Clusia hilariana, a key species on nutrient cycling in sand dune vegetation thickets

Abstract

Interspecific plant-plant interactions studies showed that Clusia hilariana plays a facilitation role in the scattered vegetation thickets of the Brazilian sandy coastal plain vegetation (Restinga). In the Clusia open formation in the Jurubatiba Restinga National Park there are thickets differing in the presence and senescence of Clusia: (1) healthy Clusia thickets (HCT); (2) senescent Clusia thickets (SCT); and also (3) thickets without Clusia (TWC). The aim of this long term study was to assess soil chemistry, litterfall mass and nutrient input and its leaf-litter decomposition in Clusia thickets, testing the hypotheses that: (1) the presence of Clusia increases soil nutrient concentrations in the thickets; (2) litterfall mass and nutrient input are dependent on the senescence stage of Clusia, being higher in HCT than in SCT; (3) decomposition and nutrient release of Clusia leaves are faster in HCT than in SCT, evaluating if C. hilariana promotes an improvement in nutrient cycling according to its presence and senescence in the thickets and reinforcing the role of Clusia as a nurse plant. Collection of nutrients in soils, litterfall and Clusia leaf decomposition rates were measured between 2001 and 2008. The HCTs presented higher annual litterfall mass and nutrient input than the SCTs, Clusia leaf-fall contributed the bulk of the total litterfall (70 % HCT, 34 % SCT). Nitrogen, as all other nutrient inputs from Clusia leaf-litter, was higher in HCT, although Clusia leaves had low N concentrations and a higher C/N ratio. Clusia-leaf decomposition was faster in HCT than in SCT during the first year of the experiment. The slow decomposition and nutrient release from Clusia leaf-litter, may be an important mechanism of nutrient conservation. We concluded that C. hilariana acts as a key species, and as a nurse plant, in relation to nutritional dynamics, organic matter, nutrient input, and decomposition via its litter, which decreased according to its senescence.