4 DISCUSSION
It is generally uncontroversial that ECM fungi promote the uptake of N
and P in plants. While the root N and P nutrition of ECM plants were
widely investigated (Franklin et al ., 2014; Almeida et
al ., 2019; Zhang et al ., 2019), relatively few studies have
attempted to determine the attributes of ECM symbionts to aboveground
nutrition in tree species (Michelsen et al. , 1996; Koele et
al. , 2012). In this study, we examined the effects of the variations in
ECM symbiosis on root and foliar N and P nutrition in A.
faxoniana across certain natural environmental gradients. Generally,
the ECM in A. faxoniana played more an important role on P uptake
than N uptake under both N and P limitations (Figure 2, Figure 3, Figure
6). We found that the root N and P concentrations in A. faxonianawere more strongly related to the ECM traits than the foliar N and P
concentrations (Figure 3), and the ECM soil exploration types played
different impacts on root and foliar N concentrations or N:P ratio
(Figure 5). During the process, soil resources and climatic factors
appeared as the primary drivers of the ECM strategies. Our findings
allow us to develop a conceptual model on the intervention of ECM
symbiosis on root and foliar N and P nutrition using A. faxonianaas a case study (Figure 6). The model illustrates that the ECM
strategies strongly affect the root nutrients, and then through the
interconnections between roots and aboveground tissues in nutrient
transportation and re-allocations, eventually influence the foliar
nutrients, with preferential effects on P under both N and P
limitations.