Abstract
AbstractAlthough large scale analyses of foliar N:P ratios suggest and overall pattern of P limitation in tropical forests, analyses within the biome are less indicative of a consistent pattern of nutrient limitation. High tree species diversity and soil heterogeneity are important factors driving the variability of foliar chemistry in the tropics; however, this variability could be reduced at the level of the functional characteristics of the species present at a site. In this study it is hypothesized that foliar N:P ratios would be more constrained when the species are grouped according to functional characteristics, and would reveal patterns of nutrient limitation. The study was conducted in a tropical forest landscape of the Porce region in Colombia, which consists of patches of primary and secondary forests of different ages. The functional groupings revealed consistent patterns of conservative N cycling in species present at young secondary sites, as well as conservative P cycling of the species present later in succession and in primary forests. Although the observed data have limitations in terms of capturing the overall variability for each functional group, the classification used here provided support for the proposed hypotheses. It is concluded that functional composition, rather than taxonomic composition, can potentially improve our understanding of nutrient cycling in tropical forests.
Highlights
Large scale analyses of foliar element concentrations suggest well constraint C:N:P ratios at a global level, as well as broad patterns of P limitation in tropical plants and forests (Hedin 2004, McGroddy et al 2004, Reich and Oleksyn 2004)
The Hawaiian ecosystems are characterized by a low level of biological and biogeochemical diversity and it could be argued that this broad pattern of P limitation may not apply everywhere in the tropics
Recent work suggests that young secondary forests exhibit N-cycling properties similar to temperate forests on young soils, but as forest ages this pattern switches to P limitation as in mature ecosystems (Davidson et al 2007)
Summary
Large scale analyses of foliar element concentrations suggest well constraint C:N:P ratios at a global level, as well as broad patterns of P limitation in tropical plants and forests (Hedin 2004, McGroddy et al 2004, Reich and Oleksyn 2004). This pattern of P limitation is conceptually supported on the Walker & Syers model of soil development, which has been elegantly tested on a long-term chronosequence in the Hawaiian islands (Crews et al 1995, Vitousek 2004). Co-limitation of both P and N is an alternative possibility that has been recently suggested (Davidson and Howarth 2007, Elser et al 2007); there is no clear evidence based on foliar analysis that indicates overall patterns of nutrient limitation in the tropics
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