Radiation and temperature drive diurnal variation of aerobic methane emissions from Scots pine canopy.

Methane emissions from plant foliage may play an important role in the global methane cycle, but their size and the underlying source processes remain poorly understood. Here, we quantify methane fluxes from the shoots of Scots pine trees, a dominant tree species in boreal forests, to identify source processes and environmental drivers, and we evaluate whether these fluxes can be constrained at the ecosystem-level by eddy covariance flux measurements. We show that shoot-level measurements conducted in forest, garden, or greenhouse settings; on mature trees and saplings; manually and with an automated CO2-, temperature-, and water-controlled chamber system; and with multiple methane analyzers all resulted in comparable daytime fluxes (0.144 ± 0.019 to 0.375 ± 0.074 nmol CH4 g-1 foliar d.w. h-1). We further find that these emissions exhibit a pronounced diurnal cycle that closely follows photosynthetically active radiation and is further modulated by temperature. These diurnal patterns indicate that methane production is associated with diurnal cycle of sunlight, indicating that this production is either a byproduct of photosynthesis-associated biochemical reactions (e.g., the methionine cycle) or produced through nonenzymatic photochemical reactions in plant biomass. Moreover, we identified a light-dependent component in stand-level methane fluxes, which showed order-of-magnitude agreement with shoot-level measurements (0.968 ± 0.031 nmol CH4 g-1 h-1) and which provides an upper limit for shoot methane emissions.

Aerobic methane production in Scots pine shoots is independent of drought or photosynthesis.

Shoot-level emissions of aerobically produced methane (CH4) may be an overlooked source of tree-derived CH4, but insufficient understanding of the interactions between their environmental and physiological drivers still prevents the reliable upscaling of canopy CH4 fluxes. We utilised a novel automated chamber system to continuously measure CH4 fluxes from the shoots of Pinus sylvestris (Scots pine) saplings under drought to investigate how canopy CH4 fluxes respond to the drought-induced alterations in their physiological processes and to isolate the shoot-level production of CH4 from soil-derived transport and photosynthesis. We found that aerobic CH4 emissions are not affected by the drought-induced stress, changes in physiological processes, or decrease in photosynthesis. Instead, these emissions vary on short temporal scales with environmental drivers such as temperature, suggesting that they result from abiotic degradation of plant compounds. Our study shows that aerobic CH4 emissions from foliage are distinct from photosynthesis-related processes. Thus, instead of photosynthesis rates, it is more reliable to construct regional and global estimates for the aerobic CH4 emission based on regional differences in foliage biomass and climate, also accounting for short-term variations of weather variables such as air temperature and solar radiation.

Twenty years of irrigation acclimation is driven by denser canopies and not by plasticity in twig- and needle-level hydraulics in a Pinus sylvestris forest.

Climate change is predicted to increase atmospheric vapor pressure deficit, exacerbating soil drought, and thus enhancing tree evaporative demand and mortality. Yet, few studies have addressed the longer-term drought acclimation strategy of trees, particularly the importance of morphological versus hydraulic plasticity. Using a long-term (20 years) irrigation experiment in a natural forest, we investigated the acclimation of Scots pine (Pinus sylvestris) morpho-anatomical traits (stomatal anatomy and crown density) and hydraulic traits (leaf water potential, vulnerability to cavitation (Ψ50), specific hydraulic conductivity (Ks), and tree water deficit) to prolonged changes in soil moisture. We found that low water availability reduced twig water potential and increased tree water deficit during the growing season. Still, the trees showed limited adjustments in most branch-level hydraulic traits (Ψ50 and Ks) and needle anatomy. In contrast, trees acclimated to prolonged irrigation by increasing their crown density and hence the canopy water demand. This study demonstrates that despite substantial canopy adjustments, P. sylvestris may be vulnerable to extreme droughts because of limited adjustment potential in its hydraulic system. While sparser canopies reduce water demand, such shifts take decades to occur under chronic water deficits and might not mitigate short-term extreme drought events.

Partitioning seasonal stem carbon dioxide efflux into stem respiration, bark photosynthesis and transport-related flux.

Stem CO2 efflux is an important component of the carbon balance in forests. The efflux is considered to principally reflect the net result of two dominating and opposing processes: stem respiration and stem photosynthesis. In addition, transport of CO2 in xylem sap is thought to play an appreciable role in affecting the net flux. This work presents an approach to partition stem CO2 efflux among these processes using sap-flux data and CO2-exchange measurements from dark and transparent chambers placed on mature Scots pine (Pinus sylvestris) trees. Seasonal changes and monthly parameters describing the studied processes were determined. Respiration contributed most to stem net CO2 flux, reaching up to 79% (considering the sum of the absolute values of stem respiration, stem photosynthesis and flux from CO2 transported in xylem sap to be 100%) in June, when stem growth was greatest. Photosynthesis contribution accounted for up to 13 % of the stem net CO2 flux, increasing over the monitoring period. CO2 transported axially with sap flow, decreased towards the end of the growing season. At a reference temperature, respiration decreased starting around midsummer, while its temperature sensitivity increased during the summer. A decline was observed for photosynthetic quantum yield around midsummer together with decreasing light-saturation point. The proposed approach facilitates modeling net stem CO2 flux at a range of time scales.

Shedding light on the increased carbon uptake by a boreal forest under diffuse solar radiation across multiple scales.

Solar radiation is scattered by cloud cover, aerosols and other particles in the atmosphere, all of which are affected by global changes. Furthermore, the diffuse fraction of solar radiation is increased by more frequent forest fires and likewise would be if climate interventions such as stratospheric aerosol injection were adopted. Forest ecosystem studies predict that an increase in diffuse radiation would result in higher productivity, but ecophysiological data are required to identify the processes responsible within the forest canopy. In our study, the response of a boreal forest to direct, diffuse and heterogeneous solar radiation conditions was examined during the daytime in the growing season to determine how carbon uptake is affected by radiation conditions at different scales. A 10-year data set of ecosystem, shoot and forest floor vegetation carbon and water-flux data was examined. Ecosystem-level carbon assimilation was higher under diffuse radiation conditions in comparison with direct radiation conditions at equivalent total photosynthetically active radiation (PAR). This was driven by both an increase in shoot and forest floor vegetation photosynthetic rate. Most notably, ecosystem-scale productivity was strongly related to the absolute amount of diffuse PAR, since it integrates both changes in total PAR and diffuse fraction. This finding provides a gateway to explore the processes by which absolute diffuse PAR enhances productivity, and the long-term persistence of this effect under scenarios of higher global diffuse radiation.

Current and future drought vulnerability for three dominant boreal tree species.

Climate change is projected to increase the frequency and severity of droughts, possibly causing sudden and elevated tree mortality. Better understanding and predictions of boreal forest responses to climate change are needed to efficiently adapt forest management. We used tree-ring width chronologies from the Swedish National Forest Inventory, sampled between 2010 and 2018, and a random forest machine-learning algorithm to identify the tree, stand, and site variables that determine drought damage risk, and to predict their future spatial-temporal evolution. The dataset consisted of 16,455 cores of Norway spruce, Scots pine, and birch trees from all over Sweden. The risk of drought damage was calculated as the probability of growth anomaly occurrence caused by past drought events during 1960-2010. We used the block cross-validation method to compute model predictions for drought damage risk under current climate and climate predicted for 2040-2070 under the RCP.2.6, RCP.4.5, and RCP.8.5 emission scenarios. We found local climatic variables to be the most important predictors, although stand competition also affects drought damage risk. Norway spruce is currently the most susceptible species to drought in southern Sweden. This species currently faces high vulnerability in 28% of the country and future increases in spring temperatures would greatly increase this area to almost half of the total area of Sweden. Warmer annual temperatures will also increase the current forested area where birch suffers from drought, especially in northern and central Sweden. In contrast, for Scots pine, drought damage coincided with cold winter and early-spring temperatures. Consequently, the current area with high drought damage risk would decrease in a future warmer climate for Scots pine. We suggest active selection of tree species, promoting the right species mixtures and thinning to reduce tree competition as promising strategies for adapting boreal forests to future droughts.

Microgeographic variation in early fitness traits of Pinus sylvestris from contrasting soils.

PREMISE: The possibility of fine-scale intraspecific adaptive divergence under gene flow is established by theoretical models and has been confirmed empirically in tree populations distributed along steep altitudinal clines or across extreme edaphic discontinuities. However, the possibility of microgeographic adaptive divergence due to less severe but more frequent kinds of soil variation is unclear. METHODS: In this study, we looked for evidence of local adaptation to calcareous versus siliceous soil types in two nearby Mediterranean Pinus sylvestris populations connected via pollen flow. Using a greenhouse experiment, we tested for variation in early (up to three years of age) seedling performance among open-pollinated maternal families originating from each edaphic provenance when experimentally grown on both types of natural local substrate. RESULTS: Although seedlings were clearly affected by the edaphic environment, exhibiting lower and slower emergence as well as higher mortality on the calcareous than in the siliceous substrate, neither the performance on each substrate nor the plasticity among substrates varied significantly with seedling edaphic provenance. CONCLUSIONS: We found no evidence of local adaptation to a non-extreme edaphic discontinuity over a small spatial scale, at least during early stages of seedling establishment. Future studies on microgeographic soil-driven adaptation should consider long-term experiments to minimize maternal effects and allow a potentially delayed expression of edaphic adaptive divergence.

A Reliable and Simple Method for the Production of Viable Pycnidiospores of the Pine Pathogen Diplodia sapinea and a Spore-Based Infection Assay on Scots Pine.

Diplodia sapinea is a globally distributed opportunistic fungal pathogen of conifers that causes severe production losses in forestry. The fungus frequently colonizes pine trees as an endophyte without causing visible symptoms but can become pathogenic when the host plant is weakened by stress, such as drought or heat. Forest damage might therefore further increase due to the effects of climate change. The future development of control strategies depends on a better understanding of the fungus' biology, which requires experimental methods for its investigation in the laboratory. An efficient, standardized protocol for the production and storage of highly viable pycnidiospores was developed, and a spore-based infection method was devised. We compared infection rates of dormant and actively growing, wounded, or nonwounded Scots pine seedlings inoculated with in vitro-produced spores and mycelium from agar-plugs. Spores were a much more efficient inoculum for causing disease symptoms on wounded plants than the conventional agar plug. The application of spores on nonwounded plants lead to high rates of asymptomatic infection, suggesting endophytic fungal development. These methods enable standardized spore infection and virulence assays and promote D. sapinea as a model organism for studying the switch from endophytic to pathogenic life styles of forest pathogens.

Volatile-mediated between-plant communication in Scots pine and the effects of elevated ozone.

Conifers are dominant tree species in boreal forests, but are susceptible to attack by bark beetles. Upon bark beetle attack, conifers release substantial quantities of volatile organic compounds known as herbivore-induced plant volatiles (HIPVs). Earlier studies of broadleaved plants have shown that HIPVs provide information to neighbouring plants, which may enhance their defences. However, the defence responses of HIPV-receiver plants have not been described for conifers. Here we advance knowledge of plant-plant communication in conifers by documenting a suite of receiver-plant responses to bark-feeding-induced volatiles. Scots pine seedlings exposed to HIPVs were more resistant to subsequent weevil feeding and received less damage. Receiver plants had both induced and primed volatile emissions and their resin ducts had an increased epithelial cell (EC) mean area and an increased number of cells located in the second EC layer. Importantly, HIPV exposure increased stomatal conductance and net photosynthesis rate of receiver plants. Receiver-plant responses were also examined under elevated ozone conditions and found to be significantly altered. However, the final defence outcome was not affected. These findings demonstrate that HIPVs modulate conifer metabolism through responses spanning photosynthesis and chemical defence. The responses are adjusted under ozone stress, but the defence benefits remain intact.

Tree allocation dynamics beyond heat and hot drought stress reveal changes in carbon storage, belowground translocation and growth.

Heatwaves combined with drought affect tree functioning with as yet undetermined legacy effects on carbon (C) and nitrogen (N) allocation. We continuously monitored shoot and root gas exchange, δ13 CO2 of respiration and stem growth in well-watered and drought-treated Pinus sylvestris (Scots pine) seedlings exposed to increasing daytime temperatures (max. 42°C) and evaporative demand. Following stress release, we used 13 CO2 canopy pulse-labeling, supplemented by soil-applied 15 N, to determine allocation to plant compartments, respiration and soil microbial biomass (SMB) over 2.5 wk. Previously heat-treated seedlings rapidly translocated 13 C along the long-distance transport path, to root respiration (Rroot ; 7.1 h) and SMB (3 d). Furthermore, 13 C accumulated in branch cellulose, suggesting secondary growth enhancement. However, in recovering drought-heat seedlings, the mean residence time of 13 C in needles increased, whereas C translocation to Rroot was delayed (13.8 h) and 13 C incorporated into starch rather than cellulose. Concurrently, we observed stress-induced low N uptake and aboveground allocation. C and N allocation during early recovery were affected by stress type and impact. Although C uptake increased quickly in both treatments, drought-heat in combination reduced the above-belowground coupling and starch accumulated in leaves at the expense of growth. Accordingly, C allocation during recovery depends on phloem translocation capacity.

Explicitly accounting for needle sugar pool size crucial for predicting intra-seasonal dynamics of needle carbohydrates δ18 O and δ13 C.

We explore needle sugar isotopic compositions (δ18 O and δ13 C) in boreal Scots pine (Pinus sylvestris) over two growing seasons. A leaf-level dynamic model driven by environmental conditions and based on current understanding of isotope fractionation processes was built to predict δ18 O and δ13 C of two hierarchical needle carbohydrate pools, accounting for the needle sugar pool size and the presence of an invariant pinitol pool. Model results agreed well with observed needle water δ18 O, δ18 O and δ13 C of needle water-soluble carbohydrates (sugars + pinitol), and needle sugar δ13 C (R2 = 0.95, 0.84, 0.60, 0.73, respectively). Relative humidity (RH) and intercellular to ambient CO2 concentration ratio (Ci /Ca ) were the dominant drivers of δ18 O and δ13 C variability, respectively. However, the variability of needle sugar δ18 O and δ13 C was reduced on diel and intra-seasonal timescales, compared to predictions based on instantaneous RH and Ci /Ca , due to the large needle sugar pool, which caused the signal formation period to vary seasonally from 2 d to more than 5 d. Furthermore, accounting for a temperature-sensitive biochemical 18 O-fractionation factor and mesophyll resistance in 13 C-discrimination were critical. Interpreting leaf-level isotopic signals requires understanding on time integration caused by mixing in the needle sugar pool.

Water taken up through the bark is detected in the transpiration stream in intact upper-canopy branches.

Alternative water uptake pathways through leaves and bark complement water supply with interception, fog or dew. Bark water-uptake contributes to embolism-repair, as demonstrated in cut branches. We tested whether bark water-uptake could also contribute to supplement xylem-water for transpiration. We applied bandages injected with 2 H-enriched water on intact upper-canopy branches of Pinus sylvestris and Fagus sylvatica in a boreal and in a temperate forest, in summer and winter, and monitored transpiration and online isotopic composition (δ2 H and δ18 O) of water vapour, before sampling for analyses of δ2 H and δ18 O in tissue waters. Xylem, bark and leaf waters from segments downstream from the bandages were 2 H-enriched whereas δ18 O was similar to controls. Transpiration was positively correlated with 2 H-enrichment. Isotopic compositions of transpiration and xylem water allowed us to calculate isotopic exchange through the bark via vapour exchange, which was negligible in comparison to estimated bark water-uptake, suggesting that water-uptake occurred via liquid phase. Results were consistent across species, forests and seasons, indicating that bark water-uptake may be more ubiquitous than previously considered. We suggest that water taken up through the bark could be incorporated into the transpiration stream, which could imply that sap-flow measurements underestimate transpiration when bark is wet.

Stomatal density in Pinus sylvestris as an indicator of temperature rather than CO2 : Evidence from a pan-European transect.

The commonly observed negative relationship between stomatal density (SD) and atmospheric CO2 has led to SD being proposed as an indicator of atmospheric CO2 concentration. The use of SD as a proxy for CO2 , however, has been hampered by an insufficient understanding of the intraspecific variation of this trait. We hypothesized that SD in Pinus sylvestris, a widely distributed conifer, varies geographically and that this variation is determined by major climatic variables. By sampling needles from naturally growing trees along a latitudinal range of 32.25°, equivalent to 13.7°C gradient of mean annual temperature (MAT) across Europe, we found that SD decreased from the warmest southern sites to the coldest sites in the north at a rate of 4 stomata per mm2 for each 1°C, with MAT explaining 44% of the variation. Additionally, samples from a provenance trial exhibited a positive relationship between SD and the MAT of the original localities, suggesting that high SD is an adaptation to warm temperature. Our study revealed one of the strongest intraspecific relationships between SD and climate in any woody species, supporting the utility of SD as a temperature, rather than direct CO2 , proxy. In addition, our results predict the response of SD to climate warming.

Trends in climatically driven extreme growth reductions of Picea abies and Pinus sylvestris in Central Europe.

Extreme tree growth reductions represent events of abrupt forest productivity decline and carbon sequestration reduction. An increase in their magnitude can represent an early warning signal of impending tree mortality. Yet the long-term trends in extreme growth reductions remain largely unknown. We analyzed the trends in the proportion of trees exhibiting extreme growth reductions in two Central-European conifer species-Pinus sylvestris (PISY) and Picea abies (PCAB)-between 1901 and 2018. We used a novel approach for extreme growth reduction quantification by relating their size to their mean recurrence interval. Twenty-eight sites throughout Czechia and Slovakia with 1120 ring width series representing high- and low-elevation forests were inspected for extreme growth reductions with recurrence intervals of 15 and 50 years along with their link to climatic drivers. Our results show the greatest growth reductions at low-elevation PCAB sites, indicating high vulnerability of PCAB to drought. The proportions of trees exhibiting extreme growth reductions increased over time at low-elevation PCAB, decreased recently following an abrupt increase in the 1970-1980s at high-elevation PCAB, and showed nonsignificant trends in high- and low-elevation PISY. Climatic drivers of extreme growth reductions, however, shifted over time for all site categories as the proportion of low-temperature-induced extreme growth reductions declined since the 1990s, whereas events caused by drought consistently increased in frequency during the same period. We observed higher growth volatility at the lower range of distribution compared with the upper range margin of PISY and PCAB. This will undoubtedly considerably impact tree growth and vitality as temperatures and incidence of drought in Central Europe are expected to further increase with ongoing climate change.

Assessing soil carbon dioxide and methane fluxes from a Scots pine raised bog-edge-woodland.

Scots pine bog edge woodland is a type of habitat typical on raised bogs where trees cohabitate with bog vegetation to form a low-density stand. Even though nowadays this habitat does not cover large areas, in a future scenario it is possible that this environment will expand, either naturally (drier climate) or anthropogenically, as the result of the application of new restoration strategies that could increase net landscape carbon benefits from both peatland and woodland environments. This study is the first reported investigation in Scotland exploring carbon flux dynamics from sparse woodlands on raised bogs. We examined how Scots pine trees directly or indirectly affected soil temperature and moisture, ground vegetation, and consequently carbon dioxide (CO2) and methane (CH4) soil fluxes. Soil CO2 and CH4 were measured at different distance from the tree and thereafter assessed for both spatial and temporal variability. Our results showed that these low-density trees were able to modify the ground vegetation composition, had no effect on soil temperature, but did affect the soil moisture, with soils close to tree roots significantly drier (0.25 ± 0.01 m3 m-3) than those on open bog (0.39 ± 0.02 m3 m-3). Soil CO2 fluxes were significantly higher in the vicinity of trees (34.13 ± 3.97 µg CO2 m-2 s-1) compared to the open bog (24.34 ± 2.86 µg CO2 m-2 s-1). On the opposite, CH4 effluxes were significantly larger in the open bog (0.07 ± 0.01 µg CH4 m-2 s-1) than close to the tree (0.01 ± 0.00 µg CH4 m-2 s-1). This suggests that Scots pine trees on bog edge woodland may affect soil C fluxes in their proximity primarily due to the contribution of root respiration, but also as a result of their effects on soil moisture, enhancing soil CO2 emissions, while reducing the CH4 fluxes. There is, however, still uncertainty about the complete greenhouse gas assessment, and further research would be needed in order to include the quantification of soil nitrous oxide (N2O) dynamics together with the analysis of complete gas exchanges at the tree-atmosphere level.

Pinus sylvestris L. and Syzygium aromaticum (L.) Merr. & L. M. Perry Essential Oils Inhibit Endotoxin-Induced Airway Hyperreactivity despite Aggravated Inflammatory Mechanisms in Mice.

Scots pine (SO) and clove (CO) essential oils (EOs) are commonly used by inhalation, and their main components are shown to reduce inflammatory mediator production. The aim of our research was to investigate the chemical composition of commercially available SO and CO by gas chromatography-mass spectrometry and study their effects on airway functions and inflammation in an acute pneumonitis mouse model. Inflammation was evoked by intratracheal endotoxin and EOs were inhaled three times during the 24 h experimental period. Respiratory function was analyzed by unrestrained whole-body plethysmography, lung inflammation by semiquantitative histopathological scoring, myeloperoxidase (MPO) activity and cytokine measurements. α-Pinene (39.4%) was the main component in SO, and eugenol (88.6%) in CO. Both SO and CO significantly reduced airway hyperresponsiveness, and prevented peak expiratory flow, tidal volume increases and perivascular edema formation. Meanwhile, inflammatory cell infiltration was not remarkably affected. In contrast, MPO activity and several inflammatory cytokines (IL-1ß, KC, MCP-1, MIP-2, TNF-α) were aggravated by both EOs. This is the first evidence that SO and CO inhalation improve airway function, but enhance certain inflammatory parameters. These results suggest that these EOs should be used with caution in cases of inflammation-associated respiratory diseases.

Rotational Activity of Trunk Parts in Scots Pine Trees: Seasonal Dynamics and Patterns.

The seasonal dynamics and relationships between the characteristics of the angles of rotation of outer sapwood layers in trunks of Scots pine (Pinus sylvestris L.) trees growing in natural stands have been studied for two years in order to improve the understanding of the trunk twisting phenomenon and its role in the tree growth and morphogenesis. The trunk twisting phenomenon is observed in all trees during the entire vegetation period, and its characteristics do not depend on the exposition and differ in various trunk parts. The rotation angles and directions of rotation of the adjacent trunk parts are positively correlated with each other. The counterclockwise direction of rotation dominates, which provides an increase in the total rotation angle over time. The directions and values of the forces causing rotation of outer sapwood layers seem to be explained by the gradients of mechanical stresses appearing between neighboring xylem parts due to their nonuniform moisture content.

Tree water uptake enhances nitrogen acquisition in a fertilized boreal forest - but not under nitrogen-poor conditions.

Understanding how plant water uptake interacts with acquisition of soil nitrogen (N) and other nutrients is fundamental for predicting plant responses to a changing environment, but it is an area where models disagree. We present a novel isotopic labelling approach which reveals spatial patterns of water and N uptake, and their interaction, by trees. The stable isotopes 15 N and 2 H were applied to a small area of the forest floor in stands with high and low soil N availability. Uptake by surrounding trees was measured. The sensitivity of N acquisition to water uptake was quantified by statistical modelling. Trees in the high-N stand acquired twice as much 15 N as in the low-N stand and around half of their N uptake was dependent on water uptake (2 H enrichment). By contrast, in the low-N stand there was no positive effect of water uptake on N uptake. We conclude that tree N acquisition was only marginally dependent on water flux toward the root surface under low-N conditions whereas under high-N conditions, the water-associated N uptake was substantial. The results suggest a fundamental shift in N acquisition strategy under high-N conditions.

Assessing model performance via the most limiting environmental driver in two differently stressed pine stands.

Climate change will impact forest productivity worldwide. Forecasting the magnitude of such impact, with multiple environmental stressors changing simultaneously, is only possible with the help of process-based models. In order to assess their performance, such models require careful evaluation against measurements. However, direct comparison of model outputs against observational data is often not reliable, as models may provide the right answers due to the wrong reasons. This would severely hinder forecasting abilities under unprecedented climate conditions. Here, we present a methodology for model assessment, which supplements the traditional output-to-observation model validation. It evaluates model performance through its ability to reproduce observed seasonal changes of the most limiting environmental driver (MLED) for a given process, here daily gross primary productivity (GPP). We analyzed seasonal changes of the MLED for GPP in two contrasting pine forests, the Mediterranean Pinus halepensis Mill. Yatir (Israel) and the boreal Pinus sylvestris L. Hyytiälä (Finland) from three years of eddy-covariance flux data. Then, we simulated the same period with a state-of-the-art process-based simulation model (LandscapeDNDC). Finally, we assessed if the model was able to reproduce both GPP observations and MLED seasonality. We found that the model reproduced the seasonality of GPP in both stands, but it was slightly overestimated without site-specific fine-tuning. Interestingly, although LandscapeDNDC properly captured the main MLED in Hyytiälä (temperature) and in Yatir (soil water availability), it failed to reproduce high-temperature and high-vapor pressure limitations of GPP in Yatir during spring and summer. We deduced that the most likely reason for this divergence is an incomplete description of stomatal behavior. In summary, this study validates the MLED approach as a model evaluation tool, and opens up new possibilities for model improvement.

Heavy metal accumulation of urban Scots pine (Pinus sylvestris L.) plantation.

In soil and plant tissues, the concentrations and reserves of manganese (Mn), zinc (Zn), nickel (Ni), copper (Cu), and lead (Pb) were calculated to measure the heavy metal quantities of the Scots pine afforestation. In the soil and plant tissues, heavy metal concentrations varied. The highest concentration of heavy metal was found in Mn and the lowest concentration in Pb in the soil. Heavy metal stocks followed the order of Mn > Zn > Ni > Cu > Pb in soil, and the order of Zn > Cu > Mn > Ni > Pb in the plant. In the Scots pine parts, Pb and Zn concentrations and BCFs follow Needle > Branch > Bark > Root > Trunk order, while Cu concentrations follow Root > Needle > Branch > Bark > Trunk order, Mn concentrations follow Needle > Branch > Bark > Trunk > Root order and Ni concentrations follow Needle > Branch > Root > Bark > Trunk order. In particular, Scots pine needles are considered to be ideal to be used as biomonitoring plants, especially in monitoring increases in heavy metal concentrations in urban areas. Besides, in order to be more effective in the retaining of heavy metals, it is proposed that mixtures of hyperaccumulator plants be added which are appropriate for climatic conditions.