Data from: Risk of short-term biodiversity loss under more persistent precipitation regimes

Recent findings indicate that atmospheric warming increases the
persistence of weather patterns in the mid-latitudes, resulting in
sequences of longer dry and wet periods compared to historic averages. The
alternation of progressively longer dry and wet extremes could
increasingly select for species with a broad environmental tolerance. As a
consequence, biodiversity may decline. Here, we explore the relationship
between the persistence of summer precipitation regimes and plant
diversity by subjecting experimental grassland mesocosms to a gradient of
dry-wet alternation frequencies whilst keeping the total precipitation
constant. The gradient varied the duration of consecutive wet and dry
periods, from 1 up to 60 days with or without precipitation, over a total
of 120 days. An alternation of longer dry and wet spells led to a severe
loss of species richness (up to –75% relative to the current rainfall
pattern in W-Europe) and functional diversity (enhanced dominance of
grasses relative to nitrogen (N)-fixers and non-N-fixing forbs). Loss of
N-fixers and non-N-fixing forbs in severe treatments was linked to lower
baseline competitive success and higher physiological sensitivity to
changes in soil moisture compared to grasses. The extent of diversity
losses also strongly depended on the timing of the dry and wet periods.
Regimes in which long droughts (≥ 20 days) coincided with above-average
temperatures showed significantly more physiological plant stress over the
experimental period, greater plant mortality, and impoverished communities
by the end of the season. Across all regimes, the duration of the longest
period below permanent wilting point was an accurate predictor of
mortality across the communities, indicating that increasingly persistent
precipitation regimes may reduce opportunities for drought stress
alleviation. We conclude that without recruitment, which was precluded in
this experiment, summer precipitation regimes with longer dry and wet
spells will likely diminish plant diversity, at least in the short term.