Soil microbial communities and reciprocal distributions of nitrogen-cycling proxies beneath legume and non-legume patches in a disturbed orchard

Daniel Tang 

The belowground interactions between plants and soil microbial communities play an important role in the recovery of historically disturbed land. However, these relationships remain poorly understood at fine spatial scales. In this exploratory study, we characterized bacterial, archaeal, and eukaryotic soil communities beneath five plant types (red clover, white clover, fescue, chicory, and common ragweed). The site was a historically disturbed orchard undergoing restoration at a regenerative farm in Virginia, USA. 16S and 18S rRNA gene amplicon sequencing was used to characterize soil communities. Out of 13 samples collected, all were retained for 16S analysis, eleven samples were retained for 18S analysis, while rarefied 18S diversity analyses retained ten samples. Alpha diversity did not differ significantly among plant groups in either 16S or 18S analyses. Beta diversity indicated some variation in 16S bacterial and archaeal community organization among plant groups (PERMANOVA R² = 0.473, p = 0.020). However, these interpretations might be limited because of unequal dispersion and unbalanced sampling. No significant association in beta diversity was found between the plant groups and the 18S community compositions (R² = 0.381, p = 0.081). A targeted exploratory analysis examined taxonomic proxies for microbial lineages that may be associated with nitrogen cycling. Archaeal ammonia-oxidizer proxies were found to be less abundant beneath legumes than beneath non-legumes (1.6% versus 11.9%, q = 0.008), while rhizobial lineage proxies showed the opposite pattern (1.6% versus 0.6%, q = 0.008). Overall, these findings indicate that plant functional type is associated with reciprocal distributions of nitrogen-cycling taxonomic proxies. The findings identify promising directions for future research on plant-microbe relationships, specifically whether the observed taxonomic patterns correspond to differences in nitrogen cycling during soil restoration.