刺槐苗木干旱胁迫过程中水力学失败和碳饥饿的交互作用

【目的】通过分析刺槐在干旱和复水过程中水力学性状和非结构碳(NSC)储藏的变化,研究在水力学失败和碳饥饿对刺槐苗木的影响,以探讨在经历导致落叶的严重干旱胁迫之后叶片恢复的影响因素。研究的结果可以阐明刺槐干旱和复水过程中水力学结构和碳代谢的交互作用方式,同时为揭示干旱半干旱地区刺槐衰败死亡的生理学机制提供思路和试验证据。【方法】测定3年生刺槐苗在严重干旱导致落叶后和复水后叶片长成时的小枝凌晨和正午水势、枝条正午气穴栓塞、叶片最大光合速率和气孔导度、单株叶面积、枝条和根的非结构碳含量,测定严重干旱后刺槐枝条的栓塞脆弱性,并比较复水后茎干基部和上部新发叶片的叶面积、比叶质量和光合作用及新发小枝的凌晨和正午水势、枝条气穴栓塞。【结果】在干旱导致全部落叶时,凌晨和正午水势分别达到-3.01和-3.73 MPa,显著低于对照;正午导水损失率(PLC)达到91%,显著高于对照;干旱导致刺槐90%以上落叶时其叶片的光合速率为负值,气孔导度也降低到趋近于0。在复水后30天叶片长成时,枝条正午PLC为81%,仍显著高于对照。经历干旱和复水处理的枝条P50(栓塞为50%时的枝条水势)为-1.09 MPa,比对照高0.37 MPa,经历干旱胁迫的枝条抗气穴栓塞能力显著降低。干旱和复水过程均显著降低了刺槐枝条和根的NSC含量,复水过程NSC降低程度更大。复水后的单株总叶面积仅为对照的38%。复水后叶片恢复的主要部位是茎基部和枝条上部,茎基部恢复叶片的叶面积、光合速率、气孔导度均显著大于枝条上部恢复叶片,茎基部新发小枝的凌晨和正午水势显著高于上部新发小枝。【结论】严重干旱导致水势降低,木质部导管栓塞加重,限制了刺槐的水分输导,进而抑制叶片光合作用,导致出现负的碳平衡。在复水阶段,前期严重干旱导致木质部导水能力下降和NSC含量下降限制了复水后新叶的生长,NSC含量降低可能会影响木质部栓塞的即时修复,水力学失败和碳饥饿的交互作用加重了干旱对刺槐的影响。     

应用热扩散技术对油松栓皮栎比导率的研究

2001年4-10月,应用热扩散技术研究北京西山地区31年生油松栓皮栎混交林标准木的比导率并对13个环境因子的变化规律进行同步观测.结果表明,在野外自然条件下,油松和栓皮栎的比导率在标准日内均呈明显的凸形变化规律,栓皮栎的比导率始终高于油松.影响树木比导率的因素基本上可以分为2类,即生物学结构的遗传特性和环境因素.在林分生长期内的不同时段,环境因子对2个树种比导率的作用各不相同,即使是同一树种,在各个时段内对其比导率产生显著影响的环境因子也不是一成不变的,但一般可用少数几个环境影响因子来比较准确地模拟出比导率的变化.     

油松的水力结构特征

在立地条件相同或相近的情况下 ,分别于夏、秋 2个季节 (7～ 9月 )用改良的冲洗法测定 4株油松幼树 (8～ 1 0a生 )各部位的水力结构参数 :导水率 (Kh ,gm·MPa- 1 min- 1 ,单位时间、单位压力梯度下的草酸溶液通过量 ) ,叶比导率 (LSC ,gm·MPa- 1 min- 1 g- 1 ,供给单位质量干叶的导水率 ) ,比导率 (Ks,gm·MPa- 1 min- 1 cm- 2 ,单位木质部横截面积的导水率 )和胡伯尔值 (HV ,cm2 ·g- 1 ,单位质量干叶的木质部横截面积积累量 )。研究表明 ,油松导水率的大小除受茎段直径大小的影响外 ,还受到茎段所在区域的影响 ,限速区 (即分杈基部 )的导水率明显低于非限速区 ;同时 ,各水力结构参数都不同程度地受到相对分枝级、冠层和方向的影响。油松叶比导率主干高于主枝 ,主枝高于侧枝 ,南向高于北向 ,非限速区高于限速区等水力结构特征决定了其生物学特性和耐旱的生态策略     

对几种针阔叶树种耐旱性生理指标的研究

应用压力室技术和PV曲线法,在地处半干旱区的呼和浩特地区,对樟子松等七个树种在相同立地条件下栽培的中龄树木进行了两年的测定研究。结果表明:被测树木小枝初始质壁分离时的整体渗透势(π_P)及与其相对应的小枝整体相对含水量(RWC)可以作为比较树木耐旱性强弱的生理指标。较大的π_P值(指绝对值,以下同)及较低的RWC值是耐旱性强的生理特征。在树木年生长周期中,上述指标有随季节和物候而变化的规律。嫩枝生长期的π_P值最小,对应的RWC值最大;枝条完全木质化的成熟期π_P值最大,对应的RWC值最低。用树木年生长周期中π_P值的最低值和年变幅表示被测树种耐旱性强弱,得到了较为满意的结果。     

美国红栌的扦插繁殖

美国红栌（Cotinus coggyaria）是一种新型的彩叶树种,具有很高的园林价值。通过使用不同浓度的生根剂一吲哚丁酸（IBA）,对美国红栌不同类型的枝条（包括半木质化枝条、完全木质化枝条、未木质化的嫩梢枝条）进行处理,测定各种插穗生根率及生根条数。结果表明：使用1500mg／L吲哚丁酸（IBA）溶液处理的美国红栌插穗生根率最高,生根条数最多;而在生根插穗中又以半木质化的插穗生根率最高,生根条数最多。     

不同干旱环境对赤松、樟子松、彰武松生理的影响

选择赤松、樟子松、彰武松3年生苗木为试验材料,研究植物体在极端干旱环境内生理生化的变化。结果表明:(1)正常状态下叶比导率(LSC)表现为彰武松赤松樟子松;木质部导水率损失百分数(PLC)为赤松彰武松樟子松;边材导水率为赤松樟子松彰武松,叶片水势日间平均樟子松最高,赤松清晨水势最低,丙二醛含量彰武松最高,3树种性状各有高低。(2)随着干旱胁迫强度的增加,3树种叶片水势和枝条导水性均呈下降趋势;木材栓塞程度和丙二醛含量呈增加趋势,3树种的PLC均值在轻度胁迫时达到20%,中度胁迫时达到32%!40%,重度胁迫时达到52%!65%,重度干旱胁迫已经对枝条的脆弱性产生了影响,但仍然较自然干旱下的重度胁迫所造成的导水率损失(80%)要小,PLC增加顺序为樟子松彰武松赤松;丙二醛含量在轻度干旱中变化并不明显,但中度和重度时有明显增加,增至20~25 mmol·g-1,增幅顺序为彰武松赤松樟子松。     

三叶木通扦插繁殖技术研究

本试验以恩施天池山野生三叶木通为试材,研究了不同季节、不同基质、不同生长调节剂处理三叶木通嫩枝、硬枝扦插生根的情况。结果如下三叶木通在3月下旬、6月中旬、10月中旬均能扦插生根,其中以3月下旬扦插生根效果最好。半木质化穗条优于完全木质化穗条。插条选用1a生,粗度>0.5cm,长度7.0~10.0cm半木质化的插穗枝条为宜;扦插基质以河沙为最好;采用浸泡法时,用浓度为50mg/L的NAA浸泡2h生根效果最好;三叶木通枝条扦插属于综合型生根类型。     

乌桕扦插育苗技术研究

分别以幼树1a生木质化、大树1a生半木质化和2a生木质化枝条为材料,将3种生根剂ABT、911、IAA配成500,200,100,0mg／kg的浓度梯度,分别快蘸5s、浸泡12h和20h,研究鸟桕插条生根率、生根数量、生根长度与不同生根剂类型、不同浓度及浸泡时间长短的关系。试验结果表明：911生根剂100mg／kg浸泡20h的半木质化嫩枝平均生根率为72．2％,1a生木质化硬枝911生根剂500mg／kg快蘸5S大田扦插的平均生根率为82．2％,根数达9．0根;半木质化嫩枝911生根剂200mg／kg浸泡12h的平均生根数达3．9根,不同浓度生根剂和浸泡时间对根系长度无显著影响。     

宝天曼三桠乌药对降雨减少后的生理生态响应

[目的]在宝天曼森林原位建立降水减少(截雨)样地后,样地内的三桠乌药出现了顶端枯死,本研究从水和碳的角度,探讨三桠乌药顶端枯死的原因。[方法]2013年4月在宝天曼锐齿栎林原位建立了3块截雨样地,在2014年生长季干旱时,采用压力室、低压液流系统和蒽酮硫酸法测定了三桠乌药的水力系统特征和非结构性碳等指标。[结果]显示:(1)三桠乌药在截雨处理后出现了顶端枯死;三桠乌药最大导管长度约为60 cm,栓塞50%时的水势(P50)为-1.43 MPa,其木质部栓塞脆弱性较大。在截雨处理1年后生长季较干旱时,净光合速率、凌晨水势、中午水势显著低于对照,中午栓塞显著高于对照,且水力安全边际为负值。(2)三桠乌药气孔导度、蒸腾速率、叶面积、导管直径、边材比导率、叶片比导率显著下降,Huber值、导管密度显著升高;而叶片、韧皮部、木质部3个器官的可溶性糖、淀粉、总非结构性碳与对照差异不显著。[结论]水力失衡是三桠乌药顶端枯死的主要原因,而蒸腾面积、水分输导系统等的变化表明三桠乌药在缺水环境下进行了一定的适应性调节,但这些调节不足以使三桠乌药在缺水情况下避免水力失衡而导致的顶端枯死。     

柳桉组培苗嫩枝扦插繁殖技术

为降低生产成本,加快繁殖速度,选取柳桉组培苗采穗母株上的半木质化枝条为试材,开展了嫩枝扦插试验。结果表明：生长激素IBA的浓度、扦插基质和组培苗插穗母株的年龄是影响柳桉嫩枝扦插育苗生根的重要因素,但IBA的处理时间以及IBA浓度与处理时间的交互作用对生根无显著影响;从1—2年生的组培苗采穗母株上选取穗条,以黄心土：糠壳灰（V：V=3：1）为扦插基质,插穗用IBA100mg／L浸泡处理0．5h是柳桉嫩枝扦插的最佳处理组合,其生根率达90％以上,平均每株生根数达5条以上。     

The Spring Change in Hydraulic Architecture Characteristics in Some Woody Plants

Ten healthy tree species with regular management were selected on the campus of Beijing Forestry University, and they belong to tall tree, shrub and liana, respectively. Water potential and hydraulic architecture parameters of one-year-old twigs were measured in sunny day in the last ten days of March to the middle ten days of May in 2002. The results show that the daily change in water potential of tree species examined appears convex, i.e. the water potential is higher in the morning and evening, and lower in the midday. The change trend of water potential is consistent among different months. The seasonal change trend of water potential appears lower in March than that in April and May. There is a similar relationship between the daily change trend of water potential and special conductivity in spring, i.e. the higher the water potential, the higher the special conductivity, but this trend of change is not entirely synchronic. The seasonal change of special conductivity of conifer species is not obvi     

A Discussion on Drought Tolerance Through Hydraulic Architecture of Woody Plants

In this paper, ten woody plants grew on the campus of the Beijing Forestry University were selected for measuring hydraulic architecture parameters and water potential of one-year-old twigs. The results show that day and night change of water potential and hydraulic architecture parameters appear to be obviously convex trend. The relationship models between water potential and hydraulic conductivity, special conductivity and leaf special conductivity were respectively established, which were simulated by equations Y=axb and Y=ax2 bx c, through which the parameters physiological meanings were discussed. The results show also show that embolism vulnerability of ten tree species was Robinia pseudoacacia> Gleditsia sinensis> Acer truncatum> Prunus davidiana> Cornus alba> Platycladus orientalis> Cedrus deodara> Pinus bungeana> Pinus tabulaeformis> Jasminum nudiflorum, and that the water transport efficiency in xylem and embolism vulnerability of the species are ring-porous species> diffuse-porous species>non     

Discussion on Pipe Model through Hydraulic Architecture of Pinus tabulaeformis Seedling

INTRODUCTIONShinozakifirstproposedthepipemodeltheoryin1964(Shinozaki,1964a,1964b).Inthistheory,thewholexylemsoftheplantisassumedasauniformpipe.Hebelievedthatperunitareaofleavesdependedonperunitofareaofthepipetogrowth.Thistheoryisagreedbyresearcherswhofoundthatthesectionareaofthexylemisdirectproportiontotheareaoftheleavesintheendofthexylem.Laterthistheorywasfoundverypracticalinestimatingtheleavesarea,understandingthegrowthandthedistributionofmaterialandenergyintrees(Shinozakig,Yoda,Hozum…     

Evaluation of the tortuosity parameter for forest soils to predict unsaturated hydraulic conductivity

In order to accurately predict the unsaturated hydraulic conductivity for forest soils, we evaluated the tortuosity parameter for forest soils and investigated the relationships between the tortuosity parameter and parent materials and soil sampling depths. Undisturbed forest soil samples were taken from three parent material types: the granite group, Mesozoic-Paleozoic, and Quaternary. Samples taken from layers corresponding to the A-horizon were categorized as topsoil and others as subsoil. After retention parameters were fitted, the tortuosity parameter was optimized using the Mualem-van Genuchten conductivity model. No significant differences were found in the average values of the tortuosity parameter among depths or among parent materials. Optimized values of the tortuosity parameter varied from 3.20 to −5.23 with a high frequency in the range of about 0 to −2. The average value was −0.94. This means that, for most forest soils, the predicted hydraulic conductivity tends to be underestimated when the most common value (0.5) of the tortuosity parameter is used. Modifying this parameter value to −0.77, as explained in this study, corrected the underestimation tendency and reduced prediction errors. When the unsaturated hydraulic conductivity for forest soils is predicted from water retention, the tortuosity parameter should thus be modified to an appropriate value for more accurate prediction.     

Hydraulic architecture and water relations of a flood-tolerant tropical tree, Annona glabra

Hydraulic architecture parameters, water relation parameters and wood anatomy were studied in roots and shoots of the flood-tolerant tree Annona glabra L. on Barro Colorado Island, Panama. Hydraulic conductivity, leaf specific conductivity, and Huber value were similar to the corresponding values for tree species living in non-flooded habitats. The vulnerability of stems to loss of hydraulic conductivity resulting from embolism was low (50% loss of conductivity at -3.3 MPa). The lowest leaf water potential measured in the field was about -1.0 MPa, indicating that A. glabra has a large margin of safety from embolism, which may provide protection against rare drought events, or may be an adaptation to brackish mangrove habitats. Low absolute conductivity of roots was compensated for by an increase in the number of roots. More than two-thirds of whole-plant resistance to water flow was located in the roots.     

Patterns of hydraulic architecture and water relations of two tropical canopy trees with contrasting leaf phenologies: Ochroma pyramidale and Pseudobombax septenatum

Many authors have attempted to explain the adaptive response of tropical plants to drought based on studies of water relations at the leaf level. Little attention has been given to the role of the xylem system in the control of plant water requirements. To evaluate this role, we studied the hydraulic architecture and water relations parameters of two tropical canopy trees with contrasting leaf phenologies: deciduous Pseudobombax septenatum (Jacq.) Dug and evergreen Ochroma pyramidale (Cav. ex lamb) Urban, both in the family Bombacaceae. The hydraulic architecture parameters studied include hydraulic conductivity, specific conductivity, leaf specific conductivity, and Huber value. Water relations parameters include leaf water potential, stem and leaf water storage capacitance, transpiration, stomatal conductance, and vulnerability of stems to cavitation and loss of hydraulic conductivity by embolisms. Compared to temperate trees, both species showed a pattern of highly vulnerable stems (50% loss of conductivity due to embolism at water potentials less than 1 MPa) with high leaf specific conductivities. The vulnerability of xylem to water-stress-induced embolism was remarkably similar for the two species but the leaf specific conductivity of petioles and leaf-bearing stems of the evergreen species, Ochroma (e.g., 9.08 and 11.4 x 10(-4) kg s(-1) m(-1) MPa(-1), respectively), were 3.4 and 2.3 times higher, respectively, than those of the deciduous species, Pseudobombax (e.g., 2.64 and 5.15 x 10(-4) kg s(-1) m(-1) MPa(-1), respectively). A runaway embolism model was used to test the ability of Ochroma and Pseudobombax stems to maintain elevated transpiration rates during the higher evaporative demand of the dry season. The percent loss of leaf area predicted by the runaway embolism model for stems of Pseudobombax ranged from 5 to 30%, not enough to explain the deciduous phenology of this tree species without analysis of root resistance or leaf and petiole vulnerability to embolism.     

Geographical variation in water relations, hydraulic architecture and terpene composition of Aleppo pine seedlings from Italian provinces

Ecotypic variations in leaf conductance, soil-to-leaf hydraulic conductance, components of tissue water potential, hydraulic architecture parameters and xylem embolism were examined in greenhouse-grown two-year-old Aleppo pine (Pinus halepensis Mill.) seedlings from six origins representing the geographic range of the species in Italy. Cortical resin composition of the seedlings was also determined. Measurements were made on well-watered seedlings and on seedlings subjected to recurring severe drought. Drought-stressed seedlings had lower mean leaf conductances, transpiration rates and soil-to-leaf hydraulic conductances than well-watered seedlings. They also exhibited more negative osmotic potentials, higher relative water deficit at incipient plasmolysis, but a similar maximum modulus of elasticity. Drought-stressed seedlings showed a higher degree of xylem embolism, a lower Huber value, lower leaf specific conductivity and lower specific conductivity than well-watered seedlings. Drought-stressed seedlings of provenances from more xeric habitats (Tremiti, Porto Pino and Mottola) had greater leaf conductances, transpiration rates and soil-to-leaf hydraulic conductances than drought-stressed seedlings of provenances from more mesic habitats (Imperia, Otricoli and Vico del Gargano). They also showed higher osmotic adjustment and a lower degree of xylem embolism. Among provenances, there were no significant differences in hydraulic architecture parameters in response to the drought treatment; however, Tremiti and Porto Pino seedlings displayed smaller drought-induced reductions in specific conductivity and leaf specific conductivity, respectively, than seedlings from other provenances. These differences suggest that seedlings from xeric provenances, especially Tremiti, have greater resistance to desiccation than seedlings from mesic provenances. No clear association was found between terpene variability and the other traits investigated, although terpene composition was related to the geographical distribution of the provenances. We conclude that the drought-tolerance responses of Tremiti make it a more suitable provenance than the others for establishment on sites prone to severe soil water deficits.     

Field determination of unsaturated hydraulic conductivity of forest soils

This study introduces a field method to determine unsaturated hydraulic conductivity which is applicable to sloping terrain with a limited water supply. A single steel ring infiltrometer and an artificial rainfall simulator are used in this method to reduce the amount of water required to attain a steady-state flux condition. Six tensiometers and a time domain reflectometry (TDR) are employed as the soil capillary pressure head and the volumetric soil water content measurement devices, respectively. Water contents measured by the TDR are corrected using a simple calibration method suggested by Hook and Livingston (1996). Unsaturated hydraulic conductivities are computed based on the instantaneous profile method using capillary pressure head and water content changes measured during a drainage process. The proposed method was applied to a forest soil profile in Rokko Mountain range. Results showed that the relationships between the unsaturated hydraulic conductivity and capillary pressure head developed by the proposed method coincide well with those measured by the conventional steady-state laboratory experiment. The proposedin-situ method is the effective simple means to determine unsaturated hydraulic conductivities of forest soils, since this method is enough accurate and consuming less amount of water and time. This research was partly supported by a Grant-in-Aid for Scientific Research (No. 08760149) from the Ministry of Education, Science, Sports, and Culture, Japan.