Linden tree stress detection: Chlorophyll-nitrogen contents and ectomycorrhizal community

Urban trees are frequently subjected to stress-causing environmental factors and cultural practices, requiring a permanent monitoring of their health condition. Stress detection in woody plants usually relies on a visual assessment of symptoms: inventories are mostly based on the parameters of the percentage of foliage reduction and leaf colour, both of which require a subjective interpretation. The main goal of this study was to detect whether the foliar chlorophyll (Chl) and nitrogen contents of linden trees, in an urban environment, can be useful and objective diagnostic indicators of the plant health and physiological performance, and whether it was possible to evaluate these data through a quick technique. Furthermore, as the ectomycorrhizal (ECM) community is a well-known bioindicator of the plant health status, its potential association with both variations in the Chl content and the different degrees of tree decline was verified. By determining the mathematical relationship between the instrument (SPAD-502) readings, the foliar Chl and nitrogen contents and the association with significant variations in the ECM community, the different stages of the visual symptoms of decline were accurately determined. This approach should help to integrate the methodology used for tree health inventories with new universal methods that do not entail individual interpretation.