Source: OKLAHOMA STATE UNIVERSITY submitted to
INVESTIGATION OF ECOPHYSIOLOGICAL PROCESSES DETERMINING PRODUCTIVITY OF LOBLOLLY PINE
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
TERMINATED
Funding Source
Reporting Frequency
Annual
Accession No.
0151813
Grant No.
(N/A)
Project No.
OKL02120
Proposal No.
(N/A)
Multistate No.
(N/A)
Program Code
(N/A)
Project Start Date
Oct 1, 2001
Project End Date
Sep 30, 2008
Grant Year
(N/A)
Project Director
Hennessey, T. C.
Recipient Organization
OKLAHOMA STATE UNIVERSITY
(N/A)
STILLWATER,OK 74078
Performing Department
NATURAL RESOURCE ECOLOGY & MANAGEMENT
Non Technical Summary
Understanding processes that control forest growth & development is key to increasing productivity & creating sustainable ecosystems. The project seeks to understand & describe the physiological processes that regulate forest productivity 1. in response to moisture & nutrient limitations & 2. among genetic sources & families of loblolly pine. The project will quantify the nutrient use efficiency of loblolly pine & evaluate the interaction of pine genotype, water & nutrients on tree function.
Animal Health Component
100%
Research Effort Categories
Basic
(N/A)
Applied
100%
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
12306111010100%
Goals / Objectives
Quantify the nutrient use efficiency (NUE) of loblolly pine over a wide range of soil environments, phenological stages and growth activities, and determine the extent soil microorganisms immobilize nutrients following fertilization. Determine the interaction of genotype, site resources (water, nutrients) and stand density of crown processes, biomass allocation patterns, and wood properties.
Project Methods
The goal of the project is to understand the physiological processes and mechanisms that regulate tree and forest carbon production and distribuiton (a) in response to moisture and nutrient availability, and (b) among sources and families of loblolly pine.

Progress 10/01/01 to 09/30/08

Outputs
OUTPUTS: (1) Multiple experiments were conducted in a 16 year old loblolly pine plantation to quantify the effects of high temperature, water stress and stand density on tree water relations, gas exchange, wood formation, canopy leaf area, and stand growth. (2) A field study of long term elevation of carbon dioxide on tree growth was conducted. (3) Studies were installed comparing the productivity and carbon allocation of 25 year old Oklahoma/Arkansas (O/A) and North Carolina coastal (NCC) sources of loblolly pine when planted on a droughty site. (4) A field experiment was conducted in a young loblolly pine plantation to better understand essential soil processes and improve nitrogen use efficiency (NUE) in forests. Data for all studies was analyzed and results were disseminated through university teaching, graduate student mentorship, Master's thesis and doctoral dissertations, refereed journal publications, symposium papers, and field days. PARTICIPANTS: Rodney Will Jr. (NREM), Ed Lorenzi (NREM), Robert Wittwer (NREM), Thomas Lynch (NREM), Shiping Deng (Pt & Soil Sci), Mark Payton (Statistics), Kiamichi Forestry Research Station Personnel, Westvaco, Weyerhaeuser Company, US Forest Service, Louisiana State University, Swedish Forest Service TARGET AUDIENCES: Forest landowners, policy makers, natural resource scientists, undergraduate and graduate students PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
Changes in Knowledge: Stand density had little effect on tree water stress. Anticipated gains in soil moisture in thinned plots were likely offset by buildup of understory vegetation. Diurnal measurements of photosynthesis (Pn) and respiration (Rd) over multiple growing seasons showed Pn of the middle and lower branches was 66 percent and 54 percent, respectively of the upper crown. Differences in branch growth within the canopy were strongly related to within-crown variation in light. Thinned trees produced more latewood (greater specific gravity) than unthinned trees. All trees produced latewood first at breast height, then at mid-bole and lastly in the upper bole. A system of equations developed to predict canopy processes showed an increase of only 2 degrees in average air temperature (24.5 to 26.5 degrees C) would result in a 27 percent reduction in leaf biomass production, or approximately 7.3 m2/ha/yr of stem wood. Data will improve models of crown processes and carbon allocation designed to predict effects of air pollutants and /or global climate change on the health and productivity of forests. Exposure of branches to elevated concentrations of carbon dioxide resulted in greatly enhanced branch and foliage growth. Pn doubled at 700 ppm CO2 as compared to ambient concentration (350 ppm) due to decreased photorespiration and increased photosynthetic capacity. Results suggest trees and forests have a large capacity to sequester atmospheric CO2 and that sustained increases in carbon fixation should result in greater forest productivity unless limited by higher temperatures or reduced precipitation. Implications for forest management include lower planting densities, earlier thinning regimes, and shorter rotation lengths with changing climate. When planted on a droughty site, 25 year old NCC sources of loblolly pine carried about 30 percent more foliage than similarly aged O/A sources, and had less branch biomass. Stem biomass, gas exchange, water relations wood specific gravity and survival did not differ between NCC and O/A sources. Planting NCC sources on droughty sites in southeast Oklahoma is a viable management option to produce higher quality wood (fewer knots). Tree density (spacing) can be used to reduce the size of the weak-wooded juvenile core in both sources by controlling radial growth. Site and environmental conditions typically limit nitrogen use efficiency (NUE) to only 15 percent of applied fertilizer. Slow-release forms of nitrogen significantly increased pine needle N and tree leaf area. Fertilization in summer and fall months increase NUE, but control of herbaceous vegetation is required. Soil microbial biomass carbon was adversely effected by fertilization and vegetation control. The sustainability of intensive forest management practices, and carbon sequestration by forests, is contingent on minimizing disruptions in essential soil processes.

Publications

  • Blazier, Michael A., Thomas C. Hennessey, P.M. Dougherty, and R. Campbell. 2006. Nitrogen accumulation and use by a young loblolly pine plantation in southeast Oklahoma: Effects of fertilizer formulation and date of application. Southern Journal of Applied Forestry. 30:66-78.
  • Blazier, Michael A., Thomas C. Hennessey, and Shiping Deng. 2005. Effects of fertilizer and vegetation control on microbial dehydrogenase activity in an intensively managed juvenile loblolly pine plantation. Forest Science. 51(5): 449-459.
  • Blazier, M.A., T.C. Hennessey, T.B. Lynch, R.F. Wittwer and M.E. Payton. 2004. Productivity, crown architecture, and gas exchange of North Carolina and Oklahoma/Arkansas families growing on a droughty site in southeastern Oklahoma. Journal of Forest Ecology and Management. 194:83-94.
  • Hennessey, T.C., P.M. Dougherty, T.B. Lynch, R.F. Wittwer and E.M. Lorenzi. 2004. Long-term growth and ecophysiological responses of a southeastern Oklahoma loblolly pine plantation to early rotation thinning. Special Volume, Journal of Forest Ecology and Management. 192:97-116.
  • Blazier, M.A., T.C. Hennessey, T.B. Lynch and R.F. Wittwer. 2002. Comparison of branch biomass relationships for North Carolina and Oklahoma/Arkansas loblolly pine seed sources growing in southeastern Oklahoma. Forest Ecology and Management 159:241-248.
  • Blazier, M.A., and T.C. Hennessey. 2008. Seasonal soil and foliage nutrient dynamics of a juvenile pine plantation: impacts of fertilization formulation and vegetation suppression. J. For. Ecol. and Manag. 255:3404-3415.


Progress 10/01/05 to 09/30/06

Outputs
Annual measurements were made at the Carter Mountain, OK, research site to quantify the effects of loblolly pine seed sources (Oklahoma/Arkansas and North Carolina coastal) and planting density (4'x4', 6'x6', 8'x8', 10'x10', and 12'x12') on height and diameter growth and leaf area development. At the Eagletown, OK, research site wood cores were obtained from 250 trees to examine the recovery of 25 year old loblolly pine to a severe ice storm in 2000. Cores were prepared for measurements of annual ring width and ring development (earlywood and latewood percentage). A new study was developed to investigate the effects of soil applied Cambistat (paclobutrazol), a tree growth regulator, on urban tree growth and development. Tree branch data was collected from approximately 100 trees.

Impacts
Improved guidelines for managing loblolly pine plantations in SE Oklahoma will be developed, including seed source & spacing recommendations, & alternatives will be proposed for managing ice damaged trees. Improved strategies for managing urban tree populations will also be developed.

Publications

  • Blazier, Michael A., Thomas C. Hennessey, P.M. Dougherty, and R. Campbell. 2006. Nitrogen accumulation and use by a young loblolly pine plantation in southeast Oklahoma: Effects of fertilizer formulation and date of application. Southern Journal of Applied Forestry. 30(2):66-78.
  • Blazier, Michael A., Thomas C. Hennessey, and Shiping Deng. 2005. Effects of fertilizer and vegetation control on microbial dehydrogenase activity in an intensively managed juvenile loblolly pine plantation. Forest Science. 51(5): 449-459.


Progress 10/01/04 to 09/30/05

Outputs
Research was conducted to explore nitrogen accumulation and use by a young loblolly pine plantation in response to (1) season of fertilizer application, (2) herbaceous vegetation suppression, and (3) fertilizer formulation. Water soluble and slow-release urea formulations were applied in January, April, June, August and October of 2001 and 2002. Foliage N accumulation was measured one and two months after fertilization. N use efficiency was measured one year after fertilization. Between 0.3 and 8.0% of applied N was recovered by the foliage within one month of application and 7 to 26% of applied N was used for stem growth within one year of application. Summer and fall applications produced the highest N accumulation and use. Suppressing herbaceous vegetation enhanced N accumulation and use when the plantation was age 3. Nitrogen accumulation and use of slow-release urea was similar to or lower than that of water soluble urea.

Impacts
Practices that enhance crop tree N accumulation and use improve the efficiency of forest fertilization operations. Forest managers may have more flexibility in applying urea than conventional guidelines suggest, with summer and fall applications potentially increasing fertilization effectiveness.

Publications

  • No publications reported this period


Progress 10/01/03 to 09/30/04

Outputs
Soil microorganism populations are of paramount importance to forest soil nutrient cycling and fertility. Research was conducted to characterize the influences of understory vegetation suppression and fertilization on microbial biomass and activity. Microbial biomass carbon (Cmic) and dehydrogenase activity were measured monthly in response to an untreated control, understory vegetation controlled with herbicide, tree removal, and nitrogen and phosphorus treatments. Both vegetation treatments decreased Cmic and dehydrogenase activity by 30 percent and 40 percent, respectively, relative to an untreated control. Fertilization apparently adversely affected labile carbon sources. Reductions in Cmic were correlated with increases in soil nitrate. Results of this study demonstrate that in this young, intensively managed loblolly pine (Pinus taeda L.) plantation labile carbon substrates from vegetation may be a predominant determinant of soil nitrogen availability through its influence on microbial biomass and activity.

Impacts
Competing vegetation suppression & fertilization have become commonplace in the management of young loblolly pine, yet little is known about the effects of these activities on soil microbes. The sustainability of intensive forest management practices is contingent upon minimizing long-term disruptions in essential soil processes & negative environmental effects.

Publications

  • No publications reported this period


Progress 10/01/02 to 09/30/03

Outputs
Biomass partitioning, carbon dioxide and water vapor exchange, and survival of North Carolina Coastal (NCC) and Oklahoma/Arkansas (O/A) provenances of loblolly pine (Pinus taeda L.) were observed on a droughty site in Southeastern Oklahoma to assess their carbon gain and above-ground biomass partitioning patterns. The O/A seed source produced more branch and foliage biomass per hectare than the NCC source, but the two provenances produced equivalent amounts of stem biomass per hectare. The O/A provenance achieved its greater branch and foliage biomass production by virtue of its support of a higher number of live branches per tree. Water use efficiency (WUE) was similar for the two seed sources, as were survival rates. Given the comparable survival and stem biomass production of the two provenances on this droughty site, as well as the NCC provenances production of wood with fewer knots, it appears that planting the NCC provenance in favor of the local seed source on excessively drained soils in the northwestern portion of the loblolly pine range is a justified management option.

Impacts
Understanding the extent of variation in drought tolerance and growth patterns among diverse seed sources of loblolly pine will provide opportunities to increase forest productivity and improve forest sustainability by appropriately matching seed sources with planting environments.

Publications

  • No publications reported this period


Progress 10/01/01 to 09/30/02

Outputs
Annually, approximately 1.5 million acres of forestland are fertilized in the southern U.S. However, tree nutrient use efficiency (NUE) is only about 15%, i.e. 85% of applied fertilizer is not taken up by trees. A study was installed in southeast Oklahoma to determine the NUE of loblolly pine when fertilizer is applied over a wide range of temperature and moisture levels. Additional objectives are to (1) determine the relative efficiency of pine vs. competing vegetation in acquiring nutrients, (2) determine the extent microorganisms immobilize nutrients following fertilization, and (3) determine the effects of slow release formulations of fertilizer on NUE. Second year results indicate (a) applying fertilizer in warm, moist conditions increases pine NUE, (b) herbaceous vegetation is a significant competitor for applied nutrients in young plantations, (c) soil microorganism are carbon limited, not nutrient limited, and (d) use of slow-release fertilizer may improve pine NUE particularly during conditions of low soil moisture.

Impacts
Understanding the site and environmental conditions that limit NUE in southern pines should lead to the development of improved forest management practices designed to improve forest productivity and enhance the long-term sustainability of forestlands.

Publications

  • Blazier, M.A., Hennessey, T.C., Lynch, T.B., and Wittwer, R.F. 2002. Comparison of branch biomass relationships for North Carolina and Oklahoma/Arkansas loblolly pine sources growing in southeastern Oklahoma. Forest Ecology and Management 159, 241-248.


Progress 10/01/00 to 09/30/01

Outputs
Forest fertilization is a common practice in the management of southern U.S. forests. In 1097, 1.9 million forested acres were fertilized. Urea (46% nitrogen) is typically applied in winter months, resulting in a nitrogen use efficiency (NUE) of only about 15%. A study was installed in southeast Oklahoma to determine the NUE of loblolly pine when fertilizer is applied over a wide range of soil temperature and moisture levels. Additional objectives are to determine the extent microorganisms immobilize nutrients following fertilization, and to determine the effects of common vs. slow-release formulations of fertilizers on NUE when competing vegetation is controlled with herbicides. First year results indicate slow-release forms of nitrogen significantly increased the nitrogen content of pine foliage and amount of foliage biomass. Fertilizing at warmer temperatures increased NUE, particularly when slow-release fertilizer formulations were applied. Fertilizer or herbicide treatments did not effect the overall soil microbial population, but microbial activity was decreased.

Impacts
Understanding the site and environmental conditions which currently limit the NUE of southern pine trees to just 15% should lead to the development of forest management practices designed to improve forest productivity, and sustain forested lands. The effective use of slow-release nitrogen formulations should reduce the risk of nitrogen loss off-site, with unintended environmental consequences. More efficient use of nitrogen fertilizers in forest management will benefit both industrial and non-industrial private forest landowners.

Publications

  • No publications reported this period


Progress 10/01/99 to 09/30/00

Outputs
One-third of the South's pine timberlands currently consists of plantations. Wood supplies will increasingly come from these plantations. A study was conducted to learn more about the quality of plantation wood, and to investigate the opportunity to influence wood quality by varying the seed source and spacing of trees within a plantation. This is a cooperative study between the OSU Forestry Department, the U.S. Forest Service Southern Research Station, and the University of Georgia School of Forestry. In general, wood from young, fast-growing plantations has properties that make it less desirable than wood from older, natural stands mainly due to a greater percentage of juvenile wood in young trees. Juvenile wood has lower specific gravity (density) and is weaker wood and more prone to warp than mature wood. Wood cores were collected from 25 year old loblolly pine trees native to North Carolina (NC) and Oklahoma/Arkansas (OA) growing in Oklahoma plantations. Original planting densities were 5'x5', 6'x6', 8'x8', 10'x10' and 12'x12'. Cores were analyzed using an x-ray densitometer for the amount of juvenile and mature wood. Preliminary results indicate all trees begin producing mature wood at age ten. Tree spacing did not effect the length of juvenility, however wider spaced trees had a significantly larger central core of juvenile wood. We believe the length of juvenility is related to environmental factors (temperature, precipitation) associated with geographic location rather than to seed source or spacing differences. Severe midsummer droughts in 1997-1998 greatly reduced the latewood percent, and thus specific gravity, in those annual rings. Results show tree spacing can be used to influence the size of the juvenile core by controlling radial growth. One graduate student was associated with this project.

Impacts
Harvested pine trees provide a significant contribution to the Oklahoma economy. Most pine trees are grown in plantations and the wood produced is inferior to that produced by natural forests. Maximizing value from plantation-grown wood will require changes in harvesting, processing, grading, end-use and resource management.

Publications

  • No publications reported this period


Progress 10/01/98 to 09/30/99

Outputs
Provenance (seed source) tests in Oklahoma and Arkansas have demonstrated increased growth of North Carolina loblolly pine over local sources when planted on sites with adequate moisture-holding capacity. The purpose of our study was to examine the productivity and carbon allocation of two provenances of loblolly pine, North Carolina Coastal (NCC) and Oklahoma/Arkansas (O/A), when planted on a droughty site in souteastern Oklahoma. Branch-level production of foliage and branch biomass for the two provenances was predicted with nonlinear regression equations as a basis for determining tree-level foliage and branch biomass. Nonlinear models were also developed to predict stem biomass production of both provenances. Measurements of photosynthesis, respiration, water relations and wood properties were also collected from several trees over the year. Results indicated the NCC provenance carried about 30% more foliage per branch than O/A branches of comparable size and location within the crown. However, the foliage and branch weight per hectare produced by the O/A provenance was significantly greater than that for the NCC provenance, as a result of more branch production per tree by the O/A source. Stem biomass production did not differ between the two seed sources, nor did gas exchange, water relations, wood specific gravity or survival. It is concluded that planting the NCC provenance on droughty sites in the northwestern portion of the natural range of loblolly pine could be a viable management option. Its survival and growth was similar to the local seed source but fewer limbs per tree were produced, resulting in higher wood quality (fewer knots). One graduate student was associated with this project, and a Master's thesis was produced and accepted by committee.

Impacts
(N/A)

Publications

  • No publications reported this period


Progress 10/01/97 to 09/30/98

Outputs
A set of experiments was initiated in a 15-year-old plantation of loblolly pine in McCurtain County, OK. The experiments are designed to test the following hypotheses: (1) NCC material will have greater growth than O/A material on a soil having low moisture-holding capacity, (2) carbon gain by the NCC source is greater than C-gain by the O/A source, (3) the fraction of the above-ground biomass in the stem, relative to branches and foliage, is greater for the NCC source, (4) growth efficiency (stemwood production per leaf area) is greater for the NCC source, (5) mortality rate as a function of basal area and age are the same for the NCC and O/A sources, and (6) exhibited site index is the same for the NCC and O/A sources. The stand under story consists of replicated one acre plots planted at different spacings (4'x4', 6'x6', 8'x'8', 10'x10' and 12'x12'). Each one acre plot is split and contains two seed sources (Oklahoma/Arkansas (O/A) or North Carolina Coastal (NCC)). In March, one-tenth acre measurement plots were established within each experimental plot across the range of stand densities. Diameter and height of each tree was recorded. In April, 22 trees outside of the measurement plots were destructively harvested, and dry weights were recorded for leaves, branches, and stem. Gas exchange (photosynthesis, stomatal conductance) and needle water potential was measured on 16 trees (8'x8' spacing) in April, June and September at three crown positions for each tree (top, middle and lower crown). Data are being processed. Due to a lengthy drought this summer, an opportunity is provided to clearly assess responses among two wide-ranging sources of loblolly pine to water stress and high temperatures. Results are expected to aid silviculturists in selecting sources of loblolly pine to favor forest health and productivity. One graduate student was associated with this project.

Impacts
(N/A)

Publications

  • No publications reported this period


Progress 10/01/96 to 09/30/97

Outputs
To assess the long-term effects of rising atmospheric CO2 on forests, photosynthesis, photorespiration & dark respiration was determined for loblolly pine branches of fertilized & unfertilized trees, after exposure to ambient and 2x ambient CO2 concentrations for almost two years. When averaged across CO2 & fertilizer treatments, doubling CO2 concentration increased net photosynthesis, decreased photorespiration, & decreased leaf dark respiration. Although elevated CO2 significantly decreased respiration, the increase in net photosynthesis was mainly attributed to increasing capacity of the photosynthetic apparatus. Relative contributions of increased capacity of the photosynthetic apparatus, decreased photorespiration & dark respiration to increased net photosynthesis observed under CO2 enrichment were 55%, 35% and 10%, respectively. These results have two implications. First, since photorespiration significantly declines with increasing CO2 concentration, efforts to increase crop productivity by minimizing photorespiration by other means may not yield large gains if atmospheric CO2 concentration increases as expected. Second, because the increase in net photosynthesis by elevated CO2 is mainly attributed to an increase in the capacity of the photosynthetic apparatus, it appears photosynthesis does not operate under its full potential in ambient air due to CO2 limitation, rather than the biochemical and physiological limitations of the photosynthetic apparatus.

Impacts
(N/A)

Publications

  • Zhang, S. and T.C. Hennessey. The corresponding responses of leaf photosynthesis, photorespiration and dark respiration of loblolly pine trees to elevated CO2. Tree Physiology.


Progress 10/01/95 to 09/30/96

Outputs
A long-term field study to evaluate the response of loblolly pine to elevated concentration of carbon dioxide, water and nutrients was continued. Light-saturated rate of photosynthesis at 1.5X and 2.0X CO2 concentration was 67% and 90% greater, respectively than at ambient CO2. No two or three-way interactions of irrigation, fertilization or CO2 were found. Leaf conductance to water vapor was significantly increased at 1.5X CO2, but decreased at 2.0X CO2. No main treatment interactions were found. Needle chlorophyll content was decreased at elevated CO2. Experiments to test the acclimation of pine foliage to light intensity as related to leaf nitrogen availability showed leaves rapidly acclimated to shaded conditions. Acclimation of photosynthesis to low light was accompanied by decreased stomatal conductance, specific leaf weight, and chlorophyll a/b ratio. No apparent redistribution of nitrogen among leaves was found. Light response curves showed fertilizer had little effect on the quantum yield of photosynthesis. Overall results suggest increased forest productivity can be expected with higher atmospheric CO2 levels unless limited by high temperatures or reduced precipitation. Implications for forest management include lower planting densities, earlier thinning regimes, and shorter rotation lengths with changing climate. Students=1.

Impacts
(N/A)

Publications

  • Hennessey, T.C. and V.K. Harinath. Elevated carbon dioxide, water and nutrient effects on photosynthesis, stomatal conductance and total chlorophyll content of young loblolly pine (P. taeda) trees. Chapter--In: The Productivity and Sustaina
  • Zhang, S., T.C. Hennessey and R.A. Heinemann. Acclimation of loblolly pine (Pinus taeda L.) foliage to light intensity as related to leaf nitrogen availability. Canadian Journal of Forest Science.


Progress 10/01/94 to 09/30/95

Outputs
A long-term field study to evaluate the response of loblolly pine to elevated concentrations of carbon dioxide was continued. Doubling the ambient CO2 level increased monthly light-saturated maximum photosynthesis by 97% and 77% for needles formed in 1994 and 1995, respectively. Accelerated rates of photosynthesis were determined to be a result of both decreased photorespiration (20%) and increased photosynthetic capacity (80%). Dark respiration was increased by 64% in elevated CO2. When averaged over the growing season, leaf stomatal conductance to water vapor was not affected by higher CO2 concentrations, nor was stomatal density on the leaf surface. Overall, these results suggest that trees and forests have a large capacity to buffer rising of CO2 in the atmosphere. Sustained increases in carbon fixation should result in forests with higher productivities as a result of elevated CO2. A separate study comparing the performance of four commercially available portable photosynthesis systems showed that direct comparisons of absolute values of gas exchange among systems is difficult but relative comparisons are appropriate.

Impacts
(N/A)

Publications


    Progress 10/01/93 to 09/30/94

    Outputs
    In order to develop physiologically-based process models to predict the effects of climate change on forest health and productivity, a framework was developed to relate monthly leaf biomass dynamics of a young loblolly pine stand to stand density and monthly variations in weather. A system of equations was developed to predict annual leaf biomass production, monthly needle growth and monthly needlefall, using six consecutive years of weather and forest stand data collected in southeast Oklahoma. Results show that although stand density is the major determinant of annual leaf biomass production, an increase in average temperature of only 2(degree)C (24.5 to 26.5(degree)C) would result in a 27% reduction in leaf biomass production. This translates to an approximate reduction of 7.3 m2/ha/yr of stemwood. First-year data was collected from an intensive field site designed to examine the effects of long-term elevation of CO2 on the growth of loblolly pine. Results show that foliage and branch growth are greatly enhanced in concentrations of 550 and 700 ppm CO2 at well-watered conditions, as compared to ambient levels of 350 ppm CO2. Net photosynthesis rates are doubled at 700 ppm CO2. No depression of stomatal activity was observed at elevated concentrations of CO2. Additional studies were initiated to examine the effects of CO2 levels on needle respiration and photorespiration, processes which are expected to be very sensitive to an altered (warmer) future climate.

    Impacts
    (N/A)

    Publications


      Progress 10/01/92 to 09/30/93

      Outputs
      Diurnal measurements of photosynthesis (Pn) and respiration (Rd) in 19 year-old loblolly pine over the growing season showed that the Pn rate of foliage in the mid and lower crown was 64% and 52%, respectively of that of the upper crown. Differences were strongly related to within-crown variations in light. Unthinned trees began latewood (LW) production 7-10 days before thinned trees. All trees produced (LW) first at breast height, then at mid-bole and lastly in the upper bole. LW initiation date was strongly related to seasonal water stress. Fourth-year measurements of branch and foliage phenology were made and will be related to within-crown differences in seasonal light availability. This information will be important in the development of crown process models designed to predict the effects of air pollutants and/or climate change on the health and productivity of mature trees. A model was developed to predict the leaf biomass dynamics of an 11-17 year-old loblolly stand. Results suggest that only a two degree C change in average temperature would significantly reduce leaf biomass and thus yield of loblolly pine growing in this region. Major effort was directed at the establishment of a new experimental site designed to examine the effects of long-term elevation of CO2 on the physiology and growth of 5-year old field grown loblolly pine. Carbon and water processes models will be developed to make ecosystem risk assessments regarding the potential effects of elevated CO2 and altered climate on loblolly pine ecosystems.

      Impacts
      (N/A)

      Publications


        Progress 10/01/91 to 09/30/92

        Outputs
        Research was continued within a 15 year old loblolly pine stand to quantify the effects of annual weather variables, stand density, bole height and canopy position on tree water relations, net photosynthesis (Pn), foliar respiration (Rd), soil moisture, canopy leaf development, needlefall, wood properties and stand growth. Over the 1992 growing season, Pn of middle and lower crown was 66% and 54%, respectively of the upper crown for irrigated trees. For non-irrigated trees, the values were 61% and 50%, respectively although above average precipitation may have masked true treatment differences. Trees on thinned plots initiated latewood cells (LW) one week earlier than unthinned trees. LW was consistently formed first at breast height, followed by midcrown and lastly at the base of the live crown. Branches in the mid and lower crown elongated only two-thirds and one-third, respectively of those in the upper crown. Branch development was strongly related to light levels within the canopy. A major new experiment was initiated to examine the response of young loblolly pine to elevated atmospheric carbon dioxide under controlled soil moisture and fertility. All the data will be used to improve models of carbon gain and allocation by forests. Two graduate students were used. Termination date: September 30, 1995.

        Impacts
        (N/A)

        Publications


          Progress 10/01/90 to 09/30/91

          Outputs
          Research was conducted within a 16 year old loblolly pine stand to quantify the effects of annual weather variables, stand density, bole height, and canopy position on tree water relations, photosynthesis (Pn), respiration (Rd), soil moisture, canopy leaf area, needlefall, branch development, wood properties and stand growth. Pn and Rd varied monthly with peak values occurring at mid-summer. Young, fully developed foliage in the upper canopy had highest rates of Pn. Rd did not differ between canopy positions, and was strongly influenced by temperature. Average total shoot length for branches in the middle and lower crown positions were 58% and 31% of those in the upper crown. Total leaf area of the upper crown was 32% greater than the mid Crown and 69% greater than the lower crown. Seasonal changes in light levels within the canopy were monitored throughout the growing season. Needlefall was collected monthly for the eighth consecutive year. Wood cores will be taken in December from upper, mid and lower bole positions for wood property analysis. Soil moisture, Pn and Rd were monitored monthly. Data will be used to improve models of carbon allocation and net carbon gain by forests and to provide a framework for interpreting the effects of air pollutants and/or global climate change on forest growth. One graduate student.

          Impacts
          (N/A)

          Publications


            Progress 10/01/89 to 09/30/90

            Outputs
            Forest stand-level research was conducted to quantify the effects of high temperature, water stress and stand density on tree water relations, photosynthesis (Pn) and respiration (Rd), wood formation, leaf area development and stand growth. Stand density had little effect on tree water stress, although large soil moisture differences were present. Macimum Pn was measured in the upper canopy with minimum Pn in the lower canopy. Models indicated variation in light explained the majority of canopy position Pn differences. Phenology research showed shoot and needle development patterns and needle senescence varied widely between crown positions. Data will be used to improve models of net carbon gain by forests and to provide a framework for interpreting the effects of air pollutants and/or global climate change on forest growth. 1 graduate student.

            Impacts
            (N/A)

            Publications