Non-stomatal Limitations Research Articles

Interactive Regimes of Reduced Irrigation and Salt Stress Depressed Tomato Water Use Efficiency at Leaf and Plant Scales by Affecting Leaf Physiology and Stem Sap Flow.

Interactive effects of reduced irrigation and salt stress on leaf physiological parameters, biomass accumulation, and water use efficiency (WUE) of tomato plants at leaf and whole plant scales were investigated in a field experiment during 2016 and a greenhouse experiment during 2017. Experiment utilized two irrigation regimes (full, 2/3 of full irrigation) and four soil salt regimes (0, 0.3, 0.6, 0.9% in 2016 season; and 0, 0.2, 0.3, 0.4% in 2017 season). Three salts, sodium chloride, magnesium sulfate, and calcium sulfate (mass ratio of 2:2:1), were homogeneously mixed with soil prior to packing into containers (0.024 m3). Li-COR 6400 was used to measure tomato leaf physiological parameters. Instantaneous water use efficiency (WUEins, μmol mmol−1) and intrinsic water use efficiency (WUEint, μmol mol−1) were determined at leaf scale, yield water use efficiency (WUEY, g L−1), and dry biomass water use efficiency (WUEDM, g L−1) were determined at whole plant scale. Plants irrigated with 2/3 of full irrigation with zero soil-salt treatment had higher dry biomass and yield per plant, resulting in the highest WUEDM and WUEY at whole plant scale. Increasing soil salinity decreased dry biomass and yield, leading to greater decreases in whole plant WUEDM and WUEY under both irrigation treatments. At full irrigation, no decreases in stomatal conductance (gs, mol m−2 s−1) and slight increase in photosynthetic rate (Pn, μmol m−2 s−1) led to higher WUEint at leaf scale during both years. Under full and reduced irrigation, increasing soil salt content decreased Pn and transpiration rate (Tr, mmol m−2 s−1) and led to reductions in WUEins at the leaf scale. However, compared to full irrigation, reduced irrigation improved WUEins with a significant decline in Tr in no salt and 0.3% soil-salt treatments during both years. For soil salt content of 0.6%, stomatal limitation due to salt stress resulted in higher WUEint, but soil salt content of 0.9% decreased WUEint due to non-stomatal limitation. Soil salt content significantly decreased sap flow, with the maximum variation of daily sap flow per plant of 7.96–31.37 g/h in 2016 and 12.52–36.02 g h−1 in 2017. Sap flow rate was linearly related to air temperature (Ta, °C), solar radiation (Rs, W m−2), and vapor pressure deficit (VPD, kPa). These results advance knowledge on tomato response to abiotic stresses and could improve management of tomato production in water- and salt-stressed areas.

A novel optimization approach incorporating non-stomatal limitations predicts stomatal behaviour in species from six plant functional types.

The primary function of stomata is to minimize plant water loss while maintaining CO2 assimilation. Stomatal water loss incurs an indirect cost to photosynthesis in the form of non-stomatal limitations (NSL) via reduced carboxylation capacity (CAP) and/or mesophyll conductance (MES). Two optimal formulations for stomatal conductance (gs) arise from the assumption of each type of NSL. In reality, both NSL could coexist, but one may prevail for a given leaf ontogenetic stage or plant functional type, depending on leaf morphology. We tested the suitability of two gs formulations (CAP versus MES) on species from six plant functional types (C4 crop, C3 grass, fern, conifer, evergreen, and deciduous angiosperm trees). MES and CAP parameters (the latter proportional to the marginal water cost to carbon gain) decreased with water availability only in deciduous angiosperm trees, while there were no clear differences between leaf ontogenetic stages. Both CAP and MES formulations fit our data in most cases, particularly under low water availability. For ferns, stomata appeared to operate optimally only when subjected to water stress. Overall, the CAP formulation provided a better fit across all species, suggesting that sub-daily stomatal responses minimize NSL by reducing carboxylation capacity predominantly, regardless of leaf morphology and ontogenetic stage.

Photosynthetic capacity, osmotic adjustment and antioxidant system in sugar beet (Beta vulgaris L.) in response to alkaline stress

Photosynthetic characteristics of sugar beet cultivars KWS0143 and Beta464 were studied under alkaline conditions, including 0 (A0, control), 25 (A1), 50 (A2), 75 (A3), and 100 mM of mixed alkali (Na2CO3:NaHCO3, 1:2). A2, A3, and A4 reduced net photosynthetic rate (PN), stomatal conductance, and transpiration rate, but rose intercellular CO2 concentration. Reduction in PN occurred probably due to nonstomatal limitation. The decrease in efficiency of photosynthetic electron transport might be the main reason for the decrease of PN. The concentrations of photosynthetic pigments were significantly reduced by high (A3 and A4) alkalinity. Changes in chloroplast ultrastructure are the reason for the decrease in chlorophyll content. Sugar beet could resist injury from alkali owing to osmotic substances and antioxidant enzymes if alkaline stress was at a lower level. The better performance of KWS0143 under alkalinity might be associated with its more efficient osmotic and antioxidant systems to resist injury of photosynthetic apparatus caused by alkalinity.

增温对宁夏北部春小麦叶片光合作用的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 增温对宁夏北部春小麦叶片光合作用的影响 DOI: 10.5846/stxb201810302343 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 宁夏高等学校科学技术研究资助项目（NGY2015055）；宁夏自然科学基金资助项目（NZ16007）；国家自然科学基金项目（31660377） Effects of elevated temperature on photosynthesis of spring wheat in northern Ningxia Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为探索宁夏北部春小麦叶片光合作用应对未来气候变化的响应机制，进一步阐明气候变暖对干旱半干旱区春小麦生长的影响。采用自动控制红外线辐射器野外增温模拟气候变化的方法，以不做增温处理的春小麦冠层温度为基础温度，设置不同增温梯度（CK：0℃、T1：0.5℃、T2：1℃、T3：1.5℃、T4：2.0℃），开展气温升高对宁夏北部春小麦全生育期叶片叶面积、光合色素含量、光合特性、叶绿素荧光参数、干物重、产量等指标的影响试验。结果表明：春小麦苗期-拔节期，温度增加0.5℃时叶片叶面积、叶绿素含量、Pn（净光合速率）、WUE（叶片水分利用效率）呈上升的趋势。温度增加1.0-2.0℃时以上指标呈下降趋势，同时Ls（气孔限制值）呈上升趋势，Ci（胞间CO2浓度）呈下降的趋势，说明此时叶片Pn的下降主要是叶绿素含量的下降和气孔限制导致的。春小麦拔节期之后，叶片叶面积、叶绿素含量、Pn、WUE、Ls随温度的增加呈下降的趋势，而Ci随温度的增加呈上升的趋势，说明此时叶片Pn的下降则主要是叶绿素含量的下降和非气孔因素导致。叶绿素荧光参数表明在苗期-拔节期，春小麦对温度升高具有一定的抗逆性，能应对增温胁迫以热耗散的形式做出自我保护。拔节期以后，春小麦叶片光系统Ⅱ反应中心受温度胁迫可逆性失活，光合机构受到破坏。另外，春小麦干物重的变化趋势与叶面积等指标的变化趋势基本一致，产量及产量构成因素小穗数、穗粒数、千粒重随温度的增加显著降低，说明春小麦拔节期之前增温0.5℃有利于提高叶片光系统Ⅱ的潜在活性，增加叶片抗逆性，促进光合作用的进行，最终使光合产物累积量增多。增温梯度过大或增温时间过长则会使春小麦受高温胁迫，导致叶片光系统Ⅱ原初光能捕获、电子传递等效率降低，光合机构受到破坏，致使叶片Pn、WUE等数值下降，光合产物累积量减少，产量减少。 Abstract:In order to explore the response mechanism of photosynthesis of spring wheat leaves to climate change in northern Ningxia, the effects of warming on the growth of spring wheat in arid and semi-arid regions were further clarified. The effects of elevated temperature on leaf area, photosynthetic pigment content, photosynthetic characteristics, chlorophyll fluorescence parameters, and dry weight of spring wheat during the growth period in northern Ningxia were tested using automatic control infrared radiator for simulating climate change in the field. The method was based on the temperature of the spring wheat canopy temperature without treatment, and different temperature gradients were set (CK:0℃, T1:0.5℃, T2:1℃, T3:1.5℃, and T4:2.0℃). The results showed that leaf area, chlorophyll content, Pn (net photosynthetic rate), and WUE (leaf water use efficiency) of spring wheat had an upward trend when the temperature increased by 0.5℃ during seedling-jointing stage. The above indices indicated a downward trend when the temperature increased by 1.0-2.0℃, while Ls (stomatal limitation value) showed an upward trend and Ci (intercellular CO2 concentration) showed a downward trend, indicating that the decrease of Pn in leaves was mainly caused by the decrease of chlorophyll content and stomatal limitation. However, after the jointing stage, the leaf area, chlorophyll content, Pn, WUE, and Ls were decreased when increasing temperature, while Ci increased, which indicating that the decrease of leaf Pn was mainly caused by a decrease in chlorophyll and non-stomatal limitation. Chlorophyll fluorescence parameters showed that spring wheat was resistant to temperature rise before jointing stage, and could cope with the warming stress to protect itself in the form of heat dissipation. After the jointing stage, the photosystem II reaction center of spring wheat leaves was reversibly inactivated by temperature stress, and the photosynthetic apparatus was destroyed. In addition, the change trend of dry weight of spring wheat was basically consistent with that of leaf area and other indicators. The yield and yield components, spikelet number, grains number per spike, and 1000-grain weight decreased significantly with rising temperature. When 0.5℃ rising before jointing stage, it was beneficial to increase the potential activity of leaf photosystem II, increase leaf resistance, promote photosynthesis, and eventually increase photosynthetic product. If the temperature gradient is too large or the heating time is too long, spring wheat will be subjected to high temperature stress, which leads to the reduction of the original light energy capture and electron transfer efficiency of the leaf photosystem II, and the photosynthetic mechanism is damaged. Finally, the values of Pn and WUE in the leaves of spring wheat decreased, the accumulation of photosynthetic products and the yield decreased. 参考文献 相似文献 引证文献

Response of gas-exchange characteristics and chlorophyll fluorescence to acute sulfur dioxide exposure in landscape plants

To explore the toxicity and action mechanism of acute sulfur dioxide (SO2) on urban landscape plants, a simulated SO2 stress environment by using fumigation chamber involving increasing SO2 concentration (0, 25, 50, 100, 200 mg m−3) was carried out among three species. After 72 h of exposure, SO2-induced oxidative damage indicated by electrolyte leakage increased with higher dose of SO2. Meanwhile, SO2 decreased the contents of chlorophyll a, chlorophyll b and carotenoid and increased the contents of sulfur. Net photosynthetic rate (Pn) decreased as a result of stomatal closure when SO2 dose was lower than 50 mg m−3, out of this range, non-stomatal limitation play a dominant role in the decline of Pn. Simultaneous measurements of chlorophyll fluorescence imaging (CFI) also revealed that the maximal quantum efficiency of PSII photochemistry in dark-adapted state (Fv/Fm) and the realized operating efficiency of PSII photochemistry (Fq'/Fm') was reduced by SO2 in a dose-dependent manner. In addition, the maximum quantum efficiency of PSII photochemistry in light-adapted state (Fv'/Fm') and the PSII efficiency factor (Fq'/Fv') decreased when exposure to SO2. These results implied that acute SO2 exposure induced photoinhibition of PSII reaction centers in landscape plants. Our study also indicated that different urban landscape plant species resist differently to SO2: Euonymus kiautschovicus > Ligustrum vicaryi > Syringa oblata according to gas-exchange characteristics and chlorophyll fluorescence responses.

Waterlogging of Winter Crops at Early and Late Stages: Impacts on Leaf Physiology, Growth and Yield.

Waterlogging is expected to increase as a consequence of global climate change, constraining crop production in various parts of the world. This study assessed tolerance to 14-days of early- or late-stage waterlogging of the major winter crops wheat, barley, rapeseed and field pea. Aerenchyma formation in adventitious roots, leaf physiological parameters (net photosynthesis, stomatal and mesophyll conductances, chlorophyll fluorescence), shoot and root growth during and after waterlogging, and seed production were evaluated. Wheat produced adventitious roots with 20–22% of aerenchyma, photosynthesis was maintained during waterlogging, and seed production was 86 and 71% of controls for early- and late-waterlogging events. In barley and rapeseed, plants were less affected by early- than by late-waterlogging. Barley adventitious roots contained 19% aerenchyma, whereas rapeseed did not form aerenchyma. In barley, photosynthesis was reduced during early-waterlogging mainly by stomatal limitations, and by non-stomatal constraints (lower mesophyll conductance and damage to photosynthetic apparatus as revealed by chlorophyll fluorescence) during late-waterlogging. In rapeseed, photosynthesis was mostly reduced by non-stomatal limitations during early- and late-waterlogging, which also impacted shoot and root growth. Early-waterlogged plants of both barley and rapeseed were able to recover in growth upon drainage, and seed production reached ca. 79–85% of the controls, while late-waterlogged plants only attained 26–32% in seed production. Field pea showed no ability to develop root aerenchyma when waterlogged, and its photosynthesis (and stomatal and mesophyll conductances) was rapidly decreased by the stress. Consequently, waterlogging drastically reduced field pea seed production to 6% of controls both at early- and late-stages with plants being unable to resume growth upon drainage. In conclusion, wheat generates a set of adaptive responses to withstand 14 days of waterlogging, barley and rapeseed can still produce significant yield if transiently waterlogged during early plant stages but are more adversely impacted at the late stage, and field pea is not suitable for areas prone to waterlogging events of 14 days at either growth stage.

PHOTOSYNTHETIC PARAMETERS AS PHYSIOLOGICAL INDICATORS OF TOLERANCE TO CADMIUM STRESS IN SUNFLOWER GENOTYPES

ABSTRACT The objective of the present study was to evaluate the tolerance to cadmium (Cd) of sunflower genotypes grown in greenhouse conditions, and the effectiveness of using photosynthetic parameters as physiological indicators of this tolerance. Seeds of two sunflower genotypes previously identified as tolerant (H358) and Cd-sensitive (AG960) to Cd were used. The seeds were germinated in plastic cups containing plant substrate; after 9 days, the seedlings were transplanted to plastic basins containing a nutrient solution with 0 or 10 µM of Cd, where they remained for 16 days. Samples of the plants were harvested every 5 days. The experiment was carried out in a randomized complete design, using a 4×2×2 factorial arrangement (4 days of grown in a nutrient solution with Cd, 2 sunflower genotypes, and 2 Cd levels) with four replications. Cd stress decreased CO2 net assimilation, stomatal conductance, carboxylation efficiency, photosynthetic pigment contents, potential quantum yield (Fv/Fm), and effective quantum yield of plants of the two evaluated genotypes. The decrease in photosynthetic rates of these plants was caused by both stomatal and non-stomatal limitations. Plants of the AG960 genotype showed more pronounced deleterious effects due to Cd stress than those of the H358 genotype. Thus, CO2 net assimilation rate, stomatal conductance, and chloroplast pigment content are good physiological indicators of sunflower tolerance to Cd and can at least in part, explain the greater tolerance of the H358 genotype to Cd stress when compared to the AG960 genotype.

Kaolin particle film modulates morphological, physiological and biochemical olive tree responses to drought and rewatering

Regarding the foreseeing climate change is reasonable to expect harmful consequences to olive tree (Olea europaea L.), an iconic species of Mediterranean region. Thus, the selection of practices that allow a better drought resistance and recovery capacity needs the immediate attention of scientific community. This study evaluates the strategies adopted by young potted olive trees, subjected to three cycles of drought and rewatering, in the presence of a reflective clay, kaolin (KL). The results demonstrated that KL induced shade-related leaf structural changes and was effective in keeping leaf water status during the most stressful periods. In general, photosynthetic activity of sprayed plants was improved by the alleviation of drought-induced stomatal and non-stomatal limitations. Moreover, during stress imposition sprayed leaves showed reduced oxidative damages, allowing lower investment in antioxidant defences. Furthermore, sprayed plants also had lower nighttime water losses due to inferior nighttime stomatal conductance, and are able to maintain higher respiration rates. Upon rewatering, the shaded effect conferred by KL limited gas exchange restauration, but improved the plants’ capacity to restore the metabolic functions. In spite of the induced physiological and biochemical changes, no significant differences were found in whole-plant water use efficiency and plant biomass accumulation, possibly by the attenuation of photosynthesis restauration during the recovery events. In conclusion, the changes induced by KL might be beneficial under severe conditions, as on realistic Mediterranean field environments.

Changes in sugar metabolism associated to stem bark thickening partially assist young tissues of Eriobotrya japonica seedlings under boron stress

Boron (B) toxicity frequently affects plant performances and productivity, especially in arid and semi-arid environments. In this experiment, loquat seedlings were subjected to 25 μM (control) or 400 μM B (B excess) to test the hypothesis that (i) B alters sugar/polyol metabolism in polyol-producing tree species as loquat and (ii) changes of leaf and stem anatomy assist young tissues against toxic effect of B. Gas exchange was monitored from the beginning of the experiment (FBE) till one week after the first visible symptoms of B toxicity appeared in the upper part of the stems (147 d FBE). At 147 FBE, plant biometric parameters and pattern of B accumulation, leaf and stem anatomy, chlorophyll a fluorescence kinetics as well as biochemical measurements were assessed in top (asymptomatic) leaves and upper stem bark. Boron accumulated principally (in the row) in top leaves > top bark > top wood in B-stressed plants, but no changes in allocation pattern were found between controls and B-stressed plants. Excess B promoted the increase in the spongy layer of top leaves and caused the development of cork and numerous collenchyma cells with increased cell wall thickness. This mechanism, which has never been described before, can be considered an attempt to store excessive B in tissues where B ions are less harmful. The accumulation of sorbitol (B-complexing polyol) in top leaves and stem bark can be considered as a further attempt to detoxify B excess. However, B toxicity drastically affects the photosynthetic rate of top leaves, mainly due to non-stomatal limitations, i.e., reduction of ambient CO2 use efficiency and of photosystem II (PSII) efficiency, modification of the partitioning excess energy dissipation in PSII, thus leading to an increased level of lipid peroxidation. Our results suggest that changes in sugar metabolism associated with leaf and stem bark thickening partially assist (but not totally preserve) young tissues of loquat plants under B stress.

Threshold effect of the groundwater depth on the photosynthetic efficiency of Tamarix chinensis in the Yellow River Delta

Groundwater is a major factor that affects the growth and distribution of Tamarix chinensis in the Yellow River Delta (YRD). The response relationship between the photosynthetic physiological processes of T. chinensis and the depth to groundwater (DGW) remains unclear. This paper aims to elucidate the response pattern of photosynthetic efficiency to the DGW and to determine the suitable DGW for the growth of T. chinensis. Three-year-old T. chinensis, a dominant species in the YRD, was used as the research object, and seven DGW treatments of 0–1.8 m under low salinity conditions were simulated to determine and analyse the biomass of T. chinensis, the light responses of leaf gas exchange parameters, and the photosynthetic productivity classification under different DGW treatments. There were significant threshold effects of the DGW on the net photosynthetic rate (Pn), transpiration rate (Tr), and water use efficiency (WUE) of T. chinensis leaves, indicating that photosynthetic parameters had significant DGW threshold effects. Different DGW treatments significantly changed the water and salt conditions in the T. chinensis-planted soil column, thereby significantly affecting T. chinensis growth, photosynthetic capacity, and WUE. With increasing the DGW, the soil relative water content and soil salt content gradually decreased, while the soil solution absolute concentration and T. chinensis biomass first decreased and then increased, followed by another decrease. The growth and photosynthetic capacity of T. chinensis at a high DGW (≥1.2 m) were significantly higher than those at a low DGW (≤0.6 m). At the medium DGW of 0.9 m, the biomass, photosynthetic capacity, water consumption associated with transpiration, and water and light use efficiencies of T. chinensis all reached their highest values. When the DGW was increased from 0.9 m to 1.8 m or decreased from 0.9 m to 0.3 m, the reduction of Pn in T. chinensis changed from a stomatal to a non-stomatal limitation. At the shallow DGW (≤0.3 m) and the deep DGW (1.8 m), the reduction in Pn was largely affected by photosynthetically active radiation. The 1.03–1.44 m DGW was referred to as the “high-yield and high-efficiency DGW”, at which T. chinensis exhibited good growth, high photosynthetic capacity, and high-efficiency physiological water use characteristics. Differences in the DGW changed the soil water content and salt content, and the soil solution absolute concentration was a key factor that affected the growth and photosynthetic efficiency of T. chinensis. However, soil drought stress at the deep DGW and soil salt stress at the shallow DGW were the main factors that affected the photosynthetic physiological processes of T. chinensis. T. chinensis exhibited adaptability characteristics of adequate tolerance to drought stress but intolerance to salt and flooding stresses.

Trans-aconitic acid inhibits the growth and photosynthesis of Glycine max

Grasses producing trans-aconitic acid, a geometric isomer of cis-aconitic acid, are often used in Glycine max rotation systems. However, the effects of trans-aconitic acid on Glycine max are unknown. We conducted a hydroponic experiment to evaluate the effects of 2.5–10 mM trans-aconitic acid on Glycine max growth and photosynthesis. The results revealed that the enhanced H2O2 production in the roots increased the membrane permeability and reduced the water uptake. These effects culminated with a reduced stomatal conductance (gs), which seems to be the main cause for a decreased photosynthetic rate (A). Due to low gs, the limited CO2 assimilation may have overexcited the photosystems, as indicated by the high production of H2O2 in leaves. After 96 h of incubation, and due to H2O2-induced damage to photosystems, a probable non-stomatal limitation for photosynthesis contributed to reducing A. This is corroborated by the significant decrease in the quantum yield of electron flow through photosystem II in vivo (ΦPSII) and the chlorophyll content. Taken together, the damage to the root system and photosynthetic apparatus caused by trans-aconitic acid significantly reduced the Glycine max plant growth.

Assessing stomatal and non-stomatal limitations to carbon assimilation under progressive drought in peanut (Arachis hypogaea L.)

Drought is known to limit carbon assimilation in plants. However, it has been debated whether photosynthesis is primarily inhibited by stomatal or non-stomatal factors. This research assessed the underlying limitations to photosynthesis in peanuts (Arachis hypogaea L.) grown under progressive drought. Specifically, field-grown peanut plants were exposed to either well-watered or drought-stressed conditions during flowering. Measurements included survey measurements of gas exchange, chlorophyll fluorescence, PSII thermotolerance, pigment content, and rapid A-Ci response (RACiR) assessments. Drought significantly decreased stomatal conductance with consequent declines in photosynthesis (AN), actual quantum yield of PSII, and electron transport rate (ETR). Pigment contents were variable and depended on stress severity. Stomatal closure on stressed plants resulted in higher leaf temperatures, but Fv/Fm and PSII thermotolerance were only slightly affected by drought. A strong, hyperbolic relationship was observed between stomatal conductance, AN, and ETR. However, when RACiR analysis was conducted, drought significantly decreased AN at Ci values comparable to drought-stressed plants, indicating non-stomatal limitations to AN. The maximum rate of carboxylation and maximum electron transport rate were severely limited by drought, and chloroplast CO2 concentration (CC) declined substantially under drought along with a comparable increase in partitioning of electron flow to photorespiration. Thus, while stomatal conductance may be a viable reference indicator of water deficit stress in peanut, we conclude that declines in AN were largely due to non-stomatal (diffusional and metabolic) limitations. Additionally, this is the first study to apply the rapid A-Ci response method to peanut, with comparable results to traditional A-Ci methods.

Physiological, biochemical and molecular responses to water stress and rehydration in Mediterranean adapted tomato landraces.

Mediterranean tomato landraces adapted to arid environments represent an option to counteract drought, and to address the complexity of responses to water deficit and recovery, which is a crucial component of plant adaptation mechanisms. We investigated physiological, biochemical and molecular responses of two Mediterranean tomato landraces, 'Locale di Salina' (Lc) and 'Pizzutello di Sciacca' (Pz) under two dehydration periods and intermediate rehydration in greenhouse pot experiments. Relationship between CO2 assimilation (A) and stomatal conductance under severe water stress (gs <0.05mol·m-2 ·s-1 ) indicated the occurrence of stomatal and non-stomatal limitations of photosynthesis. Gas exchange promptly recovered within 2-3days of rehydration. ABA and gs showed a strict exponential relationship. Both leaf ABA and proline peaked under severe water stress. Lc showed higher accumulation of ABA and higher induction of the expression of both NCED and P5CS genes than Pz. Poly(ADP-ribose) polymerase increased during imposition of stress, mainly in Lc, and decreased under severe water stress. The two landraces hardly differed in their physiological performance. Under severe water stress, gs showed low sensitivity to ABA, which instead controlled stomatal closure under moderate water stress (gs >0.15mol·m-2 ·s-1 ). The prompt recovery after rehydration of both landraces confirmed their drought-tolerant behaviour. Differences between the two landraces were instead observed at biochemical and molecular levels.

Interactive effects of seasonal drought and nitrogen deposition on carbon fluxes in a subtropical evergreen coniferous forest in the East Asian monsoon region

Subtropical forests in the East Asian monsoon region function as considerable carbon sinks in the Northern Hemisphere. Forest ecosystems in this region have experienced intensified seasonal drought that has limited their carbon sequestration capacity, but increasing atmospheric nitrogen deposition has contrarily enhanced their capacity to act as carbon sinks. Understanding and quantifying the interactive effects of seasonal drought and nitrogen deposition on the carbon sequestration of subtropical forests is of great significance for accurately predicting future changes to the terrestrial carbon cycle. In this study, we used the Community Land Model Version 4.5 (CLM4.5) to investigate how carbon fluxes, i.e. gross primary productivity (GPP), ecosystem respiration (Re), and net ecosystem productivity (NEP), respond to seasonal drought and nitrogen deposition in an evergreen coniferous forest in southern China. Our results showed that reduced GPP during the drought in the summers of 2003 and 2007 weakened the forest’s carbon sequestration capacity. The reduction in GPP mainly occurred at the sunlit canopy due to its higher sensitivity to soil water stress, and non-stomatal limitations played an important role in limiting leaf photosynthesis. The enhanced NEP by nitrogen deposition was attributed to increased plant growth, which could, in turn, be attributed to increases in leaf area. Interactions of seasonal drought and nitrogen deposition varied with drought severity. Interactive effects of the two drivers on GPP, Re, and NEP were additive under mild and moderate drought conditions but non-additive under severe drought. Their net effects on NEP shifted from +29% under mild and moderate drought conditions to -56% under severe drought. Our study highlights the importance of accounting for the interactive effects of seasonal drought and nitrogen deposition in assessing the carbon sequestration of subtropical forest ecosystems in the East Asian monsoon region.

Effect of irrigation with brackish water on photosynthesis characteristics and yield of winter wheat

In order to obtain the suitable alternative of saline water irrigation pattern and reveal the physiological and growth response mechanism for winter wheat, a field experiment was conducted in Yellow River Delta, Shandong, North China. Four irrigation treatments(irrigating 80 mm with fresh water each at jointing and heading stages, irrigating 80 mm with fresh water each at jointing, heading and milking stages, irrigating 80 mm with fresh-saline water each at jointing and heading stages, irrigating 80 mm with fresh-saline-saline water each at jointing, heading and milking stages) were designed. The collected datum were used to analyse the effects of saline water irrigation on photosynthesis characteristics, biomass and yield of winter wheat. The results show that, the winter wheat leaf stomatal regulation under saline water irrigation caused decreasing in plant transpiration rate, through improving the non-stomatal limitation factor, while ensuring a high net photosynthetic rate at milky stage, thus high efficiency of leaf water use efficiency significantly. Compared with the treatment of fully irrigated with fresh, plant height and biomass of winter wheat were inhibited, also yield decreased by 3%-13% and fresh water saved 50%-67% under the treatment with fresh-saline water. If saline water irrigation schedule is rational and rainfall reaches to the average level, the utilization of saline water for winter wheat could be prospective, which have important practical significance for the sustainable agriculture in the region.

Proteomic analysis on mangrove plant Avicennia marina leaves reveals nitric oxide enhances the salt tolerance by up-regulating photosynthetic and energy metabolic protein expression.

Avicennia marina (Forsk.) Vierh is one of the most salt-tolerant mangrove species. Our previous study revealed that nitric oxide (NO) enhanced the salt tolerance of A. marina by promoting salt secretion and Na+ sequestration under salt stress. However, little is known about the regulation of NO on proteomic profiling for this mangrove species. In this study, we used sodium nitroprusside (SNP), an NO donor, to investigate the regulatory mechanism of NO on salt tolerance of A. marina according to physiological and proteomic aspects. Photosynthesis data showed that the reduction in photosynthesis caused by high salinity treatment (400 mM NaCl) could be partially recovered by addition of SNP (100 μM). Further analysis revealed that the high salinity treatment could induce not only the stomatal limitation but also non-stomatal limitation on photosynthetic reduction, while SNP addition could restore the non-stomatal limitation, implying that the application of SNP was beneficial to the metabolic process in leaves. Proteomic analysis identified 49 differentially expressed proteins involved in various biological processes such as photosynthesis, energy metabolism, primary metabolism, RNA transcription, protein translation and stress response proteins. Under high salinity treatment, the abundances of proteins related to photosynthesis, such as ribulose-phosphate 3-epimerase (RPE, spot 3), RuBisCO large subunit (RBCL, spot 4, 5, 24), RuBisCO activase A (RCA, spot 17, 18) and quinine oxidoreductase-like protein isoform 1 (QOR1, spot 23), were significantly decreased. However, the abundance of proteins such as RBCL (spot 5, 9) and QOR1 (spot 23) were increased by SNP addition. In addition, exogenous NO supply alleviated salt tolerance by increasing the accumulation of some proteins involved in energy metabolism (spot 15), primary metabolism (spot 25, 45, 46), RNA transcription (spot 36) and stress response proteins (spot 12, 21, 26, 37, 43). The transcriptional levels of nine selected proteins were mostly consistent with their protein abundance except spot 46. Overall, the presented data demonstrated that NO has a positive effect on improving salt tolerance in A. marina by regulating the protein abundance involved in photosynthesis, energy metabolism, primary metabolism and stress response.

Photosynthetic and antioxidant response of wheat to di(2-ethylhexyl) phthalate (DEHP) contamination in the soil

Di(2-ethylhexyl) phthalate (DEHP) is a commonly used, artificially-synthesized, industrial chemical that can be released into the soil. However, to date, there is no comprehensive study on the effects of DEHP on photosynthesis, induction of reactive oxygen species, and response of the antioxidant defense system in wheat plants growing in DEHP contaminated soil. This study was conducted to address this gap in knowledge. Our results showed that after application of 10, 20, and 40 mg/kg DEHP, photosynthetic parameters, fluorescence parameters, and chlorophyll content of wheat leaves at seedling, jointing, and booting stages decreased, while the intercellular carbon dioxide concentration increased. This indicates that the observed decrease in net photosynthetic rate in wheat leaves was due to a non-stomatal limitation, wherein DEHP seems to have hindered the photoelectron transfer process. Both superoxide anion (O2-) and hydrogen peroxide (H2O2) content increased in the roots, stems, and leaves in plant under DEHP treatment compared with those in the control plants. Antioxidant enzyme activity increased with increasing DEHP stress, except under the 40 mg/kg treatment at the seedling stage. The antioxidant system had a certain protective effect on wheat, but DEHP still caused peroxidation of cell membrane lipids. The extent of DEHP damage to the roots, stems, and leaves was concentration dependent. Furthermore, enzymatic activity tolerance increased with metabolism, and long-term effects of DEHP gradually decreased with plant growth. Finally, the toxic effects of DEHP on root tissues were more serious at the seedling and jointing stages.

Effects of decomposing leaf litter of Leucaena leucocephala on photosynthetic traits of Cynodon dactylon and Medicago sativa

Leucaena leucocephala is an introduced species, which has been widely used in mountain ecological restoration in southwestern China. To investigate the allelopathic effects of decomposing L. leucocephala leaf litter, the photosynthetic physiology of seedlings of two recipient plants, Cynodon dactylon and Medicago sativa, were measured in this controlled study. As the amount of decomposing L. leucocephala leaf litter increased, the net photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs) decreased continuously, and the intercellular CO2 concentration (Ci) increased continuously in both recipient plants. In M. sativa, all abovementioned indices differed significantly compared with the control group: Pn, Gs, and Tr decreased by 41.69, 59.35, and 48.02%, respectively, and Ci increased by 28.53%. In C. dactylon, Gs decreased significantly by 27.27%. Analysis of the photosynthesis–light response curve indicated that the maximum net photosynthetic rate (Pnmax) and dark respiration rate (Rd) of C. dactylon, as well as Pnmax and light saturation point (Lsp) of M. sativa, decreased significantly as the amount of decomposing L. leucocephala leaf litter increased. These results indicated that the photosynthetic traits, light adaptation ability and physiological metabolism of recipient plants were affected by the treatment. The decreased photosynthesis was caused by the changes in pigments and soluble sugar contents induced by L. leucocephala leaf litter and is therefore considered to be associated with non-stomatal limitations. In addition, as the amount of decomposing L. leucocephala leaf litter increased, M. sativa showed decreased chlorophyll (Chla) and carotenoid (Car) contents, while C. dactylon showed decreased Chla and Chl(a + b) contents. However, both recipient plants exhibited significantly increases in their soluble sugar content. Overall, M. sativa was more sensitive than C. dactylon to the allelopathic effects induced by decomposing L. leucocephala leaf litter.

Photosynthetic, photochemical and osmotic regulation changes in tobacco resistant and susceptible to Alternaria alternata

Alternaria alternata is a necrotrophic fungus that may cause severe losses. To further elucidate the resistance mechanisms, we investigated the impacts of increasing biotic stress, or severity levels (5%, 25% and 50%), due to A. alternata infection on two tobacco cultivars with varying resistance levels. Under severe stress, the photosynthetic pigment, net photosynthetic rate (Pn), stomatal conductance (Gs) and stomatal limitation value (Ls) all decreased in both cultivars, whereas the intercellular CO2 concentration (Ci) exhibited an upward trend. Moreover, A. alternata caused adverse effects on PSII electron transport rate and chlorophyll a fluorescence parameters, including the maximal quantum yield of fluorescence (Fv/Fm), PSII potential efficiency (Fv/F0), PSII actual quantum yield (ΦPSII), photochemical quenching (qP) and non-photochemical quenching (NPQ), and ultimately decreased PSII photochemical activity. In addition, the contents of MDA, proline and total soluble sugar increased under stress. The adverse effect of A. alternata on the resistant cultivar was less harmful than the susceptible cultivar. We conclude that the reduction of photosynthesis is a result of non-stomatal limitations. However, the resistant cultivar has better self-protection of its photosynthetic system, improved light energy utilization ability and greater accumulation of osmotic regulation substances for mitigating the damage on cellular membranes. These attributes may account for the resistance to A. alternata.

Stomatal and non-stomatal limitations in savanna trees and C4 grasses grown at low, ambient and high atmospheric CO2

By the end of the century, atmospheric CO2 concentration ([CO2]a) could reach 800 ppm, having risen from ∼200 ppm ∼24 Myr ago. Carbon dioxide enters plant leaves through stomata that limit CO2 diffusion and assimilation, imposing stomatal limitation (LS). Other factors limiting assimilation are collectively called non-stomatal limitations (LNS). C4 photosynthesis concentrates CO2 around Rubisco, typically reducing LS. C4-dominated savanna grasslands expanded under low [CO2]a and are metastable ecosystems where the response of trees and C4 grasses to rising [CO2]a will determine shifting vegetation patterns. How LS and LNS differ between savanna trees and C4 grasses under different [CO2]a will govern the responses of CO2 fixation and plant cover to [CO2]a – but quantitative comparisons are lacking. We measured assimilation, within soil wetting–drying cycles, of three C3 trees and three C4 grasses grown at 200, 400 or 800 ppm [CO2]a. Using assimilation–response curves, we resolved LS and LNS and show that rising [CO2]a alleviated LS, particularly for the C3 trees, but LNS was unaffected and remained substantially higher for the grasses across all [CO2]a treatments. Because LNS incurs higher metabolic costs and recovery compared with LS, our findings indicate that C4 grasses will be comparatively disadvantaged as [CO2]a rises.