ABSTRACT
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. 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. 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. 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.
ABSTRACT
Thirteen species of Crotalaria were analysed for nitrogen compounds in the xylem root bleeding sap. Amino acids were the main form of organic nitrogen found, but only traces of ureides were present. Of the four species analysed for amino acid composition, asparagine was found to be the major amino acid, accounting for over 68% of the nitrogen transported. No striking deviations from this general pattern was found between species, between vegetative and floral stages of development, or between nodulated and non-nodulated plants. It was concluded that the Crotalaria species studied here have an asparagine-based nitrogen metabolism, consistent with many other non-ureide-producing legume species.
Treze espécies de Crotalaria foram analisadas quanto aos compostos nitrogenados presentes na seiva do xilema. Os aminoácidos foram os principais compostos nitrogenados encontrados, e apenas traços de ureídeos estavam presentes. Uma análise da composição de aminoácidos realizada para quatro espécies revelou que a asparagina é o aminoácido predominante, representando mais de 68% do nitrogênio transportado. Nenhum desvio marcante deste padrão foi encontrado entre espécies, entre plantas noduladas e não-noduladas e nem entre estádios florais e vegetativos. Chegou-se a conclusão de que as espécies aqui estudadas possuem metabolismo de nitrogênio baseado na asparagina, concordando com dados da literatura para muitas outras espécies de leguminosas que pertencem à categoria de não-produtoras de ureídeos.
ABSTRACT
Thirteen species of Crotalaria were analysed for nitrogen compounds in the xylem root bleeding sap. Amino acids were the main form of organic nitrogen found, but only traces of ureides were present. Of the four species analysed for amino acid composition, asparagine was found to be the major amino acid, accounting for over 68% of the nitrogen transported. No striking deviations from this general pattern was found between species, between vegetative and floral stages of development, or between nodulated and non-nodulated plants. It was concluded that the Crotalaria species studied here have an asparagine-based nitrogen metabolism, consistent with many other non-ureide-producing legume species.
Treze espécies de Crotalaria foram analisadas quanto aos compostos nitrogenados presentes na seiva do xilema. Os aminoácidos foram os principais compostos nitrogenados encontrados, e apenas traços de ureídeos estavam presentes. Uma análise da composição de aminoácidos realizada para quatro espécies revelou que a asparagina é o aminoácido predominante, representando mais de 68% do nitrogênio transportado. Nenhum desvio marcante deste padrão foi encontrado entre espécies, entre plantas noduladas e não-noduladas e nem entre estádios florais e vegetativos. Chegou-se a conclusão de que as espécies aqui estudadas possuem metabolismo de nitrogênio baseado na asparagina, concordando com dados da literatura para muitas outras espécies de leguminosas que pertencem à categoria de não-produtoras de ureídeos.