individual values for visual compar

individual values for visual comparisons against mean values for
Hypochoeris (Fig. 2). The 13C concentrations in NLFA 16:1x5 in
the three Dianthus roots are visually lower than the mean values for
Hypochoeris, and because 13C concentration measures recently
allocated C per unit fungal storage lipid (as indicated by NLFA
16:1x5), these lower values are not due to a lower AM fungal
abundance in Dianthus. Nor are potential differences driven by
plant size and 13C assimilation because they were comparable
between the two species (Table S2), as was the C-allocation to roots
(indicated by similar 13C concentration in the plant specific NLFA
18:2x6,9, Fig. 2). It is interesting to note, however, that NLFA
16:1x5 was enriched in all Dianthus samples compared to the
unlabeled plants (Fig. 2), suggesting that at least some C in the AM
fungi came from Dianthus. This enrichment cannot be explained
by C-fractionation during the transfer ofCfrom plant toAMfungi,
because the difference in natural abundance of 13Cbetween the two
symbionts is < 2& (Staddon et al., 1999), and the least enriched
sample showed an enrichment of > 14&. The 13Cconcentration in
NLFA 16:1x5 varied substantially within Dianthus for unknown
reasons, and the low enrichment in two of the samples may simply
have resulted from an assimilation of apoplastic C without any
active allocation from– or real cost to – the plant (see discussions in
Lekberg & Koide, 2014). The sample with the higher enrichment
may suggest a more active symbiosis, but careful pairing of costs and
benefits is needed to assess that.Wewant to stress that more samples
are required for robust conclusions, and we urge readers to view our
results as preliminary. However, our findings agree with Allen &
Allen (1990) who showed that nonhost plants contribute at least
some C for spore production, although spore numbers were much
lower than under a good host. As in Allen & Allen (1990) we
observed a higher C investment to AM fungi by the good host,
because Hypochoeris appeared to allocate more C per unit fungal
biomass and also supported a much greater fungal biomass than
Dianthus. Combined with the higher arbuscular colonization in