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A 7-year study was conducted to examine the growth (diameter and root) response of Norway spruce (Picea abies (L.) Karst.) seedlings to elevated CO2 (CO2ELV, 770 μmol (CO2) mol−1) in different mixture types (monospecific (M): a Norway spruce seedling surrounded by six spruce seedlings, group-admixture (G): a spruce seedling surrounded by three spruce and three European beech seedlings, single-admixture (S): a spruce seedling surrounded by six beech seedlings). After seven years of treatments, no significant effect from elevated CO2 was found on the root dry mass (p = 0.90) and radial growth (p = 0.98) of Norway spruce. Neither did we find a significant interaction between [CO2] × mixing treatments (p = 0.56), i.e. there was not a significant effect of CO2 concentrations [CO2] in all the admixture types. On the contrary, spruce responses to admixture treatments were significant under CO2AMB (p = 0.05), which demonstrated that spruce mainly increased its growth (diameter and root) in M and neighbouring with beech was not favourable for spruce seedlings. In particular, spruce growth diminished when growing beside high proportions/numbers of European beech (S). Here, we also evaluated the association between tree-ring formation and climatic variables (precipitation and air temperature) in different admixture types under elevated and ambient CO2 (CO2AMB, 385 μmol (CO2) mol−1). Overall, our result suggests that spruce responses to climate factors can be affected by tree species mixing and CO2 concentrations, i.e. the interaction between climatic variables × admixture types × [CO2] could alter the response of spruce to climatic variables.

Effect of drought during 2017 and 2018 resulted in radial stem increment reduction to 78% and 61%, respectively, of the levels occurring in normal year 2016 in Central Europe. Norway spruce (Picea abies (L.) Karst.) is currently the most threatened commercial tree species in Central Europe. This is due to increased drought stress from advancing climate change as well as the species’ distribution outside its natural range. Tree water status and water movement through a tree are key parameters influencing tree growth and vitality. This study is focused on the growth and stress reaction of spruce to climatic conditions, analysing stem diameter variation along an elevation gradient (381–995 m a.s.l.) in the Czech Republic. Tree water deficit based on the zero-growth concept (TWD), calculated from high-frequency dendrometer records and the temporal dynamics of radial growth, was studied for 3 years (2016–2018). Two of these 3 years were affected by severe drought during the growing season. Contrary to our expectations, the observed TWD showed no clear linear decline with rising elevation. The most severe tree desiccation was observed in experimental sites at middle elevations of about 600 m a.s.l. Here, we show that both the timing and level of tree water deficit had an impact on annual stem radial increment (SRIannual). Severe drought had a substantial negative impact on SRIannual of Norway spruce in both 2017 and 2018. Drought conditions in 2017 and 2018 resulted in reduction of SRIannual relative to measurements for the wetter year in 2016 to 78% and 61%, respectively. We report the evidence that the current climatic conditions in the Central European region are not suitable for growing Norway spruce at lower and middle elevations and that forest management needs to react immediately to this situation.

This paper explores the effects of three types of admixture treatments: (1) monospecific (M: European beech surrounded by six European beech seedlings), (2) single-admixture (S: European beech surrounded by six Norway spruce seedlings), and (3) group-admixture (G: European beech surrounded by three Norway spruce and three European beech seedlings), and two different CO2 concentrations ([CO2]): ambient [AMBCO2, 385 μmol (CO2) mol−1] and elevated [ELECO2, 770 μmol (CO2) mol−1] on the stem diameter increment (DI), based on a 7-year monitoring of the diameter growth of European beech (Fagus sylvatica L.) seedlings. Furthermore, to improve our understanding of the influence of climatic variables, we assessed the effects of precipitation and temperature on radial growth. After 7 years’ experience (irrespective of admixture treatment), our data were not able to confirm the effect of elevated CO2 on the diameter growth (p value = 0.35), but the result was changed when the effect of elevated CO2 was considered under the different types of admixture. Elevated CO2 along with single-admixture increased the diameter increment significantly (p value = 0.001). In contrast, we characterized a significant effect of AMBCO2 × G interaction on DI (p value = 0.002). But DI was unaffected by elevated CO2 in M (p value = 0.77). In both [CO2], inter-specific competition with spruce resulted in the highest radial growth. The inter-specific interaction was most pronounced in the lower proportion with spruce (S) in ELECO2, while in ambient CO2, the higher proportion with spruce (G) had the greatest effect on the radial growth. With respect to the climatic factors, our observations showed that temperature had a stronger influence than precipitation in ELECO2, but in AMBCO2, precipitation had the strongest effect on the radial growth as indicated by the statistically significant correlation between climatic variables and radial growth. Overall, our result suggested that seedlings growth was more under the control of climate and edaphic factors than dependent on tree species diversity and CO2 concentrations.

The strong effects of climate change are expected to negatively impact the long-term resilience and function of forest ecosystems, which could lead to changes in forest carbon balance and productivity. However, these forest responses may vary with local conditions and forest types. Accordingly, this study was carried out to determine gross primary productivity (GPP) sensitivity to changes in environmental parameters. Central European beech (at Štítná) and spruce species (at Bílý Kr̆íz̆ and Rájec), growing under contrasting climatic conditions, were studied. The comparative analyses of GPP were based on a five-year-long dataset of eddy covariance fluxes during the main growing season (2012–2016). Results of forest GPP responses with changes in environmental factors from a traditional Stepwise multiple linear regression model (SMLR) were used and compared with Random forest (RF) analyses. To demonstrate how actual GPP trends compare to potential GPP (GPPpot) courses expected under near-optimal environmental conditions, we computed normalized GPP (GPPnorm) with values between 0 and 1 as the ratio of the estimated daily sum of GPP to GPPpot. The study confirmed the well-known effect of total intensity of the photosynthetically active radiation and its diffuse fraction on GPPnorm across all the forest types. However, the study also showed the secondary effects of other environmental variables on forest productivity depending on the species and local climatic conditions. The reduction in forest productivity at the beech forest in Štítná was presumed to be mainly induced by edaphic drought (anisohydric behaviour). In contrast, reduced forest productivity at the spruce forest sites was presumably induced by both meteorological and hydrological drought events, especially at the moderately dry climate in Rájec. Overall, our analyses call for more studies on forest productivity across different forest types and contrasting climatic conditions, as this productivity is strongly dependent on species type and site-specific environmental conditions.

The main aim of the study is to investigate general and temporal characteristics of wind speed and direction at Ecosystem station (ES) Rajec located in southern highlands of the Czech Republic which is part of Czech Carbon Observation System (CzeCOS) network. Four years (2013-16) of eddy co-variance data from mature monoculture spruce (Picea abies) forest was used to build the wind rose and analyze the wind characteristics. The prevailing wind directions at ES Rajec were South-East and North-West and general orography of region being a highland does not impact the wind flow. Seasonal variation in the wind was observed which was mainly due to general circulation. The paper also investigates the occurrence of calm wind conditions (u < 1 m s-1) which was 6% on an average for four years and the average of day-time and night-time calm conditions were observed as 8% and 4% respectively.

One of the greatest threats posed by ongoing climate change may be regarded the drought caused by changes in precipitation distribution. The aim of presented study was to characterize reactions to dry conditions and conditions without drought stress on gross primary production (GPP) and net ecosystem production (NEP) of spruce and beech forests, as these two species dominate within the European continent. Daily courses of GPP and NEP of these two species were evaluated in relation to an expected decrease in CO2 uptake during dry days. The occurrence of CO2 uptake hysteresis in daily production was also investigated. Our study was performed at Bilý Křiž (spruce) and Stitna (beech) mountain forest sites during 2010–2012 period. We applied eddy covariance technique for the estimation of carbon fluxes, vapor pressure deficit and precipitation characteristics together with the SoilClim model for the determination of drought conditions, and the inverse of the Penman–Monteith equation to compute canopy conductance. Significant differences were found in response to reduced water supply for both species. Spruce reacts by closing its stomata before noon and maintaining a reduced photosynthetic activity for the rest of the day, while beech keeps its stomata open as long as possible and slightly reduces photosynthetic activity evenly throughout the entire day. In the spruce forest, we found substantial hysteresis in the light response curve of GPP. In the beech forest, the shape of this curve was different: evening values exceeded morning values.

Accurate wind analyses using six wind classes and twelve splitting directions were done to deeply evaluate wind conditions on Štítná CzeCOS’s ecosystem station in the Czech Republic. The analysis brings information about contribution of different part of the research-forested area to the measurement of CO2 exchange between the studied ecosystem and atmosphere. Štítná station is located inside of a forest composed of Fagus sylvatica with age 114 years and the forest can be harvested sometime forward. Total of 82 % of the wind contributions speed are in the range of 1.0 - 6.0 m s-1 and the major accumulation of winds comes from SE (9 %), SSE (17 %) and S (14 %); 13 % were calm periods. The obtained information will be useful for evaluate the conditions of the use of the eddy covariance technique in the research area.

This investigation examined the effects of two different carbon dioxide concentrations ([CO2]): Ambient (A, 385 μmol (CO2) mol−1) and elevated (E, A+385 μmol (CO2) mol−1)) on the tree-ring width and early to latewood proportion in Norway spruce for seven years (2006-2012). Further, to improve our understanding of the influence of climatic variables, we assessed the effects of precipitation and temperature. Our observations showed that spruce trees growing under elevated CO2 (EC) formed less early (p > 0.05) and latewood (p < 0.05) and hence smaller annual increments (p > 0.05) than trees in ambient CO2 (AC). Early to latewood proportion was nearly 73% and 75% in AC and EC, respectively. In both CO2 concentrations, the largest tree-rings and earlywood width was observed during 2009 and 2010, which is coincident with the highest precipitation in May (2010) and the highest air temperature in April (2009). Moreover, to determine the association between the latewood formation and air temperature during the second half of the growing season, and correlation between the earlywood formation and precipitation during the first half of the growing season we run Spearman’s correlation test, the determination coefficient values for latewood formation were r = 0.45 (AC) and r = 0.68 (EC), and for earlywood formation were r = 0.53 (AC) and r = 0.42 (EC), although coefficient values were not statistically significant (p > 0.05). Also, our study indicated that temperature had stonger influence than precipitation in EC, but in AC precipitation had the strongest effect on radial growth.

A long-term context is important for understanding past climatic variability. Although tree-ring widths (TRWs) are widely used as a proxy for reconstructing past climate, the use of annually-resolved values of δ13C and δ18O tree-ring stable isotopes (TRSIs) is increasing and may provide further valuable information. Here, we present a 487-year-long TRW chronology and 240-year-long TRSI chronology for Bosnian pine (Pinus heldreichii H. Christ) and compare them to each other. We demonstrate that both δ13C and δ18O values are better proxies for temperature, precipitation, and drought than TRW. The correlations between these climate parameters and TRSIs are strongest for the combined summer (JJA) period. The results of temporal and spatial field correlation indicate that TRSI chronologies are stable, reliable proxies for JJA precipitation reconstruction over the whole Balkan Peninsula and surrounding eastern Mediterranean region. However, the stability of the temperature signal of the both δ13C and δ18O chronologies declines after the 1950s. Our work supports the emerging evidence that TRSI data track climate variability more accurately than a conventional TRW approach and can be subsequently used for the reconstruction of past climate.

Recent climate warming has shifted the timing of spring and autumn vegetation phenological events in the temperate and boreal forest ecosystems of Europe. In many areas spring phenological events start earlier and autumn events switch between earlier and later onset. Consequently, the length of growing season in mid and high latitudes of European forest is extended. However, the lagged effects (i.e. the impact of a warm spring or autumn on the subsequent phenological events) on vegetation phenology and productivity are less explored. In this study, we have (1) characterised extreme warm spring and extreme warm autumn events in Europe during 2003-2011, and (2) investigated if direct impact on forest phenology and productivity due to a specific warm event translated to a lagged effect in subsequent phenological events. We found that warmer events in spring occurred extensively in high latitude Europe producing a significant earlier onset of greening (OG) in broadleaf deciduous forest (BLDF) and mixed forest (MF). However, this earlier OG did not show any significant lagged effects on autumnal senescence. Needleleaf evergreen forest (NLEF), BLDF and MF showed a significantly delayed end of senescence (EOS) as a result of extreme warm autumn events; and in the following year's spring phenological events, OG started significantly earlier. Extreme warm spring events directly led to significant (p=0.0189) increases in the productivity of BLDF. In order to have a complete understanding of ecosystems response to warm temperature during key phenological events, particularly autumn events, the lagged effect on the next growing season should be considered.

We evaluated the long-term pattern of leaf area index (LAI) dynamics and radiation use efficiency (RUE) in short rotation poplar in uncoppice (single stem) and coppice (multi-stem) plantations, and compared them to annual field crops (AFCs) as an alternative for bioenergy production while being more sensitive to weather fluctuation and climate change. The aim of this study was to evaluate the potential of LAI and RUE as indicators for bioenergy production and indicators of response to changing environmental conditions. For this study, we selected poplar clone J-105 (Populus nigra L. × P. maximowiczii A. Henry) and AFCs such as barley (Hordeum vulgare L.), wheat (Triticum aestivum L.), maize (Zea mays L.), and oilseed rape (Brassica napus L.), and compared their aboveground dry mass (AGDM) production in relation to their LAI development and RUE. The results of the study showed the long-term maximum LAI (LAImax) to be 9.5 in coppice poplar when compared to AFCs, where LAImax did not exceed the value 6. The RUE varied between 1.02 and 1.48 g MJ−1 in short rotation poplar and between 0.72 and 2.06 g MJ−1 in AFCs. We found both LAI and RUE contributed to AGDM production in short rotation poplar and RUE only contributed in AFCs. The study confirms that RUE may be considered an AGDM predictor of short rotation poplar and AFCs. This may be utilized for empirical estimates of yields and also contribute to improve the models of short rotation poplar and AFCs for the precise prediction of biomass accumulation in different environmental conditions.

Root structure parameters, root biomass and allometric relationships between above- and belowground biomass were investigated in young Norway spruce (Picea abies [L.] Karst.) trees cultivated inside the glass domes with ambient (AC, 375 μmol(CO2) mol−1) and elevated (EC, A + 375 μmol(CO2) mol−1) atmospheric CO2 concentrations ([CO2]). After 8 years of fumigation, a mean EC tree in comparison with AC one exhibited about 37 % higher belowground biomass. The growth of primary root structure was unaffected by elevated [CO2]; however, the biomass of secondary roots growing on the primary root structure and the biomass of secondary roots growing in the zone between the soil surface and the first primary root ramification were significantly higher in EC comparing with AC treatment about 58 and 70 %, respectively. The finest root’s (diameter up to 1 mm) biomass as well as length and surface area of both primary and secondary root structures showed the highest difference between the treatments; advancing EC to AC by 43 % on average. Therefore, Norway spruce trees cultivated under well-watered and rather nitrogen-poor soil conditions responded to the air elevated [CO2] environment by the enhancement of the secondary root structure increment, by enlargement of root length and root absorbing area, and also by alternation of root to aboveground organ biomass proportion. Higher root to leaf and root to stem basal area ratios could be beneficial for Norway spruce trees to survive periods with limited soil water availability.

Norway spruce (Picea abies L. Karst) grown under ambient (365-377 μmol(CO(2)) mol(-1); AC) and elevated (700 μmol(CO(2)) mol(-1); EC) CO(2) concentrations within glass domes with automatically adjustable windows and on an open-air control site were studied after 8 years of treatment. The effect of EC on photosynthesis, mesophyll structure and phenolics accumulation in sun and shade needles was examined. Photosynthetic assimilation and dark respiration rates were measured gasometrically; the structural parameters of mesophyll were determined using confocal microscopy and stereological methods. The contents of total soluble phenolics and lignin were assessed spectrophotometrically, and localizations of different phenolic groups were detected histochemically on needle cross-sections. EC enhanced the light-saturated CO(2) assimilation rate and reduced dark respiration in the current-year needles. No effects of CO(2) enrichment on mesophyll structural parameters were observed. Similarly, the accumulation and localization of phenolics and lignin remained unaffected by EC treatment. Needles differentiated into sun and shade ecotypes in the same manner and to the same extent irrespective of CO(2) treatment. Based on these results, it is apparent that the EC-induced enhancement of photosynthesis is not related to changes in the examined structural parameters of mesophyll and accumulation of phenolic compounds.

Studies of selected morphological needle parameters were carried out on young (17–19 year old) Norway spruce trees cultivated inside glass domes at ambient (A, 370 μmol (CO2) mol−1) and elevated (E, 700 μmol (CO2) mol−1) atmospheric CO2 concentrations [CO2] beginning in 1997. Annual analyses performed from 2002 to 2004 revealed higher values for needle length (especially for current needles, up to 18%) and projected needle area (up to 13%) accompanied by lower values for specific needle area (up to 15% lower, as quantified by needle mass to projected area ratio) in the E treatment compared to the A treatment. Statistically significant differences for most of the investigated morphological parameters were found in young needles in the well irradiated sun-adapted crown parts, particularly under water-limiting soil conditions in 2003. This was likely a result of different water relations in E compared to A trees as investigated under temperate water stress (Kuper et al. in Biol Plantarum 50:603–609, 2006). Furthermore, E trees had much higher absorbing root area, which modified and enhanced root:shoot as well as root:conductive stem area proportions. These hydraulic properties and early seasonal stimulation of photosynthesis forced advanced needle development in E trees, particularly under limited soil water conditions. The number of needles per unit shoot length was found to be unaffected by elevated [CO2].

Measurements of stem respiration were conducted for a period of four years (1999–2002) in 14-year old Norway spruce (Picea abies [L.] Karst) trees exposed to ambient (CA) and elevated CO2 concentration (CE; ambient plus 350 μmol mol−1). Stem respiration measurements of six trees per treatment were carried out 2–3 times per month during the growing season. Stem respiration in CE treatment was higher (up to 16 %) than in CA treatment. Temperature response of stem respiration (Q10) for the whole experimental period ranged between 1.65–2.57 in CA treatment and 2.24–2.56 in CE treatment. The mean stem respiration rate normalized to 10 °C (R10) in CA and CE treatments ranged between 1.67–1.95 and 2.19–2.72 μmol(CO2) m−2 s−1, respectively. Seasonal variations in stem respiration were related to temperature and tree growth.

Bud phenology and shoot elongation growth were monitored on Norway spruce ( Picea abies (L.) Karst.) trees grown inside glass domes with adjustable windows for six years under ambient (355 µmol CO 2 ∙mol -1 ) and elevated (700 µmol CO 2 ∙mol -1 ) atmospheric CO 2 concentrations CO 2 . Each treatment consisted of two stand densities - sparse (5,000 trees∙ha -1 ) and dense (10,000 trees∙ha -1 ). The age of spruce trees was 10 years at the beginning of the experiment. Elevated CO 2 slightly accelerated the consequential bud germinating phases and it significantly induced shoot elon - gation growth, especially of sun-exposed shoots in a stand with sparse density. This accelerated growth lasted one to three weeks after full bud development in E compared to A. At the end of the growing season the total shoot length did not show any differences between the treatments. We supposed that limiting nitrogen supply to needles slowed down subsequent shoot elongation growth in E treatment. Nevertheless, faster shoot growth in elevated CO 2 conditions can enhance the carbon sink in spruce due to prolongation of the growing season.

The hypothesis that elevated CO2 leads to a faster induction of photosynthesis was tested using 7–8-year-old seedlings of broadleaved Fagus sylvatica and coniferous Picea abies exposed for three growing seasons to ambient (385 μmol mol−1; AC) and elevated CO2 (700 μmol mol−1; EC). Since the photosynthetic induction is primarily determined by light modulations of Rubisco activity and stomata opening, the hypothesis was based on the following presumptions: (1) EC reduces the content of Rubisco in leaves, (2) decreases stomatal conductance, and (3) has no effect on the rates of stomatal opening and Rubisco activation upon illumination. Thus, reduced maxima of Rubisco activity and stomatal conductance should be reached faster in EC compared to AC plants after leaf transition from dark to light. The initial presumptions were confirmed, since reductions of Rubisco content (up to 28% and 48%) and light-saturated stomatal conductance (GSmax; up to 40% and 50%) were observed in EC treated F. sylvatica and P. abies as compared to AC ones. However, the presumption of constant induction rates was not confirmed. A slight decrease of the time constant for Rubisco activation (14–27%) was observed as the result of EC treatment in both tree species, whereas stomatal opening rates significantly decreased in F. sylvatica (up to 48%) and remained almost unchanged in P. abies. Thus, EC treatment led to the stimulation of the initial phase of photosynthetic induction. This was demonstrated by higher values of the induction state 60 s after leaf illumination (IS60), determined in both F. sylvatica (up to 129%) and P. abies (up to 108%) as compared to AC treatment. In contrast, the stimulation of the secondary phase of photosynthetic induction, reflecting mainly stomatal opening and described by the time required to reach 90% of maximum steady-state photosynthesis (T90(A)), was only 5–15% in F. sylvatica (non-significant) and 21–28% in P. abies (significant). The reduced rates of stomatal opening by EC treatment thus may limit the general validity of the hypothesis.

Stem wood density (SWD) of young Norway spruce trees ( Picea abies (L.) Karst.) growing at ambient (A variant, 350 µmol(CO 2 )/mol) and elevated ( E variant, A + 350 µmol(CO 2 )/mol) atmospheric CO concentration inside of the glass domes with adjustable windows was estimated after six and eight years of the cultivation. Stand density of two subvariants ( s - sparse with ca 5,000 trees/ha and d - dense with ca 10,000 trees/ha) and thinning impact (intensity of 27%) on SWD and its variation along the stem vertical profile were investigated. After six years of CO 2 fumigation, stems of sparse subvariant had about 10% lower values of SWD comparing to dense ones, although the difference was not statistically significant. In 2004 (two years after thinning), the SWD values were higher in all subvariants along the whole stem vertical profile. This increase was more obvious in E variant (about 6% in d subvariant and only 3% in s subvariant). The highest increase of SWD values was found in Ed subvariant, particularly in the middle stem part (about 8%, statistically significant increase).

Temperature responses of carbon assimilation processes were studied in four dominant species from mountain grassland ecosystem, i.e. Holcus mollis (L.), Hypericum maculatum (Cr.), Festuca rubra (L.), and Nardus stricta (L.), using the gas exchange technique. Leaf temperature (T L) of all species was adjusted within the range 13–30 °C using the Peltier thermoelectric cooler. The temperature responses of metabolic processes were subsequently modelled using the Arrhenius exponential function involving the temperature coefficient Q 10. The expected increase of global temperature led to a significant increase of dark respiration rate (R D; Q 10 = 2.0±0.5), maximum carboxylation rate (V Cmax; Q 10 = 2.2±0.6), and maximum electron transport rate (J max; Q 10 = 1.6±0.4) in dominant species of mountain grassland ecosystems. Contrariwise, the ratio between J max and V Cmax linearly decreased with T L [y = −0.884 T L + 5.24; r 2 = 0.78]. Hence temperature did not control the ratio between intercellular and ambient CO2 concentration, apparent quantum efficiency, and photon-saturated CO2 assimilation rate (P max). P max primarily correlated with maximum stomatal conductance irrespective of T L. Water use efficiency tended to decrease with T L [y = −0.21 T L + 8.1; r 2 = 0.87].

The differential pigment composition and photosynthetic activity of sun and shade leaves of deciduous (Acer pseudoplatanus, Fagus sylvatica, Tilia cordata) and coniferous (Abies alba) trees was comparatively determined by studying the photosynthetic rates via CO(2) measurements and also by imaging the Chl fluorescence decrease ratio (R(Fd)), which is an in vivo indicator of the net CO(2) assimilation rates. The thicker sun leaves and needles in all tree species were characterized by a lower specific leaf area, lower water content, higher total chlorophyll (Chl) a+b and total carotenoid (Cars) content per leaf area unit, as well as higher values for the ratio Chl a/b compared to the much thinner shade leaves and needles that possess a higher Chl a+b and Cars content on a dry matter basis and higher values for the weight ratio Chls/Cars. Sun leaves and needles exhibited higher rates of maximum net photosynthetic CO(2) assimilation (P(Nmax)) measured at saturating irradiance associated with higher maximum stomatal conductance for water vapor efflux. The differences in photosynthetic activity between sun and shade leaves and needles could also be sensed via imaging the Chl fluorescence decrease ratio R(Fd), since it linearly correlated to the P(Nmax) rates at saturating irradiance. Chl fluorescence imaging not only provided the possibility to screen the differences in P(N) rates between sun and shade leaves, but in addition permitted detection and quantification of the large gradients in photosynthetic rates across the leaf area existing in sun and shade leaves.

Leaf area index (LAI) is the most appropriate parameter for analyzing canopy structure and crop productivity. LAI and radiation use efficiency (RUE) were estimated to evaluate the productivity of a short rotation coppice culture of a poplar clone. RUE was calculated as the ratio between total aboveground woody biomass and available photosynthetic active radiation (PAR) accumulated during one growing season. Prior to coppicing, LAI reached a maximum value of 7.3 (in 2009), whereas the maximum LAI after coppicing was 6.8 (in 2012). The maximum RUE reached prior to coppicing was 0.25 g mol(-1) (in 2009), while after coppicing it was 0.20 g mol(-1) (in 2012), which did not represent a significant difference (p> 0.05).

Calamagrostis arundinacea L. (Roth.) and C. villosa (Chaix.) J.F. Gmel are two grass species substituting forest communities on deforested areas in Central Europe. They were exposed to enhanced ultraviolet-B (UV-B, λ = 290–320 nm) radiation during 22 weeks. A system of modulated lamps operating under field conditions was used to simulate a 25 % increase of incident UV-B radiation. CO2 assimilation seemed to be limited by a decrease of stomatal conductance (g s) in C. arundinacea, whereas carboxylation activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) was not affected. On the contrary, g s and RuBPCO activity decreased in C. villosa. These physiological adjustments resulted in growth changes; above-ground biomass decreased in C. villosa (prevailing negative effect) and significantly increased in C. arundinacea (prevailing positive effect) in response to enhanced UV-B radiation.

Background and aims Plants growing under elevated atmospheric CO2 concentrations often have reduced stomatal conductance and subsequently increased leaf temperature. This study therefore tested the hypothesis that under long-term elevated CO2 the temperature optima of photosynthetic processes will shift towards higher temperatures and the thermostability of the photosynthetic apparatus will increase. Methods The hypothesis was tested for saplings of broadleaved Fagus sylvatica and coniferous Picea abies exposed for 4-5 years to either ambient (AC; 385 µmol mol(-1)) or elevated (EC; 700 µmol mol(-1)) CO2 concentrations. Temperature response curves of photosynthetic processes were determined by gas-exchange and chlorophyll fluorescence techniques. Key results Initial assumptions of reduced light-saturated stomatal conductance and increased leaf temperatures for EC plants were confirmed. Temperature response curves revealed stimulation of light-saturated rates of CO2 assimilation (Amax) and a decline in photorespiration (RL) as a result of EC within a wide temperature range. However, these effects were negligible or reduced at low and high temperatures. Higher temperature optima (Topt) of Amax, Rubisco carboxylation rates (VCmax) and RL were found for EC saplings compared with AC saplings. However, the shifts in Topt of Amax were instantaneous, and disappeared when measured at identical CO2 concentrations. Higher values of Topt at elevated CO2 were attributed particularly to reduced photorespiration and prevailing limitation of photosynthesis by ribulose-1,5-bisphosphate (RuBP) regeneration. Temperature response curves of fluorescence parameters suggested a negligible effect of EC on enhancement of thermostability of photosystem II photochemistry. Conclusions Elevated CO2 instantaneously increases temperature optima of Amax due to reduced photorespiration and limitation of photosynthesis by RuBP regeneration. However, this increase disappears when plants are exposed to identical CO2 concentrations. In addition, increased heat-stress tolerance of primary photochemistry in plants grown at elevated CO2 is unlikely. The hypothesis that long-term cultivation at elevated CO2 leads to acclimation of photosynthesis to higher temperatures is therefore rejected. Nevertheless, incorporating acclimation mechanisms into models simulating carbon flux between the atmosphere and vegetation is necessary.

Total in vitro activity of RuBPCO (ribulose-1,5-bisphosphate carboxylase/oxygenase) enzyme was assayed spectrophotometrically by the continuous measurement of 3-phosphoglycerate-dependent NADH oxidation in a coupled enzyme system. RuBPCO activities were found in the ranges 1.01–2.76 and 1.23–3.10 µmol(CO2) m−2 s− 1 in current Norway spruce needles growing in ambient (AC) and elevated (EC) CO2 concentration, respectively. RuBPCO activity in AC needles from the upper layer (U) was 11–15 % higher compared to those from the middle (M) layer, and even 44–56 % higher compared to the lower (L) layer of spruce crown. Over the vegetation season, we observed a highly significant decrease of RuBPCO activity in the EC-U needles from 3.10 (July) to 1.60 (October) µmol(CO2) m−2 s−1 as a consequence of downward feedback regulation. Moreover, this down-regulation was not caused by a non-specific decrease in total leaf nitrogen content.

Diurnal courses of net CO2 assimilation, non-assimilatory processes, electron transport rate, photosystem (PS) II photochemical efficiency, and pigment composition were investigated during summer days for sun exposed needles of Norway spruce trees grown under ambient (AC) and/or elevated (EC; 700 mu mol (CO2) mol(-1)) atmospheric carbon dioxide concentration ([CO2]). Daily courses of net CO2 assimilation (AN c,) documented significantly higher values for trees cultivated under EC conditions at irradiances above 250 mu mol m(-2) s(-1). In comparison with the AC variant, EC treatment led to the diminution of midday photosynthesis depression that was predominantly caused by stomatal closure and subsequent decrease of intercellular [CO2] (Ci). A partial recovery of assimilation ability of AC shoots correlated with the partial restoration of stomatal conductivity during the afternoon hours. On the contrary, maximum depression of light-saturated assimilation rate (A(Nmax)), permanent decrease of assimilation capacity (A(Nsat)) over the day and an atypical daily course of gross photosynthesis (P-act) suggested an increased contribution of non-stomatal processes in a down-regulation of carboxylation efficiency in EC shoots during the noon and afternoon hours. The relatively high potential quantum yield of PS II photochemistry (F-V/F-M >= 0.8), estimated on both AC and EC dark adapted needles throughout the day, confirmed that PS II photoinhibition was not the primary reason of the midday depression of photosynthesis. However, the feedback effects of enhanced down-regulation of photosynthesis under EC induced: (a) slight inactivation of PS II and reduction of PS II electron transport rates, (b) enhanced demand on xanthophyll dependent non-radiative dissipation of excess light energy (accumulation of deepoxidized antheraxanthin and zeaxanthin), (c) adjustment of the light harvesting complexes (increase of chlorophyll a/b ratio). (c) 2005 Elsevier Ireland Ltd. All rights reserved.

The measurements of soil CO 2 efflux in a Norway spruce (Picea abies (L.) Karst.) forest stand are reported for a 6-month period (from May 1 st to October 26 th 1999). Forest floor CO 2 efflux was measured at four positions using a portable infra- red gas analyser (LI-COR), operating as a closed dynamic system and connected to a portable soil chamber. Soil CO 2 efflux was measured 3-4 times per month. Soil temperature at a depth of 5 cm was recorded during the whole period with an interval of ten minutes. An exponential regression was used to describe the relationship between soil temperature and soil CO 2 efflux. On the basis of this relationship Q 10 values were calculated. The averaged value of Q 10 for the studied Norway spruce forest stand was 3.74.

Cloned saplings of beech (7-y-old) were exposed to enhanced UV-B irradiation (+25 %) continuously over three growing seasons (1999–2001). Analysis of CO2 assimilation, variable chlorophyll (Chl) a fluorescence, and pigment composition was performed in late summer of the third growing season to evaluate the influence of long-term elevated UV-B irradiation. This influence was responsible for the stimulation of the net assimilation rate (P N) over a range of irradiances. The increase in P N was partially connected to increase of the area leaf mass, and thus to the increased leaf thickness. Even a higher degree of UV-B induced stimulation was observed at the level of photosystem 2 (PS2) photochemistry as judged from the irradiance response of electron transport rate and photochemical quenching of Chl a. The remarkably low irradiance-induced non-photochemical quenching of maximum Chl a fluorescence (NPQ) in the UV-B plants over the entire range of applied irradiances was attributed both to the reduced demand on non-radiative dissipation processes and to the considerably reduced contribution of the quenching localised in the inactivated PS2 reaction centres. Neither the content of Chls and total carotenoids expressed per leaf area nor the contents of lutein, neoxanthin, and the pool of xanthophyll cycle pigments (VAZ) were affected under the elevated UV-B. However, the contributions of antheraxanthin (A) and zeaxanthin (Z) to the entire VAZ pool in the dark-adapted UV-B treated plants were 1.61 and 2.14 times higher than in control leaves. Surprisingly, the retained A+Z in UV-B treated plants was not accompanied with long-term down-regulation of the PS2 photochemical efficiency, but it facilitated the non-radiative dissipation of excitation energy within light-harvesting complexes (LHC) of PS2. Thus, in the beech leaves the accumulation of A+Z, induced by other factors than excess irradiance itself, supports the resistance of PS2 against combined effects of high irradiance and elevated UV-B.

Twelve-year-old Norway spruce (Picea abies [L.] Karst.) were exposed to ambient (AC) or elevated (EC) [ambient + 350 μmol(CO2) mol−1] CO2 concentration [CO2] using the facilities of open-top-chambers (OTCs) and glass domes (GDs). A combination of gas exchange measurements and application of a biochemical model of photosynthesis were used for the evaluation of CO2 assimilation characteristics. Morphological change was assessed on the base of specific leaf area (SLA). Nitrogen (N) content in the assimilation apparatus was considered a main factor influencing the biochemical capacity. Three experiments confirm the hypothesis that an adjustment of photosynthetic capacity under EC is controlled by the combination of biochemical, morphological, and physiological feedback mechanisms. We observed periodicity of down-regulation of photosynthetic capacity (Experiment No. 1) during the vegetation seasons. In the spring months (May–June), i.e. during the occurrence of active carbon sink associated with the formation of new foliage, up-regulation (10–35 %) of photosynthetic capacity (PNsat) was observed. On the contrary, in the autumn months (September–October) down-regulation (25–35 %) of PNsat was recorded that was mainly associated with reduced carbon sink strength and biochemical change, i.e. decrease of N status (up to 32 %) and accumulation of saccharides (up to 72 %) in leaves. Different adjustments of photosynthetic activities were observed in current (C) and one-year-old (C-1) needles exposed to EC (Experiment No. 2). Strong down-regulation of PNsat and the diminution of the initial stimulation of photosynthetic rate (PNmax) was associated with decreases of both ribulose-1,5-bisphosphate carboxylase/oxygenase carboxylation activity (by 32 %) and RuBP regeneration (by 40 %). This performance was tightly correlated with the absence of active carbon sinks, decrease of N content, and starch accumulation in C-1 needles. Finally, different responses of sun- and shade-adapted needles to EC (Experiment No. 3) were associated with the balance between morphological and biochemical changes. Observed PNsat down-regulation (by 22 %) of exposed needles in EC was predominantly caused by effects of both higher assimilate accumulation and stronger N dilution, resulting from higher absolute photosynthetic rates and incident irradiances in the upper canopy.

The long-term impact of elevated concentration of CO2 on assimilation activity of sun-exposed (E) versus shaded (S) foliage was investigated in a Norway spruce stand [Picea abies (L.) Karst, age 14 years] after three years of cultivation in two domes with adjustable windows (DAW). One DAW was supplied with ambient air [AC, ca. 350 µmol(CO2) mol−1) and the second with elevated CO2 concentration [EC = AC plus 350 µmol(CO2) mol−1]. The pronounced vertical profile of the photosynthetic photon flux density (PPFD) led to the typical differentiation of the photosynthetic apparatus between the shaded and sun needles. Namely, photon-saturated values of maximal net photosynthetic rate (P Nmax) and apparent quantum yield (α) were significantly higher/lower for E-needles as compared with the S-ones. The prolonged exposure to EC was responsible for the apparent assimilatory activity stimulation observed mainly in deeply shaded needles. The degree of this stimulation decreases in the order: S-needles dense part > S-needles sparse part > E-needles dense part > E-needles sparse part. In exposed needles some signals on a manifestation of the acclimation depression of the photosynthetic activity were found. The long-term effect of EC was responsible for the decrease of nitrogen content of needles and for its smoother gradient between E- and S-needles. The obtained results indicate that the E- and S-foliage respond differently to the long-term impact of EC.

We present a new technological approach for in situ investigation of long-term impacts of elevated CO2 concentration (EC) on juvenile forests characterised by an intensive community level and canopy closure phase. Construction of the glass domes is based on the properties of earlier tested open-top chambers (OTCs). An air climatisation device together with an adjustable window system, that forms the shell cover of the domes, is able to keep the required [CO2] in both time and spatial scales with the relatively small consumption of supplied CO2. This is achieved by half-closing the windows on the windward side. We evidenced good coupling of treated trees to the atmosphere, including mutual interactions among trees. The semi-open design of the domes moderates the problems of strong wind, humidity, and temperature gradients associated with OTCs. The frequency distributions of the environmental variations within the domes indicate that: air temperature is maintained within the ambient range ±1.0 °C for ca. 80 % of the time, and changes in the relative air humidity vary from −15 to 0 % for ca. 82 % of the time. The most important chamber effect is associated with the penetration of solar irradiance, which is reduced by 26 % compared to the open condition outside the domes. The dimensions of the domes are 10×10 m in length and 7 m high in the central part. The experiment was done in three identical stands of twelve-year-old Norway spruce trees. The 56 trees are planted at two different spacings to estimate the impacts of stand spatial structure in relation to EC.

The long-term impact of elevated CO2 concentration on photosynthetic activity of sun-exposed (E) versus shaded (S) foliage was investigated in a Picea abies stand (age 12 years) after three years of cultivation in adjustable-lamella-domes (ALD). One ALD is supplied with either ambient air [ca. 350 µmol(CO2) mol−1; AC-variant) and the second with elevated CO2 concentration [ambient plus 350 µmol(CO2) mol−1; EC-variant). The pronounced vertical profile of the photosynthetically active radiation (PAR) led to the typical differentiation of the photosynthetic apparatus between the S- and E-needles in the AC-variant estimated from the irradiance-responses of various parameters of the room temperature chlorophyll (Chl) a fluorescence parameters. Namely, electron transport rate (ETR), photochemical efficiency of photosystem 2, PS2 (ΦPS2), irradiance-saturated values of non-photochemical quenching of minimum (SV0) and maximum (NPQ) fluorescence levels, and photochemical fluorescence quenching (qp) at higher irradiances were all significantly higher for E-needles as compared with the S-ones. The prolonged exposure to EC did not cause any stimulation of ETR for the E-needles but a strongly positive effect of EC on ETR was observed for the S-needles resulting in more than doubled ETR capacity in comparison with S-needles from the AC-variant. For the E-needles in EC-variant a slightly steeper reduction of the ΦPS2 and qp occurred with the increasing irradiance as compared to the E-needles of AC-variant. On the contrary, the S-needles in EC variant revealed a significantly greater capacity to maintain a high ΦPS2 at irradiances lower than 200 µmol m−2 s−1 and to prevent the over-reduction of the PS2 reaction centres. Moreover, compared to the AC-variant the relation between SV0 and NPQ exhibited a strong decrease (up to 72 %) of the SV0-NPQ slope for the E-needles and an increase (up to 76 %) of this value for the S-needles. Hence the E- and S-foliage responded differently to the long-term impact of EC. Moreover, this exposure was responsible for the smoothing of the PAR utilisation vertical gradient in PS2 photochemical and non-photochemical reactions within the canopy.

The acclimation depression of capacity of photon utilisation in photochemical reactions of photosystem 2 (PS2) can develop already after three months of cultivation of the Norway spruces (Picea abies [L.] Karst.) under elevated concentrations of CO2 (i.e., ambient, AC, + 350 µmol(CO2) mol−1 = EC) in glass domes with adjustable windows. To examine the role that duration of EC plays in acclimation response, we determined pigment contents, rate of photosynthesis, and parameters of chlorophyll a fluorescence for sun and shade needles after three seasons of EC exposure. We found responses of shaded and exposed needles to EC. Whereas the shaded needles still profited from the EC and revealed stimulated electron transport, for the exposed needles the stimulation of both electron transport activity and irradiance saturated rate of CO2 assimilation (PNmax) under EC already disappeared. No signs of the PS2 impairment were observed as judged from high values of potential quantum yield of PS2 photochemistry (FV/FM) and uniform kinetics of QA reoxidation for all variants. Therefore, the long-term acclimation of the sun-exposed needles to EC is not necessarily accompanied with the damage to the PS2 reaction centres. The eco-physiological significance of the reported differentiation between the responses of shaded and sun exposed needles to prolonged EC may be in changed contribution of the upper and lower crown layers to the production activity of the tree. Whereas for the AC spruces, PNmax of shaded needles was only less than 25 % compared to exposed ones, for the EC spruces the PNmax of shaded needles reached nearly 40 % of that estimated for the exposed ones. Thus, the lower shaded part of the crown may become an effective consumer of CO2.

Since July 28th, 1997 the two experimental mini-stands of young Norway spruce [Picea abies (L.) Karst.] have been grown in lamellar domes at ambient (AC) and elevated concentrations of CO2 [EC, i.e., ambient + 350 µmol(CO2) mol−1]. Before the start of exposure to EC (June 1997) the dependencies of photosystem 2 (PS2) quantum yield (Y) on irradiance, estimating the efficiency of PPFD utilisation in PS2 photochemistry, were the same for AC and EC shoots. After one month of EC simulation (August 1997), Y values were higher for EC needles as compared with the AC ones (by 1–42 %), whereas two months later (October 1997) an opposite effect was observed (decrease of Y by from 1 to 33 %). By chlorophyll a (Chl a) fluorescence induction the effects of EC on PS2 function were further characterised. During the first month a moderate improvement of PS2 function was estimated for EC needles from slightly higher potential yield of PS2 photochemistry (FV/FM, by 1 %) and reduced amount of inactive PS2 reaction centres (relative Fp1 level, by 15 %). However, the prolonged exposure to EC led firstly to a slight but significant decrease of FV/FM (by 3 %), secondly to a reduction of half time of fluorescence rise (t1/2, by 14 %), and finally to pronounced accumulation of inactive PS2 reaction centres (by 41 %). From the gradual response of individual Chl a fluorescence parameters we suggest a probable sequence of events determining the stimulation and subsequent depression of PS2 function for Norway spruce during the first season under EC.

In an open-top chamber experiment located in a mountain stand of 14-years-old Norway spruce (Picea abies [L.] Karst.), trees were continuously exposed to either ambient CO2 concentration (A), or ambient + 350 µmol mol−1 (E) over four growing seasons. Respiration rates of different woody parts (stem, branches, coarse roots) were measured during the last growing season. The calculated increase in the respiration rate related to a 10 °C temperature change (Q10) was different in stem compared to branches and roots. Differences between the E and A variants were statistically significant only for roots in the autumn. Stem maintenance respiration (RMs) measured in April and November (periods of no growth activity) were not different. The stem respiration values (Rs) were recalculated to a standard temperature of 15 °C to estimate the seasonal course. The obtained Rs differed significantly between used variants during July and August. At the end of the season, Rs in E decreased slower than in A, indicating some prolongation of the physiological activity under the elevated CO2 concentration. The total stem respiration carbon losses for the investigated growing season (May – September) were higher for A (2.32 kg(C) m−2 season−1) compared to E (2.12 kg(C) m−2 season−1). The respiration rates of the whorl branches (Rb) were lower compared with the stem respiration but not significantly different between the used variants. The root respiration rate was increased in E variant.

Summary Cloned saplings of Norway spruce (7 years old) were continuously exposed to enhanced UV-B irradiation (+ 25 %) over three growing seasons. An analysis of variable chlorophyll a fluorescence was performed at the beginning Gune) and the end (September) of the third growing season in order to evaluate the longterm effects of elevated UV-B irradiation on the primary photosynthetic reactions. A time-dependent response to elevated UV-B radiation was observed. The saturated PPFD electron transport rate (ETR) in the control (C-variant) was 1.92 times that of the exposed plants (E-variant). The midday depression of the maximal photochemical yield of PSII (F V /F M ) was deeper in the E-variants, and the extent of this depression, as compared with the C-variants, increased at the end of the growing season. A light-induced decline in the F V /F M ratio was followed by a bi-phasic recovery phase upon return to shade conditions. The rapid recovery phase, possibly related to epoxidation of zeaxanthin, showed a sharper slope in the UV-B exposed E-variants. Thus, the long-term exposure to the elevated UV-B radiation was related to induction of the interconversion between violaxanthin and zeaxanthin. The slow phase of recovery of the Fy/FMratio possibly represents the reactivation of PSII by means of 0 1 protein turnover. The slope of the slow phase of the recovery in E-variants was 0,58 time that of the C-variants at the end of the growing season (i.e. 16 weeks of UV-B illumination). This indicates impairment of the 01 protein turnover as a result of the long-term influence ofUV-B radiation enhancement. The results show that in Norway spruce a long-term exposure to enhanced UV-B radiation under field conditions can be a reason for negative changes at the level of primary photosynthetic reactions.

Twelve-year-old Norway spruce (Picea abies [L.] Karst.) trees were exposed to ambient (AC) or elevated (EC) [ambient + 350 µmol(CO2) mol-1] CO2 concentrations in open-top-chamber (OTC) experiment under the field conditions of a mountain stand. Short-term (4 weeks, beginning of the vegetation season) and long-term (4 growing seasons, end of the vegetation season) effects of this treatment on biochemical parameters of CO2 assimilation were evaluated. A combination of gas exchange, fluorescence of chlorophyll a, and application of a mathematical model of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) activity was used. The analysis showed that the depression of photosynthetic activity by long-term impact of elevated CO2 was mainly caused by decreased RuBPCO carboxylation rate. The electron transport rate as well as the rate of ribulose-1,5-bisphosphate (RuBP) formation were also modified. These modifications to photosynthetic assimilation depended on time during the growing season. Changes in the spring were caused mainly by local deficiency of nitrogen in the assimilating tissue. However, the strong depression of assimilation observed in the autumn months was the result of insufficient carbon sink capacity.

The effects of elevated atmospheric CO2 concentration on growth of forest tree species are difficult to predict because practical limitations restrict experiments to much shorter than the average life-span of a tree. Long-term, processbased computer models must be used to extrapolate from shorter-term experiments. A key problem is to ensure a strong flow of information between experiments and models. In this study, meta-analysis techniques were used to summarize a suite of photosynthetic model parameters obtained from 15 field-based elevated [CO2] experiments on European forest tree species. The parameters studied are commonly used in modelling photosynthesis, and include observed light-saturated photosynthetic rates (Amax), the potential electron transport rate (Jmax), the maximum Rubisco activity (Vcmax) and leaf nitrogen concentration on mass (Nm) and area (Na) bases. Across all experiments, light-saturated photosynthesis was strongly stimulated by growth in elevated [CO2]. However, significant down-regulation of photosynthesis was also observed; when measured at the same CO2 concentration, photosynthesis was reduced by 10‐20%. The underlying biochemistry of photosynthesis was affected, as shown by a down-regulation of the parameters Jmax and Vcmax of the order of 10%. This reduction in Jmax and Vcmax was linked to the effects of elevated [CO2] on leaf nitrogen concentration. It was concluded that the current model is adequate to model photosynthesis in elevated [CO2]. Tables of model parameter values for different European forest species are given.

The cloned saplings of Norway spruce (7 years old) were exposed to enhanced UV-B irradiation (+25%) continuously over three growing seasons. An analysis of CO 2 assimilation and pigment composition was performed in the beginning (June) and the end (September) of the third growing season to evaluate the influence of long-term elevated UV-B irradiation. The UV-B was administered at levels that were, at any moment, at 125% of the ambient UV-B radiation. The results of the long-term experiment supports an idea on cumulative exposure UV-B effect. Four months under the influence of enhanced UV-B radiation was responsible for the depression of A N over the whole interval of investigated PPFD/ C i . A significant decrease in A Nmax. (up to 9%) and α (up to 22%), and increase in Γ i (up to 57%) and of R D (up to 19%) was found. The long-term effect of enhanced UV-B radiation caused a significant decrease in A Nsat (up to 60%) and τ (up to 8%), and a significant increase in Γ C (up to 27%), compared to controls. The chlorophyll a + b content was significantly decreased in the UV-B exposed variant. This change was mainly caused by a decrease in the chlorophyll a content (up to 20%). Thus, the negative effect of the long-term 21% enhancement UV-B radiation on photosynthetic gas exchange and photosynthetic pigment is concluded. Investigations of the gas-exchange parameters showed that the main limitation of assimilation can be identified at the level of RuBP regeneration related to electron transport. This finding is supported by the analysis of photosynthetic pigment content that indicates a simultaneous decrease of the chlorophyll a content and the antenna size. Thus, the potential increased sensitivity to the photoinhibition of photosynthesis resulting from the long-term influence of enhanced UV-B radiation is suggested.

An attempt to reveal the causal relation between gradient of photosynthetically active radiation (PhAR) through Norway spruce crown and differentiation of photosynthetic apparatus under field conditions is presented. The exposure of exposed (E) needles to higher photosystem (PS) II excitation pressure than for shaded (S) ones led to diminution of light harvesting complexes (LHCs), increased photosynthetic capacity (PNmax, by 70%) and increased capacity of nonradiative dissipation (NPQ, by 30%). Further analyses of chlorophyll a (Chl a) fluorescence revealed several differences between S and E needles concerning NPQ: (a) for E needles the NPQ provides more efficient protection against overreduction of PS II reaction centres; (b) the steeper dependence of F0 quenching on NPQ (by 53%) in E needles than in S needles supports the view that nonradiative dissipation localized in LHCs was enhanced for E needles; (c) for E needles induction of NPQ was accompanied by a significant decrease in energy transfer from Chl b to Chl a (by 20% and/or 15%) as estimated from 77 K excitation spectra of Chl a fluorescence measured from PS II and PS I, respectively. This implied that down-regulation of light harvesting function operates in PS I as well as in PS II. The physiological significance of these results regarding the adaptation of Norway spruce photosynthetic apparatus to the gradient of PhAR through the tree crown is discussed.

Summary Fifteen-year-old Norway spruces ( Picea abies [L.] Karst.) were grown in open top chambers (OTC) at ambient (A) and elevated (i.e. ambient + 350 μmol(CO 2 ) mol −1 ) concentrations of CO 2 (E) for four growing seasons (1992–1995). During this time period several examples of the depression of photosynthetic activities were observed for E needles. In order to better characterize the nature of this depression the gas exchange and fluorescence parameters were analyzed on current year needles during the last season (July 1995). The photon flux density response curves of CO 2 uptake (P N ) revealed a significandy reduced stimulation of P N for E needles as compared with short-term exposure to doubled CO 2 . Moreover, the sudden exposure of E shoots to 350μmol(CO 2 ) mol −1 at saturating irradiance revealed a depression of both P Nmax (by 20%) and quantum yield of PS II (by 32%) compared with A shoots measured at 350μmol(CO 2 ) mol −1 . The data supporting the diminished light harvesting system of photosystem II (PS II) in E shoots compared with A shoots were obtained from pigment analysis, low temperature fluorescence spectra and Chl a fluorescence induction kinetics. The relative proportion of inactive reaction centres of PS II determined from F pl of the fluorescence induction was 20% higher for E needles. These changes found for E needles mimicked an adaptation of PS II to increased irradiance compared with A needles. As the irradiance exposure was the same for the examined needles from both E and A spruces we suggest that these changes reported for E needles resulted from the feed-back limitation of photochemical reactions due to suppressed electron transport through the plastoquinone pool.

Differences between sun (E) and shaded (S) foliage were studied in a Norway spruce (Picea abies [L.] Karst.) stand. Response curves describing the dependence of the CO2 assimilation rate (PN) on the CO2 concentration at the catalytic site of ribulose-1,5-bisphosphate carboxylase/oxygenase, RuBPCO (PN-Cc) were estimated using the simultaneous measurements of chlorophyll fluorescence and leaf gas exchange. Higher PN, higher electron transport (Ja), higher carboxylation capacity (Vc), and higher RuBPCO activity (τ) for sun acclimated needles was found. The S-needles had higher portion of internal limitation and higher CO2 compensation concentration (Γ) than the E-needles. Because higher degree of limitation of photosynthesis by carboxylation was ascertained, it can be assumed that photosynthesis in shade foliage is limited mainly by lower carboxylation capacity and by low chloroplastic CO2 concentration

Temporal and spatial variations of shoot structural parameters, including shoot silhouette to projected needle area ratio, are very important, e.g., for the correction of leaf area index estimated by indirect methods. Here we bring few examples of their evolution within mountain spruce monoculture planted in two different densities.

While downward photosynthetic acclimation in response to elevated CO(2) (EC) is frequently accompanied by reduction in Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase), the exact mechanism behind this decrease and its dynamics are not well understood. We comprehensively studied Rubisco adjustment to EC in coniferous Picea abies using an electrophoretic (protein content), spectrophotometric (initial (RA(initial)) and total (RA(total)) in vitro Rubisco activities), and gas-exchange (maximum carboxylation activity in vivo (V(Cmax))) techniques. With respect to differing carbon sink strength and nitrogen remobilization, we hypothesized greater acclimation of photosynthesis in one-year-old as compared to current-year needles and at the end than at the beginning of the vegetation season. EC treatment led to a decrease in V(Cmax) values in current-year needles, but the ribulose-1,5-bisphosphate (RuBP)-limited rate of photosynthesis (J(max)) remained unaffected. Indeed, both V(Cmax) and J(max) were reduced by the EC treatment in one-year-old needles. The extent of photosynthetic acclimation in EC plants did not increase, however, during the vegetation season. EC decreased the activation state of Rubisco (RA(initial)/RA(total)) by 16% and 5% in current-year and one-year-old needles, respectively (averaged over the growing season). While during spring (short-term effect) EC treatment did not influence the Rubisco content per unit leaf area and decreased its specific activity (activity per unit Rubisco mass) in both needle age classes studied, exposure to EC during the entire vegetation season tended to reduce the Rubisco content while increasing its specific activity. Irrespective of CO(2) treatment and needle age, a hyperbolic-decay relationship was observed between Rubisco-specific activity and its content.

This study was designed to test the hypothesis that the spectral composition of incident radiation, as defined by the relative proportions of blue (B; λmax = 455 nm) and red (R; λmax = 625 nm) photons, can affect photosynthetic induction, since B photons stimulate stomatal opening and are more effectively absorbed by leaves than R photons. Different stages of photosynthetic induction, primarily determined by the photo-modulation of Rubisco activity and stomata opening, were investigated in dark-adapted leaves of Fagus sylvatica transferred to saturating irradiance [800μmol(photon) m-2 s-1] at B/R ratios of 1/3, 1/1, or 3/1. In agreement with our hypothesis, photosynthesis was induced faster by irradiance with a high B/R ratio (3/1); as demontrated by a higher IS60 (induction state 60 s after leaf illumination) and lower T90 (the time period required to reach 90 % of maximum steady-state photosynthesis). However, there were no differences in induction between leaves receiving equal (1/1) and low (1/3) B/R ratios. Electron transport was highly sensitive to radiation quality, exhibiting faster induction kinetics with increasing B/R ratio. Such stimulation of carbon-assimilatory processes corresponds with faster activation of Rubisco and lower non-photochemical quenching (NPQ) as the proportion of B photons is increased. In contrast, the kinetics of stomatal opening was independent of the spectral composition of incoming radiation. Since slightly higher absorption efficiency of high B/R radiation does not fully explain the changes in induction kinetics, the other possible mechanisms contributing to the stimulation of electron transport and Rubisco activity are discussed. © Springer Science+Business Media B.V. 2009.

We tested the hypothesis that leaf age affects photosynthetic induction, because conductance to CO2 diffusion usually decreases with increasing leaf age. Photosynthetic inductions, primarily determined by the light modulation of Rubisco activity and stomatal opening, were investigated in both young and mature leaves, as defined by leaf plastochron index (LPI), from three poplar clones: Populus alba L., P. nigra L. and P. x euramericana (Dode) Guinier. In all clones, maximum assimilation rates (A max), maximum stomatal conductance (G Smax) and dark respiration rates (RD) were higher in young leaves (LPI = 3-5) than in mature leaves (LPI = 10-14), and A max decreased from P. alba via P. x euramericana to P. nigra. The clones with high photosynthetic capacity had low induction states 60 s after leaf illumination (IS60; indicating a slow initial induction phase), and required less time to reach 90% photosynthetic induction (T90). In contrast, the clone with the lowest photosynthetic capacity (P. nigra) exhibited high IS60 (high initial induction state) but a long induction time (high T90). A comparison of mature leaves with young leaves revealed significantly (P < 0.01) lower IS60 values in mature leaves of P. nigra only, and significantly higher T90 values in mature leaves of P. alba only. In all clones, young leaves exhibited a lower percentage of maximum transient stomatal limitation during photosynthetic induction (4-9%) compared with mature leaves (16-30%). Transient biochemical limitation, assessed on the basis of the time constants of Rubisco activation (tau), was significantly higher in mature leaves than in young leaves of P. alba; whereas there were no significant differences in tau between young and mature leaves of the other poplar clones. Thus, our hypothesis that leaf age affects photosynthetic induction was confirmed at the level of transient stomatal limitation, which was significantly higher in mature leaves than in young leaves in all clones. For the induction parameters IS60, T90 and tau, photosynthetic induction was more clone-specific and was dependent on leaf age only in some cases, an observation that may apply to other tree species.

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.

Remotely sensed passive chlorophyll fluorescence emission has a potential to become one of the major global-scale reporter signals on vegetation performance and stress. In contrast to the actively probed parameters such as maximal (FM′) or minimal (F0′) emission, the steady-state chlorophyll fluorescence, Chl-FS, (FM′ > Chl-FS > F0′) has not been adequately studied. Using fluorescence imaging of leaves, we explored the modulation of Chl-FS by actinic irradiance and by temperature in laboratory, as well as the changes that occurred in three coniferous and broadleaf plant species grown in field. The experiments revealed that Chl-FS is largely insensitive to the incident irradiance once this is above early morning or late evening levels. The characteristic, pre-noon measured Chl-FS correlated positively with the CO2 assimilation rate when measured in field during the year. It was low and stable in the cold winter months and steeply increased with the spring onset. The high values of the characteristic Chl-FS persisted throughout the vegetation season and rapidly decreased in the fall. The seasonal Chl-FS transitions coincided with the last spring frosts or the first fall frosts that persisted for several consecutive nights. The transitions were marked by an elevated variability of the Chl-FS signal. We propose that the signal variability occurring during the transition periods can be used to detect from satellites the beginning and the end of the photosynthetic activity in evergreen canopies of the temperate zone.

We examined the principal differences in photosynthetic characteristics between sun and shade foliage and determined the relative importance of biochemical and stomatal limitations during photosynthetic induction. Temperate-zone broadleaf and conifer tree species, ranging widely in shade tolerance, were investigated from one locality in the Czech Republic. The study species included strongly shade-tolerant Abies alba Mill. and Tilia cordata Mill., less shade-tolerant Fagus sylvatica L. and Acer pseudoplatanus L. and sun-demanding Picea abies (L.) Karst. In the fully activated photosynthetic state, sun foliage of all species had significantly higher maximum CO(2) assimilation rates, maximum stomatal conductance and maximum rates of carboxylation than shade foliage. Compared with shade leaves, sun leaves had significantly higher nocturnal stomatal conductances. In all species, shade foliage tended to have higher induction states 60 s after leaf illumination than sun foliage. Sun and shade foliage did not differ in the rate of disappearance of the transient biochemical limitation during the induction phase. Longer time periods were required to reach 90% photosynthetic induction and 90% stomatal induction in sun foliage than in shade foliage of the less shade-tolerant F. sylvatica and A. pseudoplatanus and in sun-demanding P. abies; however, in sun foliage of the strongly shade-tolerant species T. cordata and A. alba, the time needed for photosynthetic induction was similar to, or less than, that for shade foliage. Shade but not sun needles of P. abies and A. alba had significantly slower induction kinetics than the broadleaf tree species. Among species, the sun-demanding P. abies exhibited the shortest stomatal induction times in both sun and shade leaves. Independently of shade tolerance ranking, the transient stomatal and total limitations that characterize photosynthetic induction were relieved significantly earlier in shade foliage than in sun foliage. Sun foliage generally exhibited a hyperbolic photosynthetic induction response, whereas a sigmoidal induction response was more frequent in shade foliage. The different relative proportions of transient biochemical and stomatal limitations during photosynthetic induction in sun and shade foliage indicate an essential role of stomata in photosynthetic limitation during induction, mainly in shade foliage, with a consequent influence on the shape of the photosynthetic induction curve.

During an open-top chamber experiment performed in evergreen ‘ macchia ’ ecosystem, which was represented by the clumps of natural vegetation dominated by Quercus ilex trees, the trees were exposed to one of two CO 2 concentrations (ambient CO 2 , AC-variant and elevated CO 2 , i.e. ambient plus 350 μmol CO 2 mol −1 , EC-variant) continuously over 5 years. Clumps of natural vegetation were enclosed in open top chambers (OTCs). Within the crowns of investigated Quercus ilex trees in OTCs, two crown layers i.e. sunny (E-leaves) and shaded (S-leaves), were identified as differing in solar radiation environment. To evaluate the effect of elevated CO 2 , as well as the functional differentiation in assimilation activity of E- versus S-leaves, gas exchange and chlorophyll a fluorescence techniques were used. The stimulatory effect of the long-term elevated CO 2 on the A N –PPFD relation was evident in E- and S-leaves of investigated Quercus trees. The A N max sensitivity of AC-variant leaves to the sudden application of elevated CO 2 was higher for S-leaves (42%) than for E-leaves (24%). The PPFD saturated rate of regulated thermal energy dissipation (ERD) confirmed the foliage differentiation caused by the long-term influence of elevated CO 2 . The ERD of E- and S-leaves in the AC-variant were 1.11 times of that in the EC-variant. However, the estimated rates of photochemistry (ERP) of E- and S-leaves in the EC-variant were 1.35 and 1.22 times of E- and S-leaves in the AC-variant. The achievement of the critical value of q P =0.4 in E- and S-leaves from the EC-variant under lower values of PPFD compared to the AC-variant indicates a higher degree of PSII over-reduction. Thus, elevated CO 2 can be responsible for an increased susceptibility of photosynthetic apparatus to high irradiance. The obtained results support the hypothesis on the foliage vertical distribution effect on the whole canopy response to elevated CO 2 . The S-layers of the canopy can play an important role in providing storage space for photosynthesis under elevated CO 2 .