Litterfall dynamics and nutrient cycling in mangrove forests of Southern Everglades, Florida and Terminos Lagoon, Mexico.

摘要

The objective of this dissertation was to investigate the processes that control litterfall and nutrient dynamics in two contrasting mangrove ecosystems at the Southeastern (SE) Everglades and Terminos Lagoon. The main objectives were: (a) to determine the spatial and temporal variability of litterfall dynamics, (b) to evaluate the relative importance of nutrient use efficiency as a nutrient conservation mechanism along a natural nutrient gradient, and (c) to assess the relative importance of nutrient resorption on litterfall dynamics. Two hypotheses were tested: (a) mangrove species living in nutrient-poor environments and in nutrient-rich environments do not differ in the efficiency in using nutrients, (b) nutrient resorption and nutrient immobilization do not differ along a natural nutrient gradient.; Litterfall rates were lowest in a dwarf mangrove forest at SE Everglades and highest in fringe and riverine forests at Terminos Lagoon. Litterfall dynamics were linked to the local tidal pattern at each study site. Litter turnover rates were higher in areas most influenced by tides and lower in areas less affected by tides. In areas where tides were less frequent litterfall turnover was lower and nutrient immobilization was higher.; Laguncularia racemosa and Rhizophora mangle were more efficient In resorbing both phosphorus and nitrogen than Avicennia germinans. This pattern was similar at both study regions; however, nutrient resorption was higher at SE Everglades sites and lower at Terminos Lagoon sites. Also, phosphorus resorption was higher than that of nitrogen, indicating that in carbonate environments phosphorus is more limiting than nitrogen. Since nutrient resorption was higher at SE Everglades, dry matter degradation was slower at these sites, relative to Terminos Lagoon. Thus, nutrient resorption plays an important role in controlling the nutrient economy in mangrove forests where phosphorus is limiting.; Nutrient resorption was linked to patterns of litterfall dynamics. Thus, in mangrove forests where leaf turnover was high, nutrient conservation was enhanced at the canopy level, while at sites where leaf turnover was low, nutrient immobilization via leaf decomposition became an important mechanism to recycle nutrients.