Plant-assisted bioremediation (rhizoremediation) stands out as a potential tool to inactivate or completely remove xenobiotics from the polluted environment. Therefore, it is of key importance to find an adequate combination of plant species and microorganisms that together enhance the clean-up process. To understand the response of plants upon bioaugmentation, the antioxidative and detoxification system was analyzed in high and low erucic acid rapeseed varieties (HEAR and LEAR, respectively), after 8 weeks of their treatment with petroleum degraders and 6000 mg diesel oil/kg dry soil. The oxidative stress was enhanced in LEAR being exposed to sole diesel oil, in comparison with HEAR. However, when LEAR plants were additionally inoculated with bacteria, suppression of total catalase (CAT) and ascorbate peroxidase (APX) activity were observed. Interestingly, glutathione transferase (GST) activity was found in these plants at a much higher level than in HEAR, which correlated with a more efficient diesel removal performed by LEAR in the polluted soil and upon bioaugmentation. A distinct profile of polycyclic aromatic hydrocarbons (PAH) was detected in leaves of these plants. Neither LEAR nor HEAR experienced any changes in the photosynthetic capacity upon diesel pollution and presence of petroleum degraders, which supports the usefulness of rhizoremediation with rapeseed.

Key message: The range-wide level of genetic variation of Scots pine (Pinus sylvestrisL.) is geographically structured. High admixture and low genetic structure of populations in Central Europe and Fennoscandia suggest past recolonization from multiple sources and the influence of human-mediated gene transfer. Gene pools of marginal and isolated stands require active conservation. Some areas of Scots pine distribution need further genetic studies.Context: Scots pine (Pinus sylvestrisL.) seems to be a species of low conservation priority because it has a very wide Eurasian distribution and plays a leading role in many forest tree breeding programs. Nevertheless, considering its economic value, long breeding history, range fragmentation, and increased mortality, which is also projected in the future, it requires a more detailed description of its genetic resources.Aims: Our goal was to compare patterns of genetic variation found in biparentally inherited nuclear DNA with previous research carried out with mitochondrial and chloroplast DNA due to their different modes of transmission.Methods: We analyzed the genetic variation and relationships of 60 populations across the distribution of Scots pine in Eurasia (1262 individuals) using a set of nuclear DNA markers.Results: We confirmed the high genetic variation and low genetic differentiation of Scots pine spanning large geographical areas. Nevertheless, there was a clear division between European and Asian gene pools. The genetic variation of Asian populations was lower than in Europe. Spain, Turkey, and the Apennines constituted separate gene pools, the latter showing the lowest values of all genetic variation parameters. The analyses showed that most populations experienced genetic bottlenecks in the distant past. Ongoing admixture was found in Fennoscandia.Conclusions: Our results suggest a much simpler recolonization history of the Asian than European part of the Scots pine distribution, with migration from limited sources and possible founder effects. Eastern European stands seem to have descended from the Urals refugium. It appears that Central Europe and Fennoscandia share at least one glacial refugium in the Balkans and migrants from higher latitudes, as well as from south-eastern regions. The low genetic structure between Central Europe and Fennoscandia, along with their high genetic admixture, may result at least partially from past human activities related to the transfer of germplasm in the nineteenth and early twentieth centuries. In light of ongoing climate changes and projected range shifts of Scots pine, conservation strategies are especially needed for marginal and isolated stands of this species. Genetic research should also be complemented in parts of the species distribution that have thus far been poorly studied.

Genetic diversity is crucial to secure the survival and sustainability of ecosystems. Given anthropogenic pressure, as well as the projected alterations connected with the level and circulation of water, riparian forests are of particular concern. In this paper, we assessed the genetic variation of black poplar – one of the keystone tree species of riverine forests. The natural habitats of black poplar have been severely transformed leading to a significant decline of its population size. Using a set of 18 nuclear microsatellites and geographic location data, we studied 26 remnant populations (1,261 trees) located along the biggest river valleys in Poland. Our main goal was to assess the overall genetic variation and to verify if range fragmentation and habitat transformation have disrupted gene exchange among populations. Genotyping revealed that 261 trees were clones. The level of clonality was higher in more transformed river sections. All populations have probably gone through a drastic genetic bottleneck in the distant past, and most of them have low effective population sizes. Still, the overall level of genetic variation remains high, but certain populations require attention due to their lower genetic variation, higher clonality and strong spatial genetic structure. Genetic differentiation was low, yet Bayesian clustering supported the existence of 11 genetic clusters. According to the results, gene exchange is most prevalent between adjacent populations. Relatively free gene flow occurs only along the Vistula, particularly in its middle section which is characterized by the highest genetic variation. Noticeable genetic structuring was observed along the Oder. Populations located at the range margin showed signs of genetic divergence and reduction of variation. We conclude that human activities have impacted the gene pool of black poplar in Poland by disrupting landscape connectivity and preventing the species from generative reproduction. The study provides practical guidelines on how to develop and implement the conservation program for the gene pool of black poplar in Poland. It also presents a strong case favoring river renaturation and genetic monitoring, particularly concerning keystone species.

The black poplar (Populus nigra L.) is an ecologically and economically important tree species, characteristic for floodplain forests in Europe. It is now considered to be endangered in many European countries due to the loss of its natural habitat caused by the development of river engineering and intensive land use management of riverside areas. Multi-stem specimens can be found occasionally in natural black poplar populations. The percentage of such individuals is low, although in some stands it may be over a dozen percent. The origin of multi-stem trees may be different. As a consequence, trunks being part of such a tree can have the same or different genotypes. The study aimed to find out whether all trunks of multi-stem black poplars are ramets of the same genet or if their genotypes are different, in which case they increase the gene pool of the population. We used 13 microsatellite nuclear markers to analyze the genotypes of 83 trunks belonging to 34 multi-stem black poplar trees from five natural populations from the Oder river valley in Poland. We also performed the sibship analysis of all trunks. The results showed that the trunks being part of the particular individual had distinct genotypes in five trees (14.7%). This indicates that they were formed as a result of the fusion of two genetically different individuals. The sibship analysis revealed that one multi-stem tree was represented by full-sibs. In the remaining four trees the fused trunks were not related. Nevertheless, we found three pairs of half-sibs between different trees that were distant from each other. The majority of the multi-stem trees we examined developed most probably due to the damage to the apical meristem of the main shoot of a single-stem tree. Nevertheless, some of them were indeed formed from two distinct individuals. Therefore, if a particular population consists of a small number of individuals, we recommend to study the genotypic homogeneity of each multi-stem tree.