Effects of varied soil nitrogen supply on Norway spruce (Picea abies [L.] Karst.)

During a seven-month period the effect of different nitrogen (N) availability in soil on growth and nutrient uptake was studied in three-year-old Norway spruce (Picea abies [L.] Karst.) trees. The plants were grown in pots on N-poor forest soil supplied with various amounts and forms (inorganic and organic) of N. Increasing supply of inorganic N (as NH₄NO₃) increased the formation of new shoots and shoot dry weight. The root/shoot dry weight ratio of new growth was drastically decreased from 1.6 in plants without N supply to 0.5 in plants supplied with high levels of NH₄NO₃. This decrease in root/shoot dry weight ratio was associated with distinct changes in root morphology in favour of shorter and thicker roots. The addition of keratin as organic N source did neither affect growth nor root morphology of the trees. The amount of N taken up by plants was closely related to the supply of inorganic N, and trees supplied with highest levels of NH₄NO₃ also had the highest N contents in the dry matter of needles and roots. In contrast, N contents in needles of trees grown without additional N, or with keratin supply, were in the deficiency range. Supply of NH₄NO₃ decreased the contents of phosphate (P) and potassium (K) and therefore markedly increased N/P and N/K ratios in the needles. On the other hand, the contents of calcium (Ca), magnesium (Mg), and manganese (Mn) in the needles were increased in the plants supplied with inorganic N, suggesting high soil availability and promotion of uptake of these divalent cations by high nitrate uptake. The observed effects on root/shoot dry weight ratio, root morphology, and mineral nutrient composition of the needles indicated that high inorganic N supply may increase above-ground productivity but at the same time decrease the tolerance of trees against soil-borne (e.g. deficiency of other mineral nutrients) stress factors. Deceased 21 September 1996 Deceased 21 September 1996     

Development of biomass proportions in Norway spruce (Picea abies [L.] Karst.)

This study tests the hypotheses that (1) the above-ground structure of Norway spruce (Picea abies [L] Karst.) is derivable from the functional balance theory, and that (2) crown ratio is a key source of structural variation in trees of different age and social position. Twenty-nine trees were measured in three stands (young, middle-aged, and mature), with three thinning treatments (unthinned, normal, and intensive) in the two older stands. There was a strong linear relationship between the total cross-sectional area of branches and that of stem at crown base. Foliage mass was linearly related with stem basal area at crown base. Also an allometric relationship was found between foliage mass and crown length. The mean length (weighted by basal area) of branches obeyed an exponential function of crown length. The parameters of most of these relationships were independent of slenderness (tree height/breast height diameter) and tree age However, total branch cross-sectional area per stem cross-sectional area in the young trees was greater than in the older trees. The young trees also had slightly shorter branches than predicted by the mean branch length equation. This was probably caused by branch senescence which had not yet started in the young stand. The older trees had a relatively long lower crown segment which was growing slowly and senescing. It was proposed that a segmented crown structure is characteristic of shade tolerant tree species, and that the structural model could be further developed by making the two segments explicit.     

Decomposition and nitrogen dynamics of fine roots of Norway spruce (Picea abies (L.) Karst.) at different sites

Long-term decomposition and nitrogen dynamics of Norway spruce finest (<1 mm in diameter) and fine (<2 mm in diameter) roots were estimated using the root litter-bag techniques. The seasonal decomposition of the finest roots was investigated in a 40-year-old high site quality stand grown on brown lessive soil at different depths as part of productivity studies. The fine root decomposition studies were conducted on 8 permanent plots in the Estonia with the aim to describe the site variation. The initial material was collected from one of stands (high quality site) and incubated at the depth of 10 cm in 1989 (at one site 1990). The bags were collected once or twice a year except for one site, where the seasonal dynamics was investigated. In all initial and decomposing root samples oven-dry weight, ash and energy content and nitrogen concentration was determined. After five years the finest roots had lost 40% of their initial dry weight, half of it during the first year. The initial concentration of nitrogen was 1.29%, the mean concentrations varied during the incubation from 1.47 to 1.78%. After the first year fine roots had lost 21.0 to 32.7% of their initial dry weight, after two years the weight loss was 22.5 to 43.2%. The initial N concentration in fine roots was 0.73% and in the first years it varied from 0.97 to 1.40% at different sites.     

Influence of cultivation method on root grafting in Norway spruce (Picea abies (L.) Karst.)

Root grafting is the process by which a functional union of two or more roots subsequent to their formation is formed. The above- and below-ground parts of three Norway spruce stands (natural stand, Umbric Luvisol; row-culture and group-culture, Planosol; stand ages 40, 43 and 43, respectively) of high site quality (I) were investigated. Stand densities were 1550, 1783 and 1722 stems ha^-1, respectively. In all investigated stands, root grafting was most sensitive to tree spacing. Grafts were observed in case the distance between the trees was 0.7–1.2 m. Grafts occurred always in areas of higher rooting density, in a row of the row-culture and within a tree group in the group-culture. Root grafting was enhanced in case of a narrower humus horizon in the group culture compared with the row-culture, 16.5 and 30 cm, respectively; the humus horizon contained 99% and 95% of conducting roots with d ≥ 5 mm, respectively. Root graftings occurred in 75% of excavated trees in the group-culture, in 37.5% of excavated trees in the row-culture and in 33.3% of excavated trees in the natural stand. Stand age was 24 years in the row-culture and 22 years in the group-culture at the beginning of root grafting. No grafts occurred between two suppressed trees, whereas in 86–100% of all cases, at least one tree was dominant or codominant. In row- and group-cultivated Norway spruce stands, the initial minimum diameter of the grafted root without bark was from 1 to 3 cm in 63% of cases. Grafting of roots with d < 1 cm or d > 10 cm was rare or absent. Root grafting had usually begun at the root age of 10–20 years (46% of cases). This revised version was published online in June 2006 with corrections to the Cover Date.     

An attempt to predict long-term effects of atmospheric nitrogen deposition on the yield of Norway spruce stands (Picea abies (L.) Karst.) in southwestern Sweden

Long-term field experiments in Norway spruce stands on fertile sites (site indices 27–35 m) in southwestern Sweden were analysed with respect to volume increment. Three treatments were included (0=No fertilization, N = Fertilization with N, NP = Fertilization with N and P).Volume growth was monitored for 18 years in 10 blocks. No significant differences in annual volume increment between the treatments were detected. Volume increments in the N treatment were 97%, 99% and 107% as high as those in the 0 treatment for the periods 1–5, 6–10 and 11–15 years after the first fertilization. Corresponding values for the NP treatment were 104%, 108% and 110%, indicating that P has a small positive effect.The amount of N-fertilization would correspond to an annual N deposition of 20 kg ha^-1 during the next 30 years in southwestern Sweden. For this period, the results imply that this N deposition would not affect the growth of Norway spruce stands on fertile sites.     

Effect of nitrogen on drought strain and nutrient uptake in Norway spruce Picea abies (L.) Karst.) trees

A field lysimeter study was established with the aim of investigating the effect of nitrogen availability upon drought strain in Norway spruce trees. Forest soil (Typic Udipsamment) was filled in lysimeters 1 m in diameter and 1 m deep. Small trees of Norway spruce from five different clones were planted in the lysimeters. Roofs under the canopy of the trees ensured full control of water and nutrient input. Three levels of nitrogen were given to the trees during five years; ambient rainwater, and five and fifteen times this N concentration, respectively. Additional N was given as NH₄NO₃ in irrigation water. Mean annual N-addition during the five years corresponded to 5, 27 and 82 kg per ha and year for the three treatments, respectively. During the third and fifth growth season drought was artificially induced. In addition to a watered control, two levels of drought were applied, representing water deprivation for 2 and 3 months, respectively, in 1990 and 3 and 4 months, respectively in 1992. A higher water consumption in the nitrogen fertilized trees during the droughts resulted in a significantly lower pre-dawn shoot water potential compared to the trees receiving ambient rain N. The interaction between drought and nitrogen fertilization was clear also for photosynthesis and transpiration. A decrease in height- and diameter increment caused by drought was most pronounced in the 82 kg N ha^–1 yr^–1 treatment. A water strain integral showed a strong positive correlation to the needle biomass of the trees. Foliar concentrations of several nutrients decreased significantly with increasing drought strain in the trees. Concentration of potassium and boron were especially low and visual symptoms of deficiency occurred.     

Seasonal accumulation of ultraviolet-B screening pigments in needles of Norway spruce (Picea abies (L.) Karst.)

Conifer needles are highly effective in screening ultraviolet-B radiation (280–320 nm). This ability is mainly attributed to the presence of flavonoids and hydroxycinnamic acids in the epidermal tissue. In two field cabinet experiments with two different clones of Norway spruce we assessed the seasonal accumulation of UV-B screening pigments under near-ambient, and close-to-zero UV-B irradiation. At the beginning of needle development, i.e. in June, kaempferol 3- O -glucoside was the dominant UV-B screening pigment. It was replaced during needle differentiation by the more effective diacylated flavonol glucosides, particulary kaempferol 3- O -(3",6"- O -di- p -coumaroyl)-glucoside, which reached highest concentrations in July. In addition to the soluble pool of diacylated flavonol glucoside derivatives, a cell wall-bound UV-B screen in the epidermal cell walls was formed during needle differentiation, consisting mainly of p -coumaric acid and kaempferol 3- O -glucoside. An effect of UV-B radiation on the accumulation of diacylated flavonol glucosides was only observed in 1996 with clone 2, when the concentrations of kaempferol 3- O -(3",6"- O -di- p -coumaroyl)-glucoside were significantly higher in July and August under field, and near-ambient than under close-to-zero UV-B irradiance. For wall-bound p -coumaric acid and kaempferol 3- O -glucoside UV-B radiation enhanced the concentrations of these compounds by approximately 20% in relation to the concentrations in close-to-zero UV-B-treated plants in both field cabinet experiments.     

Soil changes in different age classes of Norway spruce (Picea abies (L.) Karst.) on afforested farmland

The aim of this study was to test the hypothesis that afforestation changes the content and distribution of soil organic carbon, nutrients and pH in the A-horizon of land previously used in agriculture, and that such soil changes depend on stand development. The investigation was evaluated as a completely randomised design with three treatments representing different age classes of trees: 20 years (Y20), 40 years (Y40) and 55 years (Y55). Eighteen trial plots, six per treatment, were established in plantations of Picea abies (L.) Karst. on soils of similar texture and mineralogy. Tree volume was 220 m³ ha^-1 in Y20, 400 in Y40 and 440 m³ ha^-1 in Y55.Concentrations of carbon (C) and nitrogen (N) were significantly higher in the uppermost part of the soil in the older stands Y40 and Y55 than in Y20. The total amount of organic C in the litter layer plus the top 15 cm of the soil differed between age classes, with Y40 and Y55 having the largest amounts. A reference layer (15–20 cm) was used in calculating the amount of soil C that had accumulated in the horizon since afforestation, being about 10 tonnes ha^-1 of C in Y20 and 19 tonnes ha^-1 in Y40 and Y55.Cation exchange capacity (CEC) and base saturation (BS) was higher in the older stands. Carbon contents and CEC were strongly correlated. In Y40 and Y55, pH was significantly lower than in Y20 in the lower part of the soil horizon. There was a general decrease with depth of C, N, CEC, K⁺ and Mg²⁺ in the soil horizon. BS, Ca²⁺, Na⁺ and pH showed a somewhat different pattern of distribution, with deceasing values in the upper part of the soil horizon and increasing values in the lower part of the soil horizon.Abbreviations BD Bulk density - CEC cation exchange capacity - BS base saturation - Ca²⁺ calcium ion - Mg²⁺ magnesium ion - K⁺ potassium ion - Na⁺ sodium ion - C carbon - Ca _a accumulated carbon content - C _t total carbon content - N nitrogen - Y20 age class 20 years - Y40 age class 40 years - Y55 age class 55 years     

The distribution of genetic variation in Norway spruce (Picea abies Karst.) populations in the western Alps

Aim  In order to look for a possible centre of survival for the Norway spruce ( Picea abies Karst.) in the south-western Alps, six natural populations of this area were investigated by means of genetic markers in order to assess the degree and the distribution of genetic diversity within the species.
Location  Western and South-western Alps.
Methods  Populations were genotyped using seven simple sequence repeat (SSR) markers. Basic population genetics parameters were estimated and the amount of genetic differentiation calculated.
Results  A large amount of variability was found (0.59 <  H _e < 0.67); genetic differentiation as measured by F _ST was 0.05, close to other similar studies; no isolation by distance was detected by a Mantel test. Analysis of molecular variance confirmed a high degree of variability within populations and a low degree of variability among populations. Finally, the number of populations from which those observed could have arisen was estimated by Bayesian analysis.
Main conclusions  The results presented here suggest that the present populations derive their genetic make-up from three inferred clusters. The possible existence in this area of a relict/refuge population during the last glaciation is discussed.     

Root distribution in a Norway spruce (Picea abies (L.) Karst.) stand subjected to drought and ammonium-sulphate application

Results of the spatial distribution of fine roots are reported from a Norway spruce (Picea abies (L.) Karst.) in SW Sweden stand subjected to drought (D) and ammonium-sulphate application (NS). The sampling was carried out by excavating monoliths in segments of 0.5 × 0.5 × 0.1 m to a depth of one meter. Root data also included in the study were obtained by excavating whole trees and soil coring.The data suggest a fairly deep distribution pattern of fine roots (< 1 mm in diameter) in the study area compared with other forest sites in SW Sweden. The weight fraction of living fine roots in the LFH-horizon amounted to 53, 36 and 55% of the total fine-root biomass and 12, 30 and 32% of the total fine-root necromass (dead fine roots) in the control, D and NS-treatment areas respectively. Drought seemed to result in a redistribution of fine roots to deeper mineral soil horizons. Ammonium sulphate application led to the reverse, viz, a concentration of fine roots to the LFH-horizon. A significantly smaller fine-root necromass was indicated in the LFH-horizon of the control areas compared with both the D and NS-treatment areas, suggesting a high mortality of fine roots in these areas. A heavy dry matter fraction accumulates in roots > 1 mm in diameter and in stumps. These root fraction, were frequently found between the trees, although the stump constitutes an important fraction in terms of dry weight.     

The climate sensitivity of Norway spruce [Picea abies (L.) Karst.] in the southeastern European Alps

To investigate the potential of Norway spruce (Picea abies L. Karst) as a palaeoclimate archive in the southeastern European Alps, tree ring chronologies were developed from trees growing at two sites in Slovenia which differed in their ecological and climatological characteristics. Ring width, maximum latewood density, annual height increment and latewood cellulose carbon isotope composition were determined at both sites and the resulting time-series compared with and verified against instrumental climate data for their common period (AD 1960–AD 2002). Results indicate that ring width sensitivity to summer temperature is very site-dependent, with opposing responses at alpine and lowland sites. Maximum density responds to September temperatures, indicating lignification after cell division has ceased. Stable carbon isotopes have most potential, responding strongly to summer temperature in both alpine and lowland stands. Height increment appears relatively insensitive to climate, and is likely to be dominated by local stand dynamics.     

Seasonal dynamics of major cations in xylem sap and needles of Norway spruce (Picea abies L. Karst.) in stands with different soil solution chemistry

Soil solution, xylem sap and needles of mature trees were sampled in three spruce stands over one vegetation period and analysed for major cations. Investigations of nutrient distribution between these three pools and evaluations of seasonal dynamics give the following results: The highest nutrient concentrations in the xylem sap occur at the time of bud break and become gradually lower during the vegetation period. The trees show similar trends of xylem sap concentrations with time for potassium, calcium and magnesium regardless of the nutritional status of the plots. No coupling of xylem sap to soil solution composition can be observed in spite of a high variability of soil solution chemistry in time. The major cations in the current needles exhibit a significantly different trend with time. No time-based correlations for nutrient contents could be found for the needles from the previous year.Despite mobilisation of storage pools in the deficient stand, trees are not able to increase the Ca and Mg contents in the needles up to the level of the other stands. Potassium could be retranslocated in sufficient extent for nutrition of current needles. Due to seasonal variability and dependence upon internal processes, such as retranslocation and mobilisation of nutrients, xylem sap does not seem to be a good tool for the estimation of the nutritional status of forest sites.It was concluded that only minor transport into new foliage via xylem sap will proceed after nutrient flush during the bud break and the nutrient content in the new biomass will be governed by dilution due to biomass growth or by nutrient transport by other means than xylem sap.     

Magnesium deficiency in young Norway spruce (Picea abies [L.] Karst.) trees induced by NH4NO3 application

Young Norway spruce trees were grown in 94 pots (2 per pot) on soil substrate derived from granite with low Mg saturation and were fertilized with different amounts of NH₄NO₃ (in total 25, 61, and 97 kmol N ha^-1) over a period of four years, partly at an experimental station, partly at a high-elevation site in the Bavarian Forest. A fourth set of trees received 9.4 kmol Mg ha^-1 in addition to 25 kmol N. Depending on the treatment, needle chlorosis developed in the course of the experiment. Improved light conditions after three years accelerated the yellowing process. The chlorotic Norway spruce trees showed a severe Mg deficiency and an imbalanced N:Mg ratio. The shoot length increment, the stem diameter, and the needle weights however were not influenced by the fertilization. Excessive applications of NH₄NO₃caused the substrate to become depleted of Mg. The successful experimental induction of the characteristic tip yellowing of older needles of Norway spruce growing on acidic soils at higher altitudes allowed hypotheses on the causes and processes of this type of forest decline to be tested.