Synergism and context dependency of interactions between arbuscular mycorrhizal fungi and rhizobia with a prairie legume

Abstract

Abstract. Biotic interactions play primary roles in major theories of the distribution and abundance of species, yet the nature of these biotic interactions can depend upon the larger ecological community. Leguminous plants, for example, commonly associate with both arbuscular mycorrhizal fungi (AMF) and rhizobia bacteria, and the pairwise interactions may depend upon the presence or identity of the third partner. To determine if the dynamics of plant-AMF and plant-rhizobia interactions are affected by the alternate symbiont, we manipulated the presence and identity of each symbiont, as well as levels of the nutrients supplied by each symbiont (nitrogen and phosphorus), on the growth of prairie legume Amorpha canescens. We found strong synergistic effects of AMF and rhizobia inoculation on plant biomass production that were independent of nutrient levels. AMF and rhizobia responses were each influenced by the other, but not in the same direction. AMF infection increased root nodule number and mass, but rhizobia inoculation decreased AMF hyphal colonization of roots. The relative benefits of each combination of symbionts depended upon phosphorus level. The effect of nitrogen was also contingent on the biotic environment where nitrogen addition decreased nodulation, but this decrease was reduced with coinfection by AMF. Our results demonstrate a strong contingency on the co-occurrence of AMF and rhizobia for the long-term fitness of A. canescens, and suggest that the belowground community is critical for the success of this species in tallgrass prairies.

Nutrient demand and fungal access to resources control the carbon allocation to the symbiotic partners in tripartite interactions of Medicago truncatula

“…We found that plants in tripartite interactions had a significantly higher root and shoot biomass, N tissue concentrations and contents, and P contents than plants that were only colonized by rhizobia or AM fungi (Figures a,b; c,d; and S3a,c). Synergistic responses in tripartite interactions have also been described by other authors especially under low P and N supply conditions (Bournaud et al, ; Larimer et al, ). The dual inoculation with rhizobia and AM fungi can lead to higher photosynthetic rates and improves the harvest index (proportion of seed yields in relation to the total plant biomass) of legumes (Afkhami & Stinchcombe, ; Kaschuk, Kuyper, Leffelaar, Hungria, & Giller, ).…”

Arbuscular Mycorrhiza Stimulates Biological Nitrogen Fixation in Two Medicago spp. through Improved Phosphorus Acquisition

“…Synergistic effects on plants of rhizobial and mycorrhizal symbioses have been described (e.g., Kaschuk et al, 2010; Larimer et al, 2014; van der Heijden et al, 2016), but the interaction of the two symbionts may also reduce plant growth (e.g., Bethlenfalvay et al, 1982; Ballhorn et al, 2016). As pointed out in a review by Larimer et al (2010), there is a need for more experimental studies relating the interaction of the symbionts to abiotic conditions because nutrient availability and other environmental factors may influence the outcome.…”

“…Ballhorn et al (2016) reported interactive effects of AM and rhizobial symbioses depending on light availability. Surprisingly, however, there is only limited and inconclusive information on how the interaction of the two symbionts changes along the P-availability gradients (see Bethlenfalvay et al, 1982; Larimer et al, 2014). …”

An ecosystem approach to understanding and managing within-host parasite community dynamics

“…Furthermore, nearly all organisms are also 'infected' with diverse, commensal microbial communities [5][6][7][8]. As in free-living ecosystems [9,10], these diverse communities of co-occurring pathogenic and non-pathogenic species may interact directly and indirectly, both with each other and with their environment (the host). Interactions among these species can have major consequences for the presence of a species (the ability of a parasite to infect a host [11]), species abundance (parasite burden/levels of parasitaemia [12]), the invasibility of a host to a novel parasite (i.e., host susceptibility to secondary infection [13]), and host response to infection (e.g., clinical impact of infection or consequences for other coinfecting species [14]).…”