Norway Spruce Saplings Research Articles

Elevated nutrient supply can exert worse effects on Norway spruce than drought, viewed through chemical defence against needle rust.

Abiotic factors such as water and nutrient availability can exert a dominant influence on the susceptibility of plants to various pathogens. Effects of abiotic environmental factors on phenolic compound concentrations in the plant tissue may represent one of the major underlying mechanisms, as these compounds are known to play a substantial role in plant resistance to pests. In particular, this applies to conifer trees, in which a large range of phenolic compounds are produced constitutively and/or induced by pathogen attack. We subjected Norway spruce saplings to water limitation and elevated nutrient supply over two years and subsequently controlled infection with the needle rust Chrysomyxa rhododendri and analysed both constitutive and inducible phenolic compound concentrations in the needles as well as the degree of infection. Compared to the control group, both drought and fertilization profoundly modified the constitutive and pathogen induced profiles of phenolic compounds, but had little impact on the total phenolic content. Fertilization predominantly affected the inducible phenolic response and led to higher infection rates by C. rhododendri. Drought stress, in contrast, mainly shaped the phenolic profiles in healthy plant parts and had no consequences on the plant susceptibility. The results show that specific abiotic effects on individual compounds seem to be decisive for the infection success of C. rhododendri, whereby the impaired induced response in saplings subjected to nutrient supplementation was most critical. Although drought effects were minor, they varied depending on the time and length of water limitation. The results indicate that prolonged drought periods in the future may not significantly alter the foliar defence of Norway spruce against C. rhododendri, but fertilization, often propagated to increase tree growth and forest productivity, can be counterproductive in areas with high pathogen pressure.

The effect of elevated CO2 on photosynthesis is modulated by nitrogen supply and reduced water availability in Picea abies.

It is assumed that the stimulatory effects of elevated CO2 concentration ([CO2]) on photosynthesis and growth may be substantially reduced by co-occurring environmental factors and the length of CO2 treatment. Here, we present the study exploring the interactive effects of three manipulated factors ([CO2], nitrogen supply and water availability) on physiological (gas-exchange and chlorophyll fluorescence), morphological and stoichiometric traits of Norway spruce (Picea abies) saplings after 2 and 3 years of the treatment under natural field conditions. Such multifactorial studies, going beyond two-way interactions, have received only limited attention until now. Our findings imply a significant reduction of [CO2]-enhanced rate of CO2 assimilation under reduced water availability which deepens with the severity of water depletion. Similarly, insufficient nitrogen availability leads to a down-regulation of photosynthesis under elevated [CO2] being particularly associated with reduced carboxylation efficiency of the Rubisco enzyme. Such adjustments in the photosynthesis machinery result in the stimulation of water-use efficiency under elevated [CO2] only when it is combined with a high nitrogen supply and reduced water availability. These findings indicate limited effects of elevated [CO2] on carbon uptake in temperate coniferous forests when combined with naturally low nitrogen availability and intensifying droughts during the summer periods. Such interactions have to be incorporated into the mechanistic models predicting changes in terrestrial carbon sequestration and forest growth in the future.

Stem notching decreases stem hydraulic conductance but does not influence drought impacts and post-drought recovery in Scots pine and Norway spruce.

The tight connection between the deterioration of xylem function and plant mortality under drought is well recognized. However, a lack of mechanistic understanding of how substantial conductivity loss influences plant performance under drought and during post-drought recovery hinders our ability to model tree responses to drought stress. We artificially induced a loss of 50% of xylem conducting area in Scots pine and Norway spruce saplings by stem notching and investigated plant performance under drought and during post-drought recovery. Plant mortality, xylem hydraulic conductivity, leaf water status and stomatal conductance were measured. We observed no preferential mortality of top plant parts (above the notches) compared to basal plant parts (below the notches), and no consistent trend in hydraulic conductivity loss was observed between top and basal parts of dying plants. Stem hydraulic conductivity, water status of the needles and stomatal conductance changed similarly between the top and basal parts during drought and post-drought recovery, which indicated the substantial hydraulic overcapacity of the stems. The recovery of stomatal conductance demonstrated prominent hysteresis due to non-hydraulic stomatal limitations. The results obtained are highly important for modelling the influence of plant hydraulic impairment on plant performance under drought and during post-drought recovery.

Localized stem heating from the rest to growth phase induces latewood-like cell formation and slower stem radial growth in Norway spruce saplings.

Recent climate projections predict a more rapid increase of winter temperature than summer and global temperature averages in temperate and cold environments. As there is relatively little experimental knowledge on the effect of winter warming on cambium phenology and stem growth in species growing in cold environments, the setting of manipulative experiments is considered of primary importance, and they can help to decipher the effect of reduced winter chilling and increased forcing temperatures on cambium reactivation, growth and xylem traits. In this study, localized stem heating was applied to investigate the effect of warming from the rest to the growth phase on cambium phenology, intra-annual stem growth dynamics and ring wood features in Picea abies (L.) H.Karst. We hypothesized that reduced winter chilling induces a postponed cambium dormancy release and decrease of stem growth, while high temperature during cell wall lignification determines an enrichment of latewood-like cells. The heating device was designed to maintain a +5°C temperature delta with respect to air temperature, thus allowing an authentic scenario of warming. Continuous stem heating from the rest (November) to the growing phase determined, at the beginning of radial growth, a reduction of the number of cell layers in the cambium, higher number of cell layers in the wall thickening phase and an asynchronous stem radial growth when comparing heated and ambient saplings. Nevertheless, heating did not induce changes in the number of produced cell layers at the end of the growing season. The analyses of two-photon fluorescence images showed that woody rings formed during heating were enriched with latewood-like cells. Our results showed that an increase of 5°C of temperature applied to the stem from the rest to growth might not influence, as generally reported, onset of cambial activity, but it could affect xylem morphology of Norway spruce in mountain environments.

Drought Stress Described by Transcriptional Responses of Picea abies (L.) H. Karst. under Pathogen Heterobasidion parviporum Attack

The major threats to the sustainable supply of forest tree products are adverse climate, pests and diseases. Climate change, exemplified by increased drought, poses a unique threat to global forest health. This is attributed to the unpredictable behavior of forest pathosystems, which can favor fungal pathogens over the host under persistent drought stress conditions in the future. Currently, the effects of drought on tree resistance against pathogens are hypothetical, thus research is needed to identify these correlations. Norway spruce (Picea abies (L.) H. Karst.) is one of the most economically important tree species in Europe and is considered highly vulnerable to changes in climate. Dedicated experiments to investigate how disturbances will affect the Norway spruce—Heterobasidion sp. pathosystem are important, in order to develop different strategies to limit the spread of H. annosum s.l. under the predicted climate change. Here, we report a transcriptional study to compare Norway spruce gene expressions to evaluate the effects of water availability and the infection of Heterobasidion parviporum. We performed inoculation studies of three-year-old saplings in a greenhouse (purchased from a nursery). Norway spruce saplings were treated in either high (+) or low (−) water groups: high water group received double the water amount than the low water group. RNA was extracted and sequenced. Similarly, we quantified gene expression levels of candidate genes in biotic stress and jasmonic acid (JA) signaling pathways using qRT-PCR, through which we discovered a unique preferential defense response of H. parviporum-infected Norway spruce under drought stress at the molecular level. Disturbances related to water availability, especially low water conditions can have negative effects on the tree host and benefit the infection ability of the pathogens in the host. From our RNA-seq analysis, 114 differentially expressed gene regions were identified between high (+) and low (−) water groups under pathogen attack. None of these gene pathways were identified to be differentially expressed from both non-treated and mock-control treatments between high (+) and low (−) water groups. Finally, only four genes were found to be associated with drought in all treatments.

Microsite-specific 25-year mortality of Norway spruce saplings

Regeneration of coniferous tree species depends on forest structures related to tree death: canopy gaps, decaying wood, and windthrow mounds and pits. This also applies to Norway spruce (Picea abies), which abundantly regenerates from seeds on dead wood and windthrow mounds, and which benefits from gaps in the forest canopy. Accumulated evidence shows much lower mortality of seedlings on elevated structures than on soil, but for saplings the long-term mortality pattern is poorly known. We studied Norway spruce sapling mortality in a natural old-growth subalpine forest in the Western Carpathians (S Poland), tracking the fate of 1304 saplings growing in different conditions. We found that the 25-year sapling mortality rate significantly differed between three types of microsites, being highest on dead wood (49%), intermediate on undisturbed soil (41%) and lowest on mounds (30%). Sapling mortality decreased with increasing canopy openness. Mortality was highest for medium-sized saplings (2–3 m high), regardless of microsite type and mortality cause. For saplings growing on dead wood, mortality increased with increasing decay class of the wood. For those growing on soil, mortality was higher in patches of Athyrium distentifolium than when surrounded by Vaccinium myrtillus and Dryopteris dilatata. We did not detect differences in mortality between saplings growing next to tree trunks and those growing away from them. The pattern of sapling mortality differed from that of seedlings, but it did not change the regeneration pattern over microsites, which is established at the seedling stage. In particular, we believe that the considerable differences in mortality rates between dead wood and the other microsites at the sapling stage cannot counterbalance increased seedling recruitment and survival on dead wood.

Is Decreased Xylem Sap Surface Tension Associated With Embolism and Loss of Xylem Hydraulic Conductivity in Pathogen-Infected Norway Spruce Saplings?

Increased abiotic stress along with increasing temperatures, dry periods and forest disturbances may favor biotic stressors such as simultaneous invasion of bark beetle and ophiostomatoid fungi. It is not fully understood how tree desiccation is associated with colonization of sapwood by fungi. A decrease in xylem sap surface tension (σxylem) as a result of infection has been hypothesized to cause xylem embolism by lowering the threshold for air-seeding at the pits between conduits and disruptions in tree water transport. However, this hypothesis has not yet been tested. We investigated tree water relations by measuring the stem xylem hydraulic conductivity (Kstem), σxylem, stem relative water content (RWCstem), and water potential (Ψstem), and canopy conductance (gcanopy), as well as the compound composition in xylem sap in Norway spruce (Picea abies) saplings. We conducted our measurements at the later stage of Endoconidiophora polonica infection when visible symptoms had occurred in xylem. Saplings of two clones (44 trees altogether) were allocated to treatments of inoculated, wounded control and intact control trees in a greenhouse. The saplings were destructively sampled every second week during summer 2016. σxylem, Kstem and RWCstem decreased following the inoculation, which may indicate that decreased σxylem resulted in increased embolism. gcanopy did not differ between treatments indicating that stomata responded to Ψstem rather than to embolism formation. Concentrations of quinic acid, myo-inositol, sucrose and alkylphenol increased in the xylem sap of inoculated trees. Myo-inositol concentrations also correlated negatively with σxylem and Kstem. Our study is a preliminary investigation of the role of σxylem in E. polonica infected trees based on previous hypotheses. The results suggest that E. polonica infection can lead to a simultaneous decrease in xylem sap surface tension and a decline in tree hydraulic conductivity, thus hampering tree water transport.

Correction of PRI for carotenoid pigment pools improves photosynthesis estimation across different irradiance and temperature conditions

We studied the influence of changing carotenoid pigments on the sensitivity of the photochemical reflectance index (PRI) to photosynthesis dynamics. The goal of the measurements was to examine how the introduction of ΔPRI into the working dataset can improve the estimation of photosynthesis. Spectral and photosynthetic characteristics of European beech and Norway spruce saplings were periodically measured in growth chambers with an adjustable irradiance and temperature. Patterns of environmental changes inside the growth chambers were created by periodic changes in irradiance and temperature. Four general irradiance periods lasting 10–12 days each were established. Introduced irradiance regimes varied in the sum of daily irradiance and amplitude of irradiance changes. Temperature was changed with more complex patterns to induce changes in xanthophyll cycle pigments at various time scales within these regimes. Our measurements confirmed the PRI linkage to photosynthetic light use efficiency (LUE). However, the strength of this connection was found to be dependent on changing pigment concentrations, specifically on the change in the ratio of chlorophylls to carotenoids. Furthermore, a negative interference in photosynthesis estimation from PRI was recorded if the temperature was lowered overnight to 12 °C. The differential PRI (ΔPRI), calculated as the simple difference between the PRI value measured during the daytime period and in early morning (PRI0), revealed a decreased effect from pigments and cold temperature on LUE estimation. The regression analysis among all measured data identified an increased association between PRI and LUE following the introduction of ΔPRI from R2 = 0.26 to 0.69 in beech and from R2 = 0.61 to 0.77 in spruce data. The analyses showed that both leaf carotenoid concentrations and the conversion state of xanthophyll cycle pigments played a significant role in determining PRI and PRI0 values and that the accurate assessment of these pigments in PRI across multiple levels of stress from irradiance and temperature might improve estimations of LUE through ΔPRI. In our data, ΔPRI appeared to be a good measure of photosynthesis, the dynamics of which differed between beech and spruce saplings upon switching temperatures.

Production of constitutive and induced secondary metabolites is coordinated with growth and storage in Norway spruce saplings.

A mechanistic understanding of how trees balance the trade-offs between growth, storage and defense is limited but crucial for predicting tree responses to abiotic and biotic stresses. Here we investigated how trees allocate storage of non-structural carbohydrates (NSC) to growth and constitutive and induced secondary metabolites (SM). We exposed Norway spruce (Picea abies) saplings to 5 weeks of complete darkness to induce light and/or carbon limitation and then applied methyl jasmonate (MeJA) to simulate biotic attack. We measured changes in biomass, NSC (sum of soluble sugars and starches), and constitutive and induced SM (sum of phenolic compounds and terpenoids) in current-year developing and previous-year mature needles and branches, as well as volatiles emitted from the canopy. Under darkness, NSC storage was preferentially used for constitutive biosynthesis of monoterpenes rather than biosynthesis of stilbenes and growth of developing organs, while SM stored in mature organs cannot be remobilized and recycled. Furthermore, MeJA-induced production of SM was constrained by low NSC availability in developing organs but not in mature organs grown in the dark. Emissions of volatiles were suppressed in the dark but after 1 h of re-illumination, emissions of both constitutive and induced monoterpene hydrocarbons recovered rapidly, whereas emissions of linalool and sesquiterpene produced via de novo synthesis did not recover. Our results highlight that light and/or carbon limitation may constrain constitutive and JA-induced biosynthesis of SM in coordination with growth, NSC storage and mobilization.

Root and shoot phenology and root longevity of Norway spruce saplings grown at different soil temperatures

Tree roots comprise a huge carbon pool. Their dynamics are driven by environmental factors and thereby affected by climate change. We studied the effects of soil temperature on root and shoot phenology and their linkages in Norway spruce (Picea abies (L.) Karst.). Saplings were grown in controlled-environment rooms for three simulated growing seasons (GS1, GS2, and GS3). Soil-temperature treatments of 9, 13, 18, and 21 °C were applied during GS2. Root growth was monitored with minirhizotrons and commenced in all treatments simultaneously. Temporal growth patterns of short and long roots were usually bimodal. Root growth was very low during the coldest treatment of GS2 but increased during GS3 as an aftereffect. During GS3, growth of short roots continued later after colder treatments than warmer treatments. Reduced sink strength of roots and increased carbohydrate accumulation into needles at 9 °C during GS2 probably enabled compensatory root growth under restored temperatures during GS3. Soil temperature did not affect shoot phenology, and root and shoot phenology varied between growing seasons; thus, the linkage of root and shoot phenology was inconsistent. In warmer soil, root longevity was shorter and turnover rate was higher than in colder soil. This can further affect soil carbon dynamics and ecosystem carbon cycling in boreal forest ecosystems.

Eyes on the future - evidence for trade-offs between growth, storage and defense in Norway spruce.

Carbon (C) allocation plays a central role in tree responses to environmental changes. Yet, fundamental questions remain about how trees allocate C to different sinks, for example, growth vs storage and defense. In order to elucidate allocation priorities, we manipulated the whole-tree C balance by modifying atmospheric CO2 concentrations [CO2 ] to create two distinct gradients of declining C availability, and compared how C was allocated among fluxes (respiration and volatile monoterpenes) and biomass C pools (total biomass, nonstructural carbohydrates (NSC) and secondary metabolites (SM)) in well-watered Norway spruce (Picea abies) saplings. Continuous isotope labelling was used to trace the fate of newly-assimilated C. Reducing [CO2 ] to 120ppm caused an aboveground C compensation point (i.e. net C balance was zero) and resulted in decreases in growth and respiration. By contrast, soluble sugars and SM remained relatively constant in aboveground young organs and were partially maintained with a constant allocation of newly-assimilated C, even at expense of root death from C exhaustion. We conclude that spruce trees have a conservative allocation strategy under source limitation: growth and respiration can be downregulated to maintain 'operational' concentrations of NSC while investing newly-assimilated C into future survival by producing SM.

Post-drought hydraulic recovery is accompanied by non-structural carbohydrate depletion in the stem wood of Norway spruce saplings

Hydraulic failure and carbon starvation are recognized as main causes of drought-induced forest decline. As water transport and carbon dynamics are strictly interdependent, it is necessary to clarify how dehydration-rehydration cycles are affecting the relations between stem embolism and non-structural carbohydrates (NSC). This is particularly needed for conifers whose embolism repair capability is still controversial. Potted Norway spruce saplings underwent two drought-re-irrigation cycles of same intensity, but performed in two consecutive summers. During the second cycle, stem percent loss of hydraulic conductivity (PLC) and NSC content showed no carry-over effects from the previous drought, indicating complete long-term recovery. The second drought treatment induced moderate PLC (20%) and did not affect total NSCs content, while starch was converted to soluble sugars in the bark. After one week of re-irrigation, PLC recovered to pre-stress values (0%) and NSCs were depleted, only in the wood, by about 30%. Our data suggest that spruce can repair xylem embolism and that, when water is newly available, NSCs stored in xylem parenchyma can be mobilized over short term to sustain respiration and/or for processes involved in xylem transport restoration. This, however, might imply dependency on sapwood NSC reserves for survival, especially if frequent drought spells occur.

Cambial response of Norway spruce to modified carbon availability by phloem girdling.

We tested the hypothesis that increase in carbon (C) availability in Norway spruce saplings (Picea abies (L.) Karst.) intensifies cambial cell division and increases cell lumen diameter (CLD) and cell wall thickness (CWT) when water availability is adequate. To accomplish this, we experimentally subjected 6-year-old P. abies saplings (n = 80 trees) to two levels of soil humidity (watered versus drought conditions) and manipulated tree C status by physically blocking phloem transport at three girdling dates (GDs). Stem girdling occurred in mid-March (day of the year (doy) 77) and in mid-May (GD doy 138), i.e., ~4 weeks before the onset of bud break and during vigorous stem growth, respectively, and in early July (GD doy 190), i.e., 6 and 4 weeks after cessation of radial growth in drought-stressed trees and shoot growth in both soil humidity (SH) treatments, respectively. In response to phloem blockage a striking increase in the number of xylem cells at all GDs and reactivation of cambial activity in drought-stressed trees was detected above the girdling zone, while below girdling xylem formation stopped in both SH-treatments. Although girdling differently affected wood anatomical parameters (CLD, CWT and CLD:CWT ratio) during earlywood and latewood formation, GD had a minor effect on cambial cell division and xylem cell differentiation. Results also revealed that phloem girdling outweighed drought effects imposed on cambial activity. We explain our findings by accumulation of carbohydrates, osmotically active sugars and/or C based signaling compound(s) in response to girdling. Altogether, we conclude that wood formation in P. abies saplings is limited by C availability, which is most likely caused by high C demand belowground especially under drought.

Deer browsing promotes Norway spruce at the expense of silver fir in the forest regeneration phase

Deer populations have dramatically increased over the last decades in Western Europe and their browsing has affected forest vegetation, especially plant community composition. High deer browsing pressure may threaten forest ecosystems and needs to be assessed over the long run. However, few studies to date have addressed the long-term impact of deer on forest regeneration.During one regeneration phase, we assessed the impact of deer (Cervus elaphus L. and Capreolus capreolus L.) browsing on mixed silver fir (Abies alba Mill.)/Norway spruce (Picea abies L. H. Karst.) stands in the Vosges Mountains in North-eastern France. For both tree species, we measured seedling and sapling density, height and diameter in 28 paired fenced – unfenced plots distributed over two sites that had been fenced 27years ago, for 10 and 23years respectively.We demonstrated that the presence of deer decreased the density, height and diameter of silver fir saplings, while it increased the height of Norway spruce saplings. We also noticed that the effect of fencing was very different depending on fencing duration, and that even 10years of fencing led to changes that were still visible 17years later.Our results confirm that deer browsing has a long-term impact on the regeneration of silver fir. Furthermore, they suggest that deer browsing may cause a species substitution, with Norway spruce gradually replacing silver fir. Such a trend would have an impact on the ecological and economical value of these forests. How browsing impacts the forest’s ability to adapt to global warming should also be considered, since browsing might impede the implementation of management policies designed to address this issue.

Stem girdling indicates prioritized carbon allocation to the root system at the expense of radial stem growth in Norway spruce under drought conditions

The early culmination of maximum radial growth (RG) in late spring has been found in several coniferous species in a dry inner Alpine environment. We hypothesized that an early decrease in RG is an adaptation to cope with drought stress, which might require an early switch of carbon (C) allocation to belowground organs. To test this hypothesis, we experimentally subjected six-year-old Norway spruce saplings (tree height: 1.35m; n=80 trees) to two levels of soil water availability (watered versus drought conditions) and manipulated tree C status by physically blocking phloem transport at three girdling dates (GD). The influence of C availability and drought on tree growth (radial and shoot growth; root biomass) in response to girdling was analyzed in both treatments. Non-structural carbohydrates (NSCs, soluble sugars and starch) were measured in the stem, root and current leader to evaluate changes in tree C status due to girdling. The main finding was a significant increase in RG of the girdled trees compared to the controls above the girdling zone (UZ). At all girdling dates the RG increase was significantly more intense in the drought-stressed compared with watered trees (c. 3.3 and 1.9-fold higher compared with controls in the drought-stressed and watered trees, respectively), most likely indicating that an early switch of C allocation to belowground occurs as an adaptation to maintain tree water status under drought conditions. Reactivation of the cambium after the cessation of its regular activity was detected in UZ in drought-stressed trees, while below the girdling zone no xylem formation was found and the NSC content was strikingly reduced. Irrespective of water availability, girdling before growth onset significantly reduced the progression of bud break (P<0.05) and the length of the current leader shoot by −47% (P<0.01) indicating a reduction in xylem hydraulic conductance, which was corroborated by significantly reduced xylem sap flow (P<0.001). Based on our findings, we conclude that during the growing season drought stress prioritizes an early switch of C allocation to the root system as an adaptation to maintain adequate tree water status in drought-prone environments.

Allocation to carbon storage pools in Norway spruce saplings under drought and low CO2.

Non-structural carbohydrates (NSCs) are critical to maintain plant metabolism under stressful environmental conditions, but we do not fully understand how NSC allocation and utilization from storage varies with stress. While it has become established that storage allocation is unlikely to be a mere overflow process, very little empirical evidence has been produced to support this view, at least not for trees. Here we present the results of an intensively monitored experimental manipulation of whole-tree carbon (C) balance (young Picea abies (L.) H Karst.) using reduced atmospheric [CO2] and drought to reduce C sources. We measured specific C storage pools (glucose, fructose, sucrose, starch) over 21 weeks and converted concentration measurement into fluxes into and out of the storage pool. Continuous labeling ((13)C) allowed us to track C allocation to biomass and non-structural C pools. Net C fluxes into the storage pool occurred mainly when the C balance was positive. Storage pools increased during periods of positive C gain and were reduced under negative C gain. (13)C data showed that C was allocated to storage pools independent of the net flux and even under severe C limitation. Allocation to below-ground tissues was strongest in control trees followed by trees experiencing drought followed by those grown under low [CO2]. Our data suggest that NSC storage has, under the conditions of our experimental manipulation (e.g., strong progressive drought, no above-ground growth), a high allocation priority and cannot be considered an overflow process. While these results also suggest active storage allocation, definitive proof of active plant control of storage in woody plants requires studies involving molecular tools.

Short-term impacts of energy wood harvesting on ectomycorrhizal fungal communities of Norway spruce saplings.

The increased demand for harvesting energy wood raises questions about its effects on the functioning of the forest ecosystems, soil processes and biodiversity. Impacts of tree stump removal on ectomycorrhizal fungal (EMF) communities of Norway spruce saplings were studied with 454-pyrosequencing in a 3-year field experiment replicated in 3 geographical areas. This is possibly the most thorough investigation of EMF communities associated with saplings grown on sites subjected to energy wood harvesting. To separate impacts of tree stump and logging residue removal on EMF and plant variables, we used three harvesting treatments with increasing complexity from patch mounding alone (P) to patch mounding combined with logging residue removal (RP), and patch mounding combined with both logging residue and stump removal (SRP). Saplings grown in uncut forests (F) served as references for harvesting treatments. A majority of sequences (>92%) and operational taxonomic units (OTUs, 55%) were assigned as EMF. EMF OTU richness, fungal community composition or sapling growth did not differ between harvesting treatments (P, RP and SRP), while EMF OTU richness, diversity and evenness were highest and sapling growth lowest in the undisturbed reference forests (F). The short study period may partially explain the similarities in fungal and sapling variables in different harvesting treatments. In conclusion, our results indicate that neither stump removal nor logging residue removal have significant additional negative impacts on EMF communities or growth of Norway spruce saplings in the short-term compared with the impacts of more conventional harvesting methods, including clear cutting and patch mounding.

Flavan-3-ols in Norway spruce: biosynthesis, accumulation, and function in response to attack by the bark beetle-associated fungus Ceratocystis polonica.

Proanthocyanidins (PAs) are common polyphenolic polymers of plants found in foliage, fruit, bark, roots, rhizomes, and seed coats that consist of flavan-3-ol units such as 2,3-trans-(+)-catechin and 2,3-cis-(-)-epicatechin. Although the biosynthesis of flavan-3-ols has been studied in angiosperms, little is known about their biosynthesis and ecological roles in gymnosperms. In this study, the genes encoding leucoanthocyanidin reductase, a branch point enzyme involved in the biosynthesis of 2,3-trans-(+)-flavan-3-ols, were identified and functionally characterized in Norway spruce (Picea abies), the most widespread and economically important conifer in Europe. In addition, the accumulation of flavan-3-ols and PAs was investigated in Norway spruce saplings after wounding or inoculation with the fungal pathogen Ceratocystis polonica, which is vectored by bark beetles (Ips typographus) and is usually present during fatal beetle attacks. Monomeric and dimeric flavan-3-ols were analyzed by reverse-phase high-pressure liquid chromatography, while the size and subunit composition of larger PAs were characterized using a novel acid hydrolysis method and normal phase chromatography. Only flavan-3-ol monomers with 2,3-trans stereochemistry were detected in spruce bark; dimeric and larger PAs contained flavan-3-ols with both 2,3-trans and 2,3-cis stereochemistry. Levels of monomers as well as PAs with a higher degree of polymerization increased dramatically in spruce bark after infection by C. polonica. In accordance with their role in the biosynthesis of 2,3-trans-(+)-flavan-3-ols, transcript abundance of Norway spruce LEUCOANTHOCYANIDIN REDUCTASE genes also increased significantly during fungal infection. Bioassays with C. polonica revealed that the levels of 2,3-trans-(+)-catechin and PAs that are produced in the tree in response to fungal infection inhibit C. polonica growth and can therefore be considered chemical defense compounds.

Thirst beats hunger – declining hydration during drought prevents carbon starvation in Norway spruce saplings

Drought-induced tree mortality results from an interaction of several mechanisms. Plant water and carbon relations are interdependent and assessments of their individual contributions are difficult. Because drought always affects both plant hydration and carbon assimilation, it is challenging to disentangle their concomitant effects on carbon balance and carbon translocation. Here, we report results of a manipulation experiment specifically designed to separate drought effects on carbon and water relations from those on carbon translocation. In a glasshouse experiment, we manipulated the carbon balance of Norway spruce saplings exposed to either drought or carbon starvation (CO2 withdrawal), or both treatments, and compared the dynamics of carbon exchange, allocation and storage in different tissues. Drought killed trees much faster than did carbon starvation. Storage C pools were not depleted at death for droughted trees as they were for starved, well-watered trees. Hence drought has a significant detrimental effect on a plant's ability to utilize stored carbon. Unless they can be transported to where they are needed, sufficient carbon reserves alone will not assure survival of a drought except under specific conditions, such as moderate drought, or in species that maintain plant water relations required for carbon re-mobilization.

Ozone fumigation effects on the morphology and biomass of Norway spruce (Picea abies L.) saplings

Abstract: The study examined Norway spruce (Picea abies) saplings morphological and biomass sensitivity to ozone fumigation using closed indoor chambers of controlled environment. 4-year-old potted saplings were exposed to three different ozone concentrations: 80 µg/m3, 160 µg/m3, and 240 µg/m3 (7 h/day, 5 days/week). Half of the saplings were harvested after the exposure, and the second half of the saplings were left in the pots in open field until next autumn. The reaction of the saplings of different timing of bud burst was also investigated. The terminal shoot length and the total current year shoot length of Norway spruce saplings after one month of ozone fumigation were significantly (p<0.05) suppressed in all the treatments comparing to the control saplings. The needles of saplings fumigated with ozone were smaller than the needles of control saplings. No significant changes of the biomass of different fractions of Norway spruce saplings were determined right after the fumigation, as well as, in 14 month after the cessation of the fumigation. Norway spruce saplings of early and late timing of bud burst reacted differently to ozone fumigation during the active growth period. The formation of new needles and shoots of the saplings of late bud burst stage was more suppressed comparing to the saplings of the early bud burst stage. The results suggest that the generatively younger organs during their formation are more susceptible to ozone stress. The differences of the needle age between ozone affected and control saplings decreased in one year after the end of fumigation keeping affected Norway spruce saplings in the open field and thus indicating the start of the recovery process.