Relationships between the litter colonization by saprotrophic and arbuscular mycorrhizal fungi with depth in a tropical forest

Fungal colonization of litter has been described mostly in terms of fructification succession in the decomposition process or the process of fungal ligninolysis. No studies have been conducted on litter colonization by arbuscular mycorrhizal fungi (AMF) and their relationship with the presence of saprotrophic fungi. The aim of the present study was to evaluate the relationships that exist in simultaneous leaf litter colonization by AMF and saprotrophic fungi and the relationships between rates of litter and associated root colonization by AMF at different soil depths. We selected Eugenia sp. and Syzygium sp. in a riparian tropical forest, with an abundant production of litter (O horizon), we evaluated litter and root colonization at different depths, its C:N ratios, and the edaphic physico-chemical parameters of the A horizon immediately below the litter layer. Litter colonization by saprotrophic fungi and AMF increased with depth, but the saprotrophic fungal colonization of some litter fragments decreased in the lowermost level of the litter while AMF litter colonization continued to increase. Plant roots were present only in the middle and bottom layers, but their mycorrhizal colonization did not correlate with litter colonization. The external hyphae length of AMF is abundant (ca. 20 m g−1 sample) and, in common with sample humidity, remained constant with increasing depth. We conclude that in zones of riparian tropical forest with abundant sufficient litter accumulation and abundant AMF external hyphae, the increase in litter colonization by AMF with depth correlates to the colonization by saprotrophic fungi, but their presence in the deepest layers is independent of both litter colonization by saprotrophic fungi and root colonization by AMF.

► We evaluated the litter colonization by saprotrophic and arbuscular mycorrhizal fungi. ► Litter colonization by saprotrophic and AMF are initially correlated. ► Colonization by saprotrophic fungi decreases after a maximum. ► Litter colonization by AMF continues increasing in deepest soil O layers. ► Litter colonization by AMF does not depend on roots colonization rate.