An arbuscular mycorrhizal fungus accelerates decomposition and acquires nitrogen directly from organic material

Arbuscular mycorrhizal fungi (order Glomales), which form mycorrhizal symbi oses with two out of three of all plant species(1), are believed to be obli gate biotrophs that are wholly dependent on the plant partner for their car bon supply(2). It is thought that they possess no degradative capability an d that they are unable to decompose complex organic molecules, the form in which most soil nutrients occur. Earlier suggestions that they could exist saprotrophically were based on observation of hyphal proliferation on organ ic materials(3,4). In contrast, other mycorrhizal types have been shown to acquire nitrogen directly from organic sources(5-7). Here we show that the arbuscular mycorrhizal symbiosis can both enhance decomposition of and incr ease nitrogen capture from complex organic material (grass leaves) in soil. Hyphal growth of the fungal partner was increased in the presence of the o rganic material, independently of the host plant.