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PubMed1999

Long-term effects of elevated carbon dioxide concentration and provenance on four clones of Sitka spruce (Picea sitchensis). II. Photosynthetic capacity and nitrogen use efficiency.

Four clones of Sitka spruce (Picea sitchensis (Bong.) Carr.) from two provenances, at 53.2 degrees N (Skidegate a and Skidegate b) and at 41.3 degrees N (North Bend a and North Bend b), were grown for three growing seasons in ambient (~350 micromol per mol) and elevated (~700 micromol per mol) CO2 concentrations. The clones were grown in stress-free conditions (adequate nutrition and water) to assess the effect of elevated [CO2] on tree physiology. Growth in elevated [CO2] significantly increased instantaneous photosynthetic rates of the clonal Sitka spruce saplings by about 62%. Downward acclimation of photosynthesis (A) was found in all four clones grown in elevated [CO2]. Rubisco activity and total chlorophyll concentration were also significantly reduced in elevated [CO2]. Provenance did not influence photosynthetic capacity. Best-fit estimates of Jmax (maximum rate of electron transport), Vcmax (RuBP-saturated rate of Rubisco) and Amax (maximum rate of assimilation) were derived from responses of A to intercellular [CO2] by using the model of Farquhar et al. (1980). At any leaf N concentration, the photosynthetic parameters were reduced by growth in elevated [CO2]. However, the ratio between Jmax and Vcmax was unaffected by CO2 growth concentration, indicating a tight coordination in the allocation of N between thylakoid and soluble proteins. In elevated [CO2], the more southerly clones had a higher initial N use efficiency (more carbon assimilated per unit of leaf N) than the more northerly clones, so that they had more N available for those processes or organs that were most limiting to growth at a particular time. This may explain the initial higher growth stimulation by elevated [CO2] in the North Bend clones than in the Skidegate clones.

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PubMed1986

Effect of low root temperature on net photosynthesis, stomatal conductance and carbohydrate concentration in Engelmann spruce (Picea engelmannii Parry ex Engelm.) seedlings.

The effect of low root temperature on net photosynthesis, stomatal conductance and carbohydrate concentration in potted Engelmann spruce (Picea engelmannii Parry ex Engelm.) seedlings was examined under controlled growth-chamber conditions. Root temperature had no effect on net photosynthesis between 10 and 20 degrees C, however, conductance and photosynthesis declined sharply below 8 degrees C. Net photosynthesis and stomatal conductance decreased to 50 and 34% of the initial values after 7 days at a root temperature of 0.7 degrees C. Low root temperature also caused a decrease in photosynthetic utilization of internal CO(2), carboxylation efficiency and apparent quantum yield, and it was concluded that the decrease in photosynthetic rate was caused primarily by nonstomatal limitations. Root chilling caused a small increase in starch content in needles and stems and induced the hydrolysis of starch to glucose in roots. The increase in glucose concentration may enable continued root growth at low temperatures.

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PubMed2000

Influence of temperature and leaf-to-air vapor pressure deficit on net photosynthesis and stomatal conductance in red spruce (Picea rubens).

The roles of temperature (T) and leaf-to-air vapor pressure deficit (VPD) in regulating net photosynthesis (A(net)) and stomatal conductance (G(s)) of red spruce (Picea rubens Sarg.) were investigated in a field study and in a controlled environment experiment. Both A(net) and G(s) exhibited a relatively flat response to temperatures between 16 and 32 degrees C. Temperatures between 32 and 36 degrees C markedly decreased both A(net) and G(s). Vapor pressure deficits above 2 kPa had significant effects on both A(net) and G(s). The influence of VPD on A(net) and G(s) fit a linear response model and did not interact significantly with T effects.

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PubMed2000

Influence of nutrient supply on shade-sun acclimation of Picea abies seedlings: effects on foliar morphology, photosynthetic performance and growth.

Norway spruce seedlings (Picea abies Karst.) were grown in low light for one year, under conditions of adequate and limiting nutrition, then transferred to high light. Three months after transfer we measured photosynthesis, leaf nitrogen concentration, leaf chlorophyll concentration and leaf mass per area (LMA) of current-year and 1-year-old shoots; silhouette area ratio (SAR, the ratio of shoot silhouette area to projected needle area) was also measured in current-year shoots. At the foliage level, the effects of light and nutrient treatments differed markedly. Light availability during foliage expansion primarily affected LMA and SAR (morphological acclimation at the needle and shoot level, respectively). By contrast, nutrient supply in high light affected photosynthetic capacity per unit of leaf tissue (physiological acclimation at the cellular level) but did not affect LMA and SAR. The capacity for shade-sun acclimation in foliage formed before transfer to high light differed greatly from that of foliage formed following the transfer. The morphological inflexibility of mature needles (measured by LMA) limited their shade-sun acclimation potential. In contrast, at high nutrient supply, shoots that developed just after the change in photosynthetic photon flux density largely acclimated, both morphologically and physiologically, to the new light environment. The acclimation response of both current- and 1-year-old shoots was prevented by nutrient limitation. Analysis of growth at the whole-plant level largely confirmed the conclusions drawn at the shoot level. We conclude that nutrient shortage subsequent to the opening of a canopy gap may strongly limit the acclimation response of Norway spruce seedlings. Successful acclimation was largely related to the plant's ability to produce sun foliage and adjust whole-plant biomass allocation rapidly.

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PubMed2000

Dependence of winter water relations of mature high-elevation Picea engelmannii and Abies lasiocarpa on summer climate.

Water relations of Engelmann spruce (Picea engelmannii Parry) and subalpine fir (Abies lasiocarpa (Hook.) Nutt.) trees growing at an elevation of 3230 m on Mt. Evans, Colorado, USA, were studied during the winters of 1995-1996 and 1996-1997. During both winters, current-year and 1-year-old shoots were collected weekly and their relative water contents (RWC) determined. Measured meteorological parameters were used in a conifer winter water relations model, WINWAT, to simulate changes in shoot RWC of P. engelmannii and A. lasiocarpa during the winter. The model failed to predict shoot RWCs in 1996-1997 when calibrated with 1995-1996 data. The cold early summer of 1995 inhibited xylem formation, which appears to have caused lower rates of water recharge to the needles during the 1995-1996 winter than during the 1996-1997 winter. We conclude that summer climate strongly affects winter water relations in these subalpine species, and that changes in both summer and winter climate must be considered when predicting future ranges of these species.

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PubMed2000

Effect of elevated [CO(2)] and varying nutrient application rates on physiology and biomass accumulation of Sitka spruce (Picea sitchensis).

Sitka spruce (Picea sitchensis (Bong.) Carr.) seedlings were supplied with solutions containing nitrogen (N) at 0.1 x or 2 x the optimum rate (low-N and high-N supply, respectively) and grown either outside in a control plot or inside open-top chambers and exposed to ambient (355 &mgr;mol mol(-1)) or elevated (700 &mgr;mol mol(-1)) CO(2) concentration ([CO(2)]). Gas exchange measurements, chlorophyll determinations and nutrient analysis were made on current-year (< 1-year-old) shoots of the upper whorl after the seedlings had been growing in the [CO(2)] treatments for 17 months and the nutrient treatments for 6 months. Total seedling biomass and biomass allocation were assessed at the end of the experiment. Nutrient treatment had a significant effect on the light response curves, irrespective of [CO(2)] or chamber treatment; seedlings supplied with high-N rates had higher net photosynthetic rates than seedlings supplied with low-N rates. The degree of photosynthetic stimulation in response to elevated [CO(2)] was larger in seedlings receiving high-N rates than in seedlings receiving low-N rates. Light-saturated net photosynthesis of seedlings grown and measured in elevated [CO(2)] was 26% higher than that of seedlings grown and measured in ambient [CO(2)]. There was no significant effect of [CO(2)] or chamber treatment on the CO(2) response curves of seedlings receiving High-N supply rates. In contrast, analysis of the CO(2) response curves of seedlings receiving Low-N supply rates showed acclimation to elevated [CO(2)]. Both maximum rate of carboxylation (V(cmax)) and maximum electron transport capacity (J(max)) were lower and J(max)/V(cmax) higher in seedlings in the elevated [CO(2)] treatment. There was no effect of elevated [CO(2)] on stomatal conductance, although it was highly dependent on foliar [N], ranging from ~60 mmol m(-2) s(-1) at ~1.5 g N m(-2) to 200 mmol m(-2) s(-1) at ~5 g N m(-2). In the high-N and low-N treatments, foliar N concentration was 10 and 28% lower in seedlings grown in elevated [CO(2)] than in seedlings grown in ambient [CO(2)], respectively. There was no [CO(2)] effect on foliar phosphorus concentration ([P]). Chlorophyll concentration increased with increasing N supply in all treatments. There was no significant effect of elevated [CO(2)] on specific leaf area. Chlorophyll concentration expressed either on an area or dry mass basis for a given foliar [N] was higher in seedlings grown in elevated [CO(2)] than in seedings grown in ambient [CO(2)]. Elevated [CO(2)] increased total biomass accumulation by 37% in seedlings in the high-N treatment but had no effect in seedlings in the low-N treatment. There was a proportionally bigger allocation of biomass to roots of seedlings in the elevated [CO(2)] + low-N supply rate treatment compared with seedlings in other treatments. This resulted in a reduction in aboveground biomass compared with corresponding seedlings grown in ambient [CO(2)].

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PubMed1987

Dynamics of indole-3-acetic acid during germination of Picea abies seeds.

High performance liquid chromatography and combined gas chromatography-mass spectrometry were used to identify indole-3-acetic acid (IAA) and indole-3-ethanol as endogenous constituents of germinating Norway spruce (Picea abies (L.) Karst.) seeds. Indole-3-methanol was tentatively identified by multiple ion monitoring. The free IAA content of the seeds rose from about 20 ng g(-1) to about 60 ng g(-1) (dry weight) during the first five days of germination and thereafter declined to around 20 ng g(-1). Indole-3-acetic acid released by alkaline hydrolysis, which was initially present at about 110 ng g(-1), decreased to 5-10 ng g(-1) during the first week of germination. The IAA content of seed lots differing in germination behavior was investigated. The findings are discussed in relation to the metabolism of IAA in conifer seeds.

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PubMed1988

Crown architecture and stemwood production in Norway spruce (Picea abies (L.) Karst.).

The morphological data for Norway spruce (Picea abies (L.) Karst.) trees published by Burger (1953) were reanalyzed to examine the relationships between crown shape, needle and branch mass density of crown volume, needle efficiency in stemwood production, harvest index and stemwood production efficiency per unit of crown projected area. Production of stemwood per unit of crown projected area was higher in narrow-crowned trees than in broad-crowned trees because the narrow-crowned trees had (i) smaller horizontal space requirements for equal crown volumes, (ii) higher leaf area index due to both the geometrical crown shape and higher needle density per unit of crown volume, and (iii) higher harvest index indicating high allocation of dry matter production to stem.

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PubMed1989

Frost hardiness of Picea rubens growing in spruce decline regions of the Appalachians.

It has been proposed that pollutants predispose Picea rubens Sarg. growing in the high Appalachians to frost damage. The pattern of autumn hardening of P. rubens growing at Whiteface Mountain, NY, and Newfound Gap, NC, was monitored by detaching shoots at 1-3 weekly intervals, air freighting them to Scotland, and freeze-testing them. The temperatures that produced freezing injury from August 1986 to January 1987 were compared with minimum air temperatures recorded in those months at nearby meteorological stations over 22 previous years. There was only weak evidence that the onset or degree of frost hardening was inadequate to protect the trees from direct freezing injury (as opposed to winter desiccation). Historically, minimum air temperatures occasionally fell below the lethal temperature for a 10% kill (LT(10)), but they rarely fell below the LT(50). The trees hardened rapidly in the autumn (max. 2.2 degrees C day(-1)) to between -30 degrees C and -40 degrees C by January (LT(50)), including trees showing visible decline on Clingman's Dome, TN. Individual trees differed in hardiness by up to 10 degrees C. It is concluded that any pollutant-induced susceptibility to freezing injury is insufficient, on its own, to account for forest decline in the Appalachians.

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PubMed1989

Root hydraulic conductivity and root growth capacity of black spruce (Picea mariana) seedlings.

The relationship between root elongation and root hydraulic conductivity was investigated in 1-year-old, overwintered black spruce (Picea mariana (Mill.) seedlings. Hydraulic conductivity was estimated by observing water flux through decapitated roots under positive pressure. Five hydraulic conductivity parameters were estimated: (1) water flux under a minimal pressure of 0.2 MPa (J(v, min)); (2) pressure at which a linear relationship between water flux and pressure began (P(min)); (3) slope of the linear water flux-pressure relationship (L(v)); (4) pressure at which the linear relationship between water flux and pressure ended (P(max)); and (5) maximum water flux (J(v, max)). Between day 1 and day 2 after thawing of the growing medium, there were significant increases in L(v) and J(v, max) but there was little, if any, root elongation. Root elongation averaged 5.4 cm seedling(-1) 5 days after thawing and 88.2 cm seedling(-1) 20 days after thawing. Root hydraulic conductivity increased with new root length initially. But between days 20 and 30, when new root length nearly doubled, P(min) was the only measure of hydraulic conductivity that increased significantly. There were significant correlations (P < 0.05) between white root length and both J(v, min) (r(2) = 0.90) and J(v, max) (r(2) = 0.91).

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PubMed1989

The elasticity and vertical distribution of stress within stems of Picea sitchensis.

Eight 22-year-old Picea sitchensis (Bong.) Carr. trees growing in a Scottish forest were bent using a winch and cable. The shapes of the bent stems were modeled using the structural theory of a cantilever beam, with non-uniform stem taper and large deflections taken into account. The Young's modulus of elasticity for the stems was estimated to be 2.0-6.4 GPa, which is lower than that reported for sawn green timber of this species, but similar to that for intact green stem sections. The longitudinal distribution of stress along the stems had a maximum at a height that was dependent on taper. Maximum stress occurred higher up in the more tapered stems.

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PubMed1989

Ultrasound emission after cycles of water stress in Picea abies.

The relationships among rate of ultrasound acoustic emission (AE), xylem water potential and transpiration rate were investigated in 5-year-old potted saplings of Picea abies Karst. after cycles of water stress. Water-stressed plants displayed minimum xylem water potentials of -3.9 MPa, near-zero transpiration rates and up to 45 AE counts per minute. After rewatering, water-stressed plants no longer produced AEs. Well-watered control plants produced only a small number of ultrasonic AEs. After three cycles of water stress (lasting 24 days in total), it was estimated that about two-thirds of the functional tracheids were embolized. The concomitant reduction in hydraulic conductance was about 70%.

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PubMed1990

Needle growth in Sitka spruce (Picea sitchensis): effects of nutrient deficiency and needle position within shoots.

Needle development and shoot growth were studied in 14- and 20-year-old Sitka spruce (Picea sitchensis (Bong.) Carr.) planted on an oligotrophic peat and fertilized with N, P and K (control), N and P (-K), N and K (-P) or unfertilized (-NPK). Shoot extension, needle number, and the size and number of needle cells were observed throughout the season. Beginning with bud burst in early May, needle growth continued for nine weeks in the control treatment. Needle growth in the mineral deficiency treatments terminated at the same time as in the controls, although it did not begin until up to three weeks later than in the control trees. Needles developed acropetally along the shoot, with basal needles completing their development first. Cell division in needles of control trees lasted about 3 weeks, with cell expansion continuing for a further 3 weeks. Initial mean cell cycle times were shortest for proximal needles following bud burst, but lengthened as the season progressed. Cell number increased from 6600 in the primordia to 200 000 in mature needles. Final needle dimensions and cell number varied according to the position of the needle on the shoot. The largest needles with the most cells were near the middle of the shoot. Relative to the controls, all mineral deficiency treatments reduced shoot length, bud and needle dimensions, and needle cell number, particularly the -P treatment. Potassium and P deficiency treatments reduced primordial cell number by up to 42%, whereas final mean cell size was 30% greater in the -P treatment, 17% greater in the -NPK treatment, but 14% smaller in the -K treatment. Mean cell size was constant for needles at all positions in any particular treatment at any time, so that final needle size was determined by cell number alone. Needle dry weight/fresh weight ratio continued to increase until early August, with significantly higher ratios in the -K and -P treatments than in the controls.

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PubMed1990

Theoretical study of variables affecting the export of assimilates from branches of Picea.

A theoretical analysis was done to identify the features of conifer branch development, based on a model for Picea sitchensis (Bong.) Carr., that affect the ability to export assimilates, assuming (i) a branch's requirement for assimilates is determined by its need for mechanical support, and (ii) the production of assimilates is a simple function of total shoot length. There were three salient findings. First, there is an optimum and maximum shoot length for assimilate export by unbranched shoots. Second, the less a shoot extends itself each year, the more assimilate it may export, all else being equal. Third, there is a larger surplus of assimilates for export when a shoot develops laterals. A combination of lateral branching, deflection and decreased elongation can enable branches to continue growing and exporting assimilates for many years, as occurs at the bases of tree crowns.

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PubMed1990

Solution aluminum and transpiration in Picea rubens and Gleditsia triacanthos seedlings.

Soil solution Al may contribute to red spruce (Picea rubens Sarg.) decline by inhibiting transpiration (Klein 1985). This study examines how Al affects transpiration in red spruce and honeylocust (Gleditsia triacanthos L.) seedlings and explores mechanisms for the observed responses. Red spruce seedlings were grown in dilute nutrient solutions containing 0 to 925 microM Al at pH 4.5 or 3.8. Solution Al had no effect on the transpiration, root hydraulic conductivity (K(r)) or shoot water potential (Psi) of red spruce. Transpiration of honeylocust was higher in the presence of 100 to 350 microM Al than 0, 500, or 600 microM Al. The Al-induced increases in transpiration of honeylocust were unrelated to shoot Psi or root K(r), but were closely correlated with the greater root lengths produced by intermediate levels of Al. In neither species was transpiration correlated with tissue concentrations of Al, P, K, Ca or Mg.

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PubMed1990

Inherited narrow crown form, harvest index and stem biomass production in Norway spruce, Picea abies.

The effect of crown form on stem biomass production was investigated in an 18-19-year-old Norway spruce stand (Picea abies (L.) Karst.). The harvest index was 0.271 in pendula trees, which have a heritable narrow crown form, and 0.235 in normal-crowned trees and the dry weights of stem biomass were 2.57 kg and 3.37 kg, respectively. However, the production of stem biomass per crown projected area was more than twice as much in pendula trees as in normal-crowned trees. Results indicate that the crown form of pendula spruce is less plastic than that of normal-crowned spruce suggesting that such trees might maintain a high stemwood yield per unit ground area with increasing stand density. Because pendula spruce has a higher harvest index and a less flexible crown than normal-crowned spruce, it might be useful for crop tree ideotype breeding.

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PubMed1991

Seasonal changes in shoot water relations of Picea rubens at two high elevation sites in the Smoky Mountains.

Seasonal changes in water relations of current-year shoots of red spruce (Picea rubens Sarg.) were examined in relation to climatic conditions in trees growing at elevations of 1720 and 1935 m on Clingman's Dome, Tennessee, USA, where increment core data have shown that red spruce decline increases with elevation. Relative height growth of trees at 1720 m was 68% greater than in trees at 1935 m. Following two weeks in July with only traces of precipitation, trees at both sites showed decreased saturated osmotic potentials. The magnitude of the reduction was greater in trees at the high elevation site than in trees at the low elevation site. However, during August and September, shoot water relations of trees at both sites were similar. Precipitation patterns and water relations measurements suggested that, at both sites, trees experienced water stress only briefly during the growing season and to a degree that could not account for the lower growth rates of trees at the high elevation site. During the period of cold hardening in October and November, trees at the low elevation site exhibited saturated osmotic potentials that were lower by 0.2 MPa and solute accumulation (osmol kg(dw) (-1)) that was 48% greater than in trees at the high elevation site.

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PubMed1991

Differential adsorption of Al, Ca, and Mg by roots of red spruce (Picea rubens Sarg.).

The surface adsorption characteristics of red spruce (Picea rubens) roots were examined as a function of changes in external acidity and cation concentrations. Root cation exchange capacity varied significantly with changes in pH, increasing from 110 micromol(c) g(-1) at pH 3.5 to 155 micromol(c) g(-1) at pH 4.5, and reaching 250 micromol(c) g(-1) at pH 7.0. In general, Al adsorption by spruce roots was much greater than either Ca or Mg adsorption under the same initial conditions. However, root affinity for the divalent cations was proportionately much more sensitive to pH changes than was root affinity for Al. The fractions of adsorbed Ca and Mg increased by 50 to 100% as pH increased from 3.5 to 4.5, whereas the fraction of adsorbed Al remained relatively constant at both initial pH conditions. Competition experiments at pH 3.5 and 4.5 indicated that Al adsorption was strongly favored over Ca adsorption, except at low Al concentrations (~10 micromol l(-1)), high solution Ca(2+)/Al(3+) ion activity ratios (> 1.5 to 5.0), and at the higher pH. These results suggest that cell wall exchange sites in red spruce roots will tend to become progressively saturated with Al under the prevailing conditions of many acidic forest soils. To the extent that root adsorbed Al interferes with the active uptake of Ca and Mg, this process of competitive cation adsorption can contribute to impaired mineral nutrition in the spruce forest community.

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