Effect of increasing persistence of alternating drought and rainfall events on grassland soil microbes intensifies over time

Climate change intensifies persistent weather patterns characterized by progressively longer dry and wet periods. However, how these weather patterns affect soil microbial communities over a long timescale remains elusive. Here we subjected grassland mesocosms to an eight-level gradient of dry-wet alternation frequencies from 1 to 60 days (representing low to high weather persistence) over two growing seasons, simultaneously initiating dry and wet phases. Results showed that the effects of weather persistence on soil microbial communities were stronger in the second year (360 and 480 days), with more divergent microbial communities between treatments, compared to the first year (120 days). Moreover, the dissimilarity of microbial communities across three sampling times decreased as weather persistence increased, except for bacterial communities at the wet conditions. The intensified impacts on microbes are due to progressively persistent weather and decreasing plant productivity. Our findings reveal distinct response mechanisms of soil microbes to weather persistence. Direct cumulative effects of persistent weather on soil microbial communities were stronger after 360 and 480 days, resulting in more divergent microbial communities as compared to after 120 days, according to grassland mesocosm experiments.