Deciphering factors driving soil microbial life-history strategies in restored grasslands

In macroecology, the concept of r- and K-strategy has been widely applied, yet, there have been limited studies on microbial life-history strategies in temperate grasslands using multiple sequencing approaches. Total phospholipid fatty acid (PLFA) analysis, high-throughput meta-genomic sequencing, and GeoChip technologies were used to examine the changes in microbial life-history traits in a chronosequence of restored grasslands (1, 5, 10, 15, 25, and 30 years since restoration). Grassland restoration increased the relative abundances of Actinobacteria, Proteobacteria, and Bacteroidetes but reduced the relative abundances of Acidobacteria, Planctomycetes, and Chloroflexi. PLFA analysis revealed that grassland restoration reduced the fungi:bacteria and Gram-positive:Gram-negative bacteria ratios. Combined with the meta-genomic data, we found that grassland restoration shifted microorganisms from oligotrophic (K-) to copiotrophic (r-) groups, consistent with the increased rRNA operon copy number of the microbial community. Structural equation modeling showed that soil properties positively (p < 0.05) while plant properties negatively (p < 0.05) affected microbial life-history traits. We built a framework to highlight the importance of plant and soil properties in driving microbial life-history traits during grassland restoration. Finally, by incorporating meta-genomic and other microbiological data, this study showed that microbial life-history traits support the idea that rRNA operon copy number is a trait that reflects resource availability to soil microorganisms.