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At least 127 records · Page 7Linked to original sources
PubMed2006

Impacts of forest fragmentation on the mating system and genetic diversity of white spruce (Picea glauca) at the landscape level.

We studied the mating system of white spruce (Picea glauca) in a landscape fragmented by agriculture in northern Ontario, Canada. We sampled 23 stands that ranged in size from 1 to >500 trees isolated by 250-3000 m from the nearest other stand. Six polymorphic allozyme loci from four enzyme systems were used to genotype approximately 10 000 embryos from 104 families. We detected no allele frequency heterogeneity in the pollen pool among stands or families (Phi(FT)=-0.025). Overall, estimates of outcrossing were high (t(m)=94% and mean t(s)=91%) but significantly different from unity. Bi-parental inbreeding (t(m)-t(s)=3.2%) was low but significantly different from zero. Allozyme-based outcrossing estimates did not differ significantly among three stand-size classes (SSCs): small (<10 trees), medium (10-100 trees) and large (> or =100 trees). The number of effective pollen donors was high in all SSCs, but was significantly lower in small stands (N(ep)=62.5) than in medium-sized and large stands (both N(ep)=143). The primary selfing rate was significantly higher in medium stands than in large stands. We found no significant difference in genetic diversity measures in the filial (seed) population among SSCs. Overall, these results indicate that white spruce stands in this fragmented landscape are resistant to genetic diversity losses, primarily through high pollen-mediated gene-flow and early selection against inbred embryos. We discuss the importance of using seed data, in conjunction with genetic data, to evaluate the impacts of fragmentation on natural populations.

Canada↗
PubMed2003

Re-organisation of the cytoskeleton during developmental programmed cell death in Picea abies embryos.

Cell and tissue patterning in plant embryo development is well documented. Moreover, it has recently been shown that successful embryogenesis is reliant on programmed cell death (PCD). The cytoskeleton governs cell morphogenesis. However, surprisingly little is known about the role of the cytoskeleton in plant embryogenesis and associated PCD. We have used the gymnosperm, Picea abies, somatic embryogenesis model system to address this question. Formation of the apical-basal embryonic pattern in P. abies proceeds through the establishment of three major cell types: the meristematic cells of the embryonal mass on one pole and the terminally differentiated suspensor cells on the other, separated by the embryonal tube cells. The organisation of microtubules and F-actin changes successively from the embryonal mass towards the distal end of the embryo suspensor. The microtubule arrays appear normal in the embryonal mass cells, but the microtubule network is partially disorganised in the embryonal tube cells and the microtubules disrupted in the suspensor cells. In the same embryos, the microtubule-associated protein, MAP-65, is bound only to organised microtubules. In contrast, in a developmentally arrested cell line, which is incapable of normal embryonic pattern formation, MAP-65 does not bind the cortical microtubules and we suggest that this is a criterion for proembryogenic masses (PEMs) to passage into early embryogeny. In embryos, the organisation of F-actin gradually changes from a fine network in the embryonal mass cells to thick cables in the suspensor cells in which the microtubule network is completely degraded. F-actin de-polymerisation drugs abolish normal embryonic pattern formation and associated PCD in the suspensor, strongly suggesting that the actin network is vital in this PCD pathway.

Actins↗
PubMed2003

Two new anti-tumor promoting serratane-type triterpenoids from the stem bark of Picea jezoensis var. jezoensis.

Two new serratane-type triterpenoids, 1 and 2, were isolated from the stem bark of Picea jezoensis Carr. var. jezoensis (Pinaceae). Their structures were determined to be 3beta-methoxyserrat-13-en-21beta-ol (1) and 13beta, l4beta-epoxy-3beta-methoxyserratan-21beta-ol (2) on the basis of spectroscopic methods and partial syntheses. Compounds 1 and 2 and their acetates were screened as potential anti-tumor promoters by using the in vitro short-term 12-O-tetradecanoylphorbol 13-acetate (TPA)-induced Epstein-Barr virus early antigen (EBV-EA) activation assay. IC50 value evaluation showed that compound 1 was more effective than others. In addition, compounds 1 and 2 were examined for anti-tumor promoting activities in a two-stage carcinogenesis assay of mouse skin tumors induced by 7,12-dimethylbenz[a]anthracene (DMBA) as an initiator and TPA as a promoter. Compounds 1 and 2 exhibited significant anti-tumor promoting effects on mouse skin carcinogenesis.

Animals↗
PubMed2004

A new seco-abietane-type diterpene from the stem bark of Picea glehni.

A new seco-abietane-type diterpenoid, 13S-hydroxy-9-oxo-9,10-seco-abiet-8(14)-en-18,10alpha-olide (1) along with a known lignan compound, pinoresinol (2) was isolated from the stem bark of Picea glehni (Fr. Schm.) Masters. Spectroscopic methods and chemical conversions were used to establish the structure of 1. In order to assess their cancer chemopreventive potential, the inhibition of Epstein-Barr virus early antigen (EBV-EA) activation induced by 12-O-tetradecanoylphorbol 13-acetate (TPA) was examined for compound 1, its synthetic analogue, 9,10-seco-8S,13S-epoxy-abiet-8(14)-en-18,10alpha-olide (la) and 2. The inhibitory effect of la on EBV-EA induction was strong (0, 20.7, 67.1 and 89.2 % inhibition at 1000, 500,100 and 10 mol ratio/TPA). The IC50 of la was 226 mol ratio/32 pmol/TPA.

Abietanes↗
PubMed2005

Crown allometry and growing space efficiency of Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica L.) in pure and mixed stands.

In pure and mixed stands of Norway spruce ( Picea abies [L.] Karst.) and European beech ( Fagus sylvatica L.) we have analyzed crown allometry and growing space efficiency at the tree level and have scaled this from tree level to stand level production. Allometry is quantified by the ratio A between the relative growth rates of laterally and vertically oriented tree dimensions. Efficiency parameters, EOC for efficiency in space occupation, EEX for efficiency in space exploitation, and EBI for efficiency in biomass investment, were evaluated, based on quantity and quality of growing space and were measured using crown size and competition index. The evaluation reveals why pure stands of spruce are preferred by foresters, even though the natural vegetation would be dominated by beech. Spruce occupies its share of resources intensively by means of tightly packed pillar-like crowns, whereas beech seizes resources extensively by means of a multi-layered, veil-like canopy. With a given relative biomass increment, beech achieves a 57 % higher increment in crown projection area and a 127 % higher increment in height due to its particular capacity of lateral and vertical expansion. Beech trees are approximately 60 % more efficient in space occupation than spruce trees, however, on average, they are about 70 % less efficient in space exploitation. As a vertical fast growing tree, spruce is efficient in space exploitation under constant conditions, but far more susceptible to disturbances and less well equipped to overcome them when compared with beech. Beech is weaker in terms of space exploitation, while being superior in space occupation, where it encircles competitors and fills gaps after disturbances, which is a successful long-term strategy. A mixture of the two species reduces stand level production by 24 % in comparison to a pure spruce stand, however, when considering enhanced stabilization of the whole stand and risk distribution in the long term, the mixed stand may exceed the production level of pure spruce stands. EEX reflects a strong ontogenetic drift and competition effect that should be considered when scaling from tree to stand level production.

Ecosystem↗
PubMed2005

Growth of adult Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica L.) under free-air ozone fumigation.

This study attempted to detect the impact of ozone on adult trees of Norway spruce ( Picea abies [L.] Karst.) and European beech ( Fagus sylvatica L.) in an experimental mixed stand in Southern Bavaria, Germany. The aim was to examine whether there is a decrease in growth when trees are exposed to higher than atmospheric concentrations of ozone. This exposure was put into effect using a free-air fumigation system at tree crown level. Growth analysis was carried out on a group of 47 spruce and 36 beech trees, where radial stem increment at breast height - a sensitive index for stress - was measured. The ozone monitoring system allowed values to be obtained for the accumulated ozone exposure (SUM00) of each individual tree, so that their radial increment over three years could be correlated with the corresponding ozone exposure for the same time period. Correlation and regression analysis were then carried out to test the influence of ozone on diameter increment. In both spruce and beech, the initial stem diameter was the most influential factor on radial increment in the following year. A linear model was applied, including the diameter of the preceding year and the ozone exposure of the current year as predicting factors. For spruce trees, a significant negative influence of ozone exposure was found. In contrast, no significant ozone effect on diameter increment of beech was detected. The effect of ozone stress on a large spruce tree can lead to a decrease in potential radial increment of 22 %. The results are discussed in relation to other stress factors such as drought and lack of light.

Fagus↗
PubMed2005

Acclimation to ozone affects host/pathogen interaction and competitiveness for nitrogen in juvenile Fagus sylvatica and Picea abies trees infected with Phytophthora citricola.

In a two-year phytotron study, juvenile trees of European beech (Fagus sylvatica) and Norway spruce (Picea abies) were grown in mixture under ambient and twice ambient ozone (O3) and infected with the root pathogen Phytophthora citricola. We investigated the influence of O3 on the trees' susceptibility to the root pathogen and assessed, through a 15N-labelling experiment, the impact of both treatments (O3 exposure and infection) on belowground competitiveness. The hypotheses tested were that: (1) both P. citricola and O3 reduce the belowground competitiveness (in view of N acquisition), and (2) that susceptibility to P. citricola infection is reduced through acclimation to enhanced O3 exposure. Belowground competitiveness was quantified via cost/benefit relationships, i.e., the ratio of structural investment in roots relative to their uptake of 15N. Beech had a lower biomass acquisition and captured less 15N under enhanced O3 and P. citricola infection alone than spruce, whereas the latter species appeared to profit from the lower resource acquisition of beech in these treatments. Nevertheless, in the combined treatment, susceptibility to P. citricola of spruce was increased, while beech growth and 15N uptake were not further reduced below the levels found under the single treatments. Potential trade-offs between stress defence, growth performance, and associated nitrogen status are discussed for trees affected through O3 and/or pathogen infection. With respect to growth performance, it is concluded that O3 enhances susceptibility to the pathogen in spruce, but apparently raises the defence capacity in beech..

Acclimatization↗
PubMed2006

Genetic diversity of Picea asperata populations based on RAPDs.

The genetic diversity of ten natural populations of Picea asperata Mast. were studied using RAPD markers. A total of 160 reproducible fragments were produced from the ten primers used. The mean number of fragments detected per individual was 114.7. Altogether 120 fragments were polymorphic among the ten populations, none of them were found to be population-specific. Nei's expected heterozygosity (H (e)) ranged from 0.233 to 0.269, and the average was 0.247. The analysis of molecular variance revealed that the coefficient of gene differentiation among populations, based on F (ST) and the unbiased estimate PhiST, equaled 0.224 and 0.290, respectively. Such high values indicate that there is significant differentiation among populations, which could result from several factors, including restricted gene flow between populations (Nm = 0.866). Founder events may be another factor attributing to the high level of genetic differentiation. In addition, it was discovered that the geographic distribution is not correlated with the genetic distances among the populations of P. asperata.

Genetic Markers↗
PubMed2004

Comparative seedling ecology of eight North American spruce (Picea) species in relation to their geographic ranges.

BACKGROUND AND AIMS: Allowing for dispersal limitation, a species' geographic distribution should reflect its environmental requirements. Comparisons among closely related species should reveal adaptive differentiation in species characteristics that are consistent with their differences in geographic distribution. This expectation was tested by comparing characteristics of seedlings of spruce species in relation to environmental factors representative of their current natural ranges. METHODS: Seedlings were grown from a total of 34 populations representing eight North American spruce (Picea) species in a controlled environment chamber for 140 d. Traits related to the potential of seedling establishment, including tolerance to stress events (high temperature, desiccation) were evaluated. Correlations were sought between these characteristics and modal values of latitude, aridity and continentality in the geographic range of each species. KEY RESULTS: Many seedling traits changed significantly in response to stress events, but only the response of chlorophyll concentration differed significantly among species. Components of seedling growth were good correlates of species distribution. Seedling relative growth rate (RGR) and specific leaf area (SLA) were positively correlated with latitude, and leaf weight ratio (LWR) negatively correlated with aridity. Seed mass was negatively correlated with latitude. CONCLUSIONS: Relationships found between seedling traits and geographical variation in environmental conditions suggest that factors such as temperature regime, water availability and perhaps litter depth affect species range in North American spruces. Seedling characteristics appear to be elements in a reasonably distinct environmental niche for each spruce species at the continental scale.

Chlorophyll↗
PubMed2005

Effects of plant leachates from four boreal understorey species on soil N mineralization, and white spruce (Picea glauca) germination and seedling growth.

BACKGROUND AND AIMS: Natural regeneration of white spruce (Picea glauca) after disturbance has been reported to be very poor. Here a study was made to determine whether C compounds released from understorey species growing together with white spruce could be involved in this regeneration failure, either by (1) changing soil nutrient dynamics, (2) inhibiting germination, and/or (3) delaying seedling growth. METHODS: Foliage leachates were obtained from two shrubs (Ledum palustre and Empetrum hermaphroditum) and one bryophyte (Sphagnum sp.) with high phenolic compound concentrations that have been reported to depress growth of conifers in boreal forests, and, as a comparison, one bryophyte (Hylocomium splendens) with negligible phenolic compounds. Mineral soil from a white spruce forest was amended with plant leachates to examine the effect of each species on net N mineralization. Additionally, white spruce seeds and seedlings were watered with plant leachates to determine their effects on germination and growth. KEY RESULTS: Leachates from the shrubs L. palustre and E. hermaphroditum contained high phenolic compound concentrations and dissolved organic carbon (DOC), while no detectable levels of C compounds were released from the bryophytes Sphagnum sp. or H. splendens. A decrease in net N mineralization was determined in soils amended with L. palustre or E. hermaphroditum leachates, and this effect was inversely proportional to the phenolic concentrations, DOC and leachate C/N ratio. The total percentage of white spruce germination and the growth of white spruce seedlings were similar among treatments. CONCLUSIONS: These results suggest that the shrubs L. palustre and E. hermaphroditum could negatively affect the performance of white spruce due to a decrease in soil N availability, but not by direct effects on plant physiology.

Bryophyta↗
PubMed2006

Effect of local heating and cooling on cambial activity and cell differentiation in the stem of Norway spruce (Picea abies).

UNLABELLED: BACKGROUND AND AIMS The effect of heating and cooling on cambial activity and cell differentiation in part of the stem of Norway spruce (Picea abies) was investigated. METHODS: A heating experiment (23-25 degrees C) was carried out in spring, before normal reactivation of the cambium, and cooling (9-11 degrees C) at the height of cambial activity in summer. The cambium, xylem and phloem were investigated by means of light- and transmission electron microscopy and UV-microspectrophotometry in tissues sampled from living trees. KEY RESULTS: Localized heating for 10 d initiated cambial divisions on the phloem side and after 20 d also on the xylem side. In a control tree, regular cambial activity started after 30 d. In the heat-treated sample, up to 15 earlywood cells undergoing differentiation were found to be present. The response of the cambium to stem cooling was less pronounced, and no anatomical differences were detected between the control and cool-treated samples after 10 or 20 d. After 30 d, latewood started to form in the sample exposed to cooling. In addition, almost no radially expanding tracheids were observed and the cambium consisted of only five layers of cells. Low temperatures reduced cambial activity, as indicated by the decreased proportion of latewood. On the phloem side, no alterations were observed among cool-treated and non-treated samples. CONCLUSIONS: Heating and cooling can influence cambial activity and cell differentiation in Norway spruce. However, at the ultrastructural and topochemical levels, no changes were observed in the pattern of secondary cell-wall formation and lignification or in lignin structure, respectively.

Cell Differentiation↗
PubMed2001

An improved procedure for production of white spruce (Picea glauca) transgenic plants using Agrobacterium tumefaciens.

An efficient and reproducible procedure for the transformation of white spruce (Picea glauca [Moench] Voss) embryogenic tissues was developed using A. tumefaciens-mediated gene transfer. Rapidly dividing white spruce embryogenic tissues were co-cultivated with disarmed A. tumefaciens strains containing additional copies of the virulence regions from plasmid PToK47. The plasmid pBi121, containing the neomycin phosphotransferase II (nptII) gene providing kanamycin resistance as a selectable marker and the beta-glucuronidase (uidA) reporter gene, was used as binary vector. The highest frequency of transformation (15 transformed tissues g(-1) FW of treated embryogenic tissue) was obtained with 5-d-old tissues grown in liquid medium and co-cultivated with Agrobacterium for 2 d in the same medium but containing 50 microM acetosyringone. Recovery of kanamycin-resistant tissues was improved when tissues were first grown for 10 d on a timentin-containing medium (400 mg l(-1)), to prevent bacterial overgrowth, before application of the selection pressure. After 6 weeks on kanamycin-selection medium, resistant tissues were obtained and showed stable uidA expression. The presence of the transgenes was demonstrated by PCR analysis and their integration into the genome was confirmed by Southern hybridization. Transgenic plants were regenerated from transformed tissues within 4 months after co-culture.

Agrobacterium tumefaciens↗
PubMed2002

High expression of putative aquaporin genes in cells with transporting and nutritive functions during seed development in Norway spruce (Picea abies).

Aquaporins mediate the bidirectional passage of water over membranes and are present in tonoplasts (TIPs) and in plasma membranes (PIPs) of plant cells. Knowing their expression in different tissues is valuable when assessing their contribution to plant water relations. A TIP-gene has been cloned from developing female gametophytes of Picea abies, a conifer displaying an embryology different from the angiosperms. Probes were made from conserved regions of the TIP gene and used for in situ hybridization to examine the gene expression pattern in developing female reproductive structures. Early during development high transcript expression was found in the spongy tissue encasing the developing female gametophyte, in cells of the future seed coat of young ovules and in vascular tissue of the ovuliferous scale. At later stages a strong signal was seen in archegonia jacket cells surrounding egg cells and, still later, at the time of storage protein accumulation, in storage parenchyma cells of the gametophyte as well. These aquaporin-homologues probably participate in regulating water balance in the cells although they could also be permeable to other molecules than water.

Amino Acid Sequence↗
PubMed2003

Expression of the viviparous 1 (Pavp1) and p34cdc2 protein kinase (cdc2Pa) genes during somatic embryogenesis in Norway spruce (Picea abies [L.] Karst).

Detailed expression analysis of the Norway spruce (Picea abies [L.] Karst) Viviparous 1 (Pavp1) and p34cdc2 (cdc2Pa) genes was carried out during somatic embryogenesis. Pavp1, a gene associated with embryo development, was expressed in proliferating embryogenic suspension cultures in the absence of exogenous ABA. When somatic embryo formation was promoting by blocking proliferation, Pavp1 expression was reduced. During maturation, exogenous ABA induced increased Pavp1 expression, which peaked at the early cotyledonary stage of somatic embryogenesis. Following partial desiccation of mature somatic embryos at high relative humidity, Pavp1 expression persisted under germination conditions. Pavp1 expression was also detected in non-dormant immature male strobili and dormant terminal buds. These data confirm the functional conservation of Pavp1 during the evolution of seed plants and extend its function beyond the embryo. Cdc2Pa, a gene associated with the cell cycle, was up-regulated when the proliferation of embryogenic cells was blocked. Expression was again up-regulated in early embryogeny and again during germination. The implications of this up-regulation of cdc2Pa are discussed.

Abscisic Acid↗
PubMed2006

Temporal and spatial pattern of embolism induced by pressure collar techniques in twigs of Picea abies.

The pressure collar technique enables the induction of embolism in plant xylem. This artificial cavitation is based on air seeding processes which occur when specific pressure gradients between the air and water phase of the xylem are exceeded. Standard pressure collars and a new point injection technique, which builds up a local potential gradient, were used to study the time and spatial pattern of this process. On twigs of Norway spruce (Picea abies), the cross-sectional and axial pattern, and the time-course of embolism formation were analysed via conductivity and ultrasonic measurements as well as staining experiments. Furthermore, the release of air from the twig surface was studied by immersing twig sections in water. In cross-sections, embolized areas induced by the point injection technique were smaller compared with the standard collar and restricted to a circle sector. Embolism propagated from the pressure collar towards the nearest distal and proximal nodes but not further. A release of air was also observed predominantly at the internode attached to the pressure collar. Embolism rates increased within minutes and reached approximately 80% loss of conductivity after 10 min treatment with the standard collar. The size of air entry points and embolism rates correlated significantly. Embolism formation in wood therefore depends not only on vulnerability thresholds but also on the extent of air-water interfaces within the xylem and on the time of exposure to pressure gradients. These aspects and the propagation of pressure within samples are crucial for pressure collar experiments. In addition, wood architecture influences the extent and pattern of embolism caused by air seeding processes.

Air↗
PubMed2001

Role of boron in drought resistance in Norway spruce (Picea abies) seedlings.

Norway spruce (Picea abies (L.) Karst.) seedlings fertilized with boron (B) at three rates were grown in a 3:7 mix of forest humus and quartz sand for 18 weeks. Half of the seedlings were not watered during the last 9 days of the experiment (drought treatment). The role of B in drought resistance was assessed by comparing the effects of seedling internal B concentration on the water relations, photosynthesis, growth and nutrition of well-watered and drought-treated seedlings. At the end of the drought treatment, needle B concentrations were 7.0 mg x kg(-1) at the lowest B supply rate and 17.5 and 23.5 mg x kg(-1), respectively, at the higher supply rates. Seedlings at the lowest B supply rate had fewer root tips and mycorrhizas than seedlings at the higher B supply rates. Drought treatment had a more pronounced effect on the water relations and net photosynthetic rate of seedlings than B treatment. Although seedlings at the higher B supply rates lost water more rapidly than seedlings at the low B supply rate-leading to faster stomatal closure and decreased photosynthesis-drought did not affect their final height, whereas drought reduced height growth of seedlings at the low B supply rate.

Boron↗
PubMed2001

Carbon dioxide concentration and nitrogen input affect the C and N storage pools in Amanita muscaria-Picea abies mycorrhizae.

We studied the influence of elevated atmospheric CO2 concentration ([CO2]) on the vacuolar storage pool of nitrogen-containing compounds and on the glycogen pool in the hyphal sheath of Amanita muscaria (L. ex Fr.) Hooker-Picea abies L. Karst. mycorrhizae grown with two concentrations of ammonium in the substrate. Mycorrhizal seedlings were grown in petri dishes on agar containing 5.3 or 53 mg N l(-1) and exposed to 350 or 700 microl CO2 l(-1) for 5 or 7 weeks, respectively. Numbers and area of nitrogen-containing bodies in the vacuoles of the mycorrhizal fungus were determined by light microscopy linked to an image analysis system. The relative concentration of nitrogen in the vacuolar bodies was measured by electron energy loss spectroscopy (EELS). Glycogen stored in the cytosol was determined at the ultrastructural level by image analysis after staining the sections (PATAg test). Shoot dry weight, net photosynthesis and relative amounts of N in vacuolar bodies were greater at the higher N and CO2 concentrations. The numbers and areas of vacuolar N-containing bodies were significantly greater at the higher N concentration only at ambient [CO2]. In the same treatment the percentage of hyphae containing glycogen declined to nearly zero. We conclude that, in the high N/low [CO2] treatment, the mycorrhizal fungus had an insufficient carbohydrate supply, partly because of increased amino acid synthesis by the non-mycorrhizal rootlets. When [CO2] was increased, the equilibrium between storage of glycogen and N-containing compounds was reestablished.

Amanita↗
PubMed2001

Dynamics of water storage in mature subalpine Picea abies: temporal and spatial patterns of change in stem radius.

Internal water reserves in bark and foliage of trees contribute to transpiration (T) and play an essential role in optimizing water transport by buffering extreme peaks of water consumption. We examined patterns of stem shrinkage and their relationship to tree water dynamics. We measured fluctuations in root radius and stem radius at different stem heights, T of twigs at the top of the crown and sap flow velocities in stem sections of mature subalpine Norway spruce (Picea abies (L.) Karst.) trees over 2 years. The output of each sensor was coupled by physical functions to a mechanistic flow and storage model of tree water relations. The data verified the model-predicted lag in water storage depletion in response to the onset of transpiration and the lag increased with increasing distance from the crown periphery. Between the crown and stem base, the delay ranged from a few minutes to several hours, depending on microclimatic conditions and tree water status. Stem volume changes were proportional to the amount of water exchanged between the elastic tissues of the bark and the rigid xylem, indicating that the "peristaltic" wave of stem contraction along the flow path represented depletion of water stored in bark. On a daily basis, stems lost between 0.2 and 0.5% of their volume as a result of bark dehydration, corresponding to about 2 to 5 l of water. This water contributed directly to T. According to the model based on hydraulic principles, there are three main components underlying the dynamics of water storage depletion: flow resistance, storage capacities of needles and bark, and T of each tree section. The resistances and capacities were proportional to the response delay, whereas T in the lower parts of the tree was inversely proportional. The pattern of T within the crown depended on water intercepted by the branches. Because of these weather-dependent factors, there was no time constant for the response delay along the flow path. Nevertheless, the upper crown and the root section tended to have longer response delays per meter of flow path than the stem. The diurnal course of stem radius fluctuations represents the sum of all external and internal conditions affecting tree water relations; stem radius fluctuations, therefore, provide a sensitive measure of tree water status.

Picea↗