The impact of anthropogenic transformation of urban soils on ectomycorrhizal fungal communities associated with silver birch (Betula pendula Roth.) growth in natural versus urban soils

Abstract

Betula pendula Roth. is considered a pioneering plant species important for urban ecosystems. Based on the sequencing of fungal ITS, we characterized the ectomycorrhizal (ECM) communities of twenty silver birch trees growing in a contaminated, highly anthropo-pressured urban environment and in a natural reserve site. We analysed chemical properties of each tree soil samples, focusing on effects of anthropogenic transformation. Three effects of urbanization: high heavy metal content, increased salinity and soil alkalinity, were highly correlated. The examined trees were divided into two forest and two urban clusters according to the level of anthropogenic soil change. The effect of soil transformation on the ECM communities was studied, with the assumption that stronger urban transformation leads to lower ECM vitality and diversity. The results of the study did not confirm the above hypothesis. The ECM colonization was above 80% in all clusters, but the forest clusters had significantly higher share of vital non-ECM root tips than the urban ones. Eleven mycorrhizal fungal species were identified varying from seven to nine and with seven species observed in the most contaminated urban plot. However, the lowest Shannon species diversity index was found in the most natural forest cluster. In conclusion, our findings demonstrate no significant negative effect of the urban stresses on the ECM communities of silver birch suggesting that both forest and urban trees have the potential to generate a similar set of ECM taxa.

Figure 1

The significant, at p value < 0.05, Spearman correlations between the chemical and ECM characteristics of the 20 individual soil samples related to the trees examined in the study. The positive correlations given in blue and negative in orange to red colours. The strongest the correlation the darker font used, according to the color-legend.

Figure 2

Dendrogram of the Agglomerative Hierarchical Clustering (AHC) of the 20 soil samples related to the examined silver birch trees. The AHC with Euclidean distance and Ward agglomeration method was used to identify clusters of trees which have grown under similar soil chemical characteristics. Trees with numbers 1 to 10 and numbers 11 to 20 were the urban and forest trees, respectively. The red dashed line indicates the division of the trees into 4 clusters.

Figure 3

PCA plot representing the chemical characteristics of the soil samples related to the examined silver birch trees. The plot explains 66.8% of the total variance in all chemical characteristics of the 20 soil samples examined in the study. Each colour represents different cluster of samples, as in Fig. 1. The ellipses are the 95% probability confidence ellipses around the mean point of each cluster. The grey vectors indicate the gradients of the major changes in the chemical composition of the soil samples: change of the pH, from acidic to alkaline; increase concentration of HMs and salts.

Figure 4

Morphotypes of ECM taxa of silver birch. (a) C. bivelus, (b) G. hispidula, (c) L. quietus, (d) R. amoenolens, (e) R. exalbicans, (f) R. ochroleuca, (g) S. citrinum, (h) T. ellisii, (i) X. pruinatus.

Figure 5

Location of studied trees on the map of Warsaw. The urban site was located in a post-industrial district of Warsaw, developed around Poland's largest factory of exhaust engines and tractors, Ursus SA. The control environment was the John III Sobieski Nature Reserve, officially protected since 1952, as a part of the Masovian Landscape Park. Figure prepared by the authors using Adobe Photoshop version 24.6.