The soil legacy produced by grass-endophyte-mycorrhizae fungi interaction increases legume establishment

Aims

Plants alter the performance of other plants by changing soil conditions. These plant-soil feedback (PSF) can be shaped by plant interactions with other organisms and may be crucial for understanding plant coexistence. Here, we analyse how specialist and generalist symbionts change the legacy left in the soil by conspecific and heterospecific plants in the absence of pathogens and litter inputs.

Methods

We conducted a two-phase experiment to evaluate Trifolium repens establishment and its ability to form symbiotic associations with AMF and rhizobia in soils conditioned by Lolium multiflorum plants with contrasting levels of endophyte infection (heterospecific soils: Lm⁺ or Lm⁻) and inoculated or not with AMF (M⁺ or M⁻). We also conditioned the soils with T. repens plants inoculated with rhizobia on M⁺ and M⁻ soils (conspecific soils: Tr).

Results

In M- treatments, the number of established seedlings showed no difference between conspecific and heterospecific soils. In M + treatments, conditioned soils by Tr and Lm⁺ increased legume establishment by 64% compared to soils conditioned with Lm⁻. AMF colonization was higher in Tr and Lm + soils compared to Lm⁻. Regardless of AMF inoculation, legume biomass was higher in conspecific soils than in heterospecific ones, consistent with nodulation changes.

Conclusions

We found that legume establishment depended significantly on the previous presence of heterospecific soils only when L. multiflorum was associated with Epichloë endophyte and AMF. The strength of PSF was determined by AMF inoculum, while the positive or negative nature of this effect was given by the level of endophyte infection. These findings unveil a new pathway by which these symbionts modulate the coexistence between legumes and grasses.