Abstract
The role of fungal endophytes (FEs) as “pioneer” decomposers has recently been recognized; however, the extent to which FEs contribute to litter loss is less well understood. The genetic and enzymatic bases of FE-mediated decomposition have also rarely been addressed. The effects of populations and individuals (with an emphasis on two dominant Lophodermium taxa) of FEs on needle-litter decomposition were assessed for Pinus massoniana, a ubiquitous pine in southern China. Data from in vivo (microcosm) experiments indicated that the percentage of litter-mass loss triggered by FEs was linearly correlated with incubation time and approached 60% after seven months. In vitro decomposition tests also confirmed that endophytic Lophodermium isolates caused 14–22% mass loss within two months. Qualitative analysis of exoenzymes (cellulase and laccase, important for lignocellulose degradation) revealed that almost all of the Lophodermium isolates showed moderate or strong positive reactions. Furthermore, partial sequences of β-glucosidase (glycoside hydrolase family 3, GH3), laccase, and cellobiohydrolase (GH7) genes were amplified from Lophodermium isolates as “functional markers” to evaluate their potential for lignocellulolytic activity. Three different genes were detected, suggesting a flexible and delicate decomposition system rich in FEs. Our work highlights the possibility that the saprophytism and endophytism of FEs may be prerequisites to initiating rapid decomposition and thus may be key in Fes’ contribution to litter decomposition, at least in the early stage. Potential indicators of the presence of core fungal decomposers are also briefly discussed.
Highlights
Microbes are the major drivers of litter decomposition due to their striking species diversity and degradation capacity [1]
Previous work has compared the decomposition ability of rare and common fungal endophytes (FEs) [23], we focused on dominant species because (1) rare fungi showed very slow growth, indicating weak or no decomposition; (2) dominant fungi always occupied a large number of spatial niches, indicating their active involvement in litter decomposition; (3) studies of conifer decomposition have described the importance of dominant needle endophytes (Lophodermium piceae and Lophodermium pinastri) as primary decomposers [24,25]
There is a large body of literature investigating microbial succession in needle litter [5], revealing the synergistic action of ligninolytic and cellulolytic fungi [10,30]
Summary
Microbes (especially saprotrophic fungi) are the major drivers of litter decomposition due to their striking species diversity and degradation capacity [1]. Decomposition is accompanied by dynamic and rapid succession in the litter-associated microbial community, as indicated by DNA- and RNA-based detection assays [2,3,4,5]. Basidiomycetous fungi are considered more effective decomposers than ascomycetes because the former typically have genes that encode for laccase and cellobiohydrolase [6,7]. Indicate that ascomycetes have similar or equal performance in litter decomposition [8]. Clear evidence indicates that plant fungal endophytes (FEs) act as ‘‘pioneer’’ decomposers because of their persistence in live, senescent or dead inner plant tissues [2,9,10]. When plant organs undergo senescence, FEs switch from obligate endophytism to facultative saprophytism [11,12,13,14,15]
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