Physiological response of riparian plants to watering in hyper-arid areas of Tarim River, China

The physiological responses and adaptive strategies of Populus euphratica Oliv. (arbor species), Tamarix ramosissima Ldb. (bush species), and Apocynum venetum L. (herb species) to variations in water and salinity stress were studied in the hyper-arid environment of the Tarim River in China. The groundwater table, the saline content of the groundwater, as well as the content of free proline, soluble sugars, plant endogenous hormones (abscisic acid (ABA), and cytokinins (CTK)) of the leaves of the three species were monitored and analyzed at the lower reaches of the Tarim River in the study area where five transects were fixed at 100 m intervals along a vertical sampling line before and after water release. Saline stress dramatically increased soluble sugar concentration of the three species. Differences in sugar accumulation were determined among the species at different transects. The free proline concentration of the leaves of T. ramosissima and P. euphratica showed a proportional decrease with various degrees of elevation of the groundwater table after water release. There was a least correlation between the soluble sugars and proline stimulation in T. ramosissima. It was strongly suggested that T. ramosissima developed a different strategy to accumulate organic solutes to adapt to the stress environment. The soluble sugars and proline accumulation responded to the changes of groundwater table independently: the former occurred under salt stress, whereas the latter was more significant under drought stress. The concentration and the increase in concentration of ABA and CTK involved in stress resistance of the three species were also determined. This increase in the hormone concentration in P. euphratica was different from that of the other two species. Expressed as a function of increase of ABA concentration in leaves, A. venetum and T. ramosissima showed a different solute accumulation in response to groundwater table. There was a significant correlation between ABA accumulation and Δ [proline] in A. venetum as well as between ABA accumulation and Δ [sugar] in T. ramosissima. Translated from Acta Ecologica Sinica, 2005, 25(8): 1966–1973 [译自: 生态学报]     

塔里木河流域荒漠河岸植物对应急输水的生理响应

选择塔里木河沿岸典型样地,以乔木树种胡杨(Populuseuphratica)、灌木柽柳(Tamarixspp.)和草本植物罗布麻(Apo-cynumvenetum)为研究材料,垂直距离输水河道500m范围内,间隔100m设置一个采样断面。监测并分析塔里木河下游应急输水前后5个断面地下水位、地下水含盐量及3种植物叶片游离脯氨酸、可溶性糖、内源植物激素脱落酸(ABA)和细胞分裂素(CTK)含量的变化。研究3种荒漠植物对水盐双重胁迫环境的生理响应及适应策略。结果表明:盐胁迫显著增加3种植物叶片或同化枝的可溶性糖浓度,断面间不同植物叶片或同化枝可溶性糖积累存在差异;输水后断面间随地下水位不同程度的抬升,胡杨和柽柳叶片或同化枝脯氨酸含量出现了成比例的下降;柽柳同化枝可溶性糖与脯氨酸积累相关性最小,发展了不同于另外两种植物的通过有机溶剂积累适应胁迫环境的策略,即同化枝可溶性糖与脯氨酸作为响应于地下水位变化的功能物质独立地起作用,可溶性糖积累对盐胁迫的响应明显,而脯氨酸积累对干旱胁迫的响应更为明显;对与胁迫抗性有关的植物内源激素ABA、CTK浓度及浓度增长量变化进行分析,发现胡杨具有不同于其他两种植物的内源ABA、CTK浓度增量变化趋势;胡杨和罗布麻叶片ABA积累量与脯氨酸积累百分量(△[脯氨酸])而柽柳中ABA积累量与可溶性糖积累百分量(△[可溶性糖])显著相关。     

塔里木河下游干旱胁迫下的胡杨生理特点分析

本运用塔里木河下游地下水位变化资料和塔里木河下游主要植物胡杨脯氨酸和脱落酸(ABA)的分析实验数据,结合野外调查,对地下水位变化与胡杨体内脯氨酸和脱落酸积累的关系进行了分析。研究表明,在塔里木河下游,塔里木河下游胡杨体内的脯氨酸和脱落酸含量与地下水位变化密切相关．以胡杨为主的天然植物受干旱胁迫程度愈大,退化愈严重,而反映在胡杨体内脯氨酸和脱落酸含量上．则随着地下水位的下降、水分胁迫程度的增加呈现出明显增加态势。在不同地下水位埋深条件下,胡杨体内脯氨酸和脱落酸累积过程的变化和差异表达了胡杨受干旱的程度;塔里木河下游胡杨的生长发育已受到严重的十旱胁迫。     

塔里木河中游地区3种植物的抗旱机理研究

对塔里木河中游地区沙吉力克、阿其河等断面地下水位进行监测并对胡杨、柽柳、芦苇3种植物的可溶性糖、脯氨酸等生理指标进行测定分析.研究显示：（1）塔里木河中游地区植物生长与地下水位变化关系密切,随着不同断面地下水位埋深程度的增加,植物体内可溶性糖与脯氨酸含量呈增加趋势;（2）在干旱胁迫情况下,植物通过可溶性糖、脯氨酸等渗透调节物质的积累来提高自身的抗旱性;（3）植物叶片可溶性糖和脯氨酸的积累存在互相补偿的关系.研究表明在相同水分胁迫下,柽柳和芦苇对地下水位的变化更为敏感,胡杨的抗旱性较强.     

白三叶和红三叶对人工融冻胁迫的生理响应差异

采用人工模拟融冻胁迫方法,通过测定白三叶(Trifolium repens)和红三叶(T.prat-ense)在融冻胁迫中叶片细胞膜透性、MDA含量、抗氧化酶(SOD、POD、CAT)活力、渗透调节物(脯氨酸、可溶性糖和蛋白质)含量变化,以揭示未来气候变化对三叶草的影响。结果表明,经历融冻胁迫循环后抗冻力强的白三叶植株能恢复生长,而抗冻力弱的红三叶枯萎死亡。在融冻阶段,两三叶草叶片细胞膜透性增大、抗氧化酶活力增高、MDA和渗透调节物含量大幅增加;在冻融阶段,两三叶草叶片细胞膜透性降低、MDA含量下降、抗氧化酶活力降低。但在融冻胁迫循环中,白三叶叶片POD和CAT活力高于红三叶,脯氨酸含量较红三叶高5倍,但细胞膜透性低于红三叶。白三叶在-5℃抗逆生理指标达到最大值,而红三叶在-10℃。白三叶对环境温度变化反应敏感,在-5℃通过快速激活抗氧化酶系统和积累渗透调节物以抑制膜脂过氧化和维护细胞水分平衡在融冻适应上起重要作用。白三叶具有较强的抗融冻能力,是未来值得应用推广的优良园林绿化植物。     

塔里木河中游地区柽柳对地下水埋深的生理响应

以塔里木河中游沙吉力克断面和阿其河断面的柽柳为研究对象,结合两断面地下水埋深的动态监测和柽柳叶片可溶性糖、脯氨酸、MDA含量及SOD、POD活性等生理指标的分析测试,研究了不同地下水埋深与柽柳生理变化的关系,以探讨该地区柽柳的抗旱机理与受胁迫程度.研究表明:随着地下水埋深的不断增加,柽柳叶片的可溶性糖含量、脯氨酸含量、MDA含量和SOD活性均显著增加,而POD活性则呈不断下降的趋势,并且柽柳各生理代谢相互协调;地下水埋深与柽柳叶片的可溶性糖、脯氨酸、MDA含量以及SOD活性呈正相关,相关系数分别为0.602*、0.548、0.735**和0.829**,与POD活性呈负相关(r=-0.709**).研究发现,塔里木河中游地区柽柳的生长已受到严重的干旱胁迫,且沙吉力克断面的柽柳所受到的干旱胁迫较重;柽柳在一定范围内能通过调节体内渗透调节物质的含量和保护酶活性来积极响应地下水埋深的变化,以增强植株自身抗旱能力.     

Water relations, activities of antioxidants, ethylene evolution and membrane integrity of pigeonpea roots as affected by soil moisture

The plants of pigeonpea (Cajanus cajan L.) cv. H77-216 were subjected to moderate [soil moisture content (SMC) = 7.3 ± 0.5 %] and severe (SMC = 4.3 ± 0.5 %) drought by withholding the irrigation at vegetative stage (45 d after sowing). The control plants were maintained at SMC of 11.0 ± 0.5 %. Half of the stressed plants were re-irrigated and their recovery was studied after 2 d. Leaf water potential, osmotic potential, and relative water content of leaf and root decreased significantly while a sharp rise in proline and total soluble sugars contents were noticed. Drought induced a significant increase in 1-aminocyclopropane 1-carboxylic acid (ACC) content and ACC oxidase activity which caused a considerable increase in ethylene evolution. Malondialdehyde content and relative stress injury were increased under drought whereas reverse was true for ascorbic acid content. The membrane integrity of roots decreased during stress and recovered on rehydration. The specific activity of total superoxide dismutase, ascorbate peroxidase, glutathione reductase, and glutathione transferase decreased to 37 – 78 %, 17 – 62 %, 29 – 36 % and 57 – 79 % at moderate and severe drought, respectively. The increase in activity of catalase and peroxidase could not overcome the accumulation of H₂O₂ content in the roots.     

塔里木河下游柽柳ABA累积对地下水位和土壤盐分的响应

近年来发现在逆境下(干旱、低温、高温、盐渍等)的植物体内大量积累ABA,从而引导人们去研究ABA与植物抗逆性之间的关系。在塔里木河下游地区影响植被正常生长发育的各种胁迫因子中,地下水位和土壤盐分是导致"绿色走廊"衰败的主要因素。柽柳是塔里木河下游荒漠植被的主体,对于改善生态环境、遏制沙漠化、保护生物多样性等诸多方面具有重要作用。因此,研究柽柳和地下水位以及土壤盐分的关系,对于维护塔里木河流域天然植被赖以生存的环境,保护柽柳这一重要的生物资源,维持生态平衡的良性循环具有重要意义。运用国际通用软件SAS6.12对塔里木河下游柽柳ABA和地下水位以及土壤盐分进行相关分析表明,柽柳ABA含量与地下水位呈极显著正相关,相关系数R=0.80305(显著性程度P=0.0003);与土壤盐分呈显著负相关,相关系数R=-0.59036(显著性程度P=0.0205)。由各断面柽柳ABA含量变化与地下水位和土壤盐分关系分析结果可以初步推断:3.12m的地下水位和0.96g/L的土壤盐分已经威胁到柽柳的正常生长发育,地下水位超过5.59m、土壤盐分大于1.61g/L则会对柽柳造成严重胁迫。在恢复和保育塔里木河流域天然植被的过程中,应该把对植被造成胁迫的外界条件的成因和植被自身的抗旱、抗盐等抗逆特性结合起来进行考虑:根据耐旱耐盐植被的合理生态水(盐)位,在主河道两岸维持一定范围的地下水位,使乔木、灌木、草本植被能良好地生长,发挥多种生态功能,这样既可以避免水资源的浪费又能充分发挥生态输水的功效,有利于从根本上解决"绿色走廊"的问题。     

Stress‐driven increase in proline levels,and not proline levels themselves,correlates with the ability to withstand excess salt in a group of 17 Italian rice genotypes

• In most plant species, a rapid increase in free proline content occurs following exposure to hyperosmotic stress conditions. However, inconsistent results were reported concerning the role of such an increase on the plant response to water shortage or excess salt. Therefore, the possibility that proline accumulation may help the cell to withstand stress conditions, or that it simply represents a stress marker, is still a matter of debate. A possible relationship between proline accumulation and salt tolerance was investigated in a set of 17 Italian rice varieties.
• Rice seedlings were exposed to increasing salt concentrations during germination and early growth. The resulting levels of free proline were measured separately in shoots and roots and compared to those in untreated controls. Results were related to the corresponding ability of a given genotype to tolerate stress conditions.
• Neither absolute proline levels in untreated or in salt‐stressed seedlings showed a straightforward relationship to the relative tolerance to salt, estimated as conductivity values able to reduce growth by 10 or 50%. Conversely, a highly significant correlation was found between the increase in proline levels in shoots and the ability to withstand stress.
• The results strengthen a recent hypothesis suggesting than an increase in proline metabolic rates, more than the resulting proline content, may help the cell to counteract the effects of abiotic stress conditions.

     

Stress memory in plants: a negative regulation of stomatal response and transient induction of rd22 gene to light in abscisic acid-entrained Arabidopsis plants

All organisms, including plants, perceive environmental stress, and they use this information to modify their behavior or development. Here, we demonstrate that Arabidopsis plants have memory functions related to repeated exposure to stressful concentrations of the phytohormone abscisic acid (ABA), which acts as a chemical signal. Repeated exposure of plants to ABA (40 micro m for 2 h) impaired light-induced stomatal opening or inhibited the response to a light stimulus after ABA-entrainment under both dark/light cycle and continuous light. Moreover, there were transient expressions of the rd22 gene during the same periods under both the growing conditions. Such acquired information in ABA-entrained plants produced a long-term sensitization. When the time of light application was changed, a transient induction of the rd22 gene in plants after ABA-entrainment indicated that these were light-associated responses. These transient effects were also observed in kin1, rab18, and rd29B. The transient expression of AtNCED3, causing the accumulation of endogenous ABA, indicated a possible regulation by ABA-dependent pathways in ABA-entrained plants. An ABA immunoassay supported this hypothesis: ABA-entrained plants showed a transient increase in endogenous ABA level from 220 to 250 pmol g-1 fresh mass at 1-2 h of the training period, whereas ABA-deficient (aba2) mutants did not. Taking into account these results, we propose that plants have the ability to memorize stressful environmental experiences, and discuss the molecular events in ABA-entrained plants.     

Stomatal responsiveness to leaf water status in common bean (Phaseolus vulgaris L.) is a function of time of day

Stomatal response to leaf water status was experimentally manipulated by pressurizing the soil and roots of potted common bean plants enclosed in a custom‐built root pressure chamber. Gas exchange was monitored using a whole‐plant cuvette and plant water status using in situ leaf psychrometry. Bean plants re‐opened their stomata upon pressurization, but the extent of re‐opening was strongly dependent on the time of day when the soil was pressurized, with maximum re‐opening in the morning hours and limited re‐opening in the afternoon. Neither leaf nor xylem abscisic acid concentrations could explain the reduced response to pressurization in the afternoon. The significance of this phenomenon is discussed in the context of circadian rhythms and of other recent findings on the ‘apparent feed‐forward response’ of the stomata of some species to vapour pressure deficit.     

Maize Rabl7 overexpression in Arabidopsis plants promotes osmotic stress tolerance

Rabl7 is a Late Embryogenesis Abundant (LEA) protein from maize, which accumulates largely during embryogenesis and also in vegetative tissues when subjected to stress conditions. We have analysed the effect of Rab 17 expression under a constitutive promoter in vegetative tissues of transgenic Arabidopsis thaliana plants. These transgenic plants have higher sugar and proline contents, and also higher water loss rate under water stress. In addition, these plants are more tolerant than non-transformed controls to high salinity and recover faster from mannitol treatment. Our results point to a protective effect of Rabl7 protein in vegetative tissues under osmotic stress conditions.     

Responses of Tamarix ramosissima ABA accumulation to changes in groundwater levels and soil salinity in the lower reaches of Tarim River, China

The Tarim River, located in central Xinjiang Uygur Autonomous Region, is situated north of the Taklimakana Desert. A reduction in groundwater levels and a concomitant increase in soil salinity have reduced vegetation in lower reaches of the river. Tamarix ramosissima is one of the dominant plant species in this riparian system. This species provides a buffer between the desert and the riparian zone, and contributes significantly to the function of the ecosystem and the maintenance of the biodiversity. Thus, an understanding of how T. ramosissima responds to changes in groundwater levels and soil salinity is necessary for ecological and economic management of this riparian system. We found a positive correlation (Pearson Correlation Coefficient = 0.80305) between T. ramosissima Abscisic Acid (ABA) and groundwater levels, and a negative correlation between ABA and soil salinity levels (Pearson Correlation Coefficient = –0.00961). From these relationships between ABA and groundwater/salinity we concluded that subsurface groundwater level of 3.12 m and soil salinity of 0.96 g/L can limit the normal growth and development of T. ramosissima; subsurface groundwater level of larger than 5.59 m and soil salinity of higher than 1.61 g/L will strongly impede the normal development of T. ramosissima. So we should take into account the resistance of plants to environmental stressors such as drought and salinity to keep the levels of salinity and groundwater on both sides of the main river within a range, in which trees, shrubs and herbs can grow well, and perform various ecological functions. Such conservation practice will not only avoid waste of water resources, but also contribute to efficient artificial water-recharge, helping to maintain the riparian zone of Tarim River and to promote “green corridor” maintenance.     

Physiological responses of four herbaceous plants to aluminum stress in South China

Different plants have physiological responses under A1 stress,but there is no systematic study to examine physiological responses of herbaceous plants under Al stress.The aim of this study is to investigate the effect of Al on physiological characteristics of four herbaceous plants,which distributed in red soil area in South China,and to analyze the differences in physiological responses to Al stress between the four herbaceous plants.Four herbaceous plants(Pharbitis nil,Cassia occidentlis,Echinochloa colonum and Aeschynomene indica)were used,and the seed germination percentage,the contents of chlorophyll,proline,and malondialdehyde(MDA),membrane permeability(MP),soluble sugar,and activities of peroxides(POD)and cata lase(CAT)in leaves under five Al3+ treatments(0,80,400,2000,and 10000 mg/L)were assayed with the sand culture method.The results showed remarkable effects of Al3+ on physiological characteristics of these four herbaceous plants.The seeds of all the four species could not germinate at 10000 mg/L.and the growth of all plants were retarded under the 2000 mg/LAr3+ treatment.Compared with the control,2000 mg/L Al3+ significantly(P＜0.05)reduced the contents of chlorophyll a and chlorophyll a+b,and increased the contents of MDA and MP.The content of proline in creased very significantly(P＜0.01)and activities of POD and CAT were depressed.The contents of MDA and MP in leaves of P.nil and A.indica decreased,and the activities of POD and CAT in leaves of the two plants increased under 80mg/L and 400 mg/L.However,the changes in C.occidentlis leaves were opposite to those of the above two plants.The changes in leaves of E.colonum were similar to those of P.nil and A.indica at 80 mg/L.but were opposite to those at 400mg/LAr3+.It is suggested that plants with higher activities of POD and CAT,more contents of chlorophyll and proline,and lower contents of MDA and MP consequently improve the tolerance to Al stress under low and middle Al treatments.     

Physiological responses of four herbaceous plants to aluminum stress in South China

Different plants have physiological responses under Al stress, but there is no systematic study to examine physiological responses of herbaceous plants under Al stress. The aim of this study is to investigate the effect of Al on physiological characteristics of four herbaceous plants, which distributed in red soil area in South China, and to analyze the differences in physiological responses to Al stress between the four herbaceous plants. Four herbaceous plants (Pharbitis nil, Cassia occidentlis, Echinochloa colonum and Aeschynomene indica) were used, and the seed germination percentage, the contents of chlorophyll, proline, and malondialdehyde (MDA), membrane permeability (MP), soluble sugar, and activities of peroxides (POD) and catalase (CAT) in leaves under five Al³⁺ treatments (0, 80, 400, 2 000, and 10 000 mg/L) were assayed with the sand culture method. The results showed remarkable effects of Al³⁺ on physiological characteristics of these four herbaceous plants. The seeds of all the four species could not germinate at 10 000 mg/L, and the growth of all plants were retarded under the 2 000 mg/L Al³⁺ treatment. Compared with the control, 2 000 mg/L Al³⁺ significantly (P < 0.05) reduced the contents of chlorophyll a and chlorophyll a + b, and increased the contents of MDA and MP. The content of proline increased very significantly (P < 0.01) and activities of POD and CAT were depressed. The contents of MDA and MP in leaves of P. nil and A. indica decreased, and the activities of POD and CAT in leaves of the two plants increased under 80 mg/L and 400 mg/L. However, the changes in C. occidentlis leaves were opposite to those of the above two plants. The changes in leaves of E. colonum were similar to those of P. nil and A. indica at 80 mg/L, but were opposite to those at 400 mg/L Al³⁺. It is suggested that plants with higher activities of POD and CAT, more contents of chlorophyll and proline, and lower contents of MDA and MP consequently improve the tolerance to Al stress under low and middle Al treatments. __________ Translated from Acta Phytoecologica Sinica, 2005, 29(4): 644–651 [译自: 植物生态学报, 2005, 29(4): 644–651]     

The effect of drought on levels of abscisic acid,cytokinins, gibberellins and ethylene in aeroponically-grown sunflower plants

Abscisic acid (ABA), cytokinins and gibberellin-like substances (GAs) were extracted from the roots and shoots of 17-day-old sunflower seedlings which had been droughted or were unstressed. Plants were grown in an aeroponic chamber which allowed for good control over degree of water stress and easy access to roots. Following methanolic extraction of lyophilized material, cytokinins were separated from the acidic growth-regulators on a cellulose PO₄ cationic exchange column. The cytokinins were analysed by paper chromatography and HPLC and the soybean hypocotyl section assay. Semipurified acidic regulators were chromatographed on SiO₂ columns and HPLC and aliquots assayed with the dwarf rice cv. Tan-ginbozu bioassay for GAs. Fractions known to contain ABA were purified by sequential reverse-phase HPLC of the acid and then of the methyl ester forms followed by quantitation as Me-ABA on GLC-EC. ABA losses were measured by using an internal standard [³H]-ABA). Ethylene production was also monitored in stressed and unstressed seedlings.The effect of drought on GAs and ethylene was minimal. The ABA levels were markedly higher in droughted plants. Stressed roots had 32 times more ABA than controls. The levels of cytokinins in the shoots of droughted plants were about half those in unstressed shoots, and qualitative differences occurred in the roots. Under stress a large peak of activity was present similar to zeatin glucoside which was not present in the unstressed condition. The results are discussed in relation to drought-effects on metabolism.     

Aquaporins influence seed dormancy and germination in response to stress

Aquaporins influence water flow in plants, yet little is known of their involvement in the water‐driven process of seed germination. We therefore investigated their role in seeds in the laboratory and under field and global warming conditions. We mapped the expression of tonoplast intrinsic proteins (TIPs) during dormancy cycling and during germination under normal and water stress conditions. We found that the two key tonoplast aquaporins, TIP3;1 and TIP3;2, which have previously been implicated in water or solute transport, respectively, act antagonistically to modulate the response to abscisic acid, with TIP3;1 being a positive and TIP3;2 a negative regulator. A third isoform, TIP4;1, which is normally expressed upon completion of germination, was found to play an earlier role during water stress. Seed TIPs also contribute to the regulation of depth of primary dormancy and differences in the induction of secondary dormancy during dormancy cycling. Protein and gene expression during annual cycling under field conditions and a global warming scenario further illustrate this role. We propose that the different responses of the seed TIP contribute to mechanisms that influence dormancy status and the timing of germination under variable soil conditions.     

Responses of Tamarix ramosissima ABA accumulation to changes in groundwater levels and soil salinity in the lower reaches of Tarim River, China

The Tarim River, located in central Xinjiang Uygur Autonomous Region, is situated north of the Taklimakana Desert. A reduction in groundwater levels and a concomitant increase in soil salinity have reduced vegetation in lower reaches of the river. Tamarix ramosissima is one of the dominant plant species in this riparian system. This species provides a buffer between the desert and the riparian zone, and contributes significantly to the function of the ecosystem and the maintenance of the biodiversity. Thus, an understanding of how T. ramosissima responds to changes in groundwater levels and soil salinity is necessary for ecological and economic management of this riparian system. We found a positive correlation (Pearson Correlation Coefficient = 0.80305) between T. ramosissima Abscisic Acid (ABA) and groundwater levels, and a negative correlation between ABA and soil salinity levels (Pearson Correlation Coefficient = –0.00961). From these relationships between ABA and groundwater/salinity we concluded that subsurface groundwater level of 3.12 m and soil salinity of 0.96 g/L can limit the normal growth and development of T. ramosissima; subsurface groundwater level of larger than 5.59 m and soil salinity of higher than 1.61 g/L will strongly impede the normal development of T. ramosissima. So we should take into account the resistance of plants to environmental stressors such as drought and salinity to keep the levels of salinity and groundwater on both sides of the main river within a range, in which trees, shrubs and herbs can grow well, and perform various ecological functions. Such conservation practice will not only avoid waste of water resources, but also contribute to efficient artificial water-recharge, helping to maintain the riparian zone of Tarim River and to promote “green corridor” maintenance.     

基于生态水位约束的下辽河平原地下水生态需水量估算

以我国北方典型的大型地下水盆地——下辽河平原为研究对象,在考虑地下水蒸发特点基础上,统筹考虑对地下水依赖程度较高的天然草地、天然湿地和河流生态系统对于地下水位的要求,综合水文和生态两方面因素确定地下水生态水位;利用Golden surfer软件的体积计算功能,计算出研究区内全年各月的地下水生态需水量;采用正态信息扩散模型,运用月保证率法得到不同保证率、不同恢复等级下的年地下水生态需水量.结果表明:下辽河平原不同月份的地下水缺水量41.83×108-60.07×108 m3、缺水区面积2.05× 104-2.34×104 km2、盈余水量2.73×108-6.68×108 m3、盈余区面积0.30×104-0.59×104 km2、地下水生态需水量35.15×108-57.33×108 m3;经月保证率法整合后的年地下水生态需水量变化规律为,随着保证率的降低,地下水生态需水量不断增加,而需水量等级越高,需水量增加幅度越大.     

Photosynthetic, Physiological and Biochemical Responses of Tomato Plants to Polyethylene Glycol-Induced Water Deficit

Polyethylene glycol （PEG 6000）-induced water deficit causes physiological as well as biochemical changes in plants. The present study reports on the results of such changes in hydroponically grown tomato plants （Lycopersicon esculentum Mill. cv. Nikita）. Plants were subjected to moderate and severe levels of water stress （i.e. water potentials in the nutrient solution of- 0.51 and -1.22 MPa, respectively）. Water stress markedly affected the parameters of gas exchange. Net photosynthetic rate （Pn） decreased with the induction of water stress. Accordingly, a decrease in the transpiration rate （E） was observed. The ratio of both （Pn/E） resulted in a decrease in water use efficiency. One of the possible reasons for the reduction in Pn is structural damage to the thylakoids, which affects the photosynthetic transport of electrons. This was indicated by an increase in non-photochemical quenching and a reduction in the quantum yield of photosystem Ⅱ. Furthermore, a decrease in both leaf water potential and leaf osmotic potential was observed, which resulted in a significant osmotic adjustment during stress conditions. Analysis of the physiological responses was complemented with a study on changes in proline content. In stressed plants, a 10-fold increase in proline content was detected compared with control plants. It is clear that water stress tolerance is the result of a cumulative action of various physiological and biochemical processes, all of which were affected by PEG 6000-induced water stress.