How does metal soil pollution change the plant mycobiome?

Microorganisms play a key role in plant adaptation to the environment. The aim of this study was to evaluate the effect of toxic metals present in the soil on the biodiversity of plant-related, endophytic mycobiota. The mycobiome of plants and soil from a Zn-Pb heap and a metal-free ruderal area were compared via Illumina sequencing of the ITS1 rDNA. The biodiversity of plants and fungi inhabiting mine dump substrate was lower than that of the metal free site. In the endosphere of Arabidopsis arenosa from the mine dump the number of endophytic fungal taxa was comparable to that in the reference population, but the community structure significantly differed. Agaricomycetes was the most notably limited class of fungi. The results of plant mycobiota evaluation from the field study were verified in terms of the role of toxic metals in plant endophytic fungi community assembly in a reconstruction experiment. The results presented in this study indicate that metal toxicity affects the structure of the plant mycobiota not by changing the pool of microorganisms available in the soil from which the fungal symbionts are recruited but most likely by altering plant and fungi behaviour and the organisms' preferences towards associating in symbiotic relationships.

Vascular plant and cryptogam abundance as well as soil chemical properties shape microbial communities in the successional gradient of glacier foreland soils.

In the glacier forelands, microbes play a fundamental role in soil development and shaping the vegetation structure. Such ecosystems represent various stages of soil development and are, therefore, an excellent place to study the interrelationship between soil, plants, and microorganisms. The aim of the study was to assess the effects of vegetation and soil physicochemical properties developing after glacier retreat on soil microbial communities. Specifically, abundance, species richness and the composition of arbuscular mycorrhizal fungi (AMF), as well as microbial biomass and community structure in soils were compared between plots established in 800-meter transects of three glacier forelands in northern Sweden. The cover of vascular plants and cryptogams, soil C content, AMF spore density and species richness, AMF biomass indicators, total microbial biomass, and bacterial phospholipid fatty acids (PLFA) were significantly and positively related to the distance from the glacier terminus. On the other hand, macronutrient concentrations and pH decreased along with increasing distance. No significant impact of the distance from the glacier terminus on the ratio fungal/bacterial PLFA was observed. Moreover, we found a significant effect of both glacier and the distance from the glacier terminus on the microbial community structure. AMF species richness and spore density in the glacier forelands were generally low, which is probably due to a limited supply of inoculum in primary successional ecosystems. Most microbial biochemical markers and AMF parameters were positively associated with the number of arbuscular mycorrhizal plant species and vascular plant and lichen cover as well as C content in soil, whereas negatively with soil macronutrients and pH. This could be related to an increase in plant cover and a decrease in soil nutrient levels as plant succession progresses. Our results showed that vegetation, soil C content, and microbial communities are interlinked and exhibit concordant patterns along successional gradients.

The Floral Signals of the Inconspicuous Orchid Malaxis monophyllos: How to Lure Small Pollinators in an Abundant Environment.

Many orchid species have evolved complex floral signals to ensure pollination efficiency. Here, the authors combined analyses of anatomical flower structure with analyses of the volatile composition and flower-visiting insects' behaviour, as well as characterised features that can attract pollinators of the inconspicuous orchid Malaxis monophyllos. During field observations, the authors found that only small Diptera (e.g., mosquitos, drosophilids, fungus gnats) visit and are interested in the flowers of M. monophyllos, which was reflected in the characterised flower features that combine well with the pollination system, which engages dipterans. Analyses of the M. monophyllos floral scent revealed substantial concentrations of aliphatic compounds, e.g., 1-octen-3-ol and 1-octanol, which condition the mushroom-like scent and a substantial fraction of alkanes, some of which have been previously described as sex mimicry and aggregation pheromones in orchids' deceptive systems. The labellum anatomical structure exhibits a highly diverse cell cuticle surface and pronounced metabolic and secretory activity of the epidermal and subepidermal cells from all parts of the labellum. Moreover, our study provides evidence for the subsequent decoys of M. monophyllos flowers, including visual signals, such as raphides located on the labellum margin and the rewarding ones connected with lipid secretion limited to the area behind the column. Taking an integrative approach to studying M. monophyllos pollination biology, the authors provide new insight into its previously vague pollination strategies and provide evidence for complex floral signal operation in luring potential pollinators. The synergistic effect of M. monophyllos flowers' volatile and visual signals, together with additional rewarding for nectar/fungus/microbe-feeding pollinators, requires further detailed investigation that will be invaluable in explaining the evolution of Diptera-specific pollination systems in orchids.

The Effect of the Distance from a Path on Abiotic Conditions and Vascular Plant Species in the Undergrowth of Urban Forests and Parks.

Urban forests and parks are essential for the maintenance of biodiversity as well as human health and well-being. Residents and tourists commonly use urban forests and parks for recreational and sport purposes, contributing to changes in vegetation. This study aimed to assess the effect of distance from formal paths on the abiotic conditions, vegetation cover, as well as ecological diversity of vascular plant species in the undergrowth of urban forests and parks. The investigations were carried out in 2021 in 10 urban forests and 10 urban parks located in Kraków (southern Poland), using a total of 400 plots (1 × 1 m) situated in close (CL) and further (FU) vicinity of formal paths. We found a positive effect of the distance from the path on the depth of the compact soil layer, vegetation cover and height of the tallest shoot in the undergrowth of urban forests and parks. On the other hand, the distance from the path had a negative effect on the number of vascular plant species in the undergrowth in both forests and parks. Forests and parks differed significantly from each other in light intensity, the content of P in soil, depth of compact soil layer, number of species, as well as in cover-abundance of species representing different life forms, dispersal types, habitat affiliations and origins. Trampling leads to low plant cover and height of the undergrowth, as well as contributing to shallow localization of the compact soil layer near paths. Human movement on paths (walking, running, biking) with accompanying pets contributes to the successful dispersal of plants, resulting in high species richness. High light intensity in urban parks enhances the total number of species, cover-abundance of meadow and grassland plants, as well as cover-abundance of hemicryptophytes. The number of alien species was higher in parks than in forests, but the cover-abundance of alien plants was higher in forests than in parks. Urban forests are more suitable for the growth and biomass production of some alien herbs than urban parks, as mowing commonly used in parks appears to be an important factor in reducing their cover abundance. Regular fertilization and irrigation contribute to the high content of phosphorus in the soil, as well as to the high cover-abundance of meadow and grassland plants in urban parks. Urban forests enhance cover abundance of plants with dispersal mechanisms of the Bidens and Lycopodium types, whereas urban parks promote cover abundance of plants with the dispersal of the Allium type. Further study is needed to confirm the role of urban forests and parks in the preservation of ancient forest species, as well as to develop an appropriate design of paths that will allow the protection of vegetation and soil in urban forests and parks.

Effect of Shoot Cutting on Trace Metal Concentration in Leaves and Capitula of Potential Phytoaccumulator, Invasive Erigeron annuus (Asteraceae).

The effect of shoot cutting was tested on cadmium, lead and zinc concentration in leaves and capitula of Erigeron annuus, an invasive species, which is considered as a potential phytoremediator. Plant material and soil were collected in the city center of Kraków, southern Poland, considered as one of the most contaminated cities in Europe. We proved that the concentration of zinc in leaves and capitula was higher after regrowth, concentration of cadmium was lower in capitula than in leaves, and the average value of bio-concentration factor for zinc and cadmium was less than 1, whereas for lead it was greater than 1 in both plant organs. Our results suggested that E. annuus can be potentially used for phytoremediation of lead and cutting the shoots can promote effectiveness of zinc removal from the contaminated soil.

Effect of cold stratification on seed germination in Solidago × niederederi (Asteraceae) and its parental species.

In this study, we investigated the influence of cold stratification on seed germination in S. × niederederi, a hybrid between the North American S. canadensis and the European S. virgaurea, using fruit samples collected in 2016 in Poland. We aimed to test the hypothesis that the low temperature exposure decreases the final percentage and speed of seed germination in the hybrid and its parental species. For each species, sets of 100 achenes in three replications were mixed with dry sand and stored in Petri dishes in darkness for 12 weeks, at -18 °C and + 4 °C, and + 25 °C. The seeds were incubated for 21 d at room temperature (+25 °C), under the 12 h photoperiod (630 lx). We showed a lack of significant differences in: (i) the final percentage of germinated seeds of studied species stored at the same conditions, (ii) the final percentage of germinated seeds between the applied stratification conditions in the hybrid and its parental species, and (iii) the mean values of Timson's index, mean germination time, and coefficient of velocity of germination between the stratification conditions in each species. The statistically significant inter-specific differences in the mean germination time parameter after the +25 °C treatment suggest that the seeds of S. × niederederi are able to germinate faster than the seeds of its parental species. However, to improve our knowledge of naturalization and invasion abilities of S. × niederederi by sexual reproduction, the seed germination and seedling survival of the hybrid should be tested in the field.