Light-saturated Rate Of Photosynthesis Research Articles

Connecting the dots: Path model to identify key phenotypic traits for screening plants with tolerance to nitrogen deficiency.

Varieties that tolerate low nitrogen (N) application rates can reduce fertilizer costs, minimize nitrate leaching and runoff losses, and lower overall CO2 emissions associated with fertilizer manufacturing. The goal of our research is to show the usefulness of path models to identify key phenotypic traits for screening plants with a tolerance to low N application rates. We grew tolerant and sensitive cultivars of poinsettia (Euphorbia pulcherrima) using a water-soluble fertilizer (15-5-15 Cal Mag) in both optimal (electrical conductivity of 2.5 dS·m-1) and N-deficient (electrical conductivity of 0.75 dS·m-1) treatments and measured 24 different traits at the cellular, leaf, and whole-plant scales in both cultivars and treatments. The experiment was laid out as a split-plot design with N treatments as main plots and cultivars as sub-plots, with five replications. Path analysis was conducted to develop sequential relationships among these traits. Statistical comparisons between tolerant and sensitive cultivars in the N-deficient treatment indicated an increase in shoot biomass (19.9 vs 14.4 g), leaf area (2775 vs 1824 cm2), leaf dry weight (14.7 vs 10.0 g), lateral root dry weight (3.7 vs 2.4 g), light-saturated photosynthesis (14.5 vs 10.1 μmol∙m-2∙s-1), maximum electron transport rate (119 vs 89 μmol∙m-2∙s-1), chlorophyll content (28.1 vs 12.9 g∙100g-1), leaf N content (27.5 vs 19.9 mg∙g-1), and fine root N content (26.1 vs 20.9 mg∙g-1), and a decrease in anthocyanin content (0.07 vs 0.16 ΔOD∙g-1). The path model indicated that an increase in the lateral root growth and fine root N content can lead to an increase in the leaf N content, in the N-deficient treatment. There were three separate paths that connected higher leaf N content to increased shoot biomass. These paths were mediated by the levels of anthocyanin, chlorophylls, and light-saturated photosynthesis rate (or rubisco capacity). The light-saturated photosynthesis model suggested that the increased uptake of N by fine roots in the tolerant cultivar was likely supported by the photosynthates translocated from the shoot to the root. Leaf N content was associated with multiple plant responses in the N-deficient treatment, and can be a useful screening trait for developing new cultivars, especially in marker-assisted molecular breeding.

Impacts of Deficit Irrigation on Photosynthetic Performance, Productivity and Nutritional Quality of Aeroponically Grown Tuscan Kale (Brassica oleracea L.) in a Tropical Greenhouse.

Tuscan kale was grown aeroponically with 5, 30 and 60 min nutrient spraying intervals (defined as 5 minNSIs, 30 minNSIs and 60 minNSIs). Four weeks after transplanting, some 5 minNSI plants were transferred to a 60 minNSI (5 minNSI → 60 minNSI) and 90 minNSI (5 minNSI → 90 minNSI) for one more week. Significantly lower light-saturated rates of photosynthesis and stomatal conductance were observed for plants grown with a 60 minNSI than with a 5 minNSI. However, all plants had similar internal CO2 concentrations and transpiration rates. Reduced light use efficiency but increased energy dissipation was observed in plants grown in a 60 minNSI. A higher nitrate concentration was observed in 60 minNSI plants compared to 5 minNSI and 30 minNSI plants, while all plants had similar concentrations of total reduced nitrogen, leaf soluble protein and Rubisco protein. Plants grown with prolonged NSIs (deficit irrigation) had lower biomass accumulation due to the inhibition of leaf initiation and expansion compared to 5 minNSIs. However, there was no substantial yield penalty in 5 minNSI → 60 minNSI plants. Enhancements in nutritional quality through deficit irrigation at pre-harvest were measured by proline and total soluble sugar. In conclusion, it is better to grow Tuscan kale with a 5 minNSI for four weeks followed by one week with a 60 minNSI before harvest to reduce water usage, yield penalty and enhance nutritional quality.

Precipitation variations, rather than N deposition, determine plant ecophysiological traits in a desert steppe in Northern China

Understanding how plant ecophysiological traits of coexisting species within a community respond to environmental changes could help to predict the shift in plant community structure and function, but it remains limited in the scenarios of co-occurring precipitation variations and N deposition. A two-year field experiment was conducted to explore the effects of large precipitation changes (reduced and increased precipitation amount by 25% and 50% relative to ambient control) and high N deposition (10 g N m−2 yr−1) on a series of leaf ecophysiological traits of three dominant species (Stipa tianschanica, a C3 grass; Cleistogenes squarrosa, a C4 grass; and Artemisia capillaris, a C3 forb) in a desert steppe in Northern China. Increasing precipitation significantly linearly promoted the leaf light-saturated photosynthesis rate (Asat) and N use efficiency of the two C3 species, irrespective of N addition. The rises in Asat of both C3 species were mainly caused by increased soil moisture, which strongly induced increases in leaf stomatal conductance (gs) and declines in quantum yield of photosystem II (ΦPSII). However, the Asat of the two C3 species was weakly correlated with their specific leaf area and leaf N concentration, whereas the Asat of the C4 grass was negatively related to its leaf N. Moreover, the Asat, height, and aboveground biomass of the forbs were much more water-sensitive than those of both grass species, with a consequence of the most dominant species turning from grass to forbs as precipitation increased. Our findings highlight that water limitation, rather than N deficit, is the largest factor controlling plant growth in drylands, and plant species-specific ecophysiological responses to precipitation fluctuations will cause a substantial shift in the production and composition of plant community.

The phytotoxicity of microplastics to the photosynthetic performance and transcriptome profiling of Nicotiana tabacum seedlings

Microplastics (MPs), as emerging “new generation” organic contaminants, have attracted extensive attention regarding their severe toxicity to aquatic and terrestrial organisms. However, the responses of plant photosynthesis to soil MP pollution are unclear. In this study, Nicotiana tabacum seedlings were grown in soils containing 0~1000 g·kg−1 polyethylene (PE)-MPs for 48 days. PE-MPs significantly increased the superoxide anion content by 15.3~44.8% but decreased the chlorophyll content and Rubisco activity by 4.3~14.0% and 4.23~30.9%, respectively. PE-MPs also inhibited RuBP carboxylation activation and regeneration, restrained light use efficiency, and prevented dark respiration, thereby reducing the light-saturated photosynthesis rate. The changed shape of OJIP transients indicated that PE-MP toxicity inhibited not only the primary photochemistry rate but also photoelectrochemical quenching, resulting in decreased quantum yields. RNA-Seq revealed thousands of differentially expressed genes (DEGs), among which 79 highly expressed DEGs were enriched in photosynthesis-related processes. Functional annotation revealed that the reduction in environment stress was mainly due to the repressed expression of light harvesting-, electron transport- and photosystem-related genes in chloroplasts. This study regarding the physiological and molecular responses of photosynthetic performance to soil PE-MP pollution provides a new viewpoint for exploring the plant photosynthesis regulating and protective mechanisms under soil MP stresses.

Intracanopy CO2 and light interactions on Humulus lupulus L. net canopy carbon gain under current and future atmospheric CO2 concentrations

Photosynthetic light response curves were measured in four cultivars of Humulus lupulus L. (hop) at CO2 concentrations of 415, 500, 600, and 700 μmol CO2 mol−1. Short-term elevated CO2 increased net photosynthesis (An), light-saturated rates of photosynthesis, and quantum yield and decreased the light compensation point and leaf respiration. To illustrate the effects on canopy carbon gain, we used a rigorously validated physiologically-explicit canopy process model (MAESTRA). The cultivar-specific leaf-level physiological response parameters at 415, 500, 600, and 700 μmol CO2 mol−1 were extrapolated throughout the canopy to reproduce the cultivar-specific carbon gain under current and future atmospheric CO2 conditions. Under sub optimal light conditions, the initial CO2 increase of 415 to 500 μmol CO2 mol−1 resulted in the highest relative carbon gain increase (∼18%), whereas enrichment from 500 to 600 and 600 to 700 μmol CO2 mol−1 resulted in an additional carbon uptake of ∼16% and ∼12%. Ratios of An to increased CO2 indicated that shaded leaves benefit more from elevated CO2 than light saturated leaves. Estimated daily canopy carbon uptake increased ∼24% from 415 to 500 µmol mol−1 CO2. Daily carbon uptake increased by ∼17% from 500 to 600 µmol mol−1 CO2 and ∼18% from 600 to 700 µmol mol−1. Thus, in comparison to leaves exposed to direct sunlight, hop canopy carbon gain in shaded diffuse light lower canopy layers may contribute a greater proportion of total canopy carbon in future atmospheric CO2 conditions.

Negative effects of long-term phosphorus additions on understory plants in a primary tropical forest

Human activities have disturbed global phosphorus (P) cycling by introducing substantial amounts of P to natural ecosystems. Although natural P gradients and fertilization studies have found that plant community traits are closely related to P availability, it remains unclear how increased P supply affects plant growth and diversity in P-deficient tropical forests. We used a decadal P-addition experiment (2007–2017) to study the effects of increased P input on plant growth and diversity in understory layer in tropical forests. We monitored the dynamics of seedling growth, survival rate, and diversity of understory plants throughout the fertilization period under control and P addition at 15 g P m−2 yr−1. To identify the drivers of responses, P concentration, photosynthesis rate and nonstructural carbon were analyzed. Results showed that long-term P addition significantly increased P concentrations both in soil pools and plant tissues. However, P addition did not increase the light-saturated photosynthesis rate or growth rate of the understory plants. Furthermore, P addition significantly decreased the survival rate of seedlings and reduced the species richness and density of understory plants. The negative effects of P addition may be attributed to an increased carbon cost due to the tissue maintenance of plants with higher P concentrations. These findings indicate that increased P supply alone is not necessary to benefit the growth of plants in ecosystems with low P availability, and P inputs can inhibit understory plants and may alter community composition. Therefore, we appeal to a need for caution when inputting P to tropical forests ecosystems.

Reduced photosynthetic thermal acclimation capacity under elevated ozone in poplar (Populus tremula) saplings.

The sensitivity of photosynthesis to temperature has been identified as a key uncertainty for projecting the magnitude of the terrestrial carbon cycle response to future climate change. Although thermal acclimation of photosynthesis under rising temperature has been reported in many tree species, whether tropospheric ozone (O3 ) affects the acclimation capacity remains unknown. In this study, temperature responses of photosynthesis (light-saturated rate of photosynthesis (Asat ), maximum rates of RuBP carboxylation (Vcmax ), and electron transport (Jmax ) and dark respiration (Rdark ) of Populus tremula exposed to ambient O3 (AO3 , maximum of 30ppb) or elevated O3 (EO3 , maximum of 110ppb) and ambient or elevated temperature (ambient +5°C) were investigated in solardomes. We found that the optimum temperature of Asat (ToptA ) significantly increased in response to warming. However, the thermal acclimation capacity was reduced by O3 exposure, as indicated by decreased ToptA , and temperature optima of Vcmax (ToptV ) and Jmax (ToptJ ) under EO3 . Changes in both stomatal conductance (gs ) and photosynthetic capacity (Vcmax and Jmax ) contributed to the shift of ToptA by warming and EO3 . Neither Rdark measured at 25°C ( ) nor the temperature response of Rdark was affected by warming, EO3 , or their combination. The responses of Asat , Vcmax , and Jmax to warming and EO3 were closely correlated with changes in leaf nitrogen (N) content and N use efficiency. Overall, warming stimulated growth (leaf biomass and tree height), whereas EO3 reduced growth (leaf and woody biomass). The findings indicate that thermal acclimation of Asat may be overestimated if the impact of O3 pollution is not taken into account.

Photosynthetic parameters of a sedge-grass marsh as a big-leaf: effect of plant species composition

The study estimates the parameters of the photosynthesis–irradiance relationship (PN/I) of a sedge-grass marsh (Czech Republic, Europe), represented as an active “green” surface—a hypothetical “big-leaf”. Photosynthetic parameters of the “big-leaf” are based on in situ measurements of the leaf PN/I curves of the dominant plant species. The non-rectangular hyperbola was selected as the best model for fitting the PN/I relationships. The plant species had different parameters of this relationship. The highest light-saturated rate of photosynthesis (Asat) was recorded for Glyceria maxima and Acorus calamus followed by Carex acuta and Phalaris arundinacea. The lowest Asat was recorded for Calamagrostis canescens. The parameters of the PN/I relationship were calculated also for different growth periods. The highest Asat was calculated for the spring period followed by the summer and autumn periods. The effect of the species composition of the local plant community on the photosynthetic parameters of the “big-leaf” was addressed by introducing both real (recorded) and hypothetical species compositions corresponding to “wet” and “dry” hydrological conditions. We can conclude that the species composition (or diversity) is essential for reaching a high Asat of the “big-leaf ”representing the sedge-grass marsh in different growth periods.

Springtime Drought Shifts Carbon Partitioning of Recent Photosynthates in 10-Year Old Picea mariana Trees, Causing Restricted Canopy Development

Springtime bud-break and shoot development induces substantial carbon (C) costs in trees. Drought stress during shoot development can impede C uptake and translocation. This is therefore a channel through which water shortage can lead to restricted shoot expansion and physiological capacity, which in turn may impact annual canopy C uptake. We studied effects of drought and re-hydration on early season shoot development, C uptake and partitioning in five individual 10-year old Picea mariana [black spruce] trees to identify and quantify dynamics of key morphological/physiological processes. Trees were subjected to one of two treatments: (i) well-watered control or (ii) drought and rehydration. We monitored changes in morphological [shoot volume, leaf mass area (LMA)], biochemical [osmolality, non-structural carbohydrates (NSC)] and physiological [rates of respiration (Rd) and light-saturated photosynthesis (Asat)] processes during shoot development. Further, to study functional compartmentalization and use of new assimilates, we 13C-pulse labeled shoots at multiple development stages, and measured isotopic signatures of leaf respiration, NSC pools and structural biomass. Shoot water potential dropped to a minimum of −2.5 MPa in shoots on the droughted trees. Development of the photosynthetic apparatus was delayed, as shoots on well-watered trees broke-even 14 days prior to shoots from trees exposed to water deficit. Rd decreased with shoot maturation as growth respiration declined, and was lower in shoots exposed to drought. We found that shoot development was delayed by drought, and while rehydration resulted in recovery of Asat to similar levels as shoots on the well-watered trees, shoot volume remained lower. Water deficit during shoot expansion resulted in longer, yet more compact (i.e., with greater LMA) shoots with greater needle osmolality. The 12C:13C isotopic patterns indicated that internal C partitioning and use was dependent on foliar developmental and hydration status. Shoots on drought-stressed trees prioritized allocating newly fixed C to respiration over structural components. In conclusion, temporary water deficit delayed new shoot development and resulted in greater LMA in black spruce. Since evergreen species such as black spruce retain active foliage for multiple years, impacts of early season drought on net primary productivity could be carried forward into subsequent years.

Source and sink activity of Holcus lanatus in response to absolute and relative supply of nitrogen and phosphorus.

Mineral nutrients influence photosynthesis and tissue formation; a shift from nitrogen (N)-limited to phosphorus (P)-limited growth induced by high N deposition may change plant growth in terms of physiology and morphology. This experiment showed that absolute and relative N and P supply affected net photosynthesis (source activity) and biomass formation (sink activity), and the relationship between source and sink activities of Holcus lanatus L. under various nutrient treatments. H. lanatus was grown at three N:P ratios (5, 15, 45) with two absolute supply levels of N and P. Between N:P 5 at low level and N:P 45 at high level, and between N:P 45 at low level and N:P 5 at high level, there was a nine-fold difference in N and P supply. Maximum light-saturated net photosynthesis rate (Amax), specific leaf area (SLA), leaf area, and shoot and root biomass were determined during and after the growth process. Amax was minimal at N:P 5 and increased only with increasing absolute N supply. Neither SLA nor leaf area were affected by N:P; increasing absolute P supply significantly increased leaf area. Shoot and root biomass were minimal at N:P 45 and increased dramatically with increasing absolute P supply. Plant biomass was not correlated with Amax. Our results highlight that H. lanatus growth is predominantly controlled by P supply and to a lesser extent by N, whereas net photosynthesis exerted no apparent control on growth under these sink-limited growth conditions. Our findings contribute to understanding of plant growth under sink-limited conditions.

The latitudinal and altitudinal variations in the biochemical mechanisms of temperature dependence of photosynthesis within Fallopia japonica

The temperature dependence of the light-saturated rate of photosynthesis has large interspecific and intraspecific variations, which may be related to adaptation to the habitat environment. As both higher latitude and altitude have lower habitat temperature, we addressed the question of whether temperature adaptation is similar between high-latitude and high-altitude ecotypes. We raised three ecotypes of Fallopia japonica collected from high-latitude and low-altitude (Hirosaki), high-altitude and low-latitude (Fuji), and low-altitude and low-latitude (Tokyo) habitats at two growth temperatures, and determined the temperature dependence of photosynthesis and related biochemical and physical traits, including mesophyll conductance. Temperature dependence of photosynthesis and related traits differed among ecotypes, but the difference was not significant between Fuji and Tokyo when grown at a low-temperature. The simulation analysis suggested that the temperature dependence of Rubisco activity and the CO2 concentration in the chloroplasts had large contributions to the variation in the temperature dependence of photosynthesis. We conclude that both ecotypes from high-altitude and high-latitude habitats tend to have a temperature dependence of photosynthesis which is adaptive to low-temperature conditions, but the mechanisms to adapt to high-altitude are not necessarily the same as compared with those to high-latitude.

Assessing cloudiness effect on soybean yield in the Southeast Brazil

The solar radiation is one of the most important weather variables for determining the potential yield of agricultural crops. Soybean is the main Brazilian agricultural commodity, with great social and economical importance for the country. It is well recognized that cloudiness is a limiting factor for crop growth rate. Few studies have been conducted to systematically evaluate how much cloud affect soybean yield and none, to our knowledge, is available for tropical soybean. The objective of this paper was to quantify the implications of cloudiness on soybean growth and development in tropical Brazil. To do so, experimental data associated with the simulations of the DSSAT/CROPGRO (DC) model was used, and two treatments were simulated: a) the first used measured solar radiation and b) the second used estimated solar radiation for non-cloud days. Thus, based on the model output variables (growth rate of aerial dry matter, grain yield, specific leaf weight, and light saturation point) and comparing the data with the literature review. We found that simulations exhibited an increase in the dry matter production rate of up to 23%, during days of clear sky, resulting in a yield increase between 26 and 37%. Also, the DC could simulate some adaptation in the plant when the solar radiation changes, like the specific foliar weight and the light-saturated photosynthesis rate.

Melatonin enhances drought resistance by regulating leaf stomatal behaviour, root growth and catalase activity in two contrasting rapeseed (Brassica napus L.) genotypes

Two contrasting rapeseed (Brassica napus L.) genotypes, Qinyou 8 (drought-sensitive) and Q2 (drought-tolerant), were studied under drought stress with or without pretreatment with melatonin to (i) explore whether melatonin enhances drought resistance by regulating root growth and (ii) determine the relationship between the belowground and aboveground responses to melatonin under drought stress. Results show that the light-saturated rate of photosynthesis (Pn), stomatal conductance (gs), water use efficiency (WUE) and chlorophyll content were decreased by drought for Qinyou 8, whereas drought only decreased Pn and chlorophyll content for Q2. Drought decreased actual photochemical efficiency in saturated light (Fv’/Fm’), actual photochemical efficiency (PhiPSⅡ), quenching of photochemical efficiency (qL) and electron transport rate (ETR) in Qinyou 8. However drought only decreased Fv’/Fm’ and qL in Q2. Drought increased malondialdehyde (MDA) and hydrogen peroxide (H2O2) contents in the roots of both genotypes. Melatonin had no significant additional effects on root guaiacol peroxidase (POD) and superoxide dismutase (SOD) activities, but enhanced root catalase (CAT) activity of droughted plants further. Melatonin promoted taproot and lateral root growth under drought stress. Melatonin also promoted stomatal opening resulting in enhanced photosynthesis in the two genotypes. The two mechanisms induced by melatonin synergistically enhance drought resistance of rapeseed as indicated by enhanced gas exchange parameters under melatonin pretreatment. The findings provide evidence for a physiological role of melatonin in improving drought resistance, especially in belowground parts.

In silico study of the role of cell growth factors in photosynthesis using a virtual leaf tissue generator coupled to a microscale photosynthesis gas exchange model.

Computational tools that allow in silico analysis of the role of cell growth and division on photosynthesis are scarce. We present a freely available tool that combines a virtual leaf tissue generator and a two-dimensional microscale model of gas transport during C3 photosynthesis. A total of 270 mesophyll geometries were generated with varying degrees of growth anisotropy, growth extent, and extent of schizogenous airspace formation in the palisade mesophyll. The anatomical properties of the virtual leaf tissue and microscopic cross-sections of actual leaf tissue of tomato (Solanum lycopersicum L.) were statistically compared. Model equations for transport of CO2 in the liquid phase of the leaf tissue were discretized over the geometries. The virtual leaf tissue generator produced a leaf anatomy of tomato that was statistically similar to real tomato leaf tissue. The response of photosynthesis to intercellular CO2 predicted by a model that used the virtual leaf tissue geometry compared well with measured values. The results indicate that the light-saturated rate of photosynthesis was influenced by interactive effects of extent and directionality of cell growth and degree of airspace formation through the exposed surface of mesophyll per leaf area. The tool could be used further in investigations of improving photosynthesis and gas exchange in relation to cell growth and leaf anatomy.

Bundle sheath extensions affect leaf structural and physiological plasticity in response to irradiance

Coordination between structural and physiological traits is key to plants' responses to environmental fluctuations. In heterobaric leaves, bundle sheath extensions (BSEs) increase photosynthetic performance (light-saturated rates of photosynthesis, Amax ) and water transport capacity (leaf hydraulic conductance, Kleaf ). However, it is not clear how BSEs affect these and other leaf developmental and physiological parameters in response to environmental conditions. The obscuravenosa (obv) mutation, found in many commercial tomato varieties, leads to absence of BSEs. We examined structural and physiological traits of tomato heterobaric and homobaric (obv) near-isogenic lines grown at two different irradiance levels. Kleaf , minor vein density, and stomatal pore area index decreased with shading in heterobaric but not in homobaric leaves, which show similarly lower values in both conditions. Homobaric plants, on the other hand, showed increased Amax , leaf intercellular air spaces, and mesophyll surface area exposed to intercellular airspace (Smes ) in comparison with heterobaric plants when both were grown in the shade. BSEs further affected carbon isotope discrimination, a proxy for long-term water-use efficiency. BSEs confer plasticity in traits related to leaf structure and function in response to irradiance levels and might act as a hub integrating leaf structure, photosynthetic function, and water supply and demand.

Red/blue light ratio strongly affects steady-state photosynthesis, but hardly affects photosynthetic induction in tomato (Solanum lycopersicum).

Plants are often subjected to rapidly alternating light intensity and quality. While both short- and long-term changes in red and blue light affect leaf photosynthesis, their impact on dynamic photosynthesis is not well documented. It was tested how dynamic and steady-state photosynthetic traits were affected by red/blue ratios, either during growth or during measurements, in tomato leaves. Four red/blue ratios were used: monochromatic red (R100 ), monochromatic blue (B100 ), a red/blue light ratio of 9:1 (R90 B10 ) and a red/blue light ratio of 7:3 (R70 B30 ). R100 grown leaves showed decreased photosynthetic capacity (maximum rates of light-saturated photosynthesis, carboxylation, electron transport and triose phosphate use), leaf thickness and nitrogen concentrations. Acclimation to various red/blue ratios had limited effects on photosynthetic induction in dark-adapted leaves. B100 -grown leaves had a approximately 15% larger initial NPQ transient than the other treatments, which may be beneficial for photoprotection under fluctuating light. B100 -grown leaves also showed faster stomatal closure when exposed to low light intensity, which likely resulted from smaller stomata and higher stomatal density. When measured under different red/blue ratios, stomatal opening rate and photosynthetic induction rate were hardly accelerated by increased fractions of blue light in both growth chamber-grown leaves and greenhouse-grown leaves. However, steady-state photosynthesis rate 30 min after photosynthetic induction was strongly reduced in leaves exposed to B100 during the measurement. We conclude that varying red/blue light ratios during growth and measurement strongly affects steady-state photosynthesis, but has limited effects on photosynthetic induction rate.

Current ambient and elevated ozone effects on poplar: A global meta-analysis and response relationships

The effects of current and future elevated O3 concentrations (e[O3]) were investigated by a meta-analysis for poplar, a widely distributed genus in the Northern Hemisphere with global economic importance. Current [O3] has significantly reduced CO2 assimilation rate (Pn) by 33% and total biomass by 4% in comparison with low O3 level (charcoal-filtered air, CF). Relative to CF, an increase in future [O3] would further enhance the reduction in total biomass by 24%, plant height by 17% and plant leaf area by 19%. Isoprene emissions could decline by 34% under e[O3], with feedback implications in reducing the formation of secondary air pollutants including O3. Reduced stomatal conductance and lower foliar area might increase runoff and freshwater availability in O3 polluted areas. Higher cumulated O3 exposure over a threshold of 40 ppb (AOT40) induced larger reductions in Pn, total biomass and isoprene emission. Relationships of light-saturated photosynthesis rates (Asat), total biomass and chlorophyll content with AOT40 using a global dataset are provided. These relationships are expected to improve O3 risk assessment and also to support the inclusion of the effect of O3 in models addressing plantation productivity and carbon sink capacity.

Increase of apoplastic ascorbate induced by ozone is insufficient to remove the negative effects in tobacco, soybean and poplar

Apoplastic ascorbate (ASCapo) is an important contributor to the detoxification of ozone (O3). The objective of the study is to explore whether ASCapo is stimulated by elevated O3 concentrations. The detoxification of O3 by ASCapo was quantified in tobacco (Nicotiana L), soybean (Glycine max (L.) Merr.) and poplar (Populus L), which were exposed to charcoal-filtered air (CF) and elevated O3 treatments (E-O3). ASCapo in the three species were significantly increased by E-O3 compared with the values in the filtered treatment. For all three species, E-O3 significantly increased the malondialdehyde (MDA) content and decreased light-saturated rate of photosynthesis (Asat), suggesting that high O3 has induced injury/damage to plants. E-O3 significantly increased redox state in the apoplast (redox stateapo) for all species, whereas no effect on the apoplastic dehydroascorbate (DHAapo) was observed. In leaf tissues, E-O3 significantly enhanced reduced-ascorbate (ASC) and total ascorbate (ASC+DHA) in soybean and poplar, but significantly reduced these in tobacco, indicating different antioxidative capacity to the high O3 levels among the three species. Total antioxidant capacity in the apoplast (TACapo) was significantly increased by E-O3 in tobacco and poplar, but leaf tissue TAC was significantly enhanced only in tobacco. Leaf tissue superoxide anion (O2•-) in poplar and hydrogen peroxide (H2O2) in tobacco and soybean were significantly increased by E-O3. The diurnal variation of ASCapo, with maximum values occurring in the late morning and lower values experienced in the afternoon, appeared to play an important role in the harmful effects of O3 on tobacco, soybean and poplar.

Interactive Effects of Ozone and Drought on Antioxidant Enzyme Activities of Poplar Leaves

Ground-level ozone (O3) pollution and drought have become major environmental factors that threaten the normal growth of plants. In this study, we determined the effects of three O3 concentrations (charcoal-filtered air, CF, non-filtered air, NF and non-filtered air+40 nmol·mol-1, NF40), two water treatments (well-watered, WW, and mild drought, MD, 60% of WW in volumetric soil water content), and their interactions on the light-saturated photosynthesis rate (Asat) and on the activity of antioxidant enzymes and soluble proteins of the poplar '546' (Populus deltoids cv. 55/56×P. deltoides cv. Imperial). Results showed that Asat significantly decreased with elevated O3, and with interactions between O3 and drought. Drought significantly reduced the activities of catalase (CAT) and superoxide dismutase (SOD) but did not affect the activities of peroxidase (POD) or ascorbate peroxidase (APX). Reduction ranges in CAT and SOD increased with drought duration. APX activity significantly decreased with increasing O3 and drought, but soluble protein content did not. Activities of antioxidant enzymes were not significantly affected by elevated O3 and their interactions. Results provide a scientific basis for protection of poplar plantations in response to increasing O3 concentrations and drought under environmental changes.

English

The present study was undertaken to investigate the photosynthetic productivity and biomass of phytoplankton for Lake Tinishu Abaya to observe the potentiality of the lake water for fish production. The study was carried out from January to December 2016. For the analysis of various physicochemical parameters, water samples collection was taken from two predefined sampling stations (open-water and nearshore). Biomass of phytoplankton was measured as concentration of chlorophyll a. Primary productivity of phytoplankton was measured at the open station within the Euphotic depth using light-dark bottle technique. It was observed from the results that the light-saturated rate of photosynthesis (Amax), ranged from 0.62 g C m-3 h-1 to 2.02 g C m-3 h-1 and biomass-specific rate of photosynthetic productivity at light saturation (Pmax) ranged 0.02 g C (mg Chl a)-1 h-1) to 0.106 g C (mg Chl a)-1 h-1). The hourly integral photosynthetic production (∑A), varied between 0.247 g C m-2 h-1 and 1.022 g C m-2 h-1, whereas the calculated pattern of variation for the daily integral rates of photosynthesis (ΣΣA) was ranged 5.43 g C m-2 d-1 to 9.194 g C m-2 d-1. The concentration of phytoplankton biomass (chlorophyll-a) was varied from 18.97mg/L to 65.05 mg/L. Based on the results of the study on various physicochemical factors, photosynthetic productivity and biomass of phytoplankton, it was concluded that the water of Lake Tinishu Abaya was chemically and biologically productive which supports most aquatic lives, production of fish, and other related multidimensional uses. Key words: Biomass, photosynthetic productivity, physicochemical factors, phytoplankton, light-dark bottle technique. &nbsp