PARENT SESSION
Poster Session # 15: Plant Ecology.

Wednesday, August 6 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Ecological and physiological responses of mangroves to the interaction between nutrients and salinity.

Ewe, Sharon^{*,1, 2}, Lovelock, Catherine², Feller, Ilka², ¹ Smithsonian Marine Station, Fort Pierce, Florida, USA² Smithsonian Environmental Research Center, Edgewater, Maryland, USA

ABSTRACT- This study compared the ecological and physiological responses of three mangrove species (Rhizophora mangle, Avicennia germinans, Laguncularia racemosa) under differing nutrient and salinity regimes to gain a better understanding of the ecological and physiological tolerances of each species. Field data (from the Indian River Lagoon, Florida) indicated that plant responses to nitrogen enrichment differed with forest type and among species. Therefore, it was hypothesized that each mangrove species was physiologically adapted to different salinity and nutrient levels and that interspecific differences would affect their distribution and overall abundance within the community. This study was conducted in a shadehouse with two daily tidal cycles. Plants were grown in sand for eight months at either 0, 17, 35, 52, 70 parts per thousand (ppt) salinity in combination with a nutrient regime (either control, nitrogen (N) or phosphorus (P)). We found that: 1) all three mangrove species grew fastest at 17 ppt salinity (0.5 times seawater strength) with N-enrichment, 2) salinity tolerance was lowest in the red mangrove (R. mangle) and highest in the black mangrove (A. germinans), 3) at high salinities (1.5 and 2 times seawater strength), N additions increased plant survivorship and 4) enrichment with P did not increase plant growth or gas exchange. Significant interspecific N-enrichment differences were observed in the ecological and physiological responses of the three mangrove species. The results imply that areas of high N and salinity will be dominated by A. germinans while high N and low salinity will contribute to L. racemosa being the dominant species. This research is significant as it provides empirical evidence of the: 1) differences in ecological and physiological responses among keystone plant species within the mangrove ecosystem in response to nutrient enrichment and 2) mechanisms by which increases in nutrient availability potentially contribute to patterns of long-term forest structure.

Key words: plant responses, nutrient enrichment