Biotic and abiotic soil amendments in prairie restorations: arbuscular mycorrhizal fungi and biochar
It is generally difficult for prairie restorations to replicate the biodiversity found in undisturbed prairie remnants. However, adding soil amendments to prairie restorations at the time of planting may aid plant establishment as well as affect plant community diversity and soil structure. Here we used a combination of biotic soil amendments in the form of inoculated arbuscular mycorrhizal (AM) fungi that establish symbiotic associations with prairie plant roots, as well as abiotic soil amendments in the form of biochar, or partially burned plant material, which can sequester carbon in the soil. AM fungi and biochar can both strongly increase prairie plant growth, but it is unclear how biochar and AM fungi together may affect plant community composition and soil structure in prairie restorations. We established prairie restoration field plots in the spring of 2013 using a full factorial design of six treatment combinations with either the presence or absence of prairie species of AM fungi inoculated into the plots using nine species of nurse plants, and either no, low (10 tons/ha), or high (20 tons/ha) amounts of biochar tilled into the soil before planting.
Inoculating nurse plants with prairie species of AM fungi gave long-term benefits of increased nurse plant growth during the first two years (2013 and 2014), and increased flowering during the second year. Plant community diversity did not change with treatment during either year, but increased significantly across all the plots between the two years (Two-sample t-test, p<0.001). Within the soil, there was a significantly greater fraction of aggregates larger than 0.5mm diameter in the high biochar treatment compared to the no biochar treatment (F1,92=16.46, p<0.001), suggesting the addition of large amounts of biochar to the soil of prairie restorations can promote soil aggregate formation. However, contrary to our hypothesis the proportion of water stable aggregates in the soil, a measure of the soil’s resistance to erosion, did not change between the first and second year or with different treatment combinations. We are currently assessing how the AM fungal community composition within plant roots may change with AM fungal inoculation or biochar addition using high throughput DNA sequencing of a portion of the ribosomal RNA gene. Overall, both inoculating prairie species of AM fungi into the soil and also amending the soil with large amounts of biochar before establishing prairie restorations can increase plant growth while also promoting soil aggregation, and may provide long-term carbon sequestration.