AMF contribution
Compared to no AMF inoculation, AMF inoculation significantly increased plant net photosynthetic rate (p < 0.001, Table 1), and significant differences in plant net photosynthetic rates among the different AMF diversity treatments were observed (p < 0.001, Table 1, Figure 3a). The net photosynthetic rate under high AMF diversity was consistently higher than that under low AMF diversity, except under microplastic and saline-alkali conditions, where the differences were not significant. Under control, antibiotic, pesticide, drought, and multiple GCFs, the net photosynthetic rate with high AMF diversity was higher than that with any single AMF species. Compared to single GCF treatments, multiple GCFs significantly reduced the net photosynthetic rate of plants inoculated with single AMF species (p < 0.001) but had no impact under mixed AMF or no AMF inoculation treatments. AMF inoculation also significantly increased aboveground biomass compared to no AMF inoculation (p < 0.001, Table 1), and significant main effect of AMF diversity on aboveground biomass was detected (p < 0.001, Table 1, Figure 3b). Within the same GCF treatment, aboveground biomass under high AMF diversity was much higher than low AMF diversity and no AMF inoculation except under microplastic and drought treatments. GCF numbers significantly affected aboveground biomass (p < 0.001, Table 1), multiple GCFs significantly reduced aboveground biomass compared to single GCF treatments.
The effect of AMF diversity on soil functions was not always significant. Significant differences in soil N2O emissions between AMF inoculated and non-inoculated treatments were observed (p < 0.01, Table 1). Under multiple GCFs, low AMF diversity treatment increased the emissions of N2O, but high AMF diversity did not affect it. A significant main effect of the number of GCFs on N2O emissions was detected (p < 0.001, Table 1). Under the inoculation of a single AMF, multiple GCFs significantly increased N2O emissions compared to single GCF and the control (p < 0.01, Figure 4a). AMF diversity and the numbers of GCF did not interactively affect CH4 emissions (p > 0.05, Table 1). Both AMF inoculation (p < 0.01) and GCF numbers (p < 0.001) significantly affected soil NO₃⁻-N content (Table 1, Figure 4c), but the effect of AMF diversity was not significant (p = 0.121). The effect of GCF numbers on soil NH₄⁺-N content was highly significant (p < 0.001, Table 1). When AMF was inoculated, NH₄⁺-N content decreased with increasing GCF numbers (Figure 4d). AMF inoculation significantly affected βG activity (p < 0.001, Table 1). AMF inoculation significantly reduced βG activity under control, antibiotic, and pesticide treatments (Figure 4e). The effect of GCF numbers was also significant (p < 0.05, Table 1). Soil CBH activity ranged from 6.84 ± 0.90, with lower activity of 2.54 ± 1.37 observed under antibiotic pollution with no AMF inoculation. Both AMF inoculation (p < 0.001) and GCF numbers (p < 0.01) significantly affected CBH activity, with AMF inoculation significantly increasing CBH activity under antibiotic, microplastic, pesticide pollution, and drought conditions (Figure 4f). No significant difference in CBH activity between low and high AMF diversity was observed. For low AMF diversity, CBH activity under multiple GCFs was significantly higher than under single GCF or no GCF treatments (p < 0.01). AMF inoculation showed a significant effect on NAG activity (p < 0.01, Table 1). AMF inoculation significantly reduced NAG activity under nitrogen addition but increased it under antibiotic, microplastic and drought conditions compared to no AMF inoculation (Figure 4g). AMF diversity, GCF numbers, and their interaction significantly affected ALP activity (all p < 0.01, Table 1). For high AMF diversity, ALP activity under no GCF was significantly higher than that under single and multiple GCF treatments (p < 0.001, Figure 4h). For low AMF diversity, ALP activity under multiple GCFs was significantly higher than that under no GCF and single GCF treatments (p < 0.001, Figure 4h).
Compared to the effects of a single AMF species inoculation on ecosystem multifunctionality, and particularly plant growth, the results showed that high AMF diversity exhibited notable complementarity effect, where the AMF mixture exhibited a greater performance than any of the single inoculated AMF, under no GCF, multiple GCFs, and some single GCF treatments. However, such advantages and complementarity effects were not evident for soil functions.