Background and Aims Amazonian savannas are isolated patches of open habitats found within the extensive matrix of Amazonian tropical forests. There remains limited evidence on how Amazonian plants from savannas differ in the traits related to drought resistance and water loss control. Previous studies have reported several xeromorphic characteristics of Amazonian Savanna plants at the leaf and branch levels that are linked to soil, solar radiation, rainfall, and seasonality. How anatomical features relate to plant hydraulic functioning in this ecosystem is less known and instrumental if we want to accurately model transitions in trait states between alternative vegetation in Amazonia. In this context, we combined studies of anatomical and hydraulic traits to understand the structure-function relationships of leaf and wood xylem in plants of Amazonian savannas. Methods We measured 22 leaf, wood, and hydraulic traits, including embolism resistance (as P50), Hydraulic Safety Margin (HSM) and isotope-based water use efficiency (WUE), for the seven woody species that account for 75% of the biomass of a typical Amazonian savanna on rocky outcrops in the state of Mato Grosso, Brazil. Key Results Few anatomical traits are related to hydraulic traits. Our findings showed wide variation exists among the seven species studied here in resistance to embolism, water use efficiency and structural anatomy, suggesting no unique dominant functional plant strategy to occupy an Amazonian savanna. We found wide variation in resistance to embolism (-1.6 ±0.1 MPa and -5.0±0.5 MPa) with species that are less efficient in water use (e.g. Kielmeyera rubriflora, Macairea radula, Simarouba versicolor, Parkia cachimboensis, and Maprounea guianensis) showing higher stomatal conductance potential, supporting xylem functioning with leaf succulence and/or safer wood anatomical structures and that species that are more efficient in water use (e.g. Norantea guianensis and Alchornea discolor) can exhibit riskier hydraulic strategies. Conclusions Our results provide a deeper understanding of how branch and leaf structural traits combine to allow for different hydraulic strategies among coexisting plants. In Amazonian savannas, this may mean investing in buffering water loss (e.g. succulence) at leaf level or safer structures (e.g. thicker pit membranes) and architectures (e.g. vessel grouping) in their branch xylem.
Amazonian savannas are isolated patches of open habitats found within an extensive matrix of tropical rain forest. The climate of Amazonia is transitioning to a state that favors savannas over forests. Still, the hydraulic functioning of savanna species in Amazonian vegetation remains unknown and unexplored. We measured 22 leaf, wood, and hydraulic traits, including embolism resistance (as P50) and isotope-based water use efficiency (WUE), for the seven dominant woody species (75% of biomass) of Amazonian savanna. We found wide variation in resistance to embolism (-1.66 ±0.06 MPa and -5.07±0.46 MPa) with species investing in at least three different hydraulic strategies based on anatomical adjustment: (1) Species with high Gmax and low water use efficiency where leaf succulence may delay embolism onset; (2) Species that have low embolism resistance and high water use efficiency by reinforcing the walls of longer vessel elements to prevent implosion; (3) Species with high Gmax and low water use efficiency where short vessel elements and thick intervascular pit membranes may minimize the embolism spread across the plant. Our results suggest no unique dominant functional strategy among Amazonian savanna species illustrating the alternative ways to survive in a hot and seasonally dry environment.
Amazonian savannas are isolated patches of open habitats found within an extensive matrix of tropical forest. Climate in Amazonia is transitioning to a state where savannas are more likely to occur than forests, but the hydraulic functioning of savannas species in Amazonian vegetation remain unknown and unexplored. We measured 22 leaf, wood and hydraulic traits, including embolism resistance (as P50), hydraulic safety margin and isotope-based water use efficiency, for the seven dominant woody species (75% of biomass) in an Amazonian savanna plants. We found a wide variation in resistance to embolism (-1.66 ±0.06 MPa and -5.07±0.46 MPa) and structural anatomy with species investing in three different functional strategies to tolerance the drought. (1) species with high leaf succulence have less efficient water use increase Gmax, minimizing the risk for xylem. (2) Species that have higher embolism resistance by reinforcement of the intervascular walls of the longest vessels. (3) Species that decrease the spread of embolism by thickening of the membrane of the intervascular pit of short vessel elements. Our results suggest no unique dominant functional strategy among Amazonian savanna species illustrating the multiple ways to adapt to increasing of seasonality in those environments.
O objetivo deste estudo foi investigar a ação da luz e de tratamentos térmicos pré-germinativos na embebição de sementes de Alcantarea imperialis. As sementes foram dispostas em unidades experimentais de 25 sementes sem desinfestação prévia e submetidas a altas e baixas temperaturas e à ausência e presença de luz. Os resultados mostraram a germinação das sementes de A. imperialis somente na presença de luz, apresentando diferenças na absorção de água entre os tratamentos térmicos ao longo do tempo e confirmando o comportamento trifásico de embebição. Apesar das diferenças encontradas entre os tratamentos, a germinação foi baixa, sugerindo que o processo possa ter sido influenciado pela viabilidade das sementes e por processos hídricos puramente físicos. Nesse sentido, ressalta-se a importância de procedimentos de desinfestação e testes de vigor, bem como a necessidade de estudos futuros das relações hídricas das sementes dessa espécie.
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