Katy registered 28.3 μmol m⁻² s⁻¹ for compensation irradiance and 823 μmol m⁻² s⁻¹ for saturation irradiance, which were 73 and 117 % of those required by Erhuacao, respectively. The optimum temperatures for cvs. Katy and Erhuacao were 25 and 35 °C in open-field and 22 and 30 °C in greenhouse, respectively. At optimal temperatures, P _N of the field-grown Katy was 16.5 μmol m⁻² s⁻¹, 21 % less than for a greenhouse-grown apricot. Both cultivars responded positively to CO₂ concentrations below the CO₂ saturation concentration, whereas Katy exhibited greater P _N (18 %) and higher carboxylation efficiency (91 %) than Erhuacao at optimal CO₂ concentration. Both cultivars exhibited greater photosynthesis in solar-heated greenhouses than in open-field, but Katy performed better than Erhuacao under greenhouse conditions.     

Diurnal Changes of Gas Exchange,Chlorophyll Fluorescence,and Stomatal Aperture of Hybrid Poplar Clones Subjected to Midday Light Stress

Diurnal changes in net photosynthetic rate (P _N), chlorophyll (Chl) fluorescence, and stomatal aperture of several hybrid poplar clones subjected to midday light stress were measured in July and August of 1996. Midday depression of P _N, photosystem 2 (PS2) efficiency, stomatal conductance (g _s), and stomatal aperture was observed in all clones, though at differing rates among them. Non-uniform stomatal closure occurred at noon and at other times, requiring a modification of intercellular CO₂ concentration (C ₁). A linear relationship was found between g _s and stomatal aperture. More than half of the photons absorbed by PS2 centre dissipated thermally when subjected to light stress at noon. There was a linear relationship between the rate of PS2 photochemical electron transport (PxPFD) and P _N. There was a consensus for two fluorescence indicators (1 – q_P/q_N and (F_m' – F)/F_m') in assessment of susceptibility of photoinhibition in the clones. According to P _N, Chl fluorescence, and stomatal aperture, we conclude that midday depression of photosynthesis can be attributed to both stomatal and non-stomatal limitations.     

Photosynthetic characteristics of <Emphasis Type="Italic">Hordeum,Triticum, Rumex</Emphasis>, and <Emphasis Type="Italic">Trifolium</Emphasis> species at contrasting altitudes

Photosynthetic characteristics were compared between plants of low altitude (LA) grown at LA (Palampur; 1 300 m) and at high altitude, HA (Kibber; 4 200 m), and plants naturally occurring at different altitudes (Palampur, 1 300 m; Palchan, 2 250 m; and Marhi, 3 250 m). Net photosynthetic rate (P _N) was not significantly different between altitudes. However, the slopes of the curve relating P _N to intercellular CO₂ concentration (C _i) were higher in plants at Palchan, Marhi, and Kibber compared to those at Palampur, indicating that plants had higher efficiency of carbon uptake (the initial slope of P _N/C _i curve is an indication) at HA. They had also higher stomatal conductance (g _s), transpiration rate, and lower water use efficiency at HA. g _s was insensitive to photosynthetic photon flux density (PPFD) for plants naturally occurring at Palampur, Palchan, and Marhi, whereas plants from LA grown at Palampur and Kibber responded linearly to increasing PPFD. Insensitivity of g _s to PPFD could be one of the adaptive features allowing wider altitudinal distribution of the plants.This research is supported by the Department of Biotechnology (DBT), Government of India vide grant number BT/PR/502/AGR/08/39/966-VI.     

Response of Photosynthesis to Radiation and Intercellular CO2 Concentration in Sun and Shade Shoots of Norway Spruce

Functional differentiation of assimilation activity of sun versus shade foliage was analysed in a Norway spruce monoculture stand (age 15 years). The investigated stand density (leaf area index 8.6) and crown structure led to variation in the photosynthetically active photon flux density (PPFD) within the crowns of the sampled trees. At the saturating PPFD, the maximum rate of CO₂ uptake (P _Nmax) of exposed shoots (E-shoots) was 1.7 times that of the shaded shoots (S-shoots). The apparent quantum yield (α) of E-shoots was 0.9 times that of the S-shoots. A lower ability to use excess energy at high PPFD in photosynthesis was observed in the S-layer. The CO₂- and PPFD-saturated rate of CO₂ uptake (P _Nsat) of the E-shoots was 1.12 times and the carboxylation efficiency (τ) 1.6 times that of the S-shoots. The CO₂-saturated rate of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) carboxylation (V_Cmax) and of actual electron transport (J_amax) in the S-needles amounted to 89 and 95 % of V_Cmax and J_amax in the E-needles. Thus, in addition to the irradiation conditions and thus limitation by low J_a, the important limitation of photosynthesis in shade needles is due to carboxylation. This limitation of photosynthesis is accompanied by lower stomatal conductance. This revised version was published online in June 2006 with corrections to the Cover Date.     

Dissipation of Excess Energy in Mehler-Peroxidase Reaction in Rumex Leaves During Salt Shock

By measurement of gas exchange and chlorophyll fluorescence, the effects of salt shock on photosynthesis and the mechanisms to protect photosynthetic machinery against photodamage during salt shock were investigated in leaves of Rumex seedlings. Salt shock induced significant decrease in photosynthesis both in 21 and 2 % O₂. In 21 % O₂, quantum yield of photosystem 2 (PS2) electron transport (_PS2) decreased slightly and q_P remained constant, suggesting that the excitation pressure on PS2 did not increase during salt shock. In 2 % O₂, however, both _PS2 and q_P decreased significantly, suggesting that the excitation pressure on PS2 increased during salt shock. NPQ increased slightly in 21 % O₂ whereas it increased significantly in 2 % O₂. The data demonstrated that during salt shock a considerable electron flow was allocated to oxygen reduction in the Mehler-peroxidase reaction (MPR). Under high irradiance and in the presence of saturating CO₂, the susceptibility of PS2 to photoinhibition in salt-shocked leaves was increased when the electron flow to oxygen in MPR was inhibited in 2 % O₂. Hence, MPR is important in photoprotection of Rumex seedlings during salt shock.     

Effects of water stress and high temperature on gas exchange and chlorophyll fluorescence in Triticum aestivum L.

Wheat plants grown in controlled growth chambers were exposed to drought stress (DS) and high temperature (HT) singly and in combination (DS+HT). The effects of these two stresses on net photosynthetic rate (P _N), stomatal conductance (g _s), intercellular CO₂ concentration (C _i), quantum efficiency of photosystem 2 (Φ_PS2), variable to maximum chlorophyll (Chl) fluorescence (F_v/F_m), photochemical (q_p) and non-photochemical (NPQ) Chl fluorescence, and yield were investigated. Grain yield was decreased by 21 % due to DS, while it was increased by 26 % due to HT. P _N, g _s, C _i, and Chl fluorescence were dramatically reduced to DS, HT, and their interaction, except NPQ which showed an increase due to HT.