Interest in biofertilizers as sustainable alternatives to chemical fertilizers has developed in recent years as the negative environmental impacts of chemical fertilization such as groundwater contamination and decreased soil quality are becoming increasingly evident. Nitrogen-fixing cyanobacteria are promising biofertilizers as they provide both nitrogen and carbon to the soil, and if successfully established, may reduce long-term fertilizer inputs. However, the effect of biofertilizers on the soil microbiome is largely unknown and unexplored, despite the vital roles soil microorganisms play in driving major soil nutrient cycles. Therefore, we sought to understand how a nitrogen-fixing cyanobacterial biofertilizer (CBF) affected crop growth, nutrient cycling, and the soil microbiome over a three-year field study (2018-2020) with perennial bioenergy crops switchgrass and tall wheatgrass. The field study is located at the MSU Arthur H. Post Research Farm near Bozeman, MT where each year we conducted monthly soil sampling from April-September on plots either fertilized with a locally isolated Nostoc sp. CBF, urea, or left unfertilized. High-throughput sequencing on the Illumina MiSeq platform of 16S and LSU rRNA gene sequences was used to capture the bacterial/archaeal and fungal soil communities respectively, while soil chemical analysis monitored changes in C, N, and pH.
Results/Conclusions
Results found that switchgrass and tall wheatgrass fertilized with CBF or urea produced similar biomass suggesting that CBF could compete with chemical fertilization to promote crop growth in this study. Minimal effects on soil nutrient cycling were detected between fertilizer treatments. Phylogenetic analysis of the soil microbial community indicated that fungi were more sensitive to changes in fertilization than bacteria and that CBF boosted fungal α-diversity compared to chemical fertilization, particularly in the rooting zone of tall wheatgrass. These results indicate that CBF has the potential to improve agricultural sustainability by reducing dependence on chemical fertilizers and has a dynamic relationship with the soil microbiome that warrants further investigation to understand the effects of CBF on long-term soil ecosystem functioning.