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Global change and community competition alter Avicennia germinans growth in the salt marsh mangrove ecotone

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Description: Our understanding of coastal plant community response to global change factors, specifically nitrogen (N) enrichment and sea level rise under interspecific competitive scenarios is limited. The salt marsh-mangrove ecotone, which is the transitional community where tropical mangrove converges with temperate salt marsh, will be most sensitive to environmental change because these species are at their physiological limits of distribution. Competition between these species under global change scenarios may lead to distribution shifts within the ecotone, causing disruptions in the important ecosystem functions that each habitat provides. Avicennia germinans , the black mangrove, intermingles with salt marsh species in Florida, Louisiana and Texas, providing an excellent opportunity to test hypotheses about global change effects on plant distributions. Two experiments, a field study and a greenhouse component, were conducted to determine how N-addition and sea level rise would impact the growth and biomass partitioning of Avicennia seedlings grown in competition with salt marsh species. Results of the field experiment carried out in Florida's salt marsh-mangrove ecotone clearly demonstrate that aboveground competition decreases leaf area and foliar C:N while N-enrichment increases mangrove leaf production, foliar N and leaf biomass. These results suggest that Avicennia seedlings are constantly vying for canopy dominance by increasing photosynthetic capture regardless of alleviation of aboveground competition or limiting nutrients. The companion greenhouse experiment results indicate that Avicennia seedlings can grow under permanently flooded conditions and N-additions do not facilitate an increase in growth. However, interspecies competition causes an increase in Avicennia leaf biomass and foliar N while simultaneously decreasing leaf production. These results, coupled with the field study results, suggest that Avicennia leaf production and foliar dynamics are an integral part of mangrove competitive ability. As global change factors act to alter species response and distribution, interspecies competition and N-enrichment may alleviate or intensify the stress placed on competing species. This work suggests that competition should be looked at more closely under global change scenarios as that it might be a deciding variable in the maintenance of a population's distribution.
Language: English
Format: Degree Work