Context dependence of plant response to mycorrhizal fungi: Testing the influence of plant life history, soil phosphorus, and precipitation

Background/Question/Methods

Tallgrass prairies are one of the planet’s most biodiverse and endangered ecosystems. While restoration efforts have intensified over the past decades, restored prairies consistently struggle to match the rich plant biodiversity of remnant prairies. Many of the rare or missing plants in restorations (i.e. late successional species) respond to arbuscular mycorrhizal fungi (AMF) more than plants that readily establish in these same restorations (i.e. early successional species). Some research suggests, however, that plants primarily benefit from AMF in low-nutrient environments. This finding would imply that AMF may not positively impact plant growth in post-agricultural soils where phosphorus (P) may be elevated. In this greenhouse experiment, we tested if late successional plant species are less flexible in their reliance on AMF than early successional plants. We grew 17 plant species of different life histories (9 early and 8 late successional) in soil that was sterile or inoculated with AMF, with ambient or high P levels, and with low or high levels of water. After several weeks, we compared the plant mass and mycorrhizal response (MR).

Results/Conclusions

In a mixed-effects model, we saw overall benefits of AMF inoculation (P < 0.001) and P addition (P < 0.001) on total plant biomass, with effects of AMF decreasing with P addition. Water level had overall little effect on plant growth (P = 0.48). We hypothesized that mycorrhizal response (MR) would be more similar in low and high nutrient treatments for late rather than early successional plants. We observed a trend towards higher plant biomass with AMF in late successional plants (P = 0.067), particularly in belowground biomass (P = 0.045), but we did not see the predicted interaction between life history, AMF, P, and water levels in terms of biomass. Interestingly, there was an interaction between life history, AMF, and water level on the allocation of plant mass as roots vs. shoots (P = 0.017). This difference, however, demonstrated a similar MR in different water levels for early rather than late successional plants. Moreover, MR for different P levels varied by species (P = 0.046). Altogether, these results support the idea that MR depends on species identity and life history traits rather than abiotic conditions alone, though we need to further investigate the patterns of these effects.