title: Environmental regulation of carbon isotope composition and crassulacean acid metabolism in three plant communities along a water availability gradient.
abstract: Expression of crassulacean acid metabolism (CAM) is characterized by extreme variability within and between taxa and its sensitivity to environmental variation. In this study, we determined seasonal fluctuations in CAM photosynthesis with measurements of nocturnal tissue acidification and carbon isotopic composition (δ(13)C) of bulk tissue and extracted sugars in three plant communities along a precipitation gradient (500, 700, and 1,000 mm year(-1)) on the Yucatan Peninsula. We also related the degree of CAM to light habitat and relative abundance of species in the three sites. For all species, the greatest tissue acid accumulation occurred during the rainy season. In the 500 mm site, tissue acidification was greater for the species growing at 30% of daily total photon flux density (PFD) than species growing at 80% PFD. Whereas in the two wetter sites, the species growing at 80% total PFD had greater tissue acidification. All species had values of bulk tissue δ(13)C less negative than -20‰, indicating strong CAM activity. The bulk tissue δ(13)C values in plants from the 500 mm site were 2‰ less negative than in plants from the wetter sites, and the only species growing in the three communities, Acanthocereus tetragonus (Cactaceae), showed a significant negative relationship between both bulk tissue and sugar δ(13)C values and annual rainfall, consistent with greater CO(2) assimilation through the CAM pathway with decreasing water availability. Overall, variation in the use of CAM photosynthesis was related to water and light availability and CAM appeared to be more ecologically important in the tropical dry forests than in the coastal dune.
authors.affiliation: Unidad de Recursos Naturales, Centro de Investigación Científica de Yucatán, Mérida, Yucatán, Mexico.
authors.forename: M Fernanda
authors.initials: MF
authors.lastname: Ricalde
authors.forename: José Luis
authors.initials: JL
authors.lastname: Andrade
authors.forename: Rafael
authors.initials: R
authors.lastname: Durán
authors.forename: Juan Manuel
authors.initials: JM
authors.lastname: Dupuy
authors.forename: J Luis
authors.initials: JL
authors.lastname: Simá
authors.forename: Roberth
authors.initials: R
authors.lastname: Us-Santamaría
authors.forename: Louis S
authors.initials: LS
authors.lastname: Santiago
mesh_terms: D000143:Acids / Q000378:metabolism / Q000528:radiation effects; D029421:Cactaceae / Q000737:chemistry / Q000378:metabolism / Q000528:radiation effects; D002245:Carbon Dioxide / Q000378:metabolism*; D002247:Carbon Isotopes / Q000378:metabolism; D029627:Crassulaceae / Q000737:chemistry / Q000378:metabolism* / Q000528:radiation effects*; D017753:Ecosystem; D008027:Light; D008800:Mexico; D011891:Rain; D012621:Seasons
chemical_list: D000143:Acids; D002247:Carbon Isotopes; D002245:Carbon Dioxide