SEARCH · PubMed Health

Results for “Pinus”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 703 records · Page 39Linked to original sources

PubMedDate not supplied

Modeling productivity and transpiration of Pinus radiata: climatic effects.

Climatic effects on annual net carbon gain, stem biomass and annual transpiration were simulated for Pinus radiata D. Don at Canberra and Mt. Gambier. Simulations were conducted with an existing process-based forest growth model (BIOMASS, Model 1) and with a modified version of the BIOMASS model (Model 2) in which response functions for carbon assimilation and leaf conductance were replaced with those derived from field gas exchange data collected at Mt. Gambier. Simulated carbon gain was compared with a published report stating that mean annual stem volume increment (MAI) at Mt. Gambier was 1.8 times greater than at Canberra and that the difference could be the result solely of differences in climate. Regional differences in climate resulted in a 20% greater simulated annual transpiration at Canberra than at Mt. Gambier but only small differences in simulated productivity, indicating that climatic differences did not account for the reported differences in productivity. With Model 1, simulated annual net carbon gain and annual increase in stem biomass were greater at Canberra than at Mt. Gambier, whereas Model 2 indicated a similar annual net carbon gain and annual stem biomass increase in both regions.

Journal Article↗

PubMedDate not supplied

Growth and water use of Eucalyptus grandis and Pinus radiata plantations irrigated with effluent.

We studied the growth and water balance of young plantations of Pinus radiata D. Don and Eucalyptus grandis W. Hill ex Maiden irrigated with effluent for 3 years in a climate of high net evaporation. The plantations were irrigated weekly with secondary-treated municipal effluent at the estimated water-use rate, or at nominally twice or half this rate. Control plots were irrigated with bore water at their estimated water-use rate. Both species grew rapidly when irrigated with either effluent or bore water. The eucalypts irrigated with effluent at the estimated water-use rate closed canopy in 24 months, and at 34 months, mean dominant height was 12.1 m, stand basal area was 12.2 m(2) ha(-1), volume was 51.2 m(3) ha(-1), LAI was 5.7, and foliage mass was 6.5 Mg ha(-1). The pines in the corresponding effluent treatment had not closed canopy by 34 months. At this time, mean height was 5.0 m, stand basal area was 9.6 m(2) ha(-1), volume was 29.7 m(3) ha(-1), LAI was 3.5, and foliage mass was 7.3 Mg ha(-1). Water use by eucalypts was consistently higher than by pines, commensurate with their more rapid early growth, but the difference was not in proportion to the difference in leaf area. In the third year (when the eucalypts had a closed canopy), the eucalypts used 22% more water than the pines, but the annual mean LAI of the eucalypts was three times greater than that of the pines. The results suggest that (1) plantation water use by the two species on the same site will be similar for the same stage of canopy development, (2) eucalypts are not inherently more profligate consumers of water than pines when soil water is not limiting, and (3) stomatal control limits growth and water use of E. grandis in arid environments.

Journal Article↗

PubMedDate not supplied

Water use by Pinus radiata trees in a plantation.

We used the heat-pulse velocity technique to estimate transpirational water use of trees in an experimental 16-year-old Pinus radiata D. Don plantation in South Australia during a 4-month period from November 1993 to March 1994 (spring-summer). Fertilization and other silvicultural treatments during the first 8 years of the plantation produced trees ranging in diameter at a height of 1.3 m from 0.251 to 0.436 m, with leaf areas ranging from 83 to 337 m(2). Daily water use was greater for large trees than for small trees, but transpiration per unit leaf area was nearly identical. Daily transpiration was highly correlated with available soil water in the upper 1 m of soil and weakly correlated with irradiance and air temperature. For the stand (0.4 ha), estimated rates of transpiration ranged from 6.8 to 1.4 mm day(-1) in wet and dry soil conditions, respectively. Total water use by the plantation during the 4-month study period was 346 mm. Water transpired by the trees was about three times that extracted from the upper 1 m of soil. Large trees extracted water from the same soil volume as small trees and did not exhibit a greater potential to extract water from deeper soil when the upper horizons become dry.

Journal Article↗

PubMedDate not supplied

Effects of branch length on carbon isotope discrimination in Pinus radiata.

Gas exchange was measured on a pruned Pinus radiata D. Don hedge and on a long-branch P. radiata tree near Hamilton, New Zealand, in spring 1993 when soil water content was close to field capacity. Foliage at the end of long branches (9.0 m) showed a marked drop in net photosynthetic rate and stomatal conductance as the saturation deficit increased, whereas foliage on short branches (0.5 m) showed little change. Mean foliage delta(13)C was -30.1 per thousand for short branches and -26.3 per thousand for long branches. Foliage delta(13)C was correlated with branch length in two genetically improved P. radiata seedlots at four stocking densities. The multinodal seedlot had shorter branches and more (13)C-depleted foliage compared with branches and foliage from the long internode seedlot. There was a strong effect of stocking density on carbon isotope composition in both seedlots. We conclude that branch morphology affects foliage gas exchange properties and foliage carbon isotope composition.

Journal Article↗

PubMedDate not supplied

Growth and photosynthesis of loblolly pine (Pinus taeda) after exposure to elevated CO(2) for 19 months in the field.

To detect seasonal and long-term differences in growth and photosynthesis of loblolly pine (Pinus taeda L.) exposed to elevated CO(2) under ambient conditions of precipitation, light, temperature and nutrient availability, seedlings were planted in soil representative of an early, abandoned agricultural field and maintained for 19 months in the field either in open-top chambers providing one of three atmospheric CO(2) partial pressures (ambient, ambient +15 Pa, and ambient +30 Pa) or in unchambered control plots. An early and positive response to elevated CO(2) substantially increased total plant biomass. Peak differences in relative biomass enhancement occurred after 11 months of CO(2) treatment when biomass of plants grown at +15 and +30 Pa CO(2) was 111 and 233% greater, respectively, than that of plants grown at ambient CO(2). After 19 months, there was no significant difference in biomass between +15 Pa CO(2)-treated plants and ambient CO(2)-treated plants, whereas biomass of +30 Pa CO(2)-treated plants was 111% greater than that of ambient CO(2)-treated plants. Enhanced rates of leaf-level photosynthesis were maintained in plants in the elevated CO(2) treatments throughout the 19-month exposure period despite reductions in both leaf N concentration and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity during the first 11 months of CO(2) exposure. Reductions in Rubisco activity indicated photosynthetic adjustment to elevated CO(2), but Rubisco-mediated control of photosynthesis was small. Seasonal shifts in sink strength affected photosynthetic rates, greatly magnifying the positive effects of elevated CO(2) on photosynthesis during periods of rapid plant growth. Greater carbon assimilation by the whole plant accelerated plant development and thereby stimulated new sinks for carbon through increased plant biomass, secondary branching and new leaf production. We conclude that elevated CO(2) will enhance photosynthesis and biomass accumulation in loblolly pine seedlings under high nutrient conditions; however, reductions over time in the relative biomass response of plants to elevated CO(2) complicate predictions of the eventual magnitude of carbon storage in this species under future CO(2) conditions.

Journal Article↗

PubMed1996

Nutrient retranslocation in the foliage of Pinus sylvestris L. growing along a heavy metal pollution gradient.

Retranslocation of N, P, K, Ca, Mg, Mn, Fe, Zn, Cu and Ni within the foliage of Scots pine (Pinus sylvestris L.) was studied during autumnal needle senescence along a heavy-metal pollution gradient in western Finland. The stands were located at distances of 0.5 (Har 0.5), 4 (Har 4) and 8 km (Har 8) to the southeast of a copper-nickel smelter at Harjavalta. A background study stand was located at Hämeenkangas (Häm), 60 km northeast of the smelter. During needle senescence, the mobile nutrients N, P and K decreased by 67-88% and needle dry mass decreased by 31-43%. Retranslocation of P and K was less efficient in the stand nearest the smelter (Har 0.5) than in the other stands. During needle senescence at stand Har 0.5, heavy metal content either decreased slightly (Zn, Ni) or increased (Fe, Cu), whereas in the background study stand, retranslocation efficiency of Cu was 75%. Net throughfall (the amount of a nutrient in throughfall minus the amount in open precipitation) was higher in stand Har 0.5 than in stand Har 8 for all of the elements measured, except N and P which were intercepted by the canopy. In stand Har 8, deposition of S, Cu and Ni was intercepted by the canopy, and net throughfall of Fe and Zn was very low. In contrast, S and heavy metal contents of net throughfall in stand Har 0.5 were greater than the decrease in these elements in the needles indicating that accumulation on needle surfaces and subsequent wash-off accounted for a major part of the fluxes. Furthermore, the Cu content in net throughfall during the senescence period was higher than the original Cu content of the needles in July, providing additional evidence that much of the needle Cu content was comprised of dry deposits of Cu on the needle surface.

Journal Article↗

PubMedDate not supplied

Seasonal root distribution and soil surface carbon fluxes for one-year-old Pinus radiata trees growing at ambient and elevated carbon dioxide concentration.

The increase in number of fine (< 0.5 mm diameter) roots of one-year-old clonal Pinus radiata D. Don trees grown in large open-top field chambers at ambient (362 micro mol mol(-1)) or elevated (654 micro mol mol(-1)) CO(2) concentration was estimated using minirhizotron tubes placed horizontally at a depth of 0.3 m. The trees were well supplied with water and nutrients. Destructive harvesting of roots along an additional tube showed that there was a linear relationship between root number estimated from the minirhizotron and both root length density, L(v), and root carbon density, C(v), in the surrounding soil. Root distribution decreased with horizontal distance from the tree. At a depth of 0.3 m, 88% of the total C(v) was concentrated within a 0.15-m radius from tree stems in the elevated CO(2) treatment, compared with 35% for trees in the ambient CO(2) treatment. Mean C(v) along the tubes ranged up to 5 x 10(-2) micro g mm(-3) and tended to be greater for trees grown at elevated CO(2) concentration, although the differences between CO(2) treatments were not significant. Root growth started in spring and continued until late summer. There was no significant difference in seasonal rates of increase in C(v) between treatments, but roots were observed four weeks earlier in the elevated CO(2) treatment. No root turnover occurred at a depth of 0.3 m during the first year after planting. Mean values of carbon dioxide flux density at the soil surface, F, increased from 0.02 to 0.13 g m(-2) h(-1) during the year, and F was 30% greater for trees grown at elevated CO(2) concentration than at ambient CO(2). Diurnal changes in F were related to air temperature. The seasonal increase in F continued through the summer and early autumn, well after air temperature had begun to decline, suggesting that the increase was partly caused by increase in C(v) as the roots colonized the soil profile.

Journal Article↗

PubMedDate not supplied

Phosphate-limitation physiology in ectomycorrhizal pitch pine (Pinus rigida) seedlings.

Foliar and root P concentrations, net H(2)PO(4) (-) (P(i)) uptake rates, and root surface acid phosphatase (APase) rates were assessed in pitch pine (Pinus rigida Mill.) seedlings inoculated with the ectomycorrhizal fungi Laccaria bicolor (Maire) Pat., Paxillus involutus (Batsch.) Fr., or Pisolithus tinctorius (Pers.) Coker and Couch, and grown at 10 or 100 micro M P(i) in sand culture. Following a 6-week period of acclimation to the P(i) regimes, seedlings grown at 100 micro M P(i) had greater foliar and root P concentrations than seedlings grown at 10 micro M P(i). Mycorrhizal colonization increased the concentration of P in roots and, under P(i)-limiting conditions, this retention was at the expense of P translocation to foliage. There were no differences in P(i) uptake rates between non-mycorrhizal and mycorrhizal roots grown at 100 micro M P(i). However, mycorrhizal colonization enhanced P(i) uptake in seedlings grown at 10 micro M P(i), with rates 1.3-, 2.6-, and 3.3-fold greater in roots colonized with L. bicolor, P. involutus, and P. tinctorius, respectively, than in non-mycorrhizal roots. Root acid phosphatase (APase) activity was greater in non-mycorrhizal roots than in roots colonized with any of the three mycorrhizal fungi, and increases in activity in response to P(i) limitation occurred only in non-mycorrhizal roots. These results highlight the importance of seedling acclimation to prevailing P(i) availability and the role of mycorrhizal fungi in altering the allocation of P between roots and shoots. The activities of the APase systems of the mycorrhizal species tested do not support the hypothesis that this enzyme system plays an important role in P(i) acquisition under P-limiting conditions.

Journal Article↗

PubMed1996

Foliage, fine-root, woody-tissue and stand respiration in Pinus radiata in relation to nitrogen status.

We measured respiration of 20-year-old Pinus radiata D. Don trees growing in control (C), irrigated (I), and irrigated + fertilized (IL) stands in the Biology of Forest Growth experimental plantation near Canberra, Australia. Respiration was measured on fully expanded foliage, live branches, boles, and fine and coarse roots to determine the relationship between CO(2) efflux, tissue temperature, and biomass or nitrogen (N) content of individual tissues. Efflux of CO(2) from foliage (dark respiration at night) and fine roots was linearly related to biomass and N content, but N was a better predictor of CO(2) efflux than biomass. Respiration (assumed to be maintenance) per unit N at 15 degrees C and a CO(2) concentration of 400 micro mol mol(-1) was 1.71 micro mol s(-1) mol(-1) N for foliage and 11.2 micro mol s(-1) mol(-1) N for fine roots. Efflux of CO(2) from stems, coarse roots and branches was linearly related to sapwood volume (stems) or total volume (branches + coarse roots) and growth, with rates for maintenance respiration at 15 degrees C ranging from 18 to 104 micro mol m(-3) s(-1). Among woody components, branches in the upper canopy and small diameter coarse roots had the highest respiration rates. Stem maintenance respiration per unit sapwood volume did not differ among treatments. Annual C flux was estimated by summing (1) dry matter production and respiration of aboveground components, (2) annual soil CO(2) efflux minus aboveground litterfall, and (3) the annual increment in coarse root biomass. Annual C flux was 24.4, 25.3 and 34.4 Mg ha(-1) year(-1) for the C, I and IL treatments, respectively. Total belowground C allocation, estimated as the sum of (2) and (3) above, was equal to the sum of root respiration and estimated root production in the IL treatment, whereas in the nutrient-limited C and I treatments, total belowground C allocation was greater than the sum of root respiration and estimated root production, suggesting higher fine root turnover or increased allocation to mycorrhizae and root exudation. Carbon use efficiency, the ratio of net primary production to assimilation, was similar among treatments for aboveground tissues (0.43-0.50). Therefore, the proportion of assimilation used for construction and maintenance respiration on an annual basis was also similar among treatments.

Journal Article↗

PubMed1996

Microculture of western white pine (Pinus monticola) by induction of shoots on bud explants from 1- to 7-year-old trees.

We developed a protocol for the production of shoots from bud explants from 1- to 7-year-old trees of western white pine (Pinus monticola Dougl.). The best explant was a 2-mm-thick cross-sectional slice of the early winter bud. Genotype of the donor tree was a significant factor affecting shoot production, but more than 80% of the genotypes tested produced shoots. Of the media tested, bud slices from 1- to 3-year-old trees grew best in Litvay's medium containing N(6)-benzyladenine in the range of 1 to 30 micro M, whereas bud slices from older trees grew best in Gupta and Durzan's DCR medium with zeatin riboside. Up to 400 shoots more than 3 mm in height were obtained from 100 bud-slice explants taken from 7-year-old western white pine trees.

Journal Article↗

PubMed1996

Responses of carbon gain and growth of Pinus radiata stands to thinning and fertilizing.

Thinning of forest stands is widely carried out to minimize the slowing of growth of individual stems that follows from increasing competition among trees as they become bigger. After thinning, there is an increase in the growth rate of remaining trees because of an increase in the availability of resources per tree. Often, there is also an increase in foliar efficiency (biomass increase/foliage amount). On sites where mineral nutrient supply is limiting, fertilizers may be applied, often in association with thinning, to boost productivity. Growth responses to fertilizer application depend on an adequate supply of other resources, but also involve nonlinear interactions among mineral nutrients and between nutrients and other growth-limiting environmental factors. The effects of thinning and fertilizing on the carbon gain and growth responses of Pinus radiata D. Don to availability of resources (light, mineral nutrients and water) and to changes in the canopy are discussed.

Journal Article↗

PubMed1996

Carbon and nitrogen allocation in ectomycorrhizal and non-mycorrhizal Pinus sylvestris L. seedlings.

We studied carbon and nitrogen allocation in mycorrhizal and non-mycorrhizal Scots pine (Pinus sylvestris L.) seedlings grown in a semi-hydroponic system with nitrogen as the growth limiting factor. Three ectomycorrhizal fungi were compared: one pioneer species (Thelephora terrestris Ehrh.: Fr.) and two late-stage fungi (Suillus bovinus (L.: Fr.) O. Kuntze, and Scleroderma citrinum Pers.). By giving all plants in each treatment the same amount of readily available nitrogen, we ensured that the external mycelium could not increase the total nitrogen content of the plants, thereby guaranteeing that any change in carbon or nitrogen partitioning was a direct effect of the mycorrhizal infection itself. Carbon and nitrogen partitioning were measured at an early and a late stage of mycorrhizal development, and at a low and a high N addition rate. Although mycorrhizal seedlings had a higher net assimilation rate and a higher shoot/root ratio than non-mycorrhizal seedlings, they had a lower rate of shoot growth. The high carbon demand of the mycobionts was consistent with the large biomass of external mycelia and the increased belowground respiration of the mycorrhizal plants. The carbon cost to the host was similar for pioneer and late-stage fungi. Above- and belowground partitioning of nitrogen was also affected by mycorrhizal infection. The external mycelia of Scleroderma citrinum retained 32% of the nitrogen supplied to the plants, thus significantly reducing nitrogen assimilation by the host plants and consequently reducing their growth rate. By contrast, the external mycelia of T. terrestris and Suillus bovinus retained less nitrogen than the mycelia of Scleroderma citrinum, hence we attributed the decreased growth rates of their host plants to a carbon drain rather than a nitrogen deficiency.

Journal Article↗

PubMed1997

Responses of Picea, Pinus and Pseudotsuga roots to heterogeneous nutrient distribution in soil.

The spatial distribution of plant-available mineral nutrients in forest soils is often highly heterogeneous. To test the hypothesis that local nutrient enrichment of soil leads to increased root proliferation in the nutrient-rich soil zone, we studied the effects of nutrient enrichment on the growth and nutrient concentrations of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) roots. Three-year-old seedlings were grown for 9 months in split-root containers filled with nutrient-poor forest mineral soil, with one side supplemented with additional mineral nutrients. Root dry weight and root length in Scots pine and Norway spruce were increased in the nutrient-supplemented soil compared with the nonsupplemented side, whereas root growth in Douglas-fir was unaffected by nutrient enrichment. Of the three species examined, Norway spruce exhibited the highest root and shoot growth and the highest nutrient demand. Specific root length (m g(-1)) and the number of root tips per unit root length were not affected by local nutrient addition in any of the species. Despite increased root growth in Norway spruce and Scots pine in nutrient-supplemented soil, their root systems contained similar nutrient concentrations on both sides of the split-root container. Thus, coniferous trees may respond to local nutrient supply by increased root proliferation, but the response varies depending on the species, and may only occur when trees are nutrient deficient. As a response to local nutrient enrichment, increases in root dry matter or root length may be better indicators of pre-existing nutrient deficiencies in conifers than increases in root nutrient concentrations.

Journal Article↗

PubMed1997

Analysis of bark proteins in blister rust-resistant and susceptible western white pine (Pinus monticola).

We compared bark proteins from four contrasting (blister rust-resistant versus susceptible) half-sib seedling pairs of western white pine (Pinus monticola D. Don). Pooled proteins from resistant and susceptible groups (four trees per group) were separated by two-dimensional gel electrophoresis, silver stained, and analyzed with the aid of a laser scanner interfaced with a computerized gel documentation system. Qualitative and quantitative protein differences were observed between resistant and susceptible groups. The number of proteins unique to a group was greater in the susceptible category than in the resistant category. Biosynthesis of some common proteins was enhanced near lesioned areas of susceptible seedlings. Many proteins shared similar charge and mass characteristics with those of pathogenesis-related (PR) proteins. Two protein bands were isolated and partially characterized by N-terminal amino acid sequencing: a 10.6-kDa band that was selectively enriched in all resistant individuals, and a 26.0-kDa band that was enriched in some susceptible individuals. The significance of these protein differences and the possible use of selected proteins as disease or resistance markers are discussed.

Journal Article↗

PubMed1997

In vitro regeneration of plantlets from mature embryos of Pinus ayacahuite.

A plantlet regeneration protocol was developed for Pinus ayacahuite var. ayacahuite (Ehrenb.). Embryos from mature seeds from ten provenances were cultured in a 16-h photoperiod for 3 days on a medium containing 30 mM sucrose and 0.7% agar. Cotyledons from these embryos were subcultured onto MCM medium (Bornman 1983) supplemented with 50 micro M N(6)-benzyladenine and 90 mM sucrose for 2 weeks. Bud development and shoot elongation were maximized by subculturing the explants on half strength AE medium (von Arnold and Ericksson 1981), supplemented with 60 mM sucrose and 0.05% activated charcoal every 30 days. Seed source had a significant effect on the responses of the embryos to the bud induction protocol. For the provenance with the best response to bud induction, about 79% of the cultured cotyledons formed buds, and each cotyledon formed a mean of 9.1 buds, so that about 70 shoots could be induced from each seed. The best rooting response (40% rooting) was obtained by treating the shoots for 8 h with 100 micro M naphthalene acetic acid.

Journal Article↗

PubMed1997

A simple model of light and water use evaluated for Pinus radiata.

An existing model of light and water use by crops (RESCAP) was adapted and evaluated for trees. In the model, growth on any given day is determined either by the amount of intercepted radiation (by means of the light utilization coefficient, epsilon) or by the maximum rate of water extraction by roots (a function of root biomass and soil water content). In either case, transpiration and growth are related by the water-use efficiency (q), which is inversely proportional to the daily mean saturation vapor pressure deficit (D). The model was applied to two Pinus radiata (D. Don) stands (control (C) and fertilized (F)) growing near Canberra, Australia, using data collected during the Biology of Forest Growth experiment (1983-1988). For both stands, predicted and measured soil water contents were in close agreement (r(2) > 0.9) over a 4-year period involving several wet-dry cycles. The parameter combination epsilon/qD was estimated to be 0.28 and 0.26 kg H(2)O (MJ total)(-1) kPa(-1) for the C and F stands, respectively. Because of the close physiological link between water use and CO(2) uptake, the results suggest that tree growth may be realistically simulated by simple models based on conservative values for epsilon and qD.

Journal Article↗

PubMed1997

Carbon dioxide gas exchange of cembran pine (Pinus cembra) at the alpine timberline during winter.

Winter CO(2) gas exchange of the last three flushes of cembran pine (Pinus cembra L.) was studied under ambient conditions at the alpine timberline, an ecotone with strong seasonal changes in climate. During the coldest months of the year, December to March, gas exchange was almost completely suppressed and even the highest irradiances and temperatures did not cause a significant increase in net photosynthesis compared to spring and fall. In general, daily CO(2) balance was negative between December and March except during extended warm periods in late winter. However, because twig respiration was also reduced to a minimum during the December-March period, daily carbon losses were minimal. Total measured carbon loss during the winter months was small, equalling the photosynthetic production of one to two warm days in spring or summer when average air temperature was above 6 degrees C.

Journal Article↗

PubMedDate not supplied

Variability in leaf-level CO(2) and water fluxes in Pinus banksiana and Picea mariana in Saskatchewan.

We measured seasonal and canopy-level gas exchange in two stands of jack pine (Pinus banksiana Lamb.) and one stand of black spruce (Picea mariana (Mill.) B.S.P.) on relatively clear days from late May until mid-September 1994. Field measurements were made with a portable infrared gas analyzer, and laboratory measurements included photosynthetic oxygen evolution and needle chemical composition. Seasonally averaged light-saturated assimilation rates in the field were 4.0 micro mol m(-2) s(-1) in jack pine and 2.7 micro mol m(-2) s(-1) in black spruce. Rates of assimilation and transpiration were highest in midsummer. The seasonal pattern was especially pronounced for black spruce, probably because cold soil temperatures limited early season gas exchange rates in this species. Among stands, instantaneous water-use efficiency was highest in a young jack pine stand early in the season and higher in the upper canopy foliage than in the lower canopy foliage at all sites at the end of the season. Needles of young jack pine exhibited higher photosynthetic capacity, dark respiration and needle N concentrations than needles of trees at the old site. In both species, slight acclimation to shading was manifested by reductions in photosynthetic capacity in the lower canopy foliage. In both species, first-year needles had greater photosynthetic capacity than older needles but in situ rates of CO(2) assimilation in the field showed little difference among needle age classes. In both species, there was a strong correlation between assimilation and stomatal conductance, indicating that assimilation was highly stomatal limited and that environmental factors that alter conductance (e.g., VPD) have a strong influence on CO(2) and water fluxes, especially after early season thawing concludes.

Journal Article↗