Endophytes shape the legacy left by the above- and below-ground litter of the host affecting the establishment of a legume

Abstract

Plant litter is a key component of plant–soil feedback (PSF), given its strong potential impacts on plant establishment and growth, through chemical and physical pathways. Although PSF of the layer of dead plant material on the soil surface (above-ground litter) has been widely studied, little is known about the role of dead roots (below-ground litter) and the impact of plant symbionts on host litter legacy. Here, we examined whether the fungal endophyte Epichloë occultans changed the effects of above- and below-ground litter of Lolium multiflorum plants on the establishment of Trifolium repens. We hypothesized that both types of litter deposited by the grass-endophyte symbiosis reduce the establishment of the legume due to the release of allelopathic compounds during the decomposition and leaching processes. To test this, we performed two experiments with different quantities of litter produced by plants of the same grass population, with high and low levels of endophyte infection (E+ and E−). Seeds of T. repens were exposed to the above-ground litter with or without the addition of below-ground litter, or to their leachates, to separate the physical and chemical pathways. We found that the treatments with the combination of the above- and below-ground litter produced by E+ plants increased the germination speed and seedling emergence of T. repens by 56% compared with both types of litter produced by E− plants. A similar effect was also observed with only the above-ground litter. However, the below-ground litter of E+ plants reduced the germination speed, seedling emergence by 76% and establishment of T. repens by 73% compared with the below-ground litter of E− plants. Besides, the below-ground litter had positive effects on the root colonization by arbuscular mycorrhizal fungi and reduced the root nodulation of T. repens. The quantity of litter did not affect any of these responses. Our results suggest that these litter legacy effects could be due to the release of endophyte-induced secondary metabolites, such as phenolic and flavonoid compounds. Changes in host plant litter inputs may have consequences for the prevalence of legume plants in grasslands and pastures, affecting their quality and dynamics. A free Plain Language Summary can be found within the Supporting Information of this article.