Understanding the mechanisms plants use to thrive in harsh climatic conditions and withstand grazing pressure is crucial for accurately predicting future biodiversity and the sustainability of dryland ecosystems.
Fernando Maestre, leading an international team at KAUST, has conducted a comprehensive assessment of 20 plant functional traits, including chemical and morphological characteristics, in response to changes in aridity and grazing pressure in drylands worldwide.
While increased aridity and grazing pressure are typically associated with reduced plant diversity, the study reveals that the diversity of plant traits actually increases above an aridity threshold of 0.7, which is close to the transition between semiarid and arid zones. Notably, this trait diversity also rises with escalating grazing pressure. This finding underscores the resilience and adaptability of plant ecosystems in challenging environments.
“Global initiatives aiming to describe plant trait diversity have focused on plant morphology and leaf carbon economy but neglected the diversity of chemical elements that sustain plant survival and growth,” says Maestre, who co-led this study as part of the BIODESERT global survey, which he designed.
“The elemental concentration in plant leaves has major implications for plant development and determines how plants respond to grazing pressure and water scarcity,” he says.
The research team conducted an extensive field survey to explore how aridity and grazing pressure impact the chemical and morphological trait diversity of perennial plants in drylands worldwide. Their study spanned 98 sites across 25 countries, thoroughly representing the global aridity gradient of dryland rangelands. They meticulously surveyed 326 plots, each encompassing various levels of grazing pressure, from ungrazed to high pressure.
The variations in plant functional traits mirror the shifts in plant adaptation strategies amid changing environmental conditions. The findings reveal that both aridity and grazing play a significant role in promoting a diverse range of strategies for coping with water scarcity and grazing, underscoring the importance of understanding these factors for effective land management.
The study measured various traits related to 14 chemical elements in plant leaves, leaf and plant size, and leaf carbon economy. The results offer valuable insights into how aridity and grazing influence the relationships and trade-offs among multiple morphological and chemical plant traits in dryland ecosystems.
High aridity levels were found to promote functionally contrasting strategies in plants. For instance, tall species with fast-growing leaves tended to adopt stress-avoidance strategies characterized by high levels of nitrogen, phosphorus, and potassium, as well as low leaf dry matter content.
On the other hand, smaller conservative species exhibited stress-tolerance strategies with low nitrogen, phosphorus, and potassium levels and high leaf dry matter content, along with either low or high concentrations of Mg-Ca and Zn-Na in their leaves.
“These elemental strategies can reflect the contrasting role of chemical elements in plants, either as a way to tolerate high aridity levels or as base elements for defensive compounds against grazers,” Maestre explains.
The research offers valuable new insights into how vascular plants react to biotic stressors and extreme environmental conditions. It also illuminates how simultaneous increases in aridity and grazing pressure may influence plant characteristics.
A significant outcome was the discovery that over half of the observed trait diversity was present only in the most arid and grazed drylands, underscoring the unique phenotypic features of these extreme environments.
These findings demonstrate that drylands serve as a global hub of plant phenotypic diversity, challenging the prevailing notion that severe environmental conditions diminish plant trait diversity.
“Our results also highlight the importance of considering a plant’s chemical composition (the elementone) to understand dryland biodiversity responses to ongoing climate change,” says Maestre. “Plants could have many alternative strategies to cope with increases in environmental stress induced by climate change and land-use intensification.”
Maestre, who commenced his position at KAUST in February 2024, conducted the study during his previous tenure at the University of Alicante. He aims to extend the BIODESERT survey to the arid and hyper-arid ecosystems of Saudi Arabia.
“Such research would contribute to the monitoring of Saudi terrestrial ecosystems, offer important insights on how Saudi plant diversity can respond to ongoing climate change, and guide the selection of the most suitable species for each Saudi region to be used in ongoing and future greening programs,” he says.
Journal reference:
- Nicolas Gross, Fernando T. Maestre, Pierre Liancourt et al. Unforeseen plant phenotypic diversity in a dry and grazed world. Nature, 2024; DOI: 10.1038/s41586-024-07731-3