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Incomplete knowledge of carbon (C) allocation dynamics in trees hinders accurate modeling and future predictions of tree growth. We studied C allocation dynamics in a mature Pinus sylvestris L. dominated forest with a novel analytical approach, allowing the first comparison of: (i) magnitude and delta C-13 of shoot, stem and soil CO2 fluxes (A(shoot), R-stem and R-soil), (ii) concentration and delta C-13 of compound-specific and/or bulk non-structural carbohydrates (NSCs) in phloem and roots and (iii) growth of stem and fine roots. Results showed a significant effect of phloem NSC concentrations on tracheid growth, and both variables significantly impacted R-stem. Also, concentrations of root NSCs, especially starch, had a significant effect on fine root growth, although no effect of root NSC concentrations or root growth was detected on R-soil. Time series analysis between delta C-13 of A(shoot) and delta C-13 of R-stem or delta C-13 of R-soil revealed strengthened C allocation to stem or roots under high C demands. Furthermore, we detected a significant correlation between delta C-13 of R-stem and delta C-13 of phloem sucrose and glucose, but not for starch or water-soluble carbohydrates. Our results indicate the need to include C allocation dynamics into tree growth models. We recommend using compound-specific concentration and delta C-13 analysis to reveal C allocation processes that may not be detected by the conventional approach that utilizes bulk organic matter.

Production of applicable and homogeneous biochar for soil amendment purposes would benefit from knowledge on how feedstock heterogeneity impacts key biochar pore properties and how the properties are transformed due to pyrolysis. This study aimed (1) to quantify how clonal differences and within-tree heterogeneity of a hybrid aspen feedstock (wood) impact biochar pore properties and (2) to estimate how pore properties of non-pyrolysed wood materials are transformed when pyrolysed into biochar. The study was conducted by collecting samples from a hybrid aspen (Populus tremula L. × Populus tremuloides Michx.) clonal field trial. Key pore properties of non-pyrolysed and pyrolysed wood samples were quantified with 3D X-ray imaging and quantitative image analyses. The results demonstrated how pyrolysis shifted distinctively bi-modal pore size distributions of the wood samples towards smaller pore size regions. The bi-modal wood tissue structure controlled the pore structure also in the biochars. Due to decreasing cell wall thicknesses, the pyrolysis increased the porosity of the materials. While the thermal process homogenized differences in the wall thicknesses, the thicknesses of the feedstock were also shown to control the resulting thicknesses in the biochars. Mechanisms of biochar pore property formation can be considered important when designing applicable biochars for a chosen purpose. Clonal differences and within-tree heterogeneity had a direct impact only on the wall thicknesses and the pore diameters of vessels. These impacts can be of interest when planning feedstock utilization in biochar production. However, the results suggest that relatively homogeneous biochar can be produced from hybrid aspen feedstocks.

Intrinsic water-use efficiency (iWUE), a key index for carbon and water balance, has been widely estimated from tree-ring delta C-13 at annual resolution, but rarely at high-resolution intraseasonal scale. We estimated high-resolution iWUE from laser-ablation delta C-13 analysis of tree-rings (iWUE(iso)) and compared it with iWUE derived from gas exchange (iWUE(gas)) and eddy covariance (iWUE(EC)) data for two Pinus sylvestris forests from 2002 to 2019. By carefully timing iWUE(iso) via modeled tree-ring growth, iWUE(iso) aligned well with iWUE(gas) and iWUE(EC) at intraseasonal scale. However, year-to-year patterns of iWUE(gas), iWUE(iso), and iWUE(EC) were different, possibly due to distinct environmental drivers on iWUE across leaf, tree, and ecosystem scales. We quantified the modification of iWUE(iso) by postphotosynthetic delta C-13 enrichment from leaf sucrose to tree rings and by nonexplicit inclusion of mesophyll and photorespiration terms in photosynthetic discrimination model, which resulted in overestimation of iWUE(iso) by up to 11% and 14%, respectively. We thus extended the application of tree-ring delta C-13 for iWUE estimates to high-resolution intraseasonal scale. The comparison of iWUE(gas), iWUE(iso), and iWUE(EC) provides important insights into physiological acclimation of trees across leaf, tree, and ecosystem scales under climate change and improves the upscaling of ecological models.

Intrinsic water-use efficiency (iWUE) is a key index for evaluating carbon and water balance of terrestrial ecosystems. A common approach to estimate iWUE is via measuring tree-ring stable carbon isotope composition (δ13C), which has been widely applied at annual resolution, but rarely at high-resolution intra-seasonal scale. In this study, we examined the reliability and accuracy of tree-ring δ13C in estimating intra-seasonal iWUE (iWUEiso), with the aid of laser ablation IRMS analysis of tree-rings, by comparing iWUEiso with iWUE derived from leaf gas exchange (iWUEgas) and eddy covariance (iWUEEC) data for two Pinus sylvestris L. dominated boreal forests from 2002 to 2019. By carefully timing iWUEiso via modelled yearly tree-ring growth, intra-seasonal variability of iWUEiso aligned well with that of iWUEgas and iWUEEC. However, absolute values of iWUEiso were apparently higher than that of iWUEgas and iWUEEC, which could be ascribed to post-photosynthetic 13C-enrichment from leaf assimilates to tree-rings and to nonexplicit inclusion of mesophyll and photorespiration terms in iWUEiso estimation. These two factors overestimated iWUEiso by up to 11% and 14%, respectively. Our study demonstrates that tree-ring δ13C data can be used to trace intra-seasonal variability of iWUE, and thus provides a valuable tool for detecting short-term dynamics in carbon and water trade for areas and periods with no instrumental data. We encourage more comparisons between iWUEgas, iWUEiso and iWUEEC, which can deepen our understanding of how trees physiologically adapt to climate change across leaf, tree and ecosystem levels.

A decline in the carbon content of agricultural soils has been reported globally. Amendments of forest industry side-streams might counteract this. We tested the effects of industrial conifer bark and its cascade process materials on the soil microbiome under barley (Hordeum vulgare L.) in clay and silt soil microcosms for 10 months, simulating the seasonal temperature changes of the boreal region. Microbial gene copy numbers were higher in clay soils than in silt. All amendments except unextracted bark increased bacterial gene copies in both soils. In turn, all other amendments, but not unextracted bark from an anaerobic digestion process, increased fungal gene copy numbers in silt soil. In clay soil, fungal increase occurred only with unextracted bark and hot water extracted bark. Soil, amendment type and simulated season affected both the bacterial and fungal community composition. Amendments increased bacteria originating from the anaerobic digestion process, as well as dinitrogen fixers and decomposers of plant cells. In turn, unextracted and hot water extracted bark determined the fungal community composition in silt. As fungal abundance increase and community diversification are related to soil carbon acquisition, bark-based amendments to soils can thus contribute to sustainable agriculture.

Hybrid aspens have long attracted scientific interest, but the research on their use as feedstocks for chemical applications are still very limited. The bark biomass of the poplar species contains many valuable extractives that can be utilized as value-added products. This paper examines the applicability of hybrid aspen (Populus tremula L. × P. tremuloides Michx.) bark extract as a precursor of rigid carbon foam and activated carbon. To explore this, the study considers 1) the basic chemical composition of the bark in terms of added value potential, 2) the basic chemical composition of the bark extract and the effect of its pretreatment on the extract composition, 3) the production of rigid carbon foam, and 4) the chemical activation of carbon foam with different impregnating agents. The study determines that the bark extract of the hybrid aspen can be used as a precursor for rigid carbon foam and further processed into an activated carbon product. Therefore, the bark extract of Populus tremula L. × P. tremuloides Michx. can be assessed as a potential value-added product that increases the use value of the hybrid aspen biomass. peerReviewed

Despite growing interest in predicting plant phenological shifts, advanced spring phenology by global climate change remains debated. Evidence documenting either small or large advancement of spring phenology to rising temperature over the spatio-temporal scales implies a potential existence of a thermal threshold in the responses of forests to global warming. We collected a unique data set of xylem cell-wall-thickening onset dates in 20 coniferous species covering a broad mean annual temperature (MAT) gradient (−3.05 to 22.9°C) across the Northern Hemisphere (latitudes 23°–66° N). Along the MAT gradient, we identified a threshold temperature (using segmented regression) of 4.9 ± 1.1°C, above which the response of xylem phenology to rising temperatures significantly decline. This threshold separates the Northern Hemisphere conifers into cold and warm thermal niches, with MAT and spring forcing being the primary drivers for the onset dates (estimated by linear and Bayesian mixed-effect models), respectively. The identified thermal threshold should be integrated into the Earth-System-Models for a better understanding of spring phenology in response to global warming and an improved prediction of global climate-carbon feedbacks.

Intrinsic water-use efficiency (iWUE), a key index for carbon and water balance, has been widely estimated from tree-ring δ

Polyphenolic stilbene glucosides are abundant in the fresh bark of Norway spruce (Picea abies [L.] Karst.) trees. Stilbene-rich bark extracts could be industrially utilized as preservatives due to their antioxidative, antifungal, and antibacterial properties. The postharvesting conditions, especially industrial debarking, influence the chemical properties of bark. Inherent variation in high-value compounds of bark is assumed to be offset by modifications within the bark supply chain; however, essential quantitative information is still rare. This study elucidated the magnitude of variation in the stilbenoid content and composition of Norway spruce bark due to (1) the geographical origin of Norway spruce seeds, (2) the geographical location of the growing site, (3) within-tree variability, and (4) industrial handling and pilot-scale extraction and fractioning processes. The inherent variation in stilbenoid content was large: the total average stilbenoid content of the inner bark varied from 70 to 110 mg/g of dry weight (DW). Sampling position in the stem and growing site explained over 50% of the total variance in stilbenoid content. Trees with a northern origin of seeds had a higher isorhapontin/astringin ratio than the trees with a southern origin of seeds, regardless of their growing site. Industrial bark from sawmills showed a significantly higher total stilbenoid content in winter than in summer, 22 mg/g and 1–3 mg/g DW, respectively. The inherent variation in the stilbenoid content was offset by the variation caused by the debarking process and experimental pilot-scale processing. To optimize the yield of stilbenoids from spruce bark, sampling of northern forests and short handling times in the supply chain are recommended.

Abies fargesii var. faxoniana (Rehder et E.H. Wilson) Tang S Liu seedlings at high elevations compensate for the low efficiency of their water conducting system and high phloem hydraulic resistance by the enhancement in xylem:leaf area, phloem:leaf area, and phloem:xylem area. Maintenance of xylem and phloem transport is particularly important for the survival and growth of trees at the treeline. How plants modify the allocation to leaf, xylem, and phloem structures to adapt to the treeline environment is an important issue. The purpose of this study was to estimate how xylem and phloem anatomy and volume as well as leaf functional traits of A. fargesii seedlings vary with elevation. We examined elevation-related differences in a variety of phloem and xylem functional areas and hydraulic conduit diameters of A. fargesii seedlings growing at elevations between 2600 and 3200 m in the subalpine conifer forest of southwest China. Xylem area, last xylem ring area, and leaf:sapwood area significantly decreased, while xylem:leaf area, phloem:leaf area, and non-collapsed phloem:xylem area significantly increased with elevation. Principal components analysis showed that xylem area, non-collapsed phloem area, and xylem:phloem area were positively correlated with growth rates. Our results showed that A. fargesii tree seedlings at the treeline tend to facilitate growth and maintain functional water and sugar balance between stem and leaves by the enhancement in xylem:leaf area, phloem:leaf area, and phloem:xylem area, but not through differences in vessel lumen diameter.

Novel bioeconomic approaches call for increasingly faster production of lignocellulosic biomass and its bettertailored use for higher added value. The high-yield capacity and structural properties of willows (Salix spp.) suggest their excellent potential for the production of designed biochar for use in agronomic, electronic and technical applications. All these applications rely on the internal pore structure of biochar. However, we lack an in-depth quantitative understanding of the interlinkages between the feedstock properties and the physical quality of the biochar produced. We studied quantitatively how the clonal and within-plant properties of five different willow clones (hybrids of Salix schwerinii E.L. Wolf) affected the micrometre-scale pore properties of the produced biochars (pyrolyzed at + 462 ?C). The porosity and pore size distribution were analysed before and after slow pyrolysis by X-ray microtomography and image analysis. We also studied the potential of conventional low-cost fibre analysis techniques to be used to predict biochar pore properties directly from fresh feedstock. The total porosity (0.55?0.62) and the pore size distribution of willow wood and derived biochars varied between clones. Approximately two-thirds of the biochar total porosity was associated with pores formed by wood fibres. Pyrolysis levelled off the structural variation detected between and within the clones. Pyrolysis-induced shrinkage reduced the pore sizes and narrowed the pore size distribution. The results suggest that conventional fibre analysis techniques could be utilized to predict biochar homogeneity. Short rotation coppice willows are suitable feedstock to produce homogenous biochar precursor for production of bio-based carbon materials to be used in high value-added technical applications. The structural homogeneity of the feedstock and produced biochar can be enhanced by selecting proper harvesting strategy and clones used in plantations. From the industrial perspective, comprehensive understanding of feedstock properties helps to control quality of the produced biochar.

In-depth knowledge about carbon (C) flows within trees and from the trees to forest ecosystem via respiration is essential for accurate modeling of tree growth and C balance. However, significant gaps still exist in our understanding about how trees allocate C for growth and respiration of different tree organs, which makes it difficult to predict the response of forest growth to climate change. A powerful tool to study C allocation within trees is stable C isotope ratio (the ratio of 13C to 12C relative to a reference, noted as δ13C), as this signal is passed from C sources to C sinks with isotopic fractionation along the pathway. In this study, we monitored the δ13C signal of CO2 fluxes of shoot (Acanopy), stem (Rstem) and soil (Rsoil) in a Scots pine (Pinus sylvestris L.) dominated boreal forest in southern Finland for summer 2018, which included a month-long dry period. We also traced the growth of current-year shoots, needles, stem, and fine roots (fibrous and pioneer roots) and the concentrations and δ13C of putative substrates (sugars and starch) in phloem and roots of Scots pine over the growing season. We calculated the correlations between substrate concentrations and respiration fluxes, as well as the correlations between δ13C of Acanopy and δ13C of Rsoil or δ13C of Rstem with varying time lags from 3 d to 14 d for different tree organ growth periods and the dry period. We found tight couplings between photosynthesis and respiration, when newly assimilated sugars were allocated to stem or roots for growth or for drought response. These couplings include: 1) a synchrony between fibrous root growth and the concentrations of bulk sugars and starch in roots, associated with increases in Rsoil under high root substrate concentrations; 2) promoted nighttime Rstem under high substrate supply to stem, which is seen as increased phloem glucose to sucrose ratio; 3) shorter time lags between δ13C of Acanopy and δ13C of Rstem under higher stem growth demands; 4) shorter time lags between δ13C of Acanopy and δ13C of Rsoil under drought stress than with no water stress. The time lags between δ13C of Acanopy and δ13C of Rsoil or δ13C of Rstem being not uniform further implies that tree C allocation patterns are dynamic over the growing season. In addition, the C allocation to stem and roots occurred after full expansion of current-year shoots or needles, reflecting a whole tree C allocation strategy for growth demands of different tree organs, which prioritizes the demands of source organs. We suggest that the dynamics of C allocation in response to tree organ growth and drought stress should be considered in whole tree C allocation models for projecting forest growth under climate change.

This study aims to promote comprehensive utilization of woody biomass by providing a knowledgebase on the utility of aspen bark as a new alternative source for fossil-based chemicals. The research focused on the analysis of clonal variation in: (1) major chemical components, i.e., hemicelluloses, cellulose, and lignin, (2) extraneous materials, i.e., bark extractives, and suberic acid, (3) condensed tannins content and composition, and (4) screening differences in antioxidative properties and total phenolic content of hot water extracts and ethanol-water extracts of hybrid aspen bark. Results of this study, the discovery of clonal variation in utilizable chemicals, pave the way for further research on added-value potential of under-utilized hybrid aspen and its bark. Clonal variation was found in notable part of chemicals with potential for utilization. Based on the results, an appropriate bark raw material can be selected for tailored processing, thus improving the resource efficiency. The results also indicate that by applying cascade processing concepts, bark chemical substances could be more efficiently utilized with more environmentally friendly methods.

Developing shoots, i.e., sprouts, and older needles of Norway spruce (Picea abies (L.) Karst.) have traditionally been used for medicinal purposes due to the high content of vitamins and antioxidants. Currently, sprouts are available as, for example, superfood and supplements. However, end-product quality and nutritive value may decline in the value-chain from raw material sourcing to processing and storage. We studied (1) impacts of different drying and extraction methods on nutritional composition and antioxidative properties of sprouts and needles, (2) differences between sprouts and needles in nutritional composition and microbiological quality, and (3) production scale quality of the sprouts. Additionally, (4) sprout powder was applied in products (ice-cream and sorbet) and consumer acceptance was evaluated. According to our results, older needles have higher content of dry matter, energy, and calcium, but lower microbial quality than sprouts. Sprouts showed a higher concentration of vitamin C, magnesium, potassium, and phosphorus than older needles. Freeze-drying was the best drying method preserving the quality of both sprouts and needles, e.g., vitamin C content. The antioxidative activity of the sprout extracts were lower than that of needles. Ethanol-water extraction resulted in a higher content of active compounds in the extract than water extraction. Sensory evaluation of food products revealed that on average, 76% of consumers considered sprout-containing products very good or good, and a creamy product was preferred over a water-based sorbet.

Significance Forest trees can live for hundreds to thousands of years, and they play a critical role in mitigating global warming by fixing approximately 15% of anthropogenic CO2 emissions annually by wood formation. However, the environmental factors triggering wood formation onset in springtime and the cellular mechanisms underlying this onset remain poorly understood, since wood forms beneath the bark and is difficult to monitor. We report that the onset of wood formation in Northern Hemisphere conifers is driven primarily by photoperiod and mean annual temperature. Understanding the unique relationships between exogenous factors and wood formation could aid in predicting how forest ecosystems respond and adapt to climate warming, while improving the assessment of long-term and high-resolution observations of global biogeochemical cycles., Wood formation consumes around 15% of the anthropogenic CO2 emissions per year and plays a critical role in long-term sequestration of carbon on Earth. However, the exogenous factors driving wood formation onset and the underlying cellular mechanisms are still poorly understood and quantified, and this hampers an effective assessment of terrestrial forest productivity and carbon budget under global warming. Here, we used an extensive collection of unique datasets of weekly xylem tissue formation (wood formation) from 21 coniferous species across the Northern Hemisphere (latitudes 23 to 67°N) to present a quantitative demonstration that the onset of wood formation in Northern Hemisphere conifers is primarily driven by photoperiod and mean annual temperature (MAT), and only secondarily by spring forcing, winter chilling, and moisture availability. Photoperiod interacts with MAT and plays the dominant role in regulating the onset of secondary meristem growth, contrary to its as-yet-unquantified role in affecting the springtime phenology of primary meristems. The unique relationships between exogenous factors and wood formation could help to predict how forest ecosystems respond and adapt to climate warming and could provide a better understanding of the feedback occurring between vegetation and climate that is mediated by phenology. Our study quantifies the role of major environmental drivers for incorporation into state-of-the-art Earth system models (ESMs), thereby providing an improved assessment of long-term and high-resolution observations of biogeochemical cycles across terrestrial biomes.

Bark of Norway spruce and Scots pine trees contain large amounts of condensed tannins. Tannins extracted with hot water could be used in different applications as they possess antioxidative and antimicrobial activities. The use of bark tannins as e.g., food preservatives calls for increases in our knowledge of their antioxidative activities when applied in foodstuffs. To assess the ability of bark tannins to prevent lipid oxidation, hot water extracts were evaluated in a liposome model. Isolated tannins were also applied in dry-cured, salty meat snacks either as liquid extracts or in dry-powder form. Consumer acceptance of the snacks was tested by a sensory evaluation panel where outlook, odor, taste, and structure of the snacks were evaluated and compared to a commercial product without tannin ingredients. Our results show that conifer bark tannin-rich extracts have high capacity to prevent lipid oxidation in the liposome model. The efficacies of pine and spruce bark extracts were ten to hundred folds higher, respectively, than those of phenolic berry extracts. The bark extracts did not significantly influence the odor or taste of the meat snacks. The findings indicate that bark extracts may be used as sustainable food ingredients. However, more research is needed to verify their safety.

Injection molded biocomposite specimens were prepared by using four different weight percentages, i.e., 10%, 20%, 30%, and 40% of aspen (Populus tremula L.) and willow (Salix caprea L.) wood particles in a biopolymeric matrix. Dog-bone test specimens were used for testing the physical, mechanical, and thermal properties, and microstructure of biocomposites. The tensile and bending strength changed with the change in weight percentages of wood particles and the bending stiffness increased with the increasing weight percentage of wood. In Brinell hardness, similar changes as a function of wood particle weight percentage were shown, and a relationship between hardness and tensile strength with wood content was also investigated. The prepared biocomposites could be an alternative for plastic-based materials and encourage the use of fast growing (aspen and willow) wood from short-rotation forests in biocomposites.

Preconditions of phloem transport in conifers are relatively unknown. We studied the variation of needle and inner bark axial osmotic gradients and xylem water potential in Scots pine and Norway spruce by measuring needle and inner bark osmolality in saplings and mature trees over several periods within a growing season. The needle and inner bark osmolality was strongly related to xylem water potential in all studied trees. Sugar concentrations were measured in Scots pine, and they had similar dynamics to inner bark osmolality. The sucrose quantity remained fairly constant over time and position, whereas the other sugars exhibited a larger change with time and position. A small osmotic gradient existed from branch to stem base under pre-dawn conditions, and the osmotic gradient between upper stem and stem base was close to zero. The turgor in branches was significantly driven by xylem water potential, and the turgor loss point in branches was relatively close to daily minimum needle water potentials typically reported for Scots pine. Our results imply that xylem water potential considerably impacts the turgor pressure gradient driving phloem transport and that gravitation has a relatively large role in phloem transport in the stems of mature Scots pine trees.

X-ray microtomography (μCT) is a three-dimensional imaging technique, which has, over the past decade, established itself as a go-to method for nondestructive visualization of plant tissue with submicrometer resolution. μCT is closely related to medical computed tomography, in that a measurement consists of acquiring a series of radiographs from different directions around the sample. Especially with synchrotron X-ray sources, these radiographs exhibit significant phase contrast. This greatly enhances soft tissue contrast, making it well suited for plant imaging. Tomographic reconstruction techniques are then employed to convert the stack of radiographs into a 3D volumetric image. Compared with the laboratory X-ray tube-based systems, synchrotron tomography beamlines also offer high throughput, with tens of samples scanned over the course of a typical 24-h beam time.Synchrotrons are typically operated as user facilities, with a staff member assisting users in aligning the beamline and all instrumentation-related matters. From the user's point of view, success of a synchrotron μCT experiment is often dependent on secure sample mounting, choice of appropriate beam parameters, and post-processing the data, i.e., extracting scientifically meaningful results from the 3D image. In this chapter, we review the issues to consider in preparation of a μCT experiment from the point of view of a phloem researcher, emphasizing those aspects which are directly under the user's control rather than technical specifics, which vary from one beamline to another.

X-ray microtomography (μCT) is a three-dimensional imaging technique, which has, over the past decade, established itself as a go-to method for nondestructive visualization of plant tissue with submicrometer resolution. μCT is closely related to medical computed tomography, in that a measurement consists of acquiring a series of radiographs from different directions around the sample. Especially with synchrotron X-ray sources, these radiographs exhibit significant phase contrast. This greatly enhances soft tissue contrast, making it well suited for plant imaging. Tomographic reconstruction techniques are then employed to convert the stack of radiographs into a 3D volumetric image. Compared with the laboratory X-ray tube-based systems, synchrotron tomography beamlines also offer high throughput, with tens of samples scanned over the course of a typical 24-h beam time.Synchrotrons are typically operated as user facilities, with a staff member assisting users in aligning the beamline and all instrumentation-related matters. From the user's point of view, success of a synchrotron μCT experiment is often dependent on secure sample mounting, choice of appropriate beam parameters, and post-processing the data, i.e., extracting scientifically meaningful results from the 3D image. In this chapter, we review the issues to consider in preparation of a μCT experiment from the point of view of a phloem researcher, emphasizing those aspects which are directly under the user's control rather than technical specifics, which vary from one beamline to another.

Softwood bark is an important by-product of forest industry. Currently, bark is under-utilized and mainly directed for energy production, although it can be extracted with hot water to obtain compounds for value-added use. In Norway spruce (Picea abies [L.] Karst.) bark, condensed tannins and stilbene glycosides are among the compounds that comprise majority of the antioxidative extractives. For developing feasible production chain for softwood bark extractives, knowledge on raw material quality is critical. This study examined the fate of spruce bark tannins and stilbenes during storage treatment with two seasonal replications (i.e., during winter and summer). In the experiment, mature logs were harvested and stored outside. During six-month-storage periods, samples were periodically collected for chemical analysis from both inner and outer bark layers. Additionally, bark extractives were analyzed for antioxidative activities by FRAP, ORAC, and H2O2 scavenging assays. According to the results, stilbenes rapidly degraded during storage, whereas tannins were more stable: only 5&ndash, 7% of the original stilbene amount and ca. 30&ndash, 50% of the original amount of condensed tannins were found after 24-week-storage. Summer conditions led to the faster modification of bark chemistry than winter conditions. Changes in antioxidative activity were less pronounced than those of analyzed chemical compounds, indicating that the derivatives of the compounds contribute to the antioxidative activity. The results of the assays showed that, on average, ca. 27% of the original antioxidative capacity remained 24 weeks after the onset of the storage treatment, while a large variation (2&ndash, 95% of the original capacity remaining) was found between assays, seasons, and bark layers. Inner bark preserved its activities longer than outer bark, and intact bark attached to timber is expected to maintain its activities longer than a debarked one. Thus, to ensure prolonged quality, no debarking before storage is suggested: outer bark protects the inner bark, and debarking enhances the degradation.

Bark of Norway spruce (Picea abies [L.] Karst.) trees contains large amounts of polyphenolic stilbene glucosides. Stilbene-rich bark extracts could be utilized as e.g., preservatives due to their antioxidative, antifungal, and antibacterial properties. As stilbenes are photosensitive compounds, ultraviolet (UV) light induces a well-known intramolecular cyclization, leading to the formation of substituted phenanthrenes via a dihydro-phenanthrene intermediate. The possible UV-induced changes in the biological activities of the stilbene extracts remain, however, poorly known. Such information is crucial for practical application development. This study elucidated for the first time, how UVA-treatments of spruce bark extracts affect the chemical composition of the extracts, and further change their antimicrobial and antioxidative activities. Norway spruce inner bark was extracted (‘Extract’) and soluble mono- and disaccharides removed using Amberlite XADHP7 (‘Extract XAD’). These extracts were then treated with UVA-light (‘Extract UV’, ‘Extract XAD UV’), and chemical properties analyzed by GC–MS and HP-SEC. The antimicrobial activities of untreated and modified extracts against Staphylococcus aureus, Candida albicans, and Escherichia coli, were evaluated. Additionally, differences in the antioxidant activity between the untreated and UV-treated bark extracts were measured at a total stilbene concentration of 0.5 mg/mL EtOH, using the FRAP and ORAC methods. Also, antioxidant effects were evaluated in a liposome model to assess the ability of the extract to prevent lipid oxidation. Our novel results show that UVA-induced modification of the stilbene-rich inner bark extracts increased the radical scavenging activity. However, UVA-irradiation decreased the capacity of the extracts to prevent lipid oxidation in the liposome system method. The results also indicate a maintained or slightly increased antimicrobial activity after UVA-modification. This study shows that Norway spruce bark stilbenoids and the compounds formed by UVA-irradiation thereof show biological activity, and thus have commercial potential as e.g., preservatives.

A process model based on hot water extraction (HWE), slow pyrolysis and anaerobic digestion (AD) were used for pine and spruce bark utilisation. First tannins (32 mg/g and 11.8 mg/g, respectively) and polyphenols were recovered via HWE. Then, the residue was pyrolysed to produce biochar (marketable quality), gas (energy source) and liquid fractions. The liquid fraction was further separated into aqueous acidic fraction and to tar fraction. Bark, extracted bark residue and acidic liquid fraction from pyrolysis were treated in AD to produce biomethane and digestate. The methane yields from pine and spruce bark and extracted bark residue were low (from 42 to 96 mLCH4/gVSadded) and showed only small differences. In conclusion, cascade processing can improve the performance of subsequent single processes and utilise biomass sources with higher efficiency. The best processing chain may vary in different cases and the overall energy balance of processing needs further research.

International audience; AbstractKey messageOnset and cessation of radial and height increment of Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) in southern Finland were independent phenomena. They both contributed to the increment period duration, which was a more crucial factor defining the magnitude of annual radial and height increment.ContextPhenology of diameter and height increment is a critical component of growth, also contributing to damage and survival of trees.AimsWe quantified annual variation in intra-annual tracheid production and height increment of Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.).MethodsThe number of tracheids and the day of the year for the onset and cessation of tracheid production were monitored from microcores collected repeatedly during growing seasons 2001–2012 in southern Finland. Weekly height increment was also measured in an adjacent sapling stand in 2008–2012.ResultsThe first tracheids in pine were found around mid-May and in spruce a week later. The cessation of the tracheid production occurred during the last week of August for both tree species. Increment onset and cessation were independent phenomena, both contributing to the magnitude of tracheid production via increment period duration, which appeared to be a more crucial factor defining the number of tracheids. Duration of the height increment period was also related to shoot length but the connection was less tight than the link between the duration of tracheid production and the number of tracheids. A thermal threshold around 100 d.d. (degree days) was found for the onset of radial increment. No single environmental factor triggered the cessation of tracheid production, but in some years, soil water availability appeared to play a role.ConclusionThe results indicate that extending growing seasons due to the climatic warming may increase growth in the Finnish forests.

Trees scale leaf (A(L)) and xylem (A(X)) areas to couple leaf transpiration and carbon gain with xylem water transport. Some species are known to acclimate in A(L) : A(X) balance in response to climate conditions, but whether trees of different species acclimate in A(L) : A(X) in similar ways over their entire (continental) distributions is unknown. We analyzed the species and climate effects on the scaling of A(L) vs A(X) in branches of conifers (Pinus sylvestris, Picea abies) and broadleaved (Betula pendula, Populus tremula) sampled across a continental wide transect in Europe. Along the branch axis, A(L) and A(X) change in equal proportion (isometric scaling: b similar to 1) as for trees. Branches of similar length converged in the scaling of A(L) vs A(X) with an exponent of b = 0.58 across European climates irrespective of species. Branches of slow- growing trees from Northern and Southern regions preferentially allocated into new leaf rather than xylem area, with older xylem rings contributing to maintaining total xylem conductivity. In conclusion, trees in contrasting climates adjust their functional balance between water transport and leaf transpiration by maintaining biomass allocation to leaves, and adjusting their growth rate and xylem production to maintain xylem conductance.

Bioactive stilbene glucosides are the major constituents of the acetone extracts of the phloem and bark of Norway spruce (Picea abies (L.) Karst.) trees. We studied their variation patterns across phloem and bark within the stems of Norway spruce. The total yields of stilbene glucosides (astringin, isorhapontin, and piceid) from trees were estimated. Bark samples were collected from young (18 years-old) and older trees (37 years-old), representing age and size typical for energy wood harvesting and the first commercial thinning, respectively. Different bark layers of younger trees had 10%–63% lower average amount of stilbene glucosides than the bark layers of older trees. The inner bark had the highest mass fraction of stilbene glucosides (2.7%–4.8% of dry weight (d.w.)) and the outermost bark showed the lowest amount (0.4%–1.2% d.w.). Axially along the stem, the highest amount of stilbene glucosides was found at the stem base in the young trees (average over bark zones 2.1% d.w.) and at the breast height and the base of the living crown in the older trees (average over bark zones 3.6% d.w.). Astringin and isorhapontin yielded the highest amounts, while the share of piceid was the smallest. The total yield of stilbene glucosides was dependent on the bark biomass, and positively correlated with total wood and bark volume. The basal stem was the most valuable stilbene source in both younger and older trees. The bark of Norway spruce from the first commercial thinnings, especially of butt and middle logs, can provide feasible source for high-value extracts.

Preconditions of phloem transport in conifers are relatively unknown. We studied the variation of needle and inner bark axial osmotic gradients and xylem water potential in Scots pine and Norway spruce by measuring needle and inner bark osmolality in saplings and mature trees over several periods within a growing season. The needle and inner bark osmolality was strongly related to xylem water potential in all studied trees. Sugar concentrations were measured in Scots pine, and they had similar dynamics to inner bark osmolality. The sucrose quantity remained fairly constant over time and position, whereas the other sugars exhibited a larger change with time and position. A small osmotic gradient existed from branch to stem base under pre-dawn conditions, and the osmotic gradient between upper stem and stem base was close to zero. The turgor in branches was significantly driven by xylem water potential, and the turgor loss point in branches was relatively close to daily minimum needle water potentials typically reported for Scots pine. Our results imply that xylem water potential considerably impacts the turgor pressure gradient driving phloem transport and that gravitation has a relatively large role in phloem transport in the stems of mature Scots pine trees.

Considerable changes in tree growth are projected due to the expected climate change. The expected changes of climate call for a better insight into the growth responses of trees to varying environmental conditions over large geographical regions. The aim of this study was to analyse the intra-annual tracheid production of Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) across a latitudinal gradient in Finland (60–68°N). The number of tracheids and the day of the year for the onset, fastest rate, and cessation of tracheid production were determined from microcores repeatedly collected in nine stands during growing seasons of 2001–2009. The onset of tracheid production varied from late May in southern Finland to mid-June in northern Finland. On all stands, tracheid production initiated earlier and ceased later for Scots pine than for Norway spruce. On average, the fastest tracheid production rate occurred slightly after the summer solstice, but variation between sites and years was high. In the northernmost Scots pine stand, the length of the growing season was less than two months and the onset of tracheid production required clearly lower TS than elsewhere. The results imply that within Finland, year-to-year weather variation has a marked impact on the timing of tracheid production. However, the results indicate that the Norway spruce and Scots pine have adapted and are able to adjust their tracheid production according to the local conditions.