成年侧柏和刺槐对春季干旱的适应策略

本研究以成年侧柏和刺槐为对象,分析春季干旱胁迫对叶片、根系形态和生理特性的影响,比较2树种在干旱胁迫下的适应策略。结果表明:春季干旱胁迫下,侧柏叶片脯氨酸和可溶性蛋白含量及SOD和POD活性显著低于刺槐叶片(P0.05),可溶性糖含量和CAT活性显著高于刺槐叶片(P0.05),两树种叶片丙二醛含量无显著差异(P0.05);侧柏根系脯氨酸和可溶性蛋白含量及POD和CAT活性显著低于刺槐根系(P0.05),可溶性糖和丙二醛含量显著高于刺槐根系(P0.05)。侧柏比叶重和根系活力显著高于刺槐(P0.05),刺槐根长密度和根面积指数显著高于侧柏(P0.05)。这说明春季干旱胁迫下成年侧柏和刺槐的渗透调节物质含量及抗氧化酶活性不同,春季干旱对两树种叶片伤害程度相似,而对侧柏根系伤害更大;成年侧柏主要采取耐旱策略,刺槐主要采用避旱策略。     

黄土高原常用造林树种水分利用特征

在适宜土壤水分、中度干旱和严重干旱3种土壤水分条件下研究了黄土高原干旱、半干旱地区常用的人工造林树种84k杨树（Populus spp．）、刺槐（Robinia pseudoacacia）、沙棘（Hippophae rhamnoides）和油松（Pinus tabulaeformis）苗木生长及水分利用特征。结果显示,干旱胁迫使各树种成活率、生长速率、光合速率均显著下降;84k杨树和刺槐单叶水分利用率（WUE）在适宜水分下最高,沙棘的在中度干旱下最高;在中度干旱下,4个树种的总水分利用率最高。而严重干旱下最低。无论干旱与否,4个树种中沙棘生长速率最高。在中度干旱条件下,4个树种均可良好生长,而严重干旱下生长均受到显著抑制,其中84k杨树受影响最大;4个树种中沙棘和油松的耐旱性较强,同时油松在各种土壤水分下其生长速度和干物质生产均显著低于其它3个树种;刺槐和84k杨树的耗水量、生物量及水分利用率在3种土壤水分下均显著高于沙棘和油松,84k杨树和刺槐均属于高耗水树种;研究结果表明。84k杨树和刺槐不适宜大面积栽植在黄土高原缺水地区,仅适合栽植在阴坡、沟道等适宜水分条件下。沙棘和油松则适宜栽植在土壤水分较低的地区,如阳坡、峁顶等立地条件上。     

干旱胁迫对苗木蒸腾耗水的影响

采用Lico-6400便携式光合系统测定仪和BP3400精密天平等仪器研究了9个北方主要造林树种的蒸腾速率及实际蒸腾耗量;用压力室法分阶段测定了苗木的叶水势。得出了苗木在正常水分条件下及干旱胁迫过程中的蒸腾耗水规律。比较分析了不同水势梯度下、昼夜不同时间段的各树种的蒸腾耗水量及蒸腾耗水速率。结果表明,蒸腾耗水以白天为主,在相同的水分条件下,不同的苗木有不同的蒸腾耗水量,同种苗木的蒸腾耗水量随干旱胁迫的加重而减少,在受到严重干旱胁迫时,针叶树油松和侧柏的耗水量均降至正常水分条件下的11.7%,阔叶乔木树种降至6．6％,灌木树种降至16．9％。通过研究苗木在不同水势梯度下的耗水特性和蒸腾耗水量。为在水量缺乏的情况下,进行有效的林木培育和植被恢复重建提供依据。     

干旱胁迫对桂西南石漠化地区主要造林树种光合与耗水特性的影响

研究植物耐旱特性和耗水问题对困难立地植被恢复的树种选择具有重要意义。以桂西南岩溶山地常见造林树种肥牛树(Cephalomappa sinensis)、香樟(Cinnamomum camphora)和仪花(Lysidice rhodostegia) 2年生实生苗为对象,采用盆栽苗木称量法和Li-6400光合系统测定方法相结合,研究不同土壤水分条件下3个树种的光合特性、水分利用效率和蒸腾耗水特性。结果表明:3个树种苗木净光合速率(Pn)、气孔导度(Gs)和蒸腾速率(Tr)随土壤干旱胁迫增强呈下降趋势;胞间CO2浓度(Ci)随干旱增强先呈下降趋势,至重度干旱时显著升高,气孔限制值(Ls)则随干旱增强呈增加趋势,至重度干旱时则显著下降(P0.05);轻度和中度干旱胁迫导致苗木Pn下降的主要原因为气孔因素;重度干旱胁迫下Pn下降的主要原因为非气孔因素。肥牛树在轻度干旱胁迫下水分利用效率最高,至重度干旱胁迫时显著下降;香樟和仪花的水分利用效率随干旱胁迫增强而增加,以中度干旱时期最高,至重度干旱时显著下降(P0.05);苗木全天耗水量均随干旱胁迫增强而下降,相同土壤水分条件下以仪花的全天耗水量最高;耗水速率日变化均为单峰曲线,耗水速率最大峰值在不同土壤水分条件下有所不同;在轻度和中度干旱下,以仪花的白天平均耗水速率最高,重度干旱下以肥牛树的白天平均耗水速率最高,仪花其次;隶属函数分析结果显示,综合评价值的大小顺序为肥牛树香樟仪花,苗木的隶属函数加权平均值介于0.3～0.5,具有中等抗旱特性。     

翅果油树幼苗抗旱性

通过盆栽试验,研究不同土壤水分条件下翅果油树（Elaeagnus mollis）幼苗的生长、叶水分和丙二醛含量等各项生理指标的变化。结果表明,轻、中度干旱（30％～35％、45％～50％）胁迫时叶片含水量和叶绿素含量下降幅度较小,水势较高,丙二醛含量较低,翅果油树幼苗能保汪基本的生长,表现出耐旱植物的生理特征;在重度干旱胁迫（20％～25％）条件下,叶含水量和叶绿素含量下降较显著,水势最低,丙二醛含量最高,植株矮小,颜色发黄,表明翅果油树幼苗受到干旱伤害严重,不能正常生长。     

干旱对苗木萌芽期水分状况、ABA含量及萌芽特性的影响

 采用4种常见造林树种沙棘（Hippophae rhamnoides L.）、油松（Pinus tabulaeformis）、刺槐（Robinia pseudoacacia L.）和杨树(Populus simonii),研究水分胁迫下苗木移栽后萌芽过程中体内水分状况与ABA累积关系,探讨干旱使苗木致死的生理学机制。结果表明,土壤干旱导致苗木组织含水量、芽体生长速率、萌芽率及成活率显著下降;各树种在萌芽过程中其芽体和韧皮部中的脱落酸（ABA）含量随土壤干旱程度的加重而升高,并与苗体组织含水量、萌芽率及成活率呈显著负相关;抗旱性强的沙棘和油松芽体和韧皮组织中ABA绝对含量比杨树和刺槐高5～10倍左右;经统计分析发现,4种苗木的萌芽速度、萌芽率以及移栽成活率均与韧皮部的组织含水量显著相关。     

土壤干旱对黄土高原乡土树种水分代谢与渗透调节物质的影响

以黄土高原4个乡土树种的幼苗为试验材料,采用盆栽方式模拟土壤干旱环境,研究土壤干旱对不同树种水分代谢与渗透调节物质的影响。结果表明,大叶细裂槭、虎榛子叶水势、叶片含水量下降迅速,叶片离体保水能力降幅明显;白刺花、辽东栎则表现为叶水势、叶片含水量缓慢下降,组织相对含水量在中度胁迫下略有上升。白刺花在不同水分处理条件下离体叶片保水力明显高于其它树种。1个树种可溶性糖含量随土壤干旱程度加剧明显增加,可溶性蛋白质含量在树种之间变化较为复杂,无明显规律性。K^ 离子含量和游离脯氨酸含量在中度水分胁迫下均有不同程度升高。白刺花在土壤干旱进程中,可溶性蛋白质含量、K^ 离子含量和游离脯氨酸含量均明显高于其它树种。综合水分代谢和渗透调节物质来看,水分胁迫条件下,白刺花以保持高水势、减少组织水分散失和增加渗透调节物质来提高细胞原生质浓度,增强其抗旱性。     

干旱对4种苗木根尖可溶性蛋白组分和含量的影响

以2年生刺槐、油松、侧柏、沙棘苗木为材料,设置包括适宜水分、中度干旱、重度干旱(分别为田间土壤持水量的70%、50%、35% )3个水分程度和短期(7 d)、中期(14 d)、长期(21 d)3个时间的人为控水胁迫实验,研究了干旱胁迫对4种苗木根尖可溶性蛋白含量及组分的影响.结果表明:刺槐根尖可溶性蛋白含量在短期中度干旱和长期重度干旱下显著减少,而在中长期中度干旱和短期重度干旱下显著增加;侧柏根尖可溶性蛋白含量在短期中度干旱和重度干旱下显著增加,长期中度干旱和中长期重度干旱下减少;随着胁迫程度加重和处理时间的延长,油松根尖可溶性蛋白含量总体增加,而沙棘则减少.4种苗木根尖可溶性蛋白组分在不同干旱胁迫程度和时间下均无明显变化,各分子量可溶性蛋白含量变化大多数与总蛋白含量变化趋于一致.可见,4种苗木根尖可溶性蛋白含量的变化在干旱胁迫程度、胁迫时间以及树种之间差异较大,其对干旱的响应是通过大部分蛋白组分较一致地变化来实现的.     

土壤干旱对辽东栎、大叶细裂槭幼苗生长及水分利用的影响

在盆栽条件下研究了不同土壤干旱条件对辽东栎和大叶细裂槭幼苗生长及水分利用率的影响。结果表明,随干旱胁迫程度加剧,两树种叶水势均下降,随胁迫时间延长水势又有一回升趋势,显示出树种自身的调节能力,大叶细裂槭调节水势的能力强于辽东栎。叶水势与叶片含水量关系密切,水势的高低决定叶片水分状况,水分含量又决定了幼苗的生长状况。大叶细裂槭新梢在5、6月增长增粗迅速,而辽东栎在4月、5月生长迅速及叶面积扩展快,适宜水分下增粗可持续至9月份。不同土壤水分处理下两树种水分利用效率差异明显。在中度干旱下整体WUE有所上升,尤其是辽东栎提高约10％;大叶细裂槭的根冠比在重度干旱下可达2以上,说明它对干旱的适应性很强,在严重干旱胁迫下也能长期维持生命,成活率高于辽东栎,接近100％,可见其适应性强于辽东栎。     

不同土壤水分下刺槐和油松的生理特征

在适宜土壤水分(70%θf)、中度干旱(55%θf)和严重干旱(40%θf)3种土壤水分条件下研究了黄土高原常见造林树种刺槐(Robinia pseudoacacia L.)和油松(Pinus tabulaeformis Carr.)的生长及水分利用特性.结果表明:干旱胁迫使2树种的成活率、干物质累积和光合速率均显著下降.在适宜水分下刺槐的单叶水分利用率(WUE)最高,严重干旱下最低.刺槐和油松的枝条快速生长期主要集中在3-6月,在中度干旱条件,2个树种均可良好生长;在严重干旱下2个树种的生长均受到显著抑制,但刺槐受影响较大,油松受影响较小.在3种土壤水分条件下刺槐耗水量、生物量及水分利用率均显著高于油松.2树种在中度干旱下的总WUE最高,严重干旱下最低.刺槐属于高耗水树种,油松属于低耗水树种,油松的耐旱性强于刺槐.研究结果表明,刺槐在黄土高原缺水地区不适宜大面积栽植,只能用于水分条件较好的立地条件下造林.油松应尽可能在含水量较高的阴坡或沟坡地带造林.     

土壤水势对水曲柳幼苗水分生态的影响

采用根区渗灌控水技术,将土壤水势长期控制在0～-20kPa(W1)、-20～-40kPa(W2)、-40～-60kPa(W3)、-60～-80kPa(W4)、-80～-160kPa(W5)范围内,系统地研究了不同土壤水势条件下水曲柳幼苗的蒸腾过程、吸水过程、根叶水势13动态过程及SPAC体系的水流阻力,结果表明,在亚饱和土壤水分状态下(W1),细根水势最高,水分由土壤进入细根的阻力最小,根系吸水速率最高,从而支持了13间强烈的蒸腾作用．在田间持水量土壤水分状态下(W2),细根吸水阻力成倍增加,吸水速率和蒸腾速率显著下降,但尚未改变蒸腾作用13动态过程的单峰模式．当土壤水分在田间持水量状态以下(W3-W5)时,随着土壤水势递降,细根吸水阻力急剧增加至几倍乃至几十倍,根系吸水速率过低,吸水与蒸腾矛盾加剧,叶水势降至很低,气孔关闭,蒸腾作用受到严重抑制,呈现明显的午休低谷．在实验范围内(0～-160kPa),土壤水分对水曲柳幼苗是非等效的,当土壤水分在田间持水量状态以下(<-40kPa)时,水曲柳全光苗发生显著的水分胁迫。     

土壤水势对水曲柳幼苗水分生态的影响

采用根区渗灌控水技术,将土壤水势长期控制在0～-20kPa(W₁)、-20～-40kPa(W₂)、-40～-60kPa(W₃)、-60～-80kPa(W₄)、-80～-160kPa(W₅)范围内,系统地研究了不同土壤水势条件下水曲柳幼苗的蒸腾过程、吸水过程、根叶水势日动态过程及SPAC体系的水流阻力.结果表明,在亚饱和土壤水分状态下(W₁),细根水势最高,水分由土壤进入细根的阻力最小,根系吸水速率最高,从而支持了日间强烈的蒸腾作用.在田间持水量土壤水分状态下(W₂),细根吸水阻力成倍增加,吸水速率和蒸腾速率显著下降,但尚未改变蒸腾作用日动态过程的单峰模式.当土壤水分在田间持水量状态以下(W₃～W₅)时,随着土壤水势递降,细根吸水阻力急剧增加至几倍乃至几十倍,根系吸水速率过低,吸水与蒸腾矛盾加剧,叶水势降至很低,气孔关闭,蒸腾作用受到严重抑制,呈现明显的午休低谷.在实验范围内(0～-160kPa),土壤水分对水曲柳幼苗是非等效的,当土壤水分在田间持水量状态以下(<-40kPa)时,水曲柳全光苗发生显著的水分胁迫.     

Growth responses of seminal roots of wheat seedlings to a reduction in the water potential of vermiculite

We examined the elongation rate, water status and solute accumulation in the seminal roots of wheat seedlings (Triticum aestivum L.) that were growing in vermiculite with a water potential (Ψ_w) ranging from −0 03 to −1 10 MPa. The elongation rate of the primary seminal root was similar to that of the first pair of seminal roots but that of the second pair of seminal roots was lower at all values of Ψ_w tested. The elongation rate was highest in vermiculite with a Ψ_w of −0.03 MPa but did not decrease significantly until the Ψ_w was reduced to −0.15 MPa. Further reductions in Ψ_w reduced the elongation rate markedly. The Ψ_w of mature tissues was always similar to that of vermiculite. The osmotic potential (Ψ_o) decreased to the same extent as the decrease in Ψ_w. Thus, the turgor pressure (Ψ_p) remained unchanged even in vermiculite with a low Ψ_w. In elongating tissues, Ψ_w and Ψ_o were far lower than they were in mature tissues and, thus, reductions in turgor were not significant. Even when the Ψ_w of vermiculite changed, there were no consistent changes in terms of a difference in Ψ_w between elongating plus mature tissues and vermiculite. There were also no consistent changes in levels of osmotica, calculated using the van’t Hoff’s law, in the elongating tissues but the levels in mature tissues increased in vermiculite with a low Ψ_w. Our results suggest that (1) reductions in root elongation in vermiculite with a low Ψ_w were caused by reductions in the extensibility and/or increases in the yield threshold of cell walls and by reductions in the hydraulic conductivity of the tissues; and (2) a seminal root regulates its growth to keep turgor pressure unchanged.     

Contrasting physiological responses of six eucalyptus species to water deficit

BACKGROUND AND AIMS: The genus Eucalyptus occupies a broad ecological range, forming the dominant canopy in many Australian ecosystems. Many Eucalyptus species are renowned for tolerance to aridity, yet inter-specific variation in physiological traits, particularly water relations parameters, contributing to this tolerance is weakly characterized only in a limited taxonomic range. The study tests the hypothesis that differences in the distribution of Eucalyptus species is related to cellular water relations. METHODS: Six eucalypt species originating from (1) contrasting environments for aridity and (2) diverse taxonomic groups were grown in pots and subjected to the effects of water deficit over a 10-week period. Water potential, relative water content and osmotic parameters were analysed by using pressure-volume curves and related to gas exchange, photosynthesis and biomass. KEY RESULTS: The six eucalypt species differed in response to water deficit. Most significantly, species from high rainfall environments (E. obliqua, E. rubida) and the phreatophyte (E. camaldulensis) had lower osmotic potential under water deficit via accumulation of cellular osmotica (osmotic adjustment). In contrast, species from low rainfall environments (E. cladocalyx, E. polyanthemos and E. tricarpa) had lower osmotic potential through a combination of both constitutive solutes and osmotic adjustment, combined with reductions in leaf water content. CONCLUSIONS: It is demonstrated that osmotic adjustment is a common response to water deficit in six eucalypt species. In addition, significant inter-specific variation in osmotic potential correlates with species distribution in environments where water is scarce. This provides a physiological explanation for aridity tolerance and emphasizes the need to identify osmolytes that accumulate under stress in the genus Eucalyptus.     

A new method of measuring water potential in tree stems by water injection

Abstract. A new method of measuring xylem water potential in the stems of trees is described. The flow rate of water injected into the xylem at two or more known pressures is measured. The xylem water potential is derived either graphically from the relationship between flow rate and applied pressure, or from the solution of simultaneous flow equations.     

Photosynthesis of six barley genotypes as affected by water stress

The effect of water stress on plant water status and net photosynthetic gas exchange (PN) in six barley genotypes (Hordeum vulgare L.) differing in productivity and drought tolerance was studied in a controlled growth chamber. Osmotic adjustment (OA), PN, stomatal conductance (gs), and the ratio intercellular/ambient. CO2 concentration (Ci/Ca) were evaluated at four different levels of soil water availability, corresponding to 75, 35, 25 and 15 % of total available water. Variability in OA capacity was observed between genotypes: the drought tolerant genotypes Albacete and Alpha showed higher OA than drought susceptible genotypes Express and Mogador. The genotype Albacete exhibited also higher PN than the others at low water potential (Ψ). The ratios of PN/gs and Ci/Ca showed that differences in photosynthetic inhibition between genotypes at low Ψ were probably due to nonstomatal effects. In Tichedrett, a landrace genotype with a very extensive root development, OA was not observed, however, it exhibited a capacity to maintain its photosynthetic activity under water stress. This revised version was published online in June 2006 with corrections to the Cover Date.     

基于叶片水势的内蒙古典型草原植物水分适应特征研究

水分是限制草原生态系统植物生存、繁殖和扩散最重要的生态因子,植物通过多样的水分适应策略适应干旱环境。为了解典型草原植物水势特征及其影响因素,在2017年和2018年的生长季对内蒙古典型草原71种植物的叶片黎明水势、午后水势、叶片和根系功能性状进行了测定与分析。结果表明:测定的71种植物叶片的黎明水势分布于-2.67—-0.63 MPa,午后水势分布于-4.67—-1.01 MPa;一年生植物的叶片具有最高的黎明水势、午后水势和最小的水势日差值(叶片的黎明水势与午后水势的差值),多年生禾草的叶片具有最低的黎明水势、午后水势和最大的水势日差值;71种植物对水分的适应策略可分为高水势保持型、低水势忍耐型和变水势波动型;叶片午后水势与叶片干物质含量和根系深度呈极显著的负相关关系(P0.01),但与比叶面积呈极显著的正相关关系(P0.01)。本研究有助于从植物生理学的角度上准确认识典型草原植物的水分适应性及水分生态特征。     

Plant water potential measured continuously in the field

Summary A simple system is described which allowed the use of a stem attached psychrometer in the field. Water was circulated between a tank buried in the soil and the psychrometer and this sytem reduced temperature gradients sufficiently to enable continuous measurements of plant water potential to be made in the field. Measurements agreed with those taken independently with a destructive pressure chamber method.     

Relations between water content, potential and permeability in stems of conifers

Abstract. The influence of sapwood water content on the conductivity of sapwood to water was measured on stem sections of Pinus contorta. A reduction in relative water content from 100 to 90% caused permeability to fall to about 10% of the saturated value.
Pressure–volume curves of branchwood and stem sapwood of Pinus contorta and Picea sitchensis have been analysed to definè the tissue capacitance and the time constant and resistance for water movement between stored water and the functional xylem as functions of tissue water potential. Three phases in water loss were discernible. In the initial phase at high water potentials (> –0.5 MPa), the capacitance was large, the time constant long and the resistance to flow large in comparison with intermediate water potentials (−0.5 to −1.5 MPa). At still lower water potentials (−1.5 to −3.0 MPa), the time constant and resistance declined still further but the capacitance had a tendency to increase again, especially in the stemwood of Sitka spruce. Typical values in the second phase were for the time constant 5 s, for the resistance 4 × 10⁻¹³ N s m⁻⁵ and for the capacitance (change in relative water content per unit change in potential) 1×10⁻¹¹ m³ Pa⁻¹. These parameters define the availability of stored water and are being used in a dynamic model of water transport in trees.     

Roles of leaf water potential and soil-to-leaf hydraulic conductance in water use by understorey woody plants

Diurnal changes of leaf water potential and stomatal conductance were measured for 12 deciduous shrubs and tree saplings in the understorey of a temperate forest. Sunflecks raised the leaf temperature by 4°C, and vapor pressure deficit to 2 kPa. Although the duration of the sunflecks was only 17% of daytime, the photon flux density (PFD) of sunflecks was 52% of total PFD on a sunny summer day. Leaf osmotic potential at full turgor decreased in summer, except in some species that have low osmotic potential in the spring. Plants that endured low leaf water potential had rigid cell walls and low osmotic potential at full turgor. These plants did not have lower relative water content and turgor potential than plants with higher leaf water potential. There were three different responses to an increase in transpiration rate: (i) plants had low leaf water potential and slightly increased soil-to-leaf hydraulic conductance; (ii) plants decreased leaf water potential and increased the hydraulic conductance; and (iii) plants had high leaf water potential and largely increased the hydraulic conductance.