Freezing temperatures in the root zone—effects on growth of containerized Pinus sylvestris and Picea abies seedlings

Roots of 1‐year‐old containerized seedlings of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) were experimentally frozen in December. The seedlings were then grown for 3 weeks in a growth chamber and evaluated with regard to root growth capacity (RGC) and shoot elongation. The subsequent RGC of Scots pine declined as root zone temperatures were lowered from ‐6°C to ‐11°C and from ‐11°C to ‐16°C. Almost no root growth was observed after exposure to ‐20°C. Shoot growth was also negatively affected by low root temperatures but less than root growth. Low root temperatures did not affect Norway spruce as much as Scots pine, although root and shoot growth of Norway spruce were reduced after exposure to the lowest test temperatures (‐16°C and ‐20°C). The length of exposure, ranging between 1 and 8 hours had no effect on subsequent growth.     

Outdoor winter storage of container stock on raised pallets—effects on root zone temperatures and seedling growth

Containerized seedlings of Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) were overwintered on the ground and above ground on pallets. Soil temperatures in elevated containers were lower and showed greater fluctuation than containers on the ground. The lowest temperatures (‐15 to ‐16°C) were observed in containers stored on pallets with little or no snow cover during the winter. Temperatures in the edge rows of containers were lower than interior bed soil temperatures. Lower temperatures were also observed in the top than in the bottom of the container. The storage on pallets resulted in reduced shoot and root growth. Although insulation preventing air movements beneath the container units improved soil temperature conditions and subsequent seedling growth, the best result was obtained when seedlings were stored directly on the ground surface.     

Root growth capacity and field performance of Pinus sylvestris and Picea abies seedlings

Correlations between root growth capacity (RGC), at the time of planting, and field performance were studied for Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) seedlings. Before planting a gradient in seedling viability was generated through exposure to low root temperatures and different winter storage regimes. The hypothesis that high RGC values would improve field performance was to some extent verified for pine seedlings while no correlations could be registered for spruce. Reasons for these results are discussed.     

Effects of different overwinter storage regimes on shoot growth and net photosynthetic capacity in Pinus Sylvestris Seedlings

Seedlings of Pinus sylvestris were cold‐stored for three or six months at ‐4°C or 2°C or overwintered outdoors. Dry weight development and net photosynthetic capacity were then measured during a 60‐day cultivation period in a controlled environment. In all storage regimes the longer storage period gave a faster growth initiation. Photosynthetic recovery was faster for seedlings stored at 2°C than at ‐4°C, due to better recovery of stomatal conductance. The results suggest that there is little difference in seedling development between storage temperatures of ‐4°C and 2°C whereas outdoor storage might cause certain negative effects on subsequent growth of seedlings. This result is discussed with regard to the present winter climate.     

Planting performance potential of Pinus sylvestris seedlings as evaluated by root growth capacity and triphenyl tetrazolium chloride reduction methods

Root growth capacity (RGC) and root viability by the reduction of triphenyl tetrazolium chloride (TTC) of Scots pine (Pinus sylvestris L.) seedlings were measured in the winter and spring after freeze‐induced stress (0, ‐10, ‐15, ‐20°C). After freezing, seedlings were also stressed with different storage temperatures, and drying. Field performance during two years at two sites was used to determine the prediction abilities of the two test methods. RGC and TTC differed between the winter and spring tests. Coefficients of variation (CV) for RGC were larger in the winter than in the spring. The opposite applied for TTC. RGC was significantly lower in the winter than in the spring. TTC reduction was lower in the spring than in the winter. RGC‐ and TTC‐values decreased as freezing temperatures were lowered. Correlation coefficients between treatment means of RGC and TTC were low. Coefficients of determination (r ²) of linear regressions of RGC to the field performance attributes, first and second year diameter increment, height increment, and survival, were between 0.30 and 0.40. For TTC the revalues ranged from 0.50 to 0.80. In general, the TTC‐method seemed to be a better indicator of Scots pine seedling performance in the field.     

Responses of Pinus sylvestris and Picea abies Seedlings to Limited Phosphorus Fertilization and Treatment with Elevated Ozone Concentrations

Scots pine ( Pinus sylvestris L.) and Norway spruce [ Picea abies (L.) Karst.] seedlings were exposed to high phosphorus (HP) or low phosphorus (LP) availability for one growing season in the open field, and to combined P availability and elevated ozone (O 3 ) concentrations (0, 55, 110 and 210 ppb for Scots pine and 0, 40, 75 and 150 ppb for Norway spruce, respectively) for 28 days in controlled laboratory chambers. Compared with HP, the LP treatment reduced Scots pine current-year (C) shoot and root dry masses and Norway spruce total dry mass, whereas the highest O 3 concentrations increased the magnesium concentration of Scots pine C needles and P concentrations of the C needles of both tree species. Chlorophyll a, a+b and carotenoid concentrations of Scots pine C needles were significantly higher in the LP treatment compared with HP under the highest O 3 concentration (210 ppb). In the mesophyll tissue of C needles of both tree species, LP treatment increased the size of mitochondria and elevated O 3 -induced granulation of chloroplast stroma and disintegration of cytoplasm. Exposure to elevated O 3 concentrations increased swelling of chloroplast thylakoids and reduced the amount of vacuolar tannin in the LP Scots pine C needles. The results suggest disturbances in needle photosynthetic machinery due to acute exposure to the combination of elevated O 3 and low P availability. However, clear additive effects were found only in needle P concentrations < 1 mg g -1 in short-term O 3 exposure.     

Damage by pine weevil Hylobius abietis to conifer seedlings after shelterwood removal

Abstract

Pine weevil (Hylobius abietis L.) damage to seedlings after overstorey removal was investigated in a survey study in six shelterwoods in the south–central part of Sweden. The shelterwoods predominantly consisted of Scots pine, except at one site where the shelter trees mainly consisted of Norway spruce. Before final cutting, 10 plots were laid out at each site and measurements of shelter trees and marked seedlings were taken. The seedlings were examined during the 2 years after final cutting. The study showed that removal of shelter trees increases the risk of severe damage by pine weevil and the variable that was most strongly correlated with the risk was the seedling root collar diameter. Both Scots pine and Norway spruce seedlings were severely damaged by pine weevil, and most of the feeding occurred during the first year after cutting. The amount of debarked area was significantly larger for Scots pine than for Norway spruce seedlings. Vitality (growth of the leading shoot before final cutting) of the seedlings also affected the probability of damage. Seedlings with high vitality were less damaged by pine weevil than seedlings with low vitality. For Scots pine the shelterwood density before final cutting was correlated to the intensity of pine weevil feeding after cutting. In conclusion, after the final cutting of a pine or spruce shelterwood, pine weevils will probably invade the area. To avoid serious damage, Norway spruce and Scots pine seedlings should have reached a diameter of at least 10–12 mm.     

Fine root morphological adaptations in Scots pine, Norway spruce and silver birch along a latitudinal gradient in boreal forests

Variability in short root morphology of the three main tree species of Europe's boreal forest (Norway spruce (Picea abies L. Karst.), Scots pine (Pinus sylvestris L.) and silver birch (Betula pendula Roth)) was investigated in four stands along a latitudinal gradient from northern Finland to southern Estonia. Silver birch and Scots pine were present in three stands and Norway spruce was present in all stands. For three fertile Norway spruce stands, fine root biomass and number of root tips per stand area or unit basal area were assessed from north to south. Principal component analysis indicated that short root morphology was significantly affected by tree species and site, which together explained 34.7% of the total variability. The range of variation in mean specific root area (SRA) was 51-74, 60-70 and 84-124 m(2) kg(-1) for Norway spruce, Scots pine and silver birch, respectively, and the corresponding ranges for specific root length were 37-47, 40-48 and 87-97 m g(-1). The range of variation in root tissue density of Norway spruce, Scots pine and silver birch was 113-182, 127-158 and 81-156 kg m(-3), respectively. Sensitivity of short root morphology to site conditions decreased in the order: Norway spruce > silver birch > Scots pine. Short root SRA increased with site fertility in all species. In Norway spruce, fine root biomass and number of root tips per m(2) decreased from north to south. The differences in morphological parameters among sites were significant but smaller than the site differences in fine root biomass and number of root tips.     

Interference of bracken (Pteridium aquilinum L. Kuhn) with Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies L. Karst.) seedling establishment

The nature of interference of bracken with Scots pine and Norway spruce seedling establishment was considered in three field experiments. In a seeding experiment, it was found that Scots pine germination was highest on exposed mineral soil and lowest when intact bracken litter and humus were present, suggesting adverse effects of litter and humus on pine regeneration probably due to phytotoxicity. In a second experiment, smothering by bracken caused high mortality of Scots pine seedlings while Norway spruce seedlings were relatively unaffected. Mortality for both Scots pine and Norway spruce seedlings was low when planted in a adjacent Scots pine-bilberry stand with no bracken. Annual shoot growth of Norway spruce was higher in bracken than in Scots pine-bilberry vegetation while no differences in shoot growth between these two vegetation types occurred for Scots pine. In a third experiment, activated carbon was added to the ground under Norway spruce seedlings planted in bracken to adsorb possible phytotoxic compounds released by bracken. The addition of carbon had no effect on seedling mortality or growth rate, indicating that the seedlings were not susceptible to allelochemicals released by bracken. Since large Norway spruce seedlings were relatively unaffected by bracken interference in this study, artificial regeneration with containerized Norway spruce seedlings is suggested to achieve an acceptable conifer tree establishment on clear-cuts invaded by bracken.     

Boron retranslocation in Scots pine and Norway spruce

We previously traced 10B-enriched boric acid from shoots to roots to demonstrate the translocation of boron (B) in Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) seedlings. To gain a more detailed understanding of B translocation, we sought: (1) to demonstrate B retranslocation directly, by showing that foliar-applied 10B is located in the new growth after dormancy; and (2) to assess whether shoot-applied B affects growth in the long term. We applied 10B-enriched boric acid to needles of Scots pine and Norway spruce seedlings. After a dormancy period and 9 weeks of growth, small but significant increases in the 10B isotope were found in the new stem and needles of both species. In Scots pine, the total B concentration of the new stem was also increased. Both species contained polyols, particularly pinitol and inositol. Boron-polyol complexes may provide a mechanism for mobilizing B in these species. To determine the long-term effects of applied B, seedlings were grown for two growing seasons after the application of 10B to shoots. In Norway spruce, the proportion of 10B in the root systems and current needles of the harvest year was slightly higher than in the controls, and in Scots pine root systems, marginally so. The B treatment had no effect on growth of Norway spruce seedlings. In Scots pine seedlings, the B treatment caused a 33% increase in total dry mass and significantly increased the number of side branches.     

Effect of uninucleate Rhizoctonia on Scots pine and Norway spruce seedlings

One‐year‐old container‐grown seedlings were planted in spring on clear cut areas: the Norway spruce (Picea abies) on a moist upland site (Myrtillus‐type) and Scots pine (Pinus sylvestris) on a dryish upland site (Vaccinium‐type). While still in the nursery, half of the seedlings of each species had been inoculated during the previous summer, with a uninucleate Rhizoctonia sp., a root dieback fungus. At outplanting all the seedlings appeared healthy and had a normal apical bud, although the height of the inoculated seedlings was less than that of the uninoculated control seedlings. At the end of the first growing season after planting, the mortality of inoculated Scots pine and Norway spruce seedlings was 25 and 69%, respectively. After two growing seasons the mortality of inoculated seedlings had increased to 38% for Scots pine and 93% for Norway spruce. The mortality of control seedlings after two growing seasons in the forest was 2% for Scots pine and 13% for Norway spruce. After outplanting the annual growth of inoculated seedlings was poor compared with the growth of control seedlings. These results show that, although Rhizoctonia‐affected seedlings are alive and green in the nursery, the disease subsequently affects both their survival and growth in the forest.     

Infection experiments with Gremmeniella abietina on seedlings of Norway spruce and Scots pine

Conidia of Gremmeniella abietina infected and caused disease symptoms in annual shoots of both Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) seedlings. In Norway spruce shoots the infection remained largely latent, with only a few seedlings showing symptoms. Mycelial growth inside the shoots was faster in Scots pine than in Norway spruce and was favoured by low temperature in both hosts. The shoots of Norway spruce seedlings had higher endophyte populations than those of Scots pine, and the populations were decreased by low temperatures. Reductions in the normal epiphytic or endophytic flora by acid mist treatments seemed to favour the development of G. abietina.     

The effects of soil and air temperature on CO2 exchange and net biomass accumulation in Norway spruce, Scots pine and silver birch seedlings

Soil temperature is proposed to affect the photosynthetic rate and carbon allocation in boreal trees through sink limitation. The aim of this study was to investigate the effect of temperature on CO(2) exchange, biomass partitioning and ectomycorrhizal (ECM) fungi of boreal tree species. We measured carbon allocation, above- and below-ground CO(2) exchange and the species composition of associated ECM fungi in the rhizosphere of Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies K.) and silver birch (Betula pendula Roth) seedlings grown in soil maintained at 7-12, 12-15 and 16-22 °C. We found increased root biomass and photosynthetic rate at higher soil temperatures, but simultaneously with photosynthesis rate, higher temperature generally increased soil respiration as well as shoot, and root and rhizosphere respiration. The net CO(2) exchange and seedling biomass did not increase significantly with increasing temperature due to a concomitant increase in carbon assimilation and respiration rates. The 2-month-long growth period in different soil temperatures did not alter the ECM fungi species composition and the below-ground carbon sink strength did not seem to be directly related to ECM biomass and species composition in any of the tree species. Ectomycorrhizal species composition and number of mycorrhiza did not explain the CO(2) exchange results at different temperatures.     

Colour responses from wood,thermally modified in superheated steam and pressurized steam atmospheres

Abstract

In this study, two different methods were used to produce thermally modified wood. One was carried out in a typical kiln drying chamber using superheated steam (SS) and the other used pressurized steam in an autoclave cylinder (PS). Overall, both processes followed the same principles and the wood was not treated with any chemicals. Two wood species were studied, Scots pine (Pinus sylvestris) and Norway spruce (Picea abies). Treatments in the autoclave were carried out under pressure using temperatures of 160°C, 170°C and 180°C. Temperatures of 190°C and 212°C were used in treatments in the chamber at normal air pressure. The colour was measured using L*C*H colour space. Results for both species showed that similar L* (lightness) can be reached at lower (20–30°C) temperatures using PS compared with SS treatment. The hue angle of PS-treated wood was smaller than that of SS-treated wood. No significant difference in C* (chroma) was detected. The difference in E value between PS- and SS-treated wood was smaller for Norway spruce than for Scots pine. The residual moisture content was about 10% higher in wood treated by the PS process compared with the SS process.     

Fine root biomass in relation to site and stand characteristics in Norway spruce and Scots pine stands

Variations in fine root biomass of trees and understory in 16 stands throughout Finland were examined and relationships to site and stand characteristics determined. Norway spruce fine root biomass varied between 184 and 370 g m(-2), and that of Scots pine ranged between 149 and 386 g m(-2). In northern Finland, understory roots and rhizomes (< 2 mm diameter) accounted for up to 50% of the stand total fine root biomass. Therefore, the fine root biomass of trees plus understory was larger in northern Finland in stands of both tree species, resulting in a negative relationship between fine root biomass and the temperature sum and a positive relationship between fine root biomass and the carbon:nitrogen ratio of the soil organic layer. The foliage:fine root ratio varied between 2.1 and 6.4 for Norway spruce and between 0.8 and 2.2 for Scots pine. The ratio decreased for both Norway spruce and Scots pine from south to north, as well as from fertile to more infertile site types. The foliage:fine root ratio of Norway spruce was related to basal area and stem surface area. The strong positive correlations of these three parameters with fine root nitrogen concentration implies that more fine roots are needed to maintain a certain amount of foliage when nutrient availability is low. No significant relationships were found between stand parameters and fine root biomass at the stand level, but the relationships considerably improved when both fine root biomass and stand parameters were calculated for the mean tree in the stand. When the northern and southern sites were analyzed separately, fine root biomass per tree of both species was significantly correlated with basal area and stem surface area per tree. Basal area, stem surface area and stand density can be estimated accurately and easily. Thus, our results may have value in predicting fine root biomass at the tree and stand level in boreal Norway spruce and Scots pine forests.     

Height growth of planted conifer seedlings in relation to solar radiation and position in Scots pine shelterwood

Seedlings of different provenances of Scots pine (Pinus sylvestris L.), lodgepole pine (Pinus contorta Dougl., var. latifolia Engelm.) and Norway spruce (Picea abies (L.) Karst.) were planted in three Scots pine shelterwoods (125, 65 and 43 stems ha⁻¹) and a clear-cut, all in northern Sweden. The sites were mounded and planting took place during 2 consecutive years (1988 and 1989). The solar radiation experienced by the individual seedlings was determined using a simulation model. Height development of the seedlings was examined during their first 6 years after planting. During the final 3 years of the study, height growth of Norway spruce was relatively poor, both in the shelterwoods and the clear-cut area. Height growth of lodgepole pine was significantly greater than that of Scots pine, both in the shelterwoods and the clear-cut. In contrast to Norway spruce, Scots pine and lodgepole pine displayed significantly greater height growth in the clear-cut than in the shelterwoods. For all three species in the shelterwoods, regression analyses showed that height growth was more strongly correlated with the distance to the nearest tree than with the amount of radiation reaching the ground, i.e. growth was reduced in the vicinity of shelter trees. Therefore, we conclude that the significant reduction in height growth of seedlings of Scots pine and lodgepole pine in Scots pine shelterwoods was partially caused by factors associated with the distance to the nearest shelter tree. Because the substrate was a nitrogen-poor sandy soil, we suggest that root competition for mineral nutrients, especially nitrogen, accounts for the reduction in height growth.     

Fast, nondestructive measurement of frost hardiness in conifer seedlings by VIS+NIR spectroscopy

Frost hardiness development from mid-August to mid-November was evaluated in seedlings of three provenances of Norway spruce (Picea abies (L.) Karst.) and three provenances of Scots pine (Pinus sylvestris L.) raised at nurseries in north, central and south Sweden. Measurements of the visible + near infrared (VIS+NIR) spectra of shoots were made simultaneously with estimates of frost hardiness based on electrolyte leakage following artificial freezing. Nine physiological variables known to influence frost hardiness were measured throughout the experiment. Multivariate analysis showed that VIS+NIR spectra explained 69% and 72% of the variation in frost hardiness in Scots pine and Norway spruce, respectively. Stem lignification, dry weight fraction, and starch, glucose, fructose, galactose, sucrose, raffinose and stachyose concentrations together explained 80% and 85% of the variation in frost hardiness in Scots pine and Norway spruce, respectively when used as independent X variables in a partial least squares model. These physiological variables could be related to varying degrees with variation in the VIS+NIR spectra. We conclude that VIS+NIR spectroscopy provides a rapid nondestructive technique for measuring frost hardiness in conifer seedlings based on causal relationships between the spectra and the physiology of seedling frost hardiness.     

From planting to 26 years of age – actual growth and estimated volume scenarios for spruces and pines

The objective of this study was to compare the survival and volume of conifer stands at 26 years of age with their status at planting. Survival, growth and damage were studied in eight clear felled stands regenerated in 1972. Five of the areas were planted with Norway spruce (Picea abies (L.) Karst.) and three with Scots pine (Pinus sylvestris L.). The plantings were examined in 1972 and 1974. In 1974, the number of living undamaged planted seedlings was low (10–15%). However, the number of undamaged seedlings was supplemented by naturally regenerated conifer and birch seedlings. The total number of undamaged seedling in 1974 was equivalent to 20–30% of the number of seedlings planted. In 1998, the main species in three stands had changed from Norway spruce to Scots pine, and in one stand from Norway spruce to birches. Actual volume in 1998 for the stands was compared to stand volume generate according to five scenarios based on recommended and actual seedling number in 1972 and 1974. The actual volume was 64% of that expected if the recommended number of trees had been planted. Naturally regenerated Scots pine and Norway spruce increased stand density in 1998. The actual volume was 37% higher than the average volume in the surrounding county. On average, 36% of the trees were damaged. More than 50% of the total damage was caused by moose (Alces alces L.). For Scots pine, moose or other browsing animals damaged 30% of the trees. The results of this study indicate that the 1998 volume was higher than expected, considering the low number of undamaged seedlings in 1974. This was mainly due to the large amount of naturally regenerated plants. In addition, the results indicate that the volume could have been higher if the initial conditions had been better. Despite the low number of undamaged seedlings in 1974, seven of the eight studied stands produced a higher volume than the average stand for the region. In practise, high numbers of seedlings should be planted on scarified areas. In most cases there will be a supply of naturally regenerated seedlings.     

Soil temperature limitations on gas exchange in 1‐year‐old Pinus sylvestris (L) seedlings

Effects of soil temperature on gas exchange of Scots pine seedlings were studied to evaluate the significance of reduced gas exchange in seedlings planted in cold soils. The patterns of net photosynthesis during the 3‐week period at the two constant soil temperatures (8°C and 12°C) were quite similar but at 12°C the photosynthetic rate was higher. After U days differences were no more significant. Photosynthesis at the increasing soil temperature, from 5.5°C to 13°C, decreased for the first 18 days and then recovered up to the level of other treatments. The same patterns were found for transpiration, stomatal conductance, and photosynthetic efficiency. Xylem pressure potentials and relative resistance to water flow after 3 weeks did not differ among soil temperatures. Initiation and development of current‐year needles affected all the results of gas exchange parameters.     

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.