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 (δ13C and δ15N values) reflected different functional strategies in 15 species of wood decay fungi. In Finnish Picea abies forests, we compared sporocarp δ13C and δ15N 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 r2 = 0.576), species accounted for 31% of variability in δ13C, with factors influencing wood δ13C 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 δ13C than nonselective white rot fungi. This was attributed to greater assimilation of 13C-enriched pentoses from hemicellulose by these fungi. The pathogenic white rot fungus Heterobasidion parviporum had higher δ15N with proximity to ground and increasing log diameter. This suggested that 15N-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.