Maximum Net Photosynthetic Rate Research Articles

Endodormancy induction and photosynthetic physiology of Myricaria laxiflora remnant populations under chronic summer submersion

Dormancy is a protective survival strategy developed by plants to face chronic, seasonal and severe abiotic stress. In this study, changes in photosynthetic indices were measured during different periods of summer dormancy in the rare and endangered plant Myricaria laxiflora to reveal the adaptation to summer flooding. Results showed that the photosynthetic activity of M. laxiflora remnant populations gradually decreased with the onset of summer dormancy. The net photosynthetic rate, rate of transpiration, and stomatal conductance continued to decrease as dormancy progressed, whereas the intercellular CO2 concentration first decreased, then increased. Characteristics that reflect the performance of photosynthesis, including the maximum net photosynthetic rate (Pnmax), apparent quantum yield (AQY), and the rate of dark respiration (Rd) also decreased in value as dormancy progressed. Overall, the total chlorophyll content, and the content of chlorophyll a, chlorophyll b, and carotenoids, exhibited continuous decreases as dormancy progressed. Correlation analysis showed that most photosynthetic physiology indices and the content of photosynthetic pigments were significantly negatively correlated with daylight duration; no significant correlations with other environmental factors were found. These results indicated that the summer dormancy of M. laxiflora remnant populations is an active dormancy that represents an adaptation of the plant to submersion in the summer. Increasing daylight duration may be the main factor that triggers summer dormancy in M. laxiflora.

Differentiation in Leaf Physiological Traits Related to Shade and Drought Tolerance Underlies Contrasting Adaptations of Two Cyclobalanopsis (Fagaceae) Species at the Seedling Stage

Adaptation and acclimation of tree seedlings to different combinations of light and water conditions can determine the species-specific patterns of distribution along environmental gradients and the underlying physiological mechanisms are fundamental to the understanding of such patterns. Seedlings of two Cyclobalanopsis species naturally occurring in southwest China, with distinct distribution and regeneration characteristics, were grown under 100%, 50% and 4% sunlight conditions and traits related to shade and drought tolerance were studied. Particularly, we investigated whether leaf hydraulics, photosynthetic traits and their functional coordination play an important role in determining seedling environmental adaptation and acclimation of the two species. Seedlings of C. helferiana showed characteristics adapted to high irradiance while C. rex had traits adapted to partially shaded environments. Cyclobalanopsis helferiana had significantly higher maximum net photosynthetic rate (Amax), light compensation point and light saturation point than C. rex and the contrasts were particularly large when they were grown under full sunlight. Cyclobalanopsis helferiana showed the highest Amax when grown under 100% sunlight, while C. rex exhibited the highest Amax at 50% sunlight. Similarly, under full sunlight conditions C. helferiana showed significantly higher leaf hydraulic conductance (Kleaf) than C. rex, i.e., 13.37 vs. 7.09 mmol m−2 s−1 MPa−1 (p < 0.01). The correlation between Kleaf and Amax followed a unified positive correlation across different light treatments of both species. Moreover, leaves of C. helferiana showed greater resistance to drought-induced hydraulic dysfunction and to desiccation than C. rex. The contrasts in functional traits between the two Cyclobalanopsis species are consistent with the hypothesis that there is a trade-off between shade tolerance and drought tolerance. Findings of the present study contribute to a deeper understanding of mechanisms of divergence between closely related (congeneric) species with respect to key ecophysiology associated with natural regeneration.

Determination of the most effective design for the measurement of photosynthetic light-response curves for planted Larix olgensis trees

A photosynthetic light-response (PLR) curve is a mathematical description of a single biochemical process and has been widely applied in many eco-physiological models. To date, many PLR measurement designs have been suggested, although their differences have rarely been explored, and the most effective design has not been determined. In this study, we measured three types of PLR curves (High, Middle and Low) from planted Larix olgensis trees by setting 31 photosynthetically active radiation (PAR) gradients. More than 530 million designs with different combinations of PAR gradients from 5 to 30 measured points were conducted to fit each of the three types of PLR curves. The influence of different PLR measurement designs on the goodness of fit of the PLR curves and the accuracy of the estimated photosynthetic indicators were analysed, and the optimal design was determined. The results showed that the measurement designs with fewer PAR gradients generally resulted in worse predicted accuracy for the photosynthetic indicators. However, the accuracy increased and remained stable when more than ten measurement points were used for the PAR gradients. The mean percent error (M%E) of the estimated maximum net photosynthetic rate (Pmax) and dark respiratory rate (Rd) for the designs with less than ten measurement points were, on average, 16.4 times and 20.1 times greater than those for the designs with more than ten measurement points. For a single tree, a unique PLR curve design generally reduced the accuracy of the predicted photosynthetic indicators. Thus, three optimal measurement designs were provided for the three PLR curve types, in which the root mean square error (RMSE) values reduced by an average of 8.3% and the coefficient of determination (R2) values increased by 0.3%. The optimal design for the High PLR curve type should shift more towards high-intensity PAR values, which is in contrast to the optimal design for the Low PLR curve type, which should shift more towards low-intensity PAR values.

Physiological profiling of invasive plant species for ecological restoration of fly ash deposits

Extensive gaps in invasive plant species research in terms of ecosystem distribution and impact are major barriers faced by global decision making bodies for scientific management of plant species invasions of native flora. Effective strategies need to be worked out which would enable simultaneous management and the use of invasive plant species for ecosystem restoration. For evaluating the photosynthetic potential of invasive plant species in restoration of degraded areas, exhaustive in situ leaf gas exchange and leaf chlorophyll fluorescence were undertaken on four plants found naturally colonizing on the fly ash deposits. The four invasive species screened for their physiological tolerances towards microclimatic and edaphic stresses in harsh fly ash deposits were: Typha latifolia, Saccharum spontaneum, Prosopis juliflora, and Ipomea carnea. Saccharum spontaneum was found to be most efficient in sequestering CO2 emissions which were reflected in its maximum net photosynthetic rate (A, 29.29 ± 0.46 μmolCO2 m−2s−1) and higher below ground biomass. Maximum water use efficiency (WUE) was observed in S. spontaneum (9.3 ± 0.5 mmolCO2 molH2O−1) among all the species owing to high carboxylation, the lowest transpiration rate (E, 3.15 ± 0.13 mmolH2Om−2s−1) and stomatal conductance (gs, 0.2 ± 0.004 molH2Om−2s−1) values supporting it’s dense growth throughout the fly ash dumps in contrast to other three species. The study provides insights into the successful use of invasive plant species for their effective management and phytorestoration of fly ash dumps by transforming them into net carbon sinks which otherwise lack any native flora.

Vertical profile of photosynthetic light response within rice canopy.

Measured leaf photosynthetic light response (PLR) curves at different positions were fitted by non-rectangular hyperbola (NRH) equation to characterize vertical profile of parameters in NRH equation, namely maximum net photosynthetic rate Pnmax, initial quantum yield of assimilation φ, dark respiration rate Rd, and convexity of the curve k, at both jointing and heading stages within rice canopy. And leaf-position-specific and canopy average NRH equations were constructed respectively based on measured PLR curves at each specific leaf position and all measured PLR curves within rice canopy. The results showed that the Pnmax, φ, and Rd reached the maximum at the top second leaf and then decreased at jointing stage and decreased in downward leaves at heading stage. The k increased with lowering leaf position at both stages. The leaf-position-specific NRH equation performed well in estimating net photosynthetic rate Pn for all leaves at different positions and stages, while the canopy average NRH equation underestimated leaf Pn at upper canopy and overestimated Pn at lower canopy. The top fourth leaf was suitable for estimating photosynthetic parameters at canopy scale, as the Pnmax, φ, Rd, and k of the top fourth leaf were near to these parameters of rice canopy, and the canopy average NRH equation performed well in estimating leaf Pn for the top fourth leaf. The results will provide basic information for upscaling leaf photosynthesis to canopy scale.

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.

Effects of nitrogen application rate on the growth traits in seedlings of different quinoa cultivars

Effects of five different nitrogen application rates (i.e., N0, 0 g·kg-1; N1, 0.05 g·kg-1; N2, 0.1 g·kg-1; N3, 0.15 g·kg-1; N4, 0.2 g·kg-1) on the growth of seedlings of eight different quinoa cultivars were investigated in a pot experiment. The results showed that: 1) Across different nitrogen application rates, cultivar GB22 and OY had the highest biomass, but cultivar B2 had the lowest value. The highest flower mass ratio, stem mass ratio, root mass ratio, and leaf mass ratio were found in cultivar B2, GB22, R1, and W23, respectively. 2) The rate of nitrogen application significantly affected seedling growth. Compared with the control (N0), the maximum net photosynthetic rate and biomass accumulation were significantly higher in the lower nitrogen applications (i.e., N1 and N2 treatments), but were lower in the higher nitrogen applications (i.e., N3 and N4 treatments). The significant interactions between cultivar and nitrogen application rate on plant biomass indicated that different quinoa cultivars responded differently to nitrogen rate. The optimum nitrogen application rate (Nopt) required for cultivar R1, MY11, GB22 and OY was 0.05 g·kg-1; while that of cultivar GB11, DB, and B2 was 0.1 g·kg-1; but for cultivar W23, Nopt was less than 0.05 g·kg-1. 3) The interactions between cultivar and nitrogen application rate significantly affected biomass allocation. Below the highest nitrogen rate used (i.e., less than 0.2 g·kg-1), the flower and leaf biomass allocation increased with the increasing nitrogen rates. 4) Across different cultivars and nitrogen application rates, plant biomass was positively correlated to the maximum net photosynthetic rate, plant height, ground diameter, and specific leaf area, respectively. These results provided valuable information for the nutrition management of different quinoa cultivars.

The potential of Paulownia fortunei seedlings for the phytoremediation of manganese slag amended with spent mushroom compost

The use of phytoremediation was an efficient strategy for the restoration of mine slag and the addition of modifier was favorable for improving the phytoremediation efficiency. Herein, spent mushroom compost (SMC) was added in manganese (Mn) slag to reveal the phytoremediation potential of Paulownia fortunei seedlings. The transportation, subcellular distribution and chemical forms of Mn in P. fortunei, the diurnal variation of photosynthesis and antioxidant enzyme activities in P. fortunei leaves were measured to reveal the effect of SMC (mass ratios of 10%, M+) on the phytoremediation of Mn slag. Results showed that the addition of SMC increased the accumulation content of Mn by 408.54% due to the increased biomass of P. fortunei seedlings. After SMC amendment, the maximum net photosynthetic rate (Pn) increased and the superoxide dismutase (SOD) activities decreased significantly (p<0.05), which was beneficial to the tolerance of leaves to Mn stress. SMC amendment maintained the cell structural integrity of P. fortunei seedlings observed by transmission electron microscope (TEM). Additionally, SMC amendment decreased the damage level of Mn to the cell of P. fortunei seedlings by using function groups (-CH3 and -COOH) to bond Mn in the cell walls and vacuoles. SMC amendment reduced the Mn toxicity to P. fortunei seedlings and improved the phytoremediation capacity.

Leaf photosynthetic light response of summer maize: comparison of models and analysis of parameters

An experiment was performed in order to study the applicability of light-response models for summer maize (Zea mays L.) by using rectangular hyperbola model, nonrectangular hyperbola model, exponential model, binomial regression model, and modified rectangular hyperbola model (Ye model), respectively. Our results showed that the fitted effect of Ye model was best and photosynthetic parameters were closest to the observation. The photoinhibition coefficient was significantly negatively correlated with the light-saturation point (Is), the light-saturation coefficient (γ), and maximum net photosynthetic rate at light-saturation point (PNmax), respectively. PNmax and Is, apparent quantum yield, and γ performed significantly positive relationship, respectively. When the soil volumetric water content varied from 13 to 21%, PNmax had significant positive correlation with the soil water content and stomatal conductance. Under water and temperature stress, the net photosynthetic rate decreased and photoinhibition occurred, which could be well simulated by the Ye model. It seems that Ye model would have more applications, especially for the regions with strong solar radiation.

Quantifying photosynthetic performance of phytoplankton based on photosynthesis\u2013irradiance response models

BackgroundClarifying the relationship between photosynthesis and irradiance and accurately quantifying photosynthetic performance are of importance to calculate the productivity of phytoplankton, whether in aquatic ecosystems modelling or obtaining more economical production.ResultsThe photosynthetic performance of seven phytoplankton species was characterized by four typical photosynthesis–irradiance (P–I) response models. However, the differences were found between the returned values to photosynthetic characteristics by different P–I models. The saturation irradiance (Isat) was distinctly underestimated by model 1, and the maximum net photosynthetic rate (Pnmax) was quite distinct from its measured values, due to the asymptotic function of the model. Models 2 and 3 lost some foundation to photosynthetic mechanisms, that the returned Isat showed significant differences with the measured data. Model 4 for higher plants could reproduce the irradiance response trends of photosynthesis well for all phytoplankton species and obtained close values to the measured data, but the fitting curves exhibited some slight deviations under the low intensity of irradiance. Different phytoplankton species showed differences in photosynthetic productivity and characteristics. Platymonas subcordiformis showed larger intrinsic quantum yield (α) and lower Isat and light compensation point (Ic) than Dunaliella salina or Isochrysis galbana. Microcystis sp., especially M. aeruginosa with the largest Pnmax and α among freshwater phytoplankton strains, exhibited more efficient light use efficiency than two species of green algae.ConclusionsThe present work will be useful both to describe the behavior of different phytoplankton in a quantitative way as well as to evaluate the flexibility and reusability of P–I models. Meanwhile we believe this research could provide important insight into the structure changes of phytoplankton communities in the aquatic ecosystems.

Effects of light quality and temperature on the photosynthesis and pigment content of a subtidal edible red alga Meristotheca papulosa (Solieriaceae, Gigartinales) from Japan

This study investigated the effects of different light spectral qualities and temperature on the photosynthesis and pigment content of a subtidal edible red alga, Meristotheca papulosa. Photosynthesis–irradiance (P–E) experiments were carried out under red (660 nm), blue (450 nm), green (525 nm, light-emitting diodes), and white light (visible light, metal halide lamp), and at 12, 20, and 28 °C, respectively. Maximum net photosynthetic rates (NPmax) were highest under green light. Other P–E parameter estimates were similar among algae under red, blue, and green light, including their lower initial slope (α) and higher saturation irradiances (Ek) as compared to those under white light. Additionally, NPmax and Ek under white light were highest at 28 °C, and lowest at 12 °C with characteristic photoinhibition at irradiances greater than 150 μmol photons m−2 s−1. Photosynthesis–temperature (P–T) experiment revealed that the maximum gross photosynthetic rate (GPmax) occurred at 22.1 °C, which was within the optimal temperature range of Fv/Fm (21.5–23.6 °C). Exposures to the different light qualities at 100 μmol photons m−2 s−1 for 7 days showed increased phycoerythrin (PE) concentration of algae under blue and green light, while chlorophyll-a and phycocyanin (PC) showed little variation in all light qualities. Therefore, considering future management prospects for M. papulosa mariculture, we suggest that green light could be utilized to enhance photosynthesis. Furthermore, if the aim is to achieve high PE content for an improved reddish-color fresh product, exposure to blue or green light could be a good alternative.

Spatiotemporal photosynthetic physiology responses of remnant Myricaria laxiflora populations to regulated water level fluctuations.

The construction of the Three Gorges–Gezhouba Dam cascade hydropower station has changed the water level fluctuation pattern of the habitats for remnant rare and endangered Myricaria laxiflora populations downstream of the dam. The present study utilized biochemical markers of photosynthetic physiology to evaluate the spatiotemporal responses of remnant populations to human-regulated water level fluctuations. The results showed that the photosynthetic physiological activities of remnant M. laxiflora populations underwent a period of rapid growth, followed by a gradual decline in the growth recovery phase after flooding. During the entire experimental period, photosynthetic physiological activities of remnant M. laxiflora populations changed with prolongation of emergence time: specifically, net photosynthetic rate and stomatal conductance initially decreased and then subsequently increased, intercellular carbon dioxide concentrations peaked at mid-phase and transpiration rate continuously increased. The maximum net photosynthetic rate, apparent photosynthetic quantum efficiency and dark respiration rate in the light–response curves of the plants continuously increased during growth. The water level gradient also significantly affected the photosynthetic physiological activities in the remnant populations, i.e. the photosynthetic physiological activities of high-altitude plants were significantly higher than the middle- and low-altitude plants. The changes in photosynthetic pigment content of plants in remnant populations during the growth recovery phase and the entire growth period were similar to those occurring in photosynthetic activities in plants. Further, canonical correspondence analysis showed that photosynthetic physiological activities in the plants were significantly correlated with changes in water levels, emergence time, elevation gradient, soil water and soil nitrogen contents. Therefore, the artificial regulation of water level fluctuations by large hydropower stations will inevitably affect the photosynthetic activities and growth of remnant M. laxiflora populations.

Translocation pattern of nitrogen within clonal network of the stoloniferous herb Glechoma longituba and its horizontal redistribution mediated by clonal integration

Clonal integration allowed translocation of nitrogen between interconnected ramets, which improved growth performance of ramets growing in patch with low nitrogen availability. However, translocation pattern of nitrogen within clonal network and its horizontal redistribution still remain poorly understood. In the experiment, clonal fragment of the stoloniferous herb Glechoma longituba with four successive ramets was used. The mother rosette was grown in high nitrogen availability patch. The proximal, middle and distal ramets were grown individually in low nitrogen availability patches. Three separate ramets were transplanted into low nitrogen availability patches as neighboring individual for the proximal, middle and distal ramets, respectively. In addition, whole clonal fragment was grown in low nitrogen availability patches as the control treatment. Stolon among interconnected ramets retained intact.Potential maximum net photosynthetic rate (Pmax) and biomass accumulation of the proximal, middle and distal ramets significantly increased as well as leaf nitrogen content (NM), chlorophyll content (ACCm) and leaf nitrogen allocation to the photosynthetic machinery (PT) when nitrogen was added to the mother rosette. Compared with the proximal and distal ramets, greater increase of the above-mentioned parameters in the middle ramets is probably a trade-off between cost and benefit of nitrogen translocation. We tentatively conclude that the translocation pattern may be the optimal adaptation strategy for the clonal fragment of Glechoma longituba suffering from heterogeneous nitrogen supply.In the control treatment, all neighboring individuals died out at the end of experiment. However, the neighboring individuals survived when nitrogen was added to the mother rosette. Compared with the neighboring individuals for the proximal and/or distal ramets, NM, ACCm, Pmax and biomass accumulation of the neighboring individuals for the middle ramets were significantly higher. The horizontal redistribution of nitrogen among patches may be mediated by clonal integration, following by its translocation pattern within clonal network.

Biocontrol potential of the endophytic Bacillus amyloliquefaciens YN201732 against tobacco powdery mildew and its growth promotion

The effectiveness of Bacillus amyloliquefaciens YN201732, a beneficial endophyte isolated from tobacco seeds was explored for control of tobacco powdery mildew and the systemic resistance mechanisms involved. The results of the study showed that endophyte YN201732 has antagonistic effects on 12pathogenic fungi. The fermentation broth can inhibit the spore germination and has good control effect on tobacco powdery mildew in the greenhouse. The control effect of the protective test and the therapeutic test at 14 days reached up to 71.09% and 86.11%, respectively. Moreover, endophyte YN201732 can also promote seed germination and seedling plant growth, and improve plant photosynthesis. Compare with water treatment, the root length, plant height, maximum leaf length, leaf width, fresh weight, dry weight, chlorophyll and net photosynthetic rate of tobacco seedlings increased by 32.27%, 86.67%, 154.92%, 107.25%, 664.71%, 207.69%, 150.33%, and 240%, respectively. Additionally, the expression of NPR1 in tobacco leaves was stable when inoculated with YN201732 at different time points, while the PDF1.2 gene was up-regulated rapidly, suggesting that jasmonic acid/ethylene signaling pathway of plant might be induced, which enhance plant resistance to powdery mildew. The chit and PPO genes were highly expressed while the PAL and POD defense enzyme genes were down-regulated, the expression of chit was up-regulated 30–70 times after induction treatment. In addition, we revealed that polyphenol oxidase and chitinases are closely related to tobacco induced resistance to powdery mildew. Thus, our study showed that B. amyloliquefaciens YN201732 has high potential to be used as biocontrol agent and plant-growth promoting bacterium in tobacco agriculture.

Ecological variations of woody species along an altitudinal gradient in the Qinling Mountains of Central China: area-based versus mass-based expression of leaf traits

Leaf trait-based research has become the preferred method to understand the ecological strategies of plants. However, there is still a debate on whether area-based or mass-based traits provide different insights into environmental adaptations and responses. In this study, seven key leaf traits (maximum net photosynthetic rate, dark respiration rate, nitrogen content, photosynthetic nitrogen use efficiency, leaf mass per area, leaf dry matter contents and leaf area) of 43 woody species were quantified on the basis of both area and mass along an altitudinal gradient (1100–2700 m) in the Qinling Mountains of China. Differences in leaf traits and bivariate correlations between the two expressions were compared. By considering different expressions, the strengths and directions of the responses of leaf traits to the altitudinal gradient were determined. Leaf traits showed large variations; interspecific variations contributed more to total variance than intraspecific variations. Bivariate correlations between photosynthetic traits and structural traits (mass per area, dry matter content, and area) were weaker on a mass basis than those on an area basis. Most traits exhibited quadratic trends along the altitudinal gradient, and these patterns were more noticeable for area-based than mass-based traits. Area-based traits were more sensitive to changes in temperature and precipitation associated with altitude. These results provide evidence that mass- versus area-based traits show different ecological responses to environmental conditions associated with altitude, even if they do not contain very broad spatial scales. Our results also indicate distinction of photosynthetic acclimation among the two expressions along an altitudinal gradient, reflecting trade-offs among leaf structure and physiological traits.

The effects of sesame/peanut intercropping on photosynthetic fluorescence characteristics in functional leaf of sesame.

To unravel functional leaf photosynthetic mechanisms underlying enhanced yield of sesame in sesame/peanut intercropping, a field experiment was carried out in 2017 and 2018 with four treatments including (1) three-row sesame intercropped with six-row peanut (IC 3:6), (2) two-row sesame intercropped with four-row peanut (IC 2:4), (3) sole cropped sesame (SS), and (4) sole cropped peanut (SP). We measured the parameters of gas exchange, characteristics of photosynthetic response curve to light and CO2, and characteristics of chlorophyll rapid fluorescence induction kinetic curves of the functional leaves of sesame. The results showed that the partial land equivalent ratio of intercropped sesame was greater than 1/3. The light saturation point (Isat), maxi-mum net photosynthetic rate (Pn max), maximum electron transport rate (Jmax), triose phosphate utilization rate (TPU), maximum carboxylation rate of Rubisco (Vc max) were increased significantly under intercropping. Further, absorption energy flux per CS (ABS/CSo), trapping energy flux per CS (TRo/CSo), number of active reaction centers per CS (RC/CSm), and electron transport flux per CS (ETo/CSo) in intercropped treatments were enhanced compared to that under sesame monoculture. However, the ratio between variable fluorescence Fk to amplitude Fj-Fo (Wk) and ratio between variable fluorescence Fj to amplitude Fp-Fo (Vj) in functional leaves of intercropped sesame were significantly decreased. The efficiency of converting light energy into electricity of PS2 reaction center (Ψo), electron transfer efficiency from PS2 to end acceptor of PS1 (ΨRo), electron transfer efficiency of the electron transport chain (δR), PS1 photochemical activity, and the coordination between PS2 and PS1 in functional leaves of intercropped sesame were increased. The net photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (Tr), Pn max, Jmax, Vc max, TPU, Ψo, ΨRo and δR were significantly higher in IC 3:6 than those in IC 2:4. We conclude that intercropping improves net photosynthetic rate and yield of sesame by increasing light absorption, electronic transmission, activity of PS2 donator/receptor sides, and CO2 fixation, with stronger effects in IC 3:6 than IC 2:4.

Physiological, morphological and anatomical leaf traits variation across leaf development in 'Corylus avellana'

The study analyzed the variations of physiological, morphological and anatomical leaf traits during its development in Corylus avellana L. saplings. Three different phases were identify during leaf development: the first phase (hereafter IP) considered in the developing leaves, the second phase (IIP) in the mature green leaves and the third phase (IIIP) in the senescent leaves. In particular, variations in parameters estimated from the photosynthetic light response curves, in chlorophyll fluorescence variables and in morphological leaf traits were analyzed during the three phases. The principal component analysis (PCA) carried out using all the considered morphological characters (leaf mass per area - LMA, and leaf tissue density - LTD) and physiological traits (the maximum net photosynthetic rates - ANmax, dark respiration rates - RD, light compensation point - LCP, light saturation point – LSP, maximum quantum yield - ɸmax, fluorescence-based maximum quantum yield of PSII photochemistry - Fv/FM and effective quantum yield of PSII photochemistry - ɸPSII) showed a complete separation among the considered phases. The results showed that the major differences occur between the phases IP and IIP. In particular, a greater variation was found for LMA, ANmax, RD. On the contrary a lower variation was observed for ɸmax which remain quite constant from IP to IIP indicating that chloroplasts present in juvenile leaves are fully functional.

Modified non-rectangular hyperbola equation with plant height for photosynthetic light-response curves of Potentilla anserina and Elymus nutans at various growth phases in the Heihe River Basin, Northwest China

The non-rectangular hyperbola (NRH) equation is the most popular method that plots the photosynthetic light-response (PLR) curve and helps to identify plant photosynthetic capability. However, the PLR curve can’t be plotted well by the NRH equation at different plant growth phases due to the variations of plant development. Recently, plant physiological parameters have been considered into the NRH equation to establish the modified NRH equation, but plant height (H), an important parameter in plant growth phases, is not taken into account. In this study, H was incorporated into the NRH equation to establish the modified NRH equation, which could be used to estimate photosynthetic capability of herbage at different growth phases. To explore photosynthetic capability of herbage, we selected the dominant herbage species Potentilla anserina L. and Elymus nutans Griseb. in the Heihe River Basin, Northwest China as the research materials. Totally, twenty-four PLR curves and H at different growth phases were measured during the growing season in 2016. Results showed that the maximum net photosynthetic rate and the initial slope of PLR curve linearly increased with H. The modified NRH equation, which is established by introducing H and an H-based adjustment factor into the NRH equation, described better the PLR curves of P. anserina and E. nutans than the original ones. The results may provide an effective method to estimate the net primary productivity of grasslands in the study area.

Effects of shading on chlorophyll content and photosynthetic characteristics in leaves of Phoebe bournei.

To explore the photosynthetic adaptation of Phoebe bournei to different light conditions, two-year-old P. bournei seedlings were grown under three light regimes (full light, shading rate 50% and 78% of full light). The chlorophyll contents, leaf gas exchange and chlorophyll fluorescence of P. bournei were measured after six-month treatment. The results showed that the contents of chlorophyll a, chlorophyll b, chlorophyll (a+b) and carotenoids in leaves were in a descending order of shading rate 78% > shading rate 50% > full light. There was no significant difference of chlorophyll a/b between natural and shade treatments. The shading treatment reduced light compensation point (LCP), but increased light saturation point (LSP) and apparent quantum yield (AQY), suggesting that plants could utilize both the weak light and the high light. Maximum net photosynthetic rate (Pn max), dark respiration rate (Rd), and maximum electron transfer rate (Jmax) increased under the shading treatment. There was significant difference between natural and shade treatment in net photosynthetic rate (Pn), stomatal conductance to CO2(gsc), intercellular CO2 concentration (Ci), and mesophyll conductance (gm). Pn and gm of different light regimes were sorted from the highest to the lowest as shading rate 78% > shading rate 50% > full light. gsc under shading rate 78% was higher than that under full light. Ci under shading rate 50% and 78% were lower than that under full light. Actual photochemical efficiency of PS2 (Fv'/Fm'), quantum yields of PS2 (ΦPS2), and electron transport rate (J) of P. bournei leaves were significantly higher under shading rate 78% than those under shading rate 50% and full light. In conclusion, P. bournei could increase Pn by increasing chlorophyll content, AQY, J, gsc, and gm under shade condition.

Drought-Induced Mortality Is Related to Hydraulic Vulnerability Segmentation of Tree Species in a Savanna Ecosystem

Vulnerability segmentation (VS) has been widely suggested to protect stems and trunks from hydraulic failure during drought events. In many ecosystems, some species have been shown to be non-segmented (NS species). However, it is unclear whether drought-induced mortality is related to VS. To understand this, we surveyed the mortality and recruitment rate and measured the hydraulic traits of leaves and stems as well as the photosynthesis of six tree species over five years (2012–2017) in a savanna ecosystem in Southwest China. Our results showed that the NS species exhibited a higher mortality rate than the co-occurring VS species. Across species, the mortality rate was not correlated with xylem tension at 50% loss of stem hydraulic conductivity (P50stem), but was rather significantly correlated with leaf water potential at 50% loss of leaf hydraulic conductance (P50leaf) and the difference in water potential at 50% loss of hydraulic conductance between the leaves and terminal stems (P50leaf-stem). The NS species had higher Huber values and maximum net photosynthetic rates based on leaf area, which compensated for a higher mortality rate and promoted rapid regeneration under the conditions of dry–wet cycles. To our knowledge, this study is the first to identify the difference in drought-induced mortality between NS species and VS species. Our results emphasize the importance of VS in maintaining hydraulic safety in VS species. Furthermore, the high mortality rate and fast regeneration in NS species may be another hydraulic strategy in regions where severe seasonal droughts are frequent.