The effect of shrubs admixture in pine forest stands on soil bacterial and fungal communities and accumulation of polycyclic aromatic hydrocarbons

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are a group of persistent toxic pollutants. The species composition of the stand is important in shaping the quality of soil organic matter and, consequently, the PAH content. The main purpose of the research was to determine the role of shrubs in shaping PAH accumulation in forest soils. The study covered the soils of the pine stands of the Rybnik Forest District, which experiences some of the highest deposition of industrial emissions in Europe. Pine stands with admixture of shrubs (alder buckthorn Frangula alnus and European hazelnut Coryllus avellana) growing in the same soil conditions were selected for the study. Samples for analyses were collected from the organic horizon (O) (from a depth of 0-7 cm) and humus mineral horizon (A) (from a depth of 7-15 cm). The organic C and total N concentrations, pH, alkaline cation content, soil enzyme activity and PAH content were determined. Additionally, the taxonomic composition of soil bacterial and fungal communities was determined. The highest activity of enzymes was noted in soils under influence of shrubs. The enzymatic activity was positively correlated with the content of total N, organic C, pH H₂O and KCl and negatively with the C/N ratio. The highest PAH content was recorded in the soils of pine stands without the admixture of shrubs. Our research indicates the importance of shrubs in shaping the properties of surface horizons of forest soil and, consequently on the accumulation of PAHs. Shrubs stimulate biochemical activity of soils which results in lower PAHs accumulation by providing more easily decomposable organic matter.

Figure 1

PAH content (μg/kg) taking into account the number of rings in the different soil horizons (O and A) depending on the benzene rings; AB—alder buckthorn, EH—European hazelnut, SP—Scots pine; small letters in the upper index (a, b) mean significant differences between different species.

Figure 2

Enzyme activity in soil under influence different species; mean and SD; CB—β-d-cellobiosidase, BG—β-glucosidase, NAG—N-acetyl-β-Glucosaminidase, XYL—β-Xylosidase, SP—sulphatase, PH—phosphatase; AB—alder buckthorn, EH—European hazelnut, SP—Scots pine; small letters in the upper index (a, b, c) mean significant differences between different species; big letters in the upper index (X, Y) mean significant differences between different horizons.

Figure 3

The projection of variables on a plane of the first and second PCA factor; CB—β-d-cellobiosidase, BG—β-glucosidase, NAG—N-acetyl-β-glucosaminidase, XYL—β-Xylosidase, SP—sulphatase, PH—phosphatase; AB—alder buckthorn, EH—European hazelnut, SP—Scots pine; O—organic horizon, A—humus mineral horizon.

Figure 4

Mean and total number of fungal (A) and bacterial (B) taxa identified in soil organic horizon under influence different species; AB—alder buckthorn, EH—European hazelnut, SP—Scots pine.

Figure 5

Relative abundance of fungal (A) and bacterial (B) phyla in soil (O—organic horizon, A—humus mineral horizon) under influence different species; AB—alder buckthorn, EH—European hazelnut, SP—Scots pine.

Figure 6

Principal coordinates analysis (PCoA) based on Bray–Curtis distances between samples of soil organic horizon under influence different plant species; AB—alder buckthorn, EH—European hazelnut, SP—Scots pine calculated for phylum (A—fungi; B—bacteria) and class (C—fungi; D—bacteria) and genus (E—fungi; F—bacteria) level (log₂(RA + 1)).

Figure 7

Heatmap illustrating the relative abundance of the fungal (A) and bacterial (B) genera in all samples used in this study with dendrograms calculated based on Canberra distances between samples; AB—alder buckthorn, EH—European hazelnut, SP—Scots pine, O—organic horizon, A—humus mineral horizon.

Figure 8

Relative abundance of the most dominant fungal genera in soil (organic horizon) under influence different species; AB—alder buckthorn, EH—European hazelnut, SP—Scots pine. The different letters mean differences between study site for particular genera of fungi.