Microorganisms and their residues under restored perennial grassland communities of varying diversity

Rising atmospheric CO2 concentration and global mean temperatures have stimulated interest in managing terrestrial systems to sequester more carbon and mitigate climate change. In a restored prairie experiment, we compared high diversity (HD, 25 species) with low diversity (LD, 6 species) prairies to investigate the effect of plant diversity on soil microbial communities and their residues with soil depth. We assayed lipid and amino sugar biomarkers for soil samples, taken after 9 years following the establishment of the prairie treatment, at 5 depth increment layers: 0–2 cm, 12–15 cm, 25–27 cm, 50–52 cm, and 98–100 cm. We found that the microbial biomass and residues decreased considerably with depth in both diversity treatments. Ordination analysis of lipid profiles indicated soil microbial communities were consistently distinct between the deeper and the upper layers, regardless of treatment, and also differed between the LD and HD treatments. Plant diversity effects on soil microbial communities strongly correlated with arbuscular mycorrhizal fungi (AMF), as indicated by the lipid marker 16:1ω5c. Soil microbial residues in deeper horizons were relatively more enriched in HD than LD treatments, suggesting that greater plant diversity might sustain higher soil carbon storage through relatively recalcitrant necromass inputs in the long term. Decreasing glucosamine/muramic acid (GluN/MurA) ratio in LD and increasing in HD with depth suggested that the new microbially-accumulated carbon was positively contributed by fungal-derived residues. Our results indicate that plant diversity drives soil microbial carbon sequestration through changes in AMF abundance in restored native tallgrass ecosystems. These findings have implications for understanding how the management of plant diversity can improve soil quality and sustainability in grasslands, and how efforts to conserve and restore diverse grasslands could mitigate greenhouse gas emissions.