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To evaluate the impact of stand age on the ecosystem's C budget, as well as the post-harvest recovery of the C storages and fluxes, a chronosequence of Scots pine stands from the clear-cut stage up to the age of 110 years was studied. An age-related trend of net primary production (NPP) demonstrated effective C accumulation in the young and middle-aged stands and their levelling out thereafter. The understorey vegetation contributed 8-46% to total NPP, being lower in the pole and middle-aged stands, but without a clear age related trend. Annual cumulative soil heterotrophic respiration (Rh) demonstrated stable values along the chronosequence, varying between 3.8 and 5.4 t C ha

Thinning changes the functioning of the whole forest ecosystem, including carbon and nitrogen (N) cycling. The input of organic matter and N into soil, as well as soil temperature and moist...

Hemiboreal forests form a transitional belt between boreal and temperate forests in Eurasia, and due to long-term climate warming they could potentially expand in a northerly direction. However, carbon (C) exchange studies in this transitional forest type are scarce. In 2014–2015 we analyzed CO2 exchange in a hemiboreal mixed forest at SMEAR Estonia (Station for Measuring Ecosystem-Atmosphere Relations) using eddy covariance (EC), soil chamber technique and biometric methods. Employing two plots that differ in forest stand composition (mixed (MP) and coniferous (CP)) located within the footprint of the EC tower, we evaluated heterotrophic and total soil respiration (Rh and Rs, respectively). Measurements showed that C, nitrogen (N), and soil organic matter (SOM) contents in topsoil were significantly higher in the coniferous plot, and the total C stock until 20 cm of mineral soil was higher by a factor of two (i.e., 170.6 and 94.8 t C ha−1 for the CP and MP, respectively). Only in 2015 there was a significant difference in Rs between the plots, while Rh exhibited no detectable difference. The cumulative Rs during the growing season was similar for both plots (CP and MP) and years: 532 and 548 g m−2, respectively, in 2014; 636 and 592 g m−2, respectively, in 2015. The same applied to Rh: 418 and 430 g m−2, respectively, in 2014; 406 and 387 g m−2, respectively, in 2015. The forest as a whole was a C sink. In 2015, net ecosystem exchange (NEE) was -585.62 ± 45.16 g C m−2 yr−1 (the average and SD of two gap-filling methods: MDS and nonlinear regressions). Gross primary production (GPP), and ecosystem respiration (RE) were -1280.62 ± 53.36, and 696.00 ± 98.51 g C m−2 yr−1, respectively (the average and SD of two flux partitioning methods: nighttime data-based and daytime data-based). NEE and GPP suggested a greater similarity to temperate forests, while RE was closer to more boreal forest stands. The mean value of net ecosystem production (NEP) of both plots, estimated using forest stand biometric, litter and chamber data was similar to the annual NEE value: 6.3 and −5.9 t C ha−1 yr−1, respectively.

Clear-cutting is a conventional method of forest management which significantly changes carbon (C) cycling at the ecosystem level for a long time. Estimation of the interim period during which the ecosystem turns from a C source to a C sink is crucial for clarifying the environmental effects of management on forest C cycling. The current study provided new knowledge of C cycling in young pine stand and demonstrated the recovery of C sequestration of the forest ecosystem during the post harvesting period. We estimated the C balance in a 6-year-old Scots pine stand by using two different methods: carbon budgeting, for estimating annual net ecosystem production (NEP), and eddy covariance (EC), for estimating net ecosystem exchange (NEE). For C budgeting, the above- and belowground biomass production of the ecosystem, as well as the soil heterotrophic respiration efflux at the studied site was estimated. Annual NEE at the studied young forest ecosystem was 1.19 ± 0.36 t C ha−1, gross primary ecosystem production was 9.87 and total ecosystem respiration was 11.06 t C ha−1. Estimated NEE was in good accordance with the results of NEP (1.37 t C ha−1), which confirms the relevance of the C budgeting method. Increased annual woody biomass production is the main factor which induced the young Scots pine ecosystem to act as a C sink: annual C accumulation in tree biomass in a 6-year-old stand was 1.0 t C ha−1 but reached already 2.4 t C ha−1 in the following year. Assuming that the annual Rh flux is of the same magnitude in the subsequent years, the ecosystem will become a C sink already during a short period after clear-cut. Annual soil respiration (Rs) and heterotrophic soil respiration (Rh) were 6.0 and 4.2 t C ha−1, respectively and the Rh/Rs ratio was 0.70. However, at this stage also the understorey vegetation contributed essentially to NEP, making up 56% of the annual C uptake accumulated in the plants. The methane flux and the leached C flux were negligible, 0.004 and 0.015 t C ha−1 yr−1, respectively. Our results demonstrate that well regenerated young Scots pine stand on a former clear-cut area will be able to turn into a C sequestering ecosystem already before ten years after cutting.

Agricultural activities can have several adverse impacts on the environment; such as important greenhouse gas (GHG) emissions. To implement effective mitigation measures and create effective policies, it is necessary to know the full carbon and nitrogen budgets of agro-ecosystems. However, very often, information regarding the pools or fluxes involved in the carbon and nitrogen cycles is limited, and essential complementary data needed for a proper interpretation is lacking.This study aimed to quantify all the relevant pools and fluxes of a winter rapeseed, a widely spread crop in the Europe and Baltic regions. The N2O and CH4 fluxes were measured weekly using the closed static chamber method from August 2016 to August 2017 in a winter rapeseed field in Central Estonia. Additionally, nutrient leaching and soil chemical parameters, as well as environmental parameters like soil moisture, electrical conductivity and temperature were monitored. At the end of the season, the rapeseed and weed biomasses were collected, weighed and analyzed. The remaining relevant fluxes in the N cycle were calculated using various non-empirical methods: NH3 volatilization was estimated from slurry and environmental parameters, N deposition and NOx emissions were obtained from national reports, and N2 emissions were calculated with the mass balance method. Regarding the C cycle, gross primary production (GPP) of the rapeseed field was also calculated by the mass balance method. Simultaneously, for comparison and validation purposes, GPP was estimated from the data provided by MOD17A2H v006 series from NASA, and N2 was estimated from the measured emissions of N2O using the N2:N2O ratio calculated from the DAYCENT model equations.N2 emissions and GPP were the biggest fluxes in the N and C cycles, respectively. N2 emissions were followed by N extracted with plant biomass in the N cycle, while in the carbon cycle soil and plant respiration and NPP were the highest fluxes after GPP. The carbon balance was positive at the soil level, with a net increase in soil carbon during the period, mainly due to GPP carbon capture. Contrarily, the nitrogen balance resulted in a net loss of N due to the losses related to gaseous emissions (N2 and N2O) and leaching.To conclude, it was possible to close the C and N budgets, despite the inherent difficulties of estimating the different C and N environmental pools and fluxes, and the uncertainties deriving from some of the fluxes estimations.

Ecosystem responses to climate change are mainly predicted based on short-term studies. However, the first response can be a temporary overreaction, different from the later response of the more acclimated ecosystem. The current paper is a follow-up study of our previous article, where the effect of elevated atmospheric humidity on forest ecosystem carbon (C) balance was studied in a young silver birch (Betula pendula Roth) forest after two years of humidification. Here, we present the C balance of the same forest measured two years later when humidification treatment had been performed for four years. We revealed that the higher C sequestration capacity of the humidified birch forest ecosystem was an initial overreaction, which levelled off after four years of humidification, when the ecosystem became more acclimated to wetter conditions. Understorey production reacted rapidly and strongly by increasing belowground production more than twofold, but this reaction ceased after four years of humidification treatment. Trees responded to a lesser extent, and the initially decreased aboveground growth was recovered after four years of humidification, when the biomass allocation to tree fine-roots was increased. Our results showed that at early forest age, understorey plant production dominated in the whole ecosystem C sequestration capacity. But in the later stage, the most important C sink was biomass production of birches, and since the tree biomass production no longer differed between the treatments, C sequestration of the whole ecosystem did not differ either. The findings confirm that a preliminary reaction of an ecosystem can be different from the later response, which needs to be taken into account when prognosing the climate change consequences for carbon sequestration.

This study analyses long-term changes in drought indices (Standardised Precipitation Index—SPI, Standardised Precipitation–Evapotranspiration Index—SPEI) at 1 and 3?months scales at 182 stations in 11 central and eastern European countries during 1949–2018. For comparative purposes, the necessary atmospheric evaporative demand (AED) to obtain SPEI was calculated using two methods, Hargreaves-Samani (SPEIH) and Penman-Monteith (SPEIP). The results show some relevant changes and tendencies in the drought indices. Statistically significant increase in SPI and SPEI during the cold season (November–March), reflecting precipitation increase, was found in the northern part of the study region, in Estonia, Latvia, Lithuania, northern Belarus and northern Poland. In the rest of study domain, a weak and mostly insignificant decrease prevailed in winter. Summer season (June–August) is characterized by changes in the opposite sign. An increase was observed in the north, while a clear decrease in SPEI, reflecting a drying trend, was typical for the southern regions: the Czech Republic, Slovakia, Hungary, Romania, Moldova and southern Poland. A general drying tendency revealed also in April, which was statistically significant over a wide area in the Czech Republic and Poland. Increasing trends in SPI and SPEI for September and October were detected in Romania, Moldova and Hungary. The use of SPEI instead of SPI generally enhances drying trends.

The decomposition of the leaf litter, fine roots (d

Climate models predict increasing amounts of precipitation and relative atmospheric humidity for high latitudes in the Northern Hemisphere. Therefore, tree species must adjust to the new climatic conditions. We studied young silver birches (Betula pendula Roth) in a long-term (2012–2018) free air humidity manipulation experiment, with the aim of clarifying the acclimation mechanisms to elevated relative atmospheric humidity. In 2016–2018, stem radial increment (measured by dendrometers) and leaf abscission were monitored, and the leaf N and P resorption efficiencies were determined. Biomass allocation was estimated, and the seasonal dynamics of foliar NPK storage was assessed. Humidification increased N resorption efficiency by 11%. The annual means of N resorption efficiency varied from 41 to 52% in control and from 50 to 59% in humidified stands. The P resorption efficiency was strongly affected by weather conditions and varied between years from 25 to 66%. Higher foliar NPK storages at the end of growing season and delayed leaf fall allowed to extend the growth period in humidified plots, which resulted in a week longer stem radial growth. Although stem diameter growth of humidified birches recovered after 5 years, tree height retardation persisted over the seven study years, resulting in increased stem taper (diameter to height ratio) under humidification. Additionally, humidification increased the share of the bark in stem biomass and the number of branches per crown length. The acclimation of silver birches to increased air humidity entails changes in forest N cycle and in birch timber quality.

Expected climate change in high latitudes includes increased air temperature, precipitation, and humidity in the coming decades. Simultaneously, climate extremes like heat waves and droughts become more frequent. In the Free-Air Humidity Manipulation (FAHM) experiment in silver birch ( Betula pendula Roth) and hybrid aspen ( Populus tremula L. × P. tremuloides Michx.) stands in Estonia, we focussed on two questions − how elevated humidity in high temperature and drought conditions influences soil greenhouse gas emissions, and what is the impact of tree species on greenhouse gas emissions. Soil carbon dioxide (CO 2 ), methane (CH 4 ), and nitrous oxide (N 2 O) fluxes were measured using the static chamber method in the 3rd and 4th years of humidification, in 2010 and 2011 respectively. Soil temperature, soil water potential (SWP), relative humidity, and precipitation were monitored; tree and understory growth, litter fluxes, substrate-induced respiration, and basal respiration were measured. During the severe drought in summer 2011 (SWP fell below −250 kPa), aspen stands had higher CO 2 emissions than birch stands and humidification increased CO 2 emission for both tree species. Generally, methane consumption was higher in control than in humidified conditions. Humidification reduced N 2 O emission in aspen stands in 2010. Hence elevated humidity, heat wave and drought, and tree species significantly affected soil greenhouse gas emissions, however CH 4 and N 2 O fluxes remained small in all cases. The results of this study can be used to infer the future greenhouse gas dynamics from mineral soils in northern forests and to forecast growth conditions for energy forestry in changing climate.

Understanding the linkage of soil respiration (Rs) with forest development is essential for long-term C cycle models. We estimated the variation and temperature sensitivity (Q10 value) of Rs and its hetero-, (Rh) and autotrophic (Ra) components in relation to abiotic and biotic factors in Norway spruce stands of different ages, and the effect of trenching on microbial and soil characteristics. Trenching method was used to partition Rs into Rh and Ra. Ingrowth core method was used to estimate fine root production. Soil microbial biomass was measured using manometric respirometers. Rs varied in differently aged stands demonstrating non-linear response to development stage. The variation of Rs was explained by changes in biotic factors rather than by changes in soil microclimate. Rh was more sensitive to Ts than Rs or Ra. After 4 years of trenching soil pH, N, SOM and dehydrogenase activity were significantly changed in trenched plots compared to control plots. Different Q10 values of Rh and Ra in stands of different ages indicate the importance of Rs partitioning. Trenching should be used during a limited number of years because of the possible changes in chemical characteristics of soil and in the activity of soil microbial community.

The interactive effects of climate variables and tree–tree competition are still insufficiently understood drivers of forest response to global climate change. Precipitation and air humidity are predicted to rise concurrently at high latitudes of the Northern Hemisphere. We investigated if the growth response of deciduous trees to elevated air humidity varies with their competitive status. The study was conducted in seed-originated silver birch and monoclonal hybrid aspen stands grown at the Free Air Humidity Manipulation (FAHM) experimental site in Estonia, in which manipulated stands (n = 3 for both species) are exposed to artificially elevated relative air humidity (6–7% over the ambient level). The study period included three growing seasons during which the stands had reached the competitive stage (trees were 7 years old in the final year). A significant ‘treatment×competitive status’ interactive effect on growth was detected in all years in birch (p < 0.01) and in one year in aspen stands (p = 0.015). Competitively advantaged trees were always more strongly affected by elevated humidity. Initially the growth of advantaged and neutral trees of both species remained significantly suppressed in humidified stands. In the following years, dominance and elevated humidity had a synergistic positive effect on the growth of birches. Aspens with different competitive status recovered more uniformly, attaining similar relative growth rates in manipulated and control stands, but preserved a significantly lower total growth yield due to severe initial growth stress. Disadvantaged trees of both species were never significantly affected by elevated humidity. Our results suggest that air humidity affects trees indirectly depending on their social status. Therefore, the response of northern temperate and boreal forests to a more humid climate in the future will likely be modified by competitive relationships among trees, which may potentially affect species composition and cause a need to change forestry practices. This article is protected by copyright. All rights reserved.

Increasing atmospheric humidity—a climate trend predicted for northern Europe—will reduce water flux through vegetation. Diminished transpirational water flux impacts various physiological processes, causing growth decline in deciduous trees. We propose, based on the results obtained from the long-term free air humidity manipulation experiment, concurrent mechanisms to explain the growth deceleration due to increases in relative air humidity. Reduced atmospheric evaporative demand diminishes nutrient uptake and leads to lower leaf nutritional status and to an unbalanced foliar phosphorus/nitrogen ratio (P:N), resulting in a decline in leaf photosynthetic capacity. Elevated relative humidity induces readjustment of foliar metabolism: disturbed N metabolism, accumulation of starch and changes in secondary metabolite contents probably impair both photosynthetic performance and growth. Increased carbohydrate content in the leaves suggests that sink strength of trees is reduced under elevated humidity. As a consequence of the stress, foliar development is hindered, observed at individual leaf or whole-tree foliage levels, lowering production potential of trees proportionally to their foliar area. Larger investments in stem xylem in relation to foliage cause an increase in the ratio of non-photosynthetic to photosynthetic tissues, leading to larger maintenance respiration costs determined by the volume of parenchymatous tissue. An increase in the proportion of living parenchyma cells in relation to dead xylem elements in sapwood additionally enhances respiration costs. Disproportionate changes in hydraulic versus stomatal conductance become a critical factor in the case of weather extremes, which limit canopy conductance and may induce dysfunction of the hydraulic system. Increasing environmental humidity creates favourable conditions for development of pathogens, increasing frequency of fungal damage.

Grey alder is a wide spread tree species in the Baltic region and a promising species for short rotation forestry. The symbiotic dinitrogen (N2) fixation ability makes this tree important for the regulation of nitrogen (N) cycle in forested areas. In a homogeneous 32-year-old natural grey alder stand (GAS) and an adjacent clear-cut (CC) in South-East Estonia (58°17′ N; 27°17′ E; set up in May 2011) we analyzed net nitrogen mineralization (NNM; with incubated bags), N leaching (with plate lysimeters), and nitrous oxide (N2O) fluxes (with static chambers). The total annual NNM did not intensify in the CC area: in the upper 0–20 cm soil layer the NNM was 169.9 and 157.0 kg ha−1 in the (GAS) and in the CC, respectively. In both cases, the share of nitrification was 100% and NNM intensity was the highest in July. During the snow-melt in April, both in the GAS and in the CC site the leaching of total N was up to 25 kg N month−1, whereas in the rest of study period it was negligible in both sites. Harvesting slightly decreased N2O emission, however, it was low at both study sites (−0.55 to 19.75 and −0.77 to 7.43 kg N2O ha−1 yr−1 in the GAS and the CC, respectively). Management of grey alder stands by traditional silvicultural methods (clear-cuts) did not to increased hazardous N losses through leaching.

Processes determining the carbon (C) balance of a forest ecosystem are influenced by a number of climatic and environmental factors. In Northern Europe, a rise in atmospheric humidity and precipitation is predicted. The study aims to ascertain the effect of elevated atmospheric humidity on the components of the C budget and on the C-sequestration capacity of a young birch forest. Biomass production, soil respiration, and other C fluxes were measured in young silver birch (Betula pendula Roth) stands growing on the Free Air Humidity Manipulation (FAHM) experimental site, located in South-East Estonia. The C input fluxes: C sequestration in trees and understory, litter input into soil, and methane oxidation, as well as C output fluxes: soil heterotrophic respiration and C leaching were estimated. Humidified birch stands stored C from the atmosphere, but control stands can be considered as C neutral. Two years of elevated air humidity increased C sequestration in the understory but decreased it in trees. Humidification treatment increased remarkably the C input to the soil. The main reason for such an increase was the higher root litter input into the soil, brought about by the more than two-fold increase of belowground biomass production of the understory in the humidification treatment. Elevated atmospheric humidity increased C sequestration in young silver birch stands, mitigating increasing CO2 concentration in the atmosphere. However, the effect of elevated atmospheric humidity is expected to decrease over time, as plants and soil organisms acclimate, and new communities emerge.

Elevated atmospheric humidity reduced bud size by restricting primordium growth and increased the frequency of bud break in fast-growing deciduous trees, but the responses are species-specific. The initiation, development, and growth potential of buds determine the structure of a tree crown. Climate change scenarios project increasing amounts of precipitation at high latitudes in the future, but the effects of a more humid climate on bud size and growth potential remain mostly unexplored. This study investigates the effects of atmospheric humidity on fast-growing deciduous trees, silver birch (Betula pendula Roth.) and hybrid aspen (Populus tremula L. × P. tremuloides Michx.), planted in a unique free-air experimental facility, designed for increasing air humidity during the growing season. Over four consecutive years (2009–2012), the size of overwintering buds was assessed in the upper crown of young trees, and additionally, annual height increments were assessed during the study period. Furthermore, bud contents, probabilities of bud death and break, and subsequent shoot growth were examined. In silver birch, misting effect on height growth depended on year, possibly due to acclimation or variable weather conditions, but bud size was consistently reduced. Nevertheless, misting restricted the growth rather than the initiation of leaf primordia in the bud, and decreased bud size did not translate into changes in the leaf area of future shoots. In contrast, the size of hybrid aspen buds was markedly reduced by misting only in 2009; however, increased humidity promoted bud break, reducing the proportion of dormant buds. The underlying mechanisms causing reduced bud size may involve interactions with shoot growth, but require further study. Although the effect of stimulated bud break is subtle in a given year, cumulative effects may modulate crown structure in the long term, facilitating the acclimation of tree growth to rising humidity in the future.

Carbon (C) budgets were compiled for silver birch chronosequence stands by synthesizing the above- and belowground C pools and fluxes with the aim to assess the impact of age on stand C sequestration and cycling. The fine root (d Soil respiration (Rs) was measured during the two growing seasons of 2010 and 2011; the trenching method was used to estimate the contribution of heterotrophic respiration (Rh) to total soil respiration. Soil temperature was the driving environmental factor of the temporal variation of Rs and Rh. Stand age affected significantly respiration rates. Annual Rs was 6.2, 9.7 and 8.2 t C ha−1 and annual Rh was 2.97, 4.21 and 3.61 t C ha−1 in the pole, middle-aged and premature silver birch stands, respectively. The annual contribution of Rh to Rs was similar in each stand ranging from 0.43 to 0.48. Total annual net primary production (NPP) of the ecosystems of 7.4, 7.9 and 8.5 t C ha−1 year−1 was estimated in the pole, middle-aged and premature stands. After balancing the C input and output fluxes in the silver birch stands of different development stages, it appeared that they all acted as effective C sinks. Net ecosystem production (NEP) was 4.4, 3.7 and 4.9 t C ha−1 year−1 in the pole, middle-aged and premature stands, respectively. In the premature stand the second layer of the spruce contributed significantly to the increased C input. The annual organic C input into the soil through above- and belowground litter occurred to be of the same magnitude as C loss via annual heterotrophic respiration. Thus, annual increment of woody biomass in fertile silver birch stands reflects annual organic C sequestration in the ecosystem. Among the studied stands, estimated NEP values were the lowest in the middle-aged stand and the highest in the oldest stand, indicating non-linear relationship between stand NEP and stand age.

The tree root–mycorhizosphere plays a key role in resource uptake, but also in the adaptation of forests to changing environments. The adaptive foraging mechanisms of ectomycorrhizal (EcM) and fine roots of Picea abies, Pinus sylvestris and Betula pendula were evaluated along a gradient from temperate to subarctic boreal forest (38 sites between latitudes 48°N and 69°N) in Europe. Variables describing tree resource uptake structures and processes (absorptive fine root biomass and morphology, nitrogen (N) concentration in absorptive roots, extramatrical mycelium (EMM) biomass, community structure of root-associated EcM fungi, soil and rhizosphere bacteria) were used to analyse relationships between root system functional traits and climate, soil and stand characteristics. Absorptive fine root biomass per stand basal area increased significantly from temperate to boreal forests, coinciding with longer and thinner root tips with higher tissue density, smaller EMM biomass per root length and a shift in soil microbial community structure. The soil carbon (C) : N ratio was found to explain most of the variability in absorptive fine root and EMM biomass, root tissue density, N concentration and rhizosphere bacterial community structure. We suggest a concept of absorptive fine root foraging strategies involving both qualitative and quantitative changes in the root–mycorrhiza–bacteria continuum along climate and soil C : N gradients.

Soil microbes play a fundamental role in forest ecosystems and respond rapidly to changes in the environment. Simultaneously with the temperature increase the climate change scenarios also predict an intensified hydrological cycle for the Baltic Sea runoff region. The aim of this study was to assess the effect of elevated air humidity on the top soil microbial community structure of a silver birch (Betula pendula Roth.) stand by using a free air humidity manipulation facility (FAHM). The bacterial community structures of bulk soil and birch rhizosphere were analyzed using high-throughput sequencing of bacteria-specific16S rRNA gene fragments and quantification of denitrification related genes. The increased air humidity altered both bulk soil and rhizosphere bacterial community structures, and changes in the bacterial communities initiated by elevated air humidity were related to modified soil abiotic and biotic variables. Network analysis revealed that variation in soil bacterial community structural units is explained by altered abiotic conditions such as increased pH value in bulk soil, while in rhizosphere the change in absorptive root morphology had a higher effect. Among root morphological traits, the absorptive root diameter was strongest related to the bacterial community structure. The changes in bacterial community structures under elevated air humidity are associated with shifts in C, N, and P turnover as well as mineral weathering processes in soil. Increased air humidity decreased the nir and nosZ gene abundance in the rhizosphere bacterial community. The potential contribution of the denitrification to the N2O emission was not affected by the elevated air humidity in birch stand soil. In addition, the study revealed a strong link between the bacterial community structure, abundance of denitrification related genes, and birch absorptive root morphology in the ecosystem system adaptation to elevated air humidity.

Climate change is predicted to bring about a rise in precipitation and atmospheric humidity at northern latitudes, which could have a considerable impact on forest ecology and management. This study investigates the effect of elevated relative air humidity (RH) on tree growth and biomass accumulation and allocation in six-year-old seedling-originated silver birch (Betula pendula Roth) and monoclonal hybrid aspen (Populus tremula L.×P. tremuloides Michx.) stands. The study was conducted in the unique Free Air Humidity Manipulation experimental facility in Estonia. Two understory vegetation types (forest and pasture) were used in the experimental plots. As a short-term response during the first manipulation years, a small rise (6–7%) in RH reduced the growth of both tree species. In the fifth humidification year, suppression of growth continued in aspen, but birch acclimated effectively to elevated RH – differences in biomass and stem diameter increments levelled out in humidified (H) and control (C) plots. The H birches ensured biomass accumulation by changing the biomass and morphology of the physiologically most active tree parts: increasing fine-root biomass, as well as specific areas of fine roots (SRA) and leaves (SLA). The effect of elevated RH on most leaf and fine root characteristics of aspens was in a similar direction as that of birches, but weaker, and the plasticity of the functional traits was also lower compared to birches, probably due to the lack of genetic variation in monoclonal aspens. The biomass of young aspens was 22% lower in H plots. The relative aboveground biomass allocation was not affected by elevated RH. The aboveground biomass of humidified birches was higher in plots with forest understory, where root competition was lower compared to the dense root systems of grasses in pasture understory plots. Aspen biomass was not affected by understory vegetation type. We conclude that young silver birches have sufficient phenotypic plasticity to acclimate to elevated RH and the forests retain biomass accumulation. However, the growth acclimation of planted forests of clonal plant material is more complicated and humidity-tolerance should be considered in the selection of new clones for areas where an increase in RH is anticipated.

In the present study the chronosequence approach was applied to the analysis of the dynamics of the growth of 2–45-year-old grey alder stands ( Alnus incana ) growing at fertile sites as well as the dynamics of carbon (C) and nitrogen (N) accumulation in woody biomass and in the soil. A new yield table was elaborated for natural grey alder stands growing at fertile sites. The average growing stock and increment of grey alder stands were lower than those presented in earlier yield tables compiled in Estonia or in the other Baltic or Nordic states. It can be explained by an uneven spatial distribution of trees in natural grey alder stands; because of this, the production of different alder stands of the same age was highly variable. However, some stands were characterised by remarkably high production, which indicates the high growth potential of this tree species. The bulk maturity of grey alder stands is achieved at the age of 12–13 years. However, the recommendable optimal harvesting age of grey alder stands could be 20–25 years, as annual woody biomass increment was high even after the age of 20 years. The average stemwood density found in this study was 396 ± 3.6 kg m −3 and the average density of the branches was 460 ± 2.9 kg m −3 . Regarding of CN accumulation in the stands, different land use histories demonstrated different patterns. First-generation grey alder stands growing on previously non-forested lands accumulated effectively C and N in the soil. The average increase of the C pool in the 10 cm topsoil layer was in the range 1.1–1.2 t ha −1 yr −1 in young stands and 0.97–0.84 t ha −1 yr −1 in older stands. In the case of second-generation grey alder stands the soil C pool in young and old stands was of same magnitude and these stands accumulated C mainly in woody biomass. The share of the soil C pool in middle-aged and old grey alder stands was roughly two times as large as the C storage accumulated in the above-ground woody biomass of the trees. The average N accumulation in first-generation grey alder stands of the age of 14–35 years was 74 kg N ha −1 yr −1 . Also a significant acidifying effect of alders on the soil pH status was revealed. The study confirmed that grey alder has the potential to be a high yielding tree in short-rotation forestry for woody biomass production. Grey alder stands serve as efficient forest ecosystems accumulating C both in biomass and in the soil. However, previous land use history plays an essential role in this respect.

The predicted increase in precipitation at northern latitudes is an important factor affecting the functioning of forest ecosystems, yet the influence of increased atmospheric humidity on the forest ecosystem carbon cycle is still largely unknown. Our objectives were to determine the effect of elevated atmospheric humidity on soil respiration in silver birch (Betula pendula Roth.) plantations in a Free Air Humidity Manipulation experimental facility (FAHM). Soil respiration was monitored monthly from May to October, in 2008 and 2009 in three control and in three misting plots; soil temperature and soil moisture were measured simultaneously. Fine-root and rhizome biomass of the understory was measured by sequential soil cores. Soil microbial biomass and basal respiration were measured using manometric respirometers. After the first two years of manipulation, humidification led to lower soil respiration. Soil temperature was the main factor influencing seasonal dynamics of soil respiration, describing up to 75% of the total variation of soil respiration. Soil moisture had a weak negative effect on soil respiration. Humidification caused a remarkable increase in below-ground biomass and the production of the understory, and a 28% increase in the basal respiration of microbes. However, above-ground biomass and root turnover rate of the understory were almost unchanged. Hence, elevated atmospheric humidity significantly affects carbon cycle of deciduous forest. However, further studies are necessary for a better understanding of soil respiration response to changes in atmospheric humidity, in order to predict carbon balance in changing climate conditions.

Climate change is predicted to bring about a rise in precipitation and air humidity at northern latitudes, which could have considerable impact on forest management. This paper investigates the effect of increased air humidity and understory composition on short root morphology and on the relative abundance of colonizing ectomycorrhizal (EcM) fungal associates in silver birch (Betula pendula Roth.) stands. Short root morphological traits of silver birch were analyzed at increased humidity and ambient conditions for two different understories (early-successional grasses and diverse “forest” understory) in three consecutive years (2009–2011). The fungal community was determined in 2010 (after three seasons of misting) using molecular methods. The study was conducted on the Free Air Humidity Manipulation (FAHM) experimental facility established in Estonia. Silver birches responded to the rise in air humidity by forming longer and thinner short roots, which can be interpreted as a morphological adaptation leading to an increase in the absorptive area. The response was stronger when humidification concurred with the species-poor understory of pioneer grasses. The inter- and intra-treatment variation in short root morphological parameters decreased by the third year. Using molecular methods, overall 64 EcM taxonomic units were distinguished. Hydrophilic fungal morphotypes dominated significantly in humidified plots, hydrophobic morphotypes in control plots. Our results suggest that rising air humidity causes a morphological stress response in EcM short roots. Young trees show the ability to adapt to climate change with great plasticity by modifying short root length, diameter and specific root length (SRL). Humidification leads to a shift in the fungal colonizers towards the dominance of hydrophilic taxa, which may alter ecosystem functioning.

An essential carbon (C) pool of forest ecosystems is stored in belowground tree biomass; however, data about belowground C and nutrient accumulation is scarce. It is crucial to involve belowground part for developing regional and global C or nitrogen (N) budgets for different forest ecosystems. Fine root ( D D ⩾ 2.0 mm) biomass were studied in a chronosequence in four silver birch ( Betula pendula Roth) stands aged 6–60 years. The soil coring method was used for estimation of birch fine root biomass and necromass in the upper 40 cm topsoil layer. Stump biomass and coarse root biomass were estimated by excavation of the root systems of model trees in a 6-year-old stand and in a 32-year-old silver birch stand. For a 14-year-old stand and for a 60-year-old stand, the developed root-shoot ratio approach was used. Carbon and nitrogen accumulation in belowground biomass was estimated as well. Fine root biomass varied between 103 g m −2 and 409 g m −2 and fine root necromass, between 22 g m −2 and 93 g m −2 ; both increased with stand age. Fine root vertical distribution showed a gradual decrease with soil depth in all profiles, however, fine root biomass shifted more to the deeper soil layers with increasing stand age. The fine root live/dead ratio decreased hyperbolically with stand age while the change was most rapid before pole age. The most active part of the fine root system – ectomycorrhizal biomass (EcMB) – was estimated for three stands (6-, 14- and 32-year-old); EcMB per basal area varied between 8 and 14 kg m −2 and was not related to stand age. Coarse root biomass increased with stand age from 7.9 Mg ha −1 in the 6-year-old stand to 40.2 Mg ha −1 in the 60-year-old stand. The root-shoot ratio decreased in silver birch stands drastically between 6 and 14 years but stabilized thereafter. Hence the use of a root-shoot ratio of 21% for calculation of belowground biomass from aboveground biomass for silver birch stands is justified. Carbon accumulation in the belowground tree biomass of silver birch stands varied between 4.0 Mg ha −1 and 19.8 Mg ha −1 , being the highest in the 60-year-old stand. The C accumulated in belowground biomass accounted for 3–4% of the total C storage of the total C storage of the forest ecosystem in the young stands and for 9.5–11% in the middle-aged and mature stands. Fine root mortality and the corresponding C flow as fine-root litter input increased with stand age. As the biomass of the trees was the main C sink, a significant share (3–28%) of C was accumulated in the belowground part of the stand. C accumulation in the fine roots was low in chronosequence birch stands; however the C flux into the soil through fine root litter may be considerable.

In the Northern and Baltic countries, grey alder is a prospective tree species for short-rotation forestry. Hence, knowledge about the functioning of such forest ecosystems is critical in order to manage them in a sustainable and environmentally sound way. The 17-year-long continuous time series study is conducted in a grey alder plantation growing on abandoned agricultural land. The results of above- and below-ground biomass and production of the 17-year-old stand are compared to the earlier published respective data from the same stand at the ages of 5 and 10 years. The objectives of the current study were to assess (1) above-ground biomass (AGB) and production; (2) below-ground biomass: coarse root biomass (CRB), fine root biomass (FRB) and fine root production (FRP); (3) carbon (C) and nitrogen (N) accumulation dynamics in grey alder stand growing on former arable land. The main results of the 17-year-old stand were as follows: AGB 120.8 t ha−1; current annual increment of the stem mass 5.7 t ha year−1; calculated CRB 22.3 t ha−1; FRB 81 ± 10 g m−2; nodule biomass 31 ± 19 g m−2; fine root necromass 11 ± 2 g m−2; FRP 53 g DM m−2 year−1; fine root turnover rate 0.54 year−1; and fine root longevity 1.9 years. FRB was strongly correlated with the stand basal area and stem mass. Fine root efficiency was the highest at the age of 10 years; at the age of 17 years, it had slightly reduced. Grey alder stand significantly increased N and Corg content in topsoil. The role of fine roots for the sequestration of C is quite modest compared to leaf litter C flux.

A study was performed on saplings of silver birch (Betula pendula Roth) growing at the free air humidity manipulation site, which was established to investigate the effect of increased air humidity on tree performance and canopy functioning. The aim of the experiment was to simulate the impact of the increasing atmospheric humidity on forest ecosystems predicted for northern Europe. Artificially elevated relative humidity (RH), which causes transpirational flux to decrease, diminished nutrient supply to the foliage; leaf nitrogen content, phosphorus content and P:N ratio decreased. The changes in leaf nutritional status brought about a considerable decline in both photosynthetic capacity (A max, V cmax, J max) and tree growth rate. The manipulation induced diverse changes in tree hydraulic architecture and other functional traits. Different segments of the soil-to-leaf water transport pathway responded differently: leaf hydraulic conductance (K L) decreased, while hydraulic conductance of root systems (K R) and leaf-specific conductivity of stem-wood increased in response to elevated RH. Humidification caused the Huber values of stems to increase, thus reflecting changes in allocation patterns; relatively more resources were allocated to vascular tissue and less to foliage. The elevated RH induced substantial changes in specific leaf area (increased), branch- (decreased) and stem-wood density (decreased). The observed responses suggest that the expected climate-change-induced increase in the growth rate of trees at northern latitudes (boreal areas) due to the earlier start of the growing season in spring or higher carbon assimilation rate could be smaller or null if temperature rise is accompanied by a rise in atmospheric absolute humidity.

The two alder species, black alder (Alnus glutinosa (L.) Gaertn.) and grey alder (Alnus incana (L.) Moench) are known to be pioneer species in the succession of new land areas, and important tree species in renewable biomass production, the restoration of post-mining sites and riparian forest ecosystems. We analyzed the influence of soil physico-chemical characteristics (soil water content, pHKCl, total N, soluble P, organic matter content, C and N ratio, and elemental content) on bacterial community structure based on pyrosequencing analysis of the 16S rRNA gene V2 and partly V3 region in two black and two grey alder stand soils with different management histories. The analyses revealed clear differences in all the measured chemical characteristics of studied soils. All the studied stands also had distinct soil bacterial communities, and the number of shared species was low. In all stands species from phylum Proteobacteria were dominant, and the next phyla by percentage were Bacteroidetes and Actinobacteria. At the family level, Chitinophagaceae and Bradyrhizobiaceae species dominated. The obtained bacterial community Inverted Simpson's diversity indices showed no difference between the studied sites. The alder species did not affect soil bacterial community structure. Distance-based regression analysis indicated that soil pH value, water content, soluble phosphorus concentration and also total boron, cadmium, and aluminium content were related to the variation of soil bacterial community structure in alder stand soils. The results of this study emphasize the importance of soil geomorphological properties in addition to soil physical and chemical characteristics in the formation of soil bacterial community structure during restoration of exhausted open mining areas, management of abandoned agricultural lands, and short rotation forests with different alder species.

The influence of forest ageing on fine-root morphology and relations between fine-root and leaf characteristics is poorly studied. The aim of this study was to analyse age-driven changes in ectomycorrhizal roots (EcM roots) and leaf morphology in a chronosequence of silver birch (Betula pendula Roth.), which would provide a better understanding of adaptation responses and acclimation capacity of tree roots and leaves. The chronosequence included six age classes (3, 6, 14, 32, 45, and 60 years.). All stands had regenerated naturally and grew in a highly productive Oxalis forest site type in Estonia. Most changes in the morphology of EcM roots and leaves of silver birch occur faster at a young age. The functional parameters—mean specific area of EcM root (SRA) and leaf specific area (SLA) as well as leaf N—decreased with age. EcM root SRA and specific root length (SRL) decreased with stand age as a result of increased mean diameter and tissue density. In age classes of 6, 14, and 32 years, the total number of dominating EcM taxa was 34, and the distribution of four different dominating EcM exploration types (contact-, short-, medium-, long-distance) was similar. We conclude that high values of SRA, SLA, and leaf N measured in young silver birch stands indicate high activity of physiological processes necessary for fast-growing young trees. A decrease of SLA and SRA and N in the chronosequence of fertile stands of silver birch is most probably caused by down-regulation of growth, affecting simultaneously leaves and fine roots.

Previous investigations have been demonstrated that night-time water flux may increase or remain unchanged at low mineral nutrient availability. At the same time, it is a well-known fact that night-time water flux is relatively high in fast-growing species, which typically grow in fertile soil. To test the impact of soil nutrient deficiency on night-time water flux and fine-root acclimation in saplings of hybrid aspen ( Populus tremula L. × Populus tremuloides Michx.), a growth chamber experiment was carried out. We set up a hypothesis that night-time sap flux density ( F ) and night-time water use percentage from daytime water use (NWU) are more intense in fertile conditions, in order to enhance or sustain the high intrinsic growth potential of hybrid aspen. The main limiting element in the low nutrient availability treatment (low-n) was nitrogen. The nitrogen concentrations of leaves and fine-roots exhibited the strongest ( R 2 = 0.95; P F and NWU were several times higher in the case of fertilized soil (high-n treatment) compared to low-n treatment ( P F disappeared at the end of the period of sap flow measurements, when the foliage area of trees was almost full-grown. Endogenous increase in water flux during predawn hours was observable only in the high-n treatment. Significantly greater NWU ( P P P

Air moisture is one of the main factors causing the greenhouse effect, but humidity has not been thoroughly studied at the ecosystem level. In 2006 a free-air humidity manipulation (FAHM) facility was established in Estonia to investigate the effect of humidity on the performance of two tree species—silver birch (Betula pendula Roth.) and hybrid aspen (Populus tremula L. × P. tremuloides Michx.). The trial is located on an Endogleyic Planosol of former arable land and offers the opportunity to change relative air humidity through controlled artificial misting and drying. We measured the CO2, CH4 and N2O emission from the FAHM system using closed chamber and gas-chromatograph techniques from July 2009 to October 2010. Measurements were carried out once a month in three humidification (h) plots and in three control (c) plots. The vegetation period was rainy in 2009, but the next summer was relatively dry. The dry summer interacted better with the humidification. The CO2 flux decreased when the air moisture was higher than in the control plots. The soil acted as a sink for methane. Less CH4 was oxidized in the soil with increased humidity. Emission of N2O did not correlate with air humidity, although one could observe a clear tendency that there was a smaller N2O flux during the period with increased humidity. Expectedly, CO2 emission and CH4 consumption demonstrated strong positive correlations with soil temperature.

The main objectives of this study were to determine how the carbon age of fine root cellulose varies between stands, tree species, root diameter and soil depth. In addition, we also compared the carbon age of fine roots from soil cores of this study with reported values from the roots of the same diameter classes of ingrowth cores on the same sites. We used natural abundance of 14C to estimate root carbon age in four boreal Norway spruce and Scots pine stands in Finland and Estonia. Age of fine root carbon was older in 1.5–2 mm diameter fine roots than in fine roots with

During recent decades, studies of the carbon (C) balance of forest ecosystems have became more actual, mainly in connection with the global increase of CO2 in the atmosphere. In the present study the stand chronosequence approach was applied to analyse C sequestration dynamics. Study was made of C accumulation both in biomass and in the soil in 6–60-year-old silver birch (Betula pendula) stands growing at fertile (Oxalis) sites. As the growth of the studied stands was vigorous, their yield was higher than that presented in several yield tables for earlier periods. The C concentration (C%) in different compartments of the trees varied between 47% and 55%. However, the weighted average of C concentration in the silver birch trees was approximately 50% regardless of stand age. The average C concentration of the herbaceous understorey plants was 43.3 ± 0.5%. The soil Corg pool was independent of stand age, and so far there occurred no C accumulation during stand succession, expressed as Corg values or stage of forest floor formation. This might indicate fast Corg turnover in the soils of the Oxalis site. The total C pool in a mature silver birch stand was 185 t ha−1 of which 50% was accumulated in the aboveground part of the trees. In young birch stands the C pool in aboveground biomass and in the soil accounted for 21–39% and 53–71%, respectively, of the total C pool of a stand. In pre-mature and mature stands the corresponding share accounted for 50–59% of the aboveground C of the trees and 29–38% of the soil C pool. Due to closed canopies, the role of herbaceous understorey plants as a C sink was modest, constituting 1% or even less of the total C pool of the older stands. The annual C flux 1.6 t ha−1 yr−1 into the soil via litter fall was the largest in the middle-age stand. Our results show that the main C sink in fertile silver birch stands is located in the wooden parts of trees. The C pool in tree biomass increased with stand age, whereas the soil Corg pool remained stable. For a more profound understanding of C cycling in silver birch forest, soil respiration fluxes should be measured.

The aim of this study was to test P-enriched filter materials from a wastewater treatment experiment regarding their fertilizing efficiency in pot experiments with silver birch (Betula pendula Roth.) seedlings. Tested materials included hydrated calcium-rich oil shale ash and well-mineralised peat. A mixture of peat and hydrated ash demonstrated the best results: seedlings grown on that mixture had the highest P concentration and an optimal N:P:K ratio in leaves. Hydrated ash has a low concentration of heavy metals and almost the same composition as common lime fertilizers. The hydrated ash sediment and its combination with well-mineralised peat enriched with phosphorus in wastewater treatment filters are promising materials for forest soil fertilization.

A facility for free air humidity manipulation (FAHM) was established to investigate the effect of increased air humidity on trees’ performance and their canopy functioning with respect to rising air humidity predicted for Northern Europe. The FAHM system enables air relative humidity (RH) to be increased up to 18 units (%) over the ambient level during mist fumigation, depending on the wind speed inside the experimental stand. Water was dispersed inside 14 × 14 m experimental plots in the form of mist with an average particle size of 50 μm from June to August in 2008, and from May to September in 2009. The average increase in RH was 7 units (%) over the whole period of humidification in 2008 ( P F ) in silver birch ( Betula pendula Roth.) trees was 24.8% ( P P P > 0.05) in silver birch on the days without misting. In hybrid aspen ( Populus tremula L. × P. tremuloides Michx.) the average difference in F between C and H plots was 61.1% ( P P F as a result of long-term acclimation to fumigation. The leaves of silver birch in a humidified plot demonstrated up to 2.4 °C lower ( P T L ) compared to the control plot in 2009. The decline in T L decreased the humidity gradient between leaf and air by about 1/3, whereas 2/3 of the effect was caused directly by changes in air humidity in the leaf boundary layer. Our preliminary data suggest that the FAHM experimental facility enables water fluxes through a deciduous tree canopy to be reduced and this effect is attributable both to the increased air humidity and decreased leaf temperature. Changes in these two basic factors may create considerable differences in the physiology, anatomy and nutrition of a whole tree, also affecting forest functioning in the light of global climate change.

Fine root acclimation to different environmental conditions is crucial for growth and sustainability of forest trees. Relatively small changes in fine root standing biomass (FRB), morphology or mycorrhizal symbiosis may result in a large change in forest carbon, nutrient and water cycles. We elucidated the changes in fine root traits and associated ectomycorrhizal (EcM) fungi in 12 Norway spruce stands across a climatic and N deposition gradient from subarctic-boreal to temperate regions in Europe (68°N–48°N). We analysed the standing FRB and the ectomycorrhizal root tip biomass (EcMB, g m−2) simultaneously with measurements of the EcM root morphological traits (e.g. mean root length, root tissue density (RTD), N% in EcM roots) and frequency of dominating EcM fungi in different stands in relation to climate, soil and site characteristics. Latitude and N deposition explained the greatest proportion of variation in fine root traits. EcMB per stand basal area (BA) increased exponentially with latitude: by about 12.7 kg m−2 with an increase of 10° latitude from southern Germany to Estonia and southern Finland and by about 44.7 kg m−2 with next latitudinal 10° from southern to northern Finland. Boreal Norway spruce forests had 4.5 to 11 times more EcM root tips per stand BA, and the tips were 2.1 times longer, with 1.5 times higher RTD and about 1/3 lower N concentration. There was 19% higher proportion of root tips colonized by long-distance exploration type forming EcM fungi in the southern forests indicating importance of EcM symbiont foraging strategy in fine root nutrient acquisition. In the boreal zone, we predict ca. 50% decrease in EcMB per stand BA with an increase of 2 °C annual mean temperature. Different fine root foraging strategies in boreal and temperate forests highlight the importance of complex studies on respective regulatory mechanisms in changing climate.

The growth, aboveground biomass production and nutrient accumulation in black alder (Alnus glutinosa (L.) Gaertn.), silver birch (Betula pendula Roth.) and Scots pine (Pinus sylvestris L.) plantations during 7 years after planting were investigated on reclaimed oil shale mining areas in Northeast Estonia with the aim to assess the suitability of the studied species for the reclamation of post-mining areas. The present study revealed changes in soil properties with increasing stand age. Soil pH and P concentration decreased and soil N concentration increased with stand age. The largest height and diameter of trees, aboveground biomass and current annual production occurred in the black alder stands. In the 7-year-old stands the aboveground biomass of black alder (2100 trees ha−1) was 2563 kg ha−1, in silver birch (1017 trees ha−1) and Scots pine (3042 trees ha−1) stands respective figures were 161 and 1899 kg ha−1. The largest amounts of N, P, K accumulated in the aboveground part were in black alder stands. In the 7th year, the amount of N accumulated in the aboveground biomass of black alder stand was 36.1 kg ha−1, the amounts of P and K were 3.0 and 8.8 kg ha−1, respectively. The larger amounts of nutrients in black alder plantations are related to the larger biomass of stands. The studied species used N and P with different efficiency for the production of a unit of biomass. Black alder and silver birch needed more N and P for biomass production, and Scots pine used nutrients most efficiently. The present study showed that during 7 years after planting, the survival and productivity of black alder were high. Therefore black alder is a promising tree species for the reclamation of oil shale post-mining areas.

Mining activities create wastelands that require reclamation. The relief of abandoned opencast oil shale mining area is rugged, and the mining spoil is extremely stony and alkaline (pH 8), with low N and organic content. Planting of fast-growing deciduous tree species such as silver birch (Betula pendula) on post-mining area is the best means to accelerate the development of a new forest ecosystem in such harsh conditions. A chronosequence of silver birch stands (1, 2, 3, 5, 29, 40 years old) was investigated to reveal changes in bulk soil (S) and rhizosphere (R) properties, in rhizosphere effect on bacterial activity and diversity, and in fine-root morphological adaptations in relation to stand development. The rhizosphere effect on bacterial activity was measured as a rhizosphere/soil (R/S) ratio and on species diversity as a similarity (%) between rhizosphere and bulk soil bacterial communities. Bacterial species diversity was determined by denaturing gradient gel electrophoresis (DGGE) technique and was expressed as Shannon diversity index. Biolog EcoPlates were used to determine the summed activity of cultivable bacteria in rhizosphere and bulk soil. Short-root morphological parameters were measured using WinRHIZO™ Pro. Soil pH and available P concentration decreased logarithmically, and N% and organic matter concentration increased linearly with increasing stand age. During the first 30 years of stand development SIR increased an order, from 0.18 to 1.90 mg C g−1. Bulk soil bacterial diversity increased logarithmically with stand age. The bacterial diversity was higher in rhizosphere than in bulk soil. Rhizosphere effect on bacterial activity was low a year after planting, increased more than two times in the next 2 years, and decreased thereafter rapidly with stand age. Rhizosphere effect, indicating plant support to rhizosphere microbial communities, was highest when soil conditions were still poor, but trees had already overcome the transplant shock. All short-root morphological parameters showed certain trends with age. Specific short-root length varied between 56 and 313 m g−1 and decreased logarithmically with stand age and soil improvement. The fastest changes in short-root morphology, rhizosphere effect, and soil pH occurred during the early development of silver birch stands – in the first 5 years; P nutrition and N use efficiency improved simultaneously. Rhizosphere effect and short-root morphological adaptation have an important role in soil and stand development on oil shale post-mining area, and silver birch is a promising tree species for reclamation of alkaline mining spoil.

The effect of adding low concentrations of a sediment/microbial community suspension to speed up the development of the denitrification capacity in the restored HSSF of a hybrid CW was studied during a one-year period after the filling of the horizontal filter with new light weight aggregates (LWA). Two HSSF filters with the same LWA substrate but different wastewater flow regimes were used as donor systems for the bioaugmentation. NO3-N concentrations in the outflows of all variants of studied MCs were significantly influenced by the time factor (p

Short-rotation energy forestry is one of the potential ways for management of abandoned agricultural areas. It helps sequestrate carbon and mitigate human-induced climate changes. Owing to symbiotic dinitrogen (N 2 ) fixation by actinomycetes and the soil fertilizing capacity and fast biomass growth of grey alders, the latter can be suitable species for short-rotation forestry. In our study of a young grey alder stand ( Alnus incana (L.) Moench) on abandoned arable land in Estonia we tested the following hypotheses: (1) afforestation of abandoned agricultural land by grey alder significantly affects the soil nitrogen (N) status already during the first rotation period; (2) input of symbiotic fixation covers an essential part of the plant annual N demand of the stand; (3) despite a considerable N input into the ecosystem of a young alder stand, there will occur no significant environmental hazards (N leaching or N 2 O emissions). The first two hypotheses can be accepted: there was a significant increase in N and C content in the topsoil (from 0.11 to 0.14%, and from 1.4 to 1.7%, respectively), and N fixation (151.5 kg N ha −1 yr −1 ) covered about 74% of the annual N demand of the stand. The third hypothesis met support as well: N 2 O emissions (0.5 kg N ha −1 yr −1 ) were low, while most of the annual gaseous N losses were in the form of N 2 (73.8 kg N ha −1 yr −1 ). Annual average NO 3 –N leaching was 15 kg N ha −1 yr −1 but the N that leached from topsoil accumulated in deeper soil layers. The soil acidifying effect of alders was clearly evident; during the 14-year period soil acidity increased 1.3 units in the upper 0–10 cm topsoil layer.

Limited nutrient acquisition from soil is a key process limiting productivity in boreal forest. We investigated short-root morphological adaptations and rhizosphere effect in relation to site conditions in interaction with tree mineral nutrition. We studied seven young (8- to 14-year-old) silver birch (Betula pendula Roth.) stands on abandoned agricultural land in Estonia. Soil pH varied from 3.8 to 7.0, and soil N % from 0.07 to 0.26%. Tree nutrient (NPK) status was expressed by leaf nutrient concentrations. Leaf N correlated negatively with short-root specific length and area. Summed activity (SA) and metabolic diversity of bacteria (by BIOLOG Ecoplate™), bacterial community diversity (by DGGE) and pHKCl were determined for rhizosphere (R) and bulk soil (S) to reveal the extent of the rhizosphere effect. Bacterial activity in rhizosphere was 1.4–4.7 times higher than in bulk soil. Ratio SAR/SAS indicating root support to the rhizosphere bacterial communities decreased with increasing bulk soil pH; however, when bulk soil pH was ≥5, the decrease in SAR/SAS was insignificant, i.e. the rhizosphere effect stayed at a stable level. Diversity of bacterial community was 6% higher in bulk soil than in rhizosphere. Rhizosphere acidification occurred in studied stands when bulk soil pHKCl ≥ 5. Short-root N % correlated positively with SAR/SAS. We concluded that tree N-nutritional status was related to short-root morphological parameters but not to studied microbiological characteristics in the soil of young silver birch stands.

We studied greenhouse gas (GHG) fluxes in two differently loaded riparian Alnus incana-dominated forests in agricultural landscapes of southern Estonia: a 33-year-old stand in Porijogi, in which the uphill agricultural activities had been abandoned since the middle of the 1990s, and a 50-year-old stand in Viiratsi, which still receives polluted lateral flow from uphill fields fertilized with pig slurry. In Porijogi, closed-chamber based sampling lasted from October 2001 to October 2009, whereas in Viiratsi the sampling period was from November 2003 to October 2009. Both temporal and spatial variations in all GHG gas fluxes were remarkable. Local differences in GHG fluxes between micro-sites (“Edge”, “Dry” and “Wet” in Porijogi, and “Wet”, “Slope” and “Dry” in Viiratsi) were sometimes greater than those between sites. Median values of GHG fluxes from both sites over the whole study period and all microsites did not differ significantly, being 45 and 42 mg CO2–C m−2 h−1, 8 and 0.5 μg CH4–C m−2 h−1, 1.0 and 2.1 mg N2–N m−2 h−1, and 5 and 9 μg N2O–N m−2 h−1, in Porijogi and Viiratsi, respectively. The N2:N2O ratio in Viiratsi (40–1200) was lower than in Porijogi (10–7600). The median values-based estimation of the Global Warming Potential of CH4 and N2O was 19 and 185 kg CO2 equivalents (eq) ha−1 yr−1 in Porijogi and −14 and 336 kg CO2 eq ha−1 yr−1 in Viiratsi, respectively. A significant Spearman rank correlation was found between the mean monthly air temperature and CO2, CH4 and N2 fluxes in Porijogi, and N2O flux in Viiratsi, and between the monthly precipitation and CH4 fluxes in both study sites. Higher groundwater level significantly increases CH4 emission and decreases CO2 and N2O emission, whereas higher soil temperature significantly increases N2O, CH4 and N2 emission values. In Porijogi, GHG emissions did not display any discernable trend, whereas in Viiratsi a significant increase in CO2, N2, and N2O emissions has been found. This may be a result of the age of the grey alder stand, but may also be caused by the long-term nutrient load of this riparian alder stand, which indicates a need for the management of similar heavily loaded riparian alder stands.

Nitrous oxide (N2O) is a powerful greenhouse gas and the main driver of stratospheric ozone depletion. Since soils are the largest source of N2O, predicting soil response to changes in climate or land use is central to understanding and managing N2O. Here we find that N2O flux can be predicted by models incorporating soil nitrate concentration (NO3−), water content and temperature using a global field survey of N2O emissions and potential driving factors across a wide range of organic soils. N2O emissions increase with NO3− and follow a bell-shaped distribution with water content. Combining the two functions explains 72% of N2O emission from all organic soils. Above 5 mg NO3−-N kg−1, either draining wet soils or irrigating well-drained soils increases N2O emission by orders of magnitude. As soil temperature together with NO3− explains 69% of N2O emission, tropical wetlands should be a priority for N2O management., In a global field survey across a wide range of organic soils, the authors find that N2O flux can be predicted by models incorporating soil nitrate concentration (NO3–), water content and temperature. N2O emission increases with NO3– and temperature and follows a bell-shaped distribution with water content.

Early survival and growth of black alder, silver birch and Scots pine were investigated on reclaimed extremely stony and heterogeneous calcareous (pH 8) opencast oil shale mining areas (OOSMAs). Biomass allocation, production, leaf and root adaptations, and mineral nutrition in relation to tree species and soil heterogeneity were analysed. The adaptive strategies of tree species in first-year plantations on OOSMA were different. Scots pine allocated 1.5–2 times more biomass into leaves and fine roots than deciduous trees. The lower leaf/fine root biomass ratio was in proportion to the better survival (%) of seedlings, decreasing in the following order: black alder (93%) ≥ Scots pine (83%) > silver birch (64%). Deciduous trees improved mineral nutrition more by fine-root morphological adaptations than Scots pine; e.g. the mean specific root length (SRL, m g−1) of short roots increased in the following order: Scots pine (62)