Timing Of Growth Cessation Research Articles

Adaptive performance of genetically improved and unimproved seedlings of Scots pine

Our main objective was to determine whether various genetically improved reproductive materials of Scots pine ( L.) differ in growth rhythm, autumn cold acclimation and resilience from unimproved materials. The study consisted of two successive indoor experiments with Scots pine seedlings representing four levels of genetic gain (unimproved natural stands, first-generation seed orchards, 1.5-generation seed orchards and seed orchards established with freezing-tested parents) and a wide range of geographical origins within Finland. The seedlings were assessed for terminal shoot elongation, growth cessation, bud set, freezing injuries and bud flushing over the first growth period. All the adaptive traits showed a latitudinal trend regardless of the genetic level. Seed orchard progenies and natural stand progenies did not differ significantly in the timing of growth cessation, bud set, and the flushing rate of the frost-injured seedlings, after the trait variation was adjusted to the latitude of origin. The differences in autumn frost hardiness were insignificant, too, except for the somewhat higher injury rate displayed by the first-generation seed orchard materials. The finding was not conclusive due to ambiguous results from the two experiments. Overall, we did not find evidence of alarming compromises in the adaptive performance of genetically improved materials.Pinus sylvestris

A simple and convenient method for determination of entrance into dormancy in woody plants

BACKGROUND: Bud dormancy is a quantitative condition that is gradually acquired and lost. Better and more convenient methods for assessment of the time of dormancy entrance of woody plants are highly needed. OBJECTIVE: To demonstrate a simple and convenient method for determination of dormancy in woody plants. METHODS: We employed a seasonal series of soft tipping of vigorously growing annual shoots and used the loss of ability of subtending lateral buds to break and grow as a measure of entrance into dormancy. RESULTS: There was a gradual decline in the ability of the buds to burst and grow during the month of July and early August, culminating with a complete loss of this ability. This coincided with the known time of growth cessation and dormancy induction in shoots of intact plants and occurred in the berry shrubs raspberry and black currant and the forest tree silver birch. CONCLUSIONS: The decline and loss of ability of the buds to grow during late summer is a direct expression of the entrance of buds into the state of endodormancy, rendering the tipping method a simple and convenient method for precise determination of the time of entrance into dormancy in woody plants.

Branching Regulator BRC1 Mediates Photoperiodic Control of Seasonal Growth in Hybrid Aspen

Cessation of growth as winter approaches is a key adaptive trait for survival of perennial plants, such as long-lived trees native to boreal and temperate regions [1, 2]. The timing of growth cessation in these plants is controlled by photoperiodic cues. As shown recently, perception of growth-repressive short photoperiod (SP) mediated via components of circadian clock results indownregulation of the tree ortholog of Arabidopsis flowering regulator FLOWERING LOCUS T(FT), FT2[3, 4]. Downregulation of FT2 results in suppression of downstream components LAP1 (orthologousto the Arabidopsis floral meristem identity gene APETALA1) and AIL1 (orthologous to AINTEGUMENTA in Arabidopsis), culminating in induction of growth cessation and bud set [5-7]. Results presented here reveal that, in addition to the CO/FT pathway, a photoperiodically controlled negative feedback loop involving a tree ortholog of Arabidopsis BRANCHED1 (BRC1) (a member of TEOSINTE BRANCHED 1, CYCLOIDEA, PCF family), LAP1, and FT2 participates in regulation of seasonal growth in the model tree hybrid aspen. In growth-promotive long photoperiod, LAP1 suppresses expression of BRC1, but upon perception of growth-repressive SP, downregulation of LAP1 de-represses expression of its downstream target BRC1. BRC1 physically interacts with FT2, and BRC1-FT interaction further reinforces the effect of SP and triggers growth cessation by antagonizing FT action. Accordingly, BRC1 gain and loss of function result in early and retarded growth cessation responses to SP, respectively. Thus, these results reveal a regulatory feedback loop that reinforces responses to SP and induction of seasonal growth cessation.

Studying and modelling winter dormancy in olive trees

The abundance of scientific papers dealing with olive reproductive phenology contrasts with the scarce information available in relation to the winter dormant state of olive vegetative structures. In this study, three experiments with young olive trees were performed in Southern Spain, aiming to provide insight into some features of the winter rest period in this evergreen species. Experiment 1 evaluated the environmental cues triggering dormancy induction by measuring leaf appearance rates in trees subjected to different conditions of temperature and daylength over the course of the 2012 autumn. In Experiment 2, several sets of plants were placed into a greenhouse at different dates along the 2013/2014 winter, testing the ability of dormant plants to resume growth upon the return of favourable temperatures. Finally, Experiment 3 was carried out during the autumns of 2016 and 2017 in two locations, and was devoted to assess differences between five cultivars in the onset of dormancy under natural conditions. Our findings revealed that dormancy induction is not controlled by photoperiod, but by low temperatures. The subsequent winter rest state seems to be easily reversed after 1–2 weeks of exposure to warm conditions, irrespective of the initial date of exposure. With regard to cultivar variability, differences in the timing of growth cessation was found to be rather small. Finally, two simple models for predicting the onset of dormancy based on the accumulation of a certain amount of chilling (either considering or not a reversal of chilling by warm temperatures) are presented. Calibration and validation was performed with independent datasets from Experiments 1, 2 and 3. Validation tests highlighted the reliability of both models in reproducing the date of growth cessation.

Genetic heterogeneity underlying variation in a locally adaptive clinal trait in Pinus sylvestris revealed by a Bayesian multipopulation analysis.

Local adaptation is a common feature of plant and animal populations. Adaptive phenotypic traits are genetically differentiated along environmental gradients, but the genetic basis of such adaptation is still poorly known. Genetic association studies of local adaptation combine data over populations. Correcting for population structure in these studies can be problematic since both selection and neutral demographic events can create similar allele frequency differences between populations. Correcting for demography with traditional methods may lead to eliminating some true associations. We developed a new Bayesian approach for identifying the loci underlying an adaptive trait in a multipopulation situation in the presence of possible double confounding due to population stratification and adaptation. With this method we studied the genetic basis of timing of bud set, a surrogate trait for timing of yearly growth cessation that confers local adaptation to the populations of Scots pine (Pinus sylvestris). Population means of timing of bud set were highly correlated with latitude. Most effects at individual loci were small. Interestingly, we found genetic heterogeneity (that is, different sets of loci associated with the trait) between the northern and central European parts of the cline. We also found indications of stronger stabilizing selection toward the northern part of the range. The harsh northern conditions may impose greater selective pressure on timing of growth cessation, and the relative importance of different environmental cues used for tracking the seasons might differ depending on latitude of origin.

Susceptibility of silver birch (Betula pendula) to herbivorous insects is associated with the size and phenology of birch – implications for climate warming

ABSTRACTSusceptibility of trees to herbivorous insects is often associated with the tree growth and phenology, both of which are sensitive to a warming climate. Therefore, changes in these traits may affect the intensity of herbivory on trees in the future. We grew silver birch (Betula pendula) populations differing in their growth and phenology in a common garden experiment, and studied the effect of these plant traits on the leaf herbivory, insect herbivore density and community composition of herbivores in two consecutive years, 2011 and 2012. Differences in size and the timing of growth cessation among the birch genotypes were related to differences in herbivore community compositions and herbivory. In 2011, the most intensive herbivore damage was observed on birch genotypes of small size, late bud burst and early growth cessation, and these genotypes originated from high-latitude populations. The differences among birch genotypes in their susceptibility to herbivore damage may lead to differences in their competitive abilities. While climate warming will affect phenology and growth of plants, our study shows, that it may indirectly affect herbivory and herbivore communities as well.

Freezing tolerance in Norway spruce, the potential role of pathogenesis-related proteins

Cold-tolerant plants may endure subzero temperatures partially by inhibiting the development of ice crystals in the intercellular spaces and the xylem through the accumulation of antifreeze proteins (AFP) and the extra production of carbohydrates. Certain proteins associated with pathogen resistance in plants have the ability to bind and alter the growth of ice crystals. In this study, the accumulation of pathogenesis-related (PR) proteins and the development of freezing tolerance in seedlings of two latitudinal distinct Norway spruce (Picea abies L. Karst.) ecotypes were investigated. Despite freezing tolerance difference, timing of growth cessation and bud set variations, our results showed that there is no significant difference in the concentration of soluble carbohydrates between the two ecotypes. Immunoblots showed the presence of several β-1,3-glucanase and thaumatin PR proteins in the apoplastic fluid and the enzymatic assay showed an extra accumulation of several isoforms of PR chitinases in cold-treated Norway spruce needles. In addition to PR proteins, a presence of de novo protein in cold-treated needles was noticed. In contrary to mature plants, total proteins isolated from freezing-tolerant Norway spruce seedling did not show antifreeze activity. Our results suggest that the activity of the PR proteins and the accumulation of soluble carbohydrates that increased during cold acclimation may have an indirect impact on the freezing tolerance in Norway spruce, however, deciphering the direct mechanism behind freezing tolerance in Norway spruce seedlings growing under controlled environmental conditions require further investigation.

Endogenous ascorbate restrains apoplastic peroxidase activity during sunflower leaf development

Several apoplastic enzymes have been implicated in the control of elongation growth of plant cells. Among them, peroxidases contribute to both loosening and stiffening of the cell wall. They appear to be regulated by various mechanisms, including the action of extracellular inhibitors. To obtain evidence of the role of the enzyme-inhibitor interaction during leaf development, the intercellular washing fluids from Helianthus annuus leaves of different ages were isolated using standard methods of vacuum infiltration and centrifugation. Peroxidase activities, assessed using tetramethylbenzidine as substrate, increased during leaf development, reaching a maximum value after the leaves were fully expanded. An inhibitor, chemically characterised as ascorbate, co-localised with the enzyme in the apoplast. Moreover, there was a strong negative correlation between the action of peroxidase and the micromolar concentration of ascorbate in the apoplastic fluid. The results show that in growing leaves, the in planta ascorbate concentration is able to restrain peroxidase enzyme activity. Then, at the time of growth cessation, the loss of extracellular ascorbate relieves the inhibition on this enzyme that contributes to wall fixation.

Influence of climate on seasonal patterns of stem increment of balsam fir in a boreal forest of Québec, Canada

It is important to develop a better understanding of the climatic factors controlling the growth of boreal forests. Dendrometer measurements were used to characterize inter-annual variation in seasonal patterns of stem diameter increment of balsam fir trees (n=3) over seven growing seasons (2004–2010) in a boreal forest of Québec, Canada. For the period studied, cumulative seasonal growth ranged from 1.1mm to 2.9mm. Cumulative seasonal growth was a function of the timing of tree growth initiation and cessation along with the maximum growth rate observed throughout the growing season. The start and finish of diameter growth showed variations of 21 and 53 days, respectively, and duration of the growing season ranged from 38 to 107 days while maximum growth rates observed throughout a season ranged from 36.0μmd−1 to 57.6μmd−1. Interestingly, similar cumulative annual growth can be achieved through very different seasonal growth patterns, depending on the inter-annual variation of the three factors mentioned above. Air temperature and photosynthetically active radiation appeared to regulate the initiation of tree growth with high photosynthetically active radiation and cool spring conditions delaying the start of growth. The maximum growth rate within a given season was related to snowpack depth and the timing of snowmelt. Deeper snowpack that melt earlier in spring was associated to higher maximum growth rates during the following season. Apart from exceptional climatic conditions that led to a very early growth cessation in 2006, the timing of growth cessation cannot be explained by climatic variables, suggesting that this phenological event is internally controlled by a physiological mechanism. Overall, the results indicate that the onset of growth as well as the maximum growth rate were regulated by climatic triggers. Consequently, changes in climate seasonality may have considerable effects on both seasonal pattern of growth and tree growth itself.

Trade-off between height growth and spring flushing in common beech (Fagus sylvatica L.)

The annual development cycle of boreal and temperate trees results from an evolutionary trade-off between two opposing forces. These are namely, the adjustment of leaf phenology to the timing of frost occurrence at the beginning and/or the end of the growth season countered by an effective adjustment to the duration of the growth season to maximise photosynthesis and biomass production during the growing season. In a provenance trial of common beech (Fagus sylvatica L.) populations, we tested whether avoiding frost events by late flushing is the primary process of frost tolerance, and also, whether longer growth seasons resulted in an increase in biomass production. We detected clines with altitude and longitude of provenances for phenological traits, in contrast to growth variables. A highly significant negative genetic correlation was detected between frost damage and budburst date which confirms that the timing of leaf flushing is the principal determinant of tolerance to late frost. Height and diameter growth were positively correlated with the length of the vegetation season. However, this effect was associated with the timing of growth cessation rather than with budburst. Stabilizing selection, selective pressure on early leaf flushing of juveniles in dense natural beech stands, and epigenetic regulation of budburst are proposed as explanations for these observations.

Bud set in poplar – genetic dissection of a complex trait in natural and hybrid populations

• The seasonal timing of growth events is crucial to tree distribution and conservation. The seasonal growth cycle is strongly adapted to the local climate that is changing because of global warming. We studied bud set as one cornerstone of the seasonal growth cycle in an integrative approach. • Bud set was dissected at the phenotypic level into several components, and phenotypic components with most genetic variation were identified. While phenotypic variation resided in the timing of growth cessation, and even so more in the duration from growth cessation to bud set, the timing of growth cessation had a stronger genetic component in both natural and hybrid populations. • Quantitative trait loci (QTL) were identified for the most discriminative phenotypic bud-set components across four poplar pedigrees. The QTL from different pedigrees were recurrently detected in six regions of the poplar genome. • These regions of 1.83-4.25 Mbp in size, containing between 202 and 394 genes, form the basis for further molecular-genetic dissection of bud set.

Vegetative phenology of alpine plants at Tateyama Murodo-daira in central Japan

The vegetative phenology of 29 alpine species, including herbaceous and woody summergreens and evergreens, was investigated. Summergreen species initiated and completed leaf growth earlier than evergreen species. The green period of leaves in summergreen plants was determined largely by the time of growth initiation. Early initiation of growth in summergreen plants contributes to the increase in photosynthetic carbon gain. Early cessation of growth in summergreens is advantageous for the growth in the following year because it leads to an increase in stored photosynthates. The growth period of leaves and stems in alpine plants correlated with the time of growth initiation more strongly than with the time of growth cessation, indicating the importance of early growth initiation for the increase in plant growth. The growth period of leaves was positively correlated with the sum of leaf lengths and the number of leaves. Herbs with a long growth period of more than 50 days had perennial shoot axes not terminated by inflorescences, suggesting a relationship between the growth period and shoot habit. Two summergreen species were completely dead by mid-September, before the air temperature decreased below 0 degrees C. The remaining summergreen species died immediately after the air temperature decreased to -1.4 degrees C in late September.

Identification of genes associated with growth cessation and bud dormancy entrance using a dormancy-incapable tree mutant.

BackgroundIn many tree species the perception of short days (SD) can trigger growth cessation, dormancy entrance, and the establishment of a chilling requirement for bud break. The molecular mechanisms connecting photoperiod perception, growth cessation and dormancy entrance in perennials are not clearly understood. The peach [Prunus persica (L.) Batsch] evergrowing (evg) mutant fails to cease growth and therefore cannot enter dormancy under SD. We used the evg mutant to filter gene expression associated with growth cessation after exposure to SD. Wild-type and evg plants were grown under controlled conditions of long days (16 h/8 h) followed by transfer to SD (8 h/16 h) for eight weeks. Apical tissues were sampled at zero, one, two, four, and eight weeks of SD and suppression subtractive hybridization was performed between genotypes at the same time points.ResultsWe identified 23 up-regulated genes in the wild-type with respect to the mutant during SD exposure. We used quantitative real-time PCR to verify the expression of the differentially expressed genes in wild-type tissues following the transition to SD treatment. Three general expression patterns were evident: one group of genes decreased at the time of growth cessation (after 2 weeks in SD), another that increased immediately after the SD exposure and then remained steady, and another that increased throughout SD exposure.ConclusionsThe use of the dormancy-incapable mutant evg has allowed us to reduce the number of genes typically detected by differential display techniques for SD experiments. These genes are candidates for involvement in the signalling pathway leading from photoperiod perception to growth cessation and dormancy entrance and will be the target of future investigations.

Mapping of Photoperiod-induced Growth Cessation in the Wild Grape Vitis riparia

In grapevines (Vitis spp.), the timing of growth cessation in the fall is an important aspect of adaptation and a key objective in breeding new grape cultivars suitable for continental climates. Growth cessation is a complex biological process that is initiated by environmental cues such as daylength and temperature, as well as water and nutrient availability. The genetic control of growth cessation in grapevines was studied by mapping quantitative trait loci (QTL) in a hybrid grape population. An F2 mapping population was developed by selfing a single F1 plant derived from a cross between an accession of the North American species Vitis riparia and the Vitis hybrid wine cultivar Seyval (Seyve-Villard 5–276). A linkage map was constructed using 115 simple sequence repeat (SSR) markers and six candidate genes in a population of 119 F2 progeny. The markers provided coverage of the 19 Vitis linkage groups with an average distance between markers of 8.4 cM. The critical photoperiod for growth cessation in lateral buds for the parents and F2 progeny was determined in a replicated field trial in 2001 and 2002 and under controlled photoperiod treatments in a greenhouse in 2002, 2003, and 2004. QTL analysis using composite interval mapping identified a single major QTL in the field and greenhouse trials. However, the field and greenhouse QTL mapped to different linkage groups in the two different environments, suggesting the presence of additional, nonphotoperiodic cues for induction of growth cessation in the field. In the greenhouse, where noninducing temperatures were maintained, a QTL on linkage group (LG) 13 explained 80.0% to 96.6% of the phenotypic variance of critical photoperiod for growth cessation. In the field, where vines experienced natural fluctuations in temperature and rainfall in addition to the naturally decreasing photoperiod, a QTL on LG 11 explained 85.4% to 94.3% of phenotypic variance.

Effect of the latitude of seed origin on moose ( Alces alces) browsing on silver birch ( Betula pendula)

Moose is a major cause of damage in young plantations of silver birch ( Betula pendula Roth) in Finland, as they break stems and browse twigs and leaves. Damage by moose was measured in a provenance trial of silver birch situated at Loppi, southern Finland. The trial includes stand seed origins from Finland, Sweden, Estonia, Scotland and Russia, ranging in latitudes from 53° to 67°. The trial was established on a typical, southern Finnish moist upland clear-cut area that had been protected against moose by fencing. After the break-down of the fence, at the age of 5–11 years, the trial was frequently visited by moose. The effects of browsing were measured in early spring 2001, when the trees were 11 years old. The average proportion of trees browsed by moose varied between 6 and 86% among the seed origins. Browsing by moose decreased with increasing latitude of seed origin and sapling height. Seed origins transferred from more southern latitudes (southern Estonia, southern Sweden, Scotland, Russia) had a higher proportion of browsed trees than the more northern native ones. A similar pattern was also seen in the proportion of trees with stem breakage and the proportion of repeatedly browsed trees. Latitude of seed origin and sapling height covariate had a significant effect on moose browsing. The moose browsed more branches per browsed tree of southern origins, whereas sapling height had no significant effect. It is suggested that the variation in moose browsing among the seed origins was related to differences in their annual physiological rhythm, i.e. timing of growth cessation, leaf discoloration and abscission, and related changes in digestibility and palatability. It was concluded that importing birch regeneration material to Finland from more southern latitudes should be avoided because of the risk of browsing damage.

Isotope records in submarine speleothems from the Adriatic coast, Croatia

Abstract Isotope studies, using 14C dating, δ13C and δ18O measurements, were performed at eight speleothems taken from three submerged caves situated along the eastern Adriatic coast, Croatia. The speleothems were taken from 17 m to 38.5 m depth below mean sea level. The samples consist of four stalagmites and four stalactites in position of growth, covered with marine biogenic overgrowth, and the length of speleothems ranges from ~80 mm to ~190 mm. The youngest (surface) and the oldest (base) layers of speleothems were radiocarbon dated and the 14C ages range from 21,600 cal B.P. to 37,000 yr B.P. During that period the global sea level was more than 40 m below the recent one, so presently submerged objects were under the subaerial conditions necessary for speleothem deposition. 14C ages of the youngest layer range from 21,600 to 32,200 cal B.P. for different submerged speleothems. This indicates the time when the speleothem growth ceased, most probably due to flooding of the cave with either fresh or brackish water. Speleothem growth during the Last Glacial Maximum (30–19 kyr ago) and different time of growth cessation for the different speleothem samples suggest that climate change was not the reason for cessation of deposition. Samples for δ13C and δ18O measurements were taken from six submerged speleothems with sampling distances of ca. 5–10 mm from the surface to the base of speleothems. Most of the δ13C values are in the range from −10.5‰ to −8.5‰, with few exceptions to −6‰. These values are typical for Dinaric karst, and very different values for marine biogenic overgrowth indicate that no isotopic exchange took place during the submerged period. δ18O values range from −6.7‰ to −4.1‰. A weak correlation between δ13C and δ18O values indicates possible kinetic isotope fractionation during the calcite precipitation. If the δ18O record is interpreted as climatic signal, it suggests similar climatic conditions for the late Pleistocene and the Holocene, especially no significant differences in temperature and/or moisture transport.

Effects of Photoperiod and Thermal Time on the Growth Rhythm of Pinus sylvestris Seedlings

The effects of photoperiod and thermal time and their interaction on the timing of growth cessation were examined in seedlings of Scots pine (Pinus sylvestris L.) in greenhouses with 20°C day and 10°C night temperatures combined with the natural development of the photoperiod. Sowing was repeated five times during both 1995 and 1996 using origins from different altitudes and latitudes (>60°N) in Sweden and Finland. In this way, gradients in temperature sums at a nearly constant photoperiod and different photoperiods at constant temperature sums were obtained. After the first growing season the timing of growth cessation of seedlings from different origins was flexible, i.e. it was determined by the specific combinations of accumulated temperature sum and night length illustrated by fitted straight lines. The photoperiod at the site of origin was a dominant factor in determining the timing of growth cessation in origins from northern latitudes. Because of predetermined growth, the sowing date did not affect the phenology during the second growing season.

Fall frost resistance in willows used for biomass production. I. Characterization of seasonal and genetic variation.

Fast-growing willow clones (six clones of Salix viminalis L. and one clone each of S. viminalis x S. schwerenii E. Wolf and S. dasyclados Wimm.) were compared with respect to growth rhythm and frost hardening in the fall. Frost resistance of stem tissues was assessed by controlled freezing followed by analysis of chlorophyll fluorescence and scoring of visible cambial discoloration. The fluorescence method proved superior to scoring based on visible cambial discoloration because it was more rapid and less subjective, but needed calibration against cambial damage. Frost hardening in mature parts of stems did not start until growth cessation was initiated in the shoot apices, irrespective of whether growth cessation occurred early or late in the fall. Frost resistance varied because of clonal variations in: (1) pre-hardening frost resistance; (2) timing of growth cessation and hence start of frost hardening; and (3) rate of frost hardening. Compared with coastal and southern clones, continental and northern clones started hardening earlier, and a continental clone proceeded through hardening more rapidly at a given temperature. A cross between a continental and coastal clone was intermediate in timing. The pre-hardening frost resistance, however, was unrelated to both growth and frost hardening characteristics.

Effects of elevated CO2 concentration on leaf characteristics and photosynthetic capacity of beech (Fagus sylvatica) during the growing season

Two-year-old beech (Fagus sylvatica L.) saplings were planted directly in the ground at high density (100 per m(2)), in an experimental design that realistically mimicked field conditions, and grown for two years in air containing CO(2) at either ambient or an elevated (ambient + 350 ppm) concentration. Plant dry mass and leaf area were increased by a two-year exposure to elevated CO(2). The saplings produced physiologically distinct types of sun leaves associated with the first and second growth flushes. Leaves of the second flush had a higher leaf mass per unit area and less chlorophyll per unit area, per unit dry mass and per unit nitrogen than leaves of the first flush. Chlorophyll content expressed per unit nitrogen decreased over time in plants grown in elevated CO(2), which suggests that, in elevated CO(2), less nitrogen was invested in machinery of the photosynthetic light reactions. In early summer, the photosynthetic capacity measured at saturating irradiance and CO(2) was slightly but not significantly higher in saplings grown in elevated CO(2) than in saplings grown in ambient CO(2). However, a decrease in photosynthetic capacity was observed after July in leaves of saplings grown in CO(2)-enriched air. The results demonstrate that photosynthetic acclimation to elevated CO(2) can occur in field-grown saplings in late summer, at the time of growth cessation.

Seasonal growth patterns of Nyssasylvatica var biflora, Nyssaaquatica, and Taxodiumdistichum s affected by hydrologic regime

Hydrologic regime is a major influence on the growth of wetland plants. We examined seasonal growth patterns of three wetland tree species, Nyssasylvatica var. biflora (Walter) Sargent, Nyssaaquatica L., and Taxodiumdistichum (L.) Rich., to determine responses to variations in hydrologie regime. Five study sites were chosen in two river-floodplain swamps to represent a gradient of hydrologie regimes, and the weekly changes in diameter of over 600 mature trees at these sites were measured with dendrometer bands throughout two growing seasons. Total growth, time of growth cessation, and length of the growth phase of canopy trees of all three species differed significantly among hydrologie regimes. Nyssasylvatica var. biflora and N. aquatica achieved greatest growth under deep periodic flooding. Maximum growth of T. distichum occurred with shallow permanent flooding. Subcanopy trees differed less among hydrologic regimes than canopy trees. These results suggest that modifications of natural hydrologie regimes can cause short-term changes in tree growth and have long-term effects on the dynamics of forested wetlands.