Regulation of photochemical efficiency of photosystem 2 in Norway spruce at the beginning of winter and in the following spring

Based on the analysis of fluorescence quenching, the nonphotochemical dissipative processes were investigated in Norway spruce needles during acclimation to winter and spring conditions. The maximum nonphotochemical fluorescence quenching (q_Nmax) was reached at lower irradiances in winter (up to 310 μmol m-2 s-1) than in spring (about 1130 μmol m-2 s-1), but its values were nearly the same (q_Nmax = 0.91±0.01) during both winter and spring measurements. In early winter the pronounced initial fluorescence quenching (q0) suggested that nonradiative energy dissipation in the antennae complexes dominated. Significantly lower q0 (by 40-60 % compared to winter needles) during acclimation of needles to spring conditions supported a significant contribution of quenching in the reaction centres. These findings support the hypothesis that the antennae systems and reaction centres cooperate in the protective dissipation of excess excitation energy. This revised version was published online in September 2006 with corrections to the Cover Date.     

Effects of soil warming during spring on photosynthetic recovery in boreal Norway spruce stands

The effect of soil thawing and soil temperature on postwinter recovery of photosynthetic capacity was studied, during late spring and early summer, in Norway spruce stands in northern Sweden. Soil temperature was manipulated by means of buried heating cables. The warming treatment was applied to stands with low (natural) and high (fertilized) availability of nutrients. Soil thawing, expressed as water availability, was followed by means of sapflow in stems, and shoot water potentials. The recovery of photosynthetic capacity was assessed by measuring the rate of light-saturated photosynthesis (A_max), and maximum photochemical efficiency of photosystem II in detached shoots, and chlorophyll a fluorescence. Accumulation of starch reserves in the needles was followed as an independent indicator of photosynthetic performance in situ. Snowmelt and soil thawing occurred more than one month earlier in heated than in unheated plots. This was expressed both as sapflow and as differences in shoot water potential between treatments. During May, the rates of A_max were significantly higher on heated than on control plots. The effect of soil warming on A_max was, however, not reflected in chlorophyll fluorescence or needle starch content. The time course of the recovery of photosynthetic capacity was mainly controlled by mean air temperature and by the frequency of severe night frosts, and to a lesser extent by earlier soil thawing and higher soil temperatures.     

The effect of nutrition on the seasonal course of needle respiration in Norway spruce stands

 Respiration of 1-year-old needles of 30-year-old Norway spruce trees [Picea abies (L.) Karst.] was studied in a nutrient optimisation experiment in northern Sweden. Respiration rates of detached needles, from ten control (C) and ten irrigated-fertilised (IL) trees, were measured on 16 occasions from June 1992 to June 1993. The aim of the study was to determine the influence of temperature on the seasonal course of needle maintenance respiration, and the effect of nitrogen concentration [N] and carbohydrate content on needle respiration in young Norway spruce trees subjected to long-term fertilisation. The IL treatment significantly affected needle size, in terms of dry mass and length, but not specific needle length (SNL). There was, however, a strong tree-specific effect on SNL (P<10^–9, R ² = 0.75). Needle starch content varied markedly with season (0–25% of total dry mass). This, unless accounted for, would cause erroneous estimates of nutrient concentrations, and of rates of needle respiration, within and between treatments. There was considerable seasonal variation in needle respiration, both in terms of maintenance respiration and temperature dependence (Q₁₀). Q₁₀ had its highest value (2.8) during winter and its lowest (2.0) in the middle of summer. In early autumn (August, September), respiration rate and needle [N] were significantly related (C: P = 0.001, IL: P<0.0005). There was no significant difference in the slope between the two regression lines, but a difference in intercept. At the same needle [N], needles from IL-plots always had a lower respiration rate than needles from control plots. No obvious explanation for the observed difference in intercept was found, but some plausible assumptions are put forward and discussed. Received: 24 January 1997 / Accepted: 1 July 1997     

Use of RAPD patterns for clone verification and in studying provenance relationships in Norway spruce (Picea abies)

 We have used the RAPD technique to analyse samples of Picea abies obtained from an improvement forestry station. Two types of plant material were harvested, the first being clones and the second provenances from various regions. We first checked the clonal identity of elite tree cuttings and clones; some differences in the RAPD patterns resulting from mis-planting or mis-labelling of cuttings were found. We also established a reference library of RAPD fingerprints for 96 clones, which will serve as a reference source in cases of litigation concerning clone identity. The RAPD technique was also used to study the genetic relationship between nine European provenances of Norway spruce. A dendogram was obtained by individual pairwise comparison of 42 RAPD bands, which separated the nine provenances into two major groups, one containing the Nordic provenances (Sweden and Bielorussia) and another the Alpine provenances (France, Austria, Germany and Belgium). The Belgian provenance, which is not indigenous, is most closely related to the German provenance. We conclude that the RAPD technique is a useful tool for forestry stations in managing propagation operations. Received: 15 June 1996 / Accepted: 11 October 1996     

Combining genetic gain and diversity by considering average coancestry in clonal selection of Norway spruce

 Genetic relationship within a population can be measured by average coancestry. This can also be expressed as an effective number which represents the relative genetic diversity of the population. The goal of breeding can be formulated to maximise genetic value minus average coancestry times a constant (the “penalty constant”). An iterative search algorithm can then be used to find the best selections for meeting this goal. Two such algorithms, one for a fixed number of selections and the other for a variable optimum number, were applied to select a mixture of field-tested Norway spruce clones with known parents. The results were compared with those from the conventional method of restricting parental contributions to the selected population as a means to control diversity. Coancestry-adjusted selection always yielded more gain than restricted selection at a given effective population size (except under circumstances where the methods were equivalent). Expressed another way, at any given level of gain, coancestry-adjusted selection maintained a larger effective population size than did restricted selection. The relative superiority of coancestry-adjusted selection declined when the effective population size approached the lowest value, that at which no penalty or restriction was applied. The method was extended by the second search algorithm to optimise the selected number of clones. The optimal number of clones can be rather large when diversity is heavily valued, but the reduction in genetic gain becomes large. Received: 7 April 1997 / Accepted: 9 June 1997     

Effects of long-term CO2 enrichment and nutrient availability in Norway spruce. II. Foliar chemistry

 Branches on 30-year-old Norway spruce trees [Picea abies (L.) Karst.] were exposed to ambient (AMB) or ambient plus 350 μmol CO₂ mol^–1 (EL) for 4 years (except winters), using the branch bag technique (BB). The trees were growing on plots with low (control) and high (irrigated-fertilised) availability of soil nutrients. The seasonal variation in foliar macronutrients and non-structural carbohydrates in current and 1-year-old shoots was monitored throughout the treatment period. When the branches were harvested at the end of treatment, macronutrients were analysed in five age classes of foliage. The concentration of all elements, except magnesium, generally increased in AMB, i.e. a ’bag effect’, but decreased as an effect of EL, i.e. a ’CO₂ effect’. At the final harvest K, P, N and S were reduced in young needles by EL, whereas Mg was reduced in older needles on both plots. A change in needle morphology by EL possibly caused a dilution effect in irrigated-fertilised needles, but not in control needles. Reductions in K and Mg are suggested to be an effect of increased phloem transport from the branch, in consequence of higher rates of carbon fixation in EL. Foliage in BBs had higher concentration of Ca, but there was no significant effect of the EL-treatment, indicating that elevated CO₂ had no effect on stomatal conductance. Quinic acid concentration decreased, but shikimic acid concentration increased in BBs, independently of CO₂ treatment. Concentrations of starch and sugars increased in the EL-treatment, but pinitol decreased. Received: 23 October 1998 / Accepted: 1 December 1998     

The use of different soil nitrogen sources by young Norway spruce plants

 Three-year-old Norway spruce trees were planted into a low-nitrogen mineral forest soil and supplied either with two different levels of mineral nitrogen (NH₄NO₃) or with a slow-release form of organic nitrogen (keratin). Supply of mineral nitrogen increased the concentrations of ammonium and nitrate in the soil solution and in CaCl₂-extracts of the rhizosphere and bulk soil. In the soil solution, in all treatments nitrate concentrations were higher than ammonium concentrations, while in the soil extracts ammonium concentrations were often higher than nitrate concentrations. After 7 months of growth, ¹⁵N labelled ammonium or nitrate was added to the soil. Plants were harvested 2 weeks later. Keratin supply to the soil did not affect growth and nitrogen accumulation of the trees. In contrast, supply of mineral nitrogen increased shoot growth and increased the ratio of above-ground to below-ground growth. The proportion of needle biomass to total above-ground biomass was not increased by mineral N supply. The atom-% ¹⁵N was higher in younger needles than in older needles, and in younger needles higher in plants supplied with ¹⁵N-nitrate than in plants supplied with ¹⁵N-ammonium. The present data show that young Norway spruce plants take up nitrate even under conditions of high plant internal N levels. Received: 1 April 1998 / Accepted: 9 October 1998     

Effects of long-term CO2 enrichment and nutrient availability in Norway spruce. I. Phenology and morphology of branches

 Branches of 30-year-old Norway spruce [Picea abies (L.) Karst.] trees were enclosed in ventilated, transparent plastic bags and flushed with air containing ambient (A≈370 μmol CO₂ mol^–1) or ambient plus 340 μmol CO₂ mol^–1 (EL). Light-saturated photosynthesis was on average 56% higher in EL compared to A. Branch phenology and morphology were strongly related to nitrogen concentration (mg g^–1 dry mass) in the foliage and to elevated temperatures in the bags, but no direct effect of EL was found. In 1995, budbreak occurred on average 4 days earlier in the bags compared to the control branches, which was partly explained by the temperature elevation in the bags. No nutrient or EL effect on budbreak was found. Increases in temperature and nitrogen supply increased shoot growth: together they explained 76% of the variation in the extension rate, 63% of the variation in extension duration and 65% of the variation in final length of leading shoots. Shoot morphology was altered both by increased nitrogen availability and by the enclosure induced environmental changes inside the bags, leading to reduced mutual shading between needles. Specific needle area (SNA) was lower in EL, but this was related to lower nitrogen concentrations. Total dry mass of the branches was unaffected by EL. It is concluded that treating individual branches of Norway spruce with elevated CO₂ does not increase branch growth. The nutrient status of the branch and climate determine its growth, i.e. its sink strength for carbon. Increased export of carbohydrates to the rest of the tree is probable in EL treated branches. Received: 20 July 1998 / Accepted 8 October 1998     

The concentrations of Fe, Zn and Co in successive needle age classes of Norway spruce [Picea abies (L.) Karst.]

The concentrations of Fe, Zn and Co were determined in up to five successive needle age classes in 54 individual Norway spruce trees from eight different sites (soil pH 3.1–7.7). Fe concentrations (12–25 μg in needles from the current year) were lower than most published values, due to the removal of surface contamination prior to analysis. Fe showed a significant positive correlation with Al. Successive needle age classes either had constant values or showed an increase for Fe concentrations; individual trees on a given site were rather uniform in their behaviour. Zn concentrations were 19–40 μg/g. On acid sites, they showed a positive correlation with total soil concentrations. The majority of trees showed decreasing Zn concentrations in successive needle age classes, but constant or increasing concentrations were also found; site homogeneity was less than with Fe. Co concentrations differed between trees on a neutral soil (12 ng/g) and on acid soils (41–174 ng/g). They showed a significant positive correlation with Mn needle concentrations. The changes of Co with needle age in most, but not all, trees were similar to those of Zn. The different changes of Fe, Zn and Co with needle age may be due to a different retranslocation. A modest retranslocation of Fe as opposed to a high retranslocation of Zn and Co (in most trees) is consistent with the observed behaviour. Received: 10 May 1999 / Accepted: 8 September 1999     

Interactive effects of host resistance and drought stress on the performance of a gall-making aphid living on Norway spruce

Four full-sib families of Norway spruce (Picea abies), of which two were resistant to a galling aphid (Adelges abietis) and two were susceptible, were exposed to drought stress for 2 years. The primary aim was to test the hypothesis that the various life stages of the aphid differ in their response to environmentally induced changes in the host plant. The drought treatment had a significant negative effect on tree growth. This was reflected in gall size which responded in a similar way to the drought stress, thus supporting the plant vigour hypothesis. Drought affected the survival of aphid stem-mothers negatively in susceptible trees but positively in resistant trees. This result was matched by the response of an individual phenolic compound which, contrary to the total phenolic concentration, tended to increase in susceptible trees exposed to drought and decrease in similarly exposed resistant trees. Thus it is possible that this single, as yet unidentified, phenolic compound could be used as a marker of resistance. The performance of surviving stem-mothers, evaluated by measuring the diameter of the wax cover they produced (a correlate of fecundity), was not significantly affected by drought, but aphids on susceptible trees produced more wax than those on resistant trees. The change in gall density over time (analysed separately for each treatment and phenotype) correlated best with patterns of stem-mother survival. This indicates that stem-mother survival, which is closely linked to host plant quality and resistance, may play a significant role in the population dynamics of this aphid. However, drought-stress-induced changes in host plant quality affected survival, and hence gall density, less than the genetically determined level of resistance. The results also support the hypothesis that an insect may respond differently to environmentally induced changes in the host plant at different stages in its development. Received: 15 September 1999 / Accepted: 3 December 1999     

Temperature and light dependent modifications of chlorophyll fluorescence kinetics in spruce needles during winter

Prompt chlorophyll a fluorescence kinetics at room temperature were measured from intact spruce needles. The fluorescence signal was recorded after varying light pretreatments. During the winter, induction curves showed characteristic changes in both the initial peak of fluorescence FV/FP (FP-FO/FP) and the steady state level F_dr (FP-FT/FP). Winter stress induced decreases in both values which showed close correlation to the light and temperature pre-history of the plants. In February changes in fluorescence induction indicative of a restoration of photosynthesis were detected and these corresponded to a rise of temperature above zero in combination with low light levels. In March increasing light intensity combined with chilling temperatures induced again decreases of both values of chlorophyll fluorescence induction suggesting the occurrence of photoinhibition.     

Effects of nutrition and soil warming on stemwood production in a boreal Norway spruce stand

The boreal forest is expected to experience the greatest warming of all forest biomes. The extent of the boreal forest, the large amount of carbon contained in the soil, and the expected climate warming, make the boreal forest a key biome to understand and represent correctly in global carbon models. It has been suggested that an increase in temperature could stimulate the release of CO₂ caused by an increased decomposition rate, more than biomass production, which could convert current carbon sinks into carbon sources. Most boreal forests are currently carbon sinks, but it is unclear for how long in the future the carbon sink capacity of the boreal forest is likely to be maintained. The impact of soil warming on stem volume growth was studied during 6 years, in irrigated (I) and irrigated‐fertilized (IL) stands of 40‐year‐old Norway spruce in Northern Sweden. From May to October heating cables were used to maintain the soil temperature on heated‐irrigated plots (Ih and ILh) 5 °C above that on unheated control plots (Ic and ILc). After six seasons' warming, stem volume production (m³ ha^?1 a^?1) was 115% higher on Ih than on unheated (Ic) plots, and on heated and irrigated‐fertilized plots (ILh) it was 57% higher than on unheated plots (ILc). The results indicate that in a future warmer climate, an increased availability of nitrogen, combined with a longer growing season, may increase biomass production substantially, on both low‐ and high‐fertility sites. It is, however, too early to decide whether the observed responses are transitory or long lasting. It is therefore crucial to gain a better understanding of the responses of boreal forest ecosystems to climate change, and to provide data to test and validate models used in predicting the impact of climate change.     

Estimating the needle area from geometric measurements: application of different calculation methods to Norway spruce

Different calculation methods, based on needle geometry, for estimating both projected area (PLA) and total surface area (TLA) of foliage in Norway spruce [Picea abies (L.) Karst.] were compared. Seventy-eight shoots of four age classes were sampled from both the basal and top thirds of crowns. Three dimensions (the length, minor and major diameters) of needles were taken, and the needle shape was approximated to a parallelepiped or ellipsoid. There was a perfect coincidence of the measured and estimated values of PLA calculated as the width of the needle projection multiplied by needle length, and corrected for needle taper (method III), or when the needle projection was treated as a rectangle joined with half-ellipses at both ends (method IV). The most reliable estimations of TLA resulted from treating the needle sides as faces of the parallelepiped tapering at their ends in the form of half-ellipses. The ratio of TLA to PLA ranged from 2.2 to 4.0 depending on the needle morphology. Needle minor diameter (anatomical width; D ₁) was found to be a better morphological index of the spruce foliage than needle flatness, i.e. the ratio of major to minor diameter. Expressing the factor for converting PLA to TLA as a function of D ₁ considerably improved the precision of the estimates. Close relationships were established between specific leaf area, expressed on both a projected area (SLA_P) and total surface area basis (SLA_T), needle dry weight (R ² was 0.799 and 0.852, respectively) and minor diameter of needles (R ² was 0.701 and 0.554, respectively). Received: 14 April 1998 / Accepted: 23 September 1999     

Ribulose-l,5-bisphosphate carboxylase activity and influence of air pollution in spruce

Methods were established, which render possible a simultaneous determination of ri-bulose-l,5-bisphosphate (RuBP) carboxylase (EC 4.1.1.39) activity and chlorophyll content of Norway spruce (Picea abies Karst.) needles from a detergent-containing aqueous crude extract. Spruce RuBP carboxylase was tentatively characterized with regard to kinetic properties. Recovery experiments employing purified wheat RuBP carboxylase proved quantitative extraction of the enzyme from spruce foliage. Five timber stands consisting of 35–62 years old spruce, two of which exhibited the typical symptoms of recent spruce decline, were compared. For the needle generations 1 to 4 the enzyme activities as well as chlorophyll and protein concentrations were determined. The results do not indicate an involvement of RuBP carboxylase in spruce decline.     

Changes in soil mineralogy and exchangeable cation pools in stands of Norway spruce planted on former pasture land

Chemical and mineralogical properties of the soils in 35- and 70-year-old stands of Norway spruce (Picea abies (L.) Karst), planted on former pasture and were studied at Asa Experimental Forest, southern Sweden. Remnant deciduous forests bordering the spruce stands were used as controls to assess possible tree-species-related effects on soil development. All soils are acid with little difference in soil pH between the spruce and deciduous stands. However, the saturation of the exchange complex with Mg is lower beneath spruce and the total exchangeable Mg pool in the upper meter of these soils is one third of the Mg store beneath the deciduous stands. Amphibole, biotite and chlorite are the major sources of Mg in the parent soil. The clay fraction of the topsoil beneath spruce has been depleted of all these easily weatherable ferromagnesian minerals. Apart from weathering-resistant primary silicates, the clay fraction consists almost exclusively of expandable, smectitic mixed-layer minerals, which are believed to be the products of advanced stages of biotite weathering. In contrast, vermiculite is the dominant secondary mineral in the A-horizon in the deciduous stands, and some chlorite has survived. Moreover, a greater depth of in situ weathering is indicated for the soil of the old spruce stands where biotite/vermiculite mixed-layers have formed in the C-horizon as products of early stages of biotite weathering. Thus, differences between the paired sites in soil solution chemistry are supported by the qualitative differences in soil mineralogy, and are believed to reflect divergent biotic and/or abiotic processes in the different stand types. This revised version was published online in August 2006 with corrections to the Cover Date.     

Seasonal variation in CO2 efflux of stems and branches of Norway spruce trees

BACKGROUND AND AIMS: Stem and branch respiration, important components of total forest ecosystem respiration, were measured on Norway spruce (Picea abies) trees from May to October in four consecutive years in order (1) to evaluate the influence of temperature on woody tissue CO2 efflux with special focus on variation in Q10 (change in respiration rate resulting from a 10 degrees C increase in temperature) within and between seasons, and (2) to quantify the contribution of above-ground woody tissue (stem and branch) respiration to the carbon balance of the forest ecosystem. METHODS: Stem and branch CO2 efflux were measured, using an IRGA and a closed gas exchange system, 3-4 times per month on 22-year-old trees under natural conditions. Measurements of ecosystem CO2 fluxes were also determined during the whole experiment by using the eddy covariance system. Stem and branch temperatures were monitored at 10-min intervals during the whole experiment. KEY RESULTS: The temperature of the woody tissue of stems and branches explained up to 68% of their CO2 efflux. The mean annual Q10 values ranged from 2.20 to 2.32 for stems and from 2.03 to 2.25 for branches. The mean annual normalized respiration rate, R10, for stems and branches ranged from 1.71 to 2.12 micromol CO2 m(-2)s (-1) and from 0.24 to 0.31 micromol CO2 m(-2) s(-1), respectively. The annual contribution of stem and branch CO2 efflux to total ecosystem respiration were, respectively, 8.9 and 8.1% in 1999, 9.2 and 9.2% in 2000, 7.6 and 8.6% in 2001, and 8.6 and 7.9% in 2002. Standard deviation for both components ranged from 3 to 8% of the mean. CONCLUSIONS: Stem and branch CO2 efflux varied diurnally and seasonally, and were related to the temperature of the woody tissue and to growth. The proportion of CO2 efflux from stems and branches is a significant component of the total forest ecosystem respiration, approx. 8% over the 4 years, and predictive models must take their contribution into account.     

Dynamics of the xanthophyll cycle and non-radiative dissipation of absorbed light energy during exposure of Norway spruce to high irradiance

The response of Norway spruce saplings (Picea abies [L.] Karst.) was monitored continuously during short-term exposure (10 days) to high irradiance (HI; 1000mumolm(-2)s(-1)). Compared with plants acclimated to low irradiance (100mumolm(-2)s(-1)), plants after HI exposure were characterized by a significantly reduced CO(2) assimilation rate throughout the light response curve. Pigment contents varied only slightly during HI exposure, but a rapid and strong response was observed in xanthophyll cycle activity, particularly within the first 3 days of the HI treatment. Both violaxanthin convertibility under HI and the amount of zeaxanthin pool sustained in darkness increased markedly under HI conditions. These changes were accompanied by an enhanced non-radiative dissipation of absorbed light energy (NRD) and the acceleration of induction of both NRD and de-epoxidation of the xanthophyll cycle pigments. We found a strong negative linear correlation between the amount of sustained de-epoxidized xanthophylls and the photosystem II (PSII) photochemical efficiency (F(V)/F(M)), indicating photoprotective down-regulation of the PSII function. Recovery of F(V)/F(M) at the end of the HI treatment revealed that Norway spruce was able to cope with a 10-fold elevated irradiance due particularly to an efficient NRD within the PSII antenna that was associated with enhanced violaxanthin convertibility and a light-induced accumulation of zeaxanthin that persisted in darkness.     

Seasonal profiles of sulphur, phosphorus, and potassium in Norway spruce wood

Seasonal profiles of sulphur, phosphorus, and potassium content in the wood of trees have been established for the first time. This became possible by using a novel laser ablation system coupled to HR-ICP-MS for measuring these elements in Norway spruce drill cores. This technique combines excellent spatial resolution with superior detection power, and makes it possible to measure low element concentrations even in relatively narrow annual rings. Despite its low quantity in wood, sulphur is an important macronutrient for plants and seems to display seasonal variations of its concentration, which correspond to actual theories of sulphur metabolism in plants. A similar seasonal pattern was also found for phosphorus, another crucial element in tree nutrition. This was unexpected, because it was previously assumed that the distribution of phosphorus remains constant throughout the year. Potassium, the third element measured, seems to be especially accumulated in the latewood. The profiles presented in this article suggest a seasonal variation, revealing some new aspects of Norway spruce (PICEA ABIES) metabolism.     

Seasonal and within‐canopy variation in shoot‐scale resource‐use efficiency trade‐offs in a Norway spruce stand

Previous leaf‐scale studies of carbon assimilation describe short‐term resource‐use efficiency (RUE) trade‐offs where high use efficiency of one resource requires low RUE of another. However, varying resource availabilities may cause long‐term RUE trade‐offs to differ from the short‐term patterns. This may have important implications for understanding canopy‐scale resource use and allocation. We used continuous gas exchange measurements collected at five levels within a Norway spruce, Picea abies (L.) karst., canopy over 3 years to assess seasonal differences in the interactions between shoot‐scale resource availability (light, water and nitrogen), net photosynthesis (A_n) and the use efficiencies of light (LUE), water (WUE) and nitrogen (NUE) for carbon assimilation. The continuous data set was used to develop and evaluate multiple regression models for predicting monthly shoot‐scale A_n. These models showed that shoot‐scale A_n was strongly dependent on light availability and was generally well described with simple one‐ or two‐parameter models. WUE peaked in spring, NUE in summer and LUE in autumn. However, the relative importance of LUE for carbon assimilation increased with canopy depth at all times. Our results suggest that accounting for seasonal and within‐canopy trade‐offs may be important for RUE‐based modelling of canopy carbon uptake.