Carbon and nitrogen stabile isotope ratio and heavy metals in Leccinum aurantiacum in a hybrid aspen plantation in agricultural land initially fertilised with biogas production residues, sewage sludge, and wood ash

Abstract

Edible mycorrhizal fungi can be harvested in the fourth year after establishment of a hybrid aspen plantation in previous agricultural land at hemiboreal conditions. It is important to understand the role of fungi in element cycling at the ecosystem level as well as the amounts of elements, including heavy metals, that are accumulated in fruitbodies of edible fungi in the context of food safety. Therefore we evaluated the carbon and nitrogen stable isotope ratio and content of heavy metals (Cr, Pb, Mn, Ni, Cd, Cu and Zn) in Leccinum aurantiacum (Bull.) Gray in a juvenile hybrid aspen (Populus tremuloides Michx. × Populus tremula L.) plantation in agricultural land initially fertilised with biogas production residues (digestate), sewage sludge and wood ash, which are potential sources of pollution of heavy metals. The research site was established in the spring of 2011, but the natural occurrence of fruitbodies of L. aurantiacum was observed in 2014. The mean isotopic data for fruitbodies of L. aurantiacum, collected in the 2014–2018 monitoring period, ranged between -27.4 and -24.5‰ for δ13C and between 7.8 and 10.1‰ for δ15N. The mean content of investigated heavy metals in fruitbodies of L. aurantiacum were up to 129 mg kg-1 for Zn, up to 99 mg kg-1 for Cu, up to 30 mg kg-1 for Mn, up to 1.5 mg kg-1 for Ni, up to 1.7 mg kg-1 for Cd, up to 1.1 mg kg-1 for Cr and up to 0.6 mg kg-1 for Pb. We concluded that the application of digestate, sewage sludge and wood ash as fertilisers to improve soil quality in hybrid aspen plantations in agricultural land did not result in increased heavy metal accumulation in fruitbodies of L. aurantiacum, but N isotopic compositions were altered (15N-enriched) for a period of up to five years after application of the organic fertilizers (digestate and sewage sludge).

  Keywords: agricultural land, hybrid aspen, Leccinum aurantiacum (Bull.) Gray, heavy metals, stable isotope ratio