PS 34-247 - Cracking the chicken and egg problem of plant – soil restoration: Biochar addition partially mitigates the impacts of agriculture prior to native plant restoration

Abstract: Although most restoration efforts are focused on restoring plant assemblages, restoring plant – soil interactions is essential to the long-term success of restored communities. The poor soil quality and altered food webs of former agricultural soils act as barriers to establishing diverse plant assemblages, but, unfortunately, soil quality and food webs can also be difficult to reestablish prior to native plant establishment. Eastern Washington University’s (EWU) Prairie Restoration Project will restore 52 hectares of wheat field to native Palouse prairie vegetation. In this study we compared soil abiotic properties and food webs between prairie remnants and EWU’s restoration site prior to the restoration of native plants, and tested whether biochar can move soil conditions at EWU’s restoration site closer to those of remnant sites prior to planting. We compared soils from EWU’s restoration site to a variety of local prairie remnants, and compared soils at the restoration site that were treated with different levels of biochar. Decades of conventional wheat production has left the restoration site with reduced soil organic matter (3.9 ± 1.4 %, mean ± SD compared to 6.8 – 10.5 % for prairie remnants) and reduced soil pH (5.9 ± 0.3 compared to 6.6 – 6.9). We used phospholipid fatty acid (PLFA) analysis to compare soil microbial communities. The restoration site had lower total microbial PLFAs, gram+ associated PLFAs, and arbuscular mycorrhizal fungal PLFAs. We used soil nematodes as an assay of the structure and functional diversity of the rest of the soil food web, and found the restoration site had lower total nematode abundance, and functional group diversity. Herbivorous and omnivorous nematodes were also at lower abundance at the restoration site, and predaceous nematodes were entirely absent. Overall, the soil food web at the restoration site appears to be smaller and simpler than at remnant prairies, as a consequence of frequent disturbance, reduced plant diversity, and altered soil conditions. Biochar addition mitigated some of the degraded soil quality at the restoration site: total nematode abundance and pH increased with the addition of biochar, both increasing to conditions similar to what is found at the prairie remnant sites. These results suggest biochar can improve some soil conditions in former agricultural lands even prior to native plant restoration, and may therefore be a valuable tool in assisting native plant establishment in former agricultural soils.