Leaf-level gas-exchange uniformity and photosynthetic capacity among loblolly pine (Pinus taeda L.) genotypes of contrasting inherent genetic variation.

Variation in leaf-level gas exchange among widely planted genetically improved loblolly pine (Pinus taeda L.) genotypes could impact stand-level water use, carbon assimilation, biomass production, C allocation, ecosystem sustainability and biogeochemical cycling under changing environmental conditions. We examined uniformity in leaf-level light-saturated photosynthesis (A(sat)), stomatal conductance (g(s)), and intrinsic water-use efficiency (A(sat)/g(s) or δ) among nine loblolly pine genotypes (selected individuals): three clones, three full-sib families and three half-sib families, during the early years of stand development (first 3 years), with each genetic group possessing varying amounts of inherent genetic variation. We also compared light- and CO(2)-response parameters between genotypes and examined the relationship between genotype productivity, gas exchange and photosynthetic capacity. Within full-sib, half-sib and clonal genotypes, the coefficient of variation (CV) for gas exchange showed no consistent pattern; the CV for g(s) and δ was similar within clonal (44.3-46.9 and 35.5-38.6%) and half-sib (41.0-49.3 and 36.8-40.9%) genotypes, while full-sibs showed somewhat higher CVs (46.9-56.0 and 40.1-45.4%). In contrast, the CVs for A(sat) were generally higher within clones. With the exception of δ, differences in gas exchange among genotypes were generally insignificant. Tree volume showed a significant positive correlation with A(sat) and δ, but the relationship varied by season. Individual-tree volume and genotype volume were positively correlated with needle dark respiration (R(d)). Our results suggest that uniformity in leaf-level physiological rates is not consistently related to the amount of genetic variation within a given genotype, and δ, A(sat) and R(d) were the leaf-level physiological parameters that were most consistently related to individual-tree and genotype productivity. An enhanced understanding of molecular and environmental factors that influence physiological variation within and between loblolly pine genotypes may improve assessments of genotype growth potential and sensitivity to global climate change.

Determining the viability response of pine pollen to atmospheric conditions during long-distance dispersal.

Pollen of forest trees can move on the scales of tens to hundreds of kilometers, but the question of its viability during this long distance dispersal (LDD) has yet to be answered. While empirical studies of pollen viability in forest tree species are rare, controlled and scalable data to outdoor studies of the contribution of UV irradiation on pollen viability are not available. A simple protocol that allows the quantification of the viability response of pollen to UV, temperature, and humidity is developed and described here. Bench-scale conditions that approximate a wide range of atmospheric conditions including different humidity, temperature, and UV irradiation condition are used to determine the independent effects of each abiotic stress factor, and empirical functions are fitted and used to scale these bench-scale experiments to outdoor conditions. As a case study, pollen was sampled from two populations of Pinus taeda during two years and was used to quantify the decrease in viability due to atmospheric conditions during LDD. Contrary to maize pollen, P. taeda pollen viability decreased due to humid and cold conditions. The viability response of pollen to UV-A and UV-B corresponded to a viability reduction of about 10% after a full day of exposure. These laboratory findings were corroborated by an outdoor solar exposure experiment. The Fu-Liou online radiation model and a data set of radiosonde observations were used to estimate the typical conditions that would be encountered by LDD pollen. If initially caught in a strong updraft, dispersing P. taeda pollen could be carried many days and thousands of kilometers in the air. The empirical equations for P. taeda pollen viability reduction due to abiotic stresses predicted that 50% of the pollen would survive 24 hours of LDD under typical external conditions. The viable range of the pollen is, therefore, shorter than the physical dispersal distance. The methods used in our experiments are applicable for determination of dispersing pollen viability, especially when effects of different adverse conditions need to be separated. The empirical viability equations that resulted from our experiments can be used in an atmospheric dispersal model to estimate the viable range of tree pollen.

Leaf traits in relation to crown development, light interception and growth of elite families of loblolly and slash pine.

Crown architecture and size influence leaf area distribution within tree crowns and have large effects on the light environment in forest canopies. The use of selected genotypes in combination with silvicultural treatments that optimize site conditions in forest plantations provide both a challenge and an opportunity to study the biological and environmental determinants of forest growth. We investigated tree growth, crown development and leaf traits of two elite families of loblolly pine (Pinus taeda L.) and one family of slash pine (P. elliottii Mill.) at canopy closure. Two contrasting silvicultural treatments -- repeated fertilization and control of competing vegetation (MI treatment), and a single fertilization and control of competing vegetation treatment (C treatment) -- were applied at two experimental sites in the West Gulf Coastal Plain in Texas and Louisiana. At a common tree size (diameter at breast height), loblolly pine trees had longer and wider crowns, and at the plot-level, intercepted a greater fraction of photosynthetic photon flux than slash pine trees. Leaf-level, light-saturated assimilation rates (A(max)) and both mass- and area-based leaf nitrogen (N) decreased, and specific leaf area (SLA) increased with increasing canopy depth. Leaf-trait gradients were steeper in crowns of loblolly pine trees than of slash pine trees for SLA and leaf N, but not for A(max). There were no species differences in A(max), except in mass-based photosynthesis in upper crowns, but the effect of silvicultural treatment on A(max) differed between sites. Across all crown positions, A(max) was correlated with leaf N, but the relationship differed between sites and treatments. Observed patterns of variation in leaf properties within crowns reflected acclimation to developing light gradients in stands with closing canopies. Tree growth was not directly related to A(max), but there was a strong correlation between tree growth and plot-level light interception in both species. Growth efficiency was unaffected by silvicultural treatment. Thus, when coupled with leaf area and light interception at the crown and canopy levels, A(max) provides insight into family and silvicultural effects on tree growth.

Short-term effects of fertilization on photosynthesis and leaf morphology of field-grown loblolly pine following long-term exposure to elevated CO(2) concentration.

We examined effects of a first nitrogen (N) fertilizer application on upper-canopy needle morphology and gas exchange in approximately 20-m-tall loblolly pine (Pinus taeda L.) exposed to elevated carbon dioxide concentration ([CO(2)]) for 9 years. Duke Forest free-air CO(2) enrichment (FACE) plots were split and half of each ring fertilized with 112 kg ha(-1) elemental N applied in two applications in March and April 2005. Measurements of needle length (L), mass per unit area (LMA), N concentration (N(l)) on a mass and an area basis, light-saturated net photosynthesis per unit leaf area (A(a)) and per unit mass (A(m)), and leaf conductance (g(L)) began after the second fertilizer application in existing 1-year-old foliage (F(O)) and later in developing current-year first-flush (F(C1)) and current-year second-flush (F(C2)) foliage. Elevated [CO(2)] increased A(a) by 43 and 52% in F(O) and F(C1) foliage, respectively, but generally had no significant effect on any other parameter. Fertilization had little or no significant effect on L, LMA, A or g(L) in F(O) foliage; although N(l) was significantly higher in fertilized trees by midsummer. In contrast, fertilization resulted in large increases in L, N(l), and A in F(C1) and F(C2) foliage, increasing A(a) by about 20%. These results suggest that, although both needle age classes accumulate N following fertilization, they use it differently-current-year foliage incorporates N into photosynthetic machinery, whereas 1-year-old foliage serves as an N store. There were no significant interaction effects of elevated [CO(2)] and fertilization on A. Elevated [CO(2)] increased the intercept of the A:N(l) relationship but did not significantly affect the slope of the relationship in either foliage age class.

1-Hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate reductase (IDS) is encoded by multicopy genes in gymnosperms Ginkgo biloba and Pinus taeda.

Isoprenoids are synthesized through the condensation of five-carbon intermediates, isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), derived from two distinct biosynthetic routes: cytosolic mevalonate (MVA) and plastidial 2-C-methyl-D: -erythritol 4-phosphate (MEP) pathways. 1-Hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate reductase (IDS; EC 1.17.1.2), which catalyzes the last step of MEP pathway, was cloned as a multicopy gene from gymnosperms Ginkgo biloba (GbIDS1, GbIDS2, and GbIDS2-1) and Pinus taeda (PtIDS1 and PtIDS2), and characterized. Phylogenetic tree constructed with other plant IDSs demonstrated gymnosperm IDSs were distinctively different from angiosperm IDSs. The gymnosperm IDS clade contained two subclades, one composed of GbIDS1 and PtIDS1, and the other composed of GbIDS2, GbIDS2-1, and PtIDS2. G. biloba IDSs, except GbIDS2-1, successfully complemented Escherichia coli DLYT1, a lytB disruptant, confirming the in vivo competency of isozymes. During the 4 weeks study period, although transcript levels of GbIDS1s were similar both in roots and leaves of cultured G. biloba embryo, the transcripts of GbIDS2 predominantly occurred in the embryo roots, where diterpene ginkgolides are biosynthesized. Levels of PtIDS2 transcripts in the diterpenoid resin-producing wood were 4-5 times higher than those in other tissues. Higher levels of GbIDS1 transcripts were induced by light, whereas those of GbIDS2 were increased by methyl jasmonate treatment. These results strongly imply GbIDS2 and PtIDS2 have high correlation with secondary metabolism. In Arabidopsis transient expression system, N-terminal 100 amino acid residues of GbIDS1 delivered fused GFP protein into chloroplast as well as cytosol and nucleus, whereas those of GbIDS2, GbIDS2-1, and two PtIDSs delivered GFP only into chloroplast.

Light quality treatments enhance somatic seedling production in three southern pine species.

Embryogenic cultures of loblolly pine (Pinus taeda L.), slash pine (Pinus elliottii Engelm.), longleaf pine (Pinus palustris Mill.) and slash pine x longleaf pine hybrids were initiated from immature seeds on an initiation medium containing 13.57 microM 2,4-dichlorophenoxyacetic acid and 2.22 microM benzylaminopurine. Embryogenic cultures proliferated and somatic embryos developed, matured and germinated following a modified protocol and media originally developed for radiata pine (Pinus radiata D. Don.) somatic seedling production. A discrete, light-sensitive pre-germination stage and a later germination (radicle emergence) stage were identified by the differential response of somatic embryos to light of different wavelengths. Different light quality treatments were applied during the pre-germination and germination steps, using cool white fluorescent bulbs or light-emitting diodes (LEDs), or both. In general, red wavelengths provided by LEDs during these steps resulted in higher frequencies of somatic embryo germination (up to 64%) and conversion (up to 50%), longer tap roots and more first-order lateral roots than the standard cool white fluorescent treatments or treatment with blue wavelengths from LEDs. In addition, exposure to red light allowed germination of somatic embryos of some clones that failed to produce germinants under fluorescent light. Germination and conversion were further enhanced by sequential application of cool white fluorescent light and red light, resulting in up to 100% germination and conversion in one experiment. Longleaf pine somatic embryos were especially responsive to the light quality treatments, resulting in the first report of somatic seedling production for this species.