Amazonian savannas plants survive drought and control water loss through a spectrum of strategies, including resistance to embolism, water use efficiency, and structural anatomy, according to a new study addressing the correlation between anatomical features and plant hydraulic functioning in these ecosystems. The study, carried out by Priscila Simioni and colleagues, found that there is no single dominant functional strategy employed by plants to thrive in the Amazonian savannas.
Amazonian savannas, isolated patches of open habitats hidden among the tropical forests, have captivated scientists for decades. Although much progress has been made in understanding the characteristics of these savannas, evidence is still lacking on how their plants differ in traits essential for surviving drought and controlling water loss.
To shed light on this issue, a study was undertaken, delving into the intricate interplay between anatomical and hydraulic traits in the leaf and wood xylem of Amazonian savanna plants. Simioni and colleagues meticulously examined 22 leaf, wood, and hydraulic traits on the seven dominant woody species that contribute to 75% of the biomass in a typical Amazonian savanna situated on rocky outcrops in the Brazilian state of Mato Grosso.
Contrary to expectations, the results showed that only a limited number of anatomical traits significantly correlated with hydraulic attributes. The research team found a broad spectrum of variations among the seven species examined, encompassing resistance to embolism (the formation of air bubbles in the plant water transport system), water use efficiency, and structural anatomy. Consequently, the immense complexity of the mechanisms at play within these ecosystems became evident.
Interestingly, the variations in embolism resistance were linked to species’ different water use efficiencies. Those species demonstrating lower water use efficiency, such as Kielmeyera rubriflora, Macairea radula, Simarouba versicolor, Parkia cachimboensis, and Maprounea guianensis, exhibited higher stomatal conductance. These findings support the hypothesis that these plants utilize leaf succulence and/or have safer wood anatomical structures to sustain xylem functionality. On the other hand, species displaying higher water use efficiency, such as Norantea guianensis and Alchornea discolor, showcased riskier hydraulic strategies.
This study uncovers the intricate relationship between the structural traits of branches and leaves, enabling diverse hydraulic strategies to coexist among Amazonian savanna plants. Within these unique ecosystems, plants employ strategies such as investing in mechanisms that buffer water loss (succulent leaves, for example) or developing safer anatomical structures (thicker pit membranes (the part of the cell wall through which a cell communicates with other cells) and vessel grouping in branch xylem, for example).
Simioni and colleagues conclude:
Our results suggest that species that inhabit hot and seasonal savannas can exhibit different strategies of drought tolerance/avoidance. These strategies can be equally successful in the maintenance of a favourable water balance, allowing species persistence and co-occurrence.Simioni et al. 2023.
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Simioni P.F., Emilio T., Giles A.L., Viana de Freitas G., Silva Oliveira R., Setime L., Pierre Vitoria A., Pireda S., Vieira da Silva I., Da Cunha M. (2023) “Anatomical traits related to leaf and branch hydraulic functioning on Amazonian savanna plants” AoB PLANTS. Available at: https://doi.org/10.1093/aobpla/plad018
Cover image: The Cerrado. Image: Angeladepaula / Wikimedia Commons