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Abstract NITROGEN AND PHOSPHORUS LIMITATION TO THE GROWTH AND CLONAL REPRODUCTION OF BATIS MARITIMA, A DOMINANT UNDERSTORY PLANT IN FLORIDA AND BELIZE MANGROVES. Dennis F. Whigham Batis maritima is a halophyte that is a dominant understory
plant in mangroves throughout much of the Caribbean. It occurs as
far north as North Carolina on the Atlantic coast and southern California
on the Pacific coast. In many habitats Batis forms a continuous
canopy cover that has the potential to influence the recruitment
and growth of mangrove seedlings. Little is known, however, about
this abundant and potentially important species in mangrove ecosystems.
The goal of this initial project was to evaluate nitrogen (N) and
phosphorus (P) limitation on the growth and asexual reproduction
of Batis at MSN sites in Belize and Florida where mangrove
growth has been shown to be limited by different nutrients. Fertilization
studies at both sites demonstrated a strong response to P in Belize
and a positive but less pronounced response to N fertilization at
the Ft. Pierce site. A greenhouse experiment at SERC in which N,
P and N+P were applied to Batis seedlings demonstrated
the lack of N and P reduces growth compared to the presence of both
nutrients. Preliminary interpretations are that sites at Carrie
Bow have sufficient nitrogen to support a strong growth response
to the addition of phosphorus. In Florida, there is sufficient phosphorus
in the substrate to support Batis growth as the addition
of N resulted in a significant, but relatively small growth response.
The relatively small response to N addition in Florida may be due
to salt stress as salinities at the sites where the study was conducted
are annually 80-100 ppt, a level that requires halophytes to use
much of the available N to maintain sufficient osmotic values to
continue to be able to maintain an adequate water balance. LINKAGES BETWEEN SURFACE HYDROLOGY AND ECOLOGICAL FUNCTIONING OF MANGROVE ECOSYSTEMS IN FORT PIERCE, FLORIDA Dennis F. Whigham1, Ilka C. Feller1,
Jos Verhoeven2, P. Baas2, H.J. Laanbroek2,
M. van der Ven2, Mark C. Rains3, Christina
E. Stringer3 In 2005, we began a 5-year project in Mosquito Impoundment 24 in
the Indian River Lagoon to examine linkages between surface and
subsurface hydrology and ecological functioning in nitrogen limited
mangrove ecosystems. The hypothesis that is being evaluated is that
ecological functions (e.g., species composition, primary production,
rates of nutrient cycling) are largely controlled by freshwater-saltwater
interactions. Five habitats form the basis of the project: a) Forest-ecotone:
Large black mangroves (Avicennia germinans) located adjacent
to upland non-wetland maritime forests dominated by Brazilian Pepper
and cabbage palm; b) Red mangrove: sites inside and outside the
impoundment that were co-dominated by red (Rhizophora mangle)
and black mangroves; c) Sparse black mangrove: sites dominated by
relatively tall, large and widely spaced black mangrove; d) Dense
black mangrove: sites dominated by dense stands of dwarf and black
mangroves of intermediate height; and, e) Salt pan: sites dominated
by low-growing species that are mostly herbaceous (Saliconia
vriginica, S. biglovii, Batis maritima) with relatively few
black mangroves and those that are present are small. Results to
date have demonstrated differences among habitats in growth rates,
concentrations of nitrogen in leaves and differences in rates of
nitrogen cycling. Molecular analyses of the ammonifying bacteria
also suggest habitat differences. Differences among habitats appear
to be mostly related to salinity patterns with areas of the highest
salinity (Salt pan and Sparse black mangrove) differing from the
other habitats in most. Salinity patterns are caused by the lack
of freshwater input from the adjacent uplands and evaporation and
evapotranspiration. Freshwater input of groundwater from adjacent
uplands appears to be blocked by a dense layer of highly saline
water underlying the Impoundment. |