Comparison of the responses to flooding of seedlings and cuttings of Gmelina

The effects of flooding on Gmelina arborea Roxb. seedlings and cuttings of the same parent stock were compared to determine their suitability as transplanting stock. Flooding caused reductions in stomatal conductance, xylem pressure potential and dry matter accumulation in both groups of plants. In seedlings, flooding induced formation of hypertrophied lenticels, stem hypertrophy and production of short, thick, adventitious roots in seedlings, whereas in cuttings, only thin roots and numerous smaller lenticels were induced. For 8 days after the flooding treatment ended, the flooded seedlings grew faster than control seedlings, whereas in cuttings, post-flooding growth was similar to that of control plants. It is suggested that seedlings may perform better than cuttings in very wet or saturated soil.     

Effects of flooding on leaf dynamics and other seedling responses in flood-tolerant Alnus japonica and flood-intolerant Betula platyphylla var. japonica

Two-year-old seedlings of Alnus japonica Steud. and Betula platyphylla var. japonica Hara were flooded from mid-June to early November, to study the effects of flooding on seedling survival and growth, morphological changes in stems and roots, leaf emergence, leaf fall, and leaf longevity. In A. japonica, growth was not affected by flooding, except for a slight decrease in height growth, but some morphological changes of stems and roots were observed, i.e., stem base hypertrophy, hypertrophied lenticels, formation of adventitious roots and development of new roots. In B. platyphylla var. japonica, growth was severely reduced by flooding and all seedlings died by the 20th week of flooding, without showing any adaptive morphological changes in stems or roots. Flooding induced rapid depression of leaf emergence, promoted leaf abscission, and reduced leaf longevity in B. platyphylla var. japonica. In contrast, in A. japonica, basal leaf senescence was delayed in flooded seedlings, thereby extending leaf longevity compared with unflooded seedlings.     

Growth and nutrient use efficiency of water tupelo seedlings in flooded and well-drained soil

Growth characteristics and nutrient utilization rate of Nyssa aquatica L. seedlings grown in pots containing flooded or well-drained soil were compared in a greenhouse study. For most of the growing season, relative height and diameter growth rates, and biomass accumulation rates were greater for seedlings in flooded soil than for seedlings in well-drained soil. The concentration of Fe in the roots of seedlings in flooded soil was almost tenfold greater than that of seedlings in well-drained soil. However, flooding had no effect on foliar Fe concentrations. The flooding treatment resulted in decreased concentrations of N in all component parts and increased concentrations of P in the roots and stem, but it had no effect on foliar P concentrations. In response to flooding, foliar K concentrations decreased, whereas the concentration of K in the roots increased. Flooding had no effect on the K concentration of the stem. Seedlings in flooded soil produced more total biomass per milligram of nutrient absorbed than seedlings in well-drained soil, suggesting that N. aquatica seedlings are more efficient at producing biomass and height growth under hydric conditions than under mesic conditions.     

Physiological, morphological and anatomical responses of Fraxinus mandshurica seedlings to flooding

Two-year-old Fraxinus mandshurica Rupr. var. japonica Maxim. seedlings were flooded to 8 cm above soil level for 70 days. The flooding treatment altered the growth, morphology, stem anatomy and ethylene production of the seedlings. Although flooding did not affect height growth, it stimulated diameter growth of the submerged stems by increasing both the number and size of wood fibers produced; however, the thickness of the cell walls of the wood fibers was reduced by flooding. In response to the flooding treatment, the seedlings formed abundant hyperhydric tissues, originating from the vicinity of lenticels on the surface of the flooded stems, and adventitious roots, which grew through the hyperhydric tissues. Aerenchyma tissues were observed in the bark of the adventitious roots. The flooding treatment did not affect dry weight increment of leaves and stems, but it reduced the total dry weight increment of the root system even though it promoted adventitious root formation. Flooding also enhanced ethylene production in the submerged portions of stems. The potential roles of flood-induced ethylene in cambial growth and adventitious root formation in flooded plants are discussed.     

Configuration and development of root systems of cuttings and seedlings of Eucalyptus globulus

Stem cuttings of Eucalyptus globulus are used within tree improvement programs and for mass deployment. To be successful, cuttings must perform as well or better than seedlings. The root systems of cuttings are fundamentally different from those of seedlings. If these differences influence growth, the differences and their consequences must be identified and the propagation system manipulated to improve performance of the propagules.Cuttings are only a viable alternative to seedlings as planting stock if the method of propagation does not affect their growth and development adversely. Full-sibling cuttings and seedlings of Eucalyptus globulus were compared under controlled environmental conditions to minimise extraneous sources of variation, and to establish whether changes in growth or development were induced by propagation. On three occasions over a period of eight weeks root-collar diameter, shoot height, leaf and stem weight, shoot/root ratios and root system morphology were measured on cuttings and seedlings. Seedlings were taller than cuttings throughout the experiment, but both plant types had similar height growth rates. Diameter growth rates were lower in cuttings than seedlings, and there were differences in both height and diameter growth rates between families. Root system configuration differed between the plant types. Seedlings had strongly gravitropic tap-roots, with two types of primary roots from which secondary roots emerged. Cuttings had no tap roots, and the main structural components of their root systems were adventitious roots formed during propagation. Cuttings did not develop further structural roots during the experiment, whereas seedlings continued to develop primary roots. Individual primary roots of cuttings were longer and had larger mid-point diameters than those of seedlings, but the total length of primary roots was greater in seedlings. Seedlings also had a greater number and total length of secondary roots. Shoot/root ratios, calculated from a range of functional measures, were higher in cuttings than seedlings.     

Effects of IBA on the rooting of branch cuttings of Chinese jujube (<Emphasis Type="Italic">Zizyphus jujuba</Emphasis> Mill.) and changes to nutrients and endogenous hormones

‘Zhongqiusucui’ jujube secondary shoots were treated with 3-indolebutyric acid (IBA) at three concentrations, 500, 1000 and 1500 mg/L. Results show that IBA could significantly enhance rooting and root characteristics of cuttings and were best with IBA at 1500 mg/L. In the rooting process, the formation of adventitious roots was related to the consumption and accumulation of nutrients (soluble sugars and proteins) and the changes in endogenous hormones in phloem, leaf tips and leaf bases. The rooting of cuttings had a positive correlation with the consumption of soluble sugars during the period of callus formation and with the accumulation of soluble sugars during adventitious root formation and growth. Rooting was positively related to the breakdown of soluble proteins in the phloem when the callus formed, and had a positive correlation with its accumulation during adventitious root formation and growth. Leaf tips and leaf bases showed a reverse trend in changes of soluble protein. However, together with the phloem, leaf tips and leaf bases regulated and controlled the formation and development of adventitious roots. The main activities of soluble proteins exist in the leaf tips as this was the main source of soluble proteins. The relation between rooting and IAA (indole-3-acetic acid) content in phloem was positive and thus a high concentration of IAA could benefit the induction and formation of adventitious roots. However, rooting was negatively related with ABA (abscisic acid) and GA (gibberellic acid) and a high concentration of both could inhibit the induction and formation of adventitious roots. Rooting had a positive correlation with phloem IAA/ABA ratios, and higher ratios could improve rooting. Low concentrations of ZR (zeatin riboside) triggered the induction of adventitious roots, while higher concentrations promoted root growth. Endogenous hormones in leaf tips and bases had an impact on rooting. The activities of endogenous hormones mainly existed in leaf tips because they play a major role in the production and consumption of IAA and its ABA content increased during rooting. The ZR in leaf tips influenced the rooting of cuttings, especially in the callus formation and rooting stage. Leaf tips were the main source of GA.     

Distinct effects of auxin and light on adventitious root development in Eucalyptus saligna and Eucalyptus globulus

Adventitious rooting is essential for vegetative propagation of woody species. We studied the effects of auxin and light on the development of adventitious roots in cuttings obtained from seedlings of Eucalyptus saligna Smith and E. globulus Labill in an attempt to characterize the adventitious rooting process and identify factors controlling rhizogenesis. Root development was scored as rooting percentage, root density (roots per rooted cutting), mean rooting time and root length. In both species, rooting time was reduced in the presence of auxin. Cuttings from 2-month-old E. saligna seedlings were responsive to lower auxin concentrations than comparable cuttings from E. globulus seedlings. Cuttings from 3-month-old E. saligna seedlings rooted promptly and rooting was not significantly affected by light conditions. In contrast, rooting of cuttings from 3-month-old E. globulus seedlings exhibited recalcitrant behavior and no roots were formed if illuminated during the root formation phase. Effective root regeneration of E. globulus cuttings was obtained by a 4-day exposure to 10 mg l(-1) IBA and culture in darkness during the root formation step. Loss of rooting capacity with seedling age was more pronounced in E. globulus than in E. saligna. The possibility of switching adventitious rooting off and on by manipulating light regime and exogenous auxin supply in E. globulus, and the constitutive nature of rooting in E. saligna may provide useful models for examining the rooting process at the biochemical and molecular levels in Eucalyptus.     

Growth,morphology and photosynthetic activity in flooded <Emphasis Type="Italic">Alnus japonica</Emphasis> seedlings

This study was conducted on Alnus japonica seedlings subjected to flooding for 2, 4, and 6 weeks to examine responses in growth, morphology, and photosynthesis to different periods of flooding. Seedlings subjected to flooding for 2 and 4 weeks were drained after flooding then watered daily. Increases in biomass of leaves, roots, and whole plants were less for 6-week-flooded seedlings. Rate of photosynthesis and stomatal conductance of flooded seedlings decreased within 2 weeks. For 2-week-flooded seedlings recovery from reduced stomatal conductance and recovery of photosynthetic activity occurred after drainage. For the 6-week-flooded seedlings stomatal conductance recovered by the end of the experiment. Adventitious root formation by the 4 and 6-week-flooded seedlings was observed from the third week of flooding. These results suggest that recovery of reduced function in leaves may progress with development of adventitious roots during the period of flooding.     

紫茎泽兰叶片浸提液对滇杨插穗抽梢和生根的影响

采用1年生滇杨扦插苗枝条作为插穗,研究了不同浓度紫茎泽兰鲜叶和冻害叶片浸提液对插穗抽梢和生根的影响。结果表明,滇杨在各处理条件下均能抽梢和生根,抽梢率和生根率在98％以上,生根类型为皮部生根。各处理条件下的平均梢长和平均不定根数达极显著水平,平均不定根长和根系效果指数差异不显著。紫茎泽兰鲜叶和冻害叶片浸提液对插穗抽梢及生根的化感作用表现一致,对梢长及不定根长有微弱的化感促进或抑制作用,对不定根数均表现出较强的化感抑制作用。     

Effect of flooding on C metabolism of flood-tolerant (Quercus robur) and non-tolerant (Fagus sylvatica) tree species

Flooding is assumed to cause an energy crisis in plants because-due to a lack of O(2)-mitochondrial respiration is replaced by alcoholic fermentation which yields considerably less energy equivalents. In the present study, the effect of flooding on the carbon metabolism of flooding-tolerant pedunculate oak (Quercus robur L.) and flooding-sensitive European beech (Fagus sylvatica L.) seedlings was characterized. Whereas soluble carbohydrate concentrations dropped in roots of F. sylvatica, they were constant in Q. robur during flooding. At the same time, root alcohol dehydrogenase activities were decreased in beech but not in oak, suggesting substrate limitation of alcoholic fermentation in beech roots. Surprisingly, leaf and phloem sap sugar concentrations increased in both species but to a much higher degree in beech. This finding suggests that the phloem unloading process in flooding-sensitive beech was strongly impaired. It is assumed that root-derived ethanol is transported to the leaves via the transpiration stream. This mechanism is considered an adaptation to flooding because it helps avoid the accumulation of toxic ethanol in the roots and supports the whole plant's carbon metabolism by channelling ethanol into the oxidative metabolism of the leaves. A labelling experiment demonstrated that in the leaves of flooded trees, ethanol metabolism does not differ between flooded beech and oak, indicating that processes in the roots are crucial for the trees' flooding tolerance.     

Carbon partitioning and allocation in northern red oak seedlings and mature trees in response to ozone

Northern red oak (Quercus rubra L.) seedlings and trees differ in their response to ozone. Previous work reported reductions in net photosynthesis, carboxylation efficiency and quantum yield of mature tree leaves, whereas seedling processes were unaffected by the same ozone exposure. To further characterize differences in ozone response between seedlings and mature trees, we examined carbon partitioning and allocation in 32-year-old trees and 4-year-old seedlings of northern red oak after exposure to subambient (seasonal SUM00 dose (sum of all hourly ozone exposures) = 31 ppm-h), ambient (SUM00 dose = 85 ppm-h) and twice ambient (SUM00 dose = 151 ppm-h) ozone concentrations for three growing seasons. For mature trees, ozone exposure decreased foliar starch partitioning, increased starch partitioning in branches and increased (14)C retention in leaves. In contrast, starch partitioning in leaves and branches, and foliar (14)C retention in seedlings were unaffected by ozone exposure, but soluble carbohydrate concentrations in coarse and fine roots of seedlings were reduced. Differences in carbohydrate demand between seedlings and mature trees may underlie the higher leaf ozone uptake rates and greater physiological response to ozone in mature northern red oak trees compared with seedlings.     

无患子硬枝扦插进程插穗内源激素和多酚类物质含量变化

为了解无患子硬枝扦插生根机制,以1年生无患子硬枝作为扦插材料,在扦插第0—80天调查愈伤组织发育和根系形成情况,测定插穗的腋芽(嫩叶)以及基部2cm长度的韧皮部内源激素和多酚类物质的含量。结果表明,无患子硬枝扦插第10天开始出现愈伤组织,第50天愈伤率达到最高值83.33%;第40天开始出现生根插穗,生根率为6.67%,随后不定根数量迅速增加,第70天生根率达到86.67%,此时平均有5.33条。之后生根数量不变,根系仍然在生长,且扦插后根系效果指数持续增高。插穗韧皮部内源激素含量变化较复杂。整体来看,高含量赤霉素(GA3)抑制愈伤组织和不定根形成,且在根原基发生期和不定根形成关键期达到峰值,在不定根速生期持续下降;高含量生长素(IAA)促进不定根的形成,且在扦插后第20天,即根原基发生期,达到峰值(92.7μg/g);玉米素核苷(ZR)对无患子硬枝扦插过程的生理作用较复杂,低含量的ZR有利于根原基的发生和不定根速生,但高含量的ZR促进不定根形成。韧皮部ZR/IAA在扦插后第20—40天呈下降趋势,第40—60天快速上升,促进不定根生长;GA3/IAA整体呈现抛物线形下降趋势,特别是在根原基发生期和不定根速生期,下降速率更快,以促进不定根的生长。无患子硬枝插穗生根进程中,多数多酚类物质对愈伤组织形成、根原基发生及不定根形成有极显著抑制作用,没食子酸抑制效果稍弱;插穗内多种激素和多酚类物质的含量均发生了变化,且对插穗生根产生重大影响。总之,插穗根原基发生和不定根形成等关键时期,IAA含量升高,GA3、ZR以及多酚类物质含量降低,植物体内多种内源物质此消彼长,达到动态平衡,共同促进插穗生根。     

铝胁迫对千年桐吸收和运输微量元素的影响

为探索千年桐体内微量元素对不同梯度铝胁迫的响应机制,分析铝胁迫下微量元素在根系和叶片间吸收和运输的规律,以土培和水培的1年生千年桐苗木为研究对象,在不同供铝水平下,测定千年桐苗木根系和叶片中微量元素(Fe、Mn、Cu、Zn)的含量。结果表明,铝处理显著促进盆栽苗根系微量元素的吸收,而对水培苗根系微量元素的吸收则表现为无显著作用或抑制作用,表明同一植物在不同生境下会形成不同的耐铝机制;微量元素在苗木不同器官的分配方式不同,千年桐盆栽苗吸收的微量元素除Mn外多集中在根系,而水培苗则除Fe外多集中在叶片;铝胁迫也会影响微量元素在苗木不同器官间的运输,如在铝浓度低于0.290 mmol·L^-1时,会促进水培苗Zn元素从根向叶的运输,而当铝浓度高于0.290 mmol·L^-1时,则会抑制Zn元素的向上运输。铝处理对千年桐盆栽苗和水培苗微量元素的影响有较大差异,与水培苗相比,盆栽苗在土壤原生环境下具有较好的抗性。因此,在今后的胁迫试验中,除了考虑植物自身的抗逆性,还要考虑原生环境的作用。     

Responses of two closely related oak species, Quercus robur and Q. petraea, to excess manganese concentrations in the rooting medium

Quercus robur (L.) and Q. petraea (Matt.) Liebl. are European oak species that often grow in forest soils with high soluble manganese (Mn2+) concentrations. We tested the effects of Mn2+ at concentrations of 0.0024 mM (control), 0.24 mM (typical of acidic forest soils) and 1.2 mM (typical of forest soils under strongly reducing conditions) on the growth, tissue anatomy, foliar element concentrations, subcellular element distribution and gas exchange of solution-cultured seedlings. At the highest Mn2+ concentration, seedlings were grown with and without an elevated concentration (1.2 mM) of magnesium (Mg2+). At 0.24 mM Mn2+, foliar Mn concentrations were higher than observed in the field. Vacuoles of the leaf epidermis and mesophyll were the main sites of manganese accumulation. High nutrient solution Mn2+ concentration significantly lowered foliar iron (Fe) and Mg concentrations. Elevated Mg2+ concentration raised the foliar Mg concentrations to control values, but Fe concentrations and gas exchange remained depressed. In seedlings grown in the 1.2 mM Mn2+ treatment without elevated Mg2+ damage to the phloem of the petioles and a reduction in root mass were observed in both species. The effects on shoot and root growth were greatest in Q. petraea. Alleviation of manganese toxicity symptoms by Mg2+ in Q. petraea was less effective than in Q. robur. Our results suggest that the soil solution Mn2+ concentrations that occur in European oak forests are unlikely to affect the distribution and performance of Q. robur and Q. petraea in the field.     

叶面肥对油茶幼苗生长和生理特征影响的研究

以1a生出圃的油茶幼苗为材料研究不同浓度无机盐配比的叶面肥对油茶幼苗生长发育的影响,以便获得有利于油茶幼苗生长的叶面肥.在N、P、K肥的基础上,对硼酸、硫酸锌、钼酸钠进行L9(34)正交试验设计来配制叶面肥,喷施油茶幼苗叶片一段时间后测定幼苗的生长及其生理生化指标,对测定结果进行了极差分析和方差分析,并对优化的叶面肥进...     

Photosynthetic light response of flooded cherrybark oak (Quercus pagoda) seedlings grown in two light regimes

Two-year-old cherrybark oak (Quercus pagoda Raf.) seedlings raised in full or partial (27%) sunlight were flooded for 30 days to study the effects of light availability and root inundation on photosynthetic light response. Compared with seedlings receiving full sunlight, seedlings receiving partial sunlight developed leaves with 90% greater blade area, 26% less mass per unit volume, and 35% lower nitrogen (N) concentration per unit area, leading to a 15% reduction in leaf photosynthetic capacity when carbon exchange rates were based on blade area. However, when carbon exchange rates were based on leaf mass, leaves acclimated to partial sunlight exhibited a 15% greater photosynthetic capacity realized primarily through an increased initial slope of the photosynthetic light response (A/PPFD) curve and increased net photosynthesis at leaf saturation (Amax). Short-term flooding increased leaf mass per unit area more than 19%, reduced foliar N concentrations per unit dry mass by 19%, and initiated reductions in Amax and apparent quantum yield (phi) of seedlings in both light regimes. Greatest impairment of Amax (56% area basis, 65% mass basis) and phi (40%) were observed in leaves receiving full sunlight, and the declines were concomitant with a 35% decrease in chlorophyll concentration. Flooding also depressed instantaneous photosynthetic N-use efficiency (PPNUE) such that Amax decreased 54%, and the initial slope of PPNUE/PPFD curves decreased 33 and 50% for leaves acclimated to partial and full sunlight, respectively. The A/PPFD patterns indicated that the magnitude of flood-induced inhibition of the photosynthetic mechanism of cherrybark oak seedlings is determined partly by the light environment.     

Carbohydrate relations during propagation of cuttings from sexually mature Pinus banksiana trees

Concentrations of glucose, sucrose, soluble reducing sugars, starch and total non-structural carbohydrate were determined during propagation of cuttings from sexually mature Pinus banksiana Lamb. trees. Such cuttings rarely initiate adventitious roots whatever the method or duration of propagation. Terminals, needles, and upper and basal stem segments of cuttings were analyzed at Day 0 and every 2 days for 18 days. Comparison of the results with those of earlier studies with cuttings of P. banksiana seedlings, which root readily, indicated pronounced differences in carbohydrate concentrations and partitioning between the two types of cutting. Compared with those from seedlings, cuttings from sexually mature trees exhibited: (1) more total non-structural carbohydrate in each tissue at Day 0; (2) decreasing rather than increasing total carbohydrate (mainly starch) concentrations in each tissue during propagation; (3) different carbohydrate concentration ratios in each tissue during propagation; and (4) higher sucrose concentrations in terminals during propagation, relative to concentrations at Day 0. Cuttings from sexually mature trees also differed from cuttings of seedlings in having a much lower rate of dry matter accumulation during propagation. These findings suggest that the poor rooting ability of cuttings from sexually mature P. banksiana is not attributable to a lack of total carbohydrate, but that the rooting abilities of cuttings from seedlings and from sexually mature trees differ because of differences between the two types of cutting in rates of net photosynthesis and starch metabolism. The difference in starch metabolism becomes apparent during the first 2 days of propagation.     

Nutrient concentrations in roots, leaves and wood of seedling and mature sugar maple and American beech at two contrasting sites

Differences in sensitivity to soil conditions across tree species and developmental stage are important to predicting forest response to environmental change. This study was conducted to compare elemental concentrations in leaves, stems, and roots of (1) sugar maple (Acer saccharum Marsh.) seedlings vs. mature trees and (2) mature sugar maple vs. mature American beech (Fagus grandifolia Ehrh.) in two sites that differ in soil base saturation and pH. Both sites are located in Huntington Forest, NY, USA; one site (hereafter ‘H’) has higher soil pH and Ca, Mg, and Mn concentrations than the other site (hereafter ‘L’). Sugar maple growth at H (14.8 cm² year⁻¹ per tree) was much greater than at L (8.6 cm² year⁻¹ per tree), but the growth of beech was not different between the two sites. Leaves, roots, and stem wood of mature beech trees and sugar maple seedlings and mature trees were sampled for nutrient analysis. Foliar Ca, K, and Al concentrations were positively correlated with soil elements, but Mn concentrations were negatively correlated. Sugar maple differed more than beech between sites in foliar K and Mn concentrations. Root Mg and P concentrations reflected soil chemistry differences, in contrast to foliar concentrations of Mg and P, which were indistinguishable between the sites. In sugar maple, seedlings differed more than in mature trees in nutrient concentrations in roots, especially for Mg and Mn. Although beech was not as responsive to nutrient availability as sugar maple in foliar and root nutrient concentrations, Ca and Mg concentrations in beech wood were higher in H (52% higher for Ca and 68% higher for Mg), while sugar maple did not differ between sites. Sugar maple regeneration failure on acidic soils in the same region is consistent with our finding that sugar maple seedlings were very sensitive to nutrient availability. This sensitivity could ultimately contribute to the replacement of sugar maple by American beech in regions of low pH and base cations if base cation leaching by anthropogenic deposition and tree harvesting continues.     

Vegetative propagation of African Mahogany: effects of auxin, node position, leaf area and cutting length

Applied auxin, node position, leaf area and cutting length were examined to investigate the requirements for rooting stem cuttings of Khaya ivorensis. All these variables were shown to be important factors affecting rooting, confirming the hypothesis that successful rooting can be achieved if these primary variables are optimised.The best concentration of the auxin IBA was found to be 200 g per cutting, which hastened rooting, increased the percentage of cuttings rooted and increased the number of roots per cutting. One clone (8013) was unresponsive to auxins in terms of the percentage of cuttings rooted, but was the most responsive in terms of the numbers of roots per cutting. A greater percentage of cuttings from basal nodes were rooted than from apical nodes. Cuttings cut squarely at the base produced a radially-arranged root system, whereas an oblique cut resulted in a one-sided root system.Trimming the leaf area of cuttings to 10 cm² gave greater rooting percentages than trimming to 100 cm². In general, long cuttings (39 mm) rooted better than short cuttings (19 mm), however, there was an interaction between leaf area and cutting length, in which cuttings with short stems and large leaves had the lowest rooting percentage.     

Long- and short-term flooding effects on survival and sink-source relationships of swamp-adapted tree species

About 95% of swamp tupelo (Nyssa sylvatica var. biflora (Walt.) Sarg.) and sweetgum (Liquidambar styraciflua L.) seedlings survived continuous root flooding for more than two years, whereas none of the swamp chestnut oak (Quercus michauxii Nutt.) and cherrybark oak (Q. falcata var. pagodifolia Ell.) seedlings survived one year of flooding. Death of oak seedlings occurred in phases associated with periods of major vegetative growth, e.g., after bud burst in spring, after summer stem elongation, and during the winter deciduous stage, suggesting that stored reserves and sources were inadequate to maintain the seedlings when vegetative sinks were forming. Additional evidence that flooding induced a source deficiency in oak was that leaves of flooded oak were 65 to 75% smaller than leaves of nonflooded oak. Flooded swamp tupelo seedlings had a normal leaf size and patchy stomatal opening compared with nonflooded seedlings. Flooding caused increases in alcohol dehydrogenase (ADH) specific activity in taproot cambial tissues and increases in starch concentrations of swamp tupelo seedlings that were reversed when seedlings were removed from flooding. Flooding had little effect on soluble sugar concentrations in swamp tupelo or sweetgum. In the long-term flood-dry-flood treatment, in which all species had survivors, upper canopy leaf photosynthetic rates were higher in all species during the dry period than in nonflooded controls, whereas their starch and soluble sugars concentrations were similar to those of nonflooded controls. Based on seedling survival and the sink-source relationships, the order of flood tolerance was: swamp tupelo > sweetgum > swamp chestnut oak > cherrybark oak.