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Fossorial rodents through their burrowing activities are important disturbance agents in grassland ecosystems. The European ground squirrel (Spermophilus citellus) is a medium-sized ground squirrel occurring in central and south-eastern Europe. The aim of the study was to explore changes of physico-chemical and biological soil properties during mound development created by the European ground squirrel. The study was conducted at three study sites in the Western Carpathians. We sampled newly created mounds consisting of fresh excavated soil without vegetation, and old mounds with developed vegetation. We also collected control samples of undisturbed soil in the distance of 5 m to the north direction from each selected mound. We took soil samples for bulk density measurements, chemical and biological analyses from the depth of 0–0.1 m. The results showed that some soil properties were unchanged by mound formation and also across the mound development (e.g., Ca2+ concentration, richness and diversity of microbial communities). Several soil properties were altered by mound formation, but with no differences during the mound development (e.g., pH, sulphur concentration). On the other hand, some soil properties showed recovery patterns during the mound development towards an undisturbed soil (e.g., soil bulk density, carbon and nitrogen concentrations). Finally, a few properties showed enhanced values on the old mounds (e.g., phosphorus and potassium concentrations, N-mineralization and heterogeneity of microbial communities). These findings suggest that the European ground squirrel through physical disturbance and resources modulation creates soil patchiness and maintains heterogeneity of European grasslands influencing functions (e.g. soil fertility) and processes (e.g. soil aeration, decomposition and nutrient cycling) in grassland soils.

Single-nucleotide polymorphisms in seven candidate genes for drought and heat tolerance identified in earlier studies were studied in 13 populations of Abies alba Mill. covering the eastern and southeastern half of the distribution range. Trees were planted in a provenance trial plot of the international experiment IUFRO 2005 in Hertnik, Slovakia. In parallel, genotyped trees were also scored for physiological traits (PSII thermotolerance, chlorophyll a fluorescence kinetics, partly gas exchange, assimilatory pigments, needle osmotic potential). For the detection of natural selection imprints, we used different methods: analysis of FST-outliers, testing of SNP–climate associations and SNP–phenotype associations. FST-outlier analysis revealed 2 SNPs with signals of selection. Moreover, three other SNPs showed significant association with latitude or bioclimatic variables; one of them (C/T polymorphism in a gene coding for serine/threonine phosphatase) was significantly associated with needle osmotic potential and marginally with other drought-related physiological traits. That may indicate its role in drought-stress response. In addition, T/C polymorphism in a gene coding for reduced epidermal fluorescence 4 was found to be involved in heat-stress response. However, migration history seems to be a more important driver of differentiation at SNPs in the studied candidate genes than recent adaptation.

The photosynthetic responses to the combined effect of drought and heat stress were studied in leaves of 19-years-old European beech (Fagus sylvatica L.) trees originating from five provenances in Central Europe differing by altitude (55–1250 m), and grown in the same experimental plot. The measurements were conducted at the beginning of heat waves, under two different conditions: during a dry period (middle of July) and after recovery in wetter period, at the beginning of August. The decreases of stomatal conductance (gs) and net photosynthesis rate (ACO2) during drought and heat wave stress were very similar in all provenances. However, we observed distinct response of PSII photochemistry on combined drought and high temperature stress, well associated with altitude of origin of the beech provenances. Measurements of pulse amplitude modulated (PAM) fluorescence identified maintenance of a high electron transport rate in beech provenances from high altitudes under drought and heat wave conditions, associated with some decrease of excitation pressure on PSII. This can be explained by enhanced capacity of alternative electron sinks to utilize the excess of electrons as a photoprotective mechanism. The analyses of fast chlorophyll fluorescence kinetics confirmed the differences in responses of PSII photochemistry between provenances originating from different altitudes. Compared with provenances at higher altitudes, we found more sensitive response (i.e. more limited electron transport at the PSII acceptor side and changes in the size of light harvesting complexes) to drought and heat stress, in those growing at low altitudes. Our results support the hypothesis that the provenances originating from higher altitudes possess enhanced phenotypic plasticity related to photoprotective responses, resulting from the long-term adaptation to marginal mountain conditions.

Changes of soil microbial community caused by the heterogeneity of abiotic and biotic environment were studied in the reserve Dobroc, Slovakia. Data on vegetation, microclimate, soil properties and microbial activity were collected on two linear transects crossing both the core of the reserve and the buffer zone. In contrast to expectations, the variation of most environmental variables was comparable or even higher in the buffer zone than in the old-growth forest. Beta diversity was much higher in the natural forest, which coincided with differentiation patterns of trees and understory plants. Mantel correlations between microbial community indicators and environmental variables showed that soil chemistry and vegetation diversity were the most important determinants of microbial activity. Redundance analysis of microbial data identified potassium content, plant richness and influence of fir as the drivers of functional group composition. Inconsistency of correlations of microbial community characteristics with environmental variables indicates that different processes associated with the demography and functions of microbiota are driven by different environmental factors. Amount and variety of substrates available for decomposition seems to influence microbial community more than microclimate.

The study focused on the temporal dynamics of soil water content (SWC) and soil microbial activity characterized by basal respiration and catalase activity in the litter (OL), fragmented (OF), and humus (OH) subhorizons of the forest floor and the mineral A-horizon, in relation to air temperature and rainfall. The study was conducted at three plots (old-growth Norway spruce (Picea abies Karst.) forest, even-aged mature commercial spruce stand, grassland dominated by Calamagrostis sp.) located in the Biosphere Reserve Polana (Slovakia, 19°28′E, 48°38′N) during four years. SWC as well as microbial activity differed among horizons as well as among plots. Generally, organic horizons in the old-growth forest exhibited higher microbial activity than in the managed forest, but no significant differences were observed for the A-horizon. On the other hand, the A-horizon showed higher catalase activity in the grassland than in both forest stands. The responses of SWC and microbial activity to air temperature and rainfall differed among horizons. SWC responded most sensitively to short-term temperature fluctuations in the OL horizon. In the underlying horizons, cumulative positive effects of high temperature (lasting 5–15 days) were reflected in the basal respiration. SWC responded rapidly to precipitations, but the effect lasted generally not more than 2 days. In contrast, catalase activity was negatively correlated with the precipitation amount; however, with increasing depth this relationship became less distinct.

In coniferous species, including Greek fir (Abies cephalonica Loud), the involvement of somatic embryo plants in breeding and reforestation programs is dependent on the success of long-term cryostorage of embryogenic cultures during clonal field testing. In the present study on Greek fir, we assayed the recovery, morphological characteristics and genetic fidelity of embryogenic cell lines 6 and 8 during proliferation and maturation after long-term cryostorage. Our results indicate successful recovery of both cell lines after 6 years in cryostorage. In the maturation phase, both cell lines were capable of producing somatic embryos although some differences were detected among experiments. However, these changes were more dependent on the differences in the components of the maturation media or in the experimental set-up than on the long-term cryostorage. During both proliferation and maturation phases, the morphological fidelity of the embryogenic cultures as well as of the somatic embryos were alike before and after cryopreservation. The genetic fidelity of the cryopreserved cell line 6 that was assayed by random amplified polymorphic DNA (i.e. RAPD) markers demonstrated some changes in the RAPD profiles. The results indicate possible genetic aberrations caused by long-term cryopreservation or somaclonal variation during the proliferation stage. However, in spite of these changes the embryogenic cultures did not lose their proliferation or maturation abilities.

The impact of secondary succession of grassland communities towards a Norway spruce forest on soil microbial community was studied on a belt transect established in the Pol’ana Mts., Central Europe. Data on understory vegetation, light availability, soil properties and microbial activity were collected on 147 plots distributed over regular grid. Moreover, distributions of functional groups of microorganisms were assessed using BIOLOG analysis on a subset of 27 plots. Mantel partial correlations between microbial community indicators and environmental variables showed that microbial activity generally decreased with increasing tree density and size, whereas it increased with increasing radiation at the soil surface, soil temperature, and cover and diversity of understory vegetation. Functional richness and diversity of microorganisms were positively correlated with solar radiation, but also with plant species richness and diversity. Abundance of several functional groups correlated closely with succession-related variables. Redundance analysis of microbial data provided slightly different outcomes. Forward selection yielded only two environmental variables significantly influencing the composition of the microbial community: tree influence potential and organic carbon content. Abundances of several functional microbial groups correlated with tree influence, documenting that microbial community changes are at least partially driven by the colonization of grassland by trees. Nevertheless, the relative importance of abiotic environment change and plant community succession on microbial community dynamics remains unresolved.

The effects of air pollution on the genetic structure of Norway spruce, European silver fir and European beech were studied at four polluted sites in Slovakia, Romania and Czech Republic. In order to reduce potential effects of site heterogeneity on the health condition, pair-wise sampling of pollution-tolerant and sensitive trees was applied. Genotypes of sampled trees were determined at 21 isozyme gene loci of spruce, 18 loci of fir and 15 loci of beech. In comparison with Norway spruce, fewer genetic differences were revealed in beech and almost no differentiation between pollution-tolerant and sensitive trees was observed in fir. In adult stands of Norway spruce, sensitive trees exhibited higher genetic multiplicity and diversity. The decline of pollution-sensitive trees may result thus in a gradual genetic depletion of pollution-exposed populations of Norway spruce through the loss of less frequent alleles with potential adaptive significance to altered stressing regimes in the future. Comparison of the subsets of sensitive and tolerant Norway spruce individuals as determined by presence or absence of discolorations ("spruce yellowing") revealed different heterozygosity at 3 out of 11 polymorphic loci.

Effects of the variation in male and female fertilities of clones, flowering phenology, and spatial distribution of clones on the genetic structure of progenies of three Scots pine seed orchards were investigated using isozyme gene markers. A pronounced variation of male and female gametic contributions was found. Most clones appear to be phenologically synchronized, but up to 15% of early or late flowering clones were found in all seed orchards. The presence of ramets, which do not belong to any seed orchard clone, does not affect allelic or genotypic diversity of the seed orchard crop. Gene-pool genetic distances based on allelic frequencies between the parental and the progeny generations are not very high, but there are certain loci exhibiting a considerable differentiation. On the other hand, variance effective population sizes indicate a substantial drift of gene frequencies between seed orchard itself and its offspring. The necessity of a cautious use of the reproductive material originating from seed orchards is emphasized.

Three Alnus glutinosa populations from central Slovakia were investigated by means of isozyme analysis. The average expected heterozygosity ranged from 0.151 to 0.173. Despite significant differences in allele frequencies among populations, genetic differentiation was low (FST=0.022). Intrapopulation fixation indices indicate no or very slight deviation from panmictic expectations towards the heterozygote deficiency. No indications were found that the investigated populations have experienced recent bottlenecks in population size. A spatial autocorrelation analysis based on Moran’s I indicates the existence of a spatial genetic structuring in the population Kral’ova. Patch size was estimated to be 70–100 m, which is more than observed in other broadleaved tree species. This difference is explained by the linear shape of alder populations and a higher mobility of seeds.

A total of 1113 oak trees from 222 populations originating from eight countries (Austria, Bosnia-Herzegovina, Croatia, Hungary, Romania, Slovakia, Slovenia, Yugoslavia) were sampled in natural populations or in provenance tests. The sampled trees belong to four different species (Quercus robur, Quercus petraea, Quercus pubescens, Quercus frainetto) and to several putative subspecies. Variation at four chloroplast DNA (cpDNA) fragments was studied using restriction enzymes, resulting in the detection of 12 haplotypes. One haplotype was present in 36% of the trees, and six were found in 6–17% of the trees. The haplotypes are shared extensively between species and subspecies. They belong to three different lineages (A, C and E) and are phylogeographically structured in the region investigated. Haplotypes of lineage E dominate to the east of the Carpathian mountains in Romania, whereas the Carpathian Basin seems to have been colonised along several different colonisation routes, from the Balkan peninsula but also from Italy. The data support the possible role of climatic instability during the late glacial period in shaping this complex geographic structure. The presence of several secondary refugia could be inferred in the region, which have played a major role in the second step of recolonisation, at the onset of the Holocene period. # 2002 Elsevier Science B.V. All rights reserved.

The effects of industrial pollution on allelic and genotypic structures of Norway spruce, European silver fir and European beech were investigated by means of isozyme analysis. In a mixed Norway spruce–silver fir forest stand in an area heavily polluted by sulphur dioxide and heavy metals in the region of Spis (eastern Slovakia), pairs of neighbouring damaged and apparently healthy trees were selected in two replicates (44 and 69 pairs in a heavily and moderately damaged stand, respectively). Pairwise sampling of trees with contrasting vitality was applied to reduce potential effects of site heterogeneity on the vitality of sampled trees. No significant differences in allelic and genotypic frequencies were found between sets of healthy and declining trees. There were differences in the single-locus heterozygosities, but these were not consistent between the replicates. However, the set of damaged trees exhibited higher levels of genetic multiplicity and diversity, possibly due to the deleterious effect of rare alleles under the conditions of air pollution. Consequently, following the decline of pollutant-sensitive trees, the remaining stand will be depleted of a part of alleles with unknown adaptive value to future selection pressures.

Isozyme analysis was applied to determine the genetic structure of 14 Norway spruce populations from Slovakia. Gene diversity as well as observed heterozygosity proved to be comparatively high. No essential differences were found between virgin forests and naturally regenerated stands. On the other hand, the genetic variation in artificially established stands proved generally to be decreased. The changed genetic structure is reflected also by large values of genetic distances of these stands from all remaining populations as well as from each other.