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Switchgrass (Panicum virgatum L.) is a prominent bioenergy crop with robust resilience to environmental stresses. However, our knowledge regarding how precipitation changes affect switchgrass photosynthesis and its responses to light and CO2 remains limited. To address this knowledge gap, we conducted a field precipitation experiment with five different treatments, including −50%, −33%, 0%, +33%, and +50% of ambient precipitation. To determine the responses of leaf photosynthesis to CO2 concentration and light, we measured leaf net photosynthesis of switchgrass under different CO2 concentrations and light levels in 2020 and 2021 for each of the five precipitation treatments. We first evaluated four light and CO2 response models (i.e., rectangular hyperbola model, nonrectangular hyperbola model, exponential model, and the modified rectangular hyperbola model) using the measurements in the ambient precipitation treatment. Based on the fitting criteria, we selected the nonrectangular hyperbola model as the optimal model and applied it to all precipitation treatments, and estimated model parameters. Overall, the model fit field measurements well for the light and CO2 response curves. Precipitation change did not influence the maximum net photosynthetic rate (Pmax) but influenced other model parameters including quantum yield (α), convexity (θ), dark respiration (Rd), light compensation point (LCP), and saturated light point (LSP). Specifically, the mean Pmax of five precipitation treatments was 17.6 μmol CO2 m−2 s−1, and the ambient treatment tended to have a higher Pmax. The +33% treatment had the highest α, and the ambient treatment had lower θ and LCP, higher Rd, and relatively lower LSP. Furthermore, precipitation significantly influenced all model parameters of CO2 response. The ambient treatment had the highest Pmax, largest α, and lowest θ, Rd, and CO2 compensation point LCP. Overall, this study improved our understanding of how switchgrass leaf photosynthesis responds to diverse environmental factors, providing valuable insights for accurately modeling switchgrass ecophysiology and productivity. [ABSTRACT FROM AUTHOR]

Abstract Switchgrass (Panicum virgatum L.) is a prominent bioenergy crop with robust resilience to environmental stresses. However, our knowledge regarding how precipitation changes affect switchgrass photosynthesis and its responses to light and CO2 remains limited. To address this knowledge gap, we conducted a field precipitation experiment with five different treatments, including −50%, −33%, 0%, +33%, and +50% of ambient precipitation. To determine the responses of leaf photosynthesis to CO2 concentration and light, we measured leaf net photosynthesis of switchgrass under different CO2 concentrations and light levels in 2020 and 2021 for each of the five precipitation treatments. We first evaluated four light and CO2 response models (i.e., rectangular hyperbola model, nonrectangular hyperbola model, exponential model, and the modified rectangular hyperbola model) using the measurements in the ambient precipitation treatment. Based on the fitting criteria, we selected the nonrectangular hyperbola model as the optimal model and applied it to all precipitation treatments, and estimated model parameters. Overall, the model fit field measurements well for the light and CO2 response curves. Precipitation change did not influence the maximum net photosynthetic rate (Pmax) but influenced other model parameters including quantum yield (α), convexity (θ), dark respiration (Rd), light compensation point (LCP), and saturated light point (LSP). Specifically, the mean Pmax of five precipitation treatments was 17.6 μmol CO2 m−2 s−1, and the ambient treatment tended to have a higher Pmax. The +33% treatment had the highest α, and the ambient treatment had lower θ and LCP, higher Rd, and relatively lower LSP. Furthermore, precipitation significantly influenced all model parameters of CO2 response. The ambient treatment had the highest Pmax, largest α, and lowest θ, Rd, and CO2 compensation point LCP. Overall, this study improved our understanding of how switchgrass leaf photosynthesis responds to diverse environmental factors, providing valuable insights for accurately modeling switchgrass ecophysiology and productivity.

To elucidate the adaptive strategies of Glechoma longituba in response to different light-quality colored films, the growth, photosynthesis, chloroplast ultrastructure, and triterpene acid accumulation were analyzed. In this study, four colored films improved electron transport and maintained the function of PSII, and allocated more light energy absorbed for photochemical reactions, thus increasing the photosynthetic capacity and ultimately improving dry mass accumulation. Additionally, blue film (BF) and green film (GF) enhanced photosynthesis by increasing stomatal openness and chlorophyll contents and maintaining chloroplast structural integrity, thereby promoting dry mass and triterpene acid (TA) accumulation of G. longituba. Red film excessively increased starch grains, inhibited photosynthate output and consequently reduced the concentration and yield of ursolic acid (UA). Yellow film decreased stomatal openness and chlorophyll concentrations, which was not conducive to chloroplast development, and also decreased the concentration and yield of UA. In conclusion, the application of BF and GF may represent an effective cultivation practice that can be used to achieve the highest TA yields in plantings of G. longituba.

Light acts as a complex signal, influencing various plant physiological, phenological and morphogenetic traits. Although previous studies have explored the effects of varying light levels on branch growth and survival, the underlying mechanisms of branch mortality under shade conditions remain poorly understood, hindering our understanding of canopy dynamics. In this study, contrasting shade conditions were imposed on Pinus taeda branches, and the changes in their water relations and carbon dynamics were evaluated. Monthly measurements of the photosynthetic light–response curve (LRC), sap flow and water potential of the branches were conducted. Furthermore, the conditions that led to the deaths of lower branches were investigated, and principal component analysis (PCA) was used to classify branches according to their mortality status. Significant shade treatment effects were observed for all photosynthetic parameters. The assimilation at light saturation (Amax), dark respiration rate (Rd), apparent quantum yield (AQY), light compensation point (LCP) and light saturation point (LSP) all decreased from full light to deepest shade, whereas the opposite was the case for the convexity term (θ). All water relations traits also decreased from full light to deepest shade; however, although significant shade effect was observed in stomatal conductance (gs) and sap flow, the differences in the pre-dawn (Ψpre-dawn) and mid-day (Ψmid-day) water potentials among treatments were not statistically significant. The PCA classification results showed that it could be used as a reliable method to screen for branch mortality as early as four months before mortality becomes evident. Our results shed more light on branch physiology and mortality under shade and have the potential to help improve the prediction of tree crown size, ultimately improving process-based forest growth models. [ABSTRACT FROM AUTHOR]

This study aimed to determine the appropriate time for the chlorophyll fluorescence light curve measurement in sago palms and to avoid high values variations. The photosynthetic status of three-year-old sago palm seedlings was evaluated through the chlorophyll fluorescence measurement. The chlorophyll fluorescence light curve of measurement was evaluated under different daytime measurements. Observations on DFm/Fm’ and ETR vs. irradiances were conducted on sago palm leaves in the morning, midday, and afternoon with light and dark adaptation. The highest ETRmax value was found under a light-adapted leaf; however, the Eopt value could not be obtained. Morning time measurement on the dark-adapted leaf is the most appropriate method and time to get an Eopt value with high ETRmax.

To elucidate the adaptive strategies of Glechoma longituba in response to different light-quality colored films, the growth, photosynthesis, chloroplast ultrastructure, and triterpene acid accumulation were analyzed. In this study, four colored films improved electron transport and maintained the function of PSII, and allocated more light energy absorbed for photochemical reactions, thus increasing the photosynthetic capacity and ultimately improving dry mass accumulation. Additionally, blue film (BF) and green film (GF) enhanced photosynthesis by increasing stomatal openness and chlorophyll contents and maintaining chloroplast structural integrity, thereby promoting dry mass and triterpene acid (TA) accumulation of G. longituba. Red film excessively increased starch grains, inhibited photosynthate output and consequently reduced the concentration and yield of ursolic acid (UA). Yellow film decreased stomatal openness and chlorophyll concentrations, which was not conducive to chloroplast development, and also decreased the concentration and yield of UA. In conclusion, the application of BF and GF may represent an effective cultivation practice that can be used to achieve the highest TA yields in plantings of G. longituba. [ABSTRACT FROM AUTHOR]

Featured Application: A potential application of irradiance adjustment simply based on leaf colorimetric characteristics for Aglaonema commutatum wide cultivation. Plants can be grouped into sun- and shade-type owing to their distinct irradiance adaptation. Aglaonema commutatum is a typical shade-tolerant perennial foliage plant native to South Asia with various leaf colorations. 'Red' cultivars are widely used for interior decorations and as courtyard ornamental plants, owing to their unique hue and bi-adaptation of both low and high irradiance. However, the underlying source of 'red' pigment-dependent irradiance bi-adaptation remains largely unknown. Therefore, four A. commutatum cultivars were comparatively evaluated in terms of pigment composition and photosynthetic rate under full light (sunlight) or 50% full light (shade) to unveil the relationship between pigmentation and irradiance bi-adaptation. Our results showed that the photosynthetic rate of sun leaves generated from light response curves was significantly correlated with anthocyanin content and chlorophyll in red cultivars, suggesting the influence of anthocyanin–light interactions on the high/low irradiance bi-adaptation of red A. commutatum. This study provides a theoretical basis for further cultivating red foliage A. commutatum cultivars under diverse light conditions. [ABSTRACT FROM AUTHOR]

The current study evaluated the canopy cover competition for light and heat in a jujube–cotton intercropping system to measure the growth and yield performance of cotton, and the optimal cotton planting configuration. In this study, a two-year field experiment (2020 and 2021) was studied with different spacing configuration modes designed as follows: two rows of cotton (CM1) planted 1.4 m apart, four rows of cotton (CM2) planted 1.0 m apart, and six rows of cotton (CM3) planted 0.5 m apart, spacing intercropped jujube trees, respectively. The control treatment consisted of monocultured cotton (CK). The light-response curve was plotted using an LI-6400 XT photosynthesis instrument. Based on the modified rectangular hyperbola model, the photosynthetic characteristics were fitted, and the dry matter distribution characteristics and yield were compared. The results showed that with the increase in photosynthetically active radiation, the net photosynthetic rate (Pn) of each growth phase decreased first and then increased rapidly in the range of 0–200 μmol·m−2·s−1 and then decreased slightly after the inflection point (light saturation point). The light-response curves of stomatal conductance and transpiration rate showed a linear relationship. The trend in the intercellular CO2 concentration response curve was opposite to that of Pn. The maximum Pn (Pmax) of intercropped cotton was significantly impacted by configuration modes, of which CM2 treatment generated 1.8% and 22.8% higher Pmax than the CM1 and CM3 treatments. The cotton yield in the two years ranked as CK > CM3 > CM2 > CM1, and the average land equivalent ratio of CM2 was significantly higher than that of CM3 (22.4%) and CM1 (95.9%). The six-row configuration resulted in greater competition with the trees, which affected the accumulation of below-ground dry matter, while the four-row configuration formed a reasonable canopy structure, which ensured that more photosynthetic substances were distributed to the generative organs. The reasonable four-rows configuration mode may improve the photosynthetic efficiency of intercropped cotton economic yield. [ABSTRACT FROM AUTHOR]

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Plants can be grouped into sun- and shade-type owing to their distinct irradiance adaptation. Aglaonema commutatum is a typical shade-tolerant perennial foliage plant native to South Asia with various leaf colorations. ‘Red’ cultivars are widely used for interior decorations and as courtyard ornamental plants, owing to their unique hue and bi-adaptation of both low and high irradiance. However, the underlying source of ‘red’ pigment-dependent irradiance bi-adaptation remains largely unknown. Therefore, four A. commutatum cultivars were comparatively evaluated in terms of pigment composition and photosynthetic rate under full light (sunlight) or 50% full light (shade) to unveil the relationship between pigmentation and irradiance bi-adaptation. Our results showed that the photosynthetic rate of sun leaves generated from light response curves was significantly correlated with anthocyanin content and chlorophyll in red cultivars, suggesting the influence of anthocyanin–light interactions on the high/low irradiance bi-adaptation of red A. commutatum. This study provides a theoretical basis for further cultivating red foliage A. commutatum cultivars under diverse light conditions.

The current study evaluated the canopy cover competition for light and heat in a jujube–cotton intercropping system to measure the growth and yield performance of cotton, and the optimal cotton planting configuration. In this study, a two-year field experiment (2020 and 2021) was studied with different spacing configuration modes designed as follows: two rows of cotton (CM1) planted 1.4 m apart, four rows of cotton (CM2) planted 1.0 m apart, and six rows of cotton (CM3) planted 0.5 m apart, spacing intercropped jujube trees, respectively. The control treatment consisted of monocultured cotton (CK). The light-response curve was plotted using an LI-6400 XT photosynthesis instrument. Based on the modified rectangular hyperbola model, the photosynthetic characteristics were fitted, and the dry matter distribution characteristics and yield were compared. The results showed that with the increase in photosynthetically active radiation, the net photosynthetic rate (Pn) of each growth phase decreased first and then increased rapidly in the range of 0–200 μmol·m−2·s−1 and then decreased slightly after the inflection point (light saturation point). The light-response curves of stomatal conductance and transpiration rate showed a linear relationship. The trend in the intercellular CO2 concentration response curve was opposite to that of Pn. The maximum Pn (Pmax) of intercropped cotton was significantly impacted by configuration modes, of which CM2 treatment generated 1.8% and 22.8% higher Pmax than the CM1 and CM3 treatments. The cotton yield in the two years ranked as CK > CM3 > CM2 > CM1, and the average land equivalent ratio of CM2 was significantly higher than that of CM3 (22.4%) and CM1 (95.9%). The six-row configuration resulted in greater competition with the trees, which affected the accumulation of below-ground dry matter, while the four-row configuration formed a reasonable canopy structure, which ensured that more photosynthetic substances were distributed to the generative organs. The reasonable four-rows configuration mode may improve the photosynthetic efficiency of intercropped cotton economic yield.

A pot experiment was performed to study the light-response curve of photosynthesis (PN-PAR curve) of Mangifera indica and the applicability of light-response models under different soil water conditions. The experimental data were fitted and analyzed using the rectangular hyperbola model, the nonrectangular hyperbola model, the exponential model, the modified rectangular hyperbola model, and the kinetic model. The results showed that the optimal range of relative soil water content (RSWC) for the normal photosynthesis of M. indica was 45.1-77.3%. The modified rectangular hyperbola model could well fit the PN-PAR curves and photosynthetic parameters under wide range of soil water conditions (RSWC 23.3-77.3%). The rectangular hyperbola model, the nonrectangular hyperbola model, the exponential model, and the kinetic model could only be used to fit the PN-PAR curves of M. indica under mild and moderate drought stress (RSWC 45.1-77.3%).

Light intensity (I) fluctuates rapidly and is the most important environmental factor affecting photosynthesis. Accurate characterization of light-response curve of leaf-scale photosynthesis (PN-I curve) is fundamental for understanding PN-I relations at the whole-plant and ecosystem scales. A robust PN-I model should be accurate in reproducing PN-I curves over light-limited, light-saturated, and photoinhibitory I levels, and ideally returning key quantitative traits defining the curves, including initial slope of increase (a), dark respiration rate (RD), the maximum net photosynthetic rate (PNmax), and the corresponding saturation intensity (Isat). We need to improve a model reproduction of (1) PN-I responses over low I levels and (2) the widely reported decline of PN at photoinhibitory I levels. Our observation-modelling comparison, shown by the widely used non-rectangular hyperbolic model, led to (1) underestimation of RD, (2) overestimation of PNmax, and (3) failure in reproducing the photoinhibitory response when I surpassed the cultivar-specific Isat. In contrast, our model addressed the above limitations extremely well. The results highlighted the accuracy and robustness of our model, especially in (1) returning key traits defining the curve and (2) reproducing the curve over both low [i.e., 0-50 µmol(photon) m-2 s-1] and photoinhibitory I levels (i.e., beyond Isat). [ABSTRACT FROM AUTHOR]

Increasing the forest's productivity is a global concern and there is a need to develop innovative technologies. The use of biochar (BC) in the restoration of degraded sites is mounting. Therefore, to assess the effects of rice straw biochar (BR) on soil physicochemical properties and physiology of Fokienia hodginsii, a one-year greenhouse pot experiment was conducted. The soil was mixed with BR at four different levels; 0, 5, 20, and 80 g kg−1of soil as B0, BR5, BR20, and BR80, respectively. The light-response curves of photosynthesis were constructed by using the modified model of rectangular hyperbola including photosynthetic pigments and biochemical attributes quarterly. BR treated seedlings responded with a significant increase in the photosynthetic rate at first, second, and fourth season, respectively. Increasing the proportion of BR in the soil significantly influenced the soil pH and P availability. At the final harvest, improved soil and physiology promoted the seedling biomass (36%) under BR80 compared to B0. Therefore, these findings suggest that BR can be used to combat soil acidification and P availability in P deficit soil. Its amendment into the soil can be useful to alleviate the physiological performance of the conifer seedlings, but its effects may vary with soil type and BC feed-stock. [ABSTRACT FROM AUTHOR]

The influences of drought stress on the photosynthesis rate, the chlorophyll fluorescence parameters, the activity of protective enzymes of potato, and the biomass fresh weights of potato leaves at seedling stage were investigated, using two different varieties of potato with significant difference in drought resistance to carry out potted plant experiment with water control. Under mild and medium drought stresses, the two potato varieties stabilized the photosynthetic organ functions by light capture reduction, heat dissipation and the regulation of enzyme activity. The damage of photosystem II and antioxidant enzyme system was the non-stomatal limitation factors for the decrease of the photosynthesis rate under serious drought stress. The influence on the physiological parameters of potato Kexin No. 1 was weaker than that of potato Kexin No. 12 under drought stresses. The higher photosynthesis rate and stronger activity of protective enzymes were the important physiological reasons for the drought resistance of Kexin No. 1.

A pot experiment was performed to study the light-response curve of photosynthesis (PN-PAR curve) of Mangifera indica and the applicability of light-response models under different soil water conditions. The experimental data were fitted and analyzed using the rectangular hyperbola model, the nonrectangular hyperbola model, the exponential model, the modified rectangular hyperbola model, and the kinetic model. The results showed that the optimal range of relative soil water content (RSWC) for the normal photosynthesis of M. indica was 45.1-77.3%. The modified rectangular hyperbola model could well fit the PN-PAR curves and photosynthetic parameters under wide range of soil water conditions (RSWC 23.3-77.3%). The rectangular hyperbola model, the nonrectangular hyperbola model, the exponential model, and the kinetic model could only be used to fit the PN-PAR curves of M. indica under mild and moderate drought stress (RSWC 45.1-77.3%). [ABSTRACT FROM AUTHOR]

In order to study the effects of water depth on the chlorophyll fluorescence characteristics of typical submerged macrophyte, Vallisneria natans and Potamogeton malaianus were selected as test materials in Poyang Lake wetland. Water levels(0.5,1.0,1.5,2.0,2.5 m)were controlled by buckets, minimum fluorescence( Fo), maximum fluorescence(Fm), the maximum actinic light efficiency of PS II(Fv/Fm), effective quantum yield [Y(II)], photochemical quenching coefficient(qP ), non-photochemical quenching coefficient(qN ), unregulated energy dissipation quantum yield [Y(NO)] were measured by a submerged, modulated fluorescence spectrometer(Diving-pam). The variation of each parameter with depths was explored. The results showed that the maximum biomass of Vallisneria natans appeared in 1.5-2.0 m water depth, and that of Potamogeton malaianus appeared in 1.0-1.5 m water depth. Fo of each macrophyte decreased first and then increased, while the fluorescence parameters [Fm, Fv/Fm, Fv/Fo, Y(II), qP] all increased first and then decreased. Fv/Fm and Fv/Fo of Vallisneria natans reached the maximum under the condition of 2.0 m, but the maximum of Potamogeton malaianus appeared at 1.5 m. At the same depth, qN of Vallisneria natans was lower than that of Potamogeton malaianus. The change trend of qP was reversed. The maximum Y(II)of Vallisneria natans appeared in the range of 1.5-2.0 m water depth, but for Potamogeton malaianus, it appeared at 1.0-1.5 m. Y(NO) showed significant differences with changes of water depths, too high or too low water depth all inhibited plant growth. The relative photosynthetic electron transport rate(ETR)was significantly different between different water depth treatments. The maximum ETR of Vallisneria natans was smaller than that of Potamogeton malaianus which indicates that it has strong resistance to weak light. In summary, under the condition of 1.5-2.0 m water depth, Vallisneria natans has the strongest photosynthetic capacity and can grow the best, and Potamogeton malaianus is the most suitable for growth in 1.0-1.5 m. [ABSTRACT FROM AUTHOR]

Seasonal variations in photosynthesis of cassava cv. Rayong 9 (RY9) under irrigated and rain-fed conditions were evaluated at the age of three and six months after planting (MAP). Photosynthetic light-response (PN/I) curves revealed that cassava leaves attained the highest maximum net photosynthetic rates (PNmax) in the rainy season, followed by the hot one, while the lowest PNmax was found in the cool season. Photosynthetic potential of the 3-month-old plants was mostly higher than that of the 6-month-old plants, and the seasonal variation in photosynthetic capacity was also more apparent in the younger plants. PN/I curves were used to predict daily net photosynthetic rate (PN) for each season based on daily average solar radiation data. The predicted PN were considerably lower than the PNmax values. This indicated that solar radiation is a limiting factor for photosynthesis, particularly in the rainy season. The data provided basic information for breeding cassava genotypes with enhanced photosynthesis during the period of unfavorable environment. Furthermore, the data are potentially useful in modeling photosynthesis and crop growth as affected by environmental factors. [ABSTRACT FROM AUTHOR]

Seasonal changes in leaf gas exchange, assimilation response to light and leaf area were monitored in bearing and nonbearing pistachio shoots. Shoot bearing status did not directly affect leaf photosynthetic rate. However, photosynthetic light-response curves strongly varied during the season demonstrating the dominant effect of the tree’s seasonal phenology on assimilation. Early in the season low photosynthetic rates were associated with high rates of dark respiration indicating limited photosynthesis in the young leaves. As leaves matured, dark respiration decreased and assimilation reached maximum values. Photosynthetic efficiency was strongly reduced late in the season due to leaf age and senescence. Fruit load precipitated an early leaf senescence and drop that resulted in a 53% decrease in leaf area in bearing vs. nonbearing shoots, strongly decreasing the seasonal photosynthetic performance of bearing shoots. Bearing shoots produced a 26% lower seasonal carbon gain compared to nonbearing shoots. [ABSTRACT FROM AUTHOR]

Adding green component to growth light had a profound effect on biomass accumulation in lettuce. However, conflicting views on photosynthetic efficiency of green light, which have been reported, might occur due to nonuniform light sources used in previous studies. In an attempt to reveal plausible mechanisms underlying the differential photosynthetic and developmental responses to green light, we established a new way of light treatment modeled according to the principle of gene 'knock out'. Lettuce ( Lactuca sativa L. var. youmaicai) was grown under two different light spectra, including a wide spectrum of light-emitting diode (LED) light (CK) and a wide spectrum LED light lacking green (480-560 nm) (LG). Total PPFD was approximately 100 µmol(photon) m s for each light source. As compared to lettuce grown under CK, shoot dry mass, photosynthetic pigment contents, total chlorophyll to carotenoids ratio, absorptance of PPFD, and CO assimilation showed a remarkable decrease under LG, although specific leaf area did not show significant difference. Furthermore, plants grown under LG showed significantly lower stomatal conductance, intercellular CO concentration, and transpiration compared with CK. The plants under CK exhibited significantly higher intrinsic quantum efficiency, respiration rate, saturation irradiance, and obviously lower compensation irradiance. Finally, we showed that the maximum ribulose-1,5-bisphosphate-saturated rate of carboxylation, the maximum rate of electron transport, and rate of triosephosphate utilization were significantly reduced by LG. These results highlighted the influence of green light on photosynthetic responses under the conditions used in this study. Adding green component (480-560 nm) to growth light affected biomass accumulation of lettuce in controllable environments, such as plant factory and Bioregenerative Life Support System. [ABSTRACT FROM AUTHOR]

The influences of drought stress on the photosynthesis rate, the chlorophyll fluorescence parameters, the activity of protective enzymes of potato, and the biomass fresh weights of potato leaves at seedling stage were investigated, using two different varieties of potato with significant difference in drought resistance to carry out potted plant experiment with water control. Under mild and medium drought stresses, the two potato varieties stabilized the photosynthetic organ functions by light capture reduction, heat dissipation and the regulation of enzyme activity. The damage of photosystem II and antioxidant enzyme system was the non-stomatal limitation factors for the decrease of the photosynthesis rate under serious drought stress. The influence on the physiological parameters of potato Kexin No. 1 was weaker than that of potato Kexin No. 12 under drought stresses. The higher photosynthesis rate and stronger activity of protective enzymes were the important physiological reasons for the drought resistance of Kexin No. 1. [ABSTRACT FROM AUTHOR]

Constructed grasslands are primary restoration measures in areas with degraded natural grasslands. Grass-legume mixtures are chosen to obtain high production and forage quality; however, the photosynthetic and other traits of such mixtures are not well understood. In this study, we evaluated the effects of grass-legume mixtures on the growth and photosynthetic capacity of three forage crops over two growing seasons. Bromus inermis and Elymus nutans were grown as monocultures or in mixtures with Medicago sativa. We analysed forage yields, quality, gas exchange and chlorophyll fluorescence parameters. The grass-legume mixtures improved the forage yield, root : shoot ratio, and contents of crude protein and lignin. Compared with the monoculture, grasses in the mixtures had higher net photosynthesis, water-use efficiency (WUE), and leaf nitrogen (N) content, but lower carbon :N ratio, and distributed more absorbed light to photosynthetic electron transport and thermal dissipation. In the mixture, B. inermis had a higher light-saturation point, indicating high light-use efficiency. Elymus nutans had a lower light-compensation point and dark respiration rate, suggesting good shade tolerance. However, water deficits decreased biomass and photosynthetic capacity in the E. nutans-M. sativa mixture, suggesting that E. nutans was sensitive to soil moisture. The B. inermis-M. sativa mixture had greater and more consistent biomass and WUE.The grass-legume mixture is an important way to construct grasslands. We analysed forage yields, quality, gas exchange and chlorophyll fluorescence in the mixtures, finding that grass-legume mixtures improved forage production and photosynthetic capacity. The study provides a scientific basis for establishment of constructed grasslands with high yield and quality. [ABSTRACT FROM AUTHOR]

To estimate global gross primary production (GPP), which is an important parameter for studies of vegetation productivity and the carbon cycle, satellite data are useful. In 2014, the Japan Aerospace Exploration Agency (JAXA) plans to launch the Global Change Observation Mission-Climate (GCOM-C) satellite carrying the second-generation global imager (SGLI). The data obtained will be used to estimate global GPP. The rate of photosynthesis depends on photosynthesis reduction and photosynthetic capacity, which is the maximum photosynthetic velocity at light saturation under adequate environmental conditions. Photosynthesis reduction is influenced by weather conditions, and photosynthetic capacity is influenced by chlorophyll and RuBisCo content. To develop the GPP estimation algorithm, we focus on photosynthetic capacity because chlorophyll content can be detected by optical sensors. We hypothesized that the maximum rate of low-stress GPP (called “GPP capacity”) is mainly dependent on the chlorophyll content that can be detected by a vegetation index (VI). The objective of this study was to select an appropriate VI with which to estimate global GPP capacity with the GCOM-C/SGLI. We analyzed reflectance data to select the VI that has the best linear correlation with chlorophyll content at the leaf scale and with GPP capacity at canopy and satellite scales. At the satellite scale, flux data of seven dominant plant functional types and reflectance data obtained by the Moderate-resolution Imaging Spectroradiometer (MODIS) were used because SGLI data were not available. The results indicated that the green chlorophyll index, CIgreen(ρNIR/ρgreen-1), had a strong linear correlation with chlorophyll content at the leaf scale (R2 = 0.87, p < 0.001) and with GPP capacity at the canopy (R2 = 0.78, p < 0.001) and satellite scales (R2 = 0.72, p < 0.01). Therefore, CIgreen is a robust and suitable vegetation index for estimating global GPP capacity.

To elucidate the mechanisms of the adaptive advantages of polyploidy, there is a need to identify physiological traits that participate in the success of polyploids. We studied selected photosynthetic characteristics, stomatal density, and specific leaf area of three ploidy levels (2n = 4x, 5x, 6x) of the geophyte Allium oleraceum that partially differ in their ecological niches. Although the cytotypes were on average similar with regard to most of the measured photosynthetic traits, the hexaploids showed more rapid initial photosynthetic induction and a tendency for a higher maximum photosynthetic rate per unit area. The stomatal density was not affected by ploidy, though the specific leaf area was reduced for the hexaploids compared to the other cytotypes. A lower intracytotype variation was found for most of the studied photosynthetic and anatomical traits for the hexaploids compared to the large variation found within other cytotypes. A comparison of the photosynthetic traits between the cytotypes showed that the ecological differentiation between cytotypes is only weakly related to the characteristics of their photosynthetic apparatus. However, contrasting ranges of variability in the measured traits between the cytotypes can be related to previously observed differences between cytotypes with regard to the ranges of intracytotype genetic variation, genome size variation, and niche breadth. A higher variability of photosynthetic traits in tetraploids and pentaploids may be related to the existence of a spectrum of types adapted to different environmental conditions. Hexaploids may represent a recently formed cytotype adapted to open environmental conditions. [ABSTRACT FROM AUTHOR]

Taken the grape cultivar 'Shine Muscat' as the material, the effect of the combination of GA3 and CPPU on the light-response curves in the fruit adjacent leaves and fruit quality were investigated two weeks after blossoming. The results showed that non-rectangular hyperbolic model was more suitable for grape fruit adjacent leaf light response curve fitting. Pn and gs of fruit adjacent leaves among all treatments increased with the increasing light intensity under the combination treatments of 25 mg . L-1 GA3 and 5, 10, 15, 20 mg . L-1 CPPU, respectively, but Ci decreased. Fruit quality increased with the increasing CPPU concentration under the combination treatments of 25 mg . L-1 GA3 and 5, 10, 15 mg . L-1 CPPU, respectively. Grape fruit adjacent leaf photosynthesis under the 25 mg · L-1 GA3+ 20 mg · L-1 CPPU treatment was higher than the other treatments. The fruit quality under the 25 mg · L-1 GA3 + 20 mg · L-1 CPPU treatment was lower than the 25 mg · L-1 GA3+ 15 mg . L-1 CPPU treatment. It indicated that reasonable CPPU treatment concentration could improve fruit adjacent leaf photosynthetic ability and fruit quality. Too high concentration made the fruit quality lower instead. The 25 mg · L-1 GA3 + 15 mg · L-1 CPPU treatment was most appropriate in two weeks after blossoming. [ABSTRACT FROM AUTHOR]

Photosynthetic responses to light environment can be useful measurements to determine favorable habitat conditions for the conservation and cultivation of medicinal species. The nonrectangular hyperbola model, rectangular hyperbola model, modified rectangular hyperbola model, exponential model, modified exponential model are used to explore the best model for describing light-response curves in two Epimedium species. The results show that the light-response curves of E. wushanense and E. acuminatum were best described by the modified exponential model, the test MSE and MAE of the modified exponential model were smaller, and the LSP and Pmax calculated by the modified exponential model were more accurate than those calculated by other models in E. wushanense and E. acuminatum. This model may be widely applicable to light-response curves of other Epimedium species. [ABSTRACT FROM AUTHOR]

Seedlings of the hypoxia-sensitive cucumber cultivar were hydroponically grown under hypoxia for 7 d in the presence or absence of 24-epibrassinolide (EBR, 2.1 nM). Hypoxia significantly inhibited growth, while EBR partially counteracted this inhibition. Leaf net photosynthetic rate ( P), stomatal conductance, transpiration rate, and water-use efficiency declined greatly, while the stomatal limitation value increased significantly. The maximum net photosynthetic rate was strongly reduced by hypoxia, indicating that stomatal limitation was not the only cause of the P decrease. EBR markedly diminished the harmful effects of hypoxia on P as well as on stomata openness. It also greatly stimulated CO fixation by the way of increasing the carboxylation capacity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), ribulose-1,5-bisphosphate regeneration, Rubisco activity, and the protection of Rubisco large subunit from degradation. Our data indicated that photosystem (PS) II was damaged by hypoxia, while EBR had the protective effect. EBR further increased nonphotochemical quenching that could reduce photodamage of the PSII reaction center. The proportion of absorbed light energy allocated for photochemical reaction (P) was reduced, while both nonphotochemical reaction dissipation of light energy and imbalanced partitioning of excitation energy between PSI and PSII increased. EBR increased P and alleviated this imbalance. The results suggest that both stomatal and nonstomatal factors limited the photosynthesis of cucumber seedlings under hypoxia. EBR alleviated the growth inhibition by improving CO asimilation and protecting leaves against PSII damage. [ABSTRACT FROM AUTHOR]

The effect of stepwise increments of red light intensities on pulse-amplitude modulated (PAM) chlorophyll (Chl) fluorescence from leaves of A. thaliana and Z. mays was investigated. Minimum and maximum fluorescence were measured before illumination ( F and F, respectively) and at the end of each light step ( $$ F^{\prime}_{0} $$ and $$ F^{\prime}_{\text{M}} $$, respectively). Calculated $$ F^{\prime}_{0} $$ values derived from F, F and $$ F^{\prime}_{\text{M}} $$ fluorescence according to Oxborough and Baker () were lower than the corresponding measured $$ F^{\prime}_{0} $$ values. Based on the concept that calculated $$ F^{\prime}_{0} $$ values are under-estimated because the underlying theory ignores PSI fluorescence, a method was devised to gain relative PSI fluorescence intensities from differences between calculated and measured $$ F^{\prime}_{0} $$. This method yields fluorometer-specific PSI data as its input data ( F, F, $$ F^{\prime}_{0} $$ and $$ F^{\prime}_{\text{M}} $$) depend solely on the spectral properties of the fluorometer used. Under the present conditions, the PSI contribution to F fluorescence was 0.24 in A. thaliana and it was independent on the light acclimation status; the corresponding value was 0.50 in Z. mays. Correction for PSI fluorescence affected Z. mays most: the linear relationship between PSI and PSII photochemical yields was clearly shifted toward the one-to-one proportionality line and maximum electron transport was increased by 50 %. Further, correction for PSI fluorescence increased the PSII reaction center-specific parameter, 1/ F − 1/ F, up to 50 % in A. thaliana and up to 400 % in Z. mays. [ABSTRACT FROM AUTHOR]

To estimate global gross primary production (GPP), which is an important parameter for studies of vegetation productivity and the carbon cycle, satellite data are useful. In 2014, the Japan Aerospace Exploration Agency (JAXA) plans to launch the Global Change Observation Mission-Climate (GCOM-C) satellite carrying the second-generation global imager (SGLI). The data obtained will be used to estimate global GPP. The rate of photosynthesis depends on photosynthesis reduction and photosynthetic capacity, which is the maximum photosynthetic velocity at light saturation under adequate environmental conditions. Photosynthesis reduction is influenced by weather conditions, and photosynthetic capacity is influenced by chlorophyll and RuBisCo content. To develop the GPP estimation algorithm, we focus on photosynthetic capacity because chlorophyll content can be detected by optical sensors. We hypothesized that the maximum rate of low-stress GPP (called "GPP capacity") is mainly dependent on the chlorophyll content that can be detected by a vegetation index (VI). The objective of this study was to select an appropriate VI with which to estimate global GPP capacity with the GCOM-C/SGLI. We analyzed reflectance data to select the VI that has the best linear correlation with chlorophyll content at the leaf scale and with GPP capacity at canopy and satellite scales. At the satellite scale, flux data of seven dominant plant functional types and reflectance data obtained by the Moderate-resolution Imaging Spectroradiometer (MODIS) were used because SGLI data were not available. The results indicated that the green chlorophyll index, CIgreen(ρNIR/ρgreen-1), had a strong linear correlation with chlorophyll content at the leaf scale (R2 = 0.87, p < 0.001) and with GPP capacity at the canopy (R2 = 0.78, p < 0.001) and satellite scales (R2 = 0.72, p < 0.01). Therefore, CIgreen is a robust and suitable vegetation index for estimating global GPP capacity. [ABSTRACT FROM AUTHOR]

Pasture soils in the Amazon become unsustainable after a short period of use, typically being replaced by emergent secondary vegetation (capoeira). The aim of this research was to investigate the photosynthetic capacity and water use in the most common tree species ( Vismia japurensis, Vismia cayennensis, Bellucia grossularioides, Laetia procera, and Goupia glabra) in successional chronosequence. This study was carried out in secondary vegetation area with ages that vary between 1 and 19 years. Responses of gas exchange were determined during different periods of precipitation. The gas exchange decreased with advancing age of the vegetation (1-19 years), except for G. glabra. Negative relationships of P as a function of aging observed for V. japurensis, V. cayennensis, B. grossularioides, and L. procera exhibited r equal to 0.59, 0.42, 0.33, and 0.58, respectively. The species of Vismia showed higher values for photosynthetic parameters in relation to other species across the chronosequence. Overall, there were differences in gas exchange only for some species between the different periods of precipitation. Therefore, our results suggest a distinct pattern of photosynthetic responses to species in early succession. Light decrease can exert a decisive role to reduce the photosynthetic rates in secondary succession species. On the other hand, the results of WUE showed weak evidence of changes for the species during dry and rainy periods in the abandoned pasture in central Amazonia. [ABSTRACT FROM AUTHOR]

The effects of 2 nitrate levels, 14 (CK) and 140 mmol L-1 (T), on the leaf gas exchange variables of cucumber (Cucumis sativus L. cv. Xintaimici) seedlings grown in hydroponic culture were investigated. Photosynthetic light- and CO2-response curves from CK and T seedlings were determined and used for the analysis of photosynthetic capacity. The results showed that nitrate stress resulted in a significant reduction of net photosynthesis of T seedlings compared with CK. At the same time, the apparent quantum yield, light-saturated net photosynthesis, carboxylation efficiency, and CO2-saturated net photosynthesis in nitrate-stressed cucumbers also decreased significantly with the increase of treatment time. At 12 days, the apparent quantum yield, light-saturated net photosynthesis, carboxylation efficiency, and CO2-saturated net photosynthesis in nitrate-stressed cucumbers were 47%, 60%, 64%, and 54% lower than CK, respectively. The relative effect of stomatal resistance on photosynthesis (S%) in nitrate-stressed cucumber seedlings increased significantly during the first 8 days and returned to the level of CK thereafter. This evidence indicates that not only stomatal but also nonstomatal limitations might be involved in the reduction of net photosynthetic rate in nitrate-stressed seedlings. [ABSTRACT FROM AUTHOR]

Abstract: Integration of CO2 flux observations with remote sensing technique and ecosystem modeling is expected to be useful for estimation of gross primary production (GPP). We focused on the changes in the two main parameters for the canopy-scale light–response curve—P max (maximum GPP at light saturation) and ϕ (initial slope)—as indicators to represent canopy photosynthetic capacity. We hypothesized that P max and ϕ could be evaluated by using spectral reflectance related to the changes in the levels of canopy nitrogen and chlorophyll. We analyzed the relationships between P max and ϕ, derived from tower-based CO2 flux observations, and ground-based spectral vegetation indices (VIs) in a temperate deciduous coniferous forest. The canopy-scale P max and ϕ showed clear seasonal changes accompanying phenological stages. Both the variations in P max and ϕ were strongly correlated with VIs, especially with the ratio vegetation index (RVI) and enhanced vegetation index (EVI), independent of the growth stages. Moreover, day-to-day short-term variations of P max and ϕ were affected by meteorological conditions such as vapor pressure deficit (VPD) and relative solar radiation which was calculated as the ratio of monitored radiation per theoretical maximum radiation. Thus, seasonal changes of P max and ϕ were effectively assessed by RVI or EVI, and their short-term variations were evaluated by the empirical relationships with VPD and relative solar radiation. We propose a new simple method for estimating GPP with good precision; by fitting the light–response function with the evaluated parameters, the estimated GPP reflects 3 types of temporal variation: diurnal, day-to-day, and seasonal. [Copyright &y& Elsevier]

© New Phytologist (2004) doi: 10.1111/j.1469-8137.2004.01000.x [ABSTRACT FROM AUTHOR]

Photosynthetic light-response curves of the deep-water Laminaria abyssalis Oliveira and of the intertidal L. digitata Lamoroux were determined and related to photoinhibition phenomena as monitored by oxygen evolution and photosystem II efficiency (FV/FM). L. abyssalis has half the pigment content, number of cells and plastids, and photosynthetic capacity per unit area compared with L. digitata. L. abyssalis showed a higher in vivo Chl a absorption coefficient and higher photosynthetic efficiency on a Chl a basis, although the two algae showed somewhat similar light-response curves on a Chl a basis. Both species showed similar Chl a/Chl c and Chl a/fucoxanthin ratios, and similar dark respiration rates and light compensation points. In addition, they also showed similar convexities in their light-response curves and no differences in their light saturation of FV/FM. Room temperature chlorophyll fluorescence induction measurements of fronds incubated in 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) suggest that both species may have a similar PSII absorption cross section. Thus, L. abyssalis appears to optimize its light absorption at very low light intensities, not by increasing the pigment content, but by absorbing light more efficiently. However, L. abyssalis was more sensitive to photoinhibition than L. digitata and showed no recovery of FV/FM and O2 evolution after a photoinhibitory treatment, even with a subsequent exposure to 24 h of dim light. L. digitata, on the other hand, recovered its photosynthetic capacity within 6 h under dim light. These results suggest that photosynthetic light-induction curves based on Chl a are not a good indicator of either the photosynthetic capacity or the sensitivity to photoinhibition when macroalgae of different species are being compared. Based on their light-response and photoinhibition characteristics, we suggest that L. abyssalis, a deep-water oceanic macroalgae, is an atypical shade alga whereas L. digitata has the properties of a sun alga. [ABSTRACT FROM AUTHOR]

A barrier to realizing Nannochloropsis oceanica's potential for omega-3 eicosapentaenoic acid (EPA) production is the disparity between conditions that are optimal for growth and those that are optimal for EPA biomass content. A case in point is temperature: higher content of polyunsaturated fatty acid, and especially EPA, is observed in low-temperature (LT) environments, where growth rates are often inhibited. We hypothesized that mutant strains of N. oceanica resistant to the singlet-oxygen photosensitizer Rose Bengal (RB) would withstand the oxidative stress conditions that prevail in the combined stressful environment of high light (HL; 250 μmol photons m-2 s-1) and LT (18°C). This growth environment caused the wild-type (WT) strain to experience a spike in lipid peroxidation and an inability to proliferate, whereas growth and homeostatic reactive oxygen species levels were observed in the mutant strains. We suggest that the mutant strains' success in this environment can be attributed to their truncated photosystem II antennas and their increased ability to diffuse energy in those antennas as heat (non-photosynthetic quenching). As a result, the mutant strains produced upward of four times more EPA than the WT strain in this HL-LT environment. The major plastidial lipid monogalactosyldiacylglycerol was a likely target for oxidative damage, contributing to the photosynthetic inhibition of the WT strain. A mutation in the NO10G01010.1 gene, causing a subunit of the 2-oxoisovalerate dehydrogenase E1 protein to become non-functional, was determined to be the likely source of tolerance in the RB113 mutant strain., (© The Author(s) 2021. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Plantago lanceolata is a gynodioecious species: In natural populations male steriles (MS) coexist with hermaphrodites (H). Since male steriles have a reproductive disadvantage, without any compensation for their loss in male function by an increase in female function, they are expected to disappear from the population. In this study we investigated the possibility that differences in ecologically important photosynthetic characteristics, between MS and H lines of P. lanceolata, play a role in maintaining gynodioecy. One MS line and two H lines were grown under conditions of high N and light availability, as well as under either N limitation or light limitation, to investigate whether the sex types respond differently to environmental constraints. Photosynthetic light-response and CO2-response curves were made, together with leaf organic N and chlorophyll determinations. There were only few small differences between the lines and since the MS line did not differ in any of the determined photosynthetic characteristics from either H line, it is unlikely that these differences are involved in maintaining male sterility in populations of P. lanceolata. The low-light-grown plants showed a high degree of acclimation as shown by a two-fold higher leaf area to leaf weight ratio (SLA), a two-fold higher investment of N in light harvesting, and higher net photosynthetic rates under low-light conditions, as compared to the high-light-grown plants. The low-N-grown plants used their organic N more efficiently in photosynthesis compared to plants grown at an optimal N supply. This was mainly due to the N-limited plants having leaves with a lower organic N content and thus lower photosynthetic capacities. To a lesser extent it was due to the higher value for the curvature factor of the light-response curves of the N-limited plants, to their decreased rates of photorespiration and possibly to their relatively higher allocation of organic N to photosynthetic functions. [ABSTRACT FROM AUTHOR]

When nitrogen fixing cell cultures of Synechococcus RF-1 were subjected to an alternating lightdark regime (12 h:12 h), a cyclic decrease in the photosynthetic oxygen evolution potential was observed during the dark periods. This rhythm of net photosynthesis rate was maintained for at least two days after transition to continuous light. The decrease in net photosynthesis was accompanied by a stimulation of dark respiration. However, the magnitude of oxygen uptake was considerably smaller than the observed decrease in oxygen evolution. The photosynthetic activity of cells taken from the dark period was characterized by ( i) a significantly lower quantum yield and ( ii) a strong reduction in the light-saturated rate of photosynthesis. Growing the cultures on nitrate or under continuous light completely suppressed this rhythm. Protein synthesis was not necessary for the recovery of the light-saturated rate of photosynthesis during the light period. The cellular content of chlorophyll a and of phycobiliproteins did not vary between light and dark period, indicating that quantitative changes in the composition of the photosynthetic apparatus are not the basis for the observed oscillations. Regulatory modifications of the photosynthetic efficiency are proposed as an adaptation mechanism to adjust the intracellular oxygen concentration to the needs for nitrogenase activity. [ABSTRACT FROM AUTHOR]

Photosynthetic responses to light environment can be useful measurements to determine favorable habitat conditions for the conservation and cultivation of medicinal species. The nonrectangular hyperbola model, rectangular hyperbola model, modified rectangular hyperbola model, exponential model, modified exponential model are used to explore the best model for describing light-response curves in two Epimedium species. The results show that the light-response curves of E. wushanense and E. acuminatum were best described by the modified exponential model, the test MSE and MAE of the modified exponential model were smaller, and the LSP and Pmax calculated by the modified exponential model were more accurate than those calculated by other models in E. wushanense and E. acuminatum. This model may be widely applicable to light-response curves of other Epimedium species.