Pea Seed Priming with Pluronic P85-Grafted Single-Walled Carbon Nanotubes Affects Photosynthetic Gas Exchange but Not Photosynthetic Light Reactions.

Nanotechnology is rapidly advancing towards the development of applications for sustainable plant growth and photosynthesis optimization. The nanomaterial/plant interaction has been intensively investigated; however, there is still a gap in knowledge regarding their effect on crop seed development and photosynthetic performance. In the present work, we apply a priming procedure with 10 and 50 mg/L Pluronic-P85-grafted single-walled carbon nanotubes (P85-SWCNT) on garden pea seeds and examine the germination, development, and photosynthetic activity of young seedlings grown on soil substrate. The applied treatments result in a distorted topology of the seed surface and suppressed (by 10-19%) shoot emergence. No priming-induced alterations in the structural and functional features of the photosynthetic apparatus in 14-day-old plants are found. However, photosynthetic gas exchange measurements reveal reduced stomatal conductance (by up to 15%) and increased intrinsic water use efficiency (by 12-15%), as compared to hydro-primed variants, suggesting the better ability of plants to cope with drought stress-an assumption that needs further verification. Our study prompts further research on the stomatal behavior and dark reactions of photosynthesis in order to gain new insights into the effect of carbon nanotubes on plant performance.

Stomatal, mesophyll and biochemical limitations to photosynthesis and their relationship with leaf structure over an elevation gradient in two conifers.

Photosynthetic responses across complex elevational gradients provides insight into fundamental processes driving responses of plant growth and net primary production to environmental change. Gas exchange of needles and twig water potential were measured in two widespread coniferous tree species, Pinus contorta and Picea engelmannii, over an 800-m elevation gradient in southeastern Wyoming, USA. We hypothesized that limitations to photosynthesis imposed by mesophyll conductance (gm) would be greatest at the highest elevation sites due to higher leaf mass per area (LMA) and that estimations of maximum rate of carboxylation (Vcmax) without including gm would obscure elevational patterns of photosynthetic capacity. We found that gm decreased with elevation for P. contorta and remained constant for P. engelmannii, but in general, limitation to photosynthesis by gm was small. Indeed, estimations of Vcmax when including gm were equivalent to those estimated without including gm and no correlation was found between gm and LMA nor between gm and leaf N. Stomatal conductance (gs) and biochemical demand for CO2 were by far the most limiting processes to photosynthesis at all sites along the elevation gradient. Photosynthetic capacity (A) and gs were influenced strongly by differences in soil water availability across the elevation transect, while gm was less responsive to water availability. Based on our analysis, variation in gm plays only a minor role in driving patterns of photosynthesis in P. contorta and P. engelmannii across complex elevational gradients in dry, continental environments of the Rocky Mountains and accurate modeling of photosynthesis, growth and net primary production in these forests may not require detailed estimation of this trait value.

Variation in the phenology of photosynthesis among eastern white pine provenances in response to warming.

In higher-latitude trees, temperature and photoperiod control the beginning and end of the photosynthetically active season. Elevated temperature (ET) has advanced spring warming and delayed autumn cooling while photoperiod remains unchanged. We assessed the effects of warming on the length of the photosynthetically active season of three provenances of Pinus strobus L. seedlings from different latitudes, and evaluated the accuracy of the photochemical reflectance index (PRI) and the chlorophyll/carotenoid index (CCI) for tracking the predicted variation in spring and autumn phenology of photosynthesis among provenances. Seedlings from northern, local and southern P. strobus provenances were planted in a temperature-free-air-controlled enhancement (T-FACE) experiment and exposed to ET (+1.5/3°C; day/night). Over 18 months, we assessed photosynthetic phenology by measuring chlorophyll fluorescence, gas exchange, leaf spectral reflectance and pigment content. During autumn, all seedlings regardless of provenance followed the same sequence of phenological events with the initial downregulation of photosynthesis, followed by the modulation of non-photochemical quenching and associated adjustments of zeaxanthin pool sizes. However, the timing of autumn downregulation differed between provenances, with delayed onset in the southern provenance (SP) and earlier onset in the northern relative to the local provenance, indicating that photoperiod at the provenance origin is a dominant factor controlling autumn phenology. Experimental warming further delayed the downregulation of photosynthesis during autumn in the SP. A provenance effect during spring was also observed but was generally not significant. The vegetation indices PRI and CCI were both effective at tracking the seasonal variations of energy partitioning in needles and the differences of carotenoid pigments indicative of the stress status of needles. These results demonstrate that PRI and CCI can be useful tools for monitoring conifer phenology and for the remote monitoring of the length of the photosynthetically active season of conifers in a changing climate.

Giant cacti: isotopic recorders of climate variation in warm deserts of the Americas.

The plant family Cactaceae is considered among the most threatened groups of organisms on the planet. The threatened status of the cacti family has created a renewed interest in the highly evolved physiological and morphological traits that underpin their persistence in some of the harshest subtropical environments in the Americas. Among the most important anatomical features of cacti is the modification of leaves into spines, and previous work has shown that the stable isotope chemistry of cacti spines records potential variations in stem water balance, stress, and Crassulacean acid metabolism (CAM). We review the opportunities, challenges, and pitfalls in measuring δ 13C, δ 2H, and δ 18O ratios captured in spine tissues that potentially reflect temporal and spatial patterns of stomatal conductance, internal to atmospheric CO2 partial pressures, and subsequent patterns of photosynthetic gas exchange. We then evaluate the challenges in stable isotope analysis in spine tissues related to variation in CAM expression, stem water compartmentalization, and spine whole-tissue composition among other factors. Finally, we describe how the analysis of all three isotopes can be used in combination to provide potentially robust analysis of photosynthetic function in cacti, and other succulent-stemmed taxa across broad spatio-temporal environmental gradients.

The defensive role of silicon in wheat against stress conditions induced by drought, salinity or cadmium.

In the crust of earth, silicon (Si) is one of the two major elements. For plant growth and development, importance of Si remains controversial due to the widely differences in ability of plants to take up this element. In this paper, pot experiments were done to study Si roles in improving salt, drought or cadmium (Cd) stress tolerance in wheat. Up to full emergence, all pots were watered at 100% field capacity (FC) every other day with nutrient solution without any treatments. Fifteen days after sowing, pots were divided into four plots, each with 40 pots for no stress (control) and three stress treatments; drought (50% FC), salinity (200 mM NaCl) and cadmium (2 mM Cd). For all plots, Si was applied at four levels (0, 2, 4 and 6 mM). Under no stress condition, Si applications increased Si content and improved growth as a result of reduced electrolyte leakage (EL), malondialdehyde (MDA) and Na+ contents. Under stress conditions, Si supplementation conferred higher growth, gas exchange, tissue water and membranes stabilities, and K+ content, and had limited MDA and Na+ contents and EL compared to those obtained without Si. Compared to those without Si, enzyme (e.g., superoxide dismutase, catalase and peroxidase) activity was improved by Si applications, which were linked with elevated antioxidants and osmoprotectants (e.g., free proline, soluble sugars, ascorbic acid and glutathione) contents, might providing antioxidant defense against abiotic stress in wheat. The level of 4 mM Si was most effective for mitigating the salt and drought stress conditions, while 6 mM Si level was most influentially for alleviating the Cd stress condition. These results suggest that Si is beneficial in remarkably affecting physiological phenomena and improving wheat growth under abiotic stress.

Influence of Habitat and Effects of Salt Stress on Biochemical and Physiological Parameters of Glycyrrhiza uralensis.

The seeds of Glycyrrhiza uralensis Fisch. used for cultivating are primarily sourced from wild populations. However, the types of habitats where wild G. uralensis grow are diverse. We studied the effects of salinity on the growth, antioxidant capacity, and photosynthetic physiology of two-month-old licorice seedlings from different habitats to evaluate their salt tolerance. With the increasing NaCl concentration, compared with non-salinized habitats, seedlings originating from seeds collected from salinized habitats showed milder inhibition in root biomass and root volume. Also, the crown diameter increased more significantly. Activities of superoxide dismutase, catalase, and peroxidase are higher. Correspondingly, the electrolyte leakage rate of the leaves is low. Their leaves had a higher photoprotection capacity and potential maximum photochemical efficiency of PSII. Net photosynthetic rate, transpiration rate, and stomatal conductance showed less inhibition under 4 and 6 g/kg NaCl treatment. The content of glycyrrhizic acid and glycyrrhetinic acid in their roots was significantly increased under 2 g/kg NaCl treatment and was significantly higher than that of seedlings from non-salinized habitats under the same NaCl treatment. In conclusion, seeds from salinized habitats show improved tolerance to salt stress at the seedling stage, which is attributed to their superior phenotypic adaptability, strong antioxidant, and especially high light protection ability.

Piriformospora indica alleviates soda saline-alkaline stress in Glycine max by modulating plant metabolism.

Soil salinization is one of the major factors limiting agricultural production. Utilizing beneficial microorganisms like Piriformospora indica (P. indica) to enhance plant tolerance to abiotic stresses is a highly effective method, but the influence of P. indica on the growth of soybean in natural saline-alkaline soil remains unclear. Therefore, we investigated the effects of non-inoculation, P. indica inoculation, and fertilization on the growth, antioxidant defense, osmotic adjustment, and photosynthetic gas exchange parameters of soybean under two different levels of saline-alkaline stress in non-sterilized natural saline-alkaline soil. The study found that: 1) P. indica inoculation significantly promoted soybean growth, increasing plant height, root length, and biomass. Under mildly saline-alkaline stress, the increases were 11.5%, 16.0%, and 14.8%, respectively, compared to non-inoculated treatment. Under higher stress, P. indica inoculation achieved the same level of biomass increase as fertilization, while fertilization only significantly improved stem diameter. 2) Under saline-alkaline stress, P. indica inoculation significantly increased antioxidant enzyme activities and reduced malondialdehyde (MDA) content. Under mildly stress, MDA content was reduced by 47.1% and 43.3% compared to non-inoculated and fertilized treatments, respectively. Under moderate stress, the MDA content in the inoculated group was reduced by 29.9% and 36.6% compared to non-inoculated and fertilized treatments, respectively. Fertilization only had a positive effect on peroxidase (POD) activity. 3) P. indica inoculation induced plants to produce more osmotic adjustment substances. Under mildly stress, proline, soluble sugars, and soluble proteins were increased by 345.7%, 104.4%, and 6.9%, respectively, compared to non-inoculated treatment. Under higher stress, the increases were 75.4%, 179.7%, and 12.6%, respectively. Fertilization had no significant positive effect on proline content. 4) With increasing stress, soybean photosynthetic capacity in the P. indica-inoculated treatment was significantly higher than in the non-inoculated treatment, with net photosynthetic rate increased by 14.8% and 37.0% under different stress levels. These results indicate that P. indica can enhance soybean's adaptive ability to saline-alkaline stress by regulating ROS scavenging capacity, osmotic adjustment substance content, and photosynthetic capacity, thereby promoting plant growth. This suggests that P. indica has great potential in improving soybean productivity in natural saline-alkaline soils.

A Brassica napus Reductase Gene Dissected by Associative Transcriptomics Enhances Plant Adaption to Freezing Stress.

Cold treatment (vernalization) is required for winter crops such as rapeseed (Brassica napus L.). However, excessive exposure to low temperature (LT) in winter is also a stress for the semi-winter, early-flowering rapeseed varieties widely cultivated in China. Photosynthetic efficiency is one of the key determinants, and thus a good indicator for LT tolerance in plants. So far, the genetic basis underlying photosynthetic efficiency is poorly understood in rapeseed. Here the current study used Associative Transcriptomics to identify genetic loci controlling photosynthetic gas exchange parameters in a diversity panel comprising 123 accessions. A total of 201 significant Single Nucleotide Polymorphisms (SNPs) and 147 Gene Expression Markers (GEMs) were detected, leading to the identification of 22 candidate genes. Of these, Cab026133.1, an ortholog of the Arabidopsis gene AT2G29300.2 encoding a tropinone reductase (BnTR1), was further confirmed to be closely linked to transpiration rate. Ectopic expressing BnTR1 in Arabidopsis plants significantly increased the transpiration rate and enhanced LT tolerance under freezing conditions. Also, a much higher level of alkaloids content was observed in the transgenic Arabidopsis plants, which could help protect against LT stress. Together, the current study showed that AT is an effective approach for dissecting LT tolerance trait in rapeseed and that BnTR1 is a good target gene for the genetic improvement of LT tolerance in plant.

[Mesophyll conductance to CO2: Methods and current knowledge].

Mesophyll conductance (gm), the total conductance of CO2 diffusion from substomatal cavity to the site of carboxylation within chloroplast, is a major limiting factor for photosynthesis and a key parameter for improving photosynthetic resource use efficiency of crops. Online 13C discrimination method is an important method for plant eco-physiological studies and a well-established method for measuring gm of C3 plants, although it has not been widely used due to challenges in methodology and high demands on experimental facilities. In this review, we summarized the characteristics of commonly used methods for gm, introduced the basic theory of the online 13C discrimination method, namely Farquhar's photosynthetic 13C discrimination model; systematically introduced the practical measurements, equations and the components of facilities; and reviewed the drivers for variation in gm of C3 plants. At the last part, we discussed the outlook of the development of methodology, new experimental protocols, and applications in measurement scenarios.

Biochar alleviates phytotoxicity in Ficus elastica grown in Zn-contaminated soil.

Zinc (Zn) immobilization by two distinct biochars in soil, together with concomitant alleviation of phytotoxic responses in Ficus elastica Roxb. ex Hornem., were examined. Rooted cuttings of F. elastica were grown in 880mgkg-1 Zn-spiked sandy soil amended with grain husk (GH) or cattle manure (CM) biochar at 0, 10, 30 and 50gkg-1 soil for a period of 6months. Addition of both GH and CM biochars had significant positive impacts on physiological parameters such as plant growth, leaf relative water content, photosynthetic pigments and leaf gas exchange characteristics. The responses to addition of CM biochar were significantly better than to GH biochar. Lipid peroxidation declined in leaves of plants grown in Zn-contaminated, biochar-amended soil. This was confirmed by luminescence and Fourier transform infrared analysis of the leaf material. Biochar significantly reduced the availability of soil Zn, as evidenced by lower concentrations of Zn in leaves and leachates of biochar treated plants relative to control plants. These findings show that biochar can effectively immobilize soil Zn, and as a result, alleviate Zn phytotoxicity by reducing its uptake and accumulation in the plant. Adding biochar to soils contaminated with metals thus holds promise as a means of restoring blighted lands.

Estimation of Photorespiratory Fluxes by Gas Exchange.

Photorespiratory fluxes can be easily estimated by photosynthetic gas exchange using an infrared gas analyzer and applying the Farquhar, von Caemmerer, and Berry (Farquhar et al. Planta 149:78-90, 1980) photosynthesis model. For a more direct measurement of photorespiratory CO2 release from glycine decarboxylation, infrared gas analysis can be coupled to membrane-inlet mass spectrometry, capable of separating the total CO2 concentration into its 12CO2 and 13CO2 components in a continuous online fashion. This chapter discusses how to calculate rates of photorespiration from Rubisco kinetics and describes in detail a method for measuring the CO2 release from glycine decarboxylation using 13CO2.

[Photosynthetic gas exchange and water utilization of flag leaf of spring wheat with bunch sowing and field plastic mulching below soil on semi-arid rain-fed area.] / åŠå¹²æ—±åŒºè†œä¸Šè¦†åœŸç©´æ’­å¯¹æ˜¥å°éº¦æ——å¶å ‰åˆä½œç”¨å’Œæ°´åˆ†åˆ©ç”¨çš„å½±å“.

Based on the field experiment which was conducted in Dingxi County of Gansu Province, and involved in the three treatments: (1) plastic mulching on entire land with soil coverage and bunching (PMS), (2) plastic mulching on entire land and bunching (PM), and (3) direct bunching without mulching (CK). The parameters of SPAD values, chlorophyll fluorescence parameters, photosynthetic gas exchange parameters, as well as leaf area index (LAI), yield, evapotranspiration, and water use efficiency in flag leaves of spring wheat were recorded and analyzed from 2012 to 2013 continuously. The results showed that SPAD values of wheat flag leaves increased in PMS by 10.0%-21.5% and 3.2%-21.6% compared to PM and CK in post-flowering stage, respectively. The maximum photochemical efficiency (Fv/Fm) , actual photochemical efficiency (ΦPS2) of photosystem 2 (PS2), and photochemical quenching coefficient (qP) of PMS were higher than those of PM and CK, the maximum increment values were 6.1%, 9.6% and 30.9% as compared with PM, and significant differences were observed in filling stage (P＜0.05). The values of qN in PMS were lowest among the three treatments, and it decreased significantly by 23.8% and 15.4% in heading stage in 2012 and 2013 respectively, as compared with PM. The stoma conductance (gs) of wheat flag leaves in PMS was higher than that of PM and CK, with significant difference being observed in filling stage, and it increased by 17.1% and 21.1% in 2012 and 2013 respectively, as compared with PM. The transpiration rate (Tr), net photosynthetic rate (Pn), and leaf instantaneous water use efficiency (WUEi) except heading stage in 2013 of PMS increased by 5.4%-16.7%, 11.2%-23.7%, and 5.6%-7.2%, respectively, as compared with PM, and significant difference of WUEi was observed in flowering stage in 2012. The leaf area index (LAI) of PMS was higher than that of PM and CK, especially, it differed significantly in seasonal drought of 2013. Consequently, the PMS increased the SPAD values in flag leaves of spring wheat, and the capacity of flag leaves for photo energy assimilation and photosynthetic gas exchange were enhanced, caused more photosynthetic energy flowing into photochemical process, as well as decreased the heat dissipation, resulted in the increment of Pn and WUEi. Based on the higher Pn and LAI, the yield and WUE of PMS increased.

Comparative study of water uptake and photosynthetic gas exchange between scrub and fringe red mangroves, Rhizophora mangle L.

The red mangrove (Rhizophora mangle L.) occurs frequently in both scrub and fringe mangrove forests. Our previous study demonstrated that individuals of this mangrove species growing in scrub and fringe forests differ significantly in both morphological and physiological characteristics. To further characterize physiological differences between scrub and fringe mangroves, we compared their differences in water uptake and photosynthetic gas exchange during different seasons. In the wet season (June-October, 1990), scrub mangroves showed lower δD and δ18O values of stem water than fringe mangroves, indicating more usage of rain-derived freshwater. In the dry season (Jan-April, 1991), however, scrub mangroves utilized the same water source as fringe mangroves, reflected by their similar δD and δ18O values of stem water. Consistently, there were significant differences in predawn water potentials between scrub and fringe mangroves in the wet season (October 1990) with higher values for scrub mangroves, but no significant differences in the dry season (January 1991). Higher elevation in the scrub forest seems to be the major factor responsible for the shift of water sources in scrub mangroves. On Apr. 27 and Aug. 8, 1990, scrub mangroves showed lower CO2 assimilation rate, stomatal conductance, and intercellular CO2 concentration than fringe mangroves. There were no differences in these gas exchange characteristics on the other two measuring dates: Oct. 17, 1990 and Jan. 11, 1991. Instantaneous water use efficiency was significantly higher for scrub mangroves than for fringe mangroves on three of the four sampling dates. Similarly, leaf carbon isotope discrimination of scrub mangroves was always significantly lower than that of fringe mangroves, indicating higher long-term water use efficiency. Higher water use efficiency in scrub mangroves is a result of stomatal limitation on photosynthesis, which may entail considerable carbon cost to the plants.