Figure 1.
Effect of drought stress on content and relative ratio of photosynthetic pigments in blue honeysuckle leaves under the control treatment (CK), lower drought stress (T1), moderate drought stress (T2), and severe drought stress (T3) in 2023: (A) Chlorophyll a content (Chl a); (B) Chlorophyll b content (Chl b); (C) Chlorophyll a content/Chlorophyll b content (Chla/b); (D) Chlorophyll a content + Chlorophyll b content (Chl a + b); (E) Carotenoids (Car); (F) Total chlorophyll content (Chlorophyll); (G) (Chlorophyll a content + Chlorophyll b content)/Total chlorophyll content (Chl (a + b)/(x + c)); (H) Carotenoids/Total chlorophyll content (Car/(x + c)). CK: control, 100% RH; T1: 85% RH; T2: 70% RH; T3: 55% RH. RH: relative soil water content. Different letters represent significant differences between treatments at p ≤ 0.05 and very significant differences between treatments at p ≤ 0.01. Values are the mean ± SE (n = 3).
Figure 1.
Effect of drought stress on content and relative ratio of photosynthetic pigments in blue honeysuckle leaves under the control treatment (CK), lower drought stress (T1), moderate drought stress (T2), and severe drought stress (T3) in 2023: (A) Chlorophyll a content (Chl a); (B) Chlorophyll b content (Chl b); (C) Chlorophyll a content/Chlorophyll b content (Chla/b); (D) Chlorophyll a content + Chlorophyll b content (Chl a + b); (E) Carotenoids (Car); (F) Total chlorophyll content (Chlorophyll); (G) (Chlorophyll a content + Chlorophyll b content)/Total chlorophyll content (Chl (a + b)/(x + c)); (H) Carotenoids/Total chlorophyll content (Car/(x + c)). CK: control, 100% RH; T1: 85% RH; T2: 70% RH; T3: 55% RH. RH: relative soil water content. Different letters represent significant differences between treatments at p ≤ 0.05 and very significant differences between treatments at p ≤ 0.01. Values are the mean ± SE (n = 3).
Figure 2.
The photosynthetic characteristics under the control treatment (CK), lower drought stress (T1), moderate drought stress (T2), and severe drought stress (T3) in 2023. (A): the net photosynthetic rate (Pn, μmol/(m2·s)); (B): stomatal conductance (Gs, mol/(m2·s)); (C): intercellular CO2 concentration (Ci, μmol/mol); (D): transpiration rate (Tr, mmol/(m2·s)); (E): leaf water use efficiency (WUE, (mmol/mol); (F): stomatal limitation (Ls). Different letters above the columns indicate a significant difference (p ≤ 0.05) and an extremely significant difference (p ≤ 0.01). CK: control, 100% RH; T1: 85% RH; T2: 70% RH; T3: 55%; RH: relative soil water content. Values are the mean ± SE (n = 3).
Figure 2.
The photosynthetic characteristics under the control treatment (CK), lower drought stress (T1), moderate drought stress (T2), and severe drought stress (T3) in 2023. (A): the net photosynthetic rate (Pn, μmol/(m2·s)); (B): stomatal conductance (Gs, mol/(m2·s)); (C): intercellular CO2 concentration (Ci, μmol/mol); (D): transpiration rate (Tr, mmol/(m2·s)); (E): leaf water use efficiency (WUE, (mmol/mol); (F): stomatal limitation (Ls). Different letters above the columns indicate a significant difference (p ≤ 0.05) and an extremely significant difference (p ≤ 0.01). CK: control, 100% RH; T1: 85% RH; T2: 70% RH; T3: 55%; RH: relative soil water content. Values are the mean ± SE (n = 3).
Figure 3.
Changes in chl a fluorescence rises kinetics OJIP of blue honeysuckle leaves after drought stress treatment. (A) Original data on a logarithmic time scale without any normalization. (B) Effects of different drought stress treatments on F0, FM and Fv/FM values. (C) Fluorescence rise kinetics normalized by F0 and FM as Vt = (Ft − F0)/(FM − F0). (D) The effect of aging PSII on the relative variable fluorescence [ΔV = ((Vt(treat) − Vt(control)))/Vt(control))] of the studied leaves. Each curve represents the average of three independent experiments of nine repetitions. CK: control, 100% RH; T1: 85% RH; 70% RH; T3: 55%. RH: relative soil water content. Values are the mean ± SE (n = 3). In (B), the uppercase letters represent the extreme significance level and the lowercase letters represent the significance level.
Figure 3.
Changes in chl a fluorescence rises kinetics OJIP of blue honeysuckle leaves after drought stress treatment. (A) Original data on a logarithmic time scale without any normalization. (B) Effects of different drought stress treatments on F0, FM and Fv/FM values. (C) Fluorescence rise kinetics normalized by F0 and FM as Vt = (Ft − F0)/(FM − F0). (D) The effect of aging PSII on the relative variable fluorescence [ΔV = ((Vt(treat) − Vt(control)))/Vt(control))] of the studied leaves. Each curve represents the average of three independent experiments of nine repetitions. CK: control, 100% RH; T1: 85% RH; 70% RH; T3: 55%. RH: relative soil water content. Values are the mean ± SE (n = 3). In (B), the uppercase letters represent the extreme significance level and the lowercase letters represent the significance level.
Figure 4.
Different normalizations of the fluorescence rise kinetics OJIP curves in a linear time scale from 0 to 300 µs under drought stress and control conditions on blue honeysuckle leaves. (A) Fluorescence rise kinetics normalized by FO and FK as WOK = (Ft − FO)/(FK − FO). (B) Difference kinetics ΔWOK = WOK (treatment) – WOK (control). (C) Fluorescence rise kinetics normalized by FO and FJ as WOJ = (Ft − FO)/(FJ − FO). (D) Difference kinetics ΔWOJ = WOJ (treatment) – WOJ (control). (E) Values of WL, ΔWL, and FL/FJ. (F) Values of WK, OEC centers, and FK/FJ. Each curve is the average of nine measurements. CK: control, 100% RH; T1: 85% RH; T2: 70% RH; T3: 55% RH. RH: relative soil water content. Values are the mean ± SE (n = 3). In (E,F), the uppercase letters represent the extreme significance level and the lowercase letters represent the significance level.
Figure 4.
Different normalizations of the fluorescence rise kinetics OJIP curves in a linear time scale from 0 to 300 µs under drought stress and control conditions on blue honeysuckle leaves. (A) Fluorescence rise kinetics normalized by FO and FK as WOK = (Ft − FO)/(FK − FO). (B) Difference kinetics ΔWOK = WOK (treatment) – WOK (control). (C) Fluorescence rise kinetics normalized by FO and FJ as WOJ = (Ft − FO)/(FJ − FO). (D) Difference kinetics ΔWOJ = WOJ (treatment) – WOJ (control). (E) Values of WL, ΔWL, and FL/FJ. (F) Values of WK, OEC centers, and FK/FJ. Each curve is the average of nine measurements. CK: control, 100% RH; T1: 85% RH; T2: 70% RH; T3: 55% RH. RH: relative soil water content. Values are the mean ± SE (n = 3). In (E,F), the uppercase letters represent the extreme significance level and the lowercase letters represent the significance level.
Figure 5.
Changes in the fluorescence O-I phase in blue honeysuckle under different drought stress treatments. (A) Variable fluorescence between steps O and I as WOJ = (Ft − FO)/(FJ − FO) (top) and ΔWOJ = W(treat) − W (control) (bottom). (B) Fluorescence rise kinetics curves normalized by FI and FP (FM) as WIP = (Ft–FI)/(Fp – FI). (D) Probability that an electron will be transported from the reduced intersystem electron acceptors to the final electron acceptors of PSI, δRo. Each curve is the average of nine measurements. CK: control, 100% RH; T1: 85% RH; T2: 70% RH; T3: 55% RH. RH: relative soil water content. Values are the mean ± SE (n = 3).
Figure 5.
Changes in the fluorescence O-I phase in blue honeysuckle under different drought stress treatments. (A) Variable fluorescence between steps O and I as WOJ = (Ft − FO)/(FJ − FO) (top) and ΔWOJ = W(treat) − W (control) (bottom). (B) Fluorescence rise kinetics curves normalized by FI and FP (FM) as WIP = (Ft–FI)/(Fp – FI). (D) Probability that an electron will be transported from the reduced intersystem electron acceptors to the final electron acceptors of PSI, δRo. Each curve is the average of nine measurements. CK: control, 100% RH; T1: 85% RH; T2: 70% RH; T3: 55% RH. RH: relative soil water content. Values are the mean ± SE (n = 3).
Figure 6.
Leaf models showing the phenomenological energy fluxes per excited cross-section (CS) of the leaves of blue honeysuckle under different drought stress treatments during the maturation period. Each relative value of the measured parameters is the mean (n = 9), and the width of each arrow corresponds to the intensity of the flux. ABS/CSM: approximated absorption flux per CS; TR0/CSM: trapped energy flux per CS; RC0/CSM: percentage of active/inactive reaction centers; ET0/CSM: electron transport flux per CS; DI0/CSM: dissipated energy flux per CS. The white circles inscribed in squares represent reduced QA reaction centers (action), and the black circles represent nonreducing QA reaction centers (inaction). Under adequate irrigation, 100% of the active reaction centers responded, with the highest mean value observed in the reference. Means followed by different letters for each parameter are significantly different (p < 0.05) or extremely significantly different (p < 0.01) according to Duncan’s test. Letters are inscribed into arrows, except for RC0/CSM, for which they are placed in a box in the lower right corner of the square with circles. Values are the mean ± SE (n = 3).
Figure 6.
Leaf models showing the phenomenological energy fluxes per excited cross-section (CS) of the leaves of blue honeysuckle under different drought stress treatments during the maturation period. Each relative value of the measured parameters is the mean (n = 9), and the width of each arrow corresponds to the intensity of the flux. ABS/CSM: approximated absorption flux per CS; TR0/CSM: trapped energy flux per CS; RC0/CSM: percentage of active/inactive reaction centers; ET0/CSM: electron transport flux per CS; DI0/CSM: dissipated energy flux per CS. The white circles inscribed in squares represent reduced QA reaction centers (action), and the black circles represent nonreducing QA reaction centers (inaction). Under adequate irrigation, 100% of the active reaction centers responded, with the highest mean value observed in the reference. Means followed by different letters for each parameter are significantly different (p < 0.05) or extremely significantly different (p < 0.01) according to Duncan’s test. Letters are inscribed into arrows, except for RC0/CSM, for which they are placed in a box in the lower right corner of the square with circles. Values are the mean ± SE (n = 3).
Figure 7.
Pipeline models of specific energy fluxes per active PSII reaction center (membrane/specific model) for blue honeysuckle under different drought stress treatments. ABS/RC: Absorbed photon flux per active PSII; TRo/RC: Trapped energy flux per active PSII; DIo/RC: Dissipated energy (as heat and fluorescence) flux per active PSII; ETo/RC: Electron flux from QA−to the PQ pool per active PSII; REo/RC: Electron flux from QA− to the final electron acceptors of PSI per active PSII. CK: control, 100% RH; T1: 85% RH; T2: 70% RH; T3: 55%. RH: relative soil water content. Means followed by different letters for each parameter are significantly different (p < 0.05) or extremely significantly different (p < 0.01) according to Duncan’s test. Letters are inscribed into arrows. Values are the mean ± SE (n = 3).
Figure 7.
Pipeline models of specific energy fluxes per active PSII reaction center (membrane/specific model) for blue honeysuckle under different drought stress treatments. ABS/RC: Absorbed photon flux per active PSII; TRo/RC: Trapped energy flux per active PSII; DIo/RC: Dissipated energy (as heat and fluorescence) flux per active PSII; ETo/RC: Electron flux from QA−to the PQ pool per active PSII; REo/RC: Electron flux from QA− to the final electron acceptors of PSI per active PSII. CK: control, 100% RH; T1: 85% RH; T2: 70% RH; T3: 55%. RH: relative soil water content. Means followed by different letters for each parameter are significantly different (p < 0.05) or extremely significantly different (p < 0.01) according to Duncan’s test. Letters are inscribed into arrows. Values are the mean ± SE (n = 3).
Figure 8.
Correlation analysis of pigment content with photosynthetic characteristics, WK, VJ, Fv/Fm, and PIABS. Chl a: chlorophyll a content; chl b: chlorophyll b content; cha/b: chlorophyll a content/chlorophyll b content; Chl a + b: the sum of chlorophyll a content and chlorophyll b content; carotene: total carotenoid concentration; chlorophyll: total chlorophyll; Chl (a + b)/(x + c): (chlorophyll a content + chlorophyll b content)/total chlorophyll content; Chl c/(x + c): total carotenoid concentration/total chlorophyll content; Pn: net photosynthetic rate; Gs: stomatal conductance; Ci: intercellular carbon dioxide concentration; Tr: transpiration rate; WUC: leaf water use efficiency; Ls: stomatal limit value; WK: normalized K point (0.3 ms) variable fluorescence; Vj: standardized variable fluorescence at J-point (2 ms); Fv/Fm: maximal photochemical efficiency of PSII; PIABS: performance index.
Figure 8.
Correlation analysis of pigment content with photosynthetic characteristics, WK, VJ, Fv/Fm, and PIABS. Chl a: chlorophyll a content; chl b: chlorophyll b content; cha/b: chlorophyll a content/chlorophyll b content; Chl a + b: the sum of chlorophyll a content and chlorophyll b content; carotene: total carotenoid concentration; chlorophyll: total chlorophyll; Chl (a + b)/(x + c): (chlorophyll a content + chlorophyll b content)/total chlorophyll content; Chl c/(x + c): total carotenoid concentration/total chlorophyll content; Pn: net photosynthetic rate; Gs: stomatal conductance; Ci: intercellular carbon dioxide concentration; Tr: transpiration rate; WUC: leaf water use efficiency; Ls: stomatal limit value; WK: normalized K point (0.3 ms) variable fluorescence; Vj: standardized variable fluorescence at J-point (2 ms); Fv/Fm: maximal photochemical efficiency of PSII; PIABS: performance index.
Table 1.
Mean squares from the analysis of variance (ANOVA) of quantum yield, efficiency/probability, and performance index of blue honeysuckle leaves under different drought stress treatments. φEo: quantum yield for electron transport (ET); φRo: quantum yield for reduction in the end electron acceptors at the PSI acceptor side (RE); ψEο: probability that an electron moves further than QA (at time 0); ΨRo: efficiency with which a single exciton trapped in the active reaction center drives a single electron from QA through the electron transport chain to the PSI acceptor side terminal electron acceptor (at time 0); δRo: probability that an electron will be transported from the reduced intersystem electron acceptors to the final electron acceptors of PSI (RE); PIABS: performance index (potential) for energy conservation from photons absorbed by PSII to the reduction in intersystem electron acceptors. CK: control, 100% RH; T1: 85% RH; T2: 70% RH; T3: 55% RH. RH: relative soil water content. Different letters represent significant differences between treatments at p ≤ 0.05, determined by Duncan’s test. Values are the mean ± SE (n = 9).
Table 1.
Mean squares from the analysis of variance (ANOVA) of quantum yield, efficiency/probability, and performance index of blue honeysuckle leaves under different drought stress treatments. φEo: quantum yield for electron transport (ET); φRo: quantum yield for reduction in the end electron acceptors at the PSI acceptor side (RE); ψEο: probability that an electron moves further than QA (at time 0); ΨRo: efficiency with which a single exciton trapped in the active reaction center drives a single electron from QA through the electron transport chain to the PSI acceptor side terminal electron acceptor (at time 0); δRo: probability that an electron will be transported from the reduced intersystem electron acceptors to the final electron acceptors of PSI (RE); PIABS: performance index (potential) for energy conservation from photons absorbed by PSII to the reduction in intersystem electron acceptors. CK: control, 100% RH; T1: 85% RH; T2: 70% RH; T3: 55% RH. RH: relative soil water content. Different letters represent significant differences between treatments at p ≤ 0.05, determined by Duncan’s test. Values are the mean ± SE (n = 9).
Treatment | Quantum Yields and Efficiencies/Probabilities | Performance Index (PIABS) |
---|
φEo | φRo |
ΨEo |
ΨRo |
δRo |
---|
CK | 0.5 ± 0.02 aA | 0.19 ± 0 aA | 0.6 ± 0 aA | 0.23 ± 0 abAB | 0.23 ± 0 abAB | 2.79 ± 0.28 aA |
T1 | 0.48 ± 0.01 aA | 0.19 ± 0 aA | 0.6 ± 0.01 abA | 0.24 ± 0.01 aAB | 0.24 ± 0.01 aAB | 2.37 ± 0.23 aAB |
T2 | 0.47 ± 0 aA | 0.2 ± 0.01 aA | 0.6 ± 0.01 abA | 0.25 ± 0.01 aA | 0.25 ± 0.01 aA | 2.31 ± 0.32 aAB |
T3 | 0.43 ± 0.09 aA | 0.16 ± 0 bB | 0.58 ± 0.01 bA | 0.22 ± 0.01 bB | 0.22 ± 0.01 bB | 1.79 ± 0.14 bB |
Table 2.
Eigenvalue and contribution rate of principal component analysis leaf photosynthetic parameters under different drought regulation treatments.
Table 2.
Eigenvalue and contribution rate of principal component analysis leaf photosynthetic parameters under different drought regulation treatments.
Composition | Eigenvalue | Variance Contribution Rate (%) | Cumulative Variance Contribution Rate (%) |
---|
1 | 5.66 | 70.76 | 70.76 |
2 | 1.29 | 16.08 | 86.84 |
3 | 0.62 | 7.75 | 94.59 |
4 | 0.22 | 2.73 | 97.32 |
5 | 0.12 | 1.47 | 98.79 |
6 | 0.07 | 0.93 | 99.71 |
7 | 0.02 | 0.27 | 99.98 |
8 | 0.00 | 0.02 | 100.00 |
Table 3.
Principal component characteristic vector of the leaf photosynthetic parameter index. Chlorophyll: chlorophyll content; Gs: stomatal conductance; WUE: water use efficiency; Fm: maximal fluorescence; Fv: variable fluorescence; Fv/Fm: maximal photochemical efficiency of PSII; Fv/Fo: PSII functional activity index standardized for ABS absorption; PIABS: performance index.
Table 3.
Principal component characteristic vector of the leaf photosynthetic parameter index. Chlorophyll: chlorophyll content; Gs: stomatal conductance; WUE: water use efficiency; Fm: maximal fluorescence; Fv: variable fluorescence; Fv/Fm: maximal photochemical efficiency of PSII; Fv/Fo: PSII functional activity index standardized for ABS absorption; PIABS: performance index.
Photosynthetic Indicators | Feature Vectors |
---|
1 | 2 |
---|
chlorophyll | 0.5846 | 0.5057 |
Gs | 0.9007 | −0.3507 |
WUC | −0.0116 | 0.9419 |
Fm | 0.9737 | 0.0201 |
Fv | 0.9731 | −0.0125 |
Fv/Fm | 0.9427 | 0.1217 |
Fv/Fo | 0.9738 | −0.0647 |
PI ABS | 0.8807 | −0.0317 |
Table 4.
Standardized data of the leaf photosynthetic parameter index. Chlorophyll: total chlorophyll content; Gs: stomatal conductance; WUE: water use efficiency; Fm: maximal fluorescence; Fv: variable fluorescence; Fv/Fm: maximal photochemical efficiency of PSII; Fv/Fo: PSII functional activity index standardized for ABS absorption; PIABS: performance index. CK: control, 100% RH; T1: 85% RH; T2 70% RH; T3: 55% RH. RH: relative soil water content.
Table 4.
Standardized data of the leaf photosynthetic parameter index. Chlorophyll: total chlorophyll content; Gs: stomatal conductance; WUE: water use efficiency; Fm: maximal fluorescence; Fv: variable fluorescence; Fv/Fm: maximal photochemical efficiency of PSII; Fv/Fo: PSII functional activity index standardized for ABS absorption; PIABS: performance index. CK: control, 100% RH; T1: 85% RH; T2 70% RH; T3: 55% RH. RH: relative soil water content.
Treatment | Chlorophyll | Gs | WUC | Fm | Fv | Fv/Fm | Fv/Fo | PIABS |
---|
CK | 0.0774 | 1.5190 | −0.9774 | 1.0963 | 1.1056 | 0.9522 | 1.1880 | 1.0992 |
T1 | 1.5086 | 0.0340 | 0.8040 | 0.4689 | 0.4454 | 0.4684 | 0.3473 | 0.1296 |
T2 | −0.7709 | −0.5326 | 0.9936 | −0.2497 | −0.2366 | −0.0668 | −0.2233 | −0.0007 |
T3 | −0.8150 | −1.0204 | −0.8201 | −1.3155 | −1.3144 | −1.3538 | −1.3120 | −1.2281 |
Table 5.
Principal component analysis score, comprehensive score, and rank of photosynthetic parameters under different drought stress treatments. P1, first principal component score; P2: second principal component score; P: synthesis score. CK: control, 100% RH; T1: 85% RH; T2 70% RH; T3: 55% RH. RH: relative soil water content.
Table 5.
Principal component analysis score, comprehensive score, and rank of photosynthetic parameters under different drought stress treatments. P1, first principal component score; P2: second principal component score; P: synthesis score. CK: control, 100% RH; T1: 85% RH; T2 70% RH; T3: 55% RH. RH: relative soil water content.
Treatment | P1 | P2 | P | Rank |
---|
CK | 6.5905 | −1.4018 | 5.1105 | 1 |
T1 | 2.6871 | 1.5424 | 2.4752 | 2 |
T2 | −1.6963 | 0.7371 | −1.2457 | 3 |
T3 | −7.5813 | −0.8777 | −6.3400 | 4 |
Table 6.
Drought acclimation treatments for ‘A5’ blue honeysuckle roots.
Table 6.
Drought acclimation treatments for ‘A5’ blue honeysuckle roots.
Treatment | Period of Flowering | Level of Deficit Adjustment |
---|
CK | 100% RH | Adequate irrigation |
T1 | 85% RH | Slight deficit adjustment |
T2 | 70% RH | Moderate deficit adjustment |
T3 | 55% RH | Severe deficit adjustment |