Nitrogen-phosphorus conservation and trade-offs in mangroves

Mangroves distributed in intertidal zones along tropical and subtropical coastlines play key roles in nutrient cycling, energy transfer, and maintenance of ecosystem balance. The maintenance of mangroves’ high productivity and ecosystem functionality in nutrient-limited environmental conditions is very important. This paper comprehensively elucidates how mangroves sustain ecological balance and survive in nutrient-limited coastal environments. The foliar nitrogen and phosphorus (N-P) concentrations and N:P ratios in different mangrove plant species and regions of the world are summarized, and results show that 73.7% and 16.4% of mangrove plants are N- and P-deficient, respectively. A comprehensive overview on the strategies employed by mangrove plants to conserve N-P in both above- and below-ground components is discussed. These strategies include N-P resorption efficiency, in short NRE and PRE, respectively, N-P use efficiency, litter quality, soil microbial activity, and N-P turnover rate. All these strategies are influenced by N-P content and their interactions, as well as secondary metabolites such as total phenolics and tannins in leaf and litter. Published data reveal mangrove leaves have higher NRE (56.2%) than PRE (48.8%), and NRE positively relates to PRE. Nutrient uptake by mangrove plants and N-P availability under different conditions, particularly global warming, rising sea levels and elevated atmospheric carbon dioxide (CO2) situations, are discussed. A framework for gaining in-depth and targeted understanding of the trade-offs associated with N-P in mangrove ecosystems is proposed. This comprehensive overview, based on the published results on N and P conservation and their trade-off in mangrove plants, provides useful information on ecological services and functioning of mangrove wetlands.