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PubMed2002

SAGE profiling and demonstration of differential gene expression along the axial developmental gradient of lignifying xylem in loblolly pine (Pinus taeda).

Wood formation has been studied extensively at the cellular and biochemical levels, but remains poorly understood with respect to gene expression and regulation. As a first step toward identifying genes specifically involved in wood formation and characterizing their roles in determining wood quality, serial analysis of gene expression (SAGE) was used to quantify gene expression in lignifying xylem from a single, 10-year-old loblolly pine (Pinus taeda L.). Two SAGE libraries were generated based on lignifying xylem isolated from either the upper (crown) or lower (base) portions of the trunk. Over 85,000 tags representing a maximum of 27,398 expressed genes were analyzed from the crown wood library, and more than 65,000 tags, representing a maximum of 25,983 expressed genes, were analyzed in the base wood library. Combining these data sets to reflect the sum of genes expressed in lignifying xylem, 150,855 tags were cataloged, representing a maximum of 42,641 different genes. Currently, this study represents the most extensive analysis of its kind in a higher plant and provides a quantitative description of the transcriptome representing the lignifying xylem of a 10-year-old loblolly pine.

DNA, Complementary↗

PubMed1996

Nitrogen metabolism in Lignifying Pinus taeda cell cultures.

The primary metabolic fate of phyenylalanine, following its deamination in plants, is conscription of its carbon skeleton for lignin, suberin, flavonoid, and related metabolite formation. Since this accounts for approximately 30-40% of all organic carbon, an effective means of recycling the liberated ammonium ion must be operative. In order to establish how this occurs, the uptake and metabolism of various 15N-labeled precursors (15N-Phe, 15NH4Cl, 15N-Gln, and 15N-Glu) in lignifying Pinus taeda cell cultures was investigated, using a combination of high performance liquid chromatography, 15N NMR, and gas chromatograph-mass spectrometry analyses. It was found that the ammonium ion released during active phenylpropanoid metabolism was not made available for general amino acid/protein synthesis. Rather it was rapidly recycled back to regenerate phenylalanine, thereby providing an effective means of maintaining active phenylpropanoid metabolism with no additional nitrogen requirement. These results strongly suggest that, in lignifying cells, ammonium ion reassimilation is tightly compartmentalized.

Amino Acids↗

PubMed1999

Monoterpene synthases of loblolly pine (Pinus taeda) produce pinene isomers and enantiomers.

The turpentine fraction of conifer oleoresin is a complex mixture of monoterpene olefins and plays important roles in defense and in the mediation of chemical communication between conifer hosts and insect predators. The stereochemistry of the turpentine monoterpenes is critical in these interactions, influencing host recognition, toxicity, and potency of derived pheromones, and the stereochemical composition of these compounds lends insight into their biogenetic origin, with implications for the numbers and types of enzymes responsible and their corresponding genes. Analysis of the oleoresin from several tissues of loblolly pine (Pinus taeda) showed the derived turpentine to consist mainly of (+)-(3R:5R)-alpha-pinene and (-)-(3S:5S)-beta-pinene. Cell-free extracts from xylem tissue yielded three monoterpene synthases which together account for the monoterpene isomer and enantiomer content of the turpentine of this tissue. The major products of these enzymes, produced from the universal precursor of monoterpenes, geranyl diphosphate, were shown to be (+)-alpha-pinene, (-)-alpha-pinene, and (-)-beta-pinene, respectively. In most properties (molecular mass of approximately 60 kDa, K(m) for geranyl diphosphate of 3 microM, requirement for monovalent and divalent cations), these enzymes resemble other monoterpene synthases from conifer species.

Animals↗

PubMed2005

DNA sequence variation and selection of tag single-nucleotide polymorphisms at candidate genes for drought-stress response in Pinus taeda L.

Genetic association studies are rapidly becoming the experimental approach of choice to dissect complex traits, including tolerance to drought stress, which is the most common cause of mortality and yield losses in forest trees. Optimization of association mapping requires knowledge of the patterns of nucleotide diversity and linkage disequilibrium and the selection of suitable polymorphisms for genotyping. Moreover, standard neutrality tests applied to DNA sequence variation data can be used to select candidate genes or amino acid sites that are putatively under selection for association mapping. In this article, we study the pattern of polymorphism of 18 candidate genes for drought-stress response in Pinus taeda L., an important tree crop. Data analyses based on a set of 21 putatively neutral nuclear microsatellites did not show population genetic structure or genomewide departures from neutrality. Candidate genes had moderate average nucleotide diversity at silent sites (pi(sil) = 0.00853), varying 100-fold among single genes. The level of within-gene LD was low, with an average pairwise r2 of 0.30, decaying rapidly from approximately 0.50 to approximately 0.20 at 800 bp. No apparent LD among genes was found. A selective sweep may have occurred at the early-response-to-drought-3 (erd3) gene, although population expansion can also explain our results and evidence for selection was not conclusive. One other gene, ccoaomt-1, a methylating enzyme involved in lignification, showed dimorphism (i.e., two highly divergent haplotype lineages at equal frequency), which is commonly associated with the long-term action of balancing selection. Finally, a set of haplotype-tagging SNPs (htSNPs) was selected. Using htSNPs, a reduction of genotyping effort of approximately 30-40%, while sampling most common allelic variants, can be gained in our ongoing association studies for drought tolerance in pine.

Base Sequence↗

PubMedDate not supplied

Abscisic acid and zygotic embryogenesis in Pinus taeda.

Indirect ELISA was used to quantify (+)-abscisic acid (ABA) in developing zygotic embryo and megagametophyte tissues from two loblolly pine (Pinus taeda L.) mother trees. On a dry weight basis, embryonic and megagametophytic ABA concentrations were highest during early development and decreased steadily to their lowest values at cone ripening. Embryonic ABA concentration was significantly higher than megagametophytic ABA concentration. The ABA content of embryos was lowest during early to mid-development; it increased rapidly during mid-development, subsequently declined, and then either remained constant or declined at cone ripening (late development). Total ABA per embryo increased rapidly just before the rapid increase in embryo dry weight. Total ABA per megagametophyte remained constant throughout development, except during mid-development when it temporarily declined.

Journal Article↗

PubMed2003

cDNA isolation, functional expression, and characterization of (+)-alpha-pinene synthase and (-)-alpha-pinene synthase from loblolly pine (Pinus taeda): stereocontrol in pinene biosynthesis.

The complex mixture of monoterpenes, sesquiterpenes, and diterpenes that comprises oleoresin provides the primary defense of conifers against bark beetles and their associated fungal pathogens. Monoterpene synthases produce the turpentine fraction of oleoresin, which allows mobilization of the diterpene resin acid component (rosin) and is also toxic toward invading insects; this is particularly the case for alpha-pinene, a prominent bicyclic monoterpene of pine turpentine. The stereochemistry of alpha-pinene is a critical determinant of host defense capability and has implications for host selection, insect pheromone biosynthesis, and tritrophic-level interactions. Pines produce both enantiomers of alpha-pinene, which appear to arise through antipodal reaction mechanisms by distinct enzymes. Using a cDNA library constructed with mRNA from flushing needles of loblolly pine (Pinus taeda), we employed a homology-based cloning strategy to isolate, and confirm by functional expression, the genes encoding (+)-(3R:5R)-alpha-pinene synthase, (-)-(3S:5S)-alpha-pinene synthase, and several other terpene synthases. The pinene synthases, which produce mirror-image products, share only 66% amino acid identity (72% similarity) but are similar in general properties to other monoterpene synthases of gymnosperms. The stereochemical control of monoterpene cyclization reactions, the evolution of "antipodal" enzymes, and the implications of turpentine composition in ecological interactions are discussed.

Amino Acid Sequence↗

PubMed1992

Purification, Characterization, and Cloning of Cinnamyl Alcohol Dehydrogenase in Loblolly Pine (Pinus taeda L.).

Cinnamyl alcohol dehydrogenase (CAD, EC 1.1.1. 195) has been purified to homogeneity from differentiating xylem tissue and developing seeds of loblolly pine (Pinus taeda L.). The enzyme is a dimer with a native molecular weight of 82,000 and a subunit molecular weight of 44,000, and is the only form of CAD involved in lignification in differentiating xylem. High levels of loblolly pine CAD enzyme were found in nonlignifying seed tissue. Characterization of the enzyme from both seeds and xylem demonstrated that the enzyme is the same in both tissues. The enzyme has a high affinity for coniferaldehyde (K(m) = 1.7 micromolar) compared with sinapaldehyde (K(m) in excess of 100 micromolar). Kinetic data strongly suggest that coniferin is a noncompetitive inhibitor of CAD enzyme activity. Protein sequences were obtained for the N-terminus (28 amino acids) and for two other peptides. Degenerate oligonucleotide primers based on the protein sequences were used to amplify by polymerase chain reaction a 1050 base pair DNA fragment from xylem cDNA. Nucleotide sequence from the cloned DNA fragment coded for the N-terminal protein sequence and an internal peptide of CAD. The N-terminal protein sequence has little similarity with the lambdaCAD4 clone isolated from bean (MH Walter, J Grima-Pettenati, C Grand, AM Boudet, CJ Lamb [1988] Proc Natl Acad Sci USA 86:5546-5550), which has homology with malic enzyme.

Journal Article↗

PubMed1998

Effects of temperature and tissue nitrogen on dormant season stem and branch maintenance respiration in a young loblolly pine (Pinus taeda) plantation.

We measured dormant season (November through February) maintenance respiration rates (R(m)) in stems and branches of 9-year-old loblolly pine (Pinus taeda L.) growing in plots under conditions of controlled nutrient and water supply in an effort to determine the relationships between R(m) and tissue size (surface area, sapwood volume, sapwood dry weight), tissue nitrogen content and temperature. Dormant season R(m) per unit size (i.e., surface area, &mgr;mol m(-2) s(-1); sapwood volume, &mgr;mol m(-3) s(-1); or sapwood dry weight, nmol g(-1) s(-1)) varied with tissue size, but was constant with respect to tissue nitrogen content (&mgr;mol mol(-1) N s(-1)). Cambium temperature accounted for 61 and 77% of the variation in stem and branch respiration, respectively. The basal respiration rate (respiration at 0 degrees C) increased with tissue nitrogen content, however, the Q(10) did not. Improved nutrition more than doubled stem basal respiration rate and increased branch basal respiration by 38%. Exponential equations were developed to model stem and branch respiration as a function of cambium temperature and tissue nitrogen content. We conclude that failure to account for tissue nitrogen effects on respiration rates will result in serious errors when estimating annual maintenance costs.

Journal Article↗

PubMed1991

Distribution of (14)C-labeled photosynthate in loblolly pine (Pinus taeda) seedlings as affected by season and time after exposure.

Distribution of (14)C-labeled photosynthate was determined in field-grown loblolly pine (Pinus taeda L.) seedlings on August 9 and October 15, 1984 and January 15 and March 12, 1985. Leaves on a lateral branch fixed (14)C photosynthetically and amounts of (14)C in seven biochemical fractions in each of six plant parts were determined 8, 24, and 72 h later. In all treatments, (14)C uptake was approximately 96% of that originally presented. Respiratory loss of (14)C ranged from 22 to 87% of uptake and increased sharply with increasing time after exposure and as the seedlings grew larger later in the study. Most (14)C was found in exposed leaves and very little occurred above the exposed branch. Amounts of (14)C decreased in the exposed leaves and increased in the roots with time after exposure and date. Sugars were generally the most heavily labeled fraction. Labeled sugar content of exposed leaves decreased by more than half between 8 and 72 h as sugars were metabolized and translocated to other parts, primarily the roots. In roots, the labeling of starch and residue (structural compounds) increased greatly with transport time and season. In all plant parts, proteins and amino acids contained very little (14)C regardless of date or time.

Journal Article↗

PubMed2004

Diurnal and seasonal variability in the radial distribution of sap flow: predicting total stem flow in Pinus taeda trees.

We monitored the radial distribution of sap flux density (v; g H2O m(-2) s(-1)) in the sapwood of six plantation-grown Pinus taeda L. trees during wet and dry soil periods. Mean basal diameter of the 32-year-old trees was 33.3 cm. For all trees, the radial distribution of sap flow in the base of the stem (i.e., radial profile) was Gaussian in shape. Sap flow occurred maximally in the outer 4 cm of sapwood, comprising 50-60% of total stem flow (F), and decreased toward the center, with the innermost 4 cm of sapwood (11-15 cm) comprising less than 10% of F. The percent of flow occurring in the outer 4 cm of sapwood was stable with time (average CV < 10%); however, the percentage of flow occurring in the remaining sapwood was more variable over time (average CV > 40%). Diurnally, the radial profile changed predictably with time and with total stem flow. Seasonally, the radial profile became less steep as the soil water content (theta) declined from 0.38 to 0.21. Throughout the season, daytime sap flow also decreased as theta decreased; however, nighttime sap flow (an estimate of stored water use) remained relatively constant. As a result, the percentage of stored water use increased as theta declined. Time series analysis of 15-min values of F, theta, photosynthetically active radiation (PAR) and vapor pressure deficit (D) showed that F lagged behind D by 0-15 min and behind PAR by 15-30 min. Diurnally, the relationship between F and D was much stronger than the relationship between F and PAR, whereas no relationship was found between F and theta. An autoregressive moving average (ARIMA) model estimated that 97% of the variability in F could be predicted by D alone. Although total sap flow in all trees responded similarly to D, we show that the radial distribution of sap flow comprising total flow could change temporally, both on daily and seasonal scales.

Circadian Rhythm↗

PubMedDate not supplied

Growth and photosynthesis of loblolly pine (Pinus taeda) after exposure to elevated CO(2) for 19 months in the field.

To detect seasonal and long-term differences in growth and photosynthesis of loblolly pine (Pinus taeda L.) exposed to elevated CO(2) under ambient conditions of precipitation, light, temperature and nutrient availability, seedlings were planted in soil representative of an early, abandoned agricultural field and maintained for 19 months in the field either in open-top chambers providing one of three atmospheric CO(2) partial pressures (ambient, ambient +15 Pa, and ambient +30 Pa) or in unchambered control plots. An early and positive response to elevated CO(2) substantially increased total plant biomass. Peak differences in relative biomass enhancement occurred after 11 months of CO(2) treatment when biomass of plants grown at +15 and +30 Pa CO(2) was 111 and 233% greater, respectively, than that of plants grown at ambient CO(2). After 19 months, there was no significant difference in biomass between +15 Pa CO(2)-treated plants and ambient CO(2)-treated plants, whereas biomass of +30 Pa CO(2)-treated plants was 111% greater than that of ambient CO(2)-treated plants. Enhanced rates of leaf-level photosynthesis were maintained in plants in the elevated CO(2) treatments throughout the 19-month exposure period despite reductions in both leaf N concentration and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity during the first 11 months of CO(2) exposure. Reductions in Rubisco activity indicated photosynthetic adjustment to elevated CO(2), but Rubisco-mediated control of photosynthesis was small. Seasonal shifts in sink strength affected photosynthetic rates, greatly magnifying the positive effects of elevated CO(2) on photosynthesis during periods of rapid plant growth. Greater carbon assimilation by the whole plant accelerated plant development and thereby stimulated new sinks for carbon through increased plant biomass, secondary branching and new leaf production. We conclude that elevated CO(2) will enhance photosynthesis and biomass accumulation in loblolly pine seedlings under high nutrient conditions; however, reductions over time in the relative biomass response of plants to elevated CO(2) complicate predictions of the eventual magnitude of carbon storage in this species under future CO(2) conditions.

Journal Article↗

PubMed1999

Simulated nitrogen cycling response to elevated CO(2) in Pinus taeda and mixed deciduous forests.

Interactions between elevated CO(2) and N cycling were explored with a nutrient cycling model (NuCM, Johnson et al. 1993, 1995) for a Pinus taeda L. site at Duke University, North Carolina, and a mixed deciduous site at Walker Branch, Tennessee. The simulations tested whether N limitation would prevent growth increases in response to elevated CO(2), and whether growth responses to CO(2) in N-limited systems could be facilitated by increasing the biomass/N ratio (reducing N concentration) or increasing litter N mineralization, or both. Nitrogen limitation precluded additional growth when target growth rates and litterfall were increased (simulating potential response to elevated CO(2)) at the Duke University site. At the Walker Branch site, increasing target growth and litterfall caused a 7% increase in growth. Reducing foliar N concentrations reduced growth because of N limitation created by reduced litter quality (C:N ratio), reduced decomposition and increased N accumulation on the forest floor. These effects were most pronounced at the Duke University site, because the forest floor N turnover rate was lower than at the Walker Branch site. Reducing wood N concentration allowed prolonged increases in growth because of greater biomass/N; however, N uptake was reduced, allowing greater N immobilization on the forest floor and in soil. Increased N mineralization caused increased growth at the Duke University site, but not at the Walker Branch site. These simulations pose the counterintuitive hypothesis that increased biogeochemical cycling of N (as a result of increased litterfall N) causes reduced growth in an N-limited system because of increased accumulations of N on the forest floor and in soil. Translocation of N from senescing leaves before litterfall mitigates this response by allowing the trees to retain a greater proportion of N taken up rather than recycle it back to the forest floor and soil where it can be immobilized. Eliminating N translocation at Walker Branch changed the direction as well as the magnitude of the responses in three of the four scenarios simulated. Because the NuCM model does not currently allow translocation in coniferous species, the effects of translocation on N cycling in the Duke University simulations are not known.

Journal Article↗

PubMed2002

Identification of QTLs influencing wood property traits in loblolly pine ( Pinus taeda L.). II. Chemical wood properties.

Chemical wood property traits were analyzed for the presence of quantitative trait loci (QTLs) in a three-generation outbred pedigree of loblolly pine ( Pinus taeda L.). These traits were assayed using pyrolysis molecular beam mass spectrometry and include mass spectrum peak intensities associated with carbohydrates, alpha-cellulose and hemicellulose sugars, and lignin. Models for projection to latent structures (PLS) were used to also estimate the chemical composition of cell walls (i.e., alpha-cellulose, galactan and lignin) from mass spectrum data using multivariate regression. Both earlywood and latewood fractions from the fifth annual ring were analyzed for each trait. An interval mapping approach designed for an outbred pedigree was used to estimate the number of QTLs, the magnitude of QTL effects, and their genomic position. Eight unique QTLs influencing cell wall chemistry were detected from multiple peak intensities and/or PLS estimates using the one- and two-QTL models. Significant differences in chemical contents were observed among the populations from North Carolina vs Oklahoma, and results from QTLxenvironment analyses suggest that QTLs interact with environmental location. QTLs should be verified in larger experiments and in different genetic and environmental backgrounds. QTL mapping will help towards eventually identifying genes having a major effect on chemical wood properties.

Journal Article↗

PubMed1988

Long-term elevation of atmospheric CO(2) concentration and the carbon exchange rates of saplings of Pinus taeda L. and Liquidambar styraciflua L.

The relationship between carbon exchange rate (CER) and internal CO(2) concentration was measured in leaves of saplings of Liquidambar styraciflua L. (sweetgum) and Pinus taeda L. (loblolly pine) grown from seed for more than 14 months at atmospheric CO(2) concentrations of either 350 or 500 microl l(-1). An elevated concentration of CO(2) during growth reduced CER at any given internal CO(2) concentration in sweetgum, but not in loblolly pine. Stomatal limitation of CER showed little response to concentration of CO(2) during measurement, but was higher in both species when grown at 500 than at 350 microl l(-1) CO(2). The net effect of a long-term increase in CO(2) concentration from 350 to 500 microl l(-1) was an increase in CER of loblolly pine, but a slight decrease in CER of sweetgum. It is suggested that the depression of CER in sweetgum resulted from a reduction in the activity of ribulose-1,5-bisphosphate carboxylase-oxygenase.

Journal Article↗

PubMed1991

Limitations of Photosynthesis in Pinus taeda L. (Loblolly Pine) at Low Soil Temperatures.

The relative importance of stomatal and nonstomatal limitations to net photosynthesis (A) and possible signals responsible for stomatal limitations were investigated in unhardened Pinus taeda seedlings at low soil temperatures. After 2 days at soil temperatures between 13 and 7 degrees C, A was reduced by 20 to 50%, respectively. The reduction in A at these moderate root-chilling conditions appeared to be the result of stomatal limitations, based on the decrease in intercellular CO(2) concentrations (c(i)). This conclusion was supported by A versus c(i) analysis and measurements of O(2) evolution at saturating CO(2), which suggested increases in stomatal but not biochemical limitations at these soil temperatures. Nonuniform stomatal apertures, which were demonstrated with abscisic acid, were not apparent 2 days after root chilling, and results of our A versus c(i) analysis appear valid. Bulk shoot water potential (psi) declined as soil temperature dropped below 16 degrees C. When half the root system of seedlings was chilled, shoot psi and gas-exchange rates did not decline. Thus, nonhydraulic root-shoot signals were not implicated in stomatal limitations. The initial decrease in leaf conductance to water vapor after root chilling appeared to precede any detectable decrease in bulk fascicle psi, but may be in response to a decrease in turgor of epidermal cells. These reductions in leaf conductance to water vapor, which occurred within 30 minutes of root chilling, could be delayed and temporarily reversed by reducing the leaf-to-air vapor-pressure deficit, suggesting that hydraulic signals may be involved in initiating stomatal closure. By independently manipulating the leaf-to-air vapor-pressure deficit of individual fascicles, we could induce uptake of water vapor through stomata, suggesting that nonsaturated conditions occur in the intercellular airspaces. There was an anomaly in our results on seedlings maintained for 2 days at soil temperatures below 7 degrees C. Lower A appeared primarily the result of nonstomatal limitations, based on large increases in calculated c(i) and A versus c(i) analysis. In contrast, measurements of O(2) evolution at saturating CO(2) concentrations implied nonstomatal limitations per se did not increase at these temperatures. One explanation for this paradox is that calculations of c(i) are unreliable at very low gas-exchange rates because of inadequate measurement resolution, and limitations of A are predominantly stomatal. An alternative interpretation is that increases in c(i) are real and the results from O(2)-evolution measurements are in error. The high CO(2) concentration used in O(2)-evolution measurements (15%) may have overcome nonstomatal limitations by enzymes that were down-regulated by a feedback mechanism. In this scenario, carbohydrate feedback limitations may be responsible for nonstomatal reductions in A after 2 days at soil temperatures below 7 degrees C.

Journal Article↗

PubMed1993

Vascular cambial sucrose metabolism and growth in loblolly pine (Pinus taeda L.) in relation to transplanting stress.

Sucrose synthase (SS) was the dominant enzyme of sucrose metabolism in both stem and root vascular cambial zone tissues of nursery-grown loblolly pine (Pinus taeda L.) seedlings. Acid invertase (AI) and neutral invertase (NT) activities were generally less than 10% of the SS activity in both tissues. In both cambial tissues, seasonal patterns of enzyme activity were observed for SS but not for AI or NI. The seasonal patterns of SS activity in stem and root cambia paralleled the periodic growth of stems and roots. Stems had high SS activity and growth during summer and early fall. Roots had substantial SS activity and growth during summer and fall, but SS activity and growth were even higher in winter. When seedlings were transplanted, about eight months elapsed before stem and root cambia resumed rates of growth and sucrose metabolism similar to those in control nontransplanted seedlings. Two months after transplanting, root SS was at its lowest, whereas AI activity in transplants was 50% higher than in control nontransplanted seedlings. In stems, SS activity decreased in response to transplanting, whereas AI and NI activities did not change appreciably. In loblolly pine tissues, SS was specific for uridylates, whereas the nucleotide triphosphate-dependent phosphofructokinase (NTP-PFK) had similar activity with either UTP or ATP. Except in winter, the NTP-PFK was less active than the pyrophosphate-dependent phosphofructokinase (PPi-PFK) during all seasons. The PPi-dependent PFK activity in nontransplanted seedlings followed similar seasonal and spatial patterns to those of SS activity. In actively growing tissues, such as stem cambial tissues in summer and root cambial tissues in winter, the measured total PFK to SS ratio ranged between 1.5/1 and 3/1. In contrast, in less actively growing tissues or transplanted seedlings, a greater decrease occurred in SS than in PFK activity, hence the ratio rose to as high as 12/1. It was concluded that: (1) SS was the dominant enzyme for sucrose metabolism in root and stem cambial tissues of loblolly pine seedlings; (2) both SS and PPi-PFK in the cambial tissues can be used as biochemical indicators of growth sink strength in stems and roots; and (3) both enzymes can be used as indicators of seedling stress caused by events such as transplanting and winter freezing.

Journal Article↗

PubMed1983

Computer-Assisted Image Analysis of Tissues of Ethrel-Treated Pinus taeda Seedlings.

A microcomputer based video image analyzer is described and demonstrated in the analysis and comparison of tissue types of 6-month-old Ethrel-treated and control seedlings of loblolly pine (Pinus taeda L.). Two different programs were employed. ;Topographer I' sought, identified, and measured cell or resin canal lumen areas, and ;Area' measured tracheid length and silhouette areas. Ethrel treatment induced an increase in radial growth and a decrease in shoot elongation and needle growth. Bark production was stimulated by the same treatment. The tracheid lumens of Ethrel-treated plants were shorter and had a smaller cross-sectional area, whereas the tracheid cell walls increased in thickness. The treatment also increased resin canal formation in the xylem.

Journal Article↗

PubMed1999

Stand-level allometry in Pinus taeda as affected by irrigation and fertilization.

Changing environmental conditions have the potential to alter allometric relationships between plant parts, possibly leading to ecosystem-level feedbacks. We quantified allometric shifts in field-grown loblolly pine (Pinus taeda L.) in response to altered resource availability based on data from multiple harvests to correct for size-related changes in biomass partitioning. A replicated factorial arrangement of irrigation and fertilization treatments was applied for 4 years to an 8-year-old loblolly pine plantation on a well-drained, low fertility site in North Carolina. Destructive and nondestructive growth measurements were used to develop treatment-specific regressions to estimate stand-level biomass for ephemeral and perennial plant parts, both above- and belowground. Stand-level allometric analysis indicated that irrigation increased biomass partitioning to fine roots and decreased partitioning to foliage, relative to other plant parts. Fertilization increased partitioning to perennial tissues (coarse roots, taproots, and branches) and decreased partitioning to ephemeral tissues (foliage and fine roots). Changes in allometry were small (< 6 %) but statistically significant, indicating that biomass partitioning in loblolly pine changes with altered resource availability, but is probably under strong ontogenetic control.

Journal Article↗