Plant Photosynthetic Capacity Research Articles

An optimality‐based model explains seasonal variation in C3 plant photosynthetic capacity

The maximum rate of carboxylation (Vcmax ) is an essential leaf trait determining the photosynthetic capacity of plants. Existing approaches for estimating Vcmax at large scale mainly rely on empirical relationships with proxies such as leaf nitrogen/chlorophyll content or hyperspectral reflectance, or on complicated inverse models from gross primary production or solar-induced fluorescence. A novel mechanistic approach based on the assumption that plants optimize resource investment coordinating with environment and growth has been shown to accurately predict C3 plant Vcmax based on mean growing season environmental conditions. However, the ability of optimality theory to explain seasonal variation in Vcmax has not been fully investigated. Here, we adapt an optimality-based model to simulate daily Vcmax,25C (Vcmax at a standardized temperature of 25°C) by incorporating the effects of antecedent environment, which affects current plant functioning, and dynamic light absorption, which coordinates with plant functioning. We then use seasonal Vcmax,25C field measurements from 10 sites across diverse ecosystems to evaluate model performance. Overall, the model explains about 83% of the seasonal variation in C3 plant Vcmax,25C across the 10 sites, with a medium root mean square error of 12.3μmolm-2 s-1 , which suggests that seasonal changes in Vcmax,25C are consistent with optimal plant function. We show that failing to account for acclimation to antecedent environment or coordination with dynamic light absorption dramatically decreases estimation accuracy. Our results show that optimality-based approach can accurately reproduce seasonal variation in canopy photosynthetic potential, and suggest that incorporating such theory into next-generation trait-based terrestrial biosphere models would improve predictions of global photosynthesis.

Freezing Tolerance of Lolium multiflorum/Festuca arundinacea Introgression Forms is Associated with the High Activity of Antioxidant System and Adjustment of Photosynthetic Activity under Cold Acclimation.

Though winter-hardiness is a complex trait, freezing tolerance was proved to be its main component. Species from temperate regions acquire tolerance to freezing in a process of cold acclimation, which is associated with the exposure of plants to low but non-freezing temperatures. However, mechanisms of cold acclimation in Lolium-Festuca grasses, important for forage production in Europe, have not been fully recognized. Thus, two L. multiflorum/F. arundinacea introgression forms with distinct freezing tolerance were used herein as models in the comprehensive research to dissect these mechanisms in that group of plants. The work was focused on: (i) analysis of cellular membranes’ integrity; (ii) analysis of plant photosynthetic capacity (chlorophyll fluorescence; gas exchange; gene expression, protein accumulation, and activity of selected enzymes of the Calvin cycle); (iii) analysis of plant antioxidant capacity (reactive oxygen species generation; gene expression, protein accumulation, and activity of selected enzymes); and (iv) analysis of Cor14b accumulation, under cold acclimation. The more freezing tolerant introgression form revealed a higher integrity of membranes, an ability to cold acclimate its photosynthetic apparatus and higher water use efficiency after three weeks of cold acclimation, as well as a higher capacity of the antioxidant system and a lower content of reactive oxygen species in low temperature.

Elevated air temperature damage to photosynthetic apparatus alleviated by enhanced cyclic electron flow around photosystem I in tobacco leaves

High temperature can lead to increased production of excess light energy, thus reducing photosynthetic capacity in plants. Photosynthetic cyclic electron flow (CEF) in photosystem I (PSI) can effectively protect photosystems, but its physiological mechanism under high temperature is poorly understood. In this study, antimycin A (AA) and thenoyltrifluoroacetone (TTFA) were used to inhibit PGR5-and NDH-dependent CEF pathways, respectively, to reveal the photoprotective functions of CEF for PSII in tobacco leaves under high temperature stress (37 °C, HT). High temperatures caused decreases in maximal photochemistry efficiency (Fv/Fm) and damaged photosystem II (PSII) in tobacco leaves. Under AA inhibition of PGR5-dependent CEF, high temperature increased the fluorescence intensity of point O (Fo) in OJIP curves, i.e., the energy absorption per active reaction center (ABS/RC), the trapping rate of the reaction center (TRo/RC), and the electron transport efficiency per reaction center (ETo/RC) in tobacco leaves. High temperature induced an increase in the hydrogen peroxide content and a decrease in pigment content in tobacco leaves. Under the high temperature treatment, inhibition of PGR5-dependent CEF reduced the activities of the PSII reaction center significantly, destroyed the oxygen-evolving complex (OEC), and impeded photosynthetic electron transfer from PSII to the plastoquinone (PQ) pool in tobacco leaves. The TTFA treatment inhibited the NDH-dependent pathway under high temperature conditions, with the relative fluorescence intensity of point I (VI) decreased significantly, and the content of hydrogen peroxide and superoxide anion increased significantly. Additionally, Fo and the redox degree of the PSII donor side (Wk) increased, and pigment content decreased compared to the control, but with little change compared to high temperature treatment, indicating that the inhibition of the NDH-dependent pathway directly weakened the capacity of the PQ pool to lead to the accumulation of reactive oxygen species (ROS) in tobacco leaves. In conclusion, CEF alleviated damage to the photosynthetic apparatus in tobacco leaves by increasing PSII heat dissipation, reducing ROS production, and maintaining the stability of the PQ pool to accommodate photosynthetic electron flow.

A general formula for calculating surface area of the similarly shaped leaves: Evidence from six Magnoliaceae species

Leaf area is an important indicator of photosynthetic capacity in plants. Knowledge of the variation of leaf shape at an individual level or a population level can help by accurately calculate leaf area. Such calculations can help us to understand the life history strategies of plants, and allow us to better understand the influence of climate change on mean leaf area as an indicator of leaf size, which is closely related to stand yields and ecological ecosystem services. The Montgomery equation (ME), which describes a proportional relationship between leaf surface area and the product of leaf length and width, has been demonstrated to hold true for many broad-leaved plants. The Magnoliaceae family has 17 genera covering ca. 300 species, of which some plants play important roles in the landscape. Many Magnoliaceae plants have similar leaf shapes, and little is known about whether ME can act as a general formula to calculate leaf surface area for these plants. This paper provides the evidence that ME can be used to measure the leaf area of Magnoliaceae species. More than 2500 mature leaves of six species within two genera (Magnolia and Michelia) of the Magnoliaceae family were selected as samples. The data of leaf length, width, and area were obtained from the scanned images. We used four models to fit these data, including (1) ME (which is actually a direct proportional function of leaf area vs. the product of leaf length and width), (2) a power-law function between leaf area and the product of leaf length and width, (3) a power function with an exponent of 2 between leaf area and leaf length, and (4) a power function between leaf area and leaf length. We found that ME and the second function have similar root-mean-square error values that are both lower than those of the other two equations. However, ME is better than the second equation because of the simplicity of its structure. We documented the validity of ME for calculating leaf area at a species level, a genus level, and even for the 6-species pooled data set. The estimated Montgomery parameter (i.e., the proportional coefficient in ME) is approximately equal to 0.68, which means that leaf area of the six investigated species can be approximated by 68% of the area of a rectangle with the leaf’s length and width as its sides. This study provides a convenient and fast approach for leaf-area calculation. In addition, we found that the Montgomery parameter can act as an indicator for measuring the similarity of leaves among different species, which provides a measurement standard for leaf morphology.

Two Festuca Species-F. arundinacea and F. glaucescens-Differ in the Molecular Response to Drought, While Their Physiological Response Is Similar.

Impact of photosynthetic and antioxidant capacities on drought tolerance of two closely related forage grasses, Festuca arundinacea and Festuca glaucescens, was deciphered. Within each species, two genotypes distinct in drought tolerance were subjected to a short-term drought, followed by a subsequent re-watering. The studies were focused on: (i) analysis of plant physiological performance, including: water uptake, abscisic acid (ABA) content, membrane integrity, gas exchange, and relative water content in leaf tissue; (ii) analysis of plant photosynthetic capacity (chlorophyll fluorescence; gene expression, protein accumulation, and activity of selected enzymes of the Calvin cycle); and (iii) analysis of plant antioxidant capacity (reactive oxygen species (ROS) generation; gene expression, protein accumulation and activity of selected enzymes). Though, F. arundinacea and F. glaucescens revealed different strategies in water uptake, and partially also in ABA signaling, their physiological reactions to drought and further re-watering, were similar. On the other hand, performance of the Calvin cycle and antioxidant system differed between the analyzed species under drought and re-watering periods. A stable efficiency of the Calvin cycle in F. arundinacea was crucial to maintain a balanced network of ROS/redox signaling, and consequently drought tolerance. The antioxidant capacity influenced mostly tolerance to stress in F. glaucescens.

Assessment of leaf ultrastructure offers insights into mechanisms regulating sugarcane performance under low-phosphorus stress

Detailed studies of plant responses to phosphorus (P) deficiency might reveal opportunities to improve sugarcane performance under nutrient stress, termed as P use efficiency. Then, we aimed through transmission electron microscopy to offer insights into the effects of varying P supply on leaf ultrastructural traits influencing photosynthesis and leaf area formation. Plants of the genotype RB86-7515 were cultivated under varying nutrient supply (0.0125, 0.05, 0.2 and 0.8 mM P) for 4 months. Diagnostic mature leaves were sampled to evaluate ultrastructural organization and P concentration. Leaf area and plant dry mass responded positively to increasing P rates and maximum values were attained at 0.55 mM P. Leaf P concentration increased as a function of nutrient supply, and the greatest area of diagnostic leaf and whole plant growth was associated with 1.80 g kg−1 P. Under severe deficiency (relative growth ≤ 30% and leaf P ≤ 0.90 g kg−1) generated with 0.0125- and 0.05-mM P, transmission electron microscopy revealed pronounced damages to leaf ultrastructure. In mesophyll cells, the changes were more intense under the lowest P rate, and included disintegration of the middle lamella, collapse of plasma membrane and distortion of thylakoids. Bundle sheath chloroplasts of the severely P-deficient plants exhibited, compared with those under 0.2- and 0.8-mM P, disorganization of lamellar membrane system. Collectively, these ultrastructural alterations offer insights into how P deficiency affects whole plant photosynthetic capacity and provide possible target traits at canopy level related to sugarcane P use efficiency.

Methane emission and sulfide levels increase in tropical seagrass sediments during temperature stress: A mesocosm experiment.

Climate change‐induced ocean warming is expected to greatly affect carbon dynamics and sequestration in vegetated shallow waters, especially in the upper subtidal where water temperatures may fluctuate considerably and can reach high levels at low tides. This might alter the greenhouse gas balance and significantly reduce the carbon sink potential of tropical seagrass meadows. In order to assess such consequences, we simulated temperature stress during low tide exposures by subjecting seagrass plants (Thalassia hemprichii) and associated sediments to elevated midday temperature spikes (31, 35, 37, 40, and 45°C) for seven consecutive days in an outdoor mesocosm setup. During the experiment, methane release from the sediment surface was estimated using gas chromatography. Sulfide concentration in the sediment pore water was determined spectrophotometrically, and the plant's photosynthetic capacity as electron transport rate (ETR), and maximum quantum yield (Fv/Fm) was assessed using pulse amplitude modulated (PAM) fluorometry. The highest temperature treatments (40 and 45°C) had a clear positive effect on methane emission and the level of sulfide in the sediment and, at the same time, clear negative effects on the photosynthetic performance of seagrass plants. The effects observed by temperature stress were immediate (within hours) and seen in all response variables, including ETR, Fv/Fm, methane emission, and sulfide levels. In addition, both the methane emission and the size of the sulfide pool were already negatively correlated with changes in the photosynthetic rate (ETR) during the first day, and with time, the correlations became stronger. These findings show that increased temperature will reduce primary productivity and increase methane and sulfide levels. Future increases in the frequency and severity of extreme temperature events could hence reduce the climate mitigation capacity of tropical seagrass meadows by reducing CO2 sequestration, increase damage from sulfide toxicity, and induce the release of larger amounts of methane.

Assessment of Seed Yield and Quality of Winter Oilseed Rape Using Chlorophyll Fluorescence Parameters of Pods

Abstract. Oilseed rape is one of the leading sources of vegetable oil in the world. Maximizing the seed yield and quality is crucial to improve the profit for farmers and meet the increasing consumer demand for healthy vegetable oil. However, the current evaluation process of seed yield and quality is tedious and inefficient due to its dependence on wet chemistry methods and/or manual measurements of small sample sizes. Because the photosynthesis of pods plays an important role in the accumulation of grain filling, this research aimed to evaluate the seed yield and quality of oilseed rape by using chlorophyll fluorescence (ChlF) parameters. The OJIP kinetics of rape pods were acquired in two independent experiments with different levels of nitrogen (N) application and different crop varieties, respectively. The JIP-test showed that the level of N fertilizer can influence the plant photosynthetic capacity and crop productivity, and the photosynthetic response also varied in the different varieties. The maximum quantum yield for primary photochemistry (Fv/Fm) was a sensitive indicator for evaluating the performance of photosystem II (PSII) activity with the different N applications and varieties. Increased quantum yield and efficiency with more active reaction centers (RCs) were observed under increased N application as well as with variety GY605, leading to higher energy utilization efficiencies. However, superior photosynthetic apparatus in pods is not recommended in high-quality seed breeding because it would increase the contents of glucosinolates and erucic acid. In addition, the random forest (RF) algorithm was proven to be effective in feature selection, and the selected fluorescence parameters mostly showed high correlations with seed yield and quality. These results demonstrate the potential of the ChlF method for assessing the seed yield and quality of oilseed rape at the early podding stage, which could also be useful for advancing crop breeding and improving agronomic management. Keywords: Agronomic management, Chlorophyll fluorescence, Crop varieties, JIP-test, Oilseed rape, Seed quality, Seed yield.

The Effect of Arbuscular Mycorrhizal Fungi on Photosystem II of the Host Plant Under Salt Stress: A Meta-Analysis

As important components of the photosynthetic apparatus, photosystems I (PS I) and II (PS II) are sensitive to salinity. Salt stress can destroy the PS II reaction center, disrupt electron transport from PS II to PS I, and ultimately lead to a decrease in the photosynthetic capacity of the plant. Arbuscular mycorrhizal fungi (AMF) can enhance the photosynthetic capacity of a host plant under salinity stress. However, this specific effect of AMF is not always predictable. Here, we conducted a meta-analysis including 436 independent observations to compare chlorophyll fluorescence parameters in response to AMF inoculation under salt stress. The results showed that AMF inoculation had a positive total impact on photosynthesis in the host plant. Subgroup analysis showed that annual host plants had better performance in terms of photosynthesis after inoculation. The mitigating effects of AMF on the photosynthetic rate (Pn), actual quantum yield of photochemical energy conversion in PS II (ɸPS II), and electron transfer rate (ETR) in C4 species were higher than those in C3 species. Moreover, the photosynthesis performance of monocotyledon species was better than that of dicotyledon species after AMF inoculation. The woody host plants had higher energy utilization by way of an enhanced electron transfer rate to reduce energy dissipation after AMF inoculation. Finally, the mitigating effect of AMF on plants under moderate salinity was stronger than that under high salinity. Among AMF species, Funneliformis mosseae was found to be the most effective in enhancing the photosynthesis performance of plants. For the analyzed dataset, AMF inoculation alleviated the detrimental effects of salinity on photosystem II of the host plant by improving the utilization of photons and photosynthetic electron transport, and also by reducing the susceptibility of photosystem II to photoinhibition.

Scaling Relationships between Leaf Shape and Area of 12 Rosaceae Species

Leaf surface area (A) and leaf shape have been demonstrated to be closely correlated with photosynthetic rates. The scaling relationship between leaf biomass (both dry weight and fresh weight) and A has been widely studied. However, few studies have focused on the scaling relationship between leaf shape and A. Here, using more than 3600 leaves from 12 Rosaceae species, we examined the relationships of the leaf-shape indices including the left to right side leaf surface area ratio (AR), the ratio of leaf perimeter to leaf surface area (RPA), and the ratio of leaf width to length (RWL) versus A. We also tested whether there is a scaling relationship between leaf dry weight and A, and between PRA and A. There was no significant correlation between AR and A for each of the 12 species. Leaf area was also found to be independent of RWL because leaf width remained proportional to leaf length across the 12 species. However, there was a negative correlation between RPA and A. The scaling relationship between RPA and A held for each species, and the estimated scaling exponent of RPA versus A approached −1/2; the scaling relationship between leaf dry weight and A also held for each species, and 11 out of the 12 estimated scaling exponents of leaf dry weight versus A were greater than unity. Our results indicated that leaf surface area has a strong scaling relationship with leaf perimeter and also with leaf dry weight but has no relationship with leaf symmetry or RWL. Additionally, our results showed that leaf dry weight per unit area, which is usually associated with the photosynthetic capacity of plants, increases with an increasing A because the scaling exponent of leaf dry weight versus A is greater than unity. This suggests that a large leaf surface area requires more dry mass input to support the physical structure of the leaf.

Improve Plant Photosynthesis by a New Slow-Release Carbon Dioxide Gas Fertilizer.

In the natural state, the concentration of carbon dioxide in the atmosphere is about 300 μmol mol–1. Plants need a suitable balance of CO2 to achieve optimal growth. The optimum CO2 content corresponding to a high photosynthesis rate is between 0.1 and 1.0% by volume. However, air has only a CO2 content of 0.03% by volume, so plants cannot use all of their growth potential. The use of fertilizer to assist in the supply of CO2 increases the rate of photosynthesis. In this work, a slow-release CO2 gas fertilizer inspired by polyphenol chemistry was prepared to provide sustainable CO2 that could improve plant photosynthetic capacity and get a higher crop yield. The core–shell structure was designed to confer gas fertilizers slow-release property. Micron-sized calcium carbonate particles with uniform particle size and regularity morphology, as carbon sources for plant photosynthesis, was a core, and tannic acid was coated on it as a shell via oxidative oligomerization and cross-linked by polyetherimide. The structure and morphology of fertilizers were characterized by scanning electron microscopy, X-ray energy dispersive spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. In vitro experiments, the prepared fertilizers were proved to have slow-release properties. And then through net photosynthesis rate, chlorophyll fluorescence parameters, chlorophyll content, leaf area, leaf mass per area, and dry matter to study the effects of slow-release CO2 gas fertilizers on plant physiology of Brassica chinensis. The results revealed that the slow-release CO2 gas fertilizers not only had good slow-release properties but also can well improve plant photosynthesis.

A photosynthesis continuous monitoring system for CAM plants

Diurnal CO2 exchanges in crassulacean acid metabolism (CAM) plants are significantly different from those in C3 and C4 plants. The instantaneous short-time CO2 exchange of a single leaf measured by commercial portable photosynthesis measuring systems with a small leaf chamber cannot reflect the plant photosynthetic capacity for CAM plants because of the CO2 fixation property. Therefore, a photosynthesis continuous monitoring system with two canopy cuvettes was developed for measuring diurnal net CO2 exchange rates for CAM plants. To evaluate stability and applicability of the photosynthesis continuous monitoring system, continuous measurement of net CO2 exchange rates of plants with different photosynthetic pathways were conducted. An obligate CAM plant (Kalanchoe daigremontiana), four facultative CAM plants (Dendrobium officinale, D. chrysotoxum, D. nobile, and D. primulinum), a C3 plant (Strawberry, Fragaria ananassa), and a C4 plant (Corn, Zea mays) were selected as model plants. K. daigremontiana had a significant CO2 absorption during the dark period and its net CO2 exchange rates fluctuated around 0 μmol/(m2•s) during the photoperiod in a growth chamber. Net CO2 exchange rates of F. ananassa and Z. mays in a greenhouse gradually increased after sunrise, reaching a maximum at about 12:00, and then gradually decreased to negative values during the night time. It is interesting to observe that D. officinale in the greenhouse and growth chamber absorbed CO2 during both day and night times. The photosynthetic pathways of D. chrysotoxum, D. nobile, and D. primulinum were also well distinguished by this photosynthesis continuous monitoring system. The results showed that the photosynthesis continuous monitoring system is capable for quantitative evaluation of diurnal net CO2 exchange characteristics not only in the CAM plants but also in small size C3 and C4 plants with low net photosynthetic rates for long-time and high-accuracy measurements. Keywords: diurnal net CO2 exchanges, infrared CO2 analyzer, mass airflow meter, net photosynthetic rate, photosynthetic pathway DOI: 10.25165/j.ijabe.20191203.4885 Citation: Cheng Y S, He D X. A photosynthesis continuous monitoring system for CAM plants. Int J Agric & Biol Eng, 2019; 12(3): 141–146.

Effects of organic fertilizer application on accumulation and distribution of assimilates in winter wheat

To understand the effects of organic fertilizer addition on accumulation and distribution of winter wheat assimilates, we compared organic carbon content in soil and wheat plants, photosynthetic characteristics and assimilation transformation under two different fertilizer treatments, CF (chemical fertilizer only) and OF (organic fertilizer with chemical fertilizer), using 13CO2 pulse labeling method. The results showed that OF increased soil organic carbon content and wheat photosynthetic parameters, resulting in higher organic carbon content and total dry biomass accumulation in wheat plants compared with CF treatment. Compared marking to maturity with that on the 7th day after the same marking, the content and distribution rate of 13C in leaves and stems of two treatments decreased; the 13C content in spikes increased at jointing stage and filling stage, decreased at anthesis stage, and the 13C distribution rate increased at all stages. OF treatment was more beneficial for the transportation of photosynthetic product from leaves to spikes at filling stage, with higher 13C distribution rate in spikes compared with CF treatment. The results of correlation analysis showed that dry matter accumulation was significantly positively correlated with the net input of 13C content and its distribution rate, but negatively correlated with organic carbon content in plants. The net input of 13C content was significantly positively correlated with its distribution rate, and negatively correlated with Fv/Fm and Pn. In conclusion, organic fertilizer application could increase the content of organic carbon in soil, improve wheat plants photosynthetic capacity and transportation of photosynthetic product to spikes, and ultimately increase dry matter accumulation in wheat spikes.

Physiological and biochemical responses of the salt-marsh plant Spartina alterniflora to long-term wave exposure

Ecosystem-based flood defence including salt-marsh as a key component is increasingly applied worldwide due to its multifunctionality and cost-effectiveness. While numerous experiments have explored the wave-attenuation effects of salt-marsh plants critical to flood protection, little is known about the physiological and biochemical responses of these species to continuous wave exposure. To address this knowledge gap, we developed a shallow-water wave simulator to expose individual Spartina alterniflora plants to waves in a greenhouse for 8 weeks. S. alterniflora individuals were partially submerged and experienced horizontal sinusoidal motion to mimic plant exposure to shallow water waves. A factorial experiment was used to test the effects of three wave heights (4.1 cm, 5.5 cm and a no-wave control) and two wave periods (2 s and 3 s) on the following key physiological and biochemical plant parameters: plant growth, antioxidant defence and photosynthetic capacity. Comparison of wave treatment and control groups supported our hypotheses that wave exposure leads to oxidative stress in plants and suppresses plant photosynthetic capacity and thereby growth. In response, the wave-exposed plants exhibited activated antioxidant enzymes. Comparison between the different wave treatment groups suggested the wave effects to be generally correlated positively with wave height and negatively with wave period, i.e. waves with greater height and frequency imposed more stress on plants. In addition, wave-exposed plants tended to allocate more biomass to their roots. Such allocation is favourable because it enhances root anchorage against the wave impact. Simulated wave exposure systems such as the one used here are an effective tool for studying the response of salt-marsh plants to long-term wave exposure, and so help inform ecosystem-based flood defence projects in terms of plant selection, suitable transplantation locations and timing, etc. Given the projected variability of the global wave environment due to climate change, understanding plant response to long-term wave exposure has important implications for salt-marsh conservation and its central role in natural flood defence.

Grazing enhances plant photosynthetic capacity by altering soil nitrogen in alpine grasslands on the Qinghai-Tibetan plateau

The eco-physiological processes associated with the influences of grazing on plant traits and soil properties of alpine grasslands has remained poorly understood. To determine the effects of grazing on photosynthesis of alpine grassland plants, we measured nutrient level in plant and soil, as well as photosynthetic parameters of common herbage species in the grazed and fenced plots of an alpine meadow and an alpine steppe on Qinghai-Tibetan plateau. The results showed that grazing significantly enhanced most herbages’ carbon(C) and nitrogen (N) content, net photosynthetic rate (A), stomatal conductance (gs), intercellular CO2 concentration (Ci), transpiration rate (Tr), water use efficiency (WUE) and light use efficiency (LUE), as well as soil C and N content. Through the SEM modeling, we found both direct and indirect paths that grazing enhanced plants photosynthetic capacity. Grazing can directly enhance soil N content and thus promote plant N uptake, further increase plant gs, WUE and LUE, finally promote the A of plants. Additionally, grazing can also directly enhanced plant photosynthetic capacity through promoting the plant gs. Soil N and plant gs are the two key factors that determine the improvement of photosynthetic capacity under grazing. Sustainable moderate grazing management is expected to promote the photosynthetic potentials of alpine plants mainly through the improvement of soil N.

Terminal heat tolerance in wheat: An overview

Since the beginning of the century, ambient temperatures have increased and are predicted to rise further under climate change. Heat stress is a rigorous threat, particularly during reproductive and grain-filling phases, that results into yield loss. Reductions in dry matter accumulation and grain yield, caused by reduced plant photosynthetic capacity through metabolic limitations and oxidative damage to chloroplasts due to heat stress. Wheat prebreeding and breeding may be based on secondary traits like chlorophyll content, chlorophyll fluorescence and grain number under heat stress. On the other hand, grain yield under heat stress can be improved by selecting genotypes for the rate of grain filling and for grain size. Wheat varieties with improved grain yield can be developed by integrating physiology and biotechnological tools with conventional breeding techniques during reproductive and grain-filling phases. In this review, we have discussed the effect of heat stress on wheat reproductive and grain-filling stages and the strategies to improve terminal heat stress tolerance in wheat. Doi.org/10.25174/2249-4065/2019/79252

Photosynthesis continuous monitoring system for CAM plants

Diurnal CO2 exchanges in crassulacean acid metabolism (CAM) plants are significantly different from those in C3 and C4 plants. The instantaneous short-time CO2 exchange of a single leaf measured by commercial portable photosynthesis measuring systems with a small leaf chamber cannot reflect the plant photosynthetic capacity for CAM plants because of the CO2 fixation property. Therefore, a photosynthesis continuous monitoring system with two canopy cuvettes was developed for measuring diurnal net CO2 exchange rates for CAM plants. To evaluate stability and applicability of the photosynthesis continuous monitoring system, continuous measurement of net CO2 exchange rates of plants with different photosynthetic pathways were conducted. An obligate CAM plant (Kalanchoe daigremontiana), four facultative CAM plants (Dendrobium officinale, D. chrysotoxum, D. nobile, and D. primulinum), a C3 plant (Strawberry, Fragaria ananassa), and a C4 plant (Corn, Zea mays) were selected as model plants. K. daigremontiana had a significant CO2 absorption during the dark period and its net CO2 exchange rates fluctuated around 0 μmol/(m2•s) during the photoperiod in a growth chamber. Net CO2 exchange rates of F. ananassa and Z. mays in a greenhouse gradually increased after sunrise, reaching a maximum at about 12:00, and then gradually decreased to negative values during the night time. It is interesting to observe that D. officinale in the greenhouse and growth chamber absorbed CO2 during both day and night times. The photosynthetic pathways of D. chrysotoxum, D. nobile, and D. primulinum were also well distinguished by this photosynthesis continuous monitoring system. The results showed that the photosynthesis continuous monitoring system is capable for quantitative evaluation of diurnal net CO2 exchange characteristics not only in the CAM plants but also in small size C3 and C4 plants with low net photosynthetic rates for long-time and high-accuracy measurements. Keywords: diurnal net CO2 exchanges, infrared CO2 analyzer, mass airflow meter, net photosynthetic rate, photosynthetic pathway DOI: 10.25165/j.ijabe.20191203.4885 Citation: Cheng Y S, He D X. A photosynthesis continuous monitoring system for CAM plants. Int J Agric & Biol Eng, 2019; 12(3): 141–146.

Impaired electron transfer accounts for the photosynthesis inhibition in wheat seedlings (Triticum aestivum L.) subjected to ammonium stress.

No single mechanism can provide an adequate explanation for the inhibition of photosynthesis when plants are supplied with ammonium (NH4 + ) as the sole nitrogen (N) source. We performed a hydroponic experiment using two N sources [5mM NH4 + and 5mM nitrate (NO3 - )] to investigate the effects of NH4 + stress on the photosynthetic capacities of two wheat cultivars (NH4 + -sensitive AK58 and NH4 + -tolerant XM25). NH4 + significantly inhibited the growth and light-saturated photosynthesis (Asat ) of both cultivars, but the extent of such inhibition was greater in the NH4 + -sensitive AK58. The CO2 concentration did not limit CO2 assimilation under NH4 + nutrition; though both stomatal and mesophyll conductance were significantly suppressed. Carboxylation efficiency (CE), light-saturated potential rate of electron transport (Jmax ), the quantum efficiency of PSII (ΦPSII ), electron transport rate through PSII [Je(PSII)], and Fv /Fm were significantly reduced by NH4 + . As a result, NH4 + nutrition resulted in a significant increase in the production of hydrogen peroxide (H2 O2 ) and superoxide anion radicals (O2 •- ), but these symptoms were less severe in the NH4 + -tolerant XM25, which had a higher capacity of removing elevated reactive oxygen species (ROS). Thus, NH4 + N sources might decreased electron transport efficiency and increased the production of ROS, exacerbating damage to the electron transport chain, leading to a reduced plant photosynthetic capacity.

Leaf traits of C3- and C4-plants indicating climatic adaptation along a latitudinal gradient in Southern Siberia and Mongolia

Increasing aridity is one of the most important trends of current climate change. Leaf functional traits suggest a substantial basis for assessing the aridity effects on vegetation. However, since plants possess diverse leaf morphology and anatomy due to different evolutionary history of taxa, the effect of aridity can hardly be revealed in a multi-species analysis. We studied leaf functional traits for 317 samples of 193 plant species in steppe and desert communities along a 1600-km latitudinal gradient in Southern Siberia (Transbaikalia, Russia) and Mongolia. We determined morphological leaf traits, quantitative anatomical parameters, physiological parameters, and photosynthetic pigments content. Different relevance of leaf traits for indication of plant response to climate has been demonstrated. The clearest changes in site-mean values along the aridity gradient were shown for leaf thickness, total chloroplast number per leaf area (Nchl/A) and total surface area of chloroplasts (Achl/A) and cells (Ames/A) per leaf area. Unlike leaf size and leaf mass per area, these quantitative mesophyll parameters related to plant photosynthetic capacity were strongly correlated with climate. We found no evidence for a decrease in sizes of mesophyll cells with aridity, but cell volume as well as chloroplast number per cell were linked with plant functional type (PFT). We revealed an increase in Nchl/A and Achl/A in desert-steppe species in comparison to steppe and forest-steppe vegetation types within each PFT of C3-plants (C3-dicot herbs, C3-dicot shrubs, C3-monocots and C3-succulents). C4-plants were generally characterized by low Achl/A and Ames/A, but had higher rate of CO2-transfer through mesophyll and chloroplast surfaces. C3- and C4-plants differed in response to aridity and showed opposite trends in changes of leaf traits along the aridity gradient. We conclude that leaf mesophyll traits contribute to important mechanism of climatic adaptation in different PFTs along a large latitudinal gradient.

Effects of drought stress on photosynthesis and chlorophyll fluorescence images of soybean (Glycine max) seedlings

The main purpose of this research is to provide a theoretical foundation for the screening of drought-resistant soybean varieties and to establish an efficient method to detect the PSII actual photochemical quantum yields efficiently. Three soybean varieties were compared in this experiment after 15 d when they were planted in a greenhouse. These varieties were then exposed to light drought stress (LD) and serious drought stress (SD) conditions. With five times’ measurement, chlorophyll fluorescence and soil-plant analysis development considered as the main basis for this study. Several parameters in SD conditions significantly reduced, such as net photosynthetic rates (Pn), stomatal conductance (Gs), PSII primary light energy conversion efficiency (Fv/FM), PSII actual photochemical quantum yields [Y(II)], photochemical quenching coefficient (qP) and non-photochemical quenching coefficient (qN). The soybeans in the seedling stage adapted to the inhibitory effect of drought stress on photosynthesis through stomatal limitation. Under serious drought stress, non-stomatal limitation damaged the plant photosynthetic system. The amplitudes of Pn and Y(II) of drought-resistant Qihuang 35 were lower than those of the two other varieties. Based on the data of this study, a new method had been developed to detect Y (II) which reflected the photosynthetic capacity of plant, R=0.85989, u=0.048803 when using multiple linear regression, and R=0.84285, u=0.054739 when using partial least square regression. Keywords: soybean seedling, drought stress, photosynthetic parameters, chlorophyll fluorescence parameters, chlorophyll fluorescence images DOI: 10.25165/j.ijabe.20181102.3390 Citation: Wang W S, Wang C, Pan D Y, Zhang Y K, Luo B, Ji J W. Effects of drought stress on photosynthesis and chlorophyll fluorescence images of soybean (Glycine max) seedlings. Int J Agric & Biol Eng, 2018; 11(2): 196–201.