Needle life span,photosynthetic rate and nutrient concentration of Picea glehnii,P. jezoensis and P. abies planted on serpentine soil in northern Japan

We investigated the adaptation of three spruce species (Picea glehnii Masters, P. jezoensis Carr. and P. abies Karst.) to growth in northern Japan on serpentine soils (characterized by high concentrations of heavy metals and Mg, a low Ca/Mg ratio and low fertility) and fertile brown forest soils. Among species, seedling survival on serpentine soil was highest in P. glehnii. Shoot growth of P. glehnii was similar whether grown on serpentine or brown forest soil, whereas shoot growth of the other species was significantly less on serpentine soil than on brown forest soil. On serpentine soil, needle life span of P. glehnii was at least 3 years longer than that of the other two species. Needle area per shoot of P. glehnii was significantly higher on serpentine soil than on brown forest soil up to a shoot age of 8 years. In all three species, light-saturated photosynthetic rate (Pmax) decreased with needle age independently of soil type. However, on serpentine soil, Pmax in P. glehnii was higher, particularly in older needles, than in the other species. Furthermore, on serpentine soil, needle concentrations of nitrogen and phosphorus were higher in P. glehnii than in the other species. We conclude that P. glehnii is better adapted to serpentine soil than P. jezoensis and P. abies at least in part because of its greater needle life span and higher needle nutrient concentrations.     

Impacts of mechanical site preparation on foliar nutrients of planted white spruce seedlings on mixed-wood boreal forest sites in Alberta

The impacts of different methods of mechanical site preparation (MSP) on performance and foliar nutrition of planted white spruce (Picea glauca (Moench) Voss) seedlings were examined at two mixed-wood boreal forest sites (Judy Creek, Fox Creek) in Alberta, Canada. The treatments included three types of MSP: disc trench, ripper plough, and bladed, the latter including thin and thick microsites (based on depth of remaining organic matter); as well as a harvested-control (no MSP). Seedlings were planted in June 1991, four months after MSP, and foliar N, P, K, Ca, Mg, S, Mn, Fe, and Al were assessed in the second and third growing seasons (13, 25, and 28 months later). Nutrient concentration and relative (among treatments) foliar nutrient content scaled up to the level of the whole seedling were examined. Following analysis of variance, significant responses were interpreted using vector analysis. MSP did not significantly affect seedling survival, height or unit needle weight. There was a non-significant trend of higher foliar biomass for seedlings in MSP areas than for control seedlings. Overall, the impact of MSP on foliar nutrient status on these sites was minimal. The only consistent positive effect of MSP on seedling nutrition was increased foliar Mg concentrations in blade-thin sites at Fox Creek. Indications of possible negative impacts of MSP include: increased Fe and Al concentrations in MSP areas at both sites; reduced P and K concentrations at both sites; and reduced Mn concentration and content at one site. The ripper treatment had the greatest positive effect on foliar nutrient status (P, K, Mn concentration). Blading (particularly blade-thin) resulted in the lowest concentrations of foliar P, K and Mn and the greatest increases in foliar Fe and Al.     

Growth, nutrition, photosynthesis and transpiration responses of longleaf pine seedlings to light, water and nitrogen

Early growth and physiology of longleaf pine (Pinus palustris Mill.) seedlings were studied in response to light, water and nitrogen under greenhouse conditions. The experiment was conducted with 1-year-old seedlings grown in 11.3 l pots. The experimental design was a split-plot factorial with two levels (low and high) of each of the factors, replicated in three blocks. The four factorial combinations of water and nitrogen were randomly applied to 15 pots (sub-plots) in each of the light treatment (main plot). Data were collected on survival, root collar diameter (RCD), and height on a monthly basis. Biomass (shoot, root and needle), leaf area index, specific needle area, and needle nutrient (N, P, K, Ca, and Mg) concentrations were determined following final harvest after 16 months. Physiological data (net photosynthesis and transpiration) were collected monthly from March to July during the second growing season.

Height and RCD were significantly influenced by nitrogen and water and by the interaction between them with no apparent effect of light. Seedlings grew 93% taller in the high nitrogen and well watered (HNWW) treatment compared to the low nitrogen and water stressed (LNWS) treatment. Similarly, a significant increase (78%) in RCD was observed for seedlings in the HNWW treatment over the LNWS treatment. Light, along with water and nitrogen, played an important role in seedling biomass growth, especially when water was not limiting. Biomass partitioning (as measured by root:shoot ratio) was affected only by nitrogen and water. Nutrient stress had a greater influence on carbon allocation (69% increase in root:shoot ratio) than water stress (19% increase). Net photosynthesis (P_net) was significantly higher for seedlings in the high resource than in the low resource treatments with significant light×water and nitrogen×water interactions. Transpiration rate was higher (75%) under the WW treatment compared to the WS treatment. Longleaf pine seedlings grown under the LNWW treatment had the lowest foliar nitrogen (0.71%) whereas seedlings in the HNWS treatment had the highest (1.46%). Increasing the availability of light (through larger canopy openings or controlling midstory density) and soil nitrogen (through fertilization) may not result in greater P_net and improved seedling growth unless soil water is not limiting.     

Effects of elevated nitrate and aluminum on the growth and nutrition of red spruce (Picea rubens) seedlings

Acidic deposition in high-elevation forests in the Appalachian Mountains of the eastern United States has been implicated in the decline of red spruce (Picea rubens Sarg.). Elevated soil acidity may increase soil Al availability and toxicity to roots. Enhanced soil solution NO(3) (-) concentrations, resulting from precipitation inputs and enhanced soil organic matter mineralization, may exacerbate Al toxicity by increasing root Al uptake. We exposed red spruce seedlings to 350, 500, 800 or 1400 micro M NO(3) (-) and 0 or 200 micro M Al in a factorial design in sand-nutrient solution culture to test if increased NO(3) (-) concentrations enhance Al uptake and toxicity. In addition to significant reductions in seedling growth parameters resulting from Al exposure, we found significant interactions between NO(3) (-) and Al for seedling height growth rate, needle weight, shoot weight and root weight. Differences in these parameters between Al treatments became more pronounced as solution NO(3) (-) concentration increased and reflected an Al-mediated inhibition of seedling response to increasing NO(3) (-) concentration. Solution NO(3) (-) concentrations above 500 micro M induced root nitrate reductase (NR) activity, whereas shoot NR activity increased in response to NO(3) (-) up to 500 micro M and declined above that concentration. In contrast, exposure to Al depressed NR activity of roots but tended to stimulate needle NR activity. Foliar N concentrations increased in seedlings grown in cultures containing between 350 and 500 micro M NO(3) (-), with no change above 500 micro M. Increasing concentrations of NO(3) (-) depressed foliar P concentrations, with reductions being greatest in seedlings exposed to 1400 micro M NO(3) (-). Exposure to Al increased foliar Ca, K and Al concentrations, decreased foliar P concentrations, and inhibited increases in foliar Mg concentration in response to increasing NO(3) (-). The consistent interactions between NO(3) (-) and Al for growth, root NR activity and foliar Mg concentration were the result of an inhibition of seedling response to NO(3) (-) mediated by Al in solution, rather than enhanced Al toxicity resulting from growth in the presence of elevated NO(3) (-) concentrations.     

Effects of silvicultural treatments and seasonal patterns on foliar nutrients in young post-fire Pinus halepensis forest stands

Tree growth and health status appear to be related to foliar nutrient contents. Foliar nutrient concentration might be the result of a complex interaction between soil nutrients and effective availability caused by climate, water and other site and treatment effects. This study examines foliar macronutrient (N, P, K, Ca, Mg) and organic C concentrations in Aleppo pine (Pinus halepensis) needles (between 5 and 18 months old), as well as time course variability (nine dates, from July 1999 to November 2001). Variability was assessed depending on quality site (two sites, Yeste and Calasparra; SE Spain) and seven silvicultural treatments including thinning, scrubbing, pruning and particular combinations of them. Foliar macronutrient concentrations for Aleppo pine in South-eastern Spain were slightly lower (N, P, K,) or higher (Mg, Ca) than the considered as adequate ranges for Aleppo pine and Pinus genera. However, our results agree well with other normal ranges reported for Aleppo pine in Spain and for other North American Pinus species such as P. elliottii, P. taeda and P. palustris. Site, treatment and date (season) affected significantly the foliar macronutrient and C concentration, although the most important was the date, likely due to the two growth periods per year that Aleppo pine has in Mediterranean sites. Silvicultural treatments affected foliar nutrient concentration, so that the concentrations of N, P and K were higher when treatments included thinning than those that did not. The contrary was true for Mg and Ca. However, treatments did not affect the time course of the concentration, i.e., seasonality was not broken due to treatments. Moreover, the effect of the treatments was markedly high along the first year after they were applied but the differences were attenuate 2 years later. Site affected the time course of N, K, Mg and C in a different way: while for N, K and C, at the end of study period, they were higher in Calasparra than in Yeste, for Mg the contrary was true. Nutrient ratios had a different behaviour regarding to single nutrient: although date was significant, we did not appreciate seasonality. In addition, some nutrient ratios were not affected by treatments (N/P, N/K, Ca/Mg,) or by site (N/Ca, K/Ca). Average foliar N concentration and Ca/Mg ratio explained significantly the mean diameter and height growth, so that higher is the foliar N concentration and lower is Ca/Mg, higher is the growth.     

Effects of Acidic Precipitation and Ectomycorrhizal Inoculation on Growth,Mineral Nutrition,and Xylem Water Potential of Juvenile Loblolly Pine and White Oak

Abstract

Individual and interactive effects of simulated acidic rainfall and mycorrhizal inoculation on growth and nutrient and water relations of loblolly pine (Pinus taedaL.) and white oak (Quercus albaL.) grown in a loam soil were examined. Seedlings of each species inoculated with basidiospores of the ectomycorrhizal fungus Pisolithus tinctorius(Pers.) Coker and Couch, a known my-cobiont of both loblolly pine and white oak, and uninoculated control seedlings received two simulated rains per week of either pH 3.6, 4.2, or 4.8 for 26 weeks. Higher acidity rainfall reduced the growth but increased mycorrhizal colonization of loblolly pine, while both loblolly pine and white oak exposed to these rains exhibited greater foliar injury. Inoculation with P. tinctoriusincreased growth and reduced foliar injury of both species. Foliar concentrations of P, S, and Cu in loblolly pine and white oak, Ca in loblolly pine, and Fe and Zn in white oak decreased with increasing rain acidity while the Al concentration of both species increased. Higher rainfall acidity also reduced soil pH and Ca and Mg concentrations while increasing soil AI. Foliage of inoculated seedlings of both species had higher N and P concentrations and lower Al concentrations than control seedlings. Following the final rain applications, a drought cycle was simulated by withholding irrigation for two weeks during which seedling xylem pressure potential and soil water potential were measured. One day after cessation of irrigation, xylem pressure potential of loblolly pine that had received pH 3.6 rains was lower than that of other treatments. Thereafter, xylem pressure potential and soil water potential of the inoculated treatment decreased below those of the control treatment in both species. These results suggest that acid deposition is detrimental to juvenile loblolly pine and white oak, but the magnitude of this effect is less than the positive response to ectomycorrhizal inoculation.     

Physiological and morphological responses to nitrogen limitation in jack pine seedlings: potential implications for drought tolerance

The morphological and physiological responses to nitrogen (N) limitation in jack pine (Pinus banksiana Lamb.) seedlings were studied following the initiation of four different dynamic N treatments for six and 15 weeks. The N treatments produced needle N concentrations from 11 to 31 mg g^-1dry weight, and seven-fold difference in dry weight at 15 weeks. Low-N jack pine seedlings: 1) had an higher root/shoot ratio; 2) extended their tap root more rapidly; 3) were better able to maintain turgor when shoot water potential declined; and 4) had a larger dry weight fraction and apoplasmic fraction than seedlings with higher foliar N concentrations. These responses may contribute collectively to enhance drought tolerance in N-limited plants, thereby affecting seedling quality. Modifying nursery fertilization regimes, other than optimal as usually applied, may thus be needed to produce stock for use on particularly droughty sites. Knowledge of the nature of drought at a particular site could be an important consideration when making decisions related to fertilization.     

Ozone, acidic rain and soil magnesium effects on growth and foliar pigments of Pinus taeda L

Height and diameter growth, biomass accumulation and leaf pigment concentrations were measured in loblolly pine (Pinus taeda L.) seedlings grown in soil containing 12 or 35 microg Mg g(-1) and exposed from May to October to subambient, ambient, or twice-ambient ozone (O(3)), and to simulated acidic rain with a pH of either 4.0 or 5.3. At the end of one growing season, height and diameter growth of seedlings exposed to twice-ambient O(3) were not statistically different from those of seedlings exposed to subambient O(3). Biomass of all plant parts was reduced by 7 to 16% in response to increasing O(3) concentration. No statistically significant growth responses to rain chemistry or soil magnesium status were observed, and there were no statistically significant interactive treatment effects. Needle pigment concentrations were not significantly affected by rain chemistry or soil Mg status and there were no visible signs of injury to needles that could be attributed to O(3) stress or Mg deficiency. Concentrations of chlorophyll a and b, and carotenes were 23, 30 and 21% higher (P 相似文献   

Diurnal changes in water conduction in loblolly pine (Pinus taeda) and Virginia pine (P. virginiana) during soil dehydration

We studied diurnal changes in water conduction during soil dehydration in 37-month-old seedlings of one Virginia pine (Pinus virginiana Mill.) and two loblolly pine (P. taeda L.) sources, one from North Carolina (NC) and the other from the "Lost Pines" areas of Texas (TX), in an environmentally controlled growth chamber. For seedlings of similar biomass, the TX source had higher values of transpiration, needle conductance, and plant hydraulic conductivity under well-watered conditions than the NC source. Under dry soil conditions, the TX source had lower values of water conduction than the NC source. The Virginia pine source responded similarly to the TX source under both well-watered and dry soil conditions. For all three pine sources, gradients between soil and needle water potentials were greatest when the seedlings were moderately stressed. The TX and Virginia pine sources had higher gradients and lower daytime needle water potentials under moderate stress conditions than the NC source. Predawn needle water potentials did not differ among the pine sources. We conclude that the TX and Virginia pine sources have decreased daytime needle water potentials and increased water potential gradients during the daytime under moderate stress conditions, but with no disruption of recovery at predawn. The greater rates of transpiration and water conduction by the TX source compared with the NC source under well-watered conditions suggest a means by which growth can be maximized prior to the onset of drought, thereby enhancing survival of loblolly pines in drought-prone environments.     

Influence of a high Mn supply on Norway spruce (Picea abies (L.) Karst.) seedlings in relation to the nitrogen source

Effects of 3, 25, 100, 200 and 800 microM Mn on biomass and pigment, starch and nitrate concentrations were studied in Norway spruce (Picea abies (L.) Karst.) seedlings grown with either NO(3) (-) or NH(4) (+) as the sole nitrogen source. After 77 days of exposure to 800 microM Mn, shoot growth had ceased in about 50% of the seedlings independently of the N source. Despite high Mn concentrations in roots and shoots of the Mn-treated seedlings, no visible symptoms of Mn toxicity were evident. The rate of root elongation was decreased by treatment with >/= 200 microM Mn when N was supplied as NO(3) (-), but not when it was supplied as NH(4) (+). This difference could be attributed to the higher Mn concentrations in root tips of the NO(3) (-)-grown seedlings compared with the NH(4) (+)-grown seedlings. In Mn-treated seedlings, the concentration of Mg, and to a lesser extent that of Ca, decreased. Depletion of these elements might account for the observed growth depression. Potassium concentrations were similar in the control and Mn-treated seedlings. Treatment of seedlings with 800 microM Mn for 50 days led to several physiological changes: starch accumulated, the concentrations of nitrate and phenolic compounds increased, pigment concentrations decreased, and in vivo nitrate reductase activity in roots was reduced.     

Growth and nutrition of nonmycorrhizal and mycorrhizal pitch pine (Pinus rigida) seedlings under phosphorus limitation

The association of ectomycorrhizal fungi with tree roots enhances the acquisition of phosphorus (P) from the soil. In addition to increasing the uptake of H(2)PO(4) (-) (P(i)), mycorrhizal fungi may increase the spectrum of P sources utilized by tree roots by mediating the dissolution of insoluble metallophosphate salts or the hydrolysis of organic P compounds. To investigate the role of ectomycorrhizal fungi in enhancing P acquisition by tree roots, pitch pine (Pinus rigida Mill.) seedlings were grown in sand culture with or without the ectomycorrhizal symbiont Pisolithus tinctorius Coker and Couch under various conditions of P limitation. Compared with nonmycorrhizal seedlings, seedlings inoculated with P. tinctorius exhibited a greater capacity to function under P limitation as evidenced by superior growth and the maintenance of normal foliar ion composition at low P(i) concentrations. Nonmycorrhizal seedlings subjected to P-limiting conditions exhibited depressed K and P and elevated Na concentrations in foliage. The association of P. tinctorius with pitch pine seedling roots maintained foliar K concentrations and prevented the accumulation of Na under P limitation. Nonmycorrhizal seedlings were unable to obtain P from either solid AlPO(4) or inositol hexaphosphate (IHP), whereas seedlings inoculated with P. tinctorius utilized AlPO(4), but not IHP as a P source. Root surface acid phosphatase (APase) activity was depressed in roots infected with the mycorrhizal symbiont and was negatively correlated with seedling growth on all P sources. Root APase activity was negatively correlated with foliar P concentrations in seedlings grown on P(i), but was not correlated with foliar P concentrations in seedlings cultured with AlPO(4) or IHP.     

Growth and Nutritional Responses of Juvenile Jeffrey Pine to Post-Planting Fertilization

Abstract

Broadcast fertilization of a three-year-old Jeffrey pine (Pinus jeffreyi Grev. & Balf.) plantation growing on an eroded Sierra Nevada site was examined for its capacity to enhance seedling growth. The amendments chosen for the study included controlled release and conventional soluble formulations that contained a variety of N forms, but all featured high N content along with other nutrients. Four application rates were used, and all amendments were distributed around the base of the seedlings as top dressing. Four seasons after treatment application, fertilized seedlings were 129% larger in height, 93% larger in diameter, and 865% greater in shoot volume than unfertilized seedlings overall. Seedling sizes generally increased with application rate, and by a small margin, the controlled release fertilizer outperformed the other formulations. Relative growth analysis suggested that stimulation by the amendments would continue beyond four seasons. Foliar analysis conducted early and again late during the study revealed that N and P concentrations were consistently raised by fertilization, which likely accounts for much of the accompanying growth gains, while Ca, Fe, Mn, B, and Al concentrations were consistently reduced. Either early or late, foliar K was also raised while Mg, S, Zn, and Cu were reduced. Collectively, these results indicate that fertilization with a variety of high N formulations can increase the availability and uptake of critical nutrients sufficiently to impart in Jeffrey pine on low quality sites a substantial growth advantage.     

Silvicultural options to promote seedling establishment on Kalmia–Vaccinium-dominated sites

Seedling growth is often hampered on sites dominated by Kalmia angustifolia. In June 2000, a trial was established on a clear-cut site in Quebec, Canada, with a high cover of Kalmia and Vaccinium species. The objectives were to evaluate how soil scarification and fertilization at the time of planting influence early growth and establishment of black spruce [Picea mariana (Mill.) BSP] and jack pine (Pinus banksiana Lamb.) seedlings. During the first 2 years, scarification reduced Kalmia cover three-fold and doubled the distance from seedlings to the nearest Kalmia stem. Scarification did not increase soil-extractable NH₄-N concentration, and reduced soil potassium, calcium and magnesium. Scarification had no effect on seedling water stress. Seedling growth improved and foliar nutrient concentrations were generally higher in scarified plots than in unscarified control plots. No differences were observed between single- and double-pass scarification for any variables except for ground-level stem diameter of seedlings, which was greater with double-pass scarification (12.1 vs 13.1 mm). Spot fertilization increased seedling growth and foliar nitrogen concentrations. Jack pine growth was greater than black spruce growth, an effect enhanced when seedlings were fertilized.     

Irrigation regime affects water and aeration conditions in peat growth medium and the growth of containerized Scots pine seedings

Containerized Scots pine seedlings growing in light Sphagnum peat growth medium in a greenhouse were subjected to three irrigation treatments. The seedlings were irrigated by saturating the growth medium with a nutrient solution (i) daily or when (ii) –5 or (iii) –10 kPa medium matric potential was achieved. In general, the nutrient concentrations in the foliage of the seedlings were rather similar for all irrigation treatments. In the wet (daily) irrigation treatment, however, the foliar concentration of N was lower and the foliar concentrations of P, Ca, S, Mn and Na were higher than in the other two treatments. In the wet irrigation treatment, height growth was lower than that in the other treatments. In this treatment the shoot to root ratio and several other morphological characteristics were also reduced, while the number of root lenticels and seedling mortality were increased compared to the other treatments. Rapid growth was obtained by irrigating at –5 to –10 kPa matric potential. In the wet irrigation treatment, the median matric potential and air-filled porosity of the peat medium were –0.4 kPa and 11%, respectively, which indicated waterlogging and very suboptimal aeration to the seedlings. The respective values for the irrigations at –5 and –10 kPa were –2.7 to –3.3 kPa and 39 to 43%, which were considered to cover the range from optimum to slightly suboptimum for average water availability and aeration.     

Growth response of Douglas-fir seedlings to nitrogen fertilization: importance of Rubisco activation state and respiration rates

High foliar nitrogen concentration ([N]) is associated with high rates of photosynthesis and thus high tree productivity; however, at excessive [N], tree productivity is reduced. Reports of excessive [N] in the Douglas-fir forests of the Oregon Coast Range prompted this investigation of growth and needle physiological responses to increasing foliar N concentrations in 1-year-old Douglas-fir seedlings. After 1 year of N fertilization, total seedling biomass increased with each successive increase in N fertilizer concentration, except in the highest N fertilization treatment. Of the many physiological responses that were analyzed, only photosynthetic capacity (i.e., Vcmax), respiration rates and leaf specific conductance (KL) differed significantly between N treatments. Photosynthetic capacity showed a curvilinear relationship with foliar [N], reaching an apparent maximum rate when needle N concentrations exceeded about 12 mg g(-1). In vitro measurements of ribulose-1,5-bisphosphate carboxylase (Rubisco) activity suggested that photosynthetic capacity was best related to activated, not total, Rubisco content. Rubisco activation state declined as foliar [N] increased, and based on its significant correlation (r2= 0.63) with foliar Mn:Mg ratios, it may be related to Mn inactivation of Rubisco. Respiration rates increased linearly as foliar N concentration increased (r2= 0.84). The value of K(L) also increased as foliar [N] increased, reaching a maximum when foliar [N] exceeded about 10 mg g(-1). Changes in K(L) were unrelated to changes in leaf area or sapwood area because leaf area to sapwood area ratios remained constant. Cumulative effects of the observed physiological responses to N fertilization were analyzed by modeling annual net CO2 assimilation (Anet) based on treatment specific values of Vcmax, dark respiration (Rdark) and KL. Estimates of Anet were highly correlated with measured total seedling biomass (r2= 0.992), suggesting that long-term, cumulative effects of maximum Rubisco carboxylation, Rdark and KL responses to N fertilization may limit seedling production when foliar N exceeds about 13 mg g(-1) or is reduced to less than about 11 mg g(-1).     

Grass interference limits resource availability and reduces growth of juvenile red pine in the field

The effects of competing grasses on resource availability, growth and ecophysiological characteristics of 3-0 red pine (Pinus resinosa Ait.) seedlings were examined the first two years following outplanting in Anoka County, Minnesota, USA. Equal numbers of seedlings were planted into suppressed and undisturbed grass communities in a sandy soil. Grass suppression was maintained throughout the first growing season, but partially discontinued thereafter on the site. During the first field season interference from grass reduced pine seedling root collar diameter, needle length, number of new root tips, and lateral root length by over 40%. Mean pre-dawn needle water potential was 0.55 MPa lower in undisturbed grass plots during a brief drought in year one, but otherwise water stress was not significantly (p=0.05) influenced by grass interference. The presence of grass also reduced, up to 50%, the photosynthetically active radiation reaching the seedling canopy. At the end of year one, total biomass N, P, K, and Ca content were significantly (p=0.05) less in seedlings growing in the undisturbed grass community. Nitrogen was deficient in seedlings growing in grass. After two growing seasons, seedling shoot length (p=0.03), root collar diameter (p=0.001), and needle length (p=0.001) were significantly less (40, 54 and 20%, respectively) for seedlings growing in undisturbed grass. Seedling growth reductions induced by grass competition were associated with multiple environmental stressors in the field and not restricted to water stress as was observed in earlier studies with pine species at low and mid-latitude sites.     

Growth and phenology of seedlings of four contrasting slash pine families in ten nitrogen regimes

Seedlings of two fast- and two slow-growing families of slash pine, Pinus elliottii Englm. var. elliottii, were grown in a greenhouse for one growing season in one of 10 nitrogen (N) regimes. Increasing the N concentration in the nutrient solution resulted in both increased growth rates during the exponential growth phase and extended duration of the growing season. The two components of total height, free growth (epicotyl length to the first bud) and summer growth (height growth after the first bud), both increased significantly with increasing N concentrations up to 40-60 mg l(-1) but decreased at N concentrations above 180 mg l(-1). Compared to seedlings grown in the presence of an optimum N concentration, seedlings grown in the presence of trace amounts of N were smaller and had less summer growth as a percentage of total growth, earlier cessation of height growth, fewer flushes, lower shoot/root ratio, higher root fibrosity, and lower N concentrations in all seedling tissues. Compared to slow-growing families, fast-growing families had more summer height growth, more flushes and later growth cessation, higher shoot/root ratios and higher root fibrosity at all N concentrations. In the presence of an optimum or higher concentration of N, the fast-growing families also had higher needle and total N concentrations than the slow-growing families. Strong family by N-treatment interactions occurred for height, phenology and biomass traits because of the extra responsiveness of one family to increasing N concentration. Several seedling traits were identified that appear promising for predicting field performance in slash pine. The results indicated that the nutrient environment greatly influences genetic expression (e.g., family patterns of summer growth were most closely related to field rankings for seedlings in the trace-N treatment).     

Shoot and root sensitivity of containerized black spruce,white spruce and jack pine seedlings to late fall freezing

Damage to containerized forest seedlings due to freezing can occur in the fall or early winter in Canadian forest nurseries. The following spring, damage to shoots and impairment of growth is observed. The objectives of this experiment were to measure the impact of late fall low temperatures (0° to --30°C) on whole seedlings of the three most common species used for reforestation in Quebec: black spruce (BS), white spruce (WS) and jack pine (JP). Impacts of freezing temperatures on (i) whole seedling and apical bud mortality, (ii) shoot growth and root mortality, (iii) stem electrical resistance, (iv) shoot and root water relations, (v) concentrations of N, P, K, Ca, Mg, and total sugars in shoots were assessed. JP showed the highest rate of whole seedling mortality while WS showed the highest rate of apical bud mortality. JP was the most severely affected: destruction of the root system at low temperatures as well as a reduction of shoot growth and stem diameter and a decrease (more negative) in shoot and root water potential. WS showed a reduction of shoot growth despite no apparent damage to the root system at low temperatures. BS was not affected by temperatures as low as --30°C. Nutrient and sugar concentrations were not affected by low temperature treatments.     

Long-term response of weed control intensity on Scots pine survival, growth and nutrition on former arable land

The effects of post-planting weed control intensity on the cover and composition of ground vegetation, and on growth, survival and foliar nutrient concentrations of 4-year old bare-rooted Scots pine (Pinus sylvestris L.) seedlings were studied over a 15-year period with experimentation on former arable land. Weed control treatments with terbuthylazine and glyphosate were carried out 1?C3 times during successive years, either as overall or as spot applications. The vegetation cover and the shading effect of vegetation decreased with increasing weed control intensity. The more intensive the weed control was, the better was the afforestation result in terms of tree seedling growth and survival. Overall application repeated three times increased seedling survival by 79 percentage points, and their final height, breast height, diameter, and stand volume after 15 years were increased by 183, 19, 15, and 822%, respectively. Weed control did not affect the foliage nutrient concentrations, except for magnesium. However, increase in weed control intensity was reflected in larger needle size 5 years after planting.     

Changes in nutrient concentrations and nutrient release in decomposing needle litter in monocultural systems of Pinus contorta and Pinus sylvestris—a comparison and synthesis

Scots pine (Pinus sylvestris) and lodgepole pine (Pinus contorta) needle litters were compared in terms of nutrient composition and its change during decomposition. Initial nutrient composition differed between the species, with lodgepole pine needle litter having significantly higher concentrations of P, Mg and Mn. However, no difference was found for concentrations of N, Ca or K. Increases in concentrations of N, P and K during decomposition were significant in both litter types. For Ca the pattern of concentration changes followed a quadratic function as decomposition proceeded. Concentrations of Mg and Mn decreased in lodgepole pine needle litter. In Scots pine litter there was also an initial decrease, but it was followed by an increase in most incubations. For both Mg and Mn, changes in concentrations during decomposition differed significantly between species. In the late decomposition stages, concentrations of Mg and Mn became similar in both litter types. Nutrient concentrations generated by the models were compared with those of the humus (F and H) layer in the stands. The model was quite accurate in predicting concentrations of N and P for both species and the concentration of Mg for lodgepole pine. By contrast, it was not accurate in predicting concentrations of Ca and Mn. Nutrient release was estimated for the two species using both measured litterfall data and long‐term estimates, and regression models were used to predict concentration changes. Rates of release of P, Mg and Mn in the lodgepole pine stands were found to be about twice as high compared with those in Scots pine. Calcium was also released to a greater extent although the difference was not significant.