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

Abstract

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.

Fertilized graminoids intensify negative drought effects on grassland productivity

“…A higher impact of drought on graminoids than on forbs, and therefore reduced proportions of graminoids under drought (Figure 4c), contrasts with earlier studies that suggested stronger drought effects on forb biomass production than on graminoid biomass production (Breshears et al, 2016;Hoover et al, 2014;Reynaert et al, 2020;Stampfli et al, 2018; but see Kübert et al, 2019). We suggest that different mechanisms are at play that can either predispose or protect different functional groups against drought impacts.…”

Drought legacies and ecosystem responses to subsequent drought

“…Also, increasing drought severity is expected to decrease resistance to and recovery from a subsequent drought (Figure 4). This hypothesis is based on studies of single drought events, where longer duration hampered resistance (Buttlar et al, 2018; Reynaert et al, 2020), and higher intensity reduced resistance (Xu et al, 2019) and recovery (Schwalm et al, 2017). Given the broad lack of evidence on the interactive effects of intrinsic and extrinsic factors, experimental and observational studies are urgently needed to improve our understanding of ecosystem responses to recurrent drought events.…”

Nitrogen Deposition Drives Response and Recovery in the Context of Precipitation Change and Its Reversal in an Arid Ecosystem

“…However, elevated N deposition could not ameliorate the harmful effects of severe drought on plant growth (Ibáñez et al., 2018; Valliere et al., 2017). A combination of precipitation alteration and N addition may lead to community compositional shifts and thus biodiversity loss (Lü et al., 2014; Ma et al., 2020; Reynaert et al., 2021; Stevens et al., 2004; Valliere et al., 2017). For instance, under increased precipitation and enriched N conditions, some species in a semiarid grassland might disappear (Bai et al., 2010).…”

“…processes (e.g., Galloway et al, 2008;Kazanski et al, 2021;Ma et al, 2020;Reynaert et al, 2021;Wilkins et al, 2022).…”