Plant-microbe interactions change along a prairie restoration chronosequence

Background/Question/Methods

Soil microbial communities are critical in determining the performance and diversity of species in plant communities.  However, their role in regulating the success of ecological restoration is much less clear. This study assessed the ability of soil microbial communities to regulate the growth and performance of two potentially dominant grasses (Andropogon gerardii and Sorghastrum nutans) and two common forbs (Silphium terebinthinaceum and Baptisia leucantha) in prairie restorations. Specifically, we examined the effects of soil microbial communities along a restoration chronosequence from agricultural fields to remnant prairies in a greenhouse study.  Plants were inoculated with live or sterilized soils from fields currently in agriculture (following soybeans and corn), young restorations (3 and 5 y), old restorations (22 and 28 y), and remnant prairies.  Biomass was determined after 60d as was the level of nodule formation in the legume B. leucantha.

Results/Conclusions

The net effects of the soil microbial community on plant performance changed along the chronosequence.  The two grass species, grew best with agricultural inoculates and experienced a decline in performance in later stages of the chronosequence.  This indicates that the microbial community shifted from being neutral/beneficial to grasses in the early stages of restoration to inhibiting grasses in the later stages or remnants. The forb, Silphium terebinthinaceum was largely unaltered by the inoculation or position along the restoration chronosquence. In contrast, the legume Baptisia leucantha, always performed better in live inoculates, where root nodules could be formed. Baptisia growth appeared limited by nodule formation in agricultural soils, peaked in young restoration soils along with module formation, but decreased in older soils as the microbial community became more antagonistic.   Negative feedbacks tended to be less important in the beginning stages of succession in these restorations but appear important in remnant and resorted prairies. Our results provide a mechanism that may explain early dominance by grasses in restoration.  It may be advantageous for management practices to take negative feedbacks into consideration when trying to maintain the diversity of prairies.