Conditioning treatment effects on soil communities and abiotic
parameters
When the cover of forbs was experimentally reduced, the relative
abundance of soil pathogenic fungi decreased concomitantly (Figure 2a,
Supplementary Table 4). Especially grass pathogens, dominated bySlopeiomyces cylindrosporus showed similar patterns as observed
for total relative abundance of pathogens (Figures 2b,c, Supplementary
Table 4). Forb-specific pathogens had a significantly higher relative
abundance in one than in two-year legacies (Figure 2d, Supplementary
Table 4) while the relative abundance of saprotrophs was higher in plots
with two-year than one-year legacies (Figure 2e, Supplementary Table 4).
Arbuscular mycorrhizal fungi were not affected by conditioning
treatments (data not shown, Supplementary Table 4).
After the conditioning
phase, the soil bacterial community structure was significantly affected
by conditioning plant community and conditioning time (Supplementary
Table 5, Supplementary Figure 7). The soil fungal community structure
was significantly affected by conditioning plant community, conditioning
time and by forb-grass ratio, but the effect of forb-grass ratio
differed between conditioning plant communities (Supplementary Table 5,
Supplementary Figure 8). The structure of soil abiotic parameters was
affected by conditioning community and conditioning time (Supplementary
Table 5).
Soil-mediated
pathways between conditioning and responding plant communities
The composition of the conditioning plant communities
significantly explained the composition of the responding plant
communities (Figure 3). The fact that these two plant communities were
separated in time (visualized by a dashed arrow) indicates that the
effects of conditioning plant community on the responding plant
communities must be mediated via the soil. The conditioning plant
community significantly explained community composition of soil fungi
and bacteria in the conditioning phase, but did not affect the
composition of soil abiotic parameters. Importantly, microbial and soil
abiotic parameters measured at the end of the conditioning phase,
significantly explained these parameters measured again three months
after the transition to responding phase. The soil fungal
composition (but not bacteria or abiotic parameters) measured in theresponding phase correlated with the composition of theresponding plant communities.