Carbon and nitrogen acquisition strategies by wood decay fungi influence their isotopic signatures in Picea abies forests

Abstract

We examined whether sporocarp carbon and nitrogen isotope ratios (δ 13 C and δ 15 N values) reflected different functional strategies in 15 species of wood decay fungi. In Finnish Picea abies forests, we compared sporocarp δ 13 C and δ 15 N against log diameter, proximity to ground, and three wood decay types, specifically brown rot, nonselective white rot, and selective white rot (targeting hemicellulose and lignin preferentially). In regression analysis (adjusted r 2 = 0.576), species accounted for 31% of variability in δ 13 C, with factors influencing wood δ 13 C accounting for the remainder. Brown rot fungi and three white rot fungi that selectively attacked hemicellulose ( Heterobasidion parviporum , Phellopilus nigrolimitatus , and Trichaptum abietinum ) were higher in δ 13 C than nonselective white rot fungi. This was attributed to greater assimilation of 13 C-enriched pentoses from hemicellulose by these fungi. The pathogenic white rot fungus Heterobasidion parviporum had higher δ 15 N with proximity to ground and increasing log diameter. This suggested that 15 N-enriched soil N contributed to decomposing logs and that Heterobasidion growing from a bigger resource base had increased access to soil N. These isotopic patterns accordingly reflected both functional diversity of wood decay fungi and site-specific factors. • We investigated strategies of C and N use in wood decay fungi using stable isotopes. • Selective white rot fungi were higher in δ 13 C than nonselective white rot fungi. • Taxa of uncertain white rot type resembled nonselective white rot fungi in δ 13 C. • Spatial arrangements of hemicellulose and cellulose fibers influenced fungal δ 13 C. • If close to ground on big logs, Heterobasidion parviporum accessed soil N.