Endophyte richness
Endophyte richness was most strongly influenced by host identity, with
endophyte richness of one host (S. chirindensis ) being
consistently lower than that of the other hosts. In contrast, several
abiotic and biotic variables showed inconsistent effects on endophyte
richness across the three host species. Reduced endophyte richness at
higher light intensity agrees with other studies: high levels of UVB
negatively impact endophyte persistence, with high UVB increasing leaf
desiccation and/or the activation of the plant’s defence responses,
ultimately leading to lower endophyte richness (Unterseher et
al. , 2007, 2012).
Other abiotic effects on endophyte richness differed between host
species which may shed some light on how such factors drive endophyte
richness in these host species. Lower endophyte richness in S.
chirindensis occurred in warmer BCs that this species occupied.
Temperature differences within BCs may drive differences in chemistry
and secondary metabolite production produced by the leaves of S.
chirindensis that experience higher temperatures (Reich et al. ,
1999; Veteli et al. , 2002), potentially leading to lower ASV
richness (Arnold and Herre, 2003; Unterseher et al. , 2012, 2013).
High temperatures can activate the plant defence response, thereby
increasing the production of secondary metabolites with potential
anti-microbial properties (Unterseher et al. , 2016) which
decreases the observed endophyte richness by reducing the number of
successful endophyte colonisations. Taller trees are usually older, and
older hosts have been shown to support decreased endophyte richness
compared to their younger conspecifics (Oono et al. , 2015). It
has been postulated that older trees invest more in defence mechanisms
which resist endophyte colonisation; alternatively established groups of
endophytes in older trees outcompete newly arriving endophytes,
ultimately leading to lower endophyte richness in older trees
(Unterseher et al. , 2007; Oono et al. , 2015).