Multiple global change factors weaken the benefits of AMF
diversity
Our results showed that ecosystem multifunctionality decreased in both
high and low AMF diversity treatments, under multiple GCFs (Fig. 1a).
And the multifunctionality was often greater with the high AMF diversity
than the average of the AMF inoculated individually, and greater than
the best performing single AMF inoculated under the control,
microplastics, drought and multiple GCFs. This indicates that there is
complementary among AMF in supporting multifunctionality under some GCF
scenarios. Our findings align with previous biodiversity-ecosystem
functioning (BEF) studies, which generally suggest that ecosystems with
high biodiversity exhibit greater niche differentiation and positive
complementarity, thereby enhancing ecosystem multifunctionality and
resilience to environmental changes (Craven et al., 2016; Godoy et al.,
2020).
However, ecosystem multifunctionality under high AMF diversity was not
the highest under nitrogen addition, pesticide pollution, and
saline-alkali treatment. Some studies also reported that communities
with higher diversity may exhibit lower productivity (Polley et al.,
2003) or ecosystem functions (Becker et al., 2012; Jousset et al.,
2011), which may be related to competition among species. In this study,
under non-GCF conditions, plant root mycorrhizal colonization rate, HLD,
and spore density were higher in high AMF diversity treatments compared
to any single AMF inoculation treatment (Figure S2a-c). However, under
conditions with multiple GCFs, the negative effects of GCFs on mixed AMF
treatments were more sever compared to individual AMF like R.
irregularis and G. etunicatum (Figure S2d-f). These observations
suggest that the presence of multiple GCFs may intensify the competition
among AMF. It has been indicated that the addition of nitrogen and
phosphorus can intensify the competition among AMF (Ma et al., 2021; Qin
et al., 2022; Tang et al., 2023).
Plant-derived carbon is the primary resource for competition among AMF
species. Research has shown that host plants allocate more carbon to AMF
species that supply more phosphorus in return (Kiers et al., 2011).
Beyond resource competition, species can also release allelochemicals to
directly affect competitors. In high-diversity communities, while
positive functional complementarity exists, complementarity in
allelopathic toxins can lead to a ‘negative complementarity effect’
(Becker et al., 2012). AMF can also release hyphosphere exudates, while
current research primarily focuses on their role in recruiting
hyphosphere microbes to explain AMF ecological functions. Studies on AMF
allelopathy are still limited.
The diminished effect of AMF diversity on ecosystem multifunctionality
under multiple GCFs, might also relate to specific GCF factor. For
example, there was no significant difference in ecosystem
multifunctionality among different AMF treatments under saline-alkali
and pesticide pollution conditions. Plant root mycorrhizal colonization
rates and HLD showed the most negative responses to saline-alkali
treatment (Figure S2d, e). Davison et al. (2021) analyzed global soil
samples and found that AMF virtual taxa are often associated with a
particularly narrow range of pH and temperature conditions. Previous
studies have investigated the mechanisms through which AMF mitigate
plant saline-alkali stress; however, there is limited research on how pH
influences the growth of AMF.