Quantification of fungal hyphae in leaves of deciduous trees by automated image analysis

Abstract

An optical method to quantify the fungal hyphae within decomposing leaves of deciduous trees was developed. The plant matrix was partially destroyed under hydrolytic conditions, and fungal hyphae and cellulose residues within the leaves were stained with Calcofluor M2R. Cellulose residues were subsequently depolymerized by cellulase, and fungal hyphae were separated from the remaining plant matrix with a pressurized air-water mixture. An image analysis program to quantify the fungal hyphae was written. The program included the recognition of fungal hyphae, the elimination of stomata from the images, and the measuring of lengths of fungal hyphae. The optical method was verified by a chemical method relying on glucosamine as an indicator of fungal biomass. The fungal biomass in leaves of Fagus silvatica and Quercus petraea at early states of decomposition was 0.2 to 0.4% of the leaf weight. The biomass reached a maximum within 2 to 4 weeks (optical method, 0.5 to 0.7%; chemical method, 1 to 1.4% of the initial leaf weight) and decreased thereafter.