Light Response Of Photosynthesis Research Articles

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.

Photosynthetic model for citrus cultivar Huangguogan

Grafting is an effective measure to improve the photosynthetic rate of citrus. The light responses of photosynthesis in leaves of two-year old grafted Huangguogan (citrus cultivar Huangguogan), Huanggougan / Trifoliate (HG/PT), Huanggougan / Tangerine (HG/CR), and Huanggougan / Ziyang Xiangcheng (HG/CJ) were studied using the LI-COR 6400 portable photosynthesis system. Light-response curves and photosynthetic parameters were analyzed and fitted using the rectangular hyperbola model (RHM), the exponential model (EM), the non rectangular hyperbola model (NRHM), and the modified rectangular hyperbola model (MRHM). The results showed that: (1) Grafting can change the photosynthetic characteristics of Huangguogan, and the value of photosynthesis rate of HG/CJ is the greatest; (2) The light-response curves of net photosynthetic rate (PN), the light compensation point (LCP), and the dark respiration rate (RD) were well fitted using the above four models. The modified rectangular hyperbola was the best model in fitting the data; the nonrectangular hyperbola model was the second, and the rectangular hyperbola model was the poorest one.

The temperature and light responses on the photosynthesis of two freshwater red algae, Virescentia helminthosa and Sheathia arcuata (Batrachospermaceae), from Japan

The temperature and light responses of photosynthesis in two freshwater red algae, Virescentia helminthosa and Sheathia arcuata (Batrachospermaceae), were determined by a pulse amplitude modulation (PAM) chlorophyll fluorometer and dissolved oxygen sensors. Net oxygenic photosynthesis–photosynthetically active radiation (PAR) models of V. helminthosa and S. arcuata revealed similar low PAR-adapted responses, with a compensation PAR (Ec) of 6.95 and 11.5 μmol photons m−2 s−1 (5.58–8.42 and 9.10–11.42, 95% Bayesian prediction interval, BPI) and saturating PAR (Ek) of 18.8 and 17.7 μmol photons m−2 s−1 (14.5–24.7 and 13.0–23.90, BPI), respectively. A temperature-dependent model of net photosynthesis and dark respiration for two species also showed similar temperature responses, and the gross photosynthetic rate (GPmax), 1.79 and 1.19 μg O2 gww−1 min−1 (1.62–1.96 and 1.08–1.29, BPI), was highest at 26.4 and 30.3 °C (23.9–28.7 and 28.3–32.1, BPI). The maximum quantum yields (Fv/Fm) for two species also had similar responses with respect to temperature; however, it was generally stable at low temperatures (8–20 °C) with the highest value of 0.52 and 0.56 (0.49–0.54 and 0.54–0.58, BPI) occurring at 18.5 and 20.9 °C (17.1–19.7 and 19.8–21.9, BPI). Continuous exposure (12 h) to PAR of 100 (low) and 1000 (high) μmol photons m−2 s−1 at 12, 16, and 24 °C revealed greater declines in their effective quantum yield (ΦPSII) in the two species under high PAR. Nevertheless, their Fv/Fm mostly recovered after a subsequent 12-h dim-light acclimation, suggesting the potential of recovery from daytime chronic photoinhibition.

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.

遮光对香果树幼苗光合特性及叶片解剖结构的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 遮光对香果树幼苗光合特性及叶片解剖结构的影响 DOI: 10.5846/stxb201810312347 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 江苏省重点研发计划（现代农业）项目（BE2017387） Effects of shading on photosynthetic characteristics and leaf anatomical structure of Emmenopterys henryi seedlings Author: Affiliation: 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:设置了全光照（L0）、透光率60%（L1）、透光率25%（L2）、透光率10%（L3）4种光环境，研究了不同遮光处理对香果树幼苗光合作用及叶片解剖结构的影响。结果表明：（1）遮光对香果树幼苗净光合速率（Pn）、蒸腾速率（Tr）、气孔导度（Gs）、气孔限制值（Ls）、胞间CO2浓度（Ci）、蒸汽压亏缺（Vpdl）均产生了显著影响。全光和L1处理下Pn和Tr日变化呈明显的双峰曲线，中午出现了明显的"午休"，其余处理的变化相对缓和，双峰和"午休"现象不明显；Gs的日变化规律与Pn基本一致；Ci的日变化整体呈先期缓慢降低后期抬升的趋势，与对照相比遮光显著提高了叶片胞间CO2浓度；Ls和Vpdl呈现出先升后降的弧形变化，并且遮光下Ls和Vpdl日均值显著低于全光照。一天中Pn和Tr的日均值大小排序为L1 > L0 > L2 > L3。（2）不同光环境下香果树幼苗的光合响应特征明显不同。全光下，香果树幼苗能够维持较高的净光合作用速率而未呈现明显的光抑制，表现出一定的光忍耐和喜光性。L1处理下的最大净光合速率（Pmax）、暗呼吸速率（Rd）和表观量子效率（AQY）显著增加，说明香果树对光强具有一定的可塑性，轻度遮光有利于光合效率提高；强度遮光（L2、L3）导致光补偿点（LCP）和光饱和点（LSP）显著降低，有利于充分利用弱光，但Pmax、Rd明显下降，光合效率受到抑制。（3）遮光显著影响了香果树叶片的气孔分布。遮光条件下香果树叶片的气孔密度显著减小，气孔器长度、宽度与单个气孔器面积也呈现类似的变化。（4）遮光条件下香果树叶片厚度减小，上表皮增厚，下表皮变薄。栅栏组织厚度（PT）变薄，海绵组织（ST）不发达，PT/ST增加；维管束内单列导管数目和导管直径均有明显增大，促进了叶片水分传导运输。（5）在育苗生产中，为了适应香果树幼苗生长发育的需求，建议有效辐射强度保持在自然光强的60%以上。 Abstract:Effects of shading on photosynthesis characteristics and leaf anatomical structure of Emmenopterys henryi seedlings were studied using four shading treatments including full sunlight (L0), 60% sunlight (L1), 25% sunlight (L2), and 15% sunlight (L3), respectively. The results showed that:(1) Shading had an significant effect on the net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), stomatal limitation value (Ls), intercellular CO2 concentration (Ci), and vapor pressure deficit (Vpdl) of E. henryi seedlings. The diurnal changes of Pn and Tr under L0 and L1 treatments showed obviously bimodal curves, and the "noon break" appeared at 12:00. Their changes under L2 and L3 treatments were relatively mild, and the "noon break" were not obvious. The variation of Gs was basically consistent with that of Pn. The variation of Ci showed a tendency of declining slowly at early stage and rising rapidly later. Compared with the control, the shading promoted significantly increase of the Ci. Both Ls and Vpdl showed the arc changes of slow rising in advance and decreasing in the latter stage, and the daily averages under shading were lower significantly than the control. The order of daily averages of Pn and Tr was L1 > L0 > L2 > L3. (2) The photosynthesis-light response characteristics of E. henryi seedlings under four light regimes were obviously different. The seedlings grown under the full sunlight condition could maintain a higher Pn without obvious photoinhibition, showing a certain degree of shading-tolerance and light-demanding. The maximum net photosynthetic rate (Pmax), dark respiration rate (Rd), and apparent quantum efficiency (AQY) under L1 treatment increased more significantly than the control. Therefore, the E. henryi seedlings had some plasticity to light intensity. The mild shading was beneficial to the improvement of photosynthetic efficiency. Serious shading (L2 and L3) resulted in a significant decrease of light compensation point (LCP) and light saturation point (LSP), which was beneficial to make full use of weak light. But they resulted in Pmax and Rd decrease obvious, which inhibited photosynthetic efficiency. (3) The shading significantly affected the stomatal distribution on leaves surface of E. henryi seedlings. Under shading condition, the stomata density decreased significantly, and the stomata length, the stomata width, and single stomatal area was similar. (4) Under shading, the leaf thickness decreased, the upper epidermis thickened, and the lower epidermis thinned. The thickness of palisade tissue (PT) decreased and sponge tissue (ST) was not fully developed, and the value of PT/ST increased. Moreover, the number of vessel in vascular bundle and the vessel diameter increased significantly, which promoted the transport of water in leaves. (5) In order to meet the needs of growth and development of E. henryi seedlings in cultivation, we suggested that the effective radiation intensity should be above 60% of natural light intensity. 参考文献 相似文献 引证文献

Simulation on photosynthetic light-responses of leaves of Quercus variabilis and Robinia pseudoacacia under different light conditions.

Photosynthesis can reflect the responses of plants to environmental changes. In this study, photosynthetic light-response curves were measured by the Li-6400XT photosynthetic system in Quercus variabilis and Robinia pseudoacacia plantations in Xiaolangdi Forest Ecosystem Research Station. Photosynthetic light-response curves were fitted by Ye model. The differences of photosynthetic parameters between inner and margin forests were examined. Stomatal conductance (gs) light-response curve were fitted using the mechanism model of gs coupled with a modified model of light-response of photosynthesis. The light-response characteristics of gs were investigated. Net photosynthetic rates (Pn) of Q. variabilis in the inner forest was higher than that in the margin. The initial light efficiency (Α) was 12.4% more in the inner forest than that in the margin in July and August when photosynthetically active radiation was less than 200 Μmol·m-2·s-1. The ability to capture and utilize weak light of Q. variabilis leaves in the inner forest was obviously higher than that in the margin. When photosynthetically active radiation was higher than 200 Μmol·m-2·s-1, Pn of Q. variabilis leaves in the margin forest was larger than that in the inner. Under weak light conditions (0-200 Μmol·m-2·s-1), Pn of R. pseudoacacia in the inner forest was higher than that in the margin. Pn of R. pseudoacacia in the inner forest was less than that in the margin when light intensity was higher than 200 Μmol·m-2·s-1. The dark respiration rate (Rd) and light compensation point (Ic) in the inner forest were 50.0% and 42.8% lower than those in the margin. The less Rd and Ic of the inner forest could reduce carbon loss and adapt to low photosynthetic rate. The stomatal conductance light-response of R. pseudoacacia in the inner forest significantly differed from that in the margin. The leaves of Q. variabilis and R. pseudoacacia had strong adaptability to the changes of light condition. The values of maximum net photosynthetic rate (Pn max) and Α of Q. variabilis leaves were mainly controlled by gs, and Rd and Ic were primarily affected by air temperature. Pn max and Α of R. pseudoacacia leaves had significant positive correlation with air temperature. The Ic and the light saturation point (Is) were remarkably correlated with leaf saturation vapor pressure deficit.

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.

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.

Phenotyping of field-grown wheat in the UK highlights contribution of light response of photosynthesis and flag leaf longevity to grain yield.

Improving photosynthesis is a major target for increasing crop yields and ensuring food security. Phenotyping of photosynthesis in the field is critical to understand the limits to crop performance in agricultural settings. Yet, detailed phenotyping of photosynthetic traits is relatively scarce in field-grown wheat, with previous studies focusing on narrow germplasm selections. Flag leaf photosynthetic traits, crop development, and yield traits were compared in 64 field-grown wheat cultivars in the UK. Pre-anthesis and post-anthesis photosynthetic traits correlated significantly and positively with grain yield and harvest index (HI). These traits included net CO2 assimilation measured at ambient CO2 concentrations and a range of photosynthetic photon flux densities, and traits associated with the light response of photosynthesis. In most cultivars, photosynthesis decreased post-anthesis compared with pre-anthesis, and this was associated with decreased Rubisco activity and abundance. Heritability of photosynthetic traits suggests that phenotypic variation can be used to inform breeding programmes. Specific cultivars were identified with traits relevant to breeding for increased crop yields in the UK: pre-anthesis photosynthesis, post-anthesis photosynthesis, light response of photosynthesis, and Rubisco amounts. The results indicate that flag leaf longevity and operating photosynthetic activity in the canopy can be further exploited to maximize grain filling in UK bread wheat.

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).

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.

Light-use efficiency of tomato seedling leaves at different CO2 concentrations.

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

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.