Loblolly Pine Trees Research Articles

Relationship between Anatomical and Mechanical Properties of Loblolly Pine (Pinus taeda)

ABSTRACT The goal of this study was to investigate the effects of thinning and fertilization on mechanical properties of loblolly pine (Pinus taeda L.) strands associated with growth ring number and height. A systematic link to forest management, anatomical properties, and mechanical properties was obtained by correlating the test results with anatomical properties. The modulus of elasticity (MOE) and ultimate tensile strength (UTS) of strands from three loblolly pine trees increased with the increment in growth ring number, whereas the MOE and UTS showed different trends with the increment in height. Prediction of the MOE and UTS with specific gravity for the trees seemed to be unreliable. A natural tree had the greatest correlation between tangential latewood cell wall thickness and the mechanical properties. A thinned tree had the greatest correlation between ring width and the mechanical properties. A fertilized tree had the greatest correlation between density and the mechanical properties. However, the correlation between a specific anatomical property and mechanical properties was weak. Different combinations of anatomical properties predicted MOE and UTS of loblolly pine strands from different forest-managed trees more closely, indicating an R2 of 0.84 to 0.95.

Storage Time and Amendments Affect Pine Tree Substrate Properties and Marigold Growth

Pine tree substrate (PTS) is a relatively new alternative to the commonly used pine bark and peat-based substrates for container crop production. Physical and chemical properties of freshly manufactured PTS have been studied; however, this new substrate will sometimes be manufactured and stored for later use by growers. The objective of this research was to determine how chemical and physical properties of PTS were affected by storage duration with or without amendments of limestone or peatmoss. We also studied how the growth of marigold was influenced by PTS storage time and by lime and peat amendments. Substrate properties studied were pH, cation exchange capacity (CEC), electrical conductivity (EC), carbon-to-nitrogen ratio (C:N), bulk density (BD), and particle size distribution. Pine tree substrate was manufactured by hammermilling chips of ≈15-year-old loblolly pine trees (Pinus taeda L.) through two screen sizes, 4.76 mm (PTS) and 15.9 mm [amended with peat (PTSP)]. Pine tree substrate and PTSP were amended with lime at five rates and a peat–perlite mix (PL) served as a control treatment. Substrates were prepared, placed in plastic storage bags, and stored on shelves in an open shed in Blacksburg, VA. Substrates were subsampled at 1, 42, 84, 168, 270, and 365 days after storage. At each subsampling day, twelve 1-L containers were filled with a subsample of each treatment. Six of the 12 were left fallow and six were planted with 14-day-old marigold (Tagetes erecta L. ‘Inca Gold’) seedlings. Substrate was also collected for analysis of CEC, C:N, BD, and particle size distribution. The pH of non-limed PTS decreased during storage, and at least 1 kg·m−3 lime was needed to maintain PTS pH 5.4 or greater over the 365-day storage period (Day 1 pH = 5.8) and 2 to 4 kg·m−3 was needed to maintain PTSP pH 5.4 or greater for 365 days (Day 1 pH = 5.2). EC measurements were highest at Day 1 (1.02 to 1.21 dS·m−1) in all treatments and decreased by Day 42. Cation exchange capacity decreased over time in non-limed PTS and PTSP. Carbon-to-nitrogen ratio and BD remained the same over time for all treatments. There were minor changes in particle size distribution for limed PTS. Marigold growth in all limed PTS and PTSP treatments was equal to or greater than in PL, except at Day 1; the lower growth in PTS and PTSP at Day 1 compared with PL suggests that freshly manufactured PTS may contain a phytotoxic substance that was not present in PTS by Day 42. Pine tree substrate and PTSP are relatively stable when stored as described previously, except for a pH decrease that can be prevented with additions of lime before storage.

Modeling mensurational relationships of plantation-grown loblolly pine (Pinus taeda L.) in Uruguay

Modeling forest trees’ mensurational relationships has many applications: from understanding physiological functional relationships (e.g. the allometric relationship of sapwood to leaf area ratio) to predicting one tree part by measuring another (e.g. above-ground tree biomass from the tree stem diameter). Simple models that relate easy to measure tree characteristics, such as diameter at breast height (DBH), to other more difficult to observe dimensions such as crown volume, are useful both in and of themselves and also as components of larger forest growth and yield and forest ecosystem models. Mensurational models of wide applicability include tree height-DBH (growth and yield models, carbon accounting, forest dynamics), bark thickness-DBH (fuels and fire models, carbon accounting, post-fire mortality), and crown dimensions-DBH (physiological models, growth and yield models, carbon accounting models). Here we develop models for plantation-grown loblolly pine (Pinus taeda L.) trees in Uruguay. We model total tree height-DBH, crown diameter-DBH, crown volume-DBH, and bark thickness stem profile given relative diameter and relative height. We do so using linear and nonlinear regression models as well as semi-parametric modeling alternatives. The data comprise 198 trees grown in even-aged plantations and spanning an age range of 8–22years. The predictive ability of the resulting models was evaluated by estimating the root mean square prediction error by predictor variable classes with the 0.063+ bootstrap method. All models presented acceptable prediction ability except the one describing the relationship of crown volume to DBH. The semi-parametric model describing the bark thickness profile along the tree stem fit the data better and had similar prediction ability compared with the parametric model. The semi-parametric modeling approach was a good alternative to describe this allometry.

Effects of loblolly pine tree age and wood properties on linerboard-grade pulp yield and sheet properties: Part 2

Results are presented on the relationships among loblolly pine tree age and wood characteristics and the properties of pulp obtained when the trees were chipped and pulped. We selected 13-year-old and 22-year-old loblolly pine trees (18 of each) to represent specified ranges of specific gravity and lignin content. The trees were further characterized by chemical analysis, near infrared (NIR) spectroscopy, and SilviScan analysis of fiber dimensions and properties before being pulped by the kraft process. Handsheets formed from the resulting pulps were characterized in terms of sheet properties that are important for linerboard grades. Multiple regression analysis was then used to identify wood characteristics that most influenced sheet properties and to derive equations relating sheet properties to tree age, specific gravity, and chemical composition. We also developed calibrations so that sheet properties could be predicted from NIR spectroscopic analysis of wood. Nearly all differences in properties of pulps made from 13- and 22-year-old trees were attributable to differences in fundamental wood properties. Sheet properties could be estimated by measuring their near NIR spectra.

An Annual Tree Survival and Diameter Growth Model for Loblolly and Slash Pine Plantations in East Texas

An annual growth model that predicts individual tree survival and diameter growth was developed for loblolly pine (Pinus taeda) and slash pine (Pinus elliottii) trees in East Texas as a function of individual-tree diameter, plantation age, basal area per acre, dominant height, quadratic mean diameter, and presence of fusiform rust (Cronartium quercuum [Berk.] Miyabe ex Shirai f. sp. fusiforme). Data from 104,035 loblolly pine and 37,515 slash pine individual tree observations collected on a 3-year cycle from 174 loblolly pine and 80 slash pine permanent plots located in plantations throughout East Texas were used in this study. The survival equation assumes that mortality is constant across the projection length, whereas the diameter growth equation incorporates whole-stand predictions to update stand-level independent variables on an annual basis. Predictions were evaluated in terms of bias and precision, with independent observations for projection lengths from 3 to 24 years. For both survival and diameter growth, bias was lowest and precision highest for 3-year projection lengths. For survival, bias increased and precision decreased as projection length increased through 24 years. For diameter growth, bias was constant (<1 in.) across all projection lengths, whereas precision decreased from <1 in. for the 3-year projection length to <2 in. for the 6—24-year projection lengths. A numerical example is provided that describes how to use the new model to project individual tree survival and diameter growth on an annual basis.

Timing and magnitude of C partitioning through a young loblolly pine (Pinus taeda L.) stand using 13C labeling and shade treatments

The dynamics of rapid changes in carbon (C) partitioning within forest ecosystems are not well understood, which limits improvement of mechanistic models of C cycling. Our objective was to inform model processes by describing relationships between C partitioning and accessible environmental or physiological measurements, with a special emphasis on short-term C flux through a forest ecosystem. We exposed eight 7-year-old loblolly pine (Pinus taeda L.) trees to air enriched with (13)CO(2) and then implemented adjacent light shade (LS) and heavy shade (HS) treatments in order to manipulate C uptake and flux. The impacts of shading on photosynthesis, plant water potential, sap flow, basal area growth, root growth and soil CO(2) efflux rate (CER) were assessed for each tree over a 3-week period. The progression of the (13)C label was concurrently tracked from the atmosphere through foliage, phloem, roots and surface soil CO(2) efflux. The HS treatment significantly reduced C uptake, sap flow, stem growth and fine root standing crop, and resulted in greater residual soil water content to 1 m depth. Soil CER was strongly correlated with sap flow on the previous day, but not the current day, with no apparent treatment effect on the relationship. Although there were apparent reductions in new C flux belowground, the HS treatment did not noticeably reduce the magnitude of belowground autotrophic and heterotrophic respiration based on surface soil CER, which was overwhelmingly driven by soil temperature and moisture. The (13)C label was immediately detected in foliage on label day (half-life = 0.5 day), progressed through phloem by Day 2 (half-life = 4.7 days), roots by Days 2-4, and subsequently was evident as respiratory release from soil which peaked between Days 3 and 6. The δ(13)C of soil CO(2) efflux was strongly correlated with phloem δ(13)C on the previous day, or 2 days earlier. While the (13)C label was readily tracked through the ecosystem, the fate of root C through respiratory, mycorrhizal or exudative release pathways was not assessed. These data detail the timing and relative magnitude of C flux through various components of a young pine stand in relation to environmental conditions.

Cultural intensity and planting density effects on aboveground biomass of 12-year-old loblolly pine trees in the Upper Coastal Plain and Piedmont of the southeastern United States

We examined the effects of cultural intensity (operational and intensive), planting density (741, 1483, 2224, 2965, 3706 and 4448 trees ha−1) and their interaction on aboveground biomass accumulation and allocation for 12-year-old loblolly pine (Pinus taeda L.) trees in the Upper Coastal Plain and Piedmont of the southeastern United States. Cultural intensity significantly affected accumulation of stem, bark, dead-branch and total aboveground biomass and biomass allocation in the dead-branch component. Accumulation of total aboveground biomass and each component biomass and biomass allocation to each component were significantly affected by planting density. The only significant culture×density interaction was for dead-branch biomass accumulation.

Computer-based synthetic data to assess the tree delineation algorithm from airborne LiDAR survey

Small Footprint LiDAR (Light Detection And Ranging) has been proposed as an effective tool for measuring detailed biophysical characteristics of forests over broad spatial scales. However, by itself LiDAR yields only a sample of the true 3D structure of a forest. In order to extract useful forestry relevant information, this data must be interpreted using mathematical models and computer algorithms that infer or estimate specific forest metrics. For these outputs to be useful, algorithms must be validated and/or calibrated using a sub-sample of `known' metrics measured using more detailed, reliable methods such as field sampling. In this paper we describe a novel method for delineating and deriving metrics of individual trees from LiDAR data based on watershed segmentation. Because of the costs involved with collecting both LiDAR data and field samples for validation, we use synthetic LiDAR data to validate and assess the accuracy of our algorithm. This synthetic LiDAR data is generated using a simple geometric model of Loblolly pine (Pinus taeda) trees and a simulation of LiDAR sampling. Our results suggest that point densities greater than 2 and preferably greater than 4 points per m2 are necessary to obtain accurate forest inventory data from Loblolly pine stands. However the results also demonstrate that the detection errors (i.e. the accuracy and biases of the algorithm) are intrinsically related to the structural characteristics of the forest being measured. We argue that experiments with synthetic data are directly useful to forest managers to guide the design of operational forest inventory studies. In addition, we argue that the development of LiDAR simulation models and experiments with the data they generate represents a fundamental and useful approach to designing, improving and exploring the accuracy and efficiency of LiDAR algorithms.

Competition among loblolly pine trees: Does genetic variability of the trees in a stand matter?

The intensity of intraspecific competition among trees in a stand was compared for seed origin versus clonal origin stands of loblolly pine using tree size-based competition indices. A method that uses maximum likelihood with simulated annealing (MLSA) and one that uses discrete radii with simple correlation coefficients (DRSC) were applied and their results compared to stand level observable effects of competition. DRSC was found to give estimates of competitor search radii that were reasonable and in line with observable stand level effects of intraspecific competition. MLSA appeared to overestimate the optimum competitor search radius, had the potential to give estimates of the competitor search radius that were not unique, and was generally not conclusive on which genetic variety had the most intense level of competition among trees in its stand. The DRSC approach provides a simple alternative to MLSA where the assumptions behind MLSA do not hold or where it may not be easy for them to be checked. A comparison of competitor search radii in the different genetic variety stands and the observable stand level effects of competition did not find evidence to support the hypothesis that greater genetic uniformity among trees in loblolly pine stands would result in more intense intraspecific competition among the trees in the stand.

Effects of loblolly pine tree age and wood properties on linerboard-grade pulp yield and sheet properties: Part 1 - Effects on pulp yield

Results are reported on the relationships of loblolly pine tree age and wood characteristics and the yield of pulp obtained when the trees were chipped and pulped by the kraft process. Eighteen 13-year old and 18 22-year-old loblolly pine trees were selected to represent specified ranges of specific gravity and lignin content. The trees were further characterized by chemical analysis and near infrared spectroscopy before kraft pulping. The resulting pulps were characterized by measurements of yield and chemical analysis. Multiple regression analysis was used to identify wood characteristics that most influenced pulp yield and to derive equations relating pulp yield to tree age, specific gravity, and wood chemical composition. In addition, near-infrared spectroscopy calibrations were developed to allow prediction of pulp yield from analysis of wood. The results showed that wood specific gravity cannot be used to predict the yield of linerboard-grade pulp from trees of either age. The yield of pulp from 13-year-old trees can be predicted from the amounts of xylan and lignin present in the wood. The yield of pulp from 22-year-old trees decreased with increasing lignin content but was unrelated to xylan content. Thirteen-year-old trees had significantly higher xylan content and the excess xylan was lost during pulping. Regression equations were developed for estimating pulp yields from 13- and 22-year-old trees, given their xylan and lignin contents. Another equation derived from the combined data for trees of both age classes will be useful for predicting yields from trees of other ages, if it is assumed that the effect of tree age is linear.

Growth of young loblolly pine trees following pruning

Pruning loblolly pine trees is sometimes practiced to improve wood quality even though reduced growth following treatment may occur. Two experiments were established in February 2000 in the Piedmont region of Virginia, USA, to examine the impact of timing and intensity of pruning on subsequent growth of young loblolly pine trees. Results of one study indicated that there is a window of opportunity during the early portion of stand development where up to 50% of the live crown length can be removed without a significant loss of long-term height or diameter growth. Within a year following pruning at ages 3, 6 and 9 (all pruning treatments occurred prior to crown closure), crown mass had been restored and growth comparable to an unpruned control resumed. By age 11 there were no significant differences in cumulative height or dbh of any of the one-lift pruning treatments and the control. Findings from a second study planted at closer spacings where pruning treatments occurred at crown closure (age 6) showed that pruning some of the trees in a loblolly pine plantation does not result in a loss of long-term height or diameter growth or crown dominance for the pruned trees as compared to their unpruned neighbors. For both studies, growth reductions following pruning were small and transitory.

Effects of Loblolly Pine Wood and Pulp Properties on Sheet Characteristics

The effects of wood properties on the strength of bleachable and linerboard grade kraft pulps from 13-year-old loblolly pine (Pinus taeda) trees were investigated. Eighteen trees were selected based on breast height wood cores to represent specified ranges of specific gravity and lignin content. Air-dry density and stiffness (modulus of elasticity [MOE]), tracheid coarseness, radial diameter, tangential diameter, specific surface area, wall thickness, and microfibril angle (MFA) were estimated using SilviScan wood analysis technology and near infrared reflectance (NIR) spectroscopy. NIR spectra collected in 10 mm sections from the surface radial strips correlated very well with air-dry density, MFA, MOE, and tracheid wall thickness and were used to develop whole tree predictions. In addition, chemical composition, fiber properties, and handsheet strength were measured for both pulp grades. Statistical analysis indicated that wood density, wood fiber coarseness, and pulp fiber length had the greatest effects on sheet properties.

A Mixed-Effects Height—Diameter Model for Individual Loblolly and Slash Pine Trees in East Texas

Abstract A new mixed-effects model was developed that predicts individual-tree total height for loblolly (Pinus taeda) and slash pine (Pinus elliottii) as a function of individual-tree diameter (in.), dominant height (ft), quadratic mean diameter (in.), and maximum stand diameter (in.). Data from 119,983 loblolly pine and 42,697 slash pine height–diameter observations collected on 185 loblolly pine and 84 slash pine permanent plots located in plantations throughout East Texas were used for model fitting. This new model is an improvement over earlier models fit with ordinary least squares, in that it can be calibrated to a new stand with observed height–diameter pairs, thus improving height prediction. An example is provided that describes how to calibrate the model to a new stand with observed data.

Water availability and genetic effects on wood properties of loblolly pine (Pinus taeda)

We studied the effect of water availability on basal area growth and wood properties of 11-year-old loblolly pine ( Pinus taeda L.) trees from contrasting Florida (FL) (a mix of half-sib families) and South Carolina coastal plain (SC) (a single, half-sib family) genetic material. Increasing soil water availability via irrigation increased average whole-core specific gravity (SG) and latewood percentage (LW%) by 0.036 and 6.93%, respectively. Irrigation did not affect latewood SG or wood stiffness, but irrigated FL and SC trees had more latewood due to a 29 day longer growing season. Irrigation did not affect the length of corewood production, but irrigated trees had earlier transition ages, producing outerwood ~3 years before rainfed trees. The increase in whole-core SG and LW% was moderate because irrigation promoted earlywood growth in corewood formed before canopy closure, but after year 7, rain-fed and irrigated trees had similar earlywood growth but irrigated trees had more latewood growth, increasing ring SG and LW%. The SC half-sib family had higher SG and greater LW% than trees from FL independent of irrigation due to greater yearly latewood growth. Thus, absence of soil water stress extended seasonal diameter cessation date but did not change latewood SG or wood stiffness.

A genomic map enriched for markers linked to Avr1 in Cronartium quercuum f.sp. fusiforme

A novel approach is presented to map avirulence gene Avr1 in the basidiomycete Cronartium quercuum f.sp. fusiforme, the causal agent of fusiform rust disease in pines. DNA markers tightly linked to resistance gene Fr1 in loblolly pine tree 10-5 were used to classify 10-5 seedling progeny as either resistant or susceptible. A single dikaryotic isolate (P2) heterozygous at the corresponding Avr1 gene was developed by crossing Fr1 avirulent isolate SC20-21 with Fr1 virulent isolate NC2-40. Bulk basidiospore inoculum derived from isolate P2 was used to challenge the pine progeny. The ability to unambiguously marker classify 10-5 progeny as resistant (selecting for virulence) or susceptible (non-selecting) permitted the genetic mapping of the corresponding Avr1 gene by bulked segregant analysis. Using this approach, 14 genetic markers significantly linked to Avr1 were identified and placed within the context of a genome-wide linkage map produced for isolate P2 using samples from susceptible seedlings.

The Effects of Irrigation and Fertilization on Specific Gravity of Loblolly Pine

Abstract The effects of two treatments, irrigation and fertilization, were examined on specific gravity (SG)-related wood properties of loblolly pine trees (Pinus taeda L.) grown in Scotland County, North Carolina. The effects on the core as a whole, on the juvenile core, on the mature core, and from year to year were all analyzed. The results indicate that fertilization significantly lowered latewood SG, overall SG, and percent latewood and did so consistently throughout the period of study. Irrigation significantly lowered earlywood SG during the phase of juvenile wood production but significantly raised latewood SG during the period of mature wood production. Significant interaction between fertilization and irrigation indicated that irrigation helped overall SG and percent latewood of fertilized trees to increase to the level of untreated trees. Therefore, this study provides evidence that although fertilization significantly affects several SG-related properties, water availability is beneficial to the fertilization process; over time, an adequate water supply may help fertilized trees to maintain SG levels similar to those of unfertilized trees.

Petroleomic Analysis of Bio-oils from the Fast Pyrolysis of Biomass: Laser Desorption Ionization−Linear Ion Trap−Orbitrap Mass Spectrometry Approach

Fast pyrolysis of biomass produces bio-oils that can be upgraded into biofuels. Despite similar physical properties to petroleum, the chemical properties of bio-oils are quite different and their chemical compositions, particularly those of non-volatile compounds, are not well-known. Here, we report the first time attempt at analyzing bio-oils using high-resolution mass spectrometry (MS), which employed laser desorption ionization−linear ion trap−Orbitrap MS. Besides a few limitations, we could determine chemical compositions for over 100 molecular compounds in a bio-oil sample produced from the pyrolysis of a loblolly pine tree. These compounds consist of 3−6 oxygens and 9−17 double-bond equivalents (DBEs). Among those, O4 compounds with a DBE of 9−13 were most abundant. Unlike petroleum oils, the lack of nearby molecules within a ±2 Da mass window for major components enabled clear isolation of precursor ions for subsequent MS/MS structural investigations. Petroleomic analysis and a comparison to low-ma...

Methods of Constructing a Pine Tree Substrate from Various Wood Particle Sizes, Organic Amendments, and Sand for Desired Physical Properties and Plant Growth

The use of freshly harvested and processed pine trees as a container substrate for greenhouse and nursery crop production is a relatively new concept, and fundamental knowledge of the construction of a pine tree substrate (PTS) for optimal physical properties is insufficient. Therefore, this research was conducted to determine the influence of mixing PTSs produced with different wood particle sizes and adding other amendments to PTS on substrate physical properties and plant growth compared with traditional substrates. Coarse pine wood chips produced from 15-year-old loblolly pine trees (Pinus taeda L.) were ground in a hammermill fitted with either a 4.76-mm screen or with no screen (PTS-NS) allowing a fine and a coarse particle PTS to be produced. Increasing proportions of the finer (4.76-mm) PTS to the coarser PTS (PTS-NS) resulted in increased container capacity (CC) and shoot growth of ‘Inca Gold’ marigold (Tagetes erecta L.). In another study, PTSs were manufactured in a hammermill fitted with different screen sizes: 4.76, 6.35, 9.54, or 15.8 mm as well as PTS-NS. After being hammermilled, each of the five PTSs was then amended (by mixing) with 10% sand (PTS-S), 25% peatmoss (PTS-PM), or left unamended. Pine tree substrates were also produced by adding 25% aged pine bark (PB) to pine wood chips before being ground in a hammermill with each of the five screen sizes mentioned (PTS-HPB). These five substrates were used unamended as well as amended with 10% sand after grinding (PTS-HPBS). Control treatments included peat-lite (PL) and 100% aged PB for a total of 27 substrates evaluated in this study. Container capacity and marigold growth increased as screen size decreased and with the additions of peatmoss (PTS-PM) or hammering with PB (PTS-HPB) to PTS. Container capacity for all substrates amended with peatmoss or PB was within the recommended range of 45% to 65% for container substrates, but only with the more finely ground PTS-4.76-mm resulted in marigold growth comparable to PL and PB. However, when the PTS-NS was amended by mixing in 25% peat or hammering with 25% PB, growth of marigold was equal to plants grown in PL or PB. In a third study, hammering PTS-NS with 25% PB followed by the addition of 10% sand increased dry weight of both azalea (Rhododendron ×hybrida ‘Girard Pleasant White’) and spirea (Spiraea nipponica Maxim. ‘Snowmound’) resulting in growth equal to plants grown in 100% PB. This work shows that amending coarsely ground PTS with finer particle PTS or with other materials (peatmoss, aged PB, or sand) can result in a substrate with comparable physical properties such as CC and plant growth compared with 100% PL or PB.

Relationships between stem CO2 efflux, substrate supply, and growth in young loblolly pine trees

*We examined the relationships between stem CO(2) efflux (E(s)), diameter growth, and nonstructural carbohydrate concentration in loblolly pine trees. Carbohydrate supply was altered via stem girdling during rapid stem growth in the spring and after growth had ceased in the autumn. We hypothesized that substrate type and availability control the seasonal variation and temperature sensitivity of E(s). *The E(s) increased and decreased above and below the girdle, respectively, within 24 h of treatment. Seasonal variation in E(s) response to girdling corresponded to changes in stem soluble sugar and starch concentration. Relative to nongirdled trees, E(s) increased 94% above the girdle and decreased 50% below in the autumn compared with a 60% and 20% response at similar positions in the spring. *The sensitivity of E(s) to temperature decreased below the girdle in the autumn and spring and increased above the girdle but only in the autumn. Temperature-corrected E(s) was linearly related to soluble sugar (R(2) = 0.57) and starch (R(2) = 0.62) concentration. *We conclude that carbohydrate supply, primarily recently fixed photosynthate, strongly influences E(s) in Pinus taeda stems. Carbohydrate availability effects on E(s) obviate the utility of applying short-term temperature response functions across seasons.

Acclimation of leaf hydraulic conductance and stomatal conductance of Pinus taeda (loblolly pine) to long‐term growth in elevated CO2 (free‐air CO2 enrichment) and N‐fertilization

We investigated how leaf hydraulic conductance (K(leaf)) of loblolly pine trees is influenced by soil nitrogen amendment (N) in stands subjected to ambient or elevated CO(2) concentrations (CO(2)(a) and CO(2)(e), respectively). We also examined how K(leaf) varies with changes in reference leaf water potential (Psi(leaf-ref)) and stomatal conductance (g(s-ref)) calculated at vapour pressure deficit, D of 1 kPa. We detected significant reductions in K(leaf) caused by N and CO(2)(e), but neither treatment affected pre-dawn or midday Psi(leaf). We also detected a significant CO(2)(e)-induced reduction in g(s-ref) and Psi(leaf-ref). Among treatments, the sensitivity of K(leaf) to Psi(leaf) was directly related to a reference K(leaf) (K(leaf-ref) computed at Psi(leaf-ref)). This liquid-phase response was reflected in a similar gas-phase response, with g(s) sensitivity to D proportional to g(s-ref). Because leaves represented a substantial component of the whole-tree conductance, reduction in K(leaf) under CO(2)(e) affected whole-tree water use by inducing a decline in g(s-ref). The consequences of the acclimation of leaves to the treatments were: (1) trees growing under CO(2)(e) controlled morning leaf water status less than CO(2)(a) trees resulting in a higher diurnal loss of K(leaf); (2) the effect of CO(2)(e) on g(s-ref) was manifested only during times of high soil moisture.