Carbon unloading in roots in relation to root senescence in Cercis chinensis seedlings under drought stress

When Cercis chinensis seedlings suffered from drought treatment, net photosynthetic rates had been significantly reduced at the end of the drought treatment. Compared with the control, the activities of acid invertases in roots had increased 5 and 11 days after drought treatment. Seventeen days after drought treatment, the activities of acid invertases in roots were significantly decreased, while activities of alkaline invertases in roots had also been significantly reduced. As the moisture in culture media decreased, so the activities of sucrose synthases in leaves decreased slightly. In roots, their activities had significantly increased 5 and 11 days after drought treatment. The contents of fructose in roots reduced as the moisture in culture media decreased and 11 and 17 days after drought treatment the reduction was significant. The content of glucose in roots clearly did not change as drought stress occurred further, but was still less than that in the control seedlings. Similarly, the content of sucrose reduced as the moisture in culture media decreased. At the beginning of the drought stress, the content of sucrose was significantly higher than that in the control and afterwards there were no differences between drought-treated seedlings and the control. The gradient of the sucrose content between leaves and roots was 0.0982 mg·g–1 FW 17 days after drought treatment, while the gradient of the seedlings under normal condition was 1.3832 mg·g–1 FW. The sucrose concentration gradient reduced by 92.9%. The reduction in the sucrose content gradient under drought stress decreased the sucrose partitioning in roots. Therefore, our results support the hypothesis of ‘shared control’.     

Effects of nutrition spatial heterogeneity on root traits and carbon usage by roots of Cercis chinensis seedlings in split root rooms

In natural ecosystems, nutrition available for plants shows great spatial heterogeneity. Much is known about plant root responses to the spatial heterogeneity of nutrition, but little is known about carbon usage in roots in nutrition-deficient patches and its effect on root longevity. In this study, split-room boxes were used for culture of Cercis chinensis seedlings, and the small rooms were supplied with different nutrition levels. The number of the first-order roots in the rooms with nutrition supply was significantly higher than that in the rooms with deficient nutrition. Specific root length (SRL) of the first-order roots in the rooms with deficient nutrition reached its peak at day 64 after nutrition treatment. There was no significant SRL differences between the two order roots during the experiment. Biomass of the first-order roots in the rooms without nutrition supply was significantly less than that of the first-order roots in the rooms with nutrition supply from day 64 to 96. The total biomass of the lateral roots in the rooms without nu-trition supply decreased from day 64 to 96. The activities of the enzymes in roots in the rooms without nutrition supply increased and the activities of alkaline invertases in roots in the two sides of split box did not change significantly. The activities of the enzymes in roots in the rooms without nutrition supply increased gradually. These results suggest that nutrition spatial heterogeneity induced the changes in root traits and plants actively controlled carbon usage in roots in nutrition-deficient patches by regulating the activities of invertases and sucrose synthases, resulting in the reduction in carbon usage in the roots in nutrition-deficient patches.     

Effects of nutrition spatial heterogeneity on root traits and carbon usage by roots of Cercis chinensis seedlings in split root rooms

In natural ecosystems, nutrition available for plants shows great spatial heterogeneity. Much is known about plant root responses to the spatial heterogeneity of nutrition, but little is known about carbon usage in roots in nutrition-deficient patches and its effect on root longevity. In this study, split-room boxes were used for culture of Cercis chinensis seedlings, and the small rooms were supplied with different nutrition levels. The number of the first-order roots in the rooms with nutrition supply was significantly higher than that in the rooms with deficient nutrition. Specific root length （SRL） of the first-order roots in the rooms with deficient nutrition reached its peak at day 64 after nutrition treatment. There was no significant SRL differences between the two order roots during the experiment. Biomass of the first-order roots in the rooms without nutrition supply was significantly less than that of the first-order roots in the rooms with nutrition supply from day 64 to 96. The total biomass of the lateral roots in the rooms without nutrition supply decreased from day 64 to 96. The activities of the enzymes in roots in the rooms without nutrition supply increased and the activities of alkaline invertases in roots in the two sides of split box did not change significantly. The activities of the enzymes in roots in the rooms without nutrition supply increased gradually. These results suggest that nutrition spatial heterogeneity induced the changes in root traits and plants actively controlled carbon usage in roots in nutrition-deficient patches by regulating the activities of invertases and sucrose synthases, resulting in the reduction in carbon usage in the roots in nutrition-deficient patches.     

Genotypic variation in drought tolerance of poplar in relation to abscisic acid

We investigated effects of water stress and external abscisic acid (ABA) supply on shoot growth, stomatal conductance and water status in 1-year-old cuttings of a drought-sensitive poplar genotype Populus x euramericana cv. I-214 (Italica) and a drought-tolerant genotype P. 'popularis 35-44' (popularis). Populus popularis was more productive and maintained higher leaf water potentials throughout the drought treatment than cv. Italica. Supply of ABA to the xylem sap caused a greater decline in growth and more leaf abscission in shoots of cv. Italica than in shoots of P. popularis. Immediately after initiation of the drought treatment in P. popularis, the ABA concentration ([ABA]) of the xylem increased rapidly and stomatal conductance declined; however, stomatal conductance had returned to control values by the third day of the drought treatment, coincident with a gradual decline in xylem [ABA]. In contrast, xylem [ABA] of cv. Italica initially increased more slowly than that of P. popularis in response to the drought treatment, but the increase continued for 3 days at which time a tenfold increase in xylem [ABA] was observed that was followed by abscission of more than 40% of the leaves. We conclude that sensitivity of poplar roots to variation in soil water content varies by clone and that a rapid short-term accumulation of ABA in shoots in response to water stress may contribute to drought tolerance.     

干旱胁迫对垂柳生理特性的影响

试验在田间条件下研究了干旱对垂柳2年生苗生理特性的影响规律,结果表明:随着干旱时间的延长,垂柳叶片内叶绿素a、叶绿素b、总叶绿素含量均有所降低,6月9日,干旱处理与对照相比分别降低了1.45、0.30、1.45mg·g^-1;干旱胁迫提高了保护酶活性,其中POD、SOD、CAT活性分别比对照提高了14.30、17.42、9.67U·g^-1;渗透物质含量在干旱持续时间超过25d后显著升高,其中可溶性蛋白、可溶性糖、游离脯氨酸含量与对照相比分别提高了40.10%、25.33%、69.46%;电导率在干旱持续15d后显著升高,MDA含量在干旱持续10d后显著升高,试验结束时分别比对照提高了21.47%、35.62%。综合分析认为,浇水25d后垂柳生理特性会发生显著变化。     

干旱胁迫及复水对绿竹容器苗生理特征的影响

[目的]探究模拟干旱环境下水分亏缺对绿竹容器苗主要营养器官生理特性的影响,为绿竹规模化育苗栽培制定适宜的经营管理及节水灌溉技术方案提供理论依据。[方法]以绿竹组培苗为试验材料,采用盆栽苗控水方式,测定分析不同干旱胁迫条件下绿竹叶片及根系抗氧化酶、膜脂渗透性、叶片光合色素含量、以及根系活力等生理指标。[结果]表明:随着干旱胁迫加重,绿竹叶片叶绿素a、叶绿素b和类胡萝卜素含量明显下降,各处理间均达到差异显著(P0.05),复水后叶绿素a、叶绿素b、及类胡萝卜素含量均明显升高,其中叶绿素a、叶绿素b达到差异显著(P0.05),但类胡萝卜素差异不显著(P0.05);干旱胁迫下,根系活力呈明显下降趋势,中度干旱胁迫(MS)和重度干旱胁迫(SS)根系活力分别比对照(CK)下降14.35%、33.31%,均达到差异显著(P0.05),复水后,根系活力均明显升高,分别达到了CK处理根系活力的96.75%、73.84%;干旱胁迫下,根系及叶片超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)活性和丙二醛(MDA)含量均呈上升趋势,且在复水后均呈现一定下降趋势,表现为中度干旱胁迫后复水(MS-CK)降低程度高于重度干旱胁迫后复水(SS-CK),各处理间均达到差异显著(P0.05)。[结论]模拟干旱环境下,增加干旱胁迫程度,绿竹的根系活力及叶片色素含量呈显著降低,MDA含量及SOD、CAT、POD活性均升高。复水后,根系活力及叶片色素含量较干旱胁迫时有所提高,MDA含量及SOD、CAT、POD活性有明显下降,不同干旱程度补偿能力不同,表现为中度干旱胁迫后复水高于重度干旱胁迫后复水,且不同营养器官对于解除干旱后消除活性氧及修复适应能力也不尽相同。绿竹根系活力和叶绿素含量与干旱胁迫程度呈负相关,而保护酶SOD、CAT、POD活性以及MDA含量均与干旱胁迫程度呈正相关。     

Survival and growth of drought hardened <Emphasis Type="Italic">Eucalyptus pilularis</Emphasis> Sm. seedlings and vegetative cuttings

Forestry requires low mortality of transplanted seedlings. Mortality shortly after planting is often associated with inadequate hydration of transplants. Seedlings can be hardened to the drought conditions they may experience after transplanting by exposing them to controlled drought conditions in the nursery. Eucalyptus pilularis Sm. seedlings were drought hardened by providing nil (severe treatment) or half (mild treatment) the daily irrigation routinely received (control treatment) for up to two non-consecutive days per week during the last 4 weeks of growth in the nursery. Drought hardening reduced stem diameter, seedling leaf area, leaf area per root biomass and seedling quality measured by the Dickson quality index, but increased root:shoot ratio. Hardened seedlings had lower stomatal conductance and leaf water potential on the days they received less irrigation that the control treatment. Hardened seedlings had greater stomatal conductance and were less water stressed than seedlings experiencing drought for the first time indicating hardened seedlings had adjusted physiologically to drought. Survival after transplanting in the controlled drought environment in a glasshouse was enhanced by the hardening treatments. Non hardened seedlings that had had their upper leaves manually removed immediately prior to transplanting to reduce leaf area (top-clipped) had similar survival to hardened seedlings. Stomatal conductance and leaf water potential after transplanting were higher in hardened and top-clipped seedlings than unhardened control seedlings or vegetative cuttings. Survival in the field trial was over 95% for all treatments, possibly as rain fell within 4 days of planting and follow-up rain occurred in the subsequent weeks. Neither the hardened or top-clipped seedlings planted in the field trial had reduced growth, increased propensity to form double leaders or worse stem form than control seedlings when measured at age 3 years.     

Effects of drought preconditioning on thermotolerance of photosystem II and susceptibility of photosynthesis to heat stress in cedar seedlings

Changes in photosystem II (PSII) thermotolerance during drought and recovery were studied under controlled conditions in three Mediterranean cedar species (Cedrus brevifolia Henry, C. libani Loudon and C. atlantica Manetti). The temperature at which the quantum yield of PSII photochemistry was reduced by 15% of its value at 25 degrees C was 3 to 4 degrees C higher in drought-treated plants than in well-watered plants. The drought-induced increase in PSII thermotolerance was already evident 8 days after water had been withheld from the seedlings, when net CO(2) assimilation was still at 80% of its initial value, and was visible for up to 12 days after re-watering. When seedlings of the three species were exposed to temperatures above 45 degrees C for 5 h, both maximal quantum yield of PSII photochemistry and net CO(2) assimilation rate were significantly reduced in unconditioned seedlings, whereas drought-preconditioned seedlings were almost unaffected by the heat treatment. Drought-preconditioned seedlings still exhibited a higher tolerance to heat stress than unconditioned seedlings 60 days after re-watering, although the transient, drought-induced osmotic adjustment had fully disappeared. Among species, C. atlantica was the most heat sensitive, whereas the heat treatment had no significant effect on the parameters measured in C. brevifolia.     

Physiological and morphological adaptations of the fruit tree Ziziphus rotundifolia in response to progressive drought stress

The physiological basis of drought resistance in Ziziphus rotundifolia Lamk., which is an important, multipurpose fruit tree of the northwest Indian arid zone, was investigated in a greenhouse experiment. Three irrigation regimes were imposed over a 34-day period: an irrigation treatment, a gradual drought stress treatment (50% of water supplied in the irrigation treatment) and a rapid drought stress treatment (no irrigation). Changes in gas exchange, water relations, carbon isotope composition and solute concentrations of leaves, stems and roots were determined. The differential rate of stress development in the two drought treatments did not result in markedly different physiological responses, but merely affected the time at which they were expressed. The initial response to decreasing soil water content was reduced stomatal conductance, effectively maintaining predawn leaf water potential (Psi(leaf)), controlling water loss and increasing intrinsic water-use efficiency, while optimizing carbon gain during drought. Carbon isotope composition (delta13C) of leaf tissue sap provided a more sensitive indicator of changes in short-term water-use efficiency than delta13C of bulk leaf tissue. As drought developed, osmotic potential at full turgor decreased and total solute concentrations increased in leaves, indicating osmotic adjustment. Decreases in leaf starch concentrations and concomitant increases in hexose sugars and sucrose suggested a shift in carbon partitioning in favor of soluble carbohydrates. In severely drought-stressed leaves, high leaf nitrate reductase activities were paralleled by increases in proline concentration, suggesting an osmoprotective role for proline. As water deficit increased, carbon was remobilized from leaves and preferentially redistributed to stems and roots, and leaves were shed, resulting in reduced whole-plant transpiration and enforced dormancy. Thus, Z. rotundifolia showed a range of responses to different drought intensities indicating a high degree of plasticity in response to water deficits.     

Drought-induced changes in flavonoids and other low molecular weight antioxidants in Cistus clusii grown under Mediterranean field conditions

Mediterranean plants have evolved a complex antioxidant defense system to cope with summer drought. Flavonoids, and particularly flavanols and flavonols, are potent in vitro antioxidants, but their in vivo significance within the complex network of antioxidant defenses remains unclear, especially in plant responses to stress. To gain insight into the role of flavonoids in the antioxidant defense system of Cistus clusii Dunal, we evaluated drought-induced changes in flavonoids in leaves and compared the response of these compounds with that of other low molecular weight antioxidants (ascorbic acid, tocopherols and carotenoids). Among the antioxidant flavonoids analyzed, epigallocatechin gallate was present in the greatest concentrations (up to about 5 micromol dm(-2)). Other flavanols, such as epicatechin and epicatechin gallate, were found at concentrations below 0.25 and 0.03 micromol dm(-2), respectively. Neither of the antioxidant flavonols analyzed, quercetin and kaempferol, were detected in C. clusii leaves. Epigallocatechin gallate, ascorbic acid and alpha-tocopherol concentrations increased to a similar extent (up to 2.8-, 2.6- and 3.3-fold, respectively) in response to drought, but the kinetics of the drought-induced increases differed. Epigallocatechin gallate, epicatechin and epicatechin gallate concentrations increased progressively during drought, reaching maximum values after 30 days of stress. Ascorbic acid concentrations increased twofold after 15 days of drought, and maximum values were attained after 50 days of drought. In contrast, alpha-tocopherol concentrations remained constant during the first 30 days of drought, but increased sharply by 3.3-fold after 50 days of drought. The maximum efficiency of photosystem II photochemistry and the extent of lipid peroxidation remained constant throughout the drought period, whereas the redox state of ascorbic acid and alpha-tocopherol shifted toward their reduced forms in response to drought, indicating that the concerted action of low molecular weight antioxidants may help prevent oxidative damage in plants.     

干旱胁迫对6种野生耐旱花卉幼苗根系保护酶活性及脂质过氧化作用的影响

从燕山东段野生花卉中筛选出6种耐旱的野生花卉,它们的耐旱性依次是叶底珠>栓翅卫矛>木半夏>孩儿拳头>南蛇藤>蚂蚱腿子,研究干旱胁迫至枯死临界点过程中其幼苗根系保护酶活性及脂质过氧化作用与耐旱性的关系.结果表明:在这一过程中各幼苗根系的MDA含量和保护酶活性的变化具有多样性的特点,其中叶底珠、孩儿拳头和栓翅卫矛根系的MDA含量具有明显的升降起伏,而南蛇藤、木半夏和蚂蚱腿子根系的MDA含量是呈缓慢上升的趋势;保护酶活性的升降起伏过程在各幼苗各有特点;叶底珠、栓翅卫矛、孩儿拳头和木半夏的POD同工酶都增加了特异谱带,南蛇藤的POD谱带没有变化,蚂蚱腿子POD 谱带部分消失.MDA含量及POD与SOD活性和耐旱性关系不明显,而POD同工酶有特异谱带增加的种类耐旱性较强.     

干旱和遮荫对中国沙棘水碳平衡和黄酮化合物含量的影响

目的 研究干旱和遮荫对中国沙棘生长、水碳代谢和黄酮类化合物含量的影响有助于全面了解沙棘的生态适应性,同时有利于了解干旱和遮荫对沙棘黄酮类化合物含量的影响。 方法 本研究以中国沙棘为研究对象,比较了干旱（40%土壤水分饱和含水量）、遮荫（遮光50%）及二者交互处理下的水势、枝条导水损失率（PLC）、光合作用、生物量、非结构性碳水化合物（NSC）含量和黄酮类化合物含量的变化。 结果 干旱处理显著降低了中国沙棘的枝条水势、净光合速率、叶生物量、根和茎的NSC含量,显著增加了枝条PLC、根生物量;遮荫显著降低了净光合速率、叶生物量、根茎叶的NSC含量和黄酮含量,干旱和遮荫的共同作用显著增加了枝条PLC,降低了叶净光合速率、根茎叶生物量和NSC含量;且叶黄酮类化合物含量与枝条水势呈显著负相关。 结论 干旱会影响中国沙棘的水分状况、碳摄取,降低茎和根的NSC储藏,增加黄酮类化合物含量,遮荫会影响中国沙棘的光合速率、根茎叶的NSC储藏,干旱和遮荫的共同作用进一步降低了中国沙棘的水分输导能力、光合作用、生物量积累和NSC储藏,遮荫降低了中国沙棘对干旱胁迫的适应能力,适度干旱有利于沙棘黄酮类化合物的合成。     

Accumulation of free amino acids in the shoots and roots of three northern conifers during drought

The effects of drought on the free amino acid pools in 21- to 23-week-old seedlings of black spruce (Picea mariana (Mill.) Britt.), white spruce (Picea glauca (Moench.) Voss) and jack pine (Pinus banksiana Lamb.) were followed during soil drying. Although water and pressure potentials were sensitive to water deficits, large changes in osmotic potential were not recorded until after the development of severe drought. Total soluble amino nitrogen in the shoots and roots of the three species rose as turgor declined, with peak concentrations attained late in the drought period when the pressure potentials of the shoots approached zero. All white spruce seedlings were alive at zero turgor and showed large decrements in osmotic potential, but concentrations of free amino nitrogen in the roots and shoots showed only modest increases, reaching 125 to 150% of their control values. In contrast, large numbers of black spruce and jack pine were dead or severely damaged at zero turgor, and only small changes in osmotic potential were detected during soil drying. Nevertheless, concentrations of soluble amino nitrogen in both species reached 150 to 200% of control values a few days before the seedlings died. Alanine, arginine, aspartic acid/asparagine, glutamic acid/glutamine, glycine, hydroxyproline and proline were the major components of the free amino acid pools under both water-stressed and non-stressed conditions, with the largest and most consistent increases observed in the roots of all three conifers. Although proline was an important and dynamic component of the free pools, absolute concentrations were commony equalled or exceeded by other free amino acids in the roots and shoots and nearly always exceeded by the concentration of aspartic acid/asparagine in both tissues. Differences in drought resistance among the three conifers were not reflected by unique patterns of amino acid accumulation or by large differences in absolute concentrations of the free amino acid pools.     

Effects of simulated drought stress on the fine roots of Japanese cedar (<Emphasis Type="Italic">Cryptomeria japonica</Emphasis>) in a plantation forest on the Kanto Plain,eastern Japan

Drought stress was simulated in a 28-year-old Japanese cedar plantation (Kanto Plain, Japan) between April and October 2004 by removing throughfall using rain shelters. Changes in fine-root parameters caused by this drought treatment were examined by sequential soil coring. Drought effects on fine roots were analyzed separately for particular soil depths (0–5, 5–15, and 15–25 cm) and root diameters (<1 and 1–2 mm). Generally, fine-root biomass and root tip numbers decreased by the drought treatment. Drought stress was most intense for fine roots in the topsoil and weakest for fine roots in the deepest soil layer. Fine roots less than 1 mm in diameter were affected more severely than 1- to 2-mm roots. The effect of drought treatment was most remarkable for the number of white root tips, which decreased to 17% of the control at the soil depth of 0–5 cm. These results suggest that white root tip is the most suitable indicator of drought stress. Simulated drought reduced production of fine roots less than 1 mm and 1–2 mm in diameter. Fine-root mortality was stimulated for roots less than 1 mm, but not for 1- to 2-mm roots. These results suggest that fine roots with larger diameters can survive drought stress at a level simulated in this study, but processes of fine-root production were inhibited regardless of the diameter classes. The duration of drought stress and phenology of fine roots should also be considered in diagnosing the effects of drought on fine-root parameters.     

Effects of nitrogen source on growth and activity of nitrogen-assimilating enzymes in Douglas-fir seedlings

Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings were grown for 68 days in a growth chamber in nutrient solutions with ammonium, nitrate or ammonium nitrate as the nitrogen source. Among the nitrogen sources tested, whole-seedling biomass, relative growth rate (RGR), root and shoot elongation, and number of lateral roots, were greatest in seedlings grown with ammonium. In the absence of nitrogen, plant growth and formation of lateral roots were poor. Initially, glutamine synthetase, NAD-glutamate dehydrogenase and aspartate aminotransferase activities were high in young roots and shoots, but all three enzymatic activities decreased after one month of culture. In root apices, glutamine synthetase and aspartate aminotransferase activities were higher than NAD-glutamate dehydrogenase activity. Enzymatic activities were often higher in ammonium-fed seedlings than in seedings supplied with the other forms of nitrogen. Activities of all three enzymes were significantly reduced in seedlings grown in the absence of nitrogen. The beneficial effect of ammonium is discussed on the basis of its involvement in the assimilation pathways of Douglas-fir.     

曲古抑菌素A对沙棘扦插苗响应干旱和复水及相关基因表达的影响

目的 研究组蛋白去乙酰化酶抑制剂曲古抑菌素A（Trichostatin A, TSA）在20%聚乙二醇模拟干旱和干旱后复水条件下,对沙棘扦插苗叶片形态、光合指标、脯氨酸、丙二醛和脱落酸含量等生理特性和组蛋白去乙酰化酶、合成脱落酸和类黄酮相关基因表达的影响。 方法 测定沙棘扦插苗干旱相关生理指标,实时定量PCR检测基因表达量。 结果 1 μmol·L−1TSA预处理的沙棘在同等干旱胁迫下耐旱性增强。与仅干旱处理相比,（1）叶片下垂和萎蔫程度降低,植株鲜质量下降程度更小,复水后植株恢复程度更大。（2）净光合速率、蒸腾速率、气孔导度、PSII最大光化学效率Fv/Fm值、PSII有效光化学量子产量Y(Ⅱ)值和叶绿素相对含量(SPAD)值均显著上调,复水后均下调。（3）脯氨酸和类黄酮含量显著上调,丙二醛和脱落酸含量显著下调,复水后趋势相同。（4）组蛋白去乙酰化酶基因HrHDA6和HrHDA19、脱落酸合成相关基因ABF1和NAC2表达均显著下调,类黄酮合成相关基因C4H2和CHS4表达均显著上调,复水后趋势相同。 结论 TSA通过调控沙棘扦插苗生理和基因表达参与对干旱胁迫的响应,可以提高沙棘的抗旱性,该研究为深入解析组蛋白乙酰化影响沙棘抗旱的调控机制奠定重要基础。     

Variability in growth, carbon isotope composition, leaf gas exchange and hydraulic traits in the eastern Mediterranean cedars Cedrus libani and C. brevifolia

Four Turkish provenances and five Lebanese provenances of Cedrus libani A. Rich. and one Cypriot provenance of C. brevifolia Henry were compared during the third year of growth in a controlled-climate greenhouse after exposure to a well-watered or moderate-drought treatment. Effects of treatment on CO(2) assimilation (A), stomatal conductance (g(s)), (13)C isotope composition (delta(13)C), growth and biomass were assessed. Hydraulic conductivity and shoot vulnerability to cavitation were measured in well-watered plants only. The Lebanese provenances of C. libani had the highest growth rates, but were the most sensitive to drought. The Turkish provenances of C. libani showed moderate growth rates and moderate drought sensitivity. Cedrus brevifolia had the lowest growth rate and was least sensitive to drought. For each provenance, mean biomass values were positively correlated with delta(13)C and intrinsic water-use efficiency (A/g(s)), and negatively correlated with g(s). Drought reduced growth and favored carbon storage in roots, increasing the ratio of root biomass to aboveground biomass. The drought treatment increased delta(13)C and A/g(s). Specific hydraulic conductivity (K(s)) was similar for the provenance groups, whereas leaf-specific conductivity (K(l)) was lower in the Lebanese provenances than in the other provenances. Within each provenance group, provenances with the highest K(l) were most susceptible to xylem cavitation, but were also the most productive. Growth and drought adaptation were linked with precipitation in each provenance's native range.     

外源生长素对杜梨组培不定芽生根及相关氧化酶的影响

【目的】为了解生长素诱导杜梨不定根发生效应,明确不定根诱导过程与氧化酶活性间的关系,从而为杜梨等难生根植物的生根研究提供理论指导和技术借鉴。【方法】以连续继代培养的杜梨不定芽为材料,调查了不同种类(NAA、IBA和IAA)和浓度(0.1、0.5、1.0、2.0 mg·L^-1)的生长素对不定芽生根的影响情况,分别在生根诱导0、4、8、12、16 d后观察不定根发育的内外组织形态,测定并分析相关酶活性的变化情况。【结果】外源生长素均能促进不定芽不定根的发生,在相同种类的生长素处理下,浓度分别为0.1和2.0 mg·L^-1处理的各项生根指标均显著低于浓度分别为0.5和1.0 mg·L^-1处理的。以NAA诱导产生的愈伤组织较大且松软易脱落,不利于其后期的移栽成活;以IBA处理的生根率显著高于NAA和IAA处理的,其中以浓度为0.5 mg·L^-1的IBA处理的各项生根指标均最优。对其组织形态的观察结果表明,杜梨不定根发生类型属于诱生根原基,经IBA处理4 d后,其茎基部表皮颜色变红,内部根原基发生于韧皮部和维...     

Carbohydrate mobilization following shoot defoliation and decapitation in hybrid poplar

The effects of shoot defoliation, decapitation, and disbudding on carbon mobilization were investigated in rooted cuttings of Populus maximowiczii x nigra L. 'MN9'. Ten days after complete shoot defoliation or decapitation, the stem starch concentration of treated plants declined to one-half that of intact plants, and there were similar or greater reductions in the concentrations of glucose, fructose, sucrose, galactose, and shikimic acid. Partial shoot defoliation (50%) and complete disbudding had no effect on stem starch concentration, but stem sucrose concentration was reduced in all treatments. Sucrose depletion preceded and may have induced other changes in the carbon status of plants subjected to leaf or shoot removal. Four days after shoot decapitation, the sucrose concentration of roots of treated plants was reduced to 25% of that of intact plants. However, the concentrations of fructose and glucose increased in the roots of treated plants and was followed by the accumulation of shikimic acid, salicyl alcohol, unknown compound A and salicin. The possible role of increased concentrations of root organic solutes in the water relations and regrowth process of decapitated plants is discussed.     

外源苯甲酸对平邑甜茶幼苗根系膜脂过氧化的影响

大多数果树都存在连作障碍(重茬、再植病、忌地现象)现象,其中苹果(Malus)、李(Prunus salicina)、桃(Prunus)等连作障碍更为严重.杨兴洪等(1991)调查苹果重茬地成活率只有40%～60%,美国华盛顿州10年间苹果产区因重茬每公顷损失4万美元,山东省烟台大量苹果园已经表现并将面临更大面积的苹果连作问题.