Decrease In Photosynthetic Rate Research Articles

A new tool for long-term studies of POM-bacteria interactions: overcoming the century-old Bottle Effect.

Downward fluxes of particulate organic matter (POM) are the major process for sequestering atmospheric CO2 into aquatic sediments for thousands of years. Budget calculations of the biological carbon pump are heavily based on the ratio between carbon export (sedimentation) and remineralization (release to the atmosphere). Current methodologies determine microbial dynamics on POM using closed vessels, which are strongly biased towards heterotrophy due to rapidly changing water chemistry (Bottle Effect). We developed a flow-through rolling tank for long term studies that continuously maintains POM at near in-situ conditions. There, bacterial communities resembled in-situ communities and greatly differed from those in the closed systems. The active particle-associated community in the flow-through system was stable for days, contrary to hours previously reported for closed incubations. In contrast to enhanced respiration rates, the decrease in photosynthetic rates on particles throughout the incubation was much slower in our system than in traditional ones. These results call for reevaluating experimentally-derived carbon fluxes estimated using traditional methods.

Application of biosolids to soil affects Cu and Zn accumulation and antioxidant activity of lettuce (Lactuca sativa L.)

abstractThe application of biosolids to agricultural fields is becoming increasingly common. The effect of biosolids on the behavior of metals in different plants has been reported to be variable and ambiguous. A greenhouse experiment was conducted on a soil spiked with four rates of copper (Cu) (0, 50, 100, and 150 mg kg−1) and zinc (Zn) (0, 150, 300, and 450 mg kg−1) in lettuce culture. When Cu and Zn were spiked to anaerobically-digested biosolids, their availability in lettuce increased. Root and shoot fresh weight decreased due to a decrease in photosynthetic rate. superoxide dismutase (SOD) and peroxidases (POD) activity increased after the application of Cu and Zn. The bioavailability of Zn in lettuce was greater than that of Cu because of a higher transfer factor in plants and due to a higher endogenous Zn concentration.These results will allow for better fertilization management when biosolids are applied to tomato culture.

Stable isotope compositions of aquatic flora as indicators of wetland eutrophication

Abstract Carbon and nitrogen stable isotopes (δ13C and δ15N) have been used as indicators for environmental changes in aquatic ecosystems. In this study, δ13C and δ15N values of select flora taxa were evaluated as indicators of human-induced eutrophication in an Everglades wetland which has been impaired by the source and quality of inflow and the alteration of hydrological pattern. Results showed that δ13C of cattail (Typha domingensis Pers.) increased with the decrease in total phosphorus (TP) concentration. Limited data for sawgrass (Cladium jamaicenses Crantz) collected at three study sites along the nutrient gradient also show a similar change in δ13C. However, δ13C of periphyton and bladderwort (Utricularia sp.) decreased with the decrease in TP concentration. The elevated δ13C values of emergent vascular plants (cattail and sawgrass) were likely the results of decreases in stomatal conductance, carboxylation and 13C fractionation under nutrient stress. This is supported by corresponding decreases in photosynthetic rate of cattail along the decreasing nutrient gradient. In contrast, δ15N values of all flora taxa increased with the increase in TP concentration. Findings from this study indicate that δ13C of emergent plants is a sensitive indicator for nutrient stress while δ15N of major flora species may serve as a robust indicator for wetland eutrophication.

Boron availability alters its distribution in plant parts of tomato

This study was performed to investigate boron (B) distribution within various parts of tomato plants (Solanum lycopersicum L. ‘Super Momotarou’) grown under either B supply (adequate, 0.5 mg·L−1) or no B (0 mg·L−1) condition. The objective was to examine how B supply affects plant growth, photosynthetic activity and the morphological response of the entire root system. When the plants were grown for 36 days under the B supply treatment, B concentration was greatest in the order of the leaf (54.3 μg·g−1), fruit cluster (27.8 μg·g−1), petiole (24.7 μg·g−1), and stem (14.1 μg·g−1). However, B deficient supply altered the B distribution so that the greatest concentration was found in the stem (7.82 μg·g−1); then the petiole (8.20 μg·g−1), the fruit cluster (5.5 μg·g−1), and lastly in the leaf (4.11 μg·g−1). No B treatment resulted an approximately 46% decrease in the calcium content of the leaf and an 87% decrease in the potassium content of the fruit cluster. No B treatment also led to a severe decrease in photosynthetic rate, stomatal conductance and transpiration, with an increase in the water vapor saturation deficit at the leaf surface. Microscopic investigation of the stomata 36 days after transplant revealed that a majority of the stomata in the epidermal layer of B-deficit leaves were closing. The total dry weights of the leaves, leaf petioles and stems of B-deficit leaves decreased by 36, 43, and 27%, respectively, at 22 days after transplant, and decreased by 60, 69, and 60%, respectively, at 36 days after transplant, compared to the values for the B-sufficient leaves. A 10-fold lower fruit cluster dry weight was also observed in the B-deficit plants. Under no B supply, the total root length at 35 days after transplant decreased by about 56%, while the average root diameter increased by 20%. This was associated with a significant decrease in the root length, which ranged between 0 and 0.2 mm in diameter, alongside a significant increase in the root length, which ranged larger than 0.9 mm in diameter. One explanation for this finding is that limited B availability leads to a lack of translocation of B to the leaf and reproductive tissues, and this alteration of B partitioning may then affect fruit quality as well as root growth. An improved understanding of B partitioning in plant tissues may help to improve B management and, in the long term, improve crop yields.

Introduction of the Arabidopsis PHYB gene increases resistance of photosynthetic apparatus in transgenic Solanum tuberosum plants to UV-B radiation

The influence of phytochrome B overproduction in 50- to 60-day-old transgenic potato plants (Solanum tuberosum L., lines Dara 5 and Dara 12 with moderate and intense expression of PHYB, respectively) on the resistance of photosynthetic apparatus to UV-B irradiation was investigated. In plants unexposed to UV-B, there was no significant difference in photosynthetic rates (P n) and fluorescence parameters (F v/F m, qN, qP) between the nontransformed (NT) line and Dara-5 and Dara-12 lines, whereas the content of photosynthetic pigments per 1 cm2 leaf area was higher in the transgenic plants. Irradiation with UV-B resulted in the decrease in photosynthetic rate in NT plants by 35–45%, whereas in Dara-12 line this rate was lowered by only 20–25%. Exposure to UV-B reduced the amplitudes of both fast and slow components of delayed fluorescence (DF), which indicated the diminished efficiency of photosystem II (PSII). The decrease in the maximum amplitude of the slow DF component was markedly lower in Dara-12 (19%) than in NT line (33%). The maximal photochemical quantum yield of PSII (F v/F m ratio) in plants exposed to UV-B was also suppressed stronger in NT line than in Dara-12. The line Dara-5 had intermediate position among other lines in terms of UV-B resistance of photosynthesis and PSII activity, but it was closer to NT than to Dara-12. Thus, the potato plants actively expressing the gene of Arabidopsis phytochrome B apoprotein (PHYB) demonstrated a higher resistance of photosynthetic apparatus to UV-B radiation compared to nontransformed plants. The elevated UV-B tolerance is most likely related to the increased leaf content of chlorophyll, carotenoids, and flavonoids.

Physiological and Ecological Effects of Spilled Motor oil on Inland Salt Marsh Communities: A Mesocosm Study

Numerous studies have investigated impacts of oil spills on coastal ecosystems, but no previous studies have tested effects of spilled oil on inland salt marshes. This study used experimental mesocosms to test effects of spilled motor oil on inland salt marsh communities in a greenhouse experiment. It was hypothesized that oil exposure would lead to decreases in photosynthesis, chlorophyll, canopy coverage, and biomass. Communities of plants were collected from a salt marsh in Kansas, USA, and used motor oil was applied at 10 L m−2 to mesocosm soil with a treatment of 10 weeks. In the dominant species, inland salt grass (Distichlis spicata), oil exposure resulted in a 91 % decrease in photosynthetic rates and an 83 % reduction in chlorophyll concentration. Community-level biomass was primarily driven by D. spicata, where above-ground biomass was reduced by 34 % for D. spicata and by 31 % for total community biomass in oil treatments. Canopy coverage measures were similar to biomass measures, with significant reductions in D. spicata with oil exposure and no difference between treatments for less abundant species. Inland marsh plants are sensitive to spilled motor oil. These results could help future studies to determine how salt marsh vegetation is impacted by spilled oil.

Effect of root aeration and form of nitrogen on photosynthetic productivity of Scots pine (Pinus silvestris L.)

The response of 1-year old pine seedlings, grown in sand and water culture, to nutrition with nitrate or ammonium form of nitrogen, as well as to various aeration of the cultures was studied. Measurements of photosynthesis and respiration were carried out. Production of organic matter and its distribution to particular organs were determined. Seedlings supplied with NH<sub>4</sub>Cl were characterized by smaller contribution of root dry weight to the total weight of the plant. Poor aeration (heavy watering) of seedlings supplied with ammonium chloride caused a decrease in the rate of photosynthesis. Plants supplied with NH<sub>4</sub>C1 did not show the typical decrease of photosynthetic rate at the end of the growing season.

Bicarbonate uptake via an anion exchange protein is the main mechanism of inorganic carbon acquisition by the giant kelp Macrocystis pyrifera (Laminariales, Phaeophyceae) under variable pH.

Macrocystis pyrifera is a widely distributed, highly productive, seaweed. It is known to use bicarbonate (HCO3 (-) ) from seawater in photosynthesis and the main mechanism of utilization is attributed to theexternal catalyzed dehydration of HCO3 (-) by the surface-bound enzyme carbonic anhydrase (CAext ). Here, we examined other putative HCO3 (-) uptake mechanisms in M.pyrifera under pHT 9.00 (HCO3 (-) : CO2 =940:1) and pHT 7.65 (HCO3 (-) : CO2 =51:1). Rates of photosynthesis, and internal CA (CAint ) and CAext activity were measured following the application of AZ which inhibits CAext , and DIDS which inhibits a different HCO3 (-) uptake system, via an anion exchange (AE) protein. We found that the main mechanism of HCO3 (-) uptake by M.pyrifera is via an AE protein, regardless of the HCO3 (-) : CO2 ratio, with CAext making little contribution. Inhibiting the AE protein led to a 55%-65% decrease in photosynthetic rates. Inhibiting both the AE protein and CAext at pHT 9.00 led to 80%-100% inhibition of photosynthesis, whereas at pHT 7.65, passive CO2 diffusion supported 33% of photosynthesis. CAint was active at pHT 7.65 and 9.00, and activity was always higher than CAext , because of its role in dehydrating HCO3 (-) to supply CO2 to RuBisCO. Interestingly, the main mechanism of HCO3 (-) uptake in M. pyrifera was different than that in other Laminariales studied (CAext -catalyzed reaction) and we suggest that species-specific knowledge of carbon uptake mechanisms is required in order to elucidate how seaweeds might respond to future changes in HCO3 (-) :CO2 due to ocean acidification.

Physiological relationship between oil tolerance and flooding tolerance in marsh plants

Coastal salt marshes are highly susceptible to accidental oil spills. Oil can cover root tissues, inhibiting gas exchange and increasing root oxygen stress. This is similar to flooding; both conditions reduce the availability of oxygen to a plant. Therefore, it was hypothesized that tolerance to both flooding and oil are related in plants, as both impede gas exchange between roots and their environment. We investigated effects of oil on respiration and photosynthesis in nine marsh species ranging from flooding sensitive (hypothesized oil sensitive) to flooding tolerant (hypothesized oil tolerant). Plants were subjected to 6Lm−2 light motor oil in greenhouse experiments for six weeks. Oil exposure caused root oxygen deficiency in all but the most flooding tolerant species. Alcohol dehydrogenase activities increased in roots of flooding sensitive species and moderately flooding tolerant plants under oil exposure, indicating oxygen stress. In contrast, flooding tolerant plants showed no sign of oxygen deficiency under oil treatment. Additionally, decreases in photosynthetic rates were measured in some species following oil exposure. Photosynthesis was reduced by non-stomatal limitations, suggesting toxic effects of oil. It was concluded that tolerance to oil relates to flooding tolerance when measured in terms of biochemical enzyme activity. Root alcohol dehydrogenase activity was a sensitive indicator of oil susceptibility, whereas leaf-level photosynthesis was less sensitive to oil. Relating flooding and oil tolerance based on physiological measures could help future efforts to protect marsh plants prior to an oil spill as well as manage coastal marshes following an oil spill.

Maize growth and developmental responses to temperature and ultraviolet-B radiation interaction

Plant response to the combination of two or more abiotic stresses is different than its response to the same stresses singly. The response of maize (Zea mays L.) photosynthesis, growth, and development processes were examined under sunlit plant growth chambers at three levels of each day/night temperatures (24/16°C, 30/22°C, and 36/28°C) and UV-B radiation levels (0, 5, and 10 kJ m –2 d –1 ) and their interaction from 4 d after emergence to 43 d. An increase in plant height, leaf area, node number, and dry mass was observed as temperature increased. However, UV-B radiation negatively affected these processes by reducing the rates of stem elongation, leaf area expansion, and biomass accumulation. UV-B radiation affected leaf photosynthesis mostly at early stage of growth and tended to be temperature-dependent. For instance, UV-B radiation caused 3–15% decrease of photosynthetic rate (PN) on the uppermost, fully expanded leaves at 24/16°C and 36/28°C, but stimulated PN about 5–18% at 30/22°C temperature. Moreover, the observed UV-B protection mechanisms, such as accumulation of phenolics and waxes, exhibited a significant interaction among the treatments where these compounds were relatively less responsive (phenolics) or more responsive (waxes) to UV-B radiation at higher temperature treatments or vice versa. Plants exposed to UV-B radiation produced more leaf waxes except at 24/16°C treatment. The detrimental effect of UV-B radiation was greater on plant growth compared to the photosynthetic processes. Results suggest that maize growth and development, especially stem elongation, is highly sensitive to current and projected UV-B radiation levels, and temperature plays an important role in the magnitude and direction of the UV-B mediated responses.

Effect of different harvest stages on photosynthetic characteristics and yield of purple yam

The effect of different harvest stages on photosynthetic characteristics and yield of purple yam was studied in the open field. The results showed that the chlorophyll content of purple yam decreased continually with the extension of the harvest stage, which led to the decrease of photosynthetic rate. The moisture content of purple yam aboveground reduced, leading to plant wilted gradually. Moreover, the inflation of tuberous root lasted throughout whole harvest stage. And the tuberous root yield was the highest during the third harvest stage. However, yield of purple yam had reached approximately maximum, due to the rapid increase of dry matter accumulation of purple yam tuberous root during the first harvest stage to the second harvest stage, and then slowed down. In consideration of nutritional components of purple yam and the cultivation of next crop, we drew a conclusion that the date between September 30th and October 15th was the best harvest stage.

城市地表硬化对银杏生境及生理生态特征的影响

城市大规模的地表硬化改变了城市环境，影响了城市中植物的正常生长。利用土壤水分温度仪ECH₂O测定了不同硬化地表下土壤含水率（<em>WCS</em>）和土壤温度（<em>Ts</em>），利用LI-6400光合仪，并配备荧光叶室，测定了银杏生长的环境因子和银杏生理生态参数。研究结果表明，城市地表硬化对银杏生长环境的影响主要表现为空气温度（<em>Ta</em>）和土壤温度（<em>Ts</em>）升高，空气相对湿度（<em>RH</em>）和土壤含水率（<em>WCS</em>）下降，银杏对地表硬化的生理生态响应表现为净光合速率（<em>Pn</em>）、蒸腾速率（<em>Tr</em>）、气孔导度（<em>Gs</em>）降低，叶面饱和水汽压亏缺（<em>VPDL</em>）增大，叶片含水率（<em>LWC</em>）下降；最大光化学效率（<em>Fv/Fm</em>）和PSⅡ实际光合电子传递量子效率（<em>Φ</em>_PSⅡ）下降，硬化程度越高，银杏受到的胁迫越重；受城市地表硬化的影响，银杏吸收的光能用于光化学反应的比例减少，而用于热耗散和荧光耗散的比例增加，城市硬化地表上银杏的水分利用效率（<em>WUE</em>）、光能利用效率（<em>LUE</em>）和CO₂利用效率（<em>CUE</em>）明显下降。;City is a kind of social-economic-natural complex ecosystem dominated by human activities. With the accelerating of urbanization, the land use is being transformed from natural landscape to impervious surface in urban areas, such as buildings, roads, roof, squares and so on. Urban imperious surface changes the environment factors, hinders energy exchange between air and soil, and influences urban plant growth. In this research we studied the effects of urban imperious surface on habitat of <em>Ginkgo biloba</em> and its ecophysiology response to the imperious surface. We designed two different types of imperious surface in urban areas. One is totally impervious cover (TIC) which is a marble square, and the coefficient of permeability is zero. The other is partially impervious cover (PIC) which is covered by bricks, and the coefficient of permeability is 33%. A turf cover (NC) was chosen as the contrast, and the coefficient of permeability is 88%. The <em>Ginkgo bilobas</em> growing on the three kinds of land covers were planted in the same time and received the same maintenance. Soil temperature (<em>Ts</em>) and water content of soil (<em>WCS</em>) were measured by ECH₂O. Gas exchange characteristics such as photosynthesis (<em>Pn</em>), transpiration (<em>Tr</em>), stomata conductance (<em>Gs</em>), saturation vapor pressure deficit of leaf (<em>VPDL</em>) were measured by Portable photosynthesis measuring system Li-6400. chlorophyll fluorescence characteristics such as optimal photochemical efficiency (<em>Fv/Fm</em>), actual photochemical efficiency <em>Φ</em>_PSⅡ, quantum efficiency of light-dependent thermal dissipation <em>Φf.D</em>, quantum efficiency of light-independent and fluorescence energy dissipation <em>ΦNPQ</em> were measured and calculated with the help of fluorescence chamber (6400-40). Relative water content of leaf was measured by weight method. The results showed that temperature of air (<em>Ta</em>) above TIC and PIC were 3.2℃ and 2.1 ℃ higher than NC, and temperature of soil (<em>Ts</em>) increased 1.5 ℃and 2.2 ℃ respectively. Relative humidity of air (<em>RH</em>) above TIC and PIC were about 5%-6% lower than NC and water content of soil (<em>WCS</em>) under TIC and PIC were about 4%-5% lower than NC in urban areas. <em>Ginkgo biloba</em>'s ecophysiology response to the imperious surface is that the decrease of photosynthetic rate (<em>Pn</em>), transpiration rate (<em>Tr</em>), conductance to H₂O (<em>Gs</em>) and leaf water content (<em>LWC</em>). The <em>Pn</em> of <em>Ginkgo biloba </em>planted on TIC and PIC were 39.3% and 22.7% lower than those on NC. <em>Tr</em> and <em>Gs</em> also had similar decrease trend. Compared to <em>Ginkgo biloba </em>planted on NC, the <em>Ginkgo biloba</em> planted on impervious surface (include TIC and PIC), the <em>Fv/Fm</em> and <em>Φ</em>_PSⅡ decreased, but <em>VPDL</em> and <em>Φf.D</em> increased, indicating that due to the impact of impervious surface approximately 10% more energy absorbed by leaf was released as heat but 5%-9% less energy was used for photosynthesis. The more urban imperious surface covered, the more severe stress to <em>Ginkgo biloba </em>suffered<em>. </em>The water use efficiency (<em>WUE</em>), light use efficiency (<em>LUE</em>) and CO₂ use efficiency (<em>CUE</em>) of <em>Ginkgo biloba</em> growing in urban imperious surface are 20%-40% less than that in the turf cover. This study revealed the response of <em>Ginkgo biloba's </em>ecophysiology characteristics and variations characters on different surface covers. It is very important to improve quality of the plant habitat and enhance ecological services of urban green space. It also provides a scientific reference for urban greening and constructing of the ecological land.

Low UV-B radiation and substrate acidity impact on photosynthetic parameters of Brassica napus

The aim of this study was to assess combined effect of 1 kJm-2d-1 UV-B radiation and substrate acidity (pH 4.8) on photosynthesis and growth of summer rape (Brassica napus) in a controlled environment. Rape were sown in a neutral (pH 6.0-6.5) peat substrate, when 2nd true leaf unfolded, growth substrate was acidified using 0.07 mM H2SO4 concentration solution and UV-B radiation exposure was started. Duration of the experiment: five days. Gas exchange parameters were measured with portable photosynthesis system LI-6400. Content of chlorophyll was evaluated spectrophotometrically. The results showed that the highest inhibition on Brassica napus growth and photosynthetic parameters was under combined effect of 1 kJm-2d-1 UV-B radiation and pH 4.8 substrate acidity. The impact of single 1 kJm-2d-1 UV-B radiation on investigated parameters was low and statistically insignificant, except transpiration rate and water use efficiency. Single substrate acidity affected in 58.6% (p &lt; 0.05) decrease in photosynthetic rate, almost twofold decrease of transpiration rate, and 3.8% (p &lt; 0.05) decrease in intercellular CO2 concentration, and 27.1% (p &lt; 0.05) increase in water use efficiency, compared to the reference treatment. Combined substrate acidity and UV-B radiation effect on photosynthetic rate was the highest, when the decrease was 80.6% (p &lt; 0.05), compared to the reference treatment. The changes of transpiration rate under combined effect of investigated stressors compared to the reference treatment were insignificant (p &gt; 0.05). The increase (by 2%, p &lt; 0.05) of intercellular CO2 concentration of Brassica napus affected by combined impact of investigated stressors shows that higher negative impact was on enzymatic reactions of photosynthesis than on transpiration. The highest negative effect on content of photosynthetic pigments and biomass accumulation also was of combined effect of investigated stressors.

Modeling loss and recovery of Zostera marina beds in the Chesapeake Bay: The role of seedlings and seed-bank viability

Loss and recovery processes following a documented large scale decline in Zostera marina beds in the York River, Virginia in 2005 were modeled by coupling production and sexual reproduction models. The reproduction model included formulations for reproductive shoot production, seed production, seed-bank density, seed viability, and seed germination. After the model was calibrated and validated using in situ water quality and plant performance measurements from two different sites, model scenarios were run for three years (1 year pre-decline, 2 years post-decline) to quantify the effects of (1) the presence or absence of sexual reproduction, (2) increases in water temperatures from ambient to ambient +5°C in 1°C increments, and (3) the potential interactive effects of light and temperature conditions on bed maintenance and re-establishment. Model projections of Z. marina production following the decline corresponded to in situ measurements of recovery only when sexual reproduction was added. However, a 1°C increase in temperature resulted in a complete loss of biomass after two consecutive years of temperature stress following the depletion of the viable sediment seed bank. Interactions between light and temperature stress resulted in overall lower production and resilience to declines under lower light conditions due to corresponding decreases in photosynthetic rates and increases in respiration. Model results highlight (1) the need to incorporate sexual reproduction into Z. marina ecosystem models, (2) the projected sensitivity of established beds to consecutive years of stress, and (3) the negative effects of multiple stressors on Z. marina resilience and recovery.

Effects of High Temperature Stress on PSII Function and Its Relation to D1 Protein in Chloroplast Thylakoid in Rice Flag Leaves

On the basis of the artificial controlled temperature treatments in growth chambers, influences of high temperature stress at rice filling stage on the expression and distribution of D1 protein in leaf chloroplast thylakoid, as well as their relations to the decline of leaf photosynthetic rate and the damage of PSII membrane system were investigated by detecting the temporal pattern of leaf photosynthetic rate and chlorophyll fluorescence parameters, with SDS-PAGE electrophoresis, western-blotting and immunogold labeling methods. The results showed that rice flag leaves exposed high temperature generally had lower net photosynthetic rate (Pn), PSII potential efficiency(Fv /Fo) and solar energy transmitting efficiency(Fv/Fm) compared with those under normal temperature, with more severe damage and remarkable function dropping in chloroplast thylakoid due to prolonging stress times and accelerating leaves senescence.The amount of D1 protein in rice leaves under high temperature stress decreased significantly. In the two types of D1 protein, the amount of non-phosphorylated D1 protein was more sensitive to high temperature stress than the phosphorylated D1 protein.The RNA transcription of psbA gene in chloroplast, controlling D1 protein synthesis, was down-regulated by high temperature stress, inhabiting mRNA transcription and protein translation in D1 protein synthesis, thereby causing the functional damage of PSII reaction centre in thylakoid and dropping leaf photosynthetic rate under high temperature stress. It could be suggested that the functional damage of PSII reaction centre under high temperature stress be caused by the combined action of D1 protein hosphorylation and psbA gene expression, resulting in the decrease of photosynthetic rate and high temperature tolerance in two rice genotypes.

Study of plant bioelectric potential response due to photosynthesis reaction

AbstractBioelectric potential is generated by ions in a plant cell; the potential changes with physiological activities of the plant. Therefore, measurement of the potential is a promising method for evaluation of plant activities. In this study, we investigated the mechanism of potential response generation due to photosynthetic reactions of plants. For this purpose, we measured the bioelectric potential with air replaced by N2 gas in order to suppress the carbon‐fixation reaction. The potential response was found to be different from the ambient gas, and we determined that several behaviors of the potential response were strongly related to the activities of the photochemical reaction and carbon‐fixation reaction. We next measured the potential when the illuminating conditions were changed to accelerate or decelerate photosynthesis. The shape of the potential response was found to be related to the increase or decrease of photosynthetic rate and can provide support for effective cultivation. © 2012 Wiley Periodicals, Inc. Electron Comm Jpn, 95(8): 10–16, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.11393

Assessment of the Tolerance of Trees to High Concentration Sulfur Dioxide

Italic textThis research utilized a custom-made air fumigation equipment to evaluate the tolerance of 10 species of side-walk trees with 600, 1000 and 2000 ppb Sulfur Dioxide (SO2) for 48 hours. The tolerance of tested trees toward SO2 pollution was analyzed. Results showed that these plants influenced by high concentration SO2 gas with physiology properties changes and the decrease of photosynthetic rates and the stomata conductance than before fumigation. The net photosynthetic rate and stomata conductance of tested trees was linearly correlated to each tested tree species. Among tested tree, the Quercus glauca had the highest tolerance in exposure with high concentration of SO2 pollutant. While the Camellia axillaries was the least.

Physiological and anatomical adaptations induced by flooding inCotula coronopifolia

Cotula coronopifolia is a wild annual Asteraceae that grows in periodically-flooded prone environments and seems highly tolerant to periodic flooding. Seedlings of about 15 cm were collected directly from the edge of Soliman sabkha (N-E Tunisia, semi-arid stage) and grown under greenhouse conditions. Two treatments were considered: drainage and flooding. After 56 days of treatment, flooded plants showed a pronounced growth increase. This performance was essentially associated with significant increment in biomass production of both shoots and roots (about 220% of the control). The appropriate response to flooding was also characterized by the ability of the species to maintain its water status under such conditions. Neither water content nor water potential showed a significant variation as compared to those of non-flooded plants. However, transpiration rate decreased slightly but significantly in flooded plants (from 0.86 to 0.64 mmol H2O m-2 s-1). Na+ and K+ concentrations were practically maintained under waterlogging conditions, except a significant increase of Na+ content in roots of flooded plants (157% of the control). These responses were concomitant with maintenance of photosynthetic rate. However, the contents of chlorophylls a and b increased to 167% and 295%, respectively. It seems that the enhancement in these photosynthetic pigments together with a significant improvement in water use efficiency (from 4.66 to 6.07 mmol CO2 mol-1 H2O) allowed to the species to compensate the decrease in photosynthetic rate. At the anatomical level, this species responded to flooding by a significant development of its root aerenchyma (+63%) and an increase in the lignification of its stem xylem tissues (+37%). Based on the presented data, the plant fitness under flooding conditions was a result of dynamic readjustment of several morphological, physiological, and anatomical adaptive traits. Flood requirement together with salt tolerance are responsible for the predominance of C. coronopifolia in a large area in its natural biotope where most plants cannot tolerate interactive effects of flooding and salinity.

Wheat Growth and Photosynthesis as Affected by Oxytetracycline as a Soil Contaminant

Extensive worldwide use of oxytetracycline (OTC), a member of the tetracyclines, has resulted in its accumulation in soils, posing a potential risk to food production and safety. A pair of OTC-sensitive (Heyou 1) and OTC-tolerant (Yannong 21) wheat ( Triticum aestivum L.) cultivars was compared hydroponically at 0.01, 0.02, 0.04, and 0.08 mmol L −1 OTC in terms of wheat growth and photosynthesis. Biomass and shoot length decreased significantly with the addition of OTC, with the decreases in dry biomass and shoot length being 5.61%-13.75% and 3.33%-8.57% larger, respectively, for Heyou 1 than Yannong 21. Photosynthesis of Heyou 1 was suppressed by OTC as indicated by the significant decreases in photosynthetic rate (PN), transpiration rate (TR), and stomatal conductance (GS) and the significant increase in intercellular CO 2 concentrations (CI), at all OTC levels. Stomatal limitation (LS) and water use efficiencies (WUE) of Heyou 1 also increased significantly, but not at 0.08 mmol L −1 OTC. However, photosynthesis of Yannong 21 was suppressed by OTC only at high OTC levels from 0.02 to 0.08 mmol L −1 as indicated by the decreases in PN, GS, TR, and LS; at 0.01 mmol L −1 OTC, PN, CI, GS, and TR significantly increased. It was noted that WUE of Yannong 21 was not affected by OTC addition. The results from this hydroponic test suggested that OTC had a potential risk to crop growth through inhibition of photosynthesis, requiring further confirmation with soil tests.

Photosynthesis, growth and survival of the Mediterranean seagrass Posidonia oceanica in response to simulated salinity increases in a laboratory mesocosm system

This study aims to examine the effect of increased salinity on the photosynthetic activity of the Mediterranean seagrass Posidonia oceanica in a laboratory mesocosm system. To do this, large rhizome fragments were transplanted in a mesocosm laboratory system and maintained at 37 (ambient salinity, control treatment), 39, 41 and 43 (hypersaline treatments) for 47 days. Pigment content, light absorption, photosynthetic characteristics (derived from P vs. E curves and fluorescence parameters), and shoot size, growth rates and net shoot change were determined at the end of the experimental period. Both net and gross photosynthetic rates of plants under hypersaline conditions were significantly reduced, with rates some 25–33% and 13–20% lower than in control plants. The pigment content (Chl a, Chl b, Chl b:Chl a molar ratio, total carotenoids and carotenoids:Chl a ratio), leaf absorptance and maximum quantum yield of PSII ( F v / F m ) of control plants showed little or no changes under hypersaline conditions, which suggests that alterations to the capacity of the photosynthetic apparatus to capture and process light were not responsible for the reduced photosynthetic rates. In contrast, dark respiration rates increased substantially, with mean values up to 98% higher than in control leaves. These results suggest that the respiratory demands of the osmoregulatory process are likely to be responsible for the observed decrease in photosynthetic rates, although alterations to photosynthetic carbon assimilation and reduction could also be involved. As a consequence, leaf carbon balance was considerably impaired and leaf growth rates decreased as salinity increased above the ambient (control) salinity. No significant differences were found in the percentage of net shoot change, but mean values were clearly negative at salinity levels of 41 and 43. Results presented here indicate that photosynthesis of P. oceanica is highly sensitive to hypersaline stress and that it likely account for the decline in leaf growth and shoot survival reported in this and previous studies in response to even small increments of the ambient salinity.