Addressing the long-standing limitations of double exponential and non-rectangular hyperbolic models in quantifying light-response of electron transport rates in different photosynthetic organisms under various conditions.

The models used to describe the light response of electron transport rate in photosynthesis play a crucial role in determining two key parameters i.e., the maximum electron transport rate (J max) and the saturation light intensity (I sat). However, not all models accurately fit J-I curves, and determine the values of J max and I sat. Here, three models, namely the double exponential (DE) model, the non-rectangular hyperbolic (NRH) model, and a mechanistic model developed by one of the coauthors (Z-P Ye) and his coworkers (referred to as the mechanistic model), were compared in terms of their ability to fit J-I curves and estimate J max and I sat. Here, we apply these three models to a series of previously collected Chl a fluorescence data from seven photosynthetic organisms, grown under different conditions. Our results show that the mechanistic model performed well in describing the J-I curves, regardless of whether photoinhibition/dynamic down-regulation of photosystem II (PSII) occurs. Moreover, both J max and I sat estimated by this model are in very good agreement with the measured data. On the contrary, although the DE model simulates quite well the J-I curve for the species studied, it significantly overestimates both the J max of Amaranthus hypochondriacus and the I sat of Microcystis aeruginosa grown under NH4 +-N supply. More importantly, the light intensity required to achieve the potential maximum of J (J s) estimated by this model exceeds the unexpected high value of 105 µmol photons m-2 s-1 for Triticum aestivum and A. hypochondriacus. The NRH model fails to characterize the J-I curves with dynamic down-regulation/photoinhibition for Abies alba, Oryza sativa and M. aeruginosa. In addition, this model also significantly overestimates the values of J max for T. aestivum at 21% O2 and A. hypochondriacus grown under normal condition, and significantly underestimates the values of J max for M. aeruginosa grown under NO3 -N supply. Our study provides evidence that the 'mechanistic model' is much more suitable than both the DE and NRH models in fitting the J-I curves and in estimating the photosynthetic parameters. This is a powerful tool for studying light harvesting properties and the dynamic down-regulation of PSII/photoinhibition.

Investigation on absorption cross-section of photosynthetic pigment molecules based on a mechanistic model of the photosynthetic electron flow-light response in C3, C4 species and cyanobacteria grown under various conditions.

Investigation on intrinsic properties of photosynthetic pigment molecules participating in solar energy absorption and excitation, especially their eigen-absorption cross-section (σ ik) and effective absorption cross-section (σ ' ik), is important to understand photosynthesis. Here, we present the development and application of a new method to determine these parameters, based on a mechanistic model of the photosynthetic electron flow-light response. The analysis with our method of a series of previously collected chlorophyll a fluorescence data shows that the absorption cross-section of photosynthetic pigment molecules has different values of approximately 10-21 m2, for several photosynthetic organisms grown under various conditions: (1) the conifer Abies alba Mill., grown under high light or low light; (2) Taxus baccata L., grown under fertilization or non-fertilization conditions; (3) Glycine max L. (Merr.), grown under a CO2 concentration of 400 or 600 µmol CO2 mol-1 in a leaf chamber under shaded conditions; (4) Zea mays L., at temperatures of 30°C or 35°C in a leaf chamber; (5) Osmanthus fragrans Loureiro, with shaded-leaf or sun-leaf; and (6) the cyanobacterium Microcystis aeruginosa FACHB905, grown under two different nitrogen supplies. Our results show that σ ik has the same order of magnitude (approximately 10-21 m2), and σ ' ik for these species decreases with increasing light intensity, demonstrating the operation of a key regulatory mechanism to reduce solar absorption and avoid high light damage. Moreover, compared with other approaches, both σ ik and σ ' ik can be more easily estimated by our method, even under various growth conditions (e.g., different light environment; different CO2, NO2, O2, and O3 concentrations; air temperatures; or water stress), regardless of the type of the sample (e.g., dilute or concentrated cell suspensions or leaves). Our results also show that CO2 concentration and temperature have little effect on σ ik values for G. max and Z. mays. Consequently, our approach provides a powerful tool to investigate light energy absorption of photosynthetic pigment molecules and gives us new information on how plants and cyanobacteria modify their light-harvesting properties under different stress conditions.

A review on light response model of photosynthesis under different environmental conditions.

Light response curve of photosynthesis (An-I curve) is a useful modeling tool to investigate how photosynthesis reacts with different abiotic factors, which would help quantify the response of photosynthetic rate to photosynthetically active radiation. Based on the mathematical characteristics of photosynthesis An-I models, we reviewed the advantages of using these model in practice and the potential caveats. We proposed the development of new mechanistic photosynthesis An-I models based on the primary light response and discussed its advantages in the field of plant ecology and physiology. Photosynthesis has three main steps, including the primary reaction, the assimilatory power forms, and the carbon assimilation. Changes in each step could directly affect the photochemical efficiency and carbon assimilation in photosynthesis. The primary reaction consists of a series of physical processes that are related to light energy absorption and utilization, including the absorption of light energy, the change of quantum state, and the transfer and de-excitation of exciton resonance of light-trapping pigment molecules. How-ever, the empirical photosynthesis An-I models can not explain some scenarios. For example, the non-photochemical quenching in plants increases with increasing light intensity in a non-linear manner. Further, the life-time of singlet chlorophyll molecules can be extended when plant light-harvesting pigment molecules absorb excessive light energy but would not be immediately used for the photochemical reaction. Meanwhile, the parameters obtained by fitting the mechanistic An-I curve model can not only reflect the primary photochemical reaction characteristics of plants, but also describe the physical characteristics of plant light harvesting pigment molecules, such as the number of light harvesting pigment molecules in the excited state (Nk) and effective light energy absorption cross-section (σik'). This can be used to further investigate the physical characteristics of light harvesting pigment molecules, including the light-response of Nk and σik' and the average life time of light harvesting pigment molecules in the lowest exciting state (τmin). In addition, it would be necessary to determine how to incorporate abiotic factors, such as temperature and CO2 concentration, into the mechanistic An-I curve model, as well as to determine the association between the abiotic factors and light harvesting pigment molecules, such as Nk, σik', and τmin.

Modeling Light Response of Electron Transport Rate and Its Allocation for Ribulose Biphosphate Carboxylation and Oxygenation.

Accurately describing the light response curve of electron transport rate (J-I curve) and allocation of electron flow for ribulose biphosphate (RuBP) carboxylation (J C-I curve) and that for oxygenation (J O-I curve) is fundamental for modeling of light relations of electron flow at the whole-plant and ecosystem scales. The non-rectangular hyperbolic model (hereafter, NH model) has been widely used to characterize light response of net photosynthesis rate (A n; A n-I curve) and J-I curve. However, NH model has been reported to overestimate the maximum A n (A nmax) and the maximum J (J max), largely due to its asymptotic function. Meanwhile, few efforts have been delivered for describing J C-I and J O-I curves. The long-standing challenge on describing A n-I and J-I curves have been resolved by a recently developed A n-I and J-I models (hereafter, Ye model), which adopt a nonasymptotic function. To test whether Ye model can resolve the challenge of NH model in reproducing J-I, J C-I and J O-I curves over light-limited, light-saturated, and photoinhibitory I levels, we compared the performances of Ye model and NH model against measurements on two C3 crops (Triticum aestivum L. and Glycine max L.) grown in field. The results showed that NH model significantly overestimated the A nmax and J max for both species, which can be accurately obtained by Ye model. Furthermore, NH model significantly overestimated the maximum electron flow for carboxylation (J C-max) but not the maximum electron flow for oxygenation (J O-max) for both species, disclosing the reason underlying the long-standing problem of NH model-overestimation of J max and A nmax.

Quantifying Light Response of Leaf-Scale Water-Use Efficiency and Its Interrelationships With Photosynthesis and Stomatal Conductance in C3 and C4 Species.

Light intensity (I) is the most dynamic and significant environmental variable affecting photosynthesis (A n), stomatal conductance (g s), transpiration (T r), and water-use efficiency (WUE). Currently, studies characterizing leaf-scale WUE-I responses are rare and key questions have not been answered. In particular, (1) What shape does the response function take? (2) Are there maximum intrinsic (WUEi; WUEi-max) and instantaneous WUE (WUEinst; WUEinst-max) at the corresponding saturation irradiances (I i-sat and I inst-sat)? This study developed WUEi-I and WUEinst-I models sharing the same non-asymptotic function with previously published A n-I and g s-I models. Observation-modeling intercomparison was conducted for field-grown plants of soybean (C3) and grain amaranth (C4) to assess the robustness of our models versus the non-rectangular hyperbola models (NH models). Both types of models can reproduce WUE-I curves well over light-limited range. However, at light-saturated range, NH models overestimated WUEi-max and WUEinst-max and cannot return I i-sat and I inst-sat due to its asymptotic function. Moreover, NH models cannot describe the down-regulation of WUE induced by high light, on which our models described well. The results showed that WUEi and WUEinst increased rapidly within low range of I, driven by uncoupled photosynthesis and stomatal responsiveness. Initial response rapidity of WUEi was higher than WUEinst because the greatest increase of A n and T r occurred at low g s. C4 species showed higher WUEi-max and WUEinst-max than C3 species-at similar I i-sat and I inst-sat. Our intercomparison highlighted larger discrepancy between WUEi-I and WUEinst-I responses in C3 than C4 species, quantitatively characterizing an important advantage of C4 photosynthetic pathway-higher A n gain but lower T r cost per unit of g s change. Our models can accurately return the wealth of key quantities defining species-specific WUE-I responses-besides A n-I and g s-I responses. The key advantage is its robustness in characterizing these entangled responses over a wide I range from light-limited to light-inhibitory light intensities, through adopting the same analytical framework and the explicit and consistent definitions on these responses. Our models are of significance for physiologists and modelers-and also for breeders screening for genotypes concurrently achieving maximized photosynthesis and optimized WUE.

Comparing two measures of leaf photorespiration rate across a wide range of light intensities.

Suppression of photorespiration by low O2 concentrations (Method 1) and simultaneous measurements of gas exchange and chlorophyll fluorescence (Method 2) are often used to estimate leaf photorespiration rate (Rp) of C3 plants. However, it is largely unknown whether Method 1 and Method 2 can be used equivalently in estimating Rp. Using a field experiment on two wheat cultivars (T. aestivum JM22 and T. aestivum Z39-118) whose leaf gas exchange and chlorophyll fluorescence at low and normal O2 concentrations (2% versus 21% O2) were simultaneously measured across a wide range of light intensities (I), this study assessed the impacts of the two measures on Rp and its response under changing irradiance conditions. All the above quantities increased with the increasing I until reaching the cultivar-specific maximum values and the corresponding saturation light intensities. However, there were significant differences between Rp estimated by Method 1 and Method 2 at the I range from 150 to 2000 µmol m-2 s-1 for T. aestivum JM22 and from 150 to 1000 µmol m-2 s-1 for T. aestivum Z39-118. These findings demonstrated that the two methods cannot be used equivalently under changing irradiance conditions.

[Photosynthetic physio-ecological characteristics in soybean leaves at different CO2 concentrations.] / 不同CO2æµ“åº¦ä¸‹å¤§è±†å¶ç‰‡çš„å ‰åˆç”Ÿç†ç”Ÿæ€ç‰¹æ€§.

The availability of CO2, a substrate for photosynthesis, affects the photosynthesis process and photosynthate production. Using the Li-6400-40B, we measured the photosynthetic electron transport rate and the photosynthetic light-response curves of soybean (Glycine max) leaves at different CO2 concentrations (300, 400, 500 and 600 µmol·mol-1). By fitting these parameters with a mechanistic model characterizing the light response of photosynthesis, we obtained aseries of photosynthetic parameters, eco-physiological parameters, as well as the physical parameters of photosynthetic pigments. The results showed that the electronic use efficiency, maximum electron transport rate, and maximum net photosynthetic rate increased with the increase of CO2 concentration. The light compensation point and dark respiration rate decreased with the increase of CO2 concentration. In addition, the light-use efficiency and intrinsic (instantaneous) water-use efficiency increased with the increase of CO2 concentration, and their values differed significantly among different CO2 concentrations. There was no significant difference on the maximum carboxylation efficiency among different CO2 concentrations. Those results suggested that CO2 concentration could affect the primary light reaction of photosynthesis in soybean leaves, and thus higher CO2 concentration could decrease the minimum average lifespan of excitons at the lowest excited state, which would enhance the velocity of light energy transport and the use efficiency of photosynthetic electron flow.

[Light-use efficiency of tomato seedling leaves at different CO2 concentrations.] / 不同CO2æµ“åº¦ä¸‹ç•ªèŒ„å¹¼è‹—å¶ç‰‡çš„å ‰èƒ½åˆ©ç”¨æ•ˆçŽ‡.

Light-use efficiency (LUE) is an important parameter to assess light energy absorption of leaf. Especially, it is a key factor to affect production and quality of ecosystem. A model of LUE was developed based on a mechanistic model of light-response of photosynthesis. The maximum LUE (LUEmax) and corresponding saturation irradiance (IL-sat) were deduced according to the LUE mo-del. At CO2 concentrations of 350, 450, 550 and 650 µmol·mol-1, the light-response curves of LUE of tomato seedling leaves were simulated. The results showed that the model of LUE described well the response curves of light use efficiency of tomato seedling leaves at four CO2 concentrations. LUE of tomato seedling leaves reached the maximum value at photosynthetically active radiation between 70-90 µmol·m-2·s-1. There were no difference of LUEmax and IL-sat at 550 and 650 µmol·mol-1. Regarding this phenomenon, it was hypothesized that the photosynthetic functions of tomato seedling leaves had acclimated to the low irradiance in greenhouse so that the intrinsic cha-racteristic of light-harvesting pigments such as the effective light absorption cross-section of light-harvesting pigments and ratio of pigment molecules in the excited state to ground state had hardly changed at high CO2 concentrations.

A mechanistic model for the photosynthesis-light response based on the photosynthetic electron transport of photosystem II in C3 and C4 species.

A new mechanistic model of the photosynthesis-light response is developed based on photosynthetic electron transport via photosystem II (PSII) to specifically describe light-harvesting characteristics and associated biophysical parameters of photosynthetic pigment molecules. This model parameterizes 'core' characteristics not only of the light response but also of difficult to measure physical parameters of photosynthetic pigment molecules in plants. Application of the model to two C3 and two C4 species grown under the same conditions demonstrated that the model reproduced extremely well (r(2) > 0.992) the light response trends of both electron transport and CO2 uptake. In all cases, the effective absorption cross-section of photosynthetic pigment molecules decreased with increasing light intensity, demonstrating novel operation of a key mechanism for plants to avoid high light damage. In parameterizing these previously difficult to measure characteristics of light harvesting in higher plants, the model provides a new means to understand the mechanistic processes underpinning variability of CO2 uptake, for example, photosynthetic down-regulation or reversible photoinhibition induced by high light and photoprotection. However, an important next step is validating this parameterization, possibly through application to less structurally complex organisms such as single-celled algae.

[A study of the diversity of different geographical populations of Emmenopterys henryi using FTIR based on principal component analysis and cluster analysis].

Emmenopterys henryi, an endemic species in China, has been one of the grade II national key conservation rare and endangered plants. The spectra of stem and leaf of Emmenopterys henryi sampling from seven different geographical populations were determined by Fourier transform infrared (FTIR) spectrometry with OMNI-sampler directly, fast and accurately. A positioning technology of OMNIC E.S.P.5.1 intelligent software and ATR correction was used. It was scanned for the background before the determination of every example. The peak value and absorbance were ascertained using a method of baseline correction in infrared spectra. Based on the indices of wave number-absorbance from 721 to 3366 cm(-1), the differences of these infrared spectra were compared by the methods of principal component analysis (PCA) and cluster analysis. Results showed that there were some differences in FTIR spectra between stem and leaf of Emmenopterys henryi, so it was better to study the diversity of different geographical populations through using the leaf, for which the distance coefficient of clustering analysis plot and the position relationship of principal component analysis three-dimensional plot of the seven populations were bigger. Being far away from others populations, the infrared spectra of Emmenopterys henryi in Dapan Mountain and Gutian mountain had special characteristics, indicating significant diversity. At the same time, the infrared spectra of Jiulong Mountain, Wuyan Mountain and Songyang populations had their own characteristics. There were no significant difference in the position relationship of three-dimensional plot and distance coefficient of clustering analysis plot, showing that the chemical compositions of these three populations were of little difference, and the diversity differentiation was not remarkable. However, there were some significant differences in populations' diversity between Fengyang Mountain and Wencheng. It was indicated that the chemical composition of Emmenopterys henryi was affected by the special geographic positions and environment conditions. In a word, the remarkable differences in the chemical compositions of Emmenopterys henryi populations were consistent with their geographic distance far and near. The results also showed that there was good correspondence between the position relationship of PCA three-dimensional plot and distance coefficient of clustering analysis plot of the samples based on the indices of wave number-absorbance of FTIR and their geographic distance relationship. Therefore, FTIR can be used widely for studying and protecting the rare and endangered plants. It is not only provides the theoretic base of community ecology and ecosystem ecology of Emmenopterys henryi, but also has important theory and realistic meaning for exploring the mechanism of species endangerment, protecting and proliferating the populations of Emmenopterys henryi.

[FTIR spectra of endangered plants Ulmus elongata and its correlation to soil nitrogen].

Ulmus elongata, an endemic species in China, is one of the grade II national key conservation rare and endangered plants. The spectra of root, stem, skin and leaf of Ulmus elongata sampled from eight different sites were determined by Fourier transform infrared (FTIR) spectrometry with OMNI-sampler directly, fast and accurately. A positioning technology of OMNIC E.S.P. 5.1 intelligent software and ATR correction was used. The background was scanned before the determination of every example. The peak value and absorbance were ascertained using a method of baseline correction in infrared spectra, and then the relativity between absorption peaks of the spectra and the soil nitrogen was analyzed. Results from the comparison of the spectra showed some differences in their FTIR spectra among root, stem, skin and leaf of Ulmus elongata from the same plant. The coefficients of correlation between chemical composition of this four different organs of Ulmus elongata and soil nitrogen were positive in different degrees. There was the significantly positive correlation between chemical composition of stem and total nitrogen (p < 0.05). When the wave-number was 3 365 cm(-1), there was a significantly positive correlation between chemical composition of skin and total nitrogen, and a low correlation between root and leave chemical composition and total nitrogen. There was also a certain extent correlation between chemical composition of this four different organs of Ulmus elongata and soil available nitrogen, but the coefficients of correlation was smaller, and the level of the statistic significance was not significant (p > 0.05). It was showed that the change in soil total nitrogen has some influence on chemical composition of different organs of Ulmus elongata, but the degree of available nitrogen was very smaller. The linear correlation between soil total nitrogen and organs chemical composition of Ulmus elongate, not only provided the theoretic basis for plant nutriology and nutrient ecology of Ulmus elongate, but also proved that the plants and soil were inseparable. The results also showed that FTIR can be used widely for analysis of the correlation between chemical composition of endangered plants and soil physical and chemical properties in the future, and indicated that the new method has practicability and reliability to a certain degree.