Extreme drought kills plant growth in open environment – 01/08/2024 – Environment

A global-scale study of the possible consequences of extreme drought on open ecosystems indicates that the impact of these events has been underestimated until now. In experiments that simulated severe droughts, the negative effect on the plants’ growth capacity was 60% more severe than that seen in more common situations of lack of rain.

The analysis, which has just been published in the specialized journal PNAS, covered 100 locations on all continents (except Antarctica). The list includes four study areas in Brazil, in the municipalities of Mamanguape (PB), Eldorado do Sul (RS) and Mineiros (GO) — in the latter case, they were two different areas in the same region. The chosen regions are in the cerrado, pampa and a transition area of ​​the Atlantic forest.

“What we have produced is a truly unprecedented quantification of the effects of a single year of extreme drought,” he told Sheet the study coordinator, Melinda Smith, from Colorado State University (southwestern USA). “It is the largest cooperative climate change field experiment conducted to date.”

Among the Brazilian collaborators in the study are researchers such as Marcus Vinicius Cianciruso, from the Federal University of Goiás, Daniela Hoss, from the Federal University of Rio Grande do Sul, and Bráulio Almeida Santos, from the Federal University of Paraíba. The teams responsible for each location produced “artificial droughts” using a simple method: transparent plastic screens, in units measuring 2 meters on each side, which were set up to cover different sections of the ground.

These “tents” were open on the sides, in order to allow air circulation, but partially prevented the rain from contacting the ground. The hundreds of areas spread across the world corresponded to varied environments, but all with low vegetation, sometimes with a predominance of grasses, sometimes with a greater presence of shrubs.

“The Brazilian locations are all in environments covered in grass and, for the most part, with high levels of rainfall and close to forests”, explains the American researcher.

The team divided the sites studied into two groups. In one of them, the researchers simulated droughts that would be within the natural variability of rainfall from year to year in their regions. In the second group, they simulated an extreme lack of rain for a year, which would only happen once every century, according to records available for the study area or nearby areas.

The idea is that this simulation would be a good way to capture the risks that low vegetation ecosystems face in a climate change scenario, in which the tendency is for an increase in the frequency and intensity of extreme events.

The measure used by scientists to assess the impact of the two types of simulated drought was the so-called primary productivity — that is, the capacity of vegetation to grow and produce more biomass through photosynthesis. Although there was considerable variability between the locations studied, on average the drop in productivity in locations with extreme drought was 35%, compared to 21%, on average, in locations with droughts considered normal.

According to Smith, the locality in Rio Grande do Sul was one of the least affected, with a reduction in plant biomass so modest that it was not possible to distinguish it from a normal situation. “But other locations proved to be more sensitive to drought,” she says.

Protecting biodiversity appears to be one of the few factors that serve as a “cushion” to minimize drought damage. In the study, places with greater species diversity suffered less from drought, perhaps because there are more species capable of adapting to new conditions, and their resilience compensates for the possible loss of other more fragile species.