Differences in transpiration of Norway spruce drought stressed trees and trees well supplied with water

The paper focuses on the evaluation of transpiration as a physiological process, which is very sensitive to drought stress. Reactions of 25-year-old Norway spruce (Picea abies (L.) Karst.) trees to drought were examined during 2009 summer. Sap flow rate (SF), meteorological and soil characteristics were measured continually. Vapour pressure deficit of the air (VPD) and cumulative transpiration deficit (KTD) was calculated. During the second half of the vegetation period, the decrease in soil water content was observed and irrigation was applied to a group of spruce trees, while the second group was treated under natural soil drought. On the days, when the differences in transpiration between irrigated (IR) and non-irrigated (NIR) trees were significant (21 days), transpiration of NIR trees was only 23% of the transpiration of IR trees. We found significant differences in transpiration when the soil water content (SWC) of NIR variant at a depth of 5–15 cm ranged from 10.4 to 13.7%. Under both regimes of water availability, daily transpiration significantly responded to atmospheric conditions. However, the influence of all assessed meteorological parameters on SF of NIR trees was significantly lower than on IR tree. The dependency of transpiration on evaporative demands of atmosphere decreased with the decreasing soil moisture. Cumulative transpiration deficit of the stand during the entire evaluated period was 50.9 mm. The difference between the transpiration of the mean NIR tree and of the mean IR tree was 278.8 L over the assessed period of 47 days (5.9 L per day). The transpiration of NIR trees was 40.3% from the transpiration of IR trees during this period.     

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.     

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.     

Effects of prolonged drought on the anatomy of sun and shade needles in young Norway spruce trees

Predicted increases in the frequency and duration of drought are expected to negatively affect tree vitality, but we know little about how water shortage will influence needle anatomy and thereby the trees’ photosynthetic and hydraulic capacity. In this study, we evaluated anatomical changes in sun and shade needles of 20‐year‐old Norway spruce trees exposed to artificial drought stress. Canopy position was found to be important for needle structure, as sun needles had significantly higher values than shade needles for all anatomical traits (i.e., cross‐sectional needle area, number of tracheids in needle, needle hydraulic conductivity, and tracheid lumen area), except proportion of xylem area per cross‐sectional needle area. In sun needles, drought reduced all trait values by 10–40%, whereas in shade needles, only tracheid maximum diameter was reduced by drought. Due to the relatively weaker response of shade needles than sun needles in drought‐stressed trees, the difference between the two needle types was reduced by 25% in the drought‐stressed trees compared to the control trees. The observed changes in needle anatomy provide new understanding of how Norway spruce adapts to drought stress and may improve predictions of how forests will respond to global climate change.     

Increasing day-length induces spring flushing of tropical dry forest trees in the absence of rain

In many conspecific trees of >50 species highly synchronous bud break with low inter-annual variation was observed during the late dry season, around the spring equinox, in semideciduous tropical forests of Argentina, Costa Rica, Java and Thailand and in tropical savannas of Central Brazil. Bud break was 6 months out of phase between the northern and southern hemispheres and started about 1 month earlier in the subtropics than at lower latitudes. These observations indicate that "spring flushing", i.e., synchronous bud break around the spring equinox and weeks before the first rains of the wet season, is induced by an increase in photoperiod of 30 min or less. Spring flushing is common in semideciduous forests characterized by a 4-6 month dry season and annual rainfall of 800-1,500 mm, but rare in neotropical forests with a shorter dry season or lower annual precipitation. Establishment of new foliage shortly before the wet growing season is likely to optimize photosynthetic gain in tropical forests with a relatively short growing season.     

Endogenous levels of oxygen,carbon dioxide and ethylene in stems of Norway spruce trees during one growing season

Summary The trees sampled in this study came from two stands of Norway spruce, Picea abies (L.) Karst., near Stockholm, Sweden, differing in mean age and height. Holes were bored perpendicular to the stem surface, and gas samples were taken from the outer part of the sapwood throughout one growing season. Endogenous levels of molecular oxygen (O₂), carbon dioxide (CO₂) and ethylene in the outer sapwood were determined by combined gas chromatography — mass spectrometry (GC-MS) and GC. O₂ concentrations began to decrease as growth started in spring. The lowest levels (<5%) were recorded around mid-summer. In the younger stand concentrations remained below 5% until September. In October, O₂ concentrations in the sapwood were similar to those of air. Concentrations of CO₂ were below 1% in spring, but began to rise in May, peaking a month later at approximately 10%. Thereafter a slow decrease occurred until October, by which time levels had returned to those recorded in spring. Ethylene concentrations in the older stand reached 75 ppm early in May, while levels in the younger stand peaked at around 30 ppm later in May. Thereafter ethylene levels in both stands started to decrease down to ppb levels. The correlation between determined gas levels and physiological events associated with the seasonal growth cycle in temperate zones is discussed.     

Stem radius changes and their relation to stored water in stems of young Norway spruce trees

Changes in the stem radius of young Norway spruce [Picea abies (L.) Karst.] were related to changes in stem water content in order to investigate the relationship between diurnal stem size fluctuations and internally stored water. Experiments were performed on living trees and on cut stem segments. The defoliated stem segments were dried under room conditions and weight (W), volume (V), and xylem water potential (O_s) were continuously monitored for 95 h. Additionally, photos of cross-sections of fresh and air-dried stem segments were taken. For stem segments we found that the change in V was linearly correlated to the change in W as long as O_s was >-2.3ǂ.3 MPa (phase transition point). Stem contraction occurred almost solely in the elastic tissues of the bark (cambium, phloem, and parenchyma), and the stem radius changes were closely coupled to bark water content. For living trees, it is therefore possible to estimate the daily contribution of "bark water" to transpiration from knowledge of the stem size and continuous measurements of the stem radius fluctuations. When O_s reaches the phase-transition point, water is also withdrawn from the inelastic tissue of the stem (xylem), which - in the experiment with stem segments - was indicated by an increasing ratio between (V and (W. We assume that for O_s below the transition point, air is sucked into the tracheids (cavitation) and water is also withdrawn from the xylem. Due to the fact that in living P. abies O_s rarely falls below -2.3ǂ.3 MPa and the xylem size is almost unaffected by radius fluctuations, dendrometers are useful instruments with which to derive the diurnal changes in the bark water contents of Norway spruce trees.     

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.     

Redistribution of water via layering branches between connected parent and daughter trees in Norway spruce clonal groups

Key message

We measured sap flow and shoot water potentials in clonally connected parent and daughter trees. We found bidirectional flow patterns in branches mediating the connection between parent and daughter trees.

Abstract

Layering is an important mode of vegetative reproduction at treeline, in which clonal daughter trees are formed by the rooting of lower (“layering”) branches of the parent tree. These branches mediate the connection between parent (PT) and daughter tree (DT). Here, we measured quantity and direction of sap flow in layering branches as well as PT and DT, and measured shoot water potentials in the crowns of a connected PT and DT. We found bidirectional sap flow pattern in layering branches, with the bidirectionality of the flow resulting from water potential dynamics of the parent and daughter trees varying diurnally. We found that 4.3 % of the total water transpired by the DT was supplied by the PT root system, with up to 25 % of the instantaneous daughter tree sap flow coming from the parent tree. In contrast, water provided by the daughter’s root system to the parent tree comprised only a negligible amount, less than 1 % of the parent’s entire sap flow. Additionally, after experimental excavation of part of the DT roots, layering branch flow towards the DT increased, while flows in the opposite direction almost vanished. This study showed that aboveground clonal connections can facilitate a new type of hydraulic redistribution where water is transported bidirectionally through branches. This transfer of water and nutrients is vital especially in the first years of the daughter tree but supplies considerable amounts of water even several years after the establishment of a new clonal tree.

     

Adaptive genetic diversity of trees for forest conservation in a future climate: a case study on Norway spruce in Austria

Genetic resources of forest trees are considered as a key factor for the persistence of forest ecosystems because the ability of tree species to survive under changing climate depends strongly on their intraspecific variation in climate response. Therefore, utilizing available genetic variation in climate response and planting alternative provenances suitable for future climatic conditions is considered as an important adaptation measure for forestry. On the other hand, the distribution of adaptive genetic diversity of many tree species is still unknown and the predicted shift of ecological zones and species’ distribution may threaten forest genetic resources that are important for adaptation. Here, we use Norway spruce in Austria as a case study to demonstrate the genetic variation in climate response and to analyse the existing network of genetic conservation units for its effectiveness to safeguard the hotspots of adaptive and neutral genetic diversity of this species. An analysis of the climate response of 480 provenances, clustered into 9 groups of climatically similar provenances, revealed high variation among provenance groups. The most productive and promising provenance clusters for future climates originate from three regions that today depict the warmest and driest areas of the natural spruce distribution in Austria. Gap analysis of the Austrian genetic conservation units in the EUFGIS Portal suggests adequate coverage of the genetic hotspots in southern parts of Austria, but not in eastern and northern Austria. Therefore conservation measures and sustainable utilization of the valuable genetic resources in these regions need to be expanded to cover their high adaptive genetic variation and local adaptation to a warmer climate. The study shows that current conservation efforts need to be evaluated for their effectiveness to protect genetic resources that are important for the survival of trees in a future climate.     

The impact of spruce aphids on nutrient flows in the canopy of Norway spruce

1 This study investigated the effects of honeydew from aphids in the canopy of Norway spruce (Picea abies (L.) Karst.) on the nitrogen chemistry of throughfall using a rainfall simulation experiment. Throughfall collected beneath infested trees was compared with that from beneath uninfested trees, while standardizing the quality and quantity of the precipitation and plant age. 2 Honeydew excreted by Cinara pilicornis (Hartig) and C. costata (Zett.) significantly increased the concentrations of dissolved organic carbon (DOC) and hexose-C in throughfall. The average concentrations of nitrogenous compounds (NH₄-N, NO₃-N) in throughfall collected beneath infested trees were significantly lower than beneath uninfested trees. 3 Multiple regression analysis indicated that the amount of rain and NH₄-N concentrations were the best predictors of the concentrations of dissolved organic nitrogen (DON) in throughfall. Parameters that were closely associated with the level of infestation (DOC, hexose-C concentrations) did not have a direct relationship with DON. About 40% of the reduction in the concentration of DON in the throughfall was attributed to aphid–micro-organism interactions. 4 Particle amino nitrogen (PAN)-concentrations were highest under infested trees in July after aphid numbers had declined, indicating a concomitant decline in microbial biomass after honeydew becomes a limiting resource. 5 The comparison of the concentrations of different nitrogen compounds in throughfall of infested and uninfested trees indicated that aphids affect the carbon and nitrogen cycles in the phyllosphere by providing energy that fuels the metabolism of the micro-organisms. These processes seem to occur very rapidly. 6 We discuss the significance of the results and the prospects of linking the ecology of micro-organisms and herbivores with flows of nutrients through the canopy of trees.     

Needle chemistry in young Norway spruce stands after application of crushed wood ash

Nutrient concentrations in current and 1-year-old needles were analyzed annually for 5 years after application of hardened wood ash in 1–4-year-old Norway spruce (Picea abies (L.) Karst.) stands within a range of climate and fertility gradients. At each site, 3000 kg ha^–1 hardened wood ash of two types, Nymölla and Perstorp, was applied in a randomized block design. Wood ash Nymölla contained 12 kg ha^–1 P, 30 kg ha^–1 K, 891 kg ha^–1 Ca, 72 kg ha^–1 Mg and wood ash Perstorp contained 12 kg ha^–1 P, 60 kg ha^–1 K, 486 kg ha^–1 Ca, and 60 kg ha^–1 Mg. The ash was intended to compensate for nutrients removed at the preceding harvest when logging residues were collected and removed from the site (whole-tree harvesting). The climate gradient included four climate zones throughout Sweden and each of these included a fertility gradient of three sites classified according to their ground vegetation type. There were no effects on nutrient concentrations in the needles 1 year after the application of wood ash. Five years after ash application, the concentrations of P, K and Ca in current and 1-year-old needles were higher than in the control plots. The results were consistent over all stands, irrespective of climate zone and fertility status. P and K concentrations were higher in spruce needles from plots treated with Perstorp wood ash, whereas Ca concentrations were higher in those of Nymölla treated plots. Analyses across all study sites revealed a treatment effect in terms of increased ratios of P:N, K:N and Ca:N in 1-year-old needles. The ratio P:N tended to increase with time in the Perstorp wood ash treatment compared with the control. The needle concentrations of Mg and S were not affected by the ash applications. The increase in needle nutrient concentrations after application of hardened wood ash suggests that wood ash recycling could be used in order to replace nutrients removed at whole-tree harvesting.     

Phenological synchrony between eastern spruce budworm and its host trees increases with warmer temperatures in the boreal forest

Climate change is predicted to alter relationships between trophic levels by changing the phenology of interacting species. We tested whether synchrony between two critical phenological events, budburst of host species and larval emergence from diapause of eastern spruce budworm, increased at warmer temperatures in the boreal forest in northeastern Canada. Budburst was up to 4.6 ± 0.7 days earlier in balsam fir and up to 2.8 ± 0.8 days earlier in black spruce per degree increase in temperature, in naturally occurring microclimates. Larval emergence from diapause did not exhibit a similar response. Instead, larvae emerged once average ambient temperatures reached 10°C, regardless of differences in microclimate. Phenological synchrony increased with warmer microclimates, tightening the relationship between spruce budworm and its host species. Synchrony increased by up to 4.5 ± 0.7 days for balsam fir and up to 2.8 ± 0.8 days for black spruce per degree increase in temperature. Under a warmer climate, defoliation could potentially begin earlier in the season, in which case, damage on the primary host, balsam fir may increase. Black spruce, which escapes severe herbivory because of a 2‐week delay in budburst, would become more suitable as a resource for the spruce budworm. The northern boreal forest could become more vulnerable to outbreaks in the future.     

Old trees as a key source of epiphytic lichen persistence and spatial distribution in mountain Norway spruce forests

Habitat loss and fragmentation can negatively impact the persistence of dispersal-limited lichen species with narrow niches. Rapid change in microclimate due to canopy dieback exposes species to additional stressors that may limit their capacity to survive and colonize. We studied the importance of old trees as micro-refuges and microclimate stability in maintaining lichen survival and diversity. The study was situated in mountain Norway spruce (Picea abies) forests of the Gorgany Mountains of the Ukrainian Carpathian mountain belt. Lichens were collected on 13 circular study plots (1000 m²). Dendrochronological methods were used to reconstruct age structure and maximum disturbance event history. A linear mixed effects model and general additive models were used to explain patterns and variability of lichens based on stand age and disturbance history for each plot. Tree age was the strongest variable influencing lichen diversity and composition. Recent (<80 years ago) severely disturbed plots were colonized only by the most common species, however, old trees (>200 years old) that survived the disturbances served as microrefuges for the habitat-specialized and/or dispersal limited species, thus epiphytic lichen biodiversity was markedly higher on those plots in comparison to plots without any old trees. Most species were able to survive microclimatic change after disturbances, or recolonize disturbed patches from surrounding old-growth forests. We concluded that the survival of old trees after disturbances could maintain and/or recover large portions of epiphytic lichen biodiversity even in altered microclimates.     

Terpenoids are transported in the xylem sap of Norway spruce

Norway spruce is a conifer storing large amounts of terpenoids in resin ducts of various tissues. Parts of the terpenoids stored in needles can be emitted together with de novo synthesized terpenoids. Since previous studies provided hints on xylem transported terpenoids as a third emission source, we tested if terpenoids are transported in xylem sap of Norway spruce. We further aimed at understanding if they might contribute to terpenoid emission from needles. We determined terpenoid content and composition in xylem sap, needles, bark, wood and roots of field grown trees, as well as terpenoid emissions from needles. We found considerable amounts of terpenoids—mainly oxygenated compounds—in xylem sap. The terpenoid concentration in xylem sap was relatively low compared with the content in other tissues, where terpenoids are stored in resin ducts. Importantly, the terpenoid composition in the xylem sap greatly differed from the composition in wood, bark or roots, suggesting that an internal transport of terpenoids takes place at the sites of xylem loading. Four terpenoids were identified in xylem sap and emissions, but not within needle tissue, suggesting that these compounds are likely derived from xylem sap. Our work gives hints that plant internal transport of terpenoids exists within conifers; studies on their functions should be a focus of future research.     

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.     

Endophyte communities vary in the needles of Norway spruce clones

Endophytic fungi show no symptoms of their presence but can influence the performance and vitality of host trees. The potential use of endophytes to indicate vitality has been previously realized, but a standard protocol has yet to be developed due to an incomplete understanding of the factors that regulate endophyte communities. Using a culture-free molecular approach, we examined the extent to which host genotype influences the abundance, species richness, and community composition of endophytic fungi in Norway spruce needles. Briefly, total DNA was extracted from the surface-sterilized needles of 30 clones grown in a nursery field and the copy number of the fungal internal transcribed spacer (ITS) region of ribosomal DNA was estimated by quantitative PCR. Fungal species richness and community composition were determined by denaturing gradient gel electrophoresis and DNA sequencing. We found that community structure and ITS copy number varied among spruce clones, whereas species richness did not. Host traits interacting with endophyte communities included needle surface area and the location of cuttings in the experimental area. Although Lophodermium piceae is considered the dominant needle endophyte of Norway spruce, we detected this species in only 33 % of samples. The most frequently observed fungus (66 %) was the potentially pathogenic Phoma herbarum. Interestingly, ITS copy number of endophytic fungi correlated negatively with the richness of ectomycorrhizal fungi and thus potential interactions between fungal communities and their influence on the host tree are discussed. Our results suggest that in addition to environmental factors, endophyte communities of spruce needles are determined by host tree identity and needle surface area.     

Induced responses in stilbenes and terpenes in fertilized Norway spruce after inoculation with blue-stain fungus, Ceratocystis polonica

In conifers, attacks by bark beetles and associated pathogenic fungi cause an induced wound response, which is characterized by accumulation of antifungal compounds and morphological changes that aid wound healing. In this article the stilbene and terpene concentrations of Norway spruce phloem were monitored as symptoms of induced wound responses in relation to changed nutrient conditions caused by fertilization. Plots of mature Norway spruce were fertilized with N, P or NPK. One year after fertilization the trees were artificially infected with Ceratocystis polonica, a pathogenic fungus associated with the bark beetle Ips typographus. The response of stilbenes to fungal inoculation was mainly qualitative. The concentration of stilbene glycosides in the phloem decreased, and in the immediate vicinity of the site of fungal inoculation, stilbene glycosides were less frequent than in mechanically wounded or unwounded phloem. Corresponding stilbene aglycones were most frequent inside the reaction lesion. The concentration of total stilbene aglycones near the inoculation site was significantly lower in N-fertilized trees than in unfertilized trees. Fungal inoculation caused a strong quantitative response in terpenes. The total terpene concentration of the phloem increased significantly, to almost 100 times greater near the inoculation site compared to the constitutive values. N fertilization significantly reduced the total terpene and total stilbene aglycone concentrations near the inoculation sites. Thus, N fertilization may reduce the ability of Norway spruce to defend itself against fungal pathogens.     

An approach for modelling the mean fine-root biomass of Norway spruce stands

The applicability of a heuristic model for estimating mean fine-root biomass of Norway spruce stands based on the coordinates and the diameters at breast height (diameter at a height of 1.3 m, dbh) of their trees was tested. The model was developed based on the following assumptions which were derived from the literature: (1) the maximum distance the roots of a tree can be found depends on the dimension of the tree and exceeds the edges of the crown; (2) fine-root biomass decreases with increasing distance from the tree trunk; (3) fine-root biomass increases with the dbh; (4) maximum fine-root biomass of a tree is not allocated directly around the trees trunk but at some distance from the stem. On the basis of these assumptions the model calculates a relative fine-root biomass at a given point within a stand. Four different versions of the model were compared, with each version differing with respect to the assumed decrease in fine roots with decreasing dbh and the approaches used to calculate the contribution of a subject tree to the fine-root biomass at a given point within a stand (additive versus consumptive). Using regression analysis we parameterised each model type with the data of 70 soil cores from a 75-year-old Norway spruce stand in southern Germany (Bavaria). The relative fine-root biomass calculated by the four different model types accounted for 62–72% of the variation of the measured fine-root biomass. The parameterised models were used to predict the fine-root biomass of 60 given points of a second Norway spruce stand based on its dbhs and stem coordinates. The comparison of measured and predicted mean fine-root biomasses of the second stand revealed no significant differences between the measured mean and the means estimated by three of the four model types. Whereas with two of the model types we achieved means and medians, respectively, nearly identical to the measured average, none of the model types was able to predict values as high as the measured maximum. Constraints of the models and points that need to be considered regarding the minimum number of soil cores needed for a reliable parameterisation of the model are discussed.