title: Differences in plant function in phosphorus- and nitrogen-limited mangrove ecosystems.
abstract: Mangrove ecosystems can be either nitrogen (N) or phosphorus (P) limited and are therefore vulnerable to nutrient pollution. Nutrient enrichment with either N or P may have differing effects on ecosystems because of underlying differences in plant physiological responses to these nutrients in either N- or P-limited settings. Using a common mangrove species, Avicennia germinans, in sites where growth was either N or P limited, we investigated differing physiological responses to N and P limitation and fertilization. We tested the hypothesis that water uptake and transport, and hydraulic architecture, were the main processes limiting productivity at the P-limited site, but that this was not the case at the N-limited site. We found that plants at the P-deficient site had lower leaf water potential, stomatal conductance and photosynthetic carbon-assimilation rates, and less conductive xylem, than those at the N-limited site. These differences were greatly reduced with P fertilization at the P-limited site. By contrast, fertilization with N at the N-limited site had little effect on either photosynthetic or hydraulic traits. We conclude that growth in N- and P-limited sites differentially affect the hydraulic pathways of mangroves. Plants experiencing P limitation appear to be water deficient and undergo more pronounced changes in structure and function with relief of nutrient deficiency than those in N-limited ecosystems.
authors.affiliation: Centre for Marine Studies, University of Queensland, St Lucia Q 4072, Australia. c.lovelock@uq.edu.au
authors.forename: Catherine E
authors.initials: CE
authors.lastname: Lovelock
authors.forename: Ilka C
authors.initials: IC
authors.lastname: Feller
authors.forename: Marilyn C
authors.initials: MC
authors.lastname: Ball
authors.forename: Bettina M J
authors.initials: BM
authors.lastname: Engelbrecht
authors.forename: Mei Ling
authors.initials: ML
authors.lastname: Ewe
mesh_terms: D001531:Belize; D017753:Ecosystem; D009584:Nitrogen / Q000378:metabolism*; D010758:Phosphorus / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology; D018515:Plant Leaves / Q000378:metabolism; D043982:Rhizophoraceae / Q000378:metabolism*; D014867:Water / Q000378:metabolism; D052584:Xylem / Q000033:anatomy & histology
chemical_list: D014867:Water; D010758:Phosphorus; D009584:Nitrogen