Temperature-dependent soil storage: Changes in microbial viability and respiration in semiarid grasslands

Storing soils at low temperatures, a common practice in microbial research, substantially impacts microbial community composition and microbial-mediated processes, leading to potential inaccuracies in conclusions. However, there is a dearth of guidance on the best practices for storing soil microbiomes, especially in regard to preserving microbial viability for future use. Here, we stored samples of four types of soil at 4 °C and −20 °C for durations of 0, 5, 40, and 210 days. For soils stored at −20 °C, we adopted two thawing methods: direct thawing at room temperature and gentle thawing at 4 °C. We investigated trends and influencing factors of microbial viability during storage and variations in microbial-mediated respiration during incubation. Our findings revealed that microbial viability was more robust at 4 °C compared to −20 °C, and wetland soils were not conducive to the maintenance of microbial viability during storage. For soils stored at −20 °C, gentle thawing at 4 °C for 3 days resulted in maximum cells viability, and was 26.2% higher than direct thawing at room temperature. In addition, the days of incubation required for respiration rates and cumulative respiration to re-equilibrate are strongly dependent on soil types. Overall, this study provides empirical evidence to guide the development of optimal soil storage and pre-incubation practices tailored to preserve living soil microorganisms' purposes and ensure accurate respiration measurements.