Chapter 15

EndophyticFungi:Hidden

ComponentsofTropical

CommunityEcology

A. Elizabeth Arnold

OVERVIEW

While the ecological importance of plant pathogenic fungi, decay fungi, and root symbionts is becoming well
established in tropical biology, the contributions of one major group of ubiquitous symbionts – fungal endophytes
of foliage – have yet to be explored. Fungal endophytes – fungi that live within plant tissues such as leaves without
causin gdisease – are found in every linea ge of plants and are especially common and diverse in tropical forests, where
individual leaves may harbor dozens of species without any obvious indication of infection. Their ecological roles are
only starting to be elucidated, but early evidence suggests that fungal endophytes play pervasive, if almost entirely
overlooked, roles in tropical forest ecology. This chapter synthesizes current knowledge regarding the natural history
of foliar endophytes in tropical forests, examines the varied evidence regarding their ecological roles, and highlights a
series of tractable questions for future research. The overarchin g goal of this chapter is to encoura ge multidisciplinary
research into the ecology of these little-known but omnipresent symbionts of tropical plants.

INTRODUCTION

Plant pathogenic and parasitic fungi play
important roles in shapin gtropical tree commu-
nities (Augspurger 1983, Dobson and Crawley
1994, Willset al.1997, Gilbert 2002, Galleryet al.
2007). Similarly, the nutrient cyclin gcarried out
by highly diverse saprophytic fungi is intrinsic to
tropical ecosystem processes (reviewed by Hyde
1997). Less obvious to ecologists are the roles
played by endosymbiotic fungi of living plants,
which live within plant tissues without causing
obvious detriment or visible symptoms (Arnold
and Lutzoni 2007). The subset of these fungi
that occur in the rhizosphere (mycorrhizal fungi)
are increasingly recognized for their impact on
tropical forest communities (e.g., Kiers et al.
2000, Husbandet al.2002, Manganet al.2004,
Herreet al.2005a). However, tropical plants also

harbor fungi in above-ground tissues such as

leaves and stems. Broadly defined, these are fun-

gal endophytes: fungi that colonize the interior

of healthy plant tissues without causin gdisease

(Petrini 1991). Endophytes are present in the pho-

tosynthetic tissues of every tropical plant studied

to date, and their diversity is remarkable: individ-

ual leaves typically harbor over a dozen species,

and the number of taxa associated with individ-

ual trees likely numbers in the thousands (Lodge

et al.1996, Fröhlich and Hyde 1999, Arnold

et al.2000, 2003, Arnold and Lutzoni 2007).

Together, these poorly known fungi represent a

trove of unexplored biodiversity, and a frequently

overlooked component of tropical ecology.

The first study quantifyin gthe richness and

species composition of endophytes associated

with a tropical dicotyledonous host was pub-

lished only a decade ago (Lodgeet al.1996). In