Extreme drought impacts have been underestimated in grasslands and shrublands globally.

Climate change is increasing the frequency and severity of short-term (~1 y) drought events-the most common duration of drought-globally. Yet the impact of this intensification of drought on ecosystem functioning remains poorly resolved. This is due in part to the widely disparate approaches ecologists have employed to study drought, variation in the severity and duration of drought studied, and differences among ecosystems in vegetation, edaphic and climatic attributes that can mediate drought impacts. To overcome these problems and better identify the factors that modulate drought responses, we used a coordinated distributed experiment to quantify the impact of short-term drought on grassland and shrubland ecosystems. With a standardized approach, we imposed ~a single year of drought at 100 sites on six continents. Here we show that loss of a foundational ecosystem function-aboveground net primary production (ANPP)-was 60% greater at sites that experienced statistically extreme drought (1-in-100-y event) vs. those sites where drought was nominal (historically more common) in magnitude (35% vs. 21%, respectively). This reduction in a key carbon cycle process with a single year of extreme drought greatly exceeds previously reported losses for grasslands and shrublands. Our global experiment also revealed high variability in drought response but that relative reductions in ANPP were greater in drier ecosystems and those with fewer plant species. Overall, our results demonstrate with unprecedented rigor that the global impacts of projected increases in drought severity have been significantly underestimated and that drier and less diverse sites are likely to be most vulnerable to extreme drought.

Research needs on the biodiversity-ecosystem functioning relationship in drylands.

Research carried out in drylands over the last decade has provided major insights on the biodiversity-ecosystem functioning relationship (BEFr) and about how biodiversity interacts with other important factors, such as climate and soil properties, to determine ecosystem functioning and services. Despite this, there are important gaps in our understanding of the BEFr in drylands that should be addressed by future research. In this perspective we highlight some of these gaps, which include: 1) the need to study the BEFr in bare soils devoid of perennial vascular vegetation and biocrusts, a major feature of dryland ecosystems, 2) evaluating how intra-specific trait variability, a key but understudied facet of functional diversity, modulate the BEFr, 3) addressing the influence of biotic interactions on the BEFr, including plant-animal interactions and those between microorganisms associated to biocrusts, 4) studying how differences in species-area relationships and beta diversity are associated with ecosystem functioning, and 5) considering the role of temporal variability and human activities, both present and past, particularly those linked to land use (e.g., grazing) and urbanization. Tackling these gaps will not only advance our comprehension of the BEFr but will also bolster the effectiveness of management and ecological restoration strategies, crucial for safeguarding dryland ecosystems and the livelihoods of their inhabitants.

Episodes of high tropospheric ozone reduce nodulation, seed production and quality in soybean (Glycine max (L.) merr.) on low fertility soils.

Driven by human activities, air pollution and soil degradation are threatening food production systems. Rising ozone in the troposphere can affect several physiological processes in plants and their interaction with symbiotic microorganisms. Plant responses to ozone may depend on both soil fertility and the ontogenetic stage in which they are exposed. In this work, we studied the effects of ozone episodes and soil fertility on soybean plants. We analysed soybean plant responses in the production of aboveground and belowground biomass, structural and functional attributes of rhizobia, and seed production and quality. The experiment was performed with plants grown in two substrates with different fertility (commercial soil, and soil diluted (50%, v/v) with sand). Plants were exposed to acute episodes of ozone during vegetative and reproductive stages. We observed that ozone significantly reduced belowground biomass (≈25%), nodule biomass (≈30%), and biological nitrogen fixation (≈21%). Plants exposed to ozone during reproductive stage growing in soil with reduced fertility had lower seed production (≈10% lower) and seed protein (≈12% lower). These responses on yield and quality can be explained by the observed changes in belowground biomass and nitrogen fixation. The negative impact of ozone on the symbiotic interaction with rhizobia, seed production and quality in soybean plants were greater in soils with reduced fertility. Our results indicate that food security could be at risk in the future if trends in ozone concentration and soil degradation processes continue to increase.