Photosynthesis Light Response Curves Research Articles

Light niche construction: Motility of sediment-inhabiting diatoms determines the experienced light environment

Diatoms are an extraordinarily diverse, evolutionarily successful, and ecologically important group of single-cell algae. Diatoms of the group of the pennates are particularly important in estuarine sedimentary habitats, where they form highly productive microphytobenthos communities that cover extensive areas of intertidal flats. The pennates are capable of directed motility, an evolutionary and unique trait amongst diatoms, which has long been hypothesized to confer a critical adaptive advantage, by enabling these cells to vertically migrate within the photic zone of the sediment and behaviorally regulate light exposure. This study investigated the role of diatom motility on the active regulation of light exposure by developing a model to quantitatively characterize and compare the experienced light environment of individual cells of two life forms of pennate diatoms that inhabit intertidal estuarine sediments: epipelic species, motile cells dominant in fine sediments, and epipsammic species, non-motile or slowly motile cells, that colonize coarser sediments. The conceptual framework of the model was based on the identification and parameterization of the main controlling factors of the light regime perceived by cells inhabiting the two types of sedimentary environments: (i) solar irradiance incident at the sediment surface, determined by the superimposition of the tidal cycle on the day-night cycle; (ii) light attenuation within the sediment; (iii) sediment mixing by tidal currents or bioturbation, repositioning the cells in the sediment column; (iv) cell velocity, as a function of light intensity and of the photoacclimation state of the cells that determines their photosynthetic light preferences. The model was run for realistic scenarios based on published ecological, photophysiological and cellular motility data (light attenuation, mixing depth, photosynthesis light-response curves, cell velocity), simulating (i) the variation in the vertical position of a diatom cell due to vertical migration and (ii) the irradiance level to which it is exposed at each moment. The results confirm the hypothesis that epipelic and epipsammic diatoms experience a significantly different light environment. Vertical migration enables motile species to experience a much less variable light regime, with increased mean daily light doses received. In contrast, non-motile species experience a much more unstable light environment, including the frequent exposure to supersaturating light levels and to periods of prolonged darkness. These results have important ecological significance, as they support the adaptive value of light-driven motility as a form of optimizing photosynthesis and growth, and they identify vertical migration as a niche-construction activity, allowing motile diatoms to regulate the light environment they experience through habitat selection.

Evaluation of the enhancement of photosynthetic rate in a komatsuna (Brassica rapa L. var. perviridis) canopy with upward lighting using an optical simulation in a plant factory with artificial light.

In a plant factory with artificial light (PFAL), upward lighting is expected to prevent senescence and decrease in the photosynthetic capacity of the lower leaves in the canopy. Upward lighting may also increase the photosynthetic rate of a canopy by improving its photosynthetic photon flux density (PPFD) distribution. However, the net photosynthetic rate (Pn) of leaves is lower when the abaxial surface is irradiated than that when the adaxial surface is irradiated. The aim of this study was to estimate the PPFD in a PFAL and the Pn of plants using three-dimensional plant models and optical simulation. First, we measured the Pn of komatsuna (Brassica rapa L. var. perviridis) leaves under different conditions of the proportion (pad ) of PPFD on the adaxial surface to total PPFD on both surfaces and developed an equation for the light response curve of photosynthesis considering pad . When PPFD was low, except when it was 30 and 70 µmol m-2 s-1, Pn increased as pad increased, because the absorptance also increased with pad . Under high PPFD conditions, Pn was maximized at 67-83% of pad because the light would be distributed more efficiently for photosynthesis. Next, using optical simulation and the developed equation, we estimated the photosynthetic rate of a komatsuna canopy (CPn) under downward and upward lighting. The CPn increased by 1.08-1.13 times by combining downward and upward lighting due to the increase in the photosynthetic photon flux (PPF) of light incident on the canopy and the decrease in the spatial variation of PPFD on the leaves in the canopy. As the depreciation of lamps for upward lighting accounts for 7.5-9.0% of the production cost in a PFAL, even if the depreciation of lamps for upward lighting increased, enhancement of CPn by upward lighting would be cost-effective. We performed optical simulations under 220 conditions and evaluated them using CPn as an index. Moreover, we provided the proportion of PPF of upward lighting that improved CPn and discussed the reason for this improvement. The result shows that optical simulation is useful for evaluating the lighting design in a PFAL and analyzing the effects of the lighting design on the light environment and photosynthesis.

Plant-Growth Promoting Microbes Change the Photosynthetic Response to Light Quality in Spinach.

In this study, the combined effect of plant growth under different light quality and the application of plant-growth-promoting microbes (PGPM) was considered on spinach (Spinacia oleracea L.) to assess the influence of these factors on the photosynthetic performance. To pursue this goal, spinach plants were grown in a growth chamber at two different light quality regimes, full-spectrum white light (W) and red-blue light (RB), with (I) or without (NI) PGPM-based inoculants. Photosynthesis-light response curves (LRC) and photosynthesis-CO2 response curves (CRC) were performed for the four growth conditions (W-NI, RB-NI, W-I, and RB-I). At each step of LRC and CRC, net photosynthesis (PN), stomatal conductance (gs), Ci/Ca ratio, water use efficiency (WUEi), and fluorescence indexes were calculated. Moreover, parameters derived from the fitting of LRC, such as light-saturated net photosynthesis (PNmax), apparent light efficiency (Qpp), and dark respiration (Rd), as well as the Rubisco large subunit amount, were also determined. In not-inoculated plants, the growth under RB- regime improved PN compared to W-light because it increased stomatal conductance and favored the Rubisco synthesis. Furthermore, the RB regime also stimulates the processes of light conversion into chemical energy through chloroplasts, as indicated by the higher values of Qpp and PNmax in RB compared to W plants. On the contrary, in inoculated plants, the PN enhancement was significantly higher in W (30%) than in RB plants (17%), which showed the highest Rubisco content among all treatments. Our results indicate that the plant-growth-promoting microbes alter the photosynthetic response to light quality. This issue must be considered when PGPMs are used to improve plant growth performance in a controlled environment using artificial lighting.

Interspecific variation in leaf traits, photosynthetic light response, and whole-plant productivity in amaranths (Amaranthus spp. L.).

Photosynthetic light response curve parameters help us understand the interspecific variation in photosynthetic traits, leaf acclimation status, carbon uptake, and plant productivity in specific environments. These parameters are also influenced by leaf traits which rely on species and growth environment. In accessions of four amaranth species (Amaranthus. hybridus, A. dubius, A. hypochondriacus, and A. cruentus), we determined variations in the net photosynthetic light response curves and leaf traits, and analysed the relationships between maximum gross photosynthetic rate, leaf traits, and whole-plant productivity. Non-rectangular hyperbolae were used for the net photosynthesis light response curves. Maximum gross photosynthetic rate (Pgmax) was the only variant parameter among the species, ranging from 22.29 to 34.21 μmol m–2 s–1. Interspecific variation existed for all the leaf traits except leaf mass per area and leaf inclination angle. Stomatal conductance, nitrogen, chlorophyll, and carotenoid contents, as well as leaf area correlated with Pgmax. Stomatal conductance and leaf nitrogen explained much of the variation in Pgmax at the leaf level. At the plant level, the slope between absolute growth rate and leaf area showed a strong linear relationship with Pgmax. Overall, A. hybridus and A. cruentus exhibited higher Pgmax at the leaf level and light use efficiency at the whole-plant level than A. dubius, and A. hypochondriacus. Thus, A. hybridus and A. cruentus tended to be more efficient with respect to carbon assimilation. These findings highlight the correlation between leaf photosynthetic characteristics, other leaf traits, and whole plant productivity in amaranths. Future studies may explore more species and accessions of Amaranthus at different locations or light environments.

Effects of photosynthetic models on the calculation results of photosynthetic response parameters in young Larix principis-rupprechtii Mayr. plantation.

Accurately predicting the crown photosynthesis of trees is necessary for better understanding the C circle in terrestrial ecosystem. However, modeling crown for individual tree is still challenging with the complex crown structure and changeable environmental conditions. This study was conducted to explore model in modeling the photosynthesis light response curve of the tree crown of young Larix principis-rupprechtii Mayr. Plantation. The rectangular hyperbolic model (RHM), non-rectangular hyperbolic model (NRHM), exponential model (EM) and modified rectangular hyperbolic model (MRHM) were used to model the photosynthetic light response curves. The fitting accuracy of these models was tested by comparing determinants coefficients (R2), mean square errors (MSE) and Akaike information criterion (AIC). The results showed that the mean value of R2 of MRHM (R2 = 0.9687) was the highest, whereas MSE value (MSE = 0.0748) and AIC value (AIC = -39.21) were the lowest. The order of fitting accuracy of the four models for Pn-PAR response curve was as follows: MRHM > EM > NRHM > RHM. In addition, the light saturation point (LSP) obtained by MRHM was slightly lower than the observed values, whereas the maximum net photosynthetic rates (Pmax) modeled by the four models were close to the measured values. Therefore, MRHM was superior to other three models in describing the photosynthetic response curve, the accurate values were that the quantum efficiency (α), maximum net photosynthetic rate (Pmax), light saturation point (LSP), light compensation point (LCP) and respiration rate (Rd) were 0.06, 6.06 μmol·m-2s-1, 802.68 μmol·m-2s-1, 10.76 μmol·m-2s-1 and 0.60 μmol·m-2s-1. Moreover, the photosynthetic response parameters values among different layers were also significant. Our findings have critical implications for parameter calibration of photosynthetic models and thus robust prediction of photosynthetic response in forests.

Expansive soil-biochar-root-water-bacteria interaction: Investigation on crack development, water management and plant growth in green infrastructure

The objectives of the study are to explore fundamental mechanism of expansive soil-biochar-root-water-bacteria interaction, and investigate crack development and hydraulic properties of biochar amended soils aiming at green infrastructures. The physical, chemical and biological effects of biochar on expansive soil have been comprehensively explored. Crack development is investigated quantificationally, and mechanism of soil damage evolution is briefly discussed base on micro-chemical analyses. During outdoor vegetation period, photosynthesis light response curves were measured to evaluate plant growth. After period of vegetation, hydraulic properties of root-soil composites and unplanted soils were compared. The study reveals that soil crack intensity factor decreases by 33.5%, 48.5% and 47.3% due to 5%, 10% and 15% biochar introduction respectively after 5 wetting-drying cycles. 15% biochar amendment helps to restrain both initiation and propagation of soil cracks. Biochar amendment of up to 5% contributes well to residual water content and plant growth (i.e., light saturation point and light compensation point). Excessive biochar addition would restrain roots elongation, and increase saturated water content. Spatial root distribution is changed due to biochar addition, which further influences hydraulic properties and crack development. Hydraulic conductivity and soil dry density share negative correlations, 5% biochar enhances hydraulic conductivity remarkably at relatively loose condition. Biochar amendment also contributes to preventing nitrogen loss and forming more complex bacterial community in soils. The study adds to our knowledge of physio-chemical interactions of biochar with expansive clay, vegetation, water and microorganism.

A comparative assessment of C02/H20 gas exchange in evergreen woody and shrubby plants under favorable and stressful environmental conditions

A comparative assessment of the adaptive response of the photosynthetic apparatus and water regime in 6 evergreen tree and shrub plant species to the effect of abiotic factors and their strategies in supporting optimal water balance in accordance with environmental conditions was carried out. Parameters of photosynthesis light response curves under conditions of full sunlight and moderate shading were determined. It is shown that due to the low plasticity to changes in the light regime Arbutus andrachne L. may have a significant lack of light in strong shading. Important adaptive features of Laurus nobilis L., Aucuba japónica Thunb. and Viburnum tinus L. is the ability of the photosynthetic apparatus to effectively use low light and maintain a positive carbon balance in conditions of strong shading. Three types of plant response to water deficit have been identified. Drought- resistant type of water balance regulation by closing stomata is characteristic of Nerium oleander L. and Laurus nobilis. In Aucuba japónica and Prunus laurocerasus L. a reaction aimed at preserving the water balance in the plant by maintaining a high level of transpiration has been identified. The third type of plant response to water deficit which combines both types of reaction provides high adaptive ability to drought Viburnum tinus and Arbutus andrachne. Drought tolerance of Arbutus andrachne was the highest among the studied species.

Study on dry matter accumulation and leaf response to light and CO2 of maize under irrigation quota

Effective irrigation can maintain the vigorous photosynthetic metabolism of leaves and lay a physiological foundation for their material production. Dry matter accumulation and leaf response to light and carbon dioxide of maize under irrigation quotas of 50 mm (Q0), 90 mm (Q1), 170 mm (Q2) and 250 mm (Q3) were studied. The results showed that the dry matter accumulation were significantly increased in Q2 and Q3 treatment compared with CK at R3, R4 and R6 stages. With the increase of light intensity, the photosynthesis-light response curves of Q2 and Q3 treatments were increased the most. The apparent quantum efficiency, maximum net photosynthetic rate, light saturation point and dark respiration rate of Q2 and Q3 treatments were significantly higher than those of Q0 and Q1 treatments at V12, R1 and R3 stages. The light compensation point was apparently lower than that of Q0 and Q1 treatments. The maize photosynthesis-CO2 response curves of Q2 and Q3 treatments demonstrated the largest increase with the increase of CO2 concentration. The CO2 saturation point, maximum net photosynthetic rate and carboxylation efficiency of Q2 and Q3 treatments were significantly higher than those of Q0 and Q1 treatments. The CO2 compensation point was obviously lower than that of Q0 and Q1 treatments. The study provides an effective irrigation and management method for maize in semi-arid area of west Jilin Province, China. When the irrigation quota reached 170 mm, the dry matter accumulation of maize and the response of maize leaves to light and CO2 were both better. 170 mm could be used as the reference value of maize irrigation quota in western Jilin Province.

Rice straw biochar impact on physiological and biochemical attributes of Fokienia hodginsii in acidic soil

ABSTRACTIncreasing 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.

Light response of photosynthesis and stomatal conductance of rose leaves in the canopy profile: the effect of lighting on the adaxial and the abaxial sides.

We investigated the light response of leaf photosynthesis, stomatal conductance and optical properties in rose plants grown in a glasshouse with bending technique. Leaves were lighted from the adaxial or the abaxial side during measurements, performed in four positions in the upright and bent shoots: top leaves, middle leaves, bottom leaves, and bent shoot leaves. Moreover, the effect of the irradiation on the adaxial or abaxial leaf side on whole canopy photosynthesis was estimated through model simulation. No significant differences were found in light transmission, reflection and absorption of leaves and in photosynthesis light response curves among the four positions. In all the leaf positions, light absorption, stomatal conductance and photosynthesis were higher when leaves were lighted from the adaxial compared with the abaxial side. The model showed that a substantial part of the light absorbed by the crop originated from light reflected from the greenhouse floor, and thus the abaxial leaf properties have impact on whole crop light absorbance and photosynthesis. Simulations were performed for crops with leaf area index (LAI) 1, 2 and 3. Simulation at LAI 1 showed the highest reduction of simulated crop photosynthesis considering abaxial properties; however, to a lesser extent photosynthesis was also reduced at LAI 2 and 3. The overall results showed that the model may be helpful in designing crop systems for improved light utilisation by changing lamp position or level of leaf bending and pruning.

Evaluation of O3 Effects on Cumulative Photosynthetic CO2 Uptake in Seedlings of Four Japanese Deciduous Broad-Leaved Forest Tree Species Based on Stomatal O3 Uptake

The current level of tropospheric ozone (O3) is expected to reduce the net primary production of forest trees. Here, we evaluated the negative effects of O3 on the photosynthetic CO2 uptake of Japanese forest trees species based on their cumulative stomatal O3 uptake, defined as the phytotoxic O3 dose (POD). Seedlings of four representative Japanese deciduous broad-leaved forest tree species (Fagus crenata, Quercus serrata, Quercus mongolica var. crispula and Betula platyphylla var. japonica) were exposed to different O3 concentrations in open-top chambers for two growing seasons. The photosynthesis–light response curves (A-light curves) and stomatal conductance were measured to estimate the leaf-level cumulative photosynthetic CO2 uptake (ΣPn_est) and POD, respectively. The whole-plant-level ΣPn_est were highly correlated with the whole-plant dry mass increments over the two growing seasons. Because whole-plant growth is largely determined by the amount of leaf area per plant and net photosynthetic rate per leaf area, this result suggests that leaf-level ΣPn_est, which was estimated from the monthly A-light curves and hourly PPFD, could reflect the cumulative photosynthetic CO2 uptake of the seedlings per unit leaf area. Although the O3-induced reductions in the leaf-level ΣPn_est were well explained by POD in all four tree species, species-specific responses of leaf-level ΣPn_est to POD were observed. In addition, the flux threshold appropriate for the linear regression of the responses of relative leaf-level ΣPn_est to POD was also species-specific. Therefore, species-specific responses of cumulative photosynthetic CO2 uptake to POD could be used to accurately evaluate O3 impact on the net primary production of deciduous broad-leaved trees.

Effects of decomposing leaf litter of Leucaena leucocephala on photosynthetic traits of Cynodon dactylon and Medicago sativa

Leucaena leucocephala is an introduced species, which has been widely used in mountain ecological restoration in southwestern China. To investigate the allelopathic effects of decomposing L. leucocephala leaf litter, the photosynthetic physiology of seedlings of two recipient plants, Cynodon dactylon and Medicago sativa, were measured in this controlled study. As the amount of decomposing L. leucocephala leaf litter increased, the net photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs) decreased continuously, and the intercellular CO2 concentration (Ci) increased continuously in both recipient plants. In M. sativa, all abovementioned indices differed significantly compared with the control group: Pn, Gs, and Tr decreased by 41.69, 59.35, and 48.02%, respectively, and Ci increased by 28.53%. In C. dactylon, Gs decreased significantly by 27.27%. Analysis of the photosynthesis–light response curve indicated that the maximum net photosynthetic rate (Pnmax) and dark respiration rate (Rd) of C. dactylon, as well as Pnmax and light saturation point (Lsp) of M. sativa, decreased significantly as the amount of decomposing L. leucocephala leaf litter increased. These results indicated that the photosynthetic traits, light adaptation ability and physiological metabolism of recipient plants were affected by the treatment. The decreased photosynthesis was caused by the changes in pigments and soluble sugar contents induced by L. leucocephala leaf litter and is therefore considered to be associated with non-stomatal limitations. In addition, as the amount of decomposing L. leucocephala leaf litter increased, M. sativa showed decreased chlorophyll (Chla) and carotenoid (Car) contents, while C. dactylon showed decreased Chla and Chl(a + b) contents. However, both recipient plants exhibited significantly increases in their soluble sugar content. Overall, M. sativa was more sensitive than C. dactylon to the allelopathic effects induced by decomposing L. leucocephala leaf litter.

三峡库区消落带不同水淹强度下池杉与落羽杉的光合生理特性

PDF HTML阅读 XML下载 导出引用 引用提醒 三峡库区消落带不同水淹强度下池杉与落羽杉的光合生理特性 DOI: 10.5846/stxb201704150673 作者: 作者单位: 三峡库区生态环境教育部重点实验室，重庆市三峡库区植物生态与资源重点实验室，西南大学生命科学学院,三峡库区生态环境教育部重点实验室，重庆市三峡库区植物生态与资源重点实验室，西南大学生命科学学院,三峡库区生态环境教育部重点实验室，重庆市三峡库区植物生态与资源重点实验室，西南大学生命科学学院,三峡库区生态环境教育部重点实验室，重庆市三峡库区植物生态与资源重点实验室，西南大学生命科学学院,三峡库区生态环境教育部重点实验室，重庆市三峡库区植物生态与资源重点实验室，西南大学生命科学学院,三峡库区生态环境教育部重点实验室，重庆市三峡库区植物生态与资源重点实验室，西南大学生命科学学院,三峡库区生态环境教育部重点实验室，重庆市三峡库区植物生态与资源重点实验室，西南大学生命科学学院 作者简介: 通讯作者: 中图分类号: 基金项目: 重庆市林业重点科技攻关项目（渝林科研2016-8）；中央财政林业科技推广示范项目（渝林科推[2017-12]）；国家林业局天然林保护工程管理中心项目（2016-01）；国际科技合作专项（2015DFA90900）；重庆市研究生科研创新项目（CYB16066） Photosynthetic characteristics of Taxodium ascendens and Taxodium distichum under different submergence in the hydro-fluctuation belt of the Three Gorges Reservoir Author: Affiliation: Key Laboratory of Eco-environment in the Three Gorges Reservoir Region of the Ministry of Education, Chongqing Key Laboratory of Plant Ecology and Resources Research in the Three Gorges Reservoir Region , School of Life Sciences, Southwest University,Key Laboratory of Eco-environment in the Three Gorges Reservoir Region of the Ministry of Education, Chongqing Key Laboratory of Plant Ecology and Resources Research in the Three Gorges Reservoir Region , School of Life Sciences, Southwest University,Key Laboratory of Eco-environment in the Three Gorges Reservoir Region of the Ministry of Education, Chongqing Key Laboratory of Plant Ecology and Resources Research in the Three Gorges Reservoir Region , School of Life Sciences, Southwest University,Key Laboratory of Eco-environment in the Three Gorges Reservoir Region of the Ministry of Education, Chongqing Key Laboratory of Plant Ecology and Resources Research in the Three Gorges Reservoir Region , School of Life Sciences, Southwest University,Key Laboratory of Eco-environment in the Three Gorges Reservoir Region of the Ministry of Education, Chongqing Key Laboratory of Plant Ecology and Resources Research in the Three Gorges Reservoir Region , School of Life Sciences, Southwest University,Key Laboratory of Eco-environment in the Three Gorges Reservoir Region of the Ministry of Education, Chongqing Key Laboratory of Plant Ecology and Resources Research in the Three Gorges Reservoir Region , School of Life Sciences, Southwest University,Key Laboratory of Eco-environment in the Three Gorges Reservoir Region of the Ministry of Education, Chongqing Key Laboratory of Plant Ecology and Resources Research in the Three Gorges Reservoir Region , School of Life Sciences, Southwest University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为探究三峡库区消落带原位人工种植的池杉（Taxodium ascendens）和落羽杉（Taxodium distichum）在该特殊生境下的适应机制，设置了浅淹（SS，海拔175m，对照）、中度水淹（MS，海拔170m）和深度水淹（DS，海拔165m）3个水淹处理组，测定了两树种在连续4个周期性水淹处理后的光合响应过程，并采用直角双曲线模型、非直角双曲线模型、直角双曲线修正模型和指数模型进行拟合，比较各模型拟合结果差异并选出最优模型，通过最优模型来分析水淹后落干期两树种的光合生理变化。结果表明：（1）不同模型间的光响应曲线拟合结果存在差异（P<0.05）。综合分析可知，4种模型中，指数模型是拟合两树种光响应曲线的最优模型，更符合植物的生理学意义。（2）两树种的光响应曲线有相似的变化规律，光合速率（Pn）的表现均为DS组 > MS组 > SS组。（3）中度水淹和深度水淹两树种的最大净光合速率（Pnmax）、表观量子效率（α）、光饱和点（LSP）均高于浅淹，而光补偿点（LCP）则显著降低。以上结果说明落干生长期两树种对强光和弱光的利用能力增强，水淹对两树种的光合潜力有一定的促进作用，这可能与其遭受水淹胁迫后的自我调节能力和光合补偿机制有关。由此表明，当生境发生不良变化时，植物的适应性变化往往表现为沿着有利于光合作用最大化的方向发展。 Abstract:After the completion of the Three Gorges Dam Project, the water level of the Three Gorges Reservoir Area (TGRA) fluctuated between 145m a.s.l. in summer and 175m a.s.l. in winter. These extreme water fluctuations along with an annual 30m water-level drawdown have led to the formation of the hydro-fluctuation zone around the reservoir, turning the terrestrial ecosystem into a wetland experiencing winter flooding every year. Under these water fluctuation conditions, the richness and diversity of the vegetation decreased and soil erosion was exacerbated, which further damaged the ecological structure and function of the riparian ecosystem of the reservoir area. The effective way to solve this problem is to restore the riparian vegetation artificially. Understanding the photosynthetic adaptation mechanism of water-tolerant species in the hydro-fluctuation zone is of great importance to undertake vegetation restoration in the TGRA. In order to research the adaptation mechanism of the species suitable to the hydro-fluctuation belt of the TGRA, we designed the following three water regimes:periodic shallow submergence (SS, 175m), moderate submergence (MS, 170m), and deep submergence (DS, 165m). Li-6400 portable photosynthetic measurement system was used to test the light response curves of photosynthesis of Taxodium ascendens and Taxodium distichum after four cycles of submergence, in situ, in the TGRA. The light response curves were fitted and analyzed using the rectangular hyperbola model, the non-rectangular hyperbola model, the rectangular hyperbola modified model, and the exponential equation model. The optimal model was screened out from the four models by analyzing proximity between the simulated and measured values of photosynthetic parameters, and then it was used to analyze the photosynthetic characteristics of the two species under different submergence conditions. Results showed that:(1) The fit of different models was significantly different. The exponential equation model was the best model for the light response curve in accordance with the physiology of the two species; (2) The light response curves of the two species showed similar trends in variation, and along with an increase in the intensity of submergence, the photosynthetic rate of the two species also increased; (3) The maximum photosynthetic rate, apparent quantum yield, and light saturation point of the two species growing under both deep and moderate submergence conditions were higher than that in shallow submergence, while the light compensation point of the two species decreased significantly in deep submergence conditions. These results suggest that the utilization capacity of both low light and high light of the two species were improved after submergence. Submergence also stimulated the photosynthetic potential of the two species, which may be related to the positive self-adjustment ability and the photosynthetic compensation of the two species after submergence stress. This also indicates that when the habitat is stressed, plants often adapt themselves to maximize photosynthesis. Thus, it is appropriate to use these two species for reconstructing the vegetation in the hydro-fluctuation belt of the TGRA. 参考文献 相似文献 引证文献

Photosynthetic responses of understory savanna plants: Implications for plant persistence in savannas under tree encroachment

Savannas are ecosystems where plants are expected to have leaf-level adaptations conferring tolerance to high irradiances, which characterizes this type of open canopy vegetation. The neotropical savannas of Brazil (Cerrado) harbour a large diversity of heliophilous herbaceous species, which are threatened by the current invasion of those open canopy habitats by forest trees, increasing tree density and canopy cover, thereby strongly reducing light availability. In this study, we measured leaf pigment concentrations, specific leaf area and light response curves of photosynthesis to determine whether herbaceous species of open savanna habitats were less tolerant to shade than the ones that were more characteristic of forested savanna. Relative to species of forested savannas, herbaceous species of open savannas had heavier leaves with higher concentration of carotenoids. They also achieved higher photosynthetic rates, reaching light compensation and saturation at higher irradiances. Based on measurements of light compensation points and of prevailing irradiances in forested savannas, leaves of most herbaceous species of more open savannas would be strongly light-limited in sites with a dense woody layer. In summary, we provide evidence that forest tree encroachment of savannas would select for leaf trait combinations in the understory vegetation that would favor shade tolerance and, depending on the degree of leaf acclimatization to shade of individual species, could strongly constrain persistence of the current understory vegetation.

The modelled photosynthetic effects of different light colours on tomato crop growth and production

Photosynthesis characteristics of tomato plants grown under LED modules that produced blue, green, red, and white light were determined. Photosynthesis rates at low light intensity of plants grown and measured under the same colour related to each other as: white › red › green › blue. However, rates measured under red/blue light also related to each other as: blue › white › red = green. Photosynthesis rates at high light intensity measured under red/blue light related to each other as: blue › white › red › green. The INTKAM crop growth model was used to quantify the potential effects of light colours and levels on crop photosynthesis and seasonal growth and production. INTKAM was extended with 1) spectral composition of light, 2) light extinction profiles for different wavelengths, 3) colour effects on initial light use efficiency, and 4) on maximum carboxylation capacity. Various scenarios were examined, in which light colours provided with LEDs were or were not combined with solar radiation, and varied over the day. Daily PAR and initial light use efficiency were important causes of simulated differences in total dry matter production. The effects of differences in maximum carboxylation capacity proved small during the winter season with low light levels. A longer duration of lighting period also proved effective, even if the total light input was kept the same, due to the non-linearity of the photosynthesis-light response curve at lower light intensities.

Comparison of photosynthetic traits of codominant subalpine conifers Abies veitchii and A. mariesii in central Japan

Evergreen conifers Abies mariesii and A. veitchii codominate in the subalpine zone in central Japan. This study compared the photosynthetic light response curves and related leaf traits of 1-year-old needles between the two species to examine whether photosynthetic traits of A. veitchii are more favorable for growth in bright conditions than those of A. mariesii. Saplings of the two species were sampled at forest edge (FE) and forest understory (FU). FE saplings of the two species showed more shade-intolerant traits (i.e., lower initial slope of photosynthesis light response curve, greater light compensation point and dark respiration rate) than FU saplings. Maximum photosynthetic rate and leaf nitrogen concentration were greater in A. veitchii than A. mariesii for both FE and FU saplings. Photosynthetic nitrogen use efficiency (PNUE) was also greater in A. veitchii than A. mariesii. On the contrary, leaf mass per area was greater in A. mariesii than A. veitchii for both FE and FU saplings. Therefore, this study showed that photosynthetic traits of A. veitchii are more favorable for growth in bright conditions compared with A. mariesii, and A. mariesii has more robust needles at the expense of PNUE.

Safety conscious or living dangerously: what is the 'right' level of plant photoprotection for fitness and productivity?

Due to their sessile nature, plants could be perceived to be relatively slow and rather un-reactive. However, a plant scientist will tell you that the inability to run away (tropism notwithstanding) actually demands a highly sophisticated physiological response to the environment. Light presents an extreme case: cloud cover and wind-induced motion can lead to irradiance changes of several orders of magnitude over timescales of seconds and minutes. Being autotrophic organisms and having evolved to harvest light, plants need to dynamically regulate their biochemistry so that it operates efficiently during these fluxes, maintaining plant fitness but minimising the risk of damage. Photosynthesis is driven at a rate that depends on the amount of available light, as shown by the schematic photosynthesis-light response curves of C3 species (Fig. 1). In nature, CO2 assimilation can go from being light-limited to being light-saturated within a very short period of time. To maximise CO2 uptake, photosynthesis should ‘track’ light levels accurately inducing and removing photoprotective processes accurately. Being able to measure photoprotection precisely in naturally fluctuating settings is difficult; however, a paper in this volume of Plant, Cell and Environment proposes a significant advance (Tietz et al. 2017).

Linking stand architecture with canopy reflectance to estimate vertical patterns of light-use efficiency

Remote sensing of plant carbon uptake, or gross primary production (GPP), in a repeatable and consistent manner remains a key element of a comprehensive understanding of the role of vegetation within the global carbon cycle. To further this understanding at a landscape level or global scale, accurate remote sensing of photosynthetic light-use efficiency (LUE) is required to understand photosynthetic down-regulation and environmental constraints to plant photosynthesis. The past decade has seen advances in detecting both leaf- and canopy-level physiological stress behaviours using the photochemical reflectance index (PRI), a narrow-waveband normalized difference index that relates LUE to a xanthophyll-induced absorption feature at 531nm. To date, however, much of this research has occurred using top of canopy measurements, while our understanding of the vertical distribution of LUE within the crown is limited. In this study, we demonstrate an approach which could be used to scale photosynthetic behaviour of vegetation vertically and horizontally using estimates of vertical canopy structure obtained from terrestrial Light Detection and Ranging (LiDAR) data to predict proportions of shaded and sunlit canopy which are then linked to predictions of LUE. We apply the approach over a mature Aspen study site located in central Saskatchewan, Canada utilising full-waveform LiDAR data provided by the ground-based laser scanner system and canopy spectra obtained by the AMSPEC II spectro-radiometer. Agreement between predictions of Gross Primary Productivity (GPP) using the developed approach compared to independent observations was highly significant at hourly intervals (R2=0.80, p<0.01) under clear sky conditions. A range of LUE vertical profiles for different stand structures across the growing season were developed providing estimations of how crown structure can impact LUE vertically in the crown. We conclude with a recommendation for ongoing research to verify these types of trends using concurrently acquired, independently derived leaf LUE from photosynthesis light-response curves, and forest structure variation from LiDAR, to provide a more exact quantification of these patterns.

Optimal model of photosynthesis-light response curve in canopy of planted Larix olgensis tree.

Rectangle hyperbola model (RH), nonrectangle hyperbola model (NRH), exponential model (EM), modified rectangle hyperbola model (MRH), and modified exponential model (MEM) were applied respectively for modeling the photosynthesis-light response curves (PLC) based on four types of curves (photosynthesis-light response curve of inhibition, PLCi, photosynthesis-light response curve of saturation, PLCs, photosynthesis-light response curve of unsaturation, PLCu andphotosynthesis-light response curve in weak light, PLCw) in canopy of 15 years old planted Larix olgensis tree in the Maoershan Forest Farm, Heilongjiang Province. The major photosynthetic physiological indexes including maximum net photosynthetic rate (Pn max), dark respiration rate (Rd), light compensation point (LCP), light saturation point at saturated light intensity (LSP) and apparent quantum yield (AQY) were calculated. All the five candidate models were comprehensively compared by the model goodness-of-fit and the precision estimations of photosynthetic physiological indexes in the four types of curves. The results showed that MEM model was only suitable for fitting the PLCi. MRH model showed the best goodness-of-fit for PLCi and PLCs(Ra2was 0.9986 and 0.9978, respectively). Meanwhile, NRH model expressed the best fitting result in PLCu and PLCw (Ra2 was 0.9996 and 0.9963, respectively). MRH had the lowest mean absolute value of relative error (MAPE) when evaluating Pn max in different types of curves (0.1%<MAPE<0.7%), but its precision estimation for LCP was relatively worse (2.5%<MAPE<9.4%). NRH model exhibited more accurate estimation for LCP of PLCs and PLCu, as well as Rd of PLCu(MAPE was 1.8%, 0.1%, and 3.9%, respectively). RH model represented better prediction effect for LCP of PLCi and Rd of PLCs(MAPE was 1.0% and 2.7%, respectively). EM was more sui-table for estimating LCP of PLCw(MAPE was 0.2%). Comprehensive analysis showed that MRH model not only proved well model goodness-of-fit and accurate estimation of photosynthetic physiological indexes, but also showed the highest stability when fitting different types of curves. As a result, MRH model was finally selected as the optimal canopy photosynthesis-light response model of planted L. olgensis tree.

Preliminary study on cold-resistance of Euonymus radicans ‘Emorald & Gold’

A comparative observation was carried out on the changes of anatomical structure and starch content in the leaves of Euonymus radicans ‘Emorald Gold’ during overwintering and cold acclimation, and the photosynthesis-light response curves from the leaves of unacclimated and acclimated seedlings as well as the leaf photosynthetic rate of acclimated and unacclimated seedlings treated at the low temperature stress were studied comparatively. The results showed that the appearance of vacuole division during overwintering and cold acclimation were highly correlated to the development of plant cold-resistance. So were the starch accumulation before the acclimation, the starch degradation after the acclimation and starch accumulation again after de-acclimation. Compared with unacclimated seedlings, the leaf photosynthetic rate and photosynthetic light compensation point of acclimated seedlings decreased, photosynthetic light saturation point increased slightly. The leaf photosynthetic rate of acclimated seedlings still maintained at a higher level after low temperature stress for 72 h , but that of unacclimated seedlings became negentropy, indicating that cold acclimation raised the stability of photosynthesis of seedlings under low temperature stress. And the relation between the above-mentioned adaptive changes and plant cold-resistance was also discussed.