Storage, not plant residues, may influence bacterial communities in air-dried soils even at -80 ℃

Abstract

Plant residue added into soils may release substances interfering DNA extraction and PCR, influencing the subsequent profiling of soil microbial community. Many field and laboratory studies investigate the effect of plant residue (e.g., straw) on soil bacterial communities after a period of time. However, whether aged plant residue will exert an interfering impact remains unanswered. Here, five air-dried soils were mixed with 5 g kg⁻¹ rice straw and then stored at room temperature (~ 25 ℃), -20 ℃, or -80 ℃. At all three temperatures, we found that compared to the unamended control soils, plant residue had a minor effect (< 10%) on bacterial abundance and no significant effect on bacterial community composition after 4 and 10 weeks. However, for two air-dried soils (soils 4 and 5), we observed a significant increase in bacterial abundance and a shift in bacterial community composition after storage for 4 and 10 weeks, compared to week 0, at all three temperatures. These findings stood when we repeated the experiment with a rice straw addition rate at 20 g kg⁻¹. Many of the phylotypes that increased after storage in soils 4 and 5, which had the highest pH and lowest nutrient contents in all soils, are reportedly tolerant to dry, alkaline, or oligotrophic conditions. Metagenomic analysis further showed that genes related to bacterial drought, cold, and alkali resistance increased in soils 4 and 5 after storage. These results suggest that aged plant residue does not affect bacterial communities in air-dried soils but for alkaline and oligotrophic air-dried soils, storage may do even at -80 ℃. This work can help us optimize the storage of soils for microbial analysis and understand microorganism survival in dry soils.