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PubMed1986

Determining nitrogen status of young loblolly pine by leaf reflectance.

Five-year-old lobloliy pine (Pinus taeda L.) seedlings were grown in sand culture in a completely randomized experimental design with eight nitrogen concentrations and three replications. Nitrogen concentration in the nutrient solution varied from 2 to 400 ppm. After a full growing season under treatment, percent reflectance of sunlight by new foliage was determined. Foliar samples were analyzed for nitrogen and chlorophyll. There was a strong positive correlation between nitrogen content and chlorophyll content (r = 0.895). The natural logarithm of percent reflectance was negatively correlated with both percent nitrogen content (r = -0.845) and chlorophyll content (r = -0.838). From these results, prediction equations for estimating nitrogen and chlorophyll content, as a function of reflectance, were formulated by regression analysis.

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PubMed1992

Comparison of methods for estimating surface area of water-stressed and fully hydrated pine needle segments for gas exchange analysis.

A nondestructive technique for repeatedly estimating total surface area of water-stressed pine (Pinus taeda L.) fascicle segments was evaluated. Fascicle radius was measured with a digital caliper and needle surface area calculated on the assumption that the needles were segments of a cylinder. High correlations (r >/= 0.94) were found between surface area estimated in this way and surface area calculated (a) from needle displacement, also on the assumption that needles are segments of a cylinder, and (b) from needle dry weight using a regression between dry weight and surface area estimated from needle displacement. The caliper-radius method gave slightly lower estimates of surface area than the other methods. However, differences among surface area estimates made with the three methods and between estimates made on water-stressed and fully hydrated needles were small relative to variances of leaf gas exchange measurements.

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PubMed1992

Biochemical composition of loblolly pine reflects pollutant exposure.

Under experimental conditions, the growth of loblolly pine (Pinus taeda L.) is often responsive to ozone at near-ambient concentrations. However, little is known of the biochemical changes associated with this or other pollutants. Loblolly pine seedlings in open-top chambers were exposed to combinations of ozone (sub-ambient, ambient, or twice-ambient), acidic precipitation (pH 3.8 or pH 5.2) and soil magnesium (0.15 or 0.32 microg g(-1) exchangeable Mg) for three growing seasons. The effects of these treatments were greater in foliage than in stems or roots. The largest treatment effect was a 50% decrease in the starch concentration of current-year foliage from the twice-ambient ozone treatment compared with current-year foliage from the sub-ambient ozone treatment. Responses to ozone were consistent with the hypothesis that ozone-induced growth reductions are associated with depletion of carbohydrate reserves resulting from injury compensation and repair processes or reduced carbon fixation or both. Addition of acidic precipitation, and to a small extent Mg, decreased sugar concentrations of tissues; however, this effect appeared to be mediated by nutrient addition rather than by acidity per se. Given the role of carbohydrates in plant resistance to environmental stress, the sensitivity of carbohydrates to experimental treatments demonstrates the potential for indirect effects of ozone, acidic precipitation, and soil properties on stress resistance. Noncarbohydrate constituents were largely unresponsive to the experimental treatments. These findings imply that tissue carbohydrate analysis may be useful for assessing the impacts of pollutants in forest ecosystems.

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PubMed1993

The effects of ultraviolet-B radiation on photosynthesis of different aged needles in field-grown loblolly pine.

We examined the effect of supplemental UV-B radiation (290-320 nm) on photosynthetic characteristics of different aged needles of 3-year-old, field-grown loblolly pine (Pinus taeda L.). Needles in four age classes were examined: I, most recently fully expanded, year 3; II, first flush, year 3; III, final flush, year 2; and IV, oldest needles still present, year 2. Enhanced UV-B radiation caused a statistically significant decrease (6%) in the ratio of variable to maximum fluorescence (F(v)/F(m)) following dark adaptation only in needles from the youngest age class, suggesting transient damage to photosynthesis. However, no effects of enhanced UV-B radiation on other instantaneous measures of photosynthesis, including maximum photosynthesis, apparent quantum yield and dark respiration, were seen for needles of any age. Foliar nitrogen concentration was unaffected by UV-B treatment. However, the (13)C/(12)C carbon isotope ratios (delta(13)C-a time integrated measure of photosynthetic function) of needles in age classes II and IV were 3% (P < 0.01) and 2% (P < 0.05) more negative, respectively, in treated plants than in control plants. Exposure to enhanced UV-B radiation caused a 20% decrease in total biomass and a 4% (P < 0.05), 25% (P < 0.01), and 9% (P < 0.01) decrease in needle length of needles in age classes I, II, and IV, respectively. The observed decreases in delta(13)C, and F(v)/F(m) of the needles in the youngest needle age class suggest subtle damage to photosynthesis, although overall growth reductions were probably a result of decreased total leaf surface rather than decreased photosynthetic capacity. Needles of age class IV had lower light- and CO(2)-saturated maximum photosynthetic rates (39%), lower dark respiration (34%), lower light saturation points (37%), lower foliar nitrogen concentration (28%), and lower delta(13)C (14%) values than needles of age class I. Apparent quantum yield and F(v)/F(m) did not change with needle age. The observed changes in photosynthesis and foliage chemical composition with needle age are consistent with previous studies of coniferous trees and may represent adaptations of older needles to shaded conditions within the canopy.

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PubMed1993

Responses of loblolly pine seedlings to elevated CO(2) and fluctuating water supply.

Osmotic adjustment of loblolly pine (Pinus taeda L.) seedlings to fluctuating water supply in elevated CO(2) was investigated. Seedlings were grown in controlled-environment chambers in either 350 or 700 micro l l(-1) CO(2) with weekly watering for four months, after which they were either watered weekly (well-watered treatment) or every two weeks (water-stress treatment) for 59 days. Osmotic adjustment was assessed by pressure-volume analysis of shoots and by analysis of soluble carbohydrates and free amino acids in roots during the last drying cycle. In well-watered seedlings, elevated CO(2) increased the concentration of soluble sugars in roots by 68%. Water stress reduced the soluble sugar concentration in roots of seedling growing in ambient CO(2) to 26% of that in roots of well-watered seedlings. Elevated CO(2) mitigated the water stress-induced decrease in the concentration of soluble sugars in roots. However, this was probably due, in part, to carbohydrate loading during the first four months when all seedlings were grown in the presence of a high water supply, rather than to osmotic adjustment to water stress. Water stress caused a doubling in the concentration of free primary amino acids in roots, whereas elevated CO(2) reduced primary amino acid and nitrogen concentrations to 32 and 74%, respectively, of those in roots of seedlings grown in ambient CO(2). There was no indication of large-scale osmotic adjustment to water stress or that elevated CO(2) enhanced osmotic adjustment in loblolly pine.

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PubMed1994

Phosphorus supply affects the photosynthetic capacity of loblolly pine grown in elevated carbon dioxide.

Effects of phosphorus supply and mycorrhizal status on the response of photosynthetic capacity to elevated CO(2) were investigated in loblolly pine (Pinus taeda L.) seedlings. Seedlings were grown in greenhouses maintained at either 35.5 or 71.0 Pa CO(2) in a full factorial experiment with or without mycorrhizal inoculum (Pisolithus tinctorius (Pers.) Coker & Couch) and with an adequate or a limiting supply of phosphorus. Assimilation versus internal CO(2) partial pressure (C(i)) curves were used to estimate maximum Rubisco activity (V(c,max)), electron transport mediated ribulose 1,5-bisphosphate regeneration capacity (J(max)), phosphate regeneration capacity (PiRC) and daytime respiration rates (R(d)). Nonmycorrhizal seedlings grown with limiting phosphorus had significantly reduced V(c,max) and PiRC compared to seedlings in other treatments. Elevated CO(2) increased photosynthetic capacity in nonmycorrhizal seedlings in the low phosphorus treatment by increasing PiRC, whereas it induced phosphorus limitation in mycorrhizal seedlings in the low phosphorus treatment and did not affect the photosynthetic capacity of seedlings in the high phosphorus treatment. Despite the variety of effects on photosynthetic capacity, seedlings in the elevated CO(2) treatments had higher net assimilation rates than seedlings in the ambient CO(2) treatments. We conclude that phosphorus supply affects photosynthetic capacity during long-term exposure to elevated CO(2) through effects on Rubisco activity and ribulose 1,5-bisphosphate regeneration rates.

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PubMedDate not supplied

Use of provenance tests to predict response to climate change: loblolly pine and Norway spruce.

Provenance tests are often used to determine genetic responses of seed sources to transfer to different climates. This study was undertaken to determine whether provenance tests can be used to predict tree response to rapid climate changes in situ. Data from provenance tests of loblolly pines (Pinus taeda L.), Norway spruce (Picea abies L. Karst) and other southern pines (subsect. AUSTRALES Loud.) were interpreted using regression models to relate growth to temperature variables. Results of different plantings were combined by expressing growth as a percent deviation from the "local" source, and expressing temperature at the source as a deviation from that of the planting site. The results of the loblolly pine and Norway spruce models predicted a loss of about 5 to 10% in height growth below that expected for a genetically adapted seed source, if the average yearly temperature increases by 4 degrees C.

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PubMed1995

Water relations and growth of loblolly pine seedlings planted under a shelterwood and in a clear-cut.

We investigated the influence of shelterwood conditions on water relations and growth of loblolly pine (Pinus taeda L.) seedlings on two harsh sites in eastern Texas. Site I was harvested to provide four overstory density treatments (0, 2.3, 4.6 and 9.2 m(2) of residual basal area per ha). To quantify the effects of overstory competition, trenched and nontrenched subplots, each containing 25 one-year-old seedlings, were established within each overstory treatment plot, and predawn and midday water potentials (Psi(w)), seedling growth and survival were measured during the growing season. Leaf area and seedling biomass partitioning were measured at the end of the growing season. Site II was harvested to provide two overstory density treatments (0 and 6.9 m(2) ha(-1)) and planted with one-year-old loblolly pine seedlings. Seedling Psi(w), stomatal conductance (g(wv)), transpiration flux density (E), leaf area, height and survival were determined. On Site I, seedling Psi(w) increased with increasing overstory basal area, whereas trenching only substantially affected Psi(w) of seedlings in the 9.2 m(2) ha(-1) overstory treatment. Growth was not affected by overstory treatment or trenching. On Site II, Psi(w) and g(wv) were highest during the morning hours and lowest in the afternoon, whereas E peaked in the afternoon. Vapor pressure deficits and photosynthetic photon flux density were major factors in determining g(wv) differences between treatments. On individual days, the presence of an overstory increased Psi(w) and reduced both g(wv) and E. On Site II, leaf area was affected by overstory treatment throughout most of the study. We conclude that the presence of an overstory can have ameliorative effects on harsh sites at the western fringe of the loblolly pine natural range.

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PubMed1995

Genetic variation in rooting ability of loblolly pine cuttings: effects of auxin and family on rooting by hypocotyl cuttings.

After about 20 days, hypocotyl cuttings from 20-day-old loblolly pine (Pinus taeda L.) seedlings rooted easily in the presence of the auxin indole-3-butyric acid (IBA), with roots forming directly from xylem parenchyma. In contrast, woody cuttings from 1-2-year-old hedged seedlings formed roots indirectly from callus tissue in 60-90 days, but IBA had little effect on rooting. Variation in rooting among hypocotyls from both half- and full-sib families was highly significant in response to IBA, and rooting did not occur within 20 days unless IBA was applied. Hypocotyls from poor rooting families tended to produce fewer roots per cutting than hypocotyls from good rooting families. Rooting by woody cuttings and hypocotyl cuttings from the same nine full-sib families was weakly correlated, raising the possibility that at least some common genetically controlled processes were affecting rooting by both types of cutting. The phytotropin N-1-naphthylphthalamic acid (NPA), supplied at 1 micro M with 10 micro M IBA, significantly inhibited rooting by hypocotyl cuttings from both good and poor rooting families, but there was no significant family x treatment interaction. Family variation in rooting ability may be a function of the frequency of occurrence of auxin-responsive cells in the hypocotyls.

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PubMed1995

Responses of foliar gas exchange to long-term elevated CO(2) concentrations in mature loblolly pine trees.

Branches of field-grown mature loblolly pine (Pinus taeda L.) trees were exposed for 2 years (1992 and 1993) to ambient or elevated CO(2) concentrations (ambient + 165 micro mol mol(-1) or ambient + 330 micro mol mol(-1) CO(2)). Exposure to elevated CO(2) concentrations enhanced rates of net photosynthesis (P(n)) by 53-111% compared to P(n) of foliage exposed to ambient CO(2). At the same CO(2) measurement concentration, the ratio of intercellular to atmospheric CO(2) concentration (C(i)/C(a)) and stomatal conductance to water vapor did not differ among foliage grown in an ambient or enriched CO(2) concentration. Analysis of the relationship between P(n) and C(i) indicated no significant change in carboxylation efficiency of ribulose-1,5-bisphosphate carboxylase/oxygenase during growth in elevated CO(2) concentrations. Based on estimates derived from P(n)/C(i) curves, there were no apparent treatment differences in dark respiration, CO(2) compensation point or P(n) at the mean C(i). In 1992, foliage in the three CO(2) treatments yielded similar estimates of CO(2)-saturated P(n) (P(max)), whereas in 1993, estimates of P(max) were higher for branches grown in elevated CO(2) than in ambient CO(2). We conclude that field-grown loblolly pine trees do not exhibit downward acclimation of leaf-level photosynthesis in their long-term response to elevated CO(2) concentrations.

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PubMedDate not supplied

Surrogate pollen induction shortens the breeding cycle in loblolly pine.

Surrogate pollen induction (SPI) was evaluated on loblolly pine (Pinus taeda L.) donor scions from 5-year-old progeny that were grafted by topworking into the lower crowns of 16-year-old loblolly pine receptor clones in a seed orchard. On each of 25 study trees, one of three pollen induction treatments (wire girdle, saw girdle or control) was applied to 10 receptor branches below the graft location. Graft survival was 76%. Of the surviving grafts, 57% produced pollen strobili in March 1993, 13 months after grafting. The pollen induction treatments did not decrease graft survival or increase pollen production. Graft survival did not vary significantly among the donor scion genotypes, but the percentage of grafts with pollen was significantly related to the donor scion genotype. The mean number of pollen clusters induced per ramet also differed significantly among the donor scions. There was a tendency for pollen phenology of the grafted scions to be modified by the receptor clone. We conclude that surrogate pollen induction, coupled with accelerated female flower stimulation, can reduce the breeding schedule in loblolly pine to 3 years.

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PubMedDate not supplied

Genetic and environmental variation of foliar nutrient concentrations and strobilus initiation in fertilized loblolly pine seed orchard ramets.

Fertilizer was applied annually for eight years to individual ramets in a loblolly pine (Pinus taeda L.) seed orchard at rates ranging from 0 to 448 kg nitrogen (N) ha(-1) year(-1). Clonal effects accounted for a major source of variation in both flowering and foliar nutrient concentrations. Foliar N concentrations were generally correlated with the intensity of fertilizer application, but were only weakly correlated with flowering. There was a long-term trend for increasing concentrations of foliar manganese (Mn) and boron (B), and decreasing concentrations of magnesium (Mg) and zinc (Zn) with increasing fertilizer rates, although only the differences in Mn concentration were statistically significant. Fertilizer had little effect on the concentrations of other foliar macro- or micronutrients during the study. The optimum fertilizer rate for flowering was 224 kg N ha(-1) year(-1).

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PubMedDate not supplied

Temporal and spatial aspects of root and stem sucrose metabolism in loblolly pine trees.

We studied root and stem sucrose metabolism in trees excavated from a 9-year-old artificially regenerated loblolly pine (Pinus taeda L.) plantation. Sucrose synthase (SS) activities in stem and taproot vascular cambial tissues followed similar seasonal patterns until they peaked during September. After September, stem SS activity disappeared quickly, whereas taproots exhibited SS activity even in January. Pyrophosphate-dependent phosphofructokinase (PPi-PFK) activity tracked SS activity. The activities of ATP-dependent PFK and several other glycolytic enzymes (e.g., phosphoglucomutase and phosphoglucoisomerase) remained relatively constant in cambial tissues of stem, taproot, and all first-order lateral roots (FOLRs) throughout the year. However, during the growing season, individual FOLRs exhibited variable sucrose metabolic activities that were independent of root diameter or position on the taproot. The FOLRs with low or no SS activity also had low PPi-PFK activity. We propose that when intense competition for sucrose occurs among different organs of a tree, the variable activities of the sucrose metabolic enzymes in FOLRs ensure that enough sucrose is allocated to the stem and taproot for growth. For a tree's long-term survival and growth, second or higher-order roots can be sacrificed, whereas FOLRs, stem and taproot are essential.

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PubMedDate not supplied

Seasonal branch and fine root growth of juvenile loblolly pine five growing seasons after fertilization.

In 1989, we established two replications of two fertilization treatments in a 10-year-old loblolly pine (Pinus taeda L.) plantation. Between March and September 1993, branch internode and needle fascicle expansion in the upper and lower third of crowns were measured weekly on three south-facing branches of each of four trees, and new root initiation and elongation were measured at 10-day intervals in three vertical rhizotrons per plot. In one replication, soil water content was measured daily. Fertilization significantly increased the expansion of first flush internodes in the upper crown and first flush needle fascicles in the upper and lower crown. New root growth was stimulated by fertilization in the second half of the growing season. The timing of root growth responses to fertilization corresponded to branch phenologies in the upper and lower crown that were conducive to increased basipetal transport of photosynthate. We conclude, therefore, that new root growth was linked to source-sink activities in the crown. Root initiation was greater in the upper than in the lower part of the soil profile; however, as the growing season progressed and water deficit increased, this relationship was reversed. The effect of soil depth on seasonal root growth was closely associated with water availability, suggesting that root initiation deep in the soil profile is critical for the continued production of new roots in environments subjected to short-term, but relatively severe, water deficits.

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PubMedDate not supplied

Responses of loblolly pine, sweetgum and crab grass roots to localized increases in nitrogen in two watering regimes.

Root responses to differences in availability of nitrogen and soil water were studied in loblolly pine (Pinus taeda L.) seedlings grown in monoculture and in competition with sweetgum (Liquidambar styraciflua L.) or crab grass (Digitaria spp.). Rhizotron cells were maintained at high soil water availability (approximately -0.1 MPa) or subjected to three dry-down cycles to low soil water availability (approximately -1.0 MPa), over two growing seasons. Localized increases in nitrogen availability were created by adding nitrogen in solution to root ingress cores placed in each rhizotron cell. Presence of competitors reduced loblolly pine root growth regardless of the nitrogen or soil water treatment. On average, both total root length density and root surface area were reduced 60% when loblolly pine seedlings were grown with crab grass and 31% when grown with sweetgum. Low water availability reduced loblolly pine root length density and root surface area by 25 and 28%, respectively, compared with well-watered seedlings. Sweetgum root surface area was reduced 18% by the low water availability treatment, whereas crab grass root surface area was unaffected by this treatment. At all soil depths, loblolly pine root surface area and root length density were increased in localized areas of increased nitrogen availability. Sweetgum and crab grass root surface areas were also greater in areas of increased nitrogen availability. In the high soil water availability treatment, loblolly pine root surface area increased 128% in localized areas of increased nitrogen in all competition treatments. In the low soil water availability treatment, loblolly pine roots responded to increased nitrogen only in the absence of competitors. In general, loblolly pine and sweetgum roots responded to increases in resource availability similarly, whereas crab grass roots were relatively less affected.

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PubMedDate not supplied

Non-nutritional stress acclimation of mycorrhizal woody plants exposed to drought.

Mycorrhizal enhancement of drought resistance of two woody plant species, loblolly pine (Pinus taeda L.) and rose (Rosa hybrida L. cv. Ferdy), occurred independently of phosphorus nutrition. Mycorrhizae tended to alter root morphology and carbon allocation patterns of shoots and roots. Increased drought resistance of mycorrhizal plants was in part attributed to drought-induced colonization by mycorrhizae and the ability of the mycorrhizal plants to maintain high transpiration rates as a result of greater lateral root formation and lower shoot mass (in ectomycorrhizal loblolly pine), and a higher root/shoot ratio and leaf abscission (in endomycorrhizal roses). Neither the endo- nor ectomycorrhizal symbionts affected osmotic adjustment of droughted plants.

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PubMed1997

Simulating the response of mature yellow poplar and loblolly pine trees to shifts in peak ozone periods during the growing season using the TREGRO model.

Multiple TREGRO simulations were conducted with meteorological data files containing different growing season peak ozone (O(3)) episodes at O(3) exposures of 1.0 and 2.0 x ambient O(3) to assess the relationship between O(3) response and the phenology of mature yellow poplar (Liriodendron tulipifera L.) and loblolly pine (Pinus taeda L.) trees. Regardless of O(3) exposure and peak O(3) episode occurrence, a peak O(3) episode in August caused the greatest reduction in carbon (C) gain in yellow poplar, whereas a peak O(3) episode in July caused the greatest reduction in C gain of loblolly pine. In both species, timing of the greatest simulated O(3) effect corresponded with the completion of the annual foliage production phenophase. Simulated C gain of yellow poplar (total tree, coarse root, and total nonstructural carbohydrate) was reduced by O(3) to a greater extent than the corresponding compartments in loblolly pine, but the opposite was true for fine roots. This differential sensitivity to O(3) reflects the fact that both C assimilation and the O(3) response of the species were parameterized according to observed field measurements of each species. The differential sensitivity to O(3) of these species may have long-term implications for species composition in southeastern USA forests.

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PubMed1997

Changes in rates of photosynthesis and respiration during needle development of loblolly pine.

Net photosynthetic rates of developing foliage and one-year-old foliage of loblolly pine (Pinus taeda L.) were measured under field conditions. In the subsequent year, net photosynthesis and dark respiration rates of current-year and one-year-old foliage were measured under controlled environmental conditions. Loblolly pine foliage grows slowly, reaching its final size 3.5 to 4 months after bud burst. Positive rates of net photosynthesis were recorded when the foliage was 13 and 18% of final length, in the controlled-environment and field study, respectively. However, because of high rates of dark respiration during the initial growth period, a positive diurnal carbon balance did not occur until foliage was about a third of final length (40 days after bud burst). Two months after bud burst, when foliage was about 55% of final length, its photosynthetic capacity exceeded that of one-year-old foliage. The highest rates of net photosynthesis were achieved when foliage was more than 90% fully expanded.

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