断根处理对银杏树体水力特征及生长的影响

以8年生银杏为试材,采用不同程度的断根处理,测定处理后树体超声（ultrasound acoustic emission,UAE）信号、枝条栓塞程度（percentage loss of hydraulic conductance,PLC）、树干液流通量、气孔导度、蒸腾速率以及叶片水势等生理指标,分析断根对银杏树体水力特征及生长状况的影响.结果表明:断根处理后,在短时间内有大量UAE信号产生,且随断根程度的加重而增大,在6 h出现最大值,随后逐渐降低;枝条的PLC在起初的12 h迅速增加,24 h后增速趋于停滞;银杏树干液流通量、叶片气孔导度、蒸腾速率和水势明显降低,各处理间差异显著.经统计分析,累积UAE（cumulative number of UAE, cUAE）信号量与PLC呈现显著的正相关关系,与液流通量和叶片水势呈负相关关系.次年的单叶面积、新生枝条长度显著下降,下降程度随断根处理的加重而加剧.断根处理在短时间内增加了银杏管胞气穴数量和木质部栓塞的程度,影响到水分输送和叶片蒸腾,最终对叶片和枝条的生长产生负面影响.     

亚低温与干旱胁迫对番茄植株水分传输和形态解剖结构的影响

为探讨亚低温和干旱对植株水分传输的影响机制,以番茄幼苗为试材,利用人工气候室设置常温(昼25 ℃/夜18 ℃)和亚低温(昼15 ℃/夜8 ℃)环境,采用盆栽进行正常灌水(75%～85%田间持水量)和干旱处理(55%～65%田间持水量),分析了温度和土壤水分对番茄植株水分传输、气孔和木质部导管形态解剖结构的影响。结果表明: 与常温正常灌水处理相比,干旱处理使番茄叶水势、蒸腾速率、气孔导度、水力导度、茎流速率、气孔长度和叶、茎、根导管直径显著减小,而使叶、茎、根导管细胞壁厚度和抗栓塞能力增强;亚低温处理下番茄叶水势、蒸腾速率、气孔导度、水力导度和叶、茎、根导管直径显著降低,但气孔变大,叶、根导管细胞壁厚度和叶、茎、根抗栓塞能力显著升高。亚低温条件下土壤水分状况对番茄叶水势、蒸腾速率、气孔导度、水力导度、气孔形态、叶、根导管结构均无显著影响。总之,干旱处理下番茄通过协同调控叶、茎、根结构使植株水分关系重新达到稳态;亚低温处理下番茄植株水分关系的调控主要通过改变叶和根导管结构实现,且受土壤水分状况的影响较小。     

胡杨木质部水分传导对盐胁迫的响应与适应北大核心CSCD

解析植物木质部导水率对逆境的响应和适应对促进植物抗逆性机理研究和受损植被恢复具有重要意义。该文以荒漠河岸林建群种胡杨(Populus euphratica)为研究对象,系统分析了胡杨幼株根、茎、叶水分传输通道对不同浓度盐胁迫的响应和适应。结果表明:(1)胡杨幼株根系对盐胁迫的敏感性高于茎和叶,盐胁迫下根系生长和根尖数显著受到抑制,根木质部易于发生栓塞,导水率明显降低。(2)胡杨幼株茎木质部导水率对盐胁迫的响应依盐浓度而定,轻度(0.05 mol·L–1 Na Cl)和中度(0.15 mol·L–1 Na Cl)盐胁迫下,胡杨可以通过协调导管输水的有效性和安全性来调节木质部的导水率,维持植物正常生长;重度(0.30 mol·L–1 Na Cl)盐胁迫下,胡杨茎木质部导管输水有效性和安全性均明显降低,木质部导水率显著下降,并伴随叶片气孔导度的显著降低,从而严重抑制了胡杨的光合和生长。     

荒漠河岸林植物木质部导水与栓塞特征及其对干旱胁迫的响应

 以同处于干旱区的塔里木河下游(铁干里克)和黑河下游(乌兰图格)断面为研究区, 比较了荒漠河岸林主要建群种胡杨(Populus euphratica)、柽柳(Tamarix spp.)、疏叶骆驼刺(Alhagi sparsifolia)和花花柴(Karelinia caspia)在长期遭受不同干旱胁迫下的根、枝条木质部导水力和栓塞化程度的变化特征, 并分析了木质部导水对干旱胁迫的响应及适应策略。结果表明: 1) 黑河下游荒漠河岸林植物的导水能力显著高于塔里木河下游, 其中柽柳、胡杨、疏叶骆驼刺和花花柴根木质部的初始比导率(K_s0)分别高11.97、6.74、7.10和3.73倍, 枝条的K_s0分别高9.48、3.65、2.07和1.88倍, 地下水埋深导致的干旱胁迫程度不同是诱发荒漠植物导水能力差异的根本原因; 2)柽柳耐干旱能力最强, 适应范围较宽, 而花花柴、疏叶骆驼刺的耐旱性相对较弱, 适生范围较窄, 这可能与植物的根系分布有关; 3)干旱胁迫较轻时, 枝条木质部是荒漠河岸林植物水分传输的主要阻力部位, 干旱胁迫严重时, 根木质部是限制植株水流的最大阻碍部位; 4)荒漠河岸林植物主要通过调节枝条木质部的水流阻力来适应干旱胁迫, 且其适应策略与干旱胁迫程度有关, 干旱胁迫轻时, 植物通过限制枝条木质部水流来协调整株植物的均匀生长; 干旱胁迫严重时, 植物通过牺牲劣势枝条、增强优势枝条水流来提高植株整体生存的机会。     

盐碱胁迫下枸杞和柽柳的水力学特性和碳代谢

盐碱胁迫是全球范围内重要的非生物胁迫形式之一,但目前对植物水力学特性和碳代谢应对盐碱胁迫响应的研究还不多。本研究以耐盐碱植物枸杞（Lycium chinense Miller）和柽柳（Tamarix chinensis Lour.）为对象,测定不同盐碱程度下两种植物的枝条水势和导水损失率（PLC）、叶片光合作用和气孔导度、不同部位的非结构性碳（NSC）浓度以及植株生长情况。结果显示,重度盐碱胁迫显著降低了两种植物凌晨和正午水势、光合速率和枝条PLC,重度胁迫下柽柳的光合速率、气孔导度和枝条PLC下降程度均大于枸杞,重度盐碱胁迫下枸杞不同部位的NSC浓度均显著降低,但柽柳的地上部分NSC浓度显著增加,根部NSC浓度显著减低。两种植物有不同的应对盐碱胁迫策略,枸杞有较强的气孔调节能力,对水力结构的维持有利,但会限制碳摄取,柽柳气孔调节能力弱,水力结构易受影响,但对碳平衡维持有利。     

胡杨木质部水分传导对盐胁迫的响应与适应

解析植物木质部导水率对逆境的响应和适应对促进植物抗逆性机理研究和受损植被恢复具有重要意义。该文以荒漠河岸林建群种胡杨(Populus euphratica)为研究对象, 系统分析了胡杨幼株根、茎、叶水分传输通道对不同浓度盐胁迫的响应和适应。结果表明: (1)胡杨幼株根系对盐胁迫的敏感性高于茎和叶, 盐胁迫下根系生长和根尖数显著受到抑制, 根木质部易于发生栓塞, 导水率明显降低。(2)胡杨幼株茎木质部导水率对盐胁迫的响应依盐浓度而定, 轻度(0.05 mol·L^-1 NaCl)和中度(0.15 mol·L^-1 NaCl)盐胁迫下, 胡杨可以通过协调导管输水的有效性和安全性来调节木质部的导水率, 维持植物正常生长; 重度(0.30 mol·L^-1 NaCl)盐胁迫下, 胡杨茎木质部导管输水有效性和安全性均明显降低, 木质部导水率显著下降, 并伴随叶片气孔导度的显著降低, 从而严重抑制了胡杨的光合和生长。     

不同林龄刺槐解剖结构及生理特性

全球变暖导致干旱强度增大、频率增加，探究黄土高原不同林龄刺槐林对干旱的响应机制对于理解该区人工林生产力稳定性具有重要意义。本研究以黄土高原半干旱区刺槐幼龄林、中龄林和成熟林为对象，探究不同林龄木质部解剖特征、水力特征和非结构性碳水化合物含量及其之间的相关关系。结果表明：幼龄林、中龄林的导管直径、纹孔总面积、纹孔面积、附着物面积和附着比例均显著大于成熟林，而纹孔密度显著小于成熟林。导管直径、纹孔面积和附着物面积与导水率之间存在显著相关性。幼龄、中龄和成熟林枝条导水率分别为2.30、2.12和0.76 kg·m^-1·s^-1·MPa^-1,栓塞程度分别为54.5%、53.8%和45.1%。导水率与可溶性糖和淀粉含量之间存在显著相关性。幼龄、中龄和成熟林枝条木质部可溶性糖含量分别为4.9%、4.2%和3.8%。成熟林刺槐木质部生长力下降，形成具有较多较小纹孔的小导管，在维持水力安全的同时降低了水分运输效率，组织内维持生长代谢的非结构性碳水化合物含量显著降低。本研究解释了不同林龄刺槐人工林对干旱的响应机制，为黄土高原不同林龄刺槐人工...     

三种裸子植物木质部结构与功能对不同生境的适应

生境异质性是影响植物生长发育的重要因素。植物木质部水力系统是土壤-植物-大气连续体的主要通路, 直接影响植物的基本行为和功能, 同时也反映了植物对环境变化的适应性。为对比天目山3种裸子植物枝条木质部水力功能、机械和解剖结构性状在不同生境(自然生境与人工生境)的差异, 揭示裸子植物对不同生境的适应机制, 该研究以金钱松(Pseudolarix amabilis)、杉木(Cunninghamia lanceolata)和雪松(Cedrus deodara)为研究对象, 测定枝木质部导水率、栓塞抗性(导水率损失50%时的水势)、机械以及解剖结构性状。结果发现: 1)人工生境植株比自然生境植株水力效率弱, 但栓塞抗性强。2)自然生境雪松木质部导水系统存在效率-安全权衡; 不论自然还是人工生境杉木、金钱松木质部导水系统均无效率-安全权衡。3)人工生境雪松和金钱松木质部存在机械-安全权衡。相比人工生境, 土壤水分有效性低的自然生境中, 植物采用增大纹孔膜直径来提高水力效率, 此外, 还可通过增加木材密度、扩大管胞直径来避免栓塞带来的威胁。     

浙江天童木本植物水力结构与树高的关联性

垂直分层是森林群落的基本结构,但有关群落不同垂直层次植物水力结构策略的研究仍然比较缺乏。以浙江天童木荷林内25株高度不同的9种木本植物为对象,通过测量其枝条直径、边材面积、干材密度、导管直径、内腔面积以及枝条水分比导率,旨在检验植物水力结构与树高的关联性。结果显示：除干材密度外,枝条直径、导管直径、枝条和导管内腔面积、边材面积、水分比导率均随树高增加而显著增大。作为重要的水力结构特征,比导率与导管直径和内腔面积、枝直径和内腔面积、边材面积显著正关联。该结果强调了局域群落内不同垂直层次植物水力结构特征的显著差异,以及植物水分生态位在不同垂直层次的分化过程。     

摘叶造成的碳限制对刺槐碳素分配和水力学特性的影响

以3年生刺槐（Robinia pseudoacacia Linn.）为研究对象,通过对其进行连续3次摘叶造成严重碳限制,检测摘叶后刺槐的生物量分配、叶片形态和不同部位的非结构性碳（NSC）浓度,同时检测其根压和根系导水率、枝条水势和导水率损失值（PLC）及茎的抗栓塞能力,研究摘叶造成的碳限制对刺槐碳素分配和水力学特性的影响。结果显示,摘叶显著降低了刺槐不同部位的生物量,其中细根生物量降低程度最大;摘叶还造成了刺槐不同部位NSC浓度显著降低,茎韧皮部、茎木质部、根韧皮部和根木质部的NSC浓度分别为对照的29.6%、20.2%、10.2%和8.7%,且根部NSC的降低程度显著高于茎;碳限制显著降低了刺槐苗木的根压和根系导水率,增加了枝条凌晨和正午的PLC,降低了其抗栓塞能力。研究结果表明摘叶造成的碳限制改变了刺槐的碳素分配模式,限制了碳素向根的分配,抑制细根的发生,进而限制根的水分吸收能力,加重枝条栓塞程度,同时还会导致枝条抗栓塞能力下降,从而降低植物水分输导的安全性。     

干旱胁迫对油松和侧柏水分运输安全性和有效性的影响

通过采用改良的冲洗法测定5年生苗木油松(Pinus tabulaeformis)和侧柏(Platycladus orientalis)在不同干旱胁迫时期的水力结构参数,结果表明随着干旱胁迫增加,不同分枝级和茎段所在区域的导水率损失(PLC)增加,比导率(Ks)减少。油松和侧柏在0级,1级和2级分枝级的发生栓塞的水势阈值分别为-0.55、-0.49、-0.43和-0.90、-0.78、-0.74MPa。随着相对分枝级的增加,油松和侧柏的水势阈值增大,栓塞脆弱性变大。非限速区PLC大而Ks小,限速区PLC小而Ks大。油松和侧柏相对分枝级和茎段所在区域的栓塞脆弱性大小为2级1级0级,限速区非限速区,且油松大于侧柏。油松和侧柏在不同干旱胁迫,不同相对分枝级,不同茎段所在区域采取不同的方式来适应由水势降低而引起的栓塞变化。其采取的生态策略包括:保持较高的水分安全性;减轻安全性而对有效性的折衷;同时降低有效性和安全性但不终止任何生产力或树高的组织生长所需水的限制。     

Cavitation vulnerability in roots and shoots: does Populus euphratica Oliv., a poplar from arid areas of Central Asia, differ from other poplar species?

Populus euphratica is a poplar species growing in arid regions of Central Asia, where its distribution remains nevertheless restricted to river-banks or to areas with an access to deep water tables. To test whether the hydraulic architecture of this species differs from that of other poplars with respect to this ecological distribution, the vulnerability to cavitation of P. euphratica was compared with that of P. alba and of P. trichocarpa x koreana. The occurrence of a potential hydraulic segmentation through cavitation was also investigated by assessing the vulnerability of roots, stems, and leaf mid-rib veins. Cryo-scanning electron microscopy (cryo-SEM) was used to assess the level of embolism in fine roots and leaf mid-ribs and a low pressure flowmeter (LPFM) was used for stems and main roots. The cryo-SEM technique was validated against LPFM measurements on paired samples. In P. alba and P. trichocarpa x koreana, leaf mid-ribs were more vulnerable to cavitation than stems and roots. In P. euphratica, leaf mid-ribs and stems were equally vulnerable and, contrary to what has been observed in other species, roots were significantly less vulnerable than shoots. P. euphratica was by far the most vulnerable. The water potential inducing 50% loss of conductivity in stems was close to -0.7 MPa, against approximately -1.45 MPa for the two others species. Such a large vulnerability was confirmed by recording losses of conductivity during a gradual drought. Moreover, significant stem embolism was recorded before stomatal closure, indicating the lack of an efficient safety margin for hydraulic functions in this species. Embolism was not reversed by rewatering. These observations are discussed with respect to the ecology of P. euphratica.     

不同水分条件下两个树种木质部栓塞对P素添加的响应

 在两种水分供给(干旱胁迫和适宜水分,土壤含水量分别为田间持水量的30%～40%和70%～80%)下,研究了耐旱树种元宝枫(Acer truncatum)和 中生树种女贞(Ligustrum lucidum )木质部栓塞(以导水率(Percentage loss of hydraulic conductivity, PLC)损失程度衡量)对P素添加的 响应。结果发现,两个树种PLC的日变化均呈现出先上升后降低的规律,表明木质部栓塞的形成与恢复是植物体的一种平常事件;除适宜水分条 件的女贞外,P素可以显著提高元宝枫和遭受干旱胁迫时女贞的PLC;两种水分条件下,干旱胁迫时元宝枫木质部栓塞明显高于适宜水分供给时 。女贞的PLC在两种水分状况下无显著差异;树种间,干旱胁迫促进了元宝枫木质部的栓塞形成,明显高于同等水分条件下的女贞。该研究结果 证实了“木质部限流耐旱假设”。     

Native root xylem embolism and stomatal closure in stands of Douglas-fir and ponderosa pine: mitigation by hydraulic redistribution

Hydraulic redistribution (HR), the passive movement of water via roots from moist to drier portions of the soil, occurs in many ecosystems, influencing both plant and ecosystem-water use. We examined the effects of HR on root hydraulic functioning during drought in young and old-growth Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] and ponderosa pine (Pinus ponderosa Dougl. Ex Laws) trees growing in four sites. During the 2002 growing season, in situ xylem embolism, water deficit and xylem vulnerability to embolism were measured on medium roots (2–4-mm diameter) collected at 20–30 cm depth. Soil water content and water potentials were monitored concurrently to determine the extent of HR. Additionally, the water potential and stomatal conductance (g_s) of upper canopy leaves were measured throughout the growing season. In the site with young Douglas-fir trees, root embolism increased from 20 to 55 percent loss of conductivity (PLC) as the dry season progressed. In young ponderosa pine, root embolism increased from 45 to 75 PLC. In contrast, roots of old-growth Douglas-fir and ponderosa pine trees never experienced more than 30 and 40 PLC, respectively. HR kept soil water potential at 20–30 cm depth above –0.5 MPa in the old-growth Douglas-fir site and –1.8 MPa in the old-growth ponderosa pine site, which significantly reduced loss of shallow root function. In the young ponderosa pine stand, where little HR occurred, the water potential in the upper soil layers fell to about –2.8 MPa, which severely impaired root functioning and limited recovery when the fall rains returned. In both species, daily maximum g_s decreased linearly with increasing root PLC, suggesting that root xylem embolism acted in concert with stomata to limit water loss, thereby maintaining minimum leaf water potential above critical values. HR appears to be an important mechanism for maintaining shallow root function during drought and preventing total stomatal closure.     

The effects of acclimation to sunlight on the xylem vulnerability to embolism in Fagus sylvatica L.

We assessed the effects of irradiance received during growth on the vulnerability of Fagus sylvatica L. xylem vessels to water-stress-induced embolism. The measurements were conducted on (1) potted saplings acclimated for 2 years under 100% and 12% incident global radiation and (2) branches collected from sun-exposed and shaded sides of adult trees. Both experiments yielded similar results. Light-acclimated shoots were less vulnerable to embolism. Xylem water potential levels producing 50% loss of hydraulic conductivity were lower in sun-exposed branches and seedlings than in shade-grown ones (–3·0 versus –2·3 MPa on average). The differences in vulnerability were not correlated with differences in xylem hydraulic conductivity nor vessel diameter. Resistance to cavitation was correlated with transpiration rates, midday xylem and leaf water potentials in adult trees. We concluded that vulnerability to cavitation in Fagus sylvatica may acclimate to contrasting ambient light conditions.     

Capacitive effect of cavitation in xylem conduits: results from a dynamic model

Embolisms decrease plant hydraulic conductance and therefore reduce the ability of the xylem to transport water to leaves provided that embolized conduits are not refilled. However, as a xylem conduit is filled with gas during cavitation, water is freed to the transpiration stream and this transiently increases xylem water potential. This capacitive effect of embolism formation on plant function has not been explicitly quantified in the past. A dynamic model is presented that models xylem water potential, xylem sap flow and cavitation, taking into account both the decreasing hydraulic conductance and the water release effect of xylem embolism. The significance of the capacitive effect increases in relation to the decreasing hydraulic conductance effect when transpiration rate is low in relation to the total amount of water in xylem conduits. This ratio is typically large in large trees and during drought.     

Rapid hydraulic recovery in Eucalyptus pauciflora after drought: linkages between stem hydraulics and leaf gas exchange

In woody plants, photosynthetic capacity is closely linked to rates at which the plant hydraulic system can supply water to the leaf surface. Drought‐induced embolism can cause sharp declines in xylem hydraulic conductivity that coincide with stomatal closure and reduced photosynthesis. Recovery of photosynthetic capacity after drought is dependent on restored xylem function, although few data exist to elucidate this coordination. We examined the dynamics of leaf gas exchange and xylem function in Eucalyptus pauciflora seedlings exposed to a cycle of severe water stress and recovery after re‐watering. Stomatal closure and leaf turgor loss occurred at water potentials that delayed the extensive spread of embolism through the stem xylem. Stem hydraulic conductance recovered to control levels within 6 h after re‐watering despite a severe drought treatment, suggesting an active mechanism embolism repair. However, stomatal conductance did not recover after 10 d of re‐watering, effecting tighter control of transpiration post drought. The dynamics of recovery suggest that a combination of hydraulic and non‐hydraulic factors influenced stomatal behaviour post drought.