Seasonal changes in water sources used by woody species in a tropical coastal dune forest
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Our aim was to investigate the water sources used by woody species under contrasting water availability and the extent of water-sources-use differentiation among dominant woody species in a tropical coastal dune forest.
We sampled 15 woody species in a Brazilian restinga forest and, through Bayesian isotope mixing models, we estimated the proportion of water sources used. We tested whether water-sources-use was (i) different between contrasting water availability conditions; (ii) dependent on growth form, plant size or crown illumination; and (iii) influenced by stand density, evenness or biomass.
We found a seasonal variation in water-sources-use, but no vertical soil-water partitioning among woody species. In wetter periods, plants used mainly water from top-soil, as a shallow water table limited water uptake to top-soil layers recharged with rainwater. Contrastingly, during drier periods, with the absence of rain and a deeper water table, plants generally relied on deeper (50 cm) soil layers. Only under less-wet conditions, a greater evenness and density implied higher water-uptake depth heterogeneity among plants. However, changes in the main water-sources used by plants were neither evoked in more dense or diverse plots, nor induced by plant size.
Our study shows that restinga species have dynamic shifts in water-uptake depth caused by seasonal water availability changes, influenced by the combined effect of insufficient moisture at shallow soil layers and water-table lowering in drier periods. These temporal shifts are common among species, implying that restinga woody community has a homogeneous strategy of water-resources acquisition. This study enhances our understanding of the effects that water variations can have on water-resource use in restinga forests.
KeywordsWater-sources-use Coastal dune ecosystem Restinga forest Stable isotope mixing model Groundwater availability Soil-water partitioning
We thank to PPG - Ecologia, Instituto de Biologia, Universidade Estadual de Campinas, for the support given to Cristina Antunes in the development of this study. This research was funded by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) – Cristina Antunes PhD scholarship PROEX 0229083, and Fundação para a Ciência e a Tecnologia (FCT) – projects PTDC/AAC-CLI/118555/2010 and UID/BIA/00329/2013. The scientific project was co-supported by the Brazilian National Research Council/CNPq (PELD Process 403710/2012-0), by the British Natural Environment Research Council/NERC and by The State of São Paulo Research Foundation/FAPESP as part of the projects Functional Gradient, PELD/BIOTA and ECOFOR (Processes 2003/12595-7, 2012/51509-8 e 2012/51872-5, within the BIOTA/FAPESP Program - The Biodiversity Virtual Institute (www.biota.org.br); COTEC/IF 002.766/2013 and 010.631/2013 permits. Namely, we would like to thank: Yvonne Bakker, Luis Quimbayo Guzmán, Thaís Pimenta de Almeida and Marisol Rios for the help given during field surveys; Mauro Lo Cascio and Andreia Anjos for the laboratory work; João Barbosa for data base management; and Rodrigo Maia for isotopic analysis at SIIAF - Faculdade de Ciências, Universidade de Lisboa. The authors have no conflict of interest to declare.
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