Conditioning treatment effects, via soil, on responding plant
communities
Soil legacies that were created by conditioning treatments
influenced responding plant communities. The forb:grass ratio in
sowing treatments in the conditioning phase resulted in grass and
forb covers that differed significantly from each other (Figure 1a, b).
This, in turn influenced the relative abundance of grasses and forbs in
the responding plant communities. Specifically, grass abundance
in the responding communities was lower in plots with a legacy of
higher grass abundance (Figure 1c), while forb abundance in theresponding communities was significantly lower in plots with a
legacy of higher forb abundance (Figure 1d). The pattern did not depend
on plant community identity and was observed in each of the six
experimental plant communities (Supplementary Figures 1,2). Furthermore,
the observed grass and forb cover in the conditioning phase and
the responding phase at the subplot level, showed the same
significant relationships (Supplementary Figure 3).
Conditioning time (i.e. 1 or 2 years) affected the total cover of theresponding plant communities, with higher total cover in the
plots during the responding phase after a two-year conditioning legacy
(mean cover ~80% vs. ~90%,
Supplementary Table 2).
There were significant main
effects of conditioning plant community, forb:grass ratio and
conditioning time on the responding plant community structure
(Supplementary Table 3). The effects of forb:grass ratio strongly
differed between the six different conditioning plant communities,
indicated by a significant interaction between the two (Supplementary
Figure 4). The forb:grass ratio significantly affected responding plant
community structure in three out of six conditioning communities. In the
affected communities (Supplementary Figure 5), responding species
of a specific functional type were often negatively associated with
their own respective abundance in the conditioning phase.
Conspecific and heterospecific soil legacy effects were assessed and
visualized using correlation plots including conditioning andresponding plant species (Supplementary Figure 6). There were
only a limited number of (predominantly positive) conspecific effects,
and these effects )were not consistent between the six plant
communities. For instance, we observed positive conspecific
relationships for Rumex acetosella (in community 4),Clinopodium vulgare (in community 5), Taraxacum officinaleand Holcus lanatus (both in community 6). Only one negative
conspecific relationship was observed, for Anthoxanthum odoratum(in community 5). Furthermore, there were heterospecific relationships
between conditioning plant species and other respondingplant species in each of the experimental communities (Supplementary
Figure 6). Finally, there were conditioning plant species that
had a strong effect on cover of specific functional types in theresponding phase. For instance, in community 2, cover in theconditioning plant community of Achillea millefoliumpositively - and H. lanatus negatively - affected grass cover in
the responding plant communities. In community 3, A.
millefolium and Briza media cover in the conditioningplant community negatively affected forb cover. In community 5,Festuca ovina cover in the conditioning plant community,
negatively affected responding grass cover (Supplementary Figure
6).