More persistent precipitation regimes induce soil degradation

In the mid-latitudes, precipitation regimes are becoming more persistent, with longer consistently dry and rainy periods. Such a rise in precipitation regime persistence (PRP) – defined as the length of consecutive dry or wet periods – could significantly affect soil properties and their role in soil–plant-water relationships. To investigate these effects, we conducted a 16-month outdoor grassland mesocosm experiment. We simulated four levels of PRP by varying the duration of alternating dry and rainy periods: 1, 6, 15, or 60 days. The regimes started with either a dry or a wet period, resulting in two levels of timing and eight different treatments altogether, all of which received the same total amount of water across the entire experiment.

Higher PRP (longer alternation periods) decreased soil aggregate stability, without a similar trend in total soil carbon. PRP also affected potential soil water repellency (SWR) in interaction with timing. Higher PRP decreased potential SWR when the timing of the dry periods coincided with summer heatwaves and plant productivity was overall hindered. However, when the dry periods coincided with less warm months and the overall plant productivity was maintained, PRP increased potential SWR. PRP enhanced actual soil water repellency measured in the field which reduced infiltration rates. Water retention was also affected, with lower field capacity and available water capacity in the more persistent treatments, and wilting point following a convex relationship across the PRP range. Furthermore, bulk density increased with PRP. Structural equation modeling revealed that these soil degradation patterns often but not always correspond with plant productivity, which in general declined with PRP. However, some soil properties proved to be more sensitive to PRP than plant productivity. Overall, more persistent precipitation regimes induced soil degradation especially by reducing aggregate stability, water retention, and infiltration, and this soil legacy may exacerbate the effects of future climate change on temperate grasslands.