Soil organic matter rather than ectomycorrhizal diversity is related to urban tree health.

Maarten Van Geel,Jérôme Ngao,Gerrit Peeters,Ben Somers,Thierry Ameglio,Olivier Honnay,Pierre Kastendeuch,Georges Najjar,Cindy Serafim,Kasper Van Acker,Paula Castro,Kang Yu,Miguel Ramos,Marc Saudreau

doi:10.1371/journal.pone.0225714

Abstract

Urban trees provide many ecosystem services, including carbon sequestration, air quality improvement, storm water attenuation and energy conservation, to people living in cities. Provisioning of ecosystem services by urban trees, however, may be jeopardized by the typically poor quality of the soils in urban areas. Given their well-known multifunctional role in forest ecosystems, ectomycorrhizal fungi (EcM) may also contribute to urban tree health and thus ecosystem service provisioning. Yet, no studies so far have directly related in situ EcM community composition to urban tree health indicators. Here, two previously collected datasets were combined: i) tree health data of 175 Tilia tomentosa trees from three European cities (Leuven, Strasbourg and Porto) estimated using a range of reflectance, chlorophyll fluorescence and physical leaf indicators, and ii) ectomycorrhizal diversity of these trees as characterized by next-generation sequencing. Tree health indicators were related to soil characteristics and EcM diversity using canonical redundancy analysis. Soil organic matter significantly explained variation in tree health indicators whereas no significant relation between mycorrhizal diversity variables and the tree health indicators was found. We conclude that mainly soil organic matter, through promoting soil aggregate formation and porosity, and thus indirectly tree water availability, positively affects the health of trees in urban areas. Our results suggest that urban planners should not overlook the importance of soil quality and its water holding capacity for the health of urban trees and potentially also for the ecosystem services they deliver. Further research should also study other soil microbiota which may independently, or in interaction with ectomycorrhiza, mediate tree performance in urban settings.

Highlights

Urban areas are heavily modified anthropogenic ecosystems and within the decade, more than half the world’s population will be living in urban areas [1]
The small angle between organic matter in the soil and performance index (PI), mSR705, leaf water content (LWC), PRI and mND705 tree health indicators indicates a high correlation between these variables (Fig 1B)
Our results reveal that soil organic matter rather than mycorrhizal diversity explained variation in urban tree health indicators

Summary

Introduction

Urban areas are heavily modified anthropogenic ecosystems and within the decade, more than half the world’s population will be living in urban areas [1] Environmental problems, such as air pollution, increased temperatures (heat island effect), noise and flooding, jeopardize health and quality of life of the urban population [2,3,4]. Urban trees commonly grow in soils sealed by buildings and urban infrastructures and are limited by a lack of rooting space and nutrient holding capacity [12] They are more prone to water deficits than forest trees, making them susceptible to pathogens and pests [13,14]. The relation between tree health and soil conditions in natural forests has been extensively studied (reviewed in [16]), the relation between soil conditions and tree health in urban areas has received relatively little attention

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