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PubMed2001

Regulation of water flux through tropical forest canopy trees: do universal rules apply?

Tropical moist forests are notable for their richness in tree species. The presence of such a diverse tree flora presents potential problems for scaling up estimates of water use from individual trees to entire stands and for drawing generalizations about physiological regulation of water use in tropical trees. We measured sapwood area or sap flow, or both, in 27 co-occurring canopy species in a Panamanian forest to determine the extent to which relationships between tree size, sapwood area and sap flow were species-specific, or whether they were constrained by universal functional relationships between tree size, conducting xylem area, and water use. For the 24 species in which active xylem area was estimated over a range of size classes, diameter at breast height (DBH) accounted for 98% of the variation in sapwood area and 67% of the variation in sapwood depth when data for all species were combined. The DBH alone also accounted for > or = 90% of the variation in both maximum and total daily sap flux density in the outermost 2 cm of sapwood for all species taken together. Maximum sap flux density measured near the base of the tree occurred at about 1,400 h in the largest trees and 1,130 h in the smallest trees studied, and DBH accounted for 93% of the variation in the time of day at which maximum sap flow occurred. The shared relationship between tree size and time of maximum sap flow at the base of the tree suggests that a common relationship between diurnal stem water storage capacity and tree size existed. These results are consistent with a recent hypothesis that allometric scaling of plant vascular systems, and therefore water use, is universal.

Panama↗
PubMed2001

Response to seasonal drought in three cultivars of Ceratonia siliqua: leaf growth and water relations.

Responses of leaf growth and leaf water relations to seasonal drought were monitored during two successive years in three cultivars (Galhosa, Espargal and Mulata) of Ceratonia siliqua L. growing in the field in southern Portugal. Leaf water relations of fully expanded leaves were characterized by pressureâ volume analysis, and morphometric measurements of petiolar xylem were made. The three cultivars differed with respect to onset of leaf initiation. In Galhosa, there was a sharp peak of leaf initiation in June that was immediately followed by a period when leaf expansion rates were highest. The onset of leaf growth occurred earlier in Espargal and Mulata than in Galhosa, and both cultivars continued producing new leaves throughout the summer period. The diurnal pattern of water relations in recently expanded leaves indicated that, during midsummer, Galhosa was the only cultivar in which leaf water potential did not fall below the turgor loss point and leaf relative water content remained above 90%. The occurrence of osmotic adjustment in recently expanded leaves of Galhosa was not demonstrated conclusively. However, during the dry season following leaf formation, a seasonal decrease in osmotic potential sufficient to maintain turgor was detected in 1-year-old leaves of Galhosa but not in 1-year-old leaves of the other cultivars. Among cultivars, Galhosa petioles had the widest xylem conduits, which may partly explain why midday leaf water potential in Galhosa never decreased below -2.0 MPa even at the end of the summer drought.

Fabaceae↗
PubMed2001

Tree stem diameter variations and transpiration in Scots pine: an analysis using a dynamic sap flow model.

A dynamic model for simulating water flow in a Scots pine (Pinus sylvestris L.) tree was developed. The model is based on the cohesion theory and the assumption that fluctuating water tension driven by transpiration, together with the elasticity of wood tissue, causes variations in the diameter of a tree stem and branches. The change in xylem diameter can be linked to water tension in accordance with Hookeâ s law. The model was tested against field measurements of the diurnal xylem diameter change at different heights in a 37-year-old Scots pine at Hyytiälä, southern Finland (61 degrees 51' N, 24 degrees 17' E, 181 m a.s.l.). Shoot transpiration and soil water potential were input data for the model. The biomechanical and hydraulic properties of wood and fine root hydraulic conductance were estimated from simulated and measured stem diameter changes during the course of 1 day. The estimated parameters attained values similar to literature values. The ratios of estimated parameters to literature values ranged from 0.5 to 0.9. The model predictions (stem diameters at several heights) were in close agreement with the measurements for a period of 6 days. The time lag between changes in transpiration rate and in sap flow rate at the base of the tree was about half an hour. The analysis showed that 40% of the resistance between the soil and the top of the tree was located in the rhizosphere. Modeling the water tension gradient and consequent woody diameter changes offer a convenient means of studying the link between wood hydraulic conductivity and control of transpiration.

Models, Biological↗
PubMed2001

Free amino acids in walnut kernels and young seedlings.

We investigated the composition of free amino acids in walnut (Juglans regia L.) seeds (embryo and cotyledons). We also examined xylem transport of free amino acids in young seedlings grown in the absence of external nutrients. A relatively high concentration of free alanine was found in seed tissue, whereas a relatively high concentration of citrulline was detected in young seedlings. Citrulline was the main free amino acid transported in the xylem to stem and leaves. The negligible presence of citrulline, a non-protein amino acid, in the kernel and its presence in high concentrations in all of the tissues of young seedlings, including cotyledons, embryonic axis, taproot and stem, suggest that citrulline is synthesized during walnut germination. We conclude that citrulline plays an important role in nitrogen translocation during walnut germination.

Amino Acids↗
PubMed2002

Response of a mature Pinus laricio plantation to a three-year restriction of water supply: structural and functional acclimation to drought.

The response of mature forest stands to a reduction in water availability has received little attention. In particular, the extent to which a short-term reduction in gas exchange can be alleviated in the long-term by acclimation processes is not well understood. We studied the impact of a severe reduction in water availability on the water relations and growth of 35-year-old Pinus laricio Poiret. trees in a replicated experiment. Sapwood and needle increments, soil and tree water status, stand transpiration, xylem embolism and plant hydraulic architecture were monitored over a 3-year period in control and drought-treated plots. Needle length was reduced in drought-treated trees by 30, 19 and 29%, and sapwood increments by 50, 27 and 24% over the 3 years. Drought did not result in tree mortality or in extensive xylem embolism or foliage dieback. On the contrary, a conservative water-use strategy was observed, because minimum leaf water potentials did not differ between treatments or over the season. Plant hydraulic resistance was also unaffected by restricted water availability. Stand transpiration was strongly reduced by drought treatment over the summer, but not during the winter, despite significant differences in leaf area between control and drought-treated trees, implying higher transpiration rates per unit leaf area in the droughted plants. This suggests that water transport capacity, rather than the amount of leaf area, controlled stand transpiration, which is at variance with expectations based on experiments with seedlings and short-term experiments with mature trees.

Disasters↗
PubMed2002

Ethylene metabolism in Scots pine (Pinus sylvestris) shoots during the year.

Ethylene evolution, concentrations of 1-aminocyclopropane-1-carboxylic acid (ACC) and ACC conjugates, activities of ACC synthase and ACC oxidase, and cambial growth as measured by tracheid production were monitored from November to July in 1-year-old shoots, and between July and September in current-year shoots, of Scots pine (Pinus sylvestris L.). Needles, buds and four stem parts (cortex, phloem, cambial region and mature xylem) were surveyed. Ethylene evolution was quantified by gas chromatography. Free ACC and bound ACC (after acidic hydrolysis of ACC conjugates) were quantified by combined gas chromatography-mass spectrometry, with [2H]ACC as an internal standard. Activities of ACC synthase and ACC oxidase were measured in crude protein extracts. We detected high activities of ACC synthase in needles and buds, but not in stem fractions except the phloem. In July, during the period of intensive shoot growth, we found ACC only in buds and needles. In contrast, ACC oxidase activity was high in stem tissues, particularly in the cambial region during the period of rapid tracheid production, but no ACC oxidase activity was detected in needles and buds. Nevertheless, needles evolved large amounts of ethylene. Ethylene was produced by all stem fractions, and the peak rate of ethylene evolution in the cambial region coincided with the period of maximal tracheid production. Conjugated ACC was present in every fraction except mature xylem. The concentration of conjugated ACC decreased when rates of tracheid production and ethylene evolution were high, suggesting that conjugated ACC may serve as a source for ACC in the cambial region. The regulation of ethylene biosynthesis in Scots pine shoots is discussed.

Amino Acid Oxidoreductases↗
PubMed2002

Role of organic acids in aluminum accumulation and plant growth in Melastoma malabathricum.

Melastoma malabathricum L. (melastoma) is an Al-accumulating woody plant that grows in tropical Southeast Asia in acid soils with high aluminum (Al) concentrations and low nutrient concentrations. Because oxalate serves as a ligand for Al accumulation in melastoma leaves and citrate is the ligand associated with Al translocation from roots to shoots, we investigated the role of organic acids in the adaptation of melastoma to growth on these soils. Phosphorus starvation increased oxalate concentration in the rhizosphere, enabling melastoma to solubilize insoluble aluminum phosphate in the rhizosphere. Increased availability of P and Al in the rhizosphere enhanced growth. In the xylem sap, the concentration of citrate increased with increasing Al concentration. In contrast, the concentrations of malate, succinate and alpha-ketoglutarate in the xylem sap decreased with increasing Al concentration, suggesting that tricarboxylic acid cycle enzymes were affected by Al treatment.

Aluminum↗
PubMed2002

Effects of summer drought and winter freezing on stem hydraulic conductivity of Rhododendron species from contrasting climates.

We studied the limits to maximum water transport in three diffuse-porous evergreen shrubs exposed to frequent winter freeze-thaw events (Rhododendron maximum L. and R. catawbiense Michaux from the Appalachian Mountains) and to a severe summer drought (R. macrophyllum G. Don. from the Oregon Cascades). Percent loss of hydraulic conductivity (PLC), vulnerability curves to xylem embolism and freezing point temperatures of stems were measured over 2 years. Controlled freeze-thaw experiments were also conducted to determine the effect of thaw rate on PLC. During both years, native PLC was significantly higher in winter than in summer for R. macrophyllum. Seasonal changes in PLC were variable in both R. catawbiense and R. maximum. Only R. maximum plants growing in gaps or clearings showed higher PLC than understory plants. A rapid (2-4 day) natural recovery of high native PLC during the winter was observed in both R. maximum and R. macrophyllum. Compared with the bench-dehydration method, vulnerability curves based on the air-injection method consistently had less negative slopes and greater variation. Fifty percent PLC (PLC(50)) obtained from vulnerability curves based on the dehydration method occurred at -1.75, -2.42 and -2.96 MPa for R. catawbiense, R. maximum and R. macrophyllum, respectively. Among the study species, R. macrophyllum, which commonly experiences a summer drought, had the most negative water potential at PLC(50). In all species, stem freezing point temperatures were not consistently lower in winter than in summer. A single fast freeze-thaw event significantly increased PLC, and R. catawbiense had the highest PLC in response to freezing treatments. Recovery to control PLC values occurred if a low positive hydraulic pressure was maintained during thawing. Rhododendron macrophyllum plants, which commonly experience few freeze-thaw events, had large stem diameters, whereas plants of R. catawbiense, which had small stem diameters, suffered high embolism in response to a single freeze-thaw event. Both drought-induced and winter-induced embolism caused a significant reduction in hydraulic conductivity in all species during periods when drought or freeze-thaw events occurred in their native habitats. However, rapid recovery of PLC following freezing or drought maintained the species above their relatively low margins of safety for complete xylem dysfunction.

Climate↗
PubMed2002

Contrasting distribution and seasonal dynamics of carbohydrate reserves in stem wood of adult ring-porous sessile oak and diffuse-porous beech trees.

We tested the hypothesis that broad-leaved forest species with contrasting wood anatomy and hydraulic system (ring-porous versus diffuse-porous) also differ in distribution and seasonal dynamics of carbohydrate reserves in stem wood. Total nonstructural carbohydrate (TNC) reserves (starch and sugars) were measured enzymatically in the 10 youngest stem xylem rings of adult oak (Quercus petraea (Matt.) Liebl.) and beech (Fagus sylvatica L.) trees during an annual cycle. Radial distribution of carbohydrates was investigated according to ring age. On all dates, oak trees had twofold higher TNC concentration than beech trees (41 versus 23 mg g(DM)(-1)), with starch accounting for the high TNC concentration in oak. Seasonal dynamics of TNC concentration were significantly (P < 0.05) more pronounced in oak (20-64 mg TNC g(DM)(-1)) than in beech (17-34 mg TNC g(DM)(-1)). A marked decrease in TNC concentration was observed in oak trees during bud burst and early wood growth, whereas seasonal fluctuations in TNC concentrations in beech trees were small. The radial distribution of TNC based on ring age differed between species: TNC was restricted to the sapwood rings in oak, whereas in beech, it was distributed throughout the wood from the outermost sapwood ring to the pith. Although the high TNC concentrations in the outermost rings accounted for most of the observed seasonal pattern, all of the 10 youngest xylem rings analyzed participated in the seasonal dynamics of TNC in beech trees. The innermost sapwood rings of oak trees had low TNC concentrations. Stem growth and accumulation of carbon reserves occurred concomitantly during the first part of the season, when there was no soil water deficit. When soil water content was depleted, stem growth ceased in both species, whereas TNC accumulation was negligibly affected and continued until leaf fall. The contrasting dynamics and distribution of carbohydrate reserves in oak and beech are discussed with reference to differences in phenology, early spring growth and hydraulic properties between ring-porous trees and diffuse-porous trees.

Carbohydrate Metabolism↗
PubMed2002

Nitrogen absorption, translocation and distribution from urea applied in autumn to leaves of young potted apple (Malus domestica) trees.

We studied the absorption, assimilation, translocation and distribution of nitrogen (N) from urea applied in autumn to leaves of 1-year-old potted Fuji/M26 apple (Malus domestica Borkh) trees. In early October, all leaves of each tree were painted with either 3% urea (enriched to 10 atom % with 15N) or water (control trees). Four trees were harvested before the treatment and N and amino acid contents were determined. Four trees from each treatment were harvested at 2, 4, 7, 10, 15 and 20 days after urea or water application. Total N, amino acids and 15N in leaves, bark, xylem, shank and roots were analyzed to determine uptake and mobilization of N from urea. Most uptake of 15N by leaves occurred during the first 2 days following application of urea. The mean rate of absorption during these 2 days was 0.29 g m-2 day-1. Amino acids in leaves, bark and roots increased significantly after urea application compared with control values. The highest concentrations of amino acids in leaves and bark occurred 4 days after application, whereas the highest concentrations of amino acids in roots occurred 10 days after application. Total 15N content in leaves peaked 2 days after urea application and then decreased, whereas 15N content in roots and bark increased throughout the experiment. Total 15N content in xylem and shank was low. Leaves absorbed 35% of the 15N applied as urea, and 63.6% of absorbed 15N was translocated out of leaves within 20 days after urea application. We conclude that N from urea was converted to amino acids in leaves after foliar application in autumn, and roots and bark were the main sinks of N from urea applied to leaves.

Absorption↗
PubMed2002

Understanding the role of the cytoskeleton in wood formation in angiosperm trees: hybrid aspen (Populus tremula x P. tremuloides) as the model species.

The involvement of microfilaments and microtubules in the development of the radial and axial components of secondary xylem (wood) in hybrid aspen (Populus tremula L. x P. tremuloides Michx.) was studied by indirect immunofluorescent localization techniques. In addition to cambial cells, the differentiated cell types considered were early- and late-wood vessel elements, axial parenchyma, normal-wood fibers and gelatinous fibers, and contact and isolation ray cells. Microfilaments were rare in ray cambial cells, but were abundant and axially arranged in their derivatives once cell elongation had begun, and persisted in that orientation in mature ray cells. Microfilaments were axially arranged in fusiform cambial cells and persisted in that orientation in all xylem derivatives of those cells. Microtubules were randomly oriented in ray and fusiform cells of the cambial zone. Dense arrays of parallel-aligned microtubules were oriented near axially in the developing gelatinous fibers, but at a wide range of angles in normal-wood fibers. Ellipses of microfilaments were associated with pit development in fiber cells and isolation ray cells. Rings of co-localized microtubules and microfilaments were associated with developing inter-vessel bordered pits and vessel-contact ray cell contact pits, and, in the case of bordered pits, these rings decreased in diameter as the over-arching pit border increased in size. Although only microtubules were seen at the periphery of the perforation plate of vessel elements, a prominent meshwork of microfilaments overlaid the perforation plate itself. A consensus view of the roles of the cytoskeleton during wood formation in angiosperm trees is presented.

Actin Cytoskeleton↗
PubMed2003

Development and recovery from winter embolism in silver birch: seasonal patterns and relationships with the phenological cycle in oceanic Scotland.

Silver birch (Betula pendula Roth) is increasingly used in the United Kingdom for reforestation. However, recent evidence indicates that, under some circumstances, planted birch can suffer serious and repeated mortality of the apical leaders and branches, with consequent loss of apical dominance and the formation of a contorted stem. Plants from 37 seed sources of silver birch from Scotland and northern England planted at two sites were compared for several characteristics related to hydraulic architecture, vulnerability to freeze-thaw cycle induced embolism and spring recovery from winter embolism during the period 2000-2002. Phenological rhythms were also monitored in late winter-early spring to document relationships between phenology and water relations parameters. Significant differences were found across seed sources in stage of bud flushing for four dates in spring. Early flushing seed sources differed by about 1 to 2 weeks from late-flushing seed sources across the two sites. Wintertime xylem embolism in stems reached a peak of about 50 to 70% loss of xylem hydraulic conductivity, depending on the size and position of the sample shoots in the canopy. Small apical shoots were significantly more embolized than large basal shoots. Development of winter embolism was coupled to the occurrence of frost events. As percent loss of hydraulic conductivity increased during the winter, wood relative water content declined. Embolism reversal occurred rapidly in spring at the time of development of positive root pressure. No significant differences in the degree of winter embolism in 2001 were found among the three seed sources examined. The investigation was expanded in the winter-spring of 2002 to include 10 seed sources across both sites. Significant differences were found in degree of winter embolism across sites, dates and seed sources. For each date, there was a significant relationship between flushing scores and wood relative water contents across the two sites and all seed sources, suggesting that differences in time of flushing across sites and seed sources were likely caused by differences in the time of occurrence of root pressure, a necessary precondition to flushing.

Betula↗
PubMed2003

Ecophysiology of riparian cottonwoods: stream flow dependency, water relations and restoration.

Cottonwoods (Populus spp.) are adapted to riparian or floodplain zones throughout the Northern Hemisphere; they are also used as parents for fast-growing hybrid poplars. We review recent ecophysiological studies of the native cottonwoods Populus angustifolia James, P. balsamifera L., P. deltoides Marsh., P. fremontii S. Watson and P. trichocarpa T. & G. in North America, and P. nigra L. in Europe. Variation exists within and across species and hybrids; however, all riparian cottonwoods are dependent on shallow alluvial groundwater that is linked to stream water, particularly in semi-arid regions. This conclusion is based on studies of their natural occurrence, decline following river damming and dewatering (water removal), water relations, isotopic composition of xylem water, and by the establishment of cottonwoods along formerly barren natural channels after flow augmentation in response to the conveyance of irrigation water. When alluvial groundwater is depleted as a result of river dewatering or groundwater pumping, riparian cottonwoods exhibit drought-stress responses including stomatal closure and reduced transpiration and photosynthesis, altered 13C composition, reduced predawn and midday water potentials, and xylem cavitation. These physiological responses are accompanied by morphological responses including reduced shoot growth, altered root growth, branch sacrifice and crown die-back. In severe cases, mortality occurs. For example, severe dewatering of channels of the braided Big Lost River in Idaho led to mortality of the narrowleaf cottonwood, P. angustifolia, and adjacent sandbar willows, Salix exigua Nutt., within 5 years, whereas riparian woodlands thrived along flowing channels nearby. The conservation and restoration of cottonwoods will rely on the provision of river flow regimes that satisfy these ecophysiological requirements for survival, growth and reproduction.

Adaptation, Physiological↗
PubMed2003

Photosynthate distribution patterns in cherrybark oak seedling sprouts.

We used 14C tracers to determine photosynthate distribution in cherrybark oak (Quercus pagoda Raf.) seedling sprouts following release from competing mid-story vegetation. Fall acquisition of labeled photosynthates by seedlings followed expected source-sink patterns, with root and basal stem tissues serving as the primary sinks. Four months after the seedlings had been labeled with 14C, they were clipped to induce sprouting. First-flush stem and leaf tissues of the resulting seedling sprouts were the primary sinks for labeled photosynthates stored in root tissues. Second-flush stem and leaf tissues, and first-flush stem and leaf tissues the following growing season, were not primary sinks for labeled photosynthates stored in root tissues despite the high radioactivity in root tissues. Root tissues appeared to deposit photosynthates in a layering process whereby the last photosynthates stored in new xylem were the first to be depleted during the initiation of a growth flush the following spring. There were more labeled photosynthates in roots of released seedling sprouts compared with non-released seedling sprouts, indicating increased vigor of released seedling sprouts in response to greater light availability. In contrast, stem and source leaf tissues of non-released seedling sprouts contained greater percentages of labeled photosynthates compared with released seedling sprouts, indicating either greater sink strength or poorly developed xylem and phloem pathways that created inefficiencies in distribution to root tissues. The 14C distribution coefficients confirmed the distribution patterns and provided additional information on the important sinks in released and non-released cherrybark oak seedling sprouts.

Photosynthesis↗
PubMed2004

Distribution and partial characterization of seasonally expressed proteins in different aged shoots and roots of 'Loring' peach (Prunus persica).

During autumnal leaf senescence, leaf nitrogen in deciduous trees is translocated to storage sites, especially bark and xylem tissues. Proteins that accumulate in large amounts in bark and xylem in winter and are absent from these organs in summer are called storage proteins, and are believed to be vehicles for storing nitrogen reserves. These reserves are important for spring growth and help trees tolerate or recover from both abiotic and biotic stresses. Based on seasonal patterns of accumulation, we previously identified three storage proteins with molecular masses of 60, 19 and 16 kDa in bark tissues of 'Loring' peach (Prunus persica (L.) Batsch). To characterize the distribution of these proteins in different-aged tissues and to determine if they have any function other than nitrogen storage, we examined their seasonal distribution in bark tissues of current-year and 1-year-old shoots, scaffold branches, main trunks and 4-5-year-old roots of 'Loring' peach. Verification of protein identity was based on molecular mass and reactions with antibodies directed against each specific protein. Protein distribution was variable. For all three proteins, the greatest amount was present in mid-winter in current-year and 1-year-old shoots. These tissues also showed the greatest seasonal variation in the amount of protein present. The 16 kDa protein was present only in the youngest shoots, whereas the 19 kDa protein was present in all tissues examined. The 60 kDa protein was absent in root tissue. The amino acid composition and sequence of each protein were determined. The 60 kDa protein was identified as a dehydrin, and the 19 kDa protein appeared to be related to a family of allergen proteins in Rosaceous plants, some members of which are associated with pathogenesis-related proteins. The amino acid sequence of the 16 kDa protein appeared to have no homology with any proteins in the SwissProt database. Therefore, it is likely that the 16 kDa protein, in a strict sense, is a bark storage protein. Defining storage proteins solely by their pattern of accumulation and the extent to which they accumulate may not be a good functional definition. It is possible that storage proteins have functional roles in addition to nitrogen storage.

Electrophoresis, Polyacrylamide Gel↗
PubMed2004

Trophic control of bud break in peach (Prunus persica) trees: a possible role of hexoses.

Vegetative buds of peach (Prunus persica L. Batsch.) trees act as strong sinks and their bud break capacity can be profoundly affected by carbohydrate availability during the rest period (November-February). Analysis of xylem sap revealed seasonal changes in concentrations of sorbitol and hexoses (glucose and fructose). Sorbitol concentrations decreased and hexose concentrations increased with increasing bud break capacity. Sucrose concentration in xylem sap increased significantly but remained low. To clarify their respective roles in the early events of bud break, carbohydrate concentrations and uptake rates, and activities of NAD-dependent sorbitol dehydrogenase (SDH), sorbitol oxidase (SOX) and cell wall invertase (CWI) were determined in meristematic tissues, cushion tissues and stem segments. Only CWI activity increased in meristematic tissues shortly before bud break. In buds displaying high bud break capacity (during January and February), concentrations of sorbitol and sucrose in meristematic tissues were almost unchanged, paralleling their low rates of uptake and utilization by meristematic tissues, and indicating that sorbitol and sucrose play a negligible role in the bud break process. Hexose concentrations in meristematic tissues and glucose imported by meristematic tissues correlated positively with bud break capacity, suggesting that hexoses are involved in the early events of bud break. These findings were confirmed by data for buds that were unable to break because they had been collected from trees deprived of cold. We therefore conclude that hexoses are of greater importance than sorbitol or sucrose in the early events of bud break in peach trees.

Carbohydrates↗
PubMed2005

Seasonal variation in gene expression for loblolly pines (Pinus taeda) from different geographical regions.

In developing xylem, gene expression levels vary in different genotypes, at different stages of development, throughout a growing season, and in response to stresses. Commercially important characteristics such as wood-specific gravity are known to differ with seed source. For example, when grown on a common site, the specific gravity of Arkansas loblolly pine (Pinus taeda L.) trees is greater than that of Louisiana loblolly pine, and Texas loblolly pines have a greater specific gravity than loblolly pines from the Atlantic coast. A microarray analysis was performed to examine variation in gene expression among trees from different geographical sources when grown on a common site, and seasonal variation in gene expression in each seed source. We used microarrays containing 2171 expressed sequence tags (ESTs) with putative functions of interest, selected from several loblolly pine xylem partial cDNA libraries and a shoot tip library. Genes with significant variation in expression for each factor were identified. Many genes preferentially expressed in latewood compared with earlywood were for proteins involved in cell wall biosynthesis. Variation in gene expression among trees from the two seed sources in each growing season suggests that there may be more differences between South Arkansas trees and South Louisiana trees in latewood than in earlywood. Variation in gene expression among trees from different regions may reflect adaptation to different environments.

Gene Expression Profiling↗
PubMed2005

Modeling the dynamics of pressure propagation and diameter variation in tree sapwood.

A non-steady-state model of water tension propagation in tree stems was developed. The model is based on the cohesion theory and the assumption that fluctuating water tension driven by transpiration together with the elasticity of wood cause variations in the diameter of a tree stem. The change in xylem diameter can be linked to water tension in accordance with Hooke's law. The model was tested against field measurements of the diurnal change in xylem diameter at different heights in a 180-year-old Scots pine tree at Hyytiälä, southern Finland. Model predictions agreed well with measurements. The effect of tree dimensions on pressure propagation was examined with the model. The model outcomes were also consistent with results of several field measurements presented in the literature.

Models, Biological↗