The effect of drought stress on chlorophyll fluorescence in Lolium-Festuca hybrids

The effects of drought on photochemical efficiency of PSII in leaves of 22 hybrids of Festuca pratensis × Lolium multiflorum and Festuca pratensis × Lolium perenne and of Festuca pratensis cv. Skra were investigated. A significant decrease of electron transport efficiency (about 25%) in PSII (Φ_PSII) was not found before 9 days of seedling growth in hydroponics with water potential (Ψ_w) equal to −0.8 MPa (simulated “soil drought”). The decrease of Φ_PSII was similarly related to that of excitation energy capture by open PSII reaction centre (Fv’/Fm’) and also to the decrease of the proportion of oxidized to reduced Q_A (photochemical fluorescence quenching, q_p). According to the drought prolongation, variation of all parameters of fluorescence between genotypes significantly increased. The seedlings of some genotypes were able to recover electron transport efficiency in PSII after increasing water potential in nutrient solution (removing the “soil drought”). When plants grew in containers with soil and 4 genotypes with the highest sensitivity of electron transport to drought (S) as well as 4 genotypes with the highest tolerance (T) were compared 17 days after watering ceased, Ψ_w in leaves considerably decreased, but the differences between S and T genotypes were often not significant in this respect. The differences between S and T genotypes, as values of Fv/Fm were concerned, also appeared small (about 5%), similarly as that of Fv’/Fm’ (5%), q_p (12%) and Φ_PSII (about 15%). Drought stress increased non-photochemical quenching of chlorophyll fluorescence (NPQ) 15 to 47% and this could protect the PSII reaction centres from damages because of energy excess. The increase of NPQ was not closely connected with drought resistance of plants because it was similar in some genotypes tolerant to dehydration as well as in sensitive ones. The results of the experiments suggest that resources of genetic variability in Festulolium may be sufficient for revealing differences between genotypes on the basis of measurement of chlorophyll a fluorescence, as far as their tolerance to soil drought is concerned. As the tolerance of PSII against drought is high, the determinations of fluorescence should be performed rather under severe stress. Such methods seem to be useful for selection of genotypes with high drought tolerance as well as with the ability to at least partial repairing of PSII after drought.     

Protective mechanism of desiccation tolerance in <Emphasis Type="Italic">Reaumuria soongorica</Emphasis>: Leaf abscission and sucrose accumulation in the stem

Reaumuria soongorica (Pall.) Maxim., a perennial semi-shrub, is widely found in semi-arid areas in northwestern China and can survive severe desiccation of its vegetative organs. In order to study the protective mechanism of desiccation tolerance in R. soongorica, diurnal patterns of net photosynthetic rate (Pn), water use efficiency (WUE) and chlorophyll fluorescence parameters of Photosystem II (PSII), and sugar content in the source leaf and stem were investigated in 6-year-old plants during progressive soil drought imposed by the cessation of watering. The results showed that R. soongorica was characterized by very low leaf water potential, high WUE, photosynthesis and high accumulation of sucrose in the stem and leaf abscission under desiccation. The maximum Pn increased at first and then declined during drought, but intrinsic WUE increased remarkably in the morning with increasing drought stress. The maximal photochemical efficiency of PSII (Fv/Fm) and the quantum efficiency of noncyclic electric transport of PSII(Φ_PSII) decreased significantly under water stress and exhibited an obvious phenomenon of photoinhibition at noon. Drought stressed plants maintained a higher capacity of dissipation of the excitation energy (measured as NPQ) with the increasing intensity of stress. Conditions of progressive drought promoted sucrose and starch accumulation in the stems but not in the leaves. However, when leaf water potential was less than −21.3 MPa, the plant leaves died and then abscised. But the stem photosynthesis remained and, afterward the plants entered the dormant state. Upon rewatering, the shoots reactivated and the plants developed new leaves. Therefore, R. soongorica has the ability to reduce water loss through leaf abscission and maintain the vigor of the stem cells to survive desiccation.     

Effects of Hydroponic Solution EC,Substrates, PPF and Nutrient Scheduling on Growth and Photosynthetic Competence During Acclimatization of Micropropagated <Emphasis Type="Italic">Spathiphyllum</Emphasis> plantlets

In vitro regenerated shoots of Spathiphyllum from bioreactor were hydroponically cultured for 30 days. The response of plant growth and photosynthesis to different substrates, photosynthetic photon flux (PPF), nutrient scheduling and electrical conductivity (EC) of hydroponic solution were studied. The best plant growth response was observed in perlite based substrates with moderate PFF (70–100μmol m⁻² s⁻¹). Highest fresh weight, dry weight, shoot length, root length, root number and photosynthetic characteristics (chlorophyll, carotenoids and Fv/Fm) was observed in continuous immersion system. Plant growth responses, photosynthetic rate, stomatal conductance and transpiration rate were also found to be affected by EC levels. The optimum EC of a balanced nutrient solution was recorded as 1.2 dS m⁻¹. Photosynthetic activity was also characterized in terms of photochemical efficiency using measurements of chlorophyll fluorescence. Fv/Fm (it is a measure of the intrinsic or maximum efficiency of PSII i.e. the quantum efficiency if all PSII centers were open) also decreased significantly in plants grown under higher EC level; a decrease in this parameter indicates down regulation of photosynthesis or photoinhibition. Antioxidant defense enzymes such as catalase (CAT), ascorbate peroxidase (APX), peroxidase (POD), glutathione reductase (GR) and monodehydroascorbate reductase (MDHAR) significantly elevated in the leaves and roots of plantlets at higher EC levels. This increase could reflect a defense response to the cellular damage provoked by higher EC levels in the nutrient solution.     

三种相思植物对短期大气污染的响应

3种2－3年生相思盆栽于代表不同污染程度的交通繁忙区、工业生产区和相对清洁区,4个月后进行植物叶片气体交换和叶绿素荧光特征参数的测定。结果表明,生长在污染区的相思植物的净光合速率（Pn）、气孔导度（gs）和光系统Ⅱ原初光化学效率（Fv／Fm）均出现不同程度的下降,下降幅度因植物种类和污染类型的不同而有差异,不同实验点上大腺相思叶片蒸腾速率（E）和水分利用效率（WUE）则维持相对稳定,多花和流苏相思的WUE均以污染环境下较低,根据Pn、gs和Fv/Fm的变化以及实验点上其它植物对应测定值比,推测3种相思植物对大气污染都表现出中等强度的抗性,且多花相思和流苏相思相对好于大腺相思。     

Protective mechanism of desiccation tolerance in Reaumuria soongorica: Leaf abscission and sucrose accumulation in the stem

Reaumuria soongorica (Pall.) Maxim., a perennial semi-shrub, is widely found in semi-arid areas in northwestern China and can survive severe desiccation of its vegetative organs. In order to study the protective mechanism of desiccation tolerance in R. soongorica, diurnal patterns of net photosynthetic rate (Pn), water use efficiency (WUE) and chlorophyll fluorescence parameters of Photosystem II (PSII), and sugar content in the source leaf and stem were investigated in 6-year-old plants during progressive soil drought imposed by the cessation of watering. The results showed that R. soongorica was characterized by very low leaf water potential, high WUE, photosynthesis and high accumulation of sucrose in the stem and leaf abscission under desiccation. The maximum Pn increased at first and then declined during drought, but intrinsic WUE increased remarkably in the morning with increasing drought stress. The maximal photochemical efficiency of PSII (Fv/Fm) and the quantum efficiency of noncyclic electric transport of PSII(Φ_PSII) decreased significantly under water stress and exhibited an obvious phenomenon of photoinhibition at noon. Drought stressed plants maintained a higher capacity of dissipation of the excitation energy (measured as NPQ) with the increasing intensity of stress. Conditions of progressive drought promoted sucrose and starch accumulation in the stems but not in the leaves. However, when leaf water potential was less than −21.3 MPa, the plant leaves died and then abscised. But the stem photosynthesis remained and, afterward the plants entered the dormant state. Upon rewatering, the shoots reactivated and the plants developed new leaves. Therefore, R. soongorica has the ability to reduce water loss through leaf abscission and maintain the vigor of the stem cells to survive desiccation. Supported by the Program of the Research of Vegetation Restoration in Arid Areas of Lanzhou (Grant No. 03-2-27) and the National Natural Science Foundation of China (Grant No. 30270243)     

Photoinhibition in cork-oak leaves under stress: influence of the bark-stripping on the chlorophyll fluorescence emission inQuercus suber L.

Quercus suber is the primary source for industrial cork and becomes bark-stripped every 9–10 years. Recurring cork extraction is a major stress factor and the large water loss from the stripped trunk surface may affect the water balance and tree productivity. To evaluate the effect of bark-stripping, fluorescence emission and stomatal conductance of leaves were determined in groups of bark-stripped and control trees. Fv/Fm ratio was found to be significantly lower in bark-stripped trees indicating a reduced photosynthetic efficiency of PSII. Photosynthesis was not found to be stomata limited. The reduction in Fv/Fm resulted from a decline in maximum and variable fluorescence while the initial fluorescence of the dark-adapted state (Fo) remained constant. A general decline in photosynthetic efficiency of PSII was found in all trees during the summer, probably reflecting the prolonged environmental stresses during a hot and dry season. Additional stress caused by the bark-stripping seems to enhance the susceptibility to photoinhibition of the trees.     

Effect of aluminum toxicity and phosphorus deficiency on the growth and photosynthesis of oil tea (<Emphasis Type="Italic">Camellia oleifera</Emphasis> Abel.) seedlings in acidic red soils

Wild and cultivated varieties of Camellia oleifera Abel. were studied for the response of their photosynthetic apparatus to Al toxicity and low-P stress in pot experiments with medium of acidic red soil. The effect was measured using physiological processes (growth, photosynthesis, chlorophyll a fluorescence), and pigment contents. The results showed that Al toxicity and low-P stress affected the seedlings’ growth and leaves’ photosynthesis, and the differences could be found between the two varieties. Lime plus P fertilizer treatment led to higher increase in the net photosynthetic rate (Pn) in the cultivar than in the wild variety. Pn increase was positively related to the increase of stomatal conductance (gs) and negatively correlated to intercellular CO₂ concentration (Ci) in both varieties. The maximum PSII quantum yield (Fv/Fm), the efficiency of excitation energy capture by open PSII reaction centers (Fv’/Fm’), the photochemical quenching (qP) and the efficiency of open PSII centers (Φ_PSII) significantly increased almost in all the treatment groups of both varieties, with the exception of an insignificant change in qP value for P₁Al₁ group of cultivar. The insensitive qP and lower Pn for cultivar indicate a higher photosynthetic efficiency for the wild variety, though the Φ_PSII was not significant between the two varieties. The pigment contents of oil tea seedlings under treatments changed significantly when lime and P were added, especially the Car/Chl ratio, suggesting carotenoid plays the role of photoprotection under high-Al and low-P stresses.     

华山新麦草光合特性对干旱胁迫的响应

以濒危植物华山新麦草为材料进行盆栽试验,设置3个水分梯度,研究生长指标、气体交换、叶绿素荧光参数、光合色素含量、光响应特征及丙二醛(MDA)含量.结果表明:随干旱胁迫的加剧,株高、叶宽和光合色素含量降低,根长和丙二醛(MDA)含量增加;水分胁迫导致净光合速率(PN)、气孔导度(gs)、蒸腾速率(E)、最大荧光(Fm)、光合电子传递速率(ETR)和光化学猝灭系数(qP)降低,胞间CO2浓度(Ci)、瞬时水分利用效率(WUE)、初始荧光(Fo)和非光化学淬灭系数(NPQ)升高;光系统Ⅱ最大光化学效率(Fv/Fm)不变;干旱胁迫下光响应曲线拟合结果显示,干旱胁迫造成最大光合速率和光能利用效率下降.综上表明,干旱对光系统Ⅱ的伤害是制约华山新麦草光合作用的主要原因.     

Increased photoinhibition in dehydrated leaves of hot pepper (Capsicum annuum L.) is not accompanied by an incremental loss of functional PSII

We examined the photosynthetic responses to photoinhibition in dehydrated leaves of hot pepper (Capsicum annuum L.). Stress was induced by immersing the roots of whole plants in Hoaglands solution containing polyethylene glycol (PEG) under high light (900 μmol photons m^-2 · s^-1). This PEG-treatment lowered the leaf water potential and the maximal rate of photosynthetic O₂ evolution (Pmax) linearly, in a time-dependent manner, to about 50% inhibition after 6 h. Pmax also decreased linearly as the period of high-light treatment lengthened. That inhibitory response was not as extreme, showing about 30% inhibition after 6 h. However, when the treatments of dehydration and high light were simultaneously administered, Pmax decreased more rapidly, in a synergistic fashion, showing about 90% inhibition within 2 h. Dehydration, in contrast to the light treatment, did not lower the maximal photochemical efficiency (Fv/Fm). Furthermore, this decline in Fv/Fm for light-treated, dehydrated leaves was almost identical to the response of photoinhibited leaves that were not dehydrated. Similar changes were observed in the number of functional PSII complexes. The decrease in Pmax and the amount of functional PSII was linearly correlated in photoinhibited leaves, but not in dehydrated leaves, regardless of light treatment. Therefore, we have demonstrated that exacerbated photoinhibition in dehydrated leaves occurs without an incremental loss of functional PSII.     

土壤水分对湿地松幼苗光合特征的影响

通过设置常规供水(CK)、轻度干旱(T1)、水饱和(T2)、水淹(T3)4个处理组,研究湿地松当年实生幼苗在不同土壤水分条件下的光合生理响应及叶绿素荧光特性。结果表明:不同水分处理对湿地松幼苗的叶片气体交换参数、水分利用效率(WUE)、光合色素、叶绿素荧光参数等指标有不同的影响;其中,T3的光合色素含量最低;T2、T3组的湿地松幼苗表现出较低的净光合速率(Pn)、电子传递速率(ETR)和PSⅡ光化学的量子效应(ΦPSⅡ),但与其他耐水淹植物相比,T3条件下的湿地松幼苗仍具有较高的Pn,说明湿地松幼苗具有较强的耐水淹能力;在T1条件下,湿地松幼苗具有较高的WUE和较低的蒸腾速率(Tr)、气孔导度(Gs)以对抗干旱的逆境,其Pn、PSⅡ最大光化学效率(Fv/Fm)、ETR和ΦPSII均有所下降,但仍能维持在相对正常的水平。研究证明,湿地松幼苗具有一定的耐淹耐旱特性,可运用于三峡库区消落带的植被重建。     

Evaluation of physiological screening tests for breeding drought resistant triticale (x <Emphasis Type="Italic">Triticosecale</Emphasis> wittmack)

Effects of soil drought on crop yield of 4 strains and 7 cultivars of spring triticale was investigated under field condition. The Drought Susceptibility Index (DSI) was evaluated in a two year experiment by the determination of grain loss in conditions of two soil moisture levels (drought-D and irrigated-IR). In the experiment response to drought was evaluated by different screening tests (leaf gaseous exchange, leaf water potential, chlorophyll content and fluorescence, leaf injury by drought and by simulated drought and heat temperature and water loss by excited leaf. The DSI values and the results of screening tests showed the genetic variation in the degree of drought tolerance. The values of DSI enabled the ranking of the tested triticale genotypes with respect to their drought tolerance and allow to divide them into three groups of drought susceptibility. Large differences among studied forms were observed also in changes of leaf water potential, fluorescence and leaf injury. For plants in vegetative stage of growth the tested breeding forms were easily separated into groups of different drought tolerance. Changes of ψ, Fv/Fm and LI as a screening tests were the most suitable techniques for estimation of degree of drought tolerance for triticale. Laboratory screening tests (leaf injury by simulated drought (LI_DS) and high temperature (LI_HT) and water loss (WL) of excited leaf conducted for nonstressed plants in most cases were significantly correlated with DSI. The statistically significant correlation between leaf water potential (ψ) was observed only with leaf fluorescence (Fv/Fm). Changes of Fv/Fm were significantly correlated with ψ, LI and LI_HT for 50 °C. Index of leaf injury (LI) by soil drought were significantly correlated with Fv/Fm, LI_DS (−1.0, −1.5 MPa), LI_HT (45 and 50°C) and water loss (WL). The correlation coefficient between the tests LI_DS and LI_HT were most of the considered cases statistically significant which indicate that the mechanism of membranes injury resulted from simulated drought or high temperature were similar in triticale. Water loss (WL) of excited leaves was the most suitable test for screening drought tolerance in triticale population. Changes of gaseous exchange parameters were not useful as screening test in this research.     

Photosynthesis, photochemistry and antioxidative defence in response to two drought severities and with re-watering in Allocasuarina luehmannii

Gas exchange, chlorophyll fluorescence and water potentials, together with ascorbate and glutathione concentrations, were studied during moderate and severe drought stress and in response to re-watering in Allocasuarina luehmannii seedlings. Moderate drought stress (MS) decreased stomatal conductance (g_s) and net CO₂ assimilation rates (A) to ∼40% and ∼60% of control values, respectively, and caused decreases in internal CO₂ concentration (C_i) and maximum light use efficiency of light-acclimated photosystem II (PSII) centres (Fv'/Fm'). Severe drought stress (SS) decreased g_s and A to ∼5% and ∼15% of the control values, respectively, and caused increases in C_i and PSII excitation pressure (1 − qP), as well as decreases in water potentials, effective quantum yield of PSII (ΦPSII), maximum efficiency of PSII (Fv/Fm) and Fv'/Fm'. Ascorbate and glutathione concentrations remained unaffected by drought treatments, but ascorbate became more oxidised under severe stress. MS seedlings recovered within 1 day (C_i, Fv'/Fm') to 1 week (A, g_s) of re-watering. In comparison, SS seedlings had longer-lasting after-stress effects, with recovery of many variables (g_s, water potentials, Fv/Fm, ΦPSII, Fv'/Fm') taking between 1 and 3 weeks from re-watering. We found no indication that interaction with antioxidants played a significant role in recovery. In conclusion, A. luehmannii seedlings appear to function normally under moderate drought, but do not seem to have particular metabolic tolerance mechanisms to endure severe drought, which may have implications for its persistence under climate change at the drier margins of its distribution.     

Changes of endogenous ABA and ACC,and their correlations to photosynthesis and water relations in mungbean (Vigna radiata (L.) Wilczak cv. KPS1) during waterlogging

The effects of waterlogging on the dynamics of leaf abscisic acid (ABA) and root 1-aminocyclopropane-1-carboxilic acid (ACC, a precursor of ethylene) contents together with those on photosynthetic rate, leaf water potential and chlorophyll fluorescence were studied in mungbean (Vigna radiata (L.) Wilczak cv. KPS1) plants under greenhouse conditions. Waterlogging reduced the photosynthetic rate and water use efficiency rapidly without any changes of stomatal conductance, transpiration rate and ABA concentrations. Rapid reduction of photosynthetic rate and Fv/Fm ratio of chlorophyll fluorescence without increase of ABA indicates that early reduction of photosynthetic rate may not be related to ABA. In addition, the slower recovery of P, P/T_r and Fv/Fm values than ABA implies that ABA is not completely involved in photosynthetic reduction. Increased concentration of ACC during the waterlogging period and after the end of waterlogging may indicate the involvement of ethylene in photosynthetic reduction through the reduction of PSII activities, although early reduction of photosynthesis could not be explained by ethylene. After 2 days of waterlogging, ABA was increased concomitantly with the rapid reduction of P, T_r and g_s. It may suggest that ABA reduces photosynthesis through some ABA-related reactions, such as stomatal closure.     

Glycinebetaine application ameliorates negative effects of drought stress in tobacco

Two tobacco (Nicotiana tabacum L.) cultivars differing in drought tolerance were used to study the effects of foliar-applied glycinebetaine (GB, 80 mM) under well-watered and water-deficit conditions. The latter affected shoot biomass and height, with a more significant decrease observed in drought-sensitive cultivar than in drought-resistant cultivar. Foliar-applied GB was absorbed, accumulated by tobacco leaves and improved growth of plants subjected to water deficit. GB-treated plants maintained leaf water status apparently due to the improved osmotic adjustment. GB application enhanced the photosynthesis in water-deficit experiencing plants, mostly due to a greater stomatal conductance and carboxylation efficiency of CO₂ assimilation. photosystem II (PSII) activity in GB-treated plants was higher, as suggested by higher actual efficiency of PSII (ΦPSII). GB increased anti-oxidative enzyme activities under water deficit. All these effects resulted in an improved shoot biomass and height. Therefore, foliar GB application at the rapid growth stage favors plant growth in drought-stressed plants, mainly by improving water status and increasing PSII activity. Published in Russian in Fiziologiya Rastenii, 2007, Vol. 54, No. 4, pp. 534–541. The text was submitted by the authors in English.     

硅和干旱胁迫对水稻叶片光合特性和矿质养分吸收的影响

硅被认为是植物生长的有益元素,它能增强植物对非生物逆境和生物逆境胁迫的抗性。以抗旱性不同的一对水稻近等基因系w-14-和w-20为实验材料,采用盆栽实验,研究了干旱胁迫下硅处理对水稻生长性状、光合生理特性和矿质养分吸收的影响。结果表明,在正常水分条件下硅处理对水稻的生长及生理特性没有明显影响。干旱胁迫显著降低水稻植株的生长,叶绿素含量、叶绿素荧光参数Fv/Fm及Fv/F0值显著降低,光合作用受到明显抑制。加硅能提高干旱胁迫条件下水稻植株的生物量、水分利用效率、叶片叶绿素含量、净光合速率和蒸腾速率,而气孔导度和细胞间隙CO2浓度则下降。无论干旱与否,施硅后水稻的叶片硅含量均显著上升。两个水稻品系叶片的无机离子含量在干旱胁迫条件下均呈显著增加的趋势,而硅处理后材料w-14的叶片K+、Na+、Ca2+、Mg2+、Fe3+含量分别降低16.38%,24.50%,19.70%,21.52%,18.58%,w-20则分别降低11.64%,12.11%,16.06%,11.11%和19.15%,并使之回复到与对照更接近的水平。研究结果表明了硅提高水稻植株的抗旱性与光合作用的改善和矿质养分的调节有关。     

Expression profiles of sugarcane under drought conditions: Variation in gene regulation

Drought is a major factor in decreased sugarcane productivity because of the resulting morphophysiological effects that it causes. Gene expression studies that have examined the influence of water stress in sugarcane have yielded divergent results, indicating the absence of a fixed pattern of changes in gene expression. In this work, we investigated the expression profiles of 12 genes in the leaves of a drought-tolerant genotype (RB72910) of sugarcane and compared the results with those of other studies. The genotype was subjected to 80–100% water availability (control condition) and 0–20% water availability (simulated drought). To analyze the physiological status, the SPAD index, Fv/Fm ratio, net photosynthesis (A), stomatal conductance (g _s) and stomatal transpiration (E) were measured. Total RNA was extracted from leaves and the expression of SAMDC, ZmPIP2-1 protein, ZmTIP4-2 protein, WIP protein, LTP protein, histone H3, DNAj, ferredoxin I, β-tubulin, photosystem I, gene 1 and gene 2 was analyzed by quantitative real-time PCR (RT-PCR). Important differences in the expression profiles of these genes were observed when compared with other genotypes, suggesting that complex defense mechanisms are activated in response to water stress. However, there was no recognizable pattern for the changes in expression of the different proteins associated with tolerance to drought stress.     

铝胁迫对蓼科植物生长和光合、蒸腾特性的影响

采用水培试验,设置5种铝处理浓度,研究了铝对3种蓼科植物酸模叶蓼、杠板归和辣蓼叶片光合、蒸腾和叶绿素荧光参数的影响。结果表明,高铝处理(400μmol.L-1)显著抑制3种蓼科植物地上部和根系生长,并且导致3种蓼科植物叶片叶绿素含量、Chla/Chlb、净光合速率(Pn)、水分利用效率(WUE)、PSII光合电子传递量子效率(φPSII)和光化学猝灭系数(qP)显著下降。中低铝处理(25~100μmol.L-1)时,与对照相比,酸模叶蓼生物量显著增加,杠板归显著减少,辣蓼先增加后减少。其中,酸模叶蓼和辣蓼叶绿素含量、Chla/Chlb、Pn、蒸腾速率(Tr)、胞间CO2浓度(Ci)、PSII最大光化学效率(Fv/Fm)、qP均未发生显著变化,但辣蓼WUE、φPSII和非光化学猝灭系数(NPQ)显著下降,酸模叶蓼无显著变化;而杠板归除Ci、Fv/Fm外,其余叶片光合、蒸腾及叶绿素荧光参数均出现显著下降。上述结果表明,酸模叶蓼在中低铝处理条件下可通过保持较高的叶绿素含量、Chla/Chlb、WUE、Pn、PSII反应中心光化学反应效率以及提高非辐射能量耗散来增强其对铝的耐性。     

干旱胁迫和CO2浓度升高条件下白羊草的光合特征

采用盆栽控制试验,研究了黄土丘陵区乡土种白羊草在不同水分水平(80%FC和40%FC)和CO₂浓度(375和750 μmol·m^-2·s^-1) 处理下的光合生理变化特征.结果表明： 干旱胁迫使白羊草的最大净光合速率(P_nmax)、表观量子效率(AQE)、气孔导度(g_s)、蒸腾速率(T_r)、最大光化学效率(F_v/F_m)、潜在光化学效率(F_v/F_o)和光合色素含量降低,丙二醛(MDA)和脯氨酸(Pro)含量升高.水分充足条件下,与正常大气CO₂浓度相比,大气CO₂浓度倍增下白羊草的P_{n max}、MDA和Pro含量无显著差异.干旱胁迫下,CO₂浓度升高提高了白羊草的最大荧光(F_m)、F_v/F_m、F_v/F_o、叶绿素含量和AQE, P_nmax比正常CO₂浓度下高23.3%,差异达到显著水平,而MDA和Pro含量均显著降低.CO₂浓度升高对干旱胁迫引起的白羊草光合能力下降有一定的补偿作用,减轻了干旱胁迫对白羊草的伤害.     

Physiological and anatomical changes induced by drought in two olive cultivars (cv Zalmati and Chemlali)

Photosynthetic gas exchange, vegetative growth, water relations and fluorescence parameters as well as leaf anatomical characteristics were investigated on young plants of two Olea europaea L. cultivars (Chemlali and Zalmati), submitted to contrasting water availability regimes. Two-year-old olive trees, grown in pots in greenhouse, were not watered for 2 months. Relative growth rate (RGR), leaf water potential (Ψ_LW) and the leaf relative water content (LWC) of the two cultivars decreased with increasing water stress. Zalmati showed higher values of RGR and LWC and lower decreased values of Ψ_LW than Chemlali, in response to water deficit, particularly during severe drought stress. Water stress also caused a marked decline on photosynthetic capacity and chlorophyll fluorescence. The net photosynthetic rate, stomatal conductance, transpiration rate, the maximal photochemical efficiency of PSII (F _v/F _m) and the intrinsic efficiency of open PSII reaction centres (F′ _v/F′ _m) decreased as drought stress developed. In addition, drought conditions, reduced leaf chlorophyll and carotenoids contents especially at severe water stress. However, Zalmati plants were the less affected when compared with Chemlali. In both cultivars, stomatal control was the major factor affecting photosynthesis under moderate drought stress. At severe drought-stress levels, the non-stomatal component of photosynthesis is inhibited and inactivation of the photosystem II occurs. Leaf anatomical parameters show that drought stress resulted in an increase of the upper epidermis and palisade mesophyll thickness as well as an increase of the stomata and trichomes density. These changes were more characteristic in cv. ‘Zalmati’. Zalmati leaves also revealed lower specific leaf area and had higher density of foliar tissue. From the behaviour of Zalmati plants, with a smaller reduction in relative growth rate, net assimilation rate and chlorophyll fluorescence parameters, and with a thicker palisade parenchyma, and a higher stomatal and trichome density, we consider this cultivar more drought-tolerant than cv. Chemlali and therefore, very promising for cultivation in arid areas.     

Effects of root flooding and stage of development on the growth and photosynthesis of field bean (Vicia faba L. minor)

Field bean plants were subjected to flooding stress for 7 days, during two stages of development: at the vegetative phase (4-week-old seedlings) and at the generative phase (8-week-old plants). The height of plants, total area of leaves, the number of undamaged leaves, dry plant matter, chlorophyll content, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) activity, the maximum quantum yield of PS2 photochemistry (Fv/Fm ratio), the photosynthesis rate (P _N) and stomatal conductance (g _s) were determined. A strong reduction in stem elongation and leaf area as well as in dry matter production was observed as a result of flooding. The responses from vegetative plants were greater than in generative plants. Waterlogging decreased chlorophyll a and b in leaves, notably at the vegetative stage, and persisted after cessation of flooding. After flooding, photosynthesis was strongly reduced and positively correlated with decreased stomatal conductance. Damage to the photosynthetic apparatus resulted in a lower Fv/Fm especially in young seedlings. In vegetative plants Fv/Fm quickly returned to the control levels after the soil was drained. The results show that an excess of water in the soil limits growth and injures the photosynthetic apparatus in field beans, but that the extent of the injury is strongly age dependent.