Shoot Biomass Productivity Correlated with Rhizobacteria Community Composition in Wheat.

The phylogenetic identities of rhizobacteria associated with biomass productivity remains largely unknown. In this study we correlated specific rhizobacteria phylotypes with shoot biomass productivity. Triticum aestivum was grown for 8 weeks in a homogenized field soil for three cycles of planting and harvesting. At the third cycle, rhizospheres were extracted and bulked into five categories based on shoot biomass. DNA was extracted and the 16s rRNA gene was pyrosequenced to yield 26,348 sequences averaging 453 bp in length. Phylotype classification was determined by the RDP II pyrosequencing pipeline, and numbers of sequences for each phylotype was correlated with biomass by linear and nonlinear regression. Shannon and Chao1 indices were used to assess the relationship between diversity and productivity. The most significant positive phylotype associations with biomass were: Luteimonas, Kofleria, Brevundimonas, Pseudoxanthomonas, Microbacterium, Planctoycetes, Bacillus, and Sphingopyxis. The most significant negative associations were Pectobacterium, Enterobacteriaceae, Famly XIII, Enterobacter, Family I, Verrucomicrobia, Aquificae, and Cyanobacteria. At the highest taxonomic levels Proteobacteria, Acidobacteria and Actinobacteria included the most phylotypes associated with biomass. The most abundant phylotypes without regard to productivity were Duganella (proteobacteria), Gp4 (Acidobacteria), Gemmatimonas (Gemmatimonadetes), and Gp6 (Acidobacteria). Richness (Chao1) was highly correlated with productivity at the lowest (R2=0.99) and highest (R2=0.89) but not the mid-levels of phylogeny. Diversity and evenness (Shannon and E indices) increased nonlinearly (cubic) from low to high with biomass productivity at all levels of phylogeny (R2~ 0.99). Many of the phylotypes associated with biomass productivity were from groups with few culturable representatives and with no previous association with plant productivity. Further investigations into the functional basis of productivity with specific isolates are in order.