Risk of short‐term biodiversity loss under more persistent precipitation regimes

• Published in: Global change biology 2021-04, Vol.27 (8), p.1614-1626
• Main Authors: Reynaert, Simon, De Boeck, Hans J., Verbruggen, Erik, Verlinden, Maya, Flowers, Nina, Nijs, Ivan
• Format: Article
• Language: English
• Subjects: Atmospheric precipitations; Biodiversity; Biodiversity loss; climate change; Drought; Droughts; Europe; Fixing; Forbs; gradient design; Grasses; Grassland; grassland diversity; Grasslands; Herbivores; Mesocosms; Mortality; Nitrogen; Physiology; Plant diversity; Plant stress; Plants; Precipitation; precipitation regimes; Rain; Rainfall; Soil; Soil moisture; Species richness; Summer; Weather; Weather patterns; weather persistence; Wilting; Wilting point
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1111/gcb.15501

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. Climate change is causing more persistent summer precipitation regimes in the mid‐latitudes which could increasingly favour species with a broad environmental tolerance. Using an experimental replicated gradient design, we found that precipitation regimes with increasingly longer dry and wet spells may lead to increased dominance of grasses in spite of forbs due to differences in species‐specific responses to the length and timing of summ