Leaf Chamber Research Articles

Investigation on absorption cross-section of photosynthetic pigment molecules based on a mechanistic model of the photosynthetic electron flow-light response in C3, C4 species and cyanobacteria grown under various conditions.

Investigation on intrinsic properties of photosynthetic pigment molecules participating in solar energy absorption and excitation, especially their eigen-absorption cross-section (σ ik) and effective absorption cross-section (σ ' ik), is important to understand photosynthesis. Here, we present the development and application of a new method to determine these parameters, based on a mechanistic model of the photosynthetic electron flow-light response. The analysis with our method of a series of previously collected chlorophyll a fluorescence data shows that the absorption cross-section of photosynthetic pigment molecules has different values of approximately 10-21 m2, for several photosynthetic organisms grown under various conditions: (1) the conifer Abies alba Mill., grown under high light or low light; (2) Taxus baccata L., grown under fertilization or non-fertilization conditions; (3) Glycine max L. (Merr.), grown under a CO2 concentration of 400 or 600 μmol CO2 mol-1 in a leaf chamber under shaded conditions; (4) Zea mays L., at temperatures of 30°C or 35°C in a leaf chamber; (5) Osmanthus fragrans Loureiro, with shaded-leaf or sun-leaf; and (6) the cyanobacterium Microcystis aeruginosa FACHB905, grown under two different nitrogen supplies. Our results show that σ ik has the same order of magnitude (approximately 10-21 m2), and σ ' ik for these species decreases with increasing light intensity, demonstrating the operation of a key regulatory mechanism to reduce solar absorption and avoid high light damage. Moreover, compared with other approaches, both σ ik and σ ' ik can be more easily estimated by our method, even under various growth conditions (e.g., different light environment; different CO2, NO2, O2, and O3 concentrations; air temperatures; or water stress), regardless of the type of the sample (e.g., dilute or concentrated cell suspensions or leaves). Our results also show that CO2 concentration and temperature have little effect on σ ik values for G. max and Z. mays. Consequently, our approach provides a powerful tool to investigate light energy absorption of photosynthetic pigment molecules and gives us new information on how plants and cyanobacteria modify their light-harvesting properties under different stress conditions.

Evaluate the photosynthesis and chlorophyll fluorescence of Epimedium brevicornu Maxim

The diurnal variation of photosynthesis, light response curve and CO2 response curve in Epimedium brevicornu Maxim leaves were determined with Li-6400 photosynthesis system to evaluate the photosynthesis of E. brevicornu. Fluorescence of chlorophyll in the leaves were determined with PAM-2500 portable chlorophyll fluorescence apparatus in the study. The results showed that the midday depression of photosynthesis was very obvious in the E. brevicornu leaves. The light compensation point of E. brevicornu leaves was about 15 µmol m−2 s−1. The light saturation point of E. brevicornu leaves was below 800 µmol m−2 s−1, which was lower than the general sunlight intensity at noon in summer. The CO2 saturation point of E. brevicornu leaves was much higher than the content of CO2 in general air. E. brevicornu was a typical shade plant and could survive in very low sunlight. E. brevicornu could not endure strong sunlight and high air temperature. The net photosynthetic rate of E. brevicornu leaves linearly correlated with the content of CO2 in the leaf chamber when the content was below CO2 saturation point. E. brevicornu possessed great potential of photosynthesis.

Tracing plant source water dynamics during drought by continuous transpiration measurements: An in-situ stable isotope approach.

The isotopic composition of xylem water (δX ) is of considerable interest for plant source water studies. In-situ monitored isotopic composition of transpired water (δT ) could provide a nondestructive proxy for δX -values. Using flow-through leaf chambers, we monitored 2-hourly δT -dynamics in two tropical plant species, one canopy-forming tree and one understory herbaceous species. In an enclosed rainforest (Biosphere 2), we observed δT -dynamics in response to an experimental severe drought, followed by a 2 H deep-water pulse applied belowground before starting regular rain. We also sampled branches to obtain δX -values from cryogenic vacuum extraction (CVE). Daily flux-weighted δ18 OT -values were a good proxy for δ18 OX -values under well-watered and drought conditions that matched the rainforest's water source. Transpiration-derived δ18 OX -values were mostly lower than CVE-derived values. Transpiration-derived δ2 HX -values were relatively high compared to source water and consistently higher than CVE-derived values during drought. Tracing the 2 H deep-water pulse in real-time showed distinct water uptake and transport responses: a fast and strong contribution of deep water to canopy tree transpiration contrasting with a slow and limited contribution to understory species transpiration. Thus, the in-situ transpiration method is a promising tool to capture rapid dynamics in plant water uptake and use by both woody and nonwoody species.

Construction of a photosynthetic rate prediction model for greenhouse strawberries with distributed regulation of light environment.

In winter and spring, for greenhouses with larger areas and stereoscopic cultivation, distributed light environment regulation based on photosynthetic rate prediction model can better ensure good crop growth. In this paper, strawberries at flowering-fruit stage were used as the test crop, and the LI-6800 portable photosynthesis system was used to control the leaf chamber environment and obtain sample data by nested photosynthetic rate combination experiments under temperature, light and CO2 concentration conditions to study the photosynthetic rate prediction model construction method. For a small-sample, nonlinear real experimental data set validated by grey relational analysis, a photosynthetic rate prediction model was developed based on Support vector regression (SVR), and the particle swarm algorithm (PSO) was used to search the influence of the empirical values of parameters, such as the penalty parameter C, accuracy ε and kernel constant g, on the model prediction performance. The modeling and prediction results show that the PSO-SVR method outperforms the commonly used algorithms such as MLR, BP, SVR and RF in terms of prediction performance and generalization on a small sample data set. The research in this paper achieves accurate prediction of photosynthetic rate of strawberry and lays the foundation for subsequent distributed regulation of greenhouse strawberry light environment.

Are Wild Blueberries a Crop with Low Photosynthetic Capacity? Chamber-Size Effects in Measuring Photosynthesis

Wild lowbush blueberries, an important fruit crop native to North America, contribute significantly to the economy of Maine, USA, Atlantic Canada, and Quebec. However, its photosynthetic capacity has not been well-quantified, with only a few studies showing its low photosynthetic rates. Its small leaves make accurate leaf-level photosynthetic measurements difficult and introduce potential uncertainties in using large leaf chambers. Here, we determined the photosynthetic rate for five different wild blueberry genotypes using a big leaf chamber enclosing multiple leaves and a small leaf chamber with a single leaf to test whether using big leaf chambers (branch-level measurements) underestimates the photosynthetic capacity. Photosynthetic rates of wild blueberries were significantly (35–47%) lower when using the big leaf chamber, and they are not a crop with low photosynthetic capacity, which can be as high as 16 μmol m−2 s−1. Additionally, wild blueberry leaves enclosed in the big chamber at different positions of a branch did not differ in chlorophyll content and photosynthetic rate, suggesting that the difference was not caused by variation among leaves but probably due to leaf orientations and self-shading in the big chamber. A significant linear relationship between the photosynthetic rate measured by the small and big leaf chambers suggests that the underestimation in leaf photosynthetic capacity could be corrected. Therefore, chamber-size effects need to be considered in quantifying photosynthetic capacity for small-leaf crops, and our study provided important guidelines for future photosynthesis research. We also established the relationship between the Electron Transport Rate (ETR) and photosynthetic CO2 assimilation for wild blueberries. ETR provides an alternative to quantify photosynthesis, but the correlation coefficient of the relationship (R2 = 0.65) suggests that caution is needed in this case.

Behavioural responses of females of the eriophyoid mite, Aculops allotrichus, to the presence of injured conspecifics

ABSTRACT In many animal taxa, the presence of injured conspecifics triggers escape or freezing behaviour. We examined these anti-predatory responses in the eriophyoid mite Aculops allotrichus from Robinia pseudoacacia. The mite was tested on leaflets in cages with two leaf chambers connected by a tunnel, on compound leaves, on which only two opposite leaflets remained, and on leaf discs placed on glass. We released females onto a site with freshly pierced individuals and allowed them to move to a “safe” place. Females did not escape from dangerous patches in any of our tests. They did not refrain from oviposition or become motionless in the presence of damaged conspecifics, either. On the contrary, in the test with old leaf discs, females prolonged their stay on “risky” patches. Additionally, after five hours the proportion of females in chambers with pierced conspecifics was significantly higher than in the control, and only after 24 hours were there no differences between the two combinations. It indicates that the presence of injured conspecifics is not a cue of predation risk for A. allotrichus. In contrast, the eriophyoid can be arrested on “dangerous” leaves, and possible factors underlying this phenomenon are discussed.

MIC-100, a new system for high-throughput phenotyping of instantaneous leaf photosynthetic rate in the field.

Photosynthesis occurs mainly in plant leaves and is a fundamental process in the global carbon cycle and in crop production. The exploitation of natural genetic variation in leaf photosynthetic capacity is a promising strategy to meet the increasing demand for crops. The present study reports the newly developed photosynthesis measurement system 'MIC-100,' with a higher throughput for measuring instantaneous photosynthetic rate in the field. MIC-100 is established based on the closed system and directly detects the CO2 absorption in the leaf chamber. The reproducibility, accuracy, and measurement throughput of MIC-100 were tested using soybean (Glycine max L. (Merr.)) and rice (Oryza sativa L.) grown under field conditions. In most cases, the coefficient of variance (CV) for repeated-measurements of the same leaf was less than 0.1. The photosynthetic rates measured with the MIC-100 model showed a significant correlation (R2 = 0.93-0.95) with rates measured by a widely used gas-exchange system. The measurement throughput of the MIC-100 is significantly greater than that of conventional open gas-exchange systems under field conditions. Although MIC-100 solely detects the instantaneous photosynthetic rate under a given environment, this study demonstrated that the MIC-100 enables the rough evaluation of leaf photosynthesis within the large-scale plant populations grown in the field.

Modification of a gas exchange system to measure active and passive chlorophyll fluorescence simultaneously under field conditions.

Solar-induced fluorescence (SIF) is a promising tool to estimate photosynthesis across scales; however, there has been limited research done at the leaf level to investigate the relationship between SIF and photosynthesis. To help bridge this gap, a LI-COR LI-6800 gas exchange instrument was modified with a visible-near-infrared (VIS-NIR) spectrometer to measure active and passive fluorescence simultaneously. The system was adapted by drilling a hole into the bottom plate of the leaf chamber and inserting a fibre-optic to measure passive steady-state fluorescence (F t , λ , analogous to SIF) from the abaxial surface of a leaf. This new modification can concurrently measure gas exchange, passive fluorescence and active fluorescence over the same leaf area and will allow researchers to measure leaf-level F t , λ in the field to validate tower-based and satellite measurements. To test the modified instrument, measurements were performed on leaves of well-watered and water-stressed walnut plants at three light levels and a constant air temperature. Measurements on these same plants were also conducted using a similarly modified Walz GFS-3000 gas exchange instrument to compare results. We found a positive linear correlation between F t , λ measurements from the modified LI-6800 and GFS-3000 instruments. We also report a positive linear relationship between F t , λ and normalized steady-state chlorophyll fluorescence (F t /F o ) from the pulse-amplitude modulation (PAM) fluorometer of the LI-6800 system. Accordingly, this modification will inform the link between spectrally resolved F t , λ and gas exchange-leading to improved interpretation of how remotely sensed SIF tracks changes in the light reactions of photosynthesis.

Measuring Biosphere-Atmosphere Exchange of Short-Lived Climate Forcers and Their Precursors.

Exchange of reactive trace gases over the biosphere is a key source of reactive organic carbon to the atmosphere and thus influences the formation of both ozone (O3) and secondary organic aerosol (SOA). Both O3 and aerosol particles are short-lived climate forcers and impact the radiative balance of the planet, and their sources and sinks are chemically complex. However, the biosphere also acts as a deposition sink for organic and inorganic compounds, including O3, aerosols, and their precursors. Wet and dry deposition provides a key lever on the lifetime of trace gases and particles in the atmosphere and thus on their potential to influence the radiative balance of the planet. The fluxes of reactive trace gases and particles are part of an atmospheric biogeochemical cycle that includes feedbacks through drought and other climate components.Recent advances in measurement techniques have enabled new field observations of trace gas and particle fluxes. Our method development has focused on the leaf, branch, and forest level, although satellite measurements coupled to modeling also provide promising new approaches to constraining trace gas fluxes. Leaf chamber measurements of volatile organic compound (VOC) emissions highlight leaf-to-leaf and plant-to-plant variability in both photosynthesis and emissions of individual VOCs, in addition to differences in emissions across different isomers of monoterpenes. Isomers obviously have different chemical properties (e.g., reaction rates with OH radicals, SOA yield) and thus hold different potentials as precursors for short-lived climate forcers.The biosphere acts as both sources and sinks of the oxidation products of monoterpenes and other biogenic VOCs. Developments in chemical ionization mass spectrometry have recently enabled measurements of volatile organic acids, which demonstrate a strong temperature-dependent ecosystem source, as well as a source from in-canopy chemistry. In-canopy chemistry also influences particle fluxes, although deposition should dominate their net exchange. Our field observations of chemically resolved particle fluxes demonstrate the simultaneous, competing processes driving forest exchange. To separate out these competing processes, we use black carbon as an inert tracer for particle deposition. Our recent measurements demonstrate the importance of wet deposition in controlling particle lifetime in the atmosphere. Overall, new measurement techniques have enabled both field and laboratory observations to improve our understanding of biosphere-atmosphere interactions and their influence on climate processes.

Measuring Rapid A-Ci Curves in Boreal Conifers: Black Spruce and Balsam Fir.

Climate change is steering tree breeding programs towards the development of families and genotypes that will be adapted and more resilient to changing environments. Making genotype–phenotype–environment connections is central to these predictions and it requires the evaluation of functional traits such as photosynthetic rates that can be linked to environmental variables. However, the ability to rapidly measure photosynthetic parameters has always been limiting. The estimation of V c,max and J max using CO2 response curves has traditionally been time consuming, taking anywhere from 30 min to more than an hour, thereby drastically limiting the number of trees that can be assessed per day. Technological advancements have led to the development of a new generation of portable photosynthesis measurement systems offering greater chamber environmental control and automated sampling and, as a result, the proposal of a new, faster, method (RACiR) for measuring V c,maxand J max. This method was developed using poplar trees and involves measuring photosynthetic responses to CO2 over a range of CO2 concentrations changing at a constant rate. The goal of the present study was to adapt the RACiR method for use on conifers whose measurement usually requires much larger leaf chambers. We demonstrate that the RACiR method can be used to estimate V c,max and J max in conifers and provide recommendations to enhance the method. The use our method in conifers will substantially reduce measurement time, thus greatly improving genotype evaluation and selection capabilities based on photosynthetic traits. This study led to the developpement of an R package (RapidACi, https://github.com/ManuelLamothe/RapidACi) that facilitates the correction of multiple RACiR files and the post-measurement correction of leaf areas.

The quantitative impact of different leaf temperature determination on computed values of stomatal conductance and internal CO2 concentrations

The LI-COR 6400 portable photosynthesis system is the most widely used and cited instrument for measuring leaf gas exchange in plant physiology. The focus of this paper is to evaluate three ways of computing/measuring leaf temperature: the LI-COR energy budget computation, the LI-COR leaf thermocouple (T/C), and an infra-red (IR) sensor chip (MLX90615) incorporated into the LI-6400 leaf chamber. The IR-sensor was calibrated against known targets, and then used to cross check the other two methods. The results showed that the IR-sensor was superior to the LI-COR thermocouple and agreed closer with the energy budget values of leaf temperature. The magnitudes of the errors were quantified in terms of °C difference in leaf temperature measured by T/C (as control) and IR sensor versus percentage difference in stomatal conductance (gs) and intercellular CO2 concentration (Ci) computed from leaf temperature. The temperature difference (IR versus other methods) in the range of -1.89 to 1.58 °C resulted in relative errors in gs from 14.7% to -18.0% and Ci from 16.5% to -7.8% of the values reported by the standard LI-6400 calculations depending on species and temperature. Reasons are given for trusting the IR-sensor over the other methods and it is suggested that the next generation LI-COR photosynthesis system include an IR-sensor.

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.

A novel approach for real-time monitoring of leaf wounding responses demonstrates unprecedently fast and high emissions of volatiles from cut leaves

Wounding is a key plant stress that results in a rapid, within seconds to a few minutes, release of ubiquitous stress volatiles and stored volatiles in species with storage structures. Understanding the timing and extent of wound-dependent volatile elicitation is needed to gain an insight into different emission controls, but real-time monitoring of plant emissions through wounding treatments has been hampered by the need to stop the measurements to perform the wounding, slow stabilization of gas flows upon chamber closure and smearing out the signal by large chambers and long sampling lines. We developed a novel leaf cutter that allows to rapidly perform highly precise leaf cuts within the leaf chamber. The cutter was fitted to the standard Walz GFS-3000 portable gas-exchange system leaf chamber and chamber exhaust air for analysis with a proton transfer reaction time-of-flight mass-spectrometer (PTR-TOF-MS) was taken right at the leaf chamber outlet. Wounding experiments in four species of contrasting leaf structure demonstrated significant species differences in timing, extent and blend of emitted volatiles, and showed unprecedently high emission rates of several stress volatiles and stored monoterpenes. In light of the rapid rise of release of de novo synthesized and stored volatiles, the results of this study suggest that past studies have underestimated the rate of elicitation and maximum emission rates of wound-dependent volatiles.

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.

Changes in photosynthesis with increasing salinity in mangrove ecosystem

The present study was carried out in Lumnitzera racemosa Willd. a dicotyledonous mangrove (family: Combretaceae). NaCl at the rate of 0 (control), 100, 200, 300, 400, 500, 600, 700, 800, 900 and 1000 mM were given to 1 month old and fully established seedlings. Samplings were done on 60th 120th and 180th days after NaCl treatment. Chlorophyll, carotenoids, Net leaf photosynthesis, photosynthetic carboxylases and amylases were estimated from the samples. Salinity from sodium chloride encouraged the synthesis of carotenoid and chlorophyll in L. racemosa to the ideal concentration. When NaCl salinity is increased, photosynthetic properties such net leaf photosynthesis, stomatal conductance, transpiration, leaf chamber temperature, and intercellular CO2 concentration decreased. This information can be used to assess the effect of increasing concentration of salinity in crop plants.

The effect of ozone fumigation on the biogenic volatile organic compounds (BVOCs) emitted from Brassica napus above- and below-ground.

The emissions of BVOCs from oilseed rape (Brassica napus), both when the plant is exposed to clean air and when it is fumigated with ozone at environmentally-relevant mixing ratios (ca. 135 ppbv), were measured under controlled laboratory conditions. Emissions of BVOCs were recorded from combined leaf and root chambers using a recently developed Selective Reagent Ionisation—Time of Flight—Mass Spectrometer (SRI-ToF-MS) enabling BVOC detection with high time and mass resolution, together with the ability to identify certain molecular functionality. Emissions of BVOCs from below-ground were found to be dominated by sulfur compounds including methanethiol, dimethyl disulfide and dimethyl sulfide, and these emissions did not change following fumigation of the plant with ozone. Emissions from above-ground plant organs exposed to clean air were dominated by methanol, monoterpenes, 4-oxopentanal and methanethiol. Ozone fumigation of the plants caused a rapid decrease in monoterpene and sesquiterpene concentrations in the leaf chamber and increased concentrations of ca. 20 oxygenated species, almost doubling the total carbon lost by the plant leaves as volatiles. The drop in sesquiterpenes concentrations was attributed to ozonolysis occurring to a major extent on the leaf surface. The drop in monoterpene concentrations was attributed to gas phase reactions with OH radicals deriving from ozonolysis reactions. As plant-emitted terpenoids have been shown to play a role in plant-plant and plant-insect signalling, the rapid loss of these species in the air surrounding the plants during photochemical pollution episodes may have a significant impact on plant-plant and plant-insect communications.

A multiplexed gas exchange system for increased throughput of photosynthetic capacity measurements

BackgroundExisting methods for directly measuring photosynthetic capacity (Amax) have low throughput, which creates a key bottleneck for pre-breeding and ecological research. Currently available commercial leaf gas exchange systems are not designed to maximize throughput, on either a cost or time basis.ResultsWe present a novel multiplexed semi-portable gas exchange system, OCTOflux, that can measure Amax with approximately 4–7 times the throughput of commercial devices, despite a lower capital cost. The main time efficiency arises from having eight leaves simultaneously acclimate to saturating CO2 and high light levels; the long acclimation periods for each leaf (13.8 min on average in this study) thus overlap to a large degree, rather than occurring sequentially. The cost efficiency arises partly from custom-building the system and thus avoiding commercial costs like distribution, marketing and profit, and partly from optimizing the system’s design for Amax throughput rather than flexibility for other types of measurements.ConclusionThroughput for Amax measurements can be increased greatly, on both a cost and time basis, by multiplexing gas streams from several leaf chambers connected to a single gas analyzer. This can help overcome the bottleneck in breeding and ecological research posed by limited phenotyping throughput for Amax.

Persistent negative temperature response of mesophyll conductance in red raspberry (Rubus idaeus L.) leaves under both high and low vapour pressure deficits: A role for abscisic acid?

Plant, Cell & Environment (2017) 40: 1940–1959 Version of Record online: 14 AUG 2017, DOI: 10.1111/pce.12997

Uptake and Volatilization of Gaseous Elemental Mercury by Paddy Rice

Wetlands are important sinks for mercury, and its reducing substrate favors the production of gaseous elemental mercury. In order to adapt to the anoxic condition, wetland plants usually have developed aerenchyma to transfer oxygen from the shoots to the roots to supply their roots respiration. In this study, a typical wetland plant, rice, is used to investigate whether its aerenchyma can also be a channel for the transportation of rhizosphere gaseous mercury into the atmosphere. In addition, the underlying mechanisms will be evaluated. In this study, the roots of rice were separated from the shoots by an air-tight chamber. Roots were exposed to saturated mercury vapor in the root chamber, and the gaseous mercury volatilized from the leaf chamber was absorbed by an active carbon absorbent. The results showed that gaseous elemental mercury could be transferred to shoots after absorption by the roots. The mercury in the roots decreased polynomially with root porosity (R=0.8309, P<0.01), while the mercury in the above ground tissues showed a positive correlation with root surface area and root volume (R=0.896, P<0.01; R=0.871, P<0.01). It was also indicated that the mercury absorbed by the roots could be volatilized into the atmosphere through the leaves. The volatilization of the mercury from the leaves increased positively with the leaf area (R=0.897, P<0.01). There was also a significant positive correlation between the mercury volatilization per unit leaf area and transpiration intensity (R=0.73,P<0.01). The results proved that rice can absorb gaseous elemental mercury through its roots and transfer it above ground for emission into the atmosphere through the stomata of the leaves. This provides a scientific basis for further investigations to reveal mercury behavior and its mechanisms in wetland ecosystems.

Stomatal opening in response to the simultaneous increase in vapor pressure deficit and temperature over a 24-h period under constant light in a tropical rainforest of the central Amazon

Stomatal functioning is modulated by several factors and, in most circumstances, stomatal aperture declines with increasing leaf-to-air vapor pressure difference (VPDL) and temperature, but stomatal functioning under the humid conditions of the tropical rainforest understory has been scarcely investigated. The aim of this study was to determine how stomatal conductance of saplings responds to the changing understory temperatures of a tropical rainforest. We measured gas-exchange in four saplings of Guarea carinata (1–2 m tall). On each plant, stomatal conductance (g s), VPDL and leaf temperature were measured continuously at 3-min intervals during 24 h. We used a constant irradiance of 50 µmol m−2 s−1 and nearly constant relative humidity (75.8 ± 1.9%). Within the leaf chamber, leaf temperature over plants varied from 25.8 to 30.7 °C and VPDL from 0.62 to 0.93 kPa. Contrary to expectations, g s increased with the increase in leaf temperature and VPDL, and throughout the 24-h cycle, g s was maximum (0.123 mol m−2 s−1) at midday when temperatures were higher and minimum (0.016 mol m−2 s−1) after midnight, when the lower temperatures were recorded. There was a positive relationship between g s and both leaf temperature (p < 0.0001) and VPDL (p < 0.0001). If global temperature continues to increase as predicted by models, the direct increase in g s of saplings associated with an increase in temperature can be nullified if global warming negatively affects the water balance of plants (e.g. Guarea carinata) in this part of the Amazon.