A Genetic linkage map of Pinyon pine (Pinus edulis) based on amplified fragment length polymorphisms

 Amplified fragment length polymorphisms (AFLP) were used to rapidly generate a dense linkage map for pinyon pine (Pinus edulis). The map population consisted of 40 megagametophytes derived from one tree at Sunset Crater, Arizona. A total of 78 primer combinations, each with three to five selective nucleotides, amplified 542 polymorphic markers. Of these, 33 markers showed significant deviation from the expected Mendelian genotypic segregation ratio of 1 : 1, and 164 showed complete linkage with another marker. This resulted in 338 unique markers mapping to 25 linkage groups, each of which ranged from 2 to 22 markers, averaging 80 centiMorgans (cM) in size and covering 2,012 cM (2,200 cM with the inclusion of 25 cM for each of 7 unlinked markers). Pairwise linkage values gave a genome size estimate of 2,390 cM, suggesting comprehensive coverage of the genome. A search for subsets of primer combinations giving the best map coverage found 10 primer combinations which together marked 72% of the linkage map to within 10 cM; an additional 10 primer combinations increased this percentage to 85%. Our map represents an initial step towards the identification of quantitative trait loci associated with pest resistance and water stress in pinyons and will further allow us to examine introgression rates between P. edulis and P. californiarum. Received: 14 October 1997 / Accepted: 29 April 1998     

Effect of ozone and sulphur dioxide on membrane enzyme activities of Pinus sylvestris needles

 One- and 2-year-old Pinus sylvestris saplings were exposed to chronic doses of ozone (O₃) and sulphur dioxide (SO₂) in short-term (3 months) and long-term (18 months) experiments. Microsomal and plasma membrane fractions were purified by phase partitioning from current-year needles. The following membrane enzyme activities were determined in the microsomal and/or purified plasma membrane fractions: K⁺, Mg²⁺-ATPase (EC 3.6.1.3), NADH ferricyanide oxidoreductase (EC 1.6.99.3), NADH-duroquinone reductase (EC 1.6.5.1), NADH oxidase type I (EC 1.6.99.2), NADH oxidase type II or peroxidase-like enzyme (EC 1.11.1.7) and pyrophosphatase (EC 3.6.1.1). NADH oxidase type I was slightly stimulated in the microsomal fraction after a short-term exposure to O₃ whereas NADH-dependent duroquinone reductase was not affected by this pollutant. However, in the long term experiment, NADH oxidase type II measured in the plasma membrane fraction was more than 2-fold stimulated in the SO₂ treated pines and more than 4-fold when O₃ was added to SO₂. However, pyrophosphatase was decreased by 50% in trees treated with SO₂+O₃ and remained unchanged in the SO₂ treatment, indicating that this enzyme is probably sensitive to oxidation. K⁺, Mg²⁺-ATPase showed a trend towards an enhancement of activity when exposed to chronic concentrations of air pollutants, this enhancement was more important in the long-term experiment after the combined effect of SO₂ and O₃. However, the K⁺-stimulated component was inhibited by the combination of both pollutants. Finally, NADH ferricyanide reductase was significantly enhanced after O₃ and SO₂+O₃ exposures appearing as the most sensitive oxidoreductase to these air pollutants. The stimulation of ATPase and membrane oxidoreductases could facilitate the adaptation and defense of trees by maintaining an adequate redox potential in the plasma membrane region and perhaps stimulating the reduction of extracellular electron acceptors generated by the exposure to air pollutants. Received: 15 September 1997 / Accepted: 4 May 1998     

Soybean leaf growth and gas exchange response to drought under carbon dioxide enrichment

This study was conducted to determine the response in leaf growth and gas exchange of soybean (Glycine max Merr.) to the combined effects of water deficits and carbon dioxide (CO₂) enrichment. Plants grown in pots were allowed to develop initially in a glasshouse under ambient CO₂ and well-watered conditions. Four-week old plants were transferred into two different glasshouses with either ambient (360 μmol mol^-1) or elevated (700 μmol mol^-1) CO₂. Following a 2-day acclimation period, the soil of the drought-stressed pots was allowed to dry slowly over a 2-week period. The stressed pots were watered daily so that the soil dried at an equivalent rate under the two CO₂ levels. Elevated [CO₂] decreased water loss rate and increased leaf area development and photosynthetic rate under both well-watered and drought-stressed conditions. There was, however, no significant effect of [CO₂] in the response relative to soil water content of normalized leaf gas exchange and leaf area. The drought response based on soil water content for transpiration, leaf area, and photosynthesis provide an effective method for describing the responses of soybean physiological processes to the available soil water, independent of [CO₂].     

Genetic variation and migration pathways of maritime pine (Pinus pinaster Ait) in the Iberian peninsula

The genetic variability and migration pathways of Pinus pinaster after glaciation in the Iberian peninsula was studied by means of 18 loci from 12 natural populations of the species. The analysis showed the existence of three groups of populations with different levels of diversity and patterns of recolonization. The southern Iberian group displays a high level of diversity, with a stepping-stone model of variation. The presence of rare alleles in this group and their position in the phylogenetic tree suggest the existence of refugia during glaciations in this zone. The eastern Iberian group also has high levels of diversity but is clearly separate from the first group based on their genetic distances. The Atlantic group displays a low level of diversity that could be interpreted as a rapid recolonization of the entire area by the Eastern group that has not yet developed to a divergence in this area. The southern Iberian range is indicated to be the dispersal centre of the species after the last glaciation. Received: 15 February 1999 / Accepted: 30 April 1999     

Genetic variability and structure of natural and domesticated populations of Caribbean pine (Pinus caribaea Morelet)

 Isozyme analysis of seed samples derived from natural and managed populations of the tropical pine Pinus caribaea vars ‘bahamensis’ and ‘caribaea’ was used to assess population genetic structure in its native range and to detect changes occurring during early domestication of the species. Baseline data from natural populations of the two varieties showed that populations sampled as seed are characterized by high gene diversity (mean H_e=0.26) and a low level of inbreeding ( mean F_is=0.15). A UPGMA tree of genetic relatedness among populations indicates that the two varieties represent distinct evolutionary units. Within each variety there is significant differentiation among populations, and this is greater for the more fragmented populations of var ‘bahamensis’ (F_st=0.08) than for var ‘caribaea’ (F_st=0.02). Seed from a seed orchard population of var ‘caribaea’ established within its natural range showed no change in genetic diversity but did show a reduced inbreeding coefficient (F_is=0.09) compared with its progenitor populations, suggesting a decrease in selfing and/or biparental inbreeding. A bulked seed sample from an exotic plantation of var ‘bahamensis’ in Australia displayed a large increase in the inbreeding coefficient (F_is=0.324) compared with that found in natural populations, possibly due to elevated self-fertilization. Finally, a bulked seed sample from an exotic plantation population of var ‘caribaea’ from China showed enhanced genetic diversity, an increase in the inbreeding coefficient and more linkage disequilibrium than its presumed progenitor populations. It was also genetically divergent from them. RFLP analysis of chloroplast DNA variation in the Chinese sample suggested that seeds of the related taxa P. elliottii and P. taeda, or seeds derived from hybridization with these taxa growing in the seed production area, had been included in the seed crop during harvesting. We conclude that monitoring of appropriate genetic markers may be an effective means of identifying potentially deleterious genetic changes occurring during forest tree domestication. Received: 10 August 1998 / Accepted: 8 September 1998     

RAPD markers linked to a gene for resistance to pine needle gall midge in Japanese black pine (Pinus thunbergii)

Linkage of RAPD markers to a single dominant gene for resistance to pine needle gall midge was investigated in Japanese black pine (Pinus thunbergii). Three primers that generated linked markers were found after 1160 primers were screened by bulked segregant analysis. The distances between the resistance gene, R, and the marker genes OPC06580, OPD01700, and OPAX192100 were 5.1 cM, 6.7 cM and 13.6 cM, respectively. OPC06580 was in coupling phase to R, whereas OPD01700 and OPAX192100 were in repulsion phase to R. A linkage map for a resistant tree was constructed using 96 macrogametophytes. In linkage analysis, 98 out of 127 polymorphic markers were assigned to 17 linkage groups and six linked pairs. The total length of this map was 1469.8 cM, with an average marker density of 15.6 cM. The genome length was estimated to be 2138.3 cM, and the derived linkage map covered 67.5% of the genome. Although the linked markers OPC06580, OPAX192100, and OPD01700, belonged to the same linkage group, no precise positions were found for OPC06580 or OPD01700. Received: 15 May 1999 / Accepted: 29 July 1999     

Climate-tree-growth relationships of Scots pine stands (Pinus sylvestris L.) exposed to soil dryness

 Dendroclimatological techniques were used to assess the impact of climatic factors on radial tree growth (total ring-width and latewood-width) of stunted Scots pine trees (Pinus sylvestris L.) exposed to soil dryness and nutrient deficiency on a dolomite substrate. The response of eight scattered populations representing various habitats, yet influenced by the same regional climate was investigated. Total ring-width and latewood-width were dated, standardized and several chronology statistics, which estimate the chronology signal strength and the potential climate signal in the series, were determined. Dendroclimatic analysis comprised evaluation of event/pointer years as well as response function elements. Response function analysis indicates that at most sites wide rings are significantly associated with high precipitation in April to June and cool conditions in May of the current year, and high precipitation in August to September of the preceding year. Latewood chronologies show a lower climate signal at all sites. Limited water availability causes a homogeneous relationship of radial tree growth to climate at all habitats, though site characteristics (slope magnitude, slope aspect, soil depth, vegetation cover) differ substantially. Cluster analysis of negative event/pointer years suggests that within the study area stands react to extreme climatic events depending on susceptibility to soil dryness, which is primarily determined by site topography. Received: 5 January 1998 / Accepted: 22 April 1998     

Identification of quantitative trait loci influencing annual height- and diameter-increment growth in loblolly pine (Pinus taeda L.)

 Quantitative trait loci (QTLs) for annual height- and diameter-increment growth were estimated in each of two three-generation loblolly pine pedigrees. Annual height-increment was measured in three consecutive years in the BASE pedigree and in four consecutive years in the QTL pedigree. Annual diameter-increment was measured only in the QTL pedigree for two consecutive years. An interval mapping-approach was used to estimate the number of QTLs, the magnitude of QTL effects, and their position on genetic linkage maps. Thirteen different height-increment and eight different diameter-increment QTLs were detected, suggesting that the these traits are, at least in part, controlled by a few genes of large effect. Little evidence was found for the expression of individual QTLs in multiple years or in multiple genetic backgrounds. These results were discussed in terms of the power of the experiment and their consequences for marker-assisted breeding. Received: 12 July 1998/Accepted: 5 August 1998     

Effects of root hypoxia and a low P supply on relative growth, carbon dioxide exchange rates and carbon partitioning in Pinus serotina seedlings

The present study was conducted to determine how 10 weeks of root hypoxia and a low P supply altered relative growth, and carbon acquisition and partitioning in a moderately flood tolerant pine. Pond pine (Pinus serotina Michx.) seedlings were grown in continuously flowing solution culture at 5 or 100 μM P, under aerobic or hypoxic solution conditions. Staggered harvests were used to ascertain changes in biomass allocation and relative growth over time. Carbon dioxide exchange rates (CER) were determined by infrared gas analysis, and needles were analyzed for inorganic P (Pi), sucrose, reducing sugars and starch. Although aeration treatment had no significant effect on shoot dry weight or shoot ontogeny, root dry weight of hypoxic seedlings was significantly lower than that of aerobic seedliings after 8 weeks, regardless of the P treatment. Mean relative growth rates (RGR) of roots in the high P treatment initially decreased under hypoxia, but recovered by the sixth week with the production of adventitious roots. Two weeks of hypoxic growth conditions decreased CER and stomatal conductances of seedlings in the high P treatment by more than 30% relative to their aerobic counterparts. Stomatal closure was not accompanied by a decrease in intracellular CO₂, but was accompanied by an increase in starch accumulation. Recoveries of CER, stomatal conductance and carbohydrate metabolism coincided with the recovery of root growth. Low P growth conditions did not significantly affect shoot or root dry weight until the sixth week of treatment. However, differences in seedling RGR, particularly needle RGR, were discernable during the first 2 weeks. Low P treatment effects on CER paralleled changes in needle RGR, with needle RGR more affected than CER. After 6 weeks, CER of aerobically grown seedlings in the low P treatment were only 15% lower than CER of seedlings in the high P treatment, despite a 31% and 75% reduction in needle RGR and Pi concentrations, respectively. Increased starch concentrations of recently expanded needles at this time were probably a result of diminished growth. The inhibitory effect of a low P supply on shoot growth, more specifically on needle expansion and emergence of new fascicular needles, probably limited net carbon fixed per plant more than any direct effect of low P on CER per se.     

大气CO2浓度增高对麦田土壤硝化和反硝化细菌的影响

硝化和反硝化细菌是土壤中与氮转化有关的微生物菌群 ,大气CO2 浓度升高可能对它们的数量产生影响。位于中国无锡的稻 麦轮作农田生态系统FACE平台 2 0 0 1年 6月开始运行。本试验在 2 0 0 3年小麦生长季研究了土壤 (0～ 5cm和 5～ 10cm土层 )中硝化和反硝化细菌在大气CO2 浓度升高条件下的变化。试验采用最大可能法 (MPN)计这两种微生物菌群的数量。结果表明 ,0～ 5cm土层硝化菌数拔节期和成熟期FACE低于对照 ,而孕穗期FACE高于对照 ,5～ 10cm土层硝化菌数越冬期与成熟期FACE低于对照 ,大气CO2 浓度升高使得麦田土壤硝化细菌数目减少。 0～ 5cm土层各个生长期反硝化菌数FACE与对照均没有明显差异 ,5～ 10cm土层反硝化菌数拔节期FACE低于对照 ,大气CO2 浓度升高对麦田土壤反硝化菌的影响不大。     

Ectomycorrhizal, vesicular-arbuscular and dark septate fungal colonization of bishop pine (Pinus muricata) seedlings in the first 5 months of growth after wildfire

 We followed the colonization frequency of ectomycorrhizal (EM), vesicular-arbuscular mycorrhizal (VAM), and dark septate (DS) fungi in 1- to 5-month-old bishop pine seedlings reestablishing after a wildfire. Seedlings were collected on a monthly basis at either a VAM-dominated chaparral scrub site or an EM-dominated forest site, both of which were burned. In both vegetation types, fully developed EM were observed from the third month after germination. EM fungi observed on the seedlings from the scrub site were limited to Rhizopogon subcaerulescens, R. ochraceorubens and Suillus pungens. Seedlings from the forest were colonized by a greater variety of EM fungi including Amanita spp., Russula brevipes and a member of the Cantharellaceae. VAM structures (vesicles, arbuscules or hyphal coils) were observed in the seedling root systems beginning 1 month after germination at the scrub site and 3 months after germination at the forest site. Seedlings from the scrub site consistently had more frequent VAM fungal colonization than those from the forest site through the fifth month after germination. DS fungi were observed in most seedlings from both the scrub and forest sites beginning in the first month post-germination. We propose that these fungi survived as a resident inoculum in the soils and did not disperse into the sites after the fire. Accepted: 14 February 1998     

Ectomycorrhizae of Tomentella albomarginata (Thelephoraceae) on Scots pine

 The ectomycorrhizae of Tomentella albomarginata are comprehensively described and compared to ectomycorrhizae of other Tomentella species and to ectomycorrhizae of some members of Thelephoraceae ss. Stalpers and Bankeraceae ss. Stalpers. The ectomycorrhizae of T. albomarginata are characterized by a hyphal net lying on a pseudoparenchymatous mantle surface, by tubular outgrowths of irregularly angular mantle cells, and by clamp-bearing emanating hyphae. Accepted: 15 July 1995     

Variations in maturation strains and root shape in root systems of Maritime pine (Pinus pinaster Ait.)

 In order to determine if different types of wood were being laid down in the root system of Maritime pine (Pinus pinaster Ait), in response to wind loading, longitudinal residual maturation strains (LRMS), indicating the existence of mechanical stress in developing wood cells, were measured in the trunk and lateral roots. Two age groups of trees (5- and 13-year- old) were compared. LRMS were greater in the trunk and roots of 13-year-old trees than in 5-year-old trees. This phenomenon may be due to increased competition between older trees. LRMS in leeward roots of both age-groups were positive i.e. the wood cells had developed under compression, as also occurs in reaction wood of gymnosperms. As leeward roots are placed under compression during tree sway, an abnormal type of wood may form in the roots in order to counteract the increased stress. In other roots, the strains were negative i.e. the cells had developed under tension, as occurs in normal wood. In the roots of younger trees, LRMS were also positive nearer the stem, thus indicating that wood formation may also be influenced by bending stresses experienced in this zone. In addition to LRMS measurements, radial growth in roots was examined in order to determine the influence of mechanical loading on secondary growth. In older trees, there was a significant increase of 34% in woody growth below the biological centre, compared to that above. This eccentricity is unlike that found in most other tree species, where secondary growth is usually greater on the upper side of the root. However, Maritime pine has a tap root, which will alter the pattern of stress within the root system. Under wind loading, a concentration of mechanical stress will develop at the bases of the stem, lateral roots and tap root. Received: 7 July 1997 / Accepted: 11 December 1997     

Segregation and linkage relationships of isoenzymes in shortleaf pine (Pinus echinata Mill.)

 Segregation and linkage relationships were analyzed between 28 isoenzyme loci in ten natural stands representing much of the natural range of Pinus echinata Mill. (shortleaf pine). A total of 203 possible two-locus combinations were tested. Three linkage groups were revealed in this study at a linkLOD of 4.0. The first linkage group (A) consisted of Pgi and Adh-1; Gdh, Idh, Skdh-2, G6pd-2 and Aco were mapped to the second linkage group (B); the third group (C) had 2 loci: Mdh-2 and Mdh-3. A moderate linkage between Mnr-2 and Dia-2 and weak linkages between Mnr-1 and Dia-1, and Got-2 and 6pgd-2 were also detected. The significance of these results in shortleaf pine is discussed and compared to linkage maps previously reported in other conifers, including pines. Received: 7 April 1997 / Accepted: 25 April 1997     

Effects of mycorrhizal fungus isolates on mineral acquisition by Panicum virgatum in acidic soil

 Plant ability to withstand acidic soil mineral deficiencies and toxicities can be enhanced by root-arbuscular mycorrhizal fungus (AMF) symbioses. The AMF benefits to plants may be attributed to enhanced plant acquisition of mineral nutrients essential to plant growth and restricted acquisition of toxic elements. Switchgrass (Panicum virgatum L.) was grown in pH_Ca (soil:10 mM CaCl₂, 1 : 1) 4 and 5 soil (Typic Hapludult) inoculated with Glomus clarum, G. diaphanum, G. etunicatum, G. intraradices, Gigaspora albida, Gi. margarita, Gi. rosea, and Acaulospora morrowiae to determine differences among AMF isolates for mineral acquisition. Shoots of mycorrhizal (AM) plants had 6.2-fold P concentration differences when grown in pH_Ca 4 soil and 2.9-fold in pH_Ca 5 soil. Acquisition trends for the other mineral nutrients essential for plant growth were similar for AM plants grown in pH_Ca 4 and 5 soil, and differences among AMF isolates were generally higher for plants grown in pH_Ca 4 than in pH_Ca 5 soil. Both declines and increases in shoot concentrations of N, S, K, Ca, Mg, Zn, Cu, and Mn relative to nonmycorrhizal (nonAM) plants were noted for many AM plants. Differences among AM plants for N and Mg concentrations were relatively small (<2-fold) and were large (2- to 9-fold) for the other minerals. Shoot concentrations of mineral nutrients did not relate well to dry matter produced or to percentage root colonization. Except for Mn and one AMF isolate, shoot concentrations of Mn, Fe, B, and Al in AM plants were lower than in nonAM plants, and differences among AM plants for these minerals ranged from a low of 1.8-fold for Fe to as high as 6.9-fold for Mn. Some AMF isolates were effective in overcoming acidic soil mineral deficiency and toxicity problems that commonly occur with plants grown in acidic soil. Accepted: 14 June 1999     

Ectomycorrhizal root growth in scots pine stands in response to manipulation of litter and humus layers

 The effect on ectomycorrhizal root growth in a nitrogen-enriched planted stand of Scots pine (Pinus sylvestris L.) on podzolic sandy soil to manipulation of litter and humus layers (removal, doubling and control treatments) was examined, and compared to ectomycorrhizal root growth in an untreated naturally established Scots pine stand on nutrient-poor non-podzolic sandy soil. Half a year after manipulation of litter and humus layers in the planted stand, ingrowth-cores to a depth of 60 cm were installed in both stands. Scots pine roots were sampled four times during two growing seasons. Ectomycorrhizal roots were found at all sampled soil depths to 60 cm in all plots. Root growth and ectomycorrhizal development were greater in the naturally established stand than in all plots in the planted stand. Numbers of ectomycorrhizal root tips in the litter and humus removal plots were generally higher than in the control plots in the planted stand until May 1992. Doubling litter and humus did not significantly affect root length or the numbers of ectomycorrhizal root tips. The N _dissolved , NH₄ ⁺ and NO₃ ^– concentrations and the organic matter content in the upper 5 cm of the mineral soil in the planted stand on podzolic sandy soil were generally higher and the pH significantly lower than in the naturally established stand on non-podzolic sandy soil. Root growth and ectomycorrhizal development in the secondary stand may have been negatively affected by the chemical composition of the podzolic sandy soil. Accepted: 19 March 1997     

Atmospheric CO2 concentration, N availability, and water status affect patterns of ergastic substance deposition in longleaf pine (Pinus palustris Mill.) foliage

 Leaf chemistry alterations due to increasing atmospheric CO₂ will reflect plant physiological changes and impact ecosystem function. Longleaf pine was grown for 20 months at two levels of atmospheric CO₂ (720 and 365 μmol mol^–1), two levels of soil N (4 g m^–2 year^–1 and 40 g m^–2 year^–1), and two soil moisture levels (– 0.5 and – 1.5 MPa) in open top chambers. After 20 months of exposure, needles were collected and ergastic substances including starch grains and polyphenols were assessed using light microscopy, and calcium oxalate crystals were assessed using light microscopy, scanning electron microscopy, and transmission electron microscopy. Polyphenol content was also determined using the Folin-Denis assay and condensed tannins were estimated by precipitation with protein. Evaluation of phenolic content histochemically was compared to results obtained using the Folin-Denis assay. Total leaf polyphenol and condensed tannin content were increased by main effects of elevated CO₂, low soil N and well-watered conditions. Elevated CO₂ and low soil N decreased crystal deposition within needle phloem. Elevated CO₂ had no effect on the percentage of cells within the mesophyll, endodermis, or transfusion tissue which contained visible starch inclusions. With respect to starch accumulation in response to N stress, mesophyll > endodermis > transfusion tissue. The opposite was true in the case of starch accumulation in response to main effects of water stress: mesophyll < endodermis < transfusion tissue. These results indicate that N and water conditions significantly affect deposition of leaf ergastic substances in longleaf pine, and that normal variability in leaf tissue quality resulting from gradients in soil resources will be magnified under conditions of elevated CO₂. Received: 5 November 1996 / Accepted: 7 March 1997     

Annual basal area increment and growth duration of Pinus taeda in response to eight years of free-air carbon dioxide enrichment

Rising CO₂ is predicted to increase forest productivity, although the duration of the response and how it might be altered by variation in rainfall, temperature and other environmental variables are not well understood. We measured the basal area of rapidly growing Pinus taeda trees exposed to free‐air CO₂ enrichment for 8 years and used these measurements to estimate monthly and annual growth. We used these measurements in a statistical model to estimate the start and end of growth in each year. Elevated CO₂ increased the basal area increment (BAI) of trees by 13–27%. In most years, exposure to elevated CO₂ increased the growth rate but not the duration of the active growth period. With the exception of 1 year following an extreme drought and a severe ice storm, BAI was positively correlated with the amount of rainfall during the active growth period. The interannual variation in the relative enhancement of BAI caused by elevated CO₂ was strongly related to temperature and rainfall, and was greatest in years with high vapor pressure deficit. There was no evidence of a systematic reduction in the stimulation of growth during the first 8 years of this experiment, suggesting that the hypothesized limitation of the CO₂ response caused by nitrogen availability has yet to occur.     

Effect of carbon dioxide, fertilization and irrigation on loblolly pine branch morphology

 Foliage and wood parameters of branches of 12-year-old loblolly pine (Pinus taeda L.) trees were characterized after 21 months of exposure to fertilizer, irrigation and elevated CO₂ treatments. Branches of loblolly pine trees were enclosed in plastic chambers and exposed to ambient, ambient +175 and ambient +350 umol mol^–1 CO₂ concentrations. Measurements of foliage and wood at the fascicle, flush and branch levels were made at the end of the 21 month study period. The +350 CO₂ treatment did not significantly increase fascicle radius or length but did increase the number of fascicles on the first flush. Fertilization significantly increased fascicle radius and length, while irrigation significantly increased number of fascicles and flush length of first flush. The +350 CO₂ treatment also significantly increased flush length of the first flush. Significant interaction of fertilization and irrigation with CO₂ was observed for fascicle length. Significant interactions of fertilization and irrigation were also observed for flush length, number of fascicles and fascicle length. Observed increases in fascicle radius, fascicle length, number of fascicles and flush length may have been responsible for the significantly higher flush leaf area observed for the all three treatments. Also, a combination of fertilization and irrigation increased leaf area by 82% compared to that in the control when averaged across CO₂ treatments. At the branch level +350 CO₂ treatment significantly increased shoot length but not the number of flushes on the branch. In general with the exception of bark density and total number of needle scales, neither fertilization nor irrigation had any significant effect on other branch level parameters. Results from this study indicate that with ‘global change’ an increase in CO₂ alone may increase leaf area via an increase in flush length and number of fascicles. Combining increases in CO₂ with fertilization and irrigation could greatly enhance leaf area which when coupled to observed increases in net photosynthesis as a result of elevated CO₂ could greatly increase productivity of loblolly pine trees. Received: 22 August 1996 / Accepted: 5 March 1997