Recent climatic changes have resulted in an increased frequency and prolonged periods of drought and strained water resources affecting plant production. We explored the possibility of reducing irrigation in a container nursery and studied the growth responses of seedlings of four economically important forest trees: broadleaf deciduous angiosperms Fagus sylvatica L., Quercus petraea (Matt.) Liebl., and evergreen conifers Abies alba Mill. and Pinus sylvestris L. We also studied markers of water stress including modifications of biomass allocation, leaf anatomy, proline accumulation, and expression of selected genes. Growth of the broadleaved deciduous species was more sensitive to the reduced water supply than that of conifers. Remarkably, growth of the shade tolerant Abies was not affected. Adjustment of biomass allocations was strongest in P. sylvestris, with a remarkable increase in allocation to roots. In response to water deficit both deciduous species accumulated proline in leaves and produced leaves with shorter palisade cells, reduced vascular tissues, and smaller conduit diameters. These responses did not occur in conifers. Relative transcript abundance of a gene encoding the Zn-finger protein in Q. petraea and a gene encoding the pore calcium channel protein 1 in A. alba increased as water deficit increased. Our study shows major differences between functional groups in response to irrigation, with seedlings of evergreen conifers having higher tolerance than the deciduous species. This suggests that major water savings could be achieved by adjusting irrigation regime to functional group or species requirements.

The sessile oak is one of the most significant forest tree species in Europe. This species is vulnerable to various stresses, among which drought and powdery mildew have been the most serious threats. The aim of this study was to determine the influence of irrigation levels (overhead sprinklers) on the damage caused by powdery mildew to Quercus petraea growing in a nursery setting. Four irrigation rates were used: 100%, 75%, 50% and 25% of the full rate. The area of the leaves was measured and the ratio between the dry mass of the roots and the dry mass of the entire plant was calculated after the growing season in years’ 2015 and 2016. Limiting the total amount of water provided to a level between 53.6 mm × m⁻² and 83.6 mm × m⁻², particularly in the months when total precipitation was low (VII and VIII 2015), a supplemental irrigation rate between 3 and 9 mm × m⁻² resulted in a lower severity of oak powdery mildew on leaves and lead to a favorable allocation of the biomass of the sessile oak seedlings to the root system. The severity of infection on oak leaf blades was lower when irrigation rates were reduced. The greatest mean degree of infestation in 2015 was noted in the 100% irrigation rate (14.6%), 75% (6.25%), 50% (4.35%) and 25% (5.47%). In 2016, there was no significant difference between the mean area of leaves infected by powdery mildew depending on the applied irrigation rate. The shoot-root biomass rate showed greater variation under limited irrigation rates. Controlling the irrigation rate can become an effective component of integrated protection strategies against this pathogen.

The objective of this study was to investigate pollen morphology and ranges of intraspecific variability of Abies alba Mill. Pollen grains were collected from nine clonal seed orchards of A. alba in the Sudety Mountains, (South-Western Poland). At each seed orchard, 4–6 grafts were selected. Each individual (graft) was represented by 30 pollen grains and 1440 pollen grains were measured totally. Eight quantitative and four qualitative features of pollen grains were analysed. The diagnostic features of pollen grains for the studied species were: Exine surface of pollen corpus (cappa and leptoma) and sacci, the length of the polar axis (P), pollen shape (P/E ratio), and a new trait—saccus shape (A/B ratio — saccus width (A) to his length (B)). Pollen features made possible to differentiate seven individual genotypes (samples). To our knowledge, this is the first time that the intraspecific and interindividual variability of pollen grains of A. alba were investigated. The most different were the pollen grains from samples—genotypes 13 (Bystrzyca Kłodzka) and 18 (Jugów), and also (although to a lesser extent) genotypes—11 (Kamienna Góra), 30, 31 (Jugów), and 44 (Szklarska Poręba). No significant relationships were observed between the pollen grain traits and the geographical location of the collection sites.

In multisite forest genetic experiments, the presence of genotype × environment interaction (GEI) is common. GEI may negatively affect the estimates of genetic variance and hamper selection decisions in tree breeding programs. Several measures exist to evaluate the stability of tested genotypes’ performance across environments with a choice of the method likely affecting breeders’ decisions. In this study, we evaluated variation in diameter and height growth performance in the progeny test established at 4 sites with 80 open-pollinated half-sib families of Scots pine. We found significant variation among examined progeny at age 10, reaching up to 31% for diameter and 20% for height depending on site, and significant GEI in both traits. We estimated contribution of each family to GEI using various methods and tools of GEI analysis—AMMI, GGE biplots, heterogeneity of regression coefficients (b_i’s), the deviation mean squares from regression (s²_di) and Kang’s yield-stability index (YS_i). Despite the presence of the cross-over interaction, family ranks did not vary much among sites. The selections based on the phenotype, YS_i and restricted b_i corresponded well to each other leading to the expected response to selection up to 7.8% on diameter and 4.4% on height, whereas those based on the AMMI stability variance were different and lead to a slight loss in both traits. We discuss our results in the context of the usefulness of those measures of genotype stability for tree breeding programs and propose the procedure to follow for making selection decisions in forest experiments with GEI.

Phenotypic differentiation of Abies alba was identified among selected provenances originating from the northern edge of this species’ natural geographic range. We posited that although the seed sources of the study populations were not geographically distant, progenies would differ with respect to growth, needle pigment concentration, and values of photochemical parameters in response to contrasting light conditions. Potted seedlings of six provenances were grown for two seasons under low light (LL, 40% of full irradiance) or high light (HL, 100% of full irradiance). The results showed that the provenances differed in diameter at root collar (DRC) and in relative growth rates of height (RGR). Seedlings grown in full light had a greater mean value of DRC than those in LL. LL increased total needle chlorophyll (Chl_tot) and carotenoid concentrations compared with HL, and Chl_tot was modified by the provenance of the seedlings. The provenance “Syców”, localized at the northern limit of the species range, showed the lowest value of maximal electron transfer rate (ETR_max) and lower values of growth parameters compared with the other study provenances. Relative growth rate, Chl_tot, and non-photochemical quenching of fluorescence (NPQ) were correlated with some climatic characteristics of seed stands and formed clusters indicating the local adaptation of the study populations. These results provide evidence of low intraspecific A. alba differentiation in terms of growth dynamics, photochemical capacity, and tolerance to different light regimes. The intraspecific diversity found in our study among the northern lead populations could be, however, important for the natural expansion of this species further north and for the selection of provenances to be used in the programme of the A. alba restoration in the Sudety Mountains, southern Poland, where decline of this species has been observed.

Rhizosphere microbial communities can influence plant growth and development. Natural regeneration processes take place in the tree stands of protected areas, which makes it possible to observe the natural changes taking place in the rhizosphere along with the development of the plants. This study aimed to determine the diversity (taxonomic and functional) of the rhizosphere fungal communities of Norway spruce growing in one of four developmental stages. Our research was based on the ITS region using Illumina system sequencing. Saprotrophs dominated in the studied rhizospheres, but their percentage share decreased with the age of the development group (for 51.91 from 43.13%). However, in the case of mycorrhizal fungi, an opposite trend was observed (16.96–26.75%). The most numerous genera were: saprotrophic Aspergillus (2.54–3.83%), Penicillium (6.47–12.86%), Pyrenochaeta (1.39–11.78%), pathogenic Curvularia (0.53–4.39%), and mycorrhizal Cortinarius (1.80–5.46%), Pseudotomentella (2.94–5.64%) and Tomentella (4.54–15.94%). The species composition of rhizosphere fungal communities was favorable for the regeneration of natural spruce and the development of multi-generational Norway spruce stands. The ratio of the abundance of saprotrophic and mycorrhizal fungi to the abundance of pathogens was high and promising for the durability of the large proportion of spruce in the Wigry National Park and for forest ecosystems in general.