The effects of reduced mycorrhizae and soil N availability on plant growth and native vs. non-native species in a prairie restoration experiment

Background/Question/Methods
Challenges to prairie restoration efforts include non-native species and soils which may be altered from past land use practices. While the field of restoration ecology is productive, there still is much need for empirical support to facilitate success. To improve restoration techniques, we need to better understand the underlying mechanisms and the biotic and abiotic interactions that play out during grassland community assembly. This study was conducted as part of a larger 4.5-ha experimental prairie on a post agricultural site with high soil fertility. The following questions were addressed: 1) Does adding carbon to the soil reduce available N? 2) Does reducing soil N availability facilitate better establishment of native compared to non-native species? 3) Do arbuscular mycorrhizal fungi (AMF) modulate plant response in favor of native compared to non-native species? To test these questions, native species were seeded and natural trajectories were then allowed in 246 m² plots (n=27) with ambient or reduced levels of AMF (chlorothalonil fungicide reduced MF root colonization by 41%) and ambient or elevated soil N (+NH₄NO₃). Within each plot, 1-m² subplots were treated with carbon (sawdust and sugar) to reduce soil N availability. 
Results/Conclusions

Soil to which carbon was added had 74% lower available N than ambient soil (P<0.0001). Plots with reduced soil N availability had significantly lower non-native grass aboveground biomass (-34%) and plots with elevated soil N had significantly greater non-native grass aboveground biomass (+33%) compared to plots with ambient soil N, while native species aboveground biomass was not significantly affected by soil N availability treatments. Plots with reduced AMF had significantly lower aboveground biomass compared to ambient plots and non-native and native biomass responded similarly. Results show that N availability plays a significant role in community assembly. It may therefore be useful in prairie restoration efforts to consider soil fertility manipulations that favor establishment of native species that are inherently low nutrient-adapted.