Temporal variation of management effects on soil microbial communities

Alpha and beta diversities are widely used to assess microbial community dynamics. However, little is known about the optimum sampling times for microbial alpha and beta diversity analysis between various cropland management systems across seasons, and whether changes in alpha and beta diversities of bacteria and fungi in response to temporal variation are synchronized. To investigate shifts in microbial alpha and beta diversities between soil environments caused by cropland management during the transition from winter to summer, a longterm field experiment was conducted under three different conditions: (1) natural regeneration after the cropland was abandoned, (2) mineral fertilizer application alone, and (3) 7500 kg ha-1 of wheat straw combined with mineral fertilizers incorporated into the cropland. Illumina HiSeq sequencing was performed, targeting the bacterial 16S rRNA V4-5 and fungal ITS1 regions. The results showed that the alpha and beta diversities of bacteria and fungi responded differently to seasonal change, and the temporal changes in beta diversity between treatments were not synchronized with those of alpha diversity. Compared to fungi, seasonal change had a more complex influence on soil bacterial beta diversity due to the interaction between land management and sampling time. Thus, using only one or a few sampling times within a season is an oversimplified approach when assessing bacterial beta diversity between land management systems and the impacts of environmental factors on bacterial diversity. For soil fungi, it was possible to assess their beta diversity between management practices without considering temporal variation. This research provides an opportunity to assess the effects of temporal variation on microbial diversity under various land management styles.