Long-Term Monitoring Studies of the Mycorrhizal Colonization of Aesculus hippocastanum L. Roots and the Vitality of Soil Microorganisms in Urban and Non-Urban Environments

Abstract

Stress factors typical in urban environments adversely affect the productivity and vigor of trees and may limit the development of tree roots with associated soil fungi and bacteria. Studies on mycorrhizal symbiosis and the activity of soil microorganisms are important in monitoring the adaptation of trees to urban conditions. We compared the symbiotic activity of arbuscular mycorrhizal fungi (AMF) living in the rhizosphere of mature white chestnut trees (Aesculus hippocastanum L.) in an urban ecosystem at sites with varying degrees of anthropopressure and in a rural area. We used two methods: (1) direct analysis of the root samples, (2) assessment of the colonization of trap plants grown in the soil taken from under selected white horse chestnut trees. The seasonality of mycorrhizal colonization and soil microbial respiration based on the enzyme activity of nonspecific dehydrogenase (DHA) was studied over several growing seasons. The concentrations of macronutrients in the soil from all study sites were in the ranges accepted as normal for the upper soil layer. However, the C/N ratio indicated carbon limitation in the soil at urban and rural study sites. The results showed that arbuscular mycorrhizal fungi indigenous in the rhizosphere of A. hippocastanum developed a functioning mycorrhizal symbiosis at all research sites, including at highly disturbed urban locations, and that the mycorrhizal colonization varied between the study sites and the research term. The trap culture method confirmed the high biological potential of the soil microbial community, including AMF in urban ecosystems, which was comparable to that at the reference site in the rural environment. Soil moisture strongly affected the overall soil microbial vitality. This research showed that the mycorrhizal status of A. hippocastanum is more strongly influenced by climatic conditions and seasonal rhythms of trees than by urban/non-urban locations.