PS 71-134 - Ecophysiological differentiation in Curatella americana populations from Neotropical savannas

Thursday, August 6, 2009
Exhibit Hall NE & SE, Albuquerque Convention Center
Zdravko Baruch , Estudios Ambientales, Universidad Simon Bolivar, Caracas, Venezuela
Background/Question/Methods

Curatella americana is a medium sized (3m tall), evergreen and fire tolerant tree with twisted and branched trunks. Due to its high density and biomass it is a dominant tree in the savannas of Venezuela,Colombia,and norhern Brazil. Therefore, Curatella is crucial in the carbon and nutrient balance of the savanna and in maintaining its ecological stability. In Venezuela, populations of Curatella inhabit the lowland savannas of the Llanos region on both margins of the Orinoco River. The persistence of some Curatella populations is endangered due to expanding land use changes and oil explotation. Despite its apparent uniformity, the savannas encompass large variations in rainfall, soils and disturbance regimes where Curatella predominates. This large environmental variation may have promoted local selection events reflected in population differences in ecophysiological traits. The objectives of this study were: (i) to determine the scale of ecophysiological traits variability in Curatella populations and (ii) to relate it to local environments and geographic distance among populations. During the rainy season, 8 populations of Curatella were sampled for specific leaf area (SLA), photosynthesis (Aarea), transpiration (E), leaf N and P content, and stable isotope (13C) signature. Water and nitrogen use efficiencies (WUE and NUE) were calculated. Soils were sampled and climatic data collected. Differences among populations were tested with ANOVA. The relationships among and between populations traits and environment were determined by classification (UPGMA), ordination (PCA), and Mantel tests.

Results/Conclusions

Rainfall and soil fertility vary five- and three-fold respectively between the populations habitats. Both increase from eastern to western savannas. SLA, Amass, and NUE differed significantly among populations being lowest at the two driest sites. Instantaneous WUE (Aarea /E) and long term WUE (δ13C) were highest in the same populations. Leaf N and P content also differed among populations and their ratio indicates that Curatella was P limited in the sandier soils. Classification and ordination show a clear separation between two Curatella populations from the eastern Llanos with low rainfall and low P from the western populations at both margins of the. The results of this study reveal a large variability in ecophysiological traits among Curatella populations as a response to local environment variability. The results may be valuable for implementing conservation and restoration projects for the savanna biome.

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