Abstract
Inundation associated with flooding and sea level rise is predicted to have major impacts on survival, growth and productivity of mangroves. A manipulative mesocosm experiment was conducted to assess whether nutrient enrichment enhances growth and photosynthesis of waterlogged and salinity stressed seedlings of the mangrove Heritiera littoralis Dryand. Seedlings were fertilized with a three-component granular farm NPK (Nitrogen-Phosphorous-Potassium, 20:20:20) at varied loads under waterlogging with four levels of salinity. Growth was assessed through biomass accumulation, and photosynthesis through photosynthetic quantum yield and leaf Chl content. When seedlings were exposed to both nutrient enrichment and increased salinity, a significant shift of biomass to roots was observed. Seedlings had low value of Chl a/b ratio and photosynthetic distraction resulting in mortality was high in the highest salinity and nutrient levels. These results are useful in explaining failure of regeneration in natural stands of riverine and freshwater bound mangroves following unprecedented flooding events that accrue land based nutrient loads into estuaries and deltas.
Highlights
Mangroves inhabit the land-sea interface where tidal inundation and salinity gradients are a natural phenomenon
Mangrove seedlings had a significant shift of biomass to roots with increase in salinity, conflicting with advantageous availability of nutrients for shoot growth. [3] reported contrasting species specificity in response to interactive flooding, nutrient and salinity where, for example, L. racemosa recorded higher growth with shifts of biomass to shoots than roots compared to A. germinans and R. mangle which showed a reverse pattern when subjected to prolonged flooding.Higher biomass allocation to roots indicated that the seedlings are more tolerant to low nutrient condition in the presence of stress from other sediment factors of waterlogging and salinity
These findings contrasts what [19] suggested that mangroves which were exposed to high nutrient availability, and had relatively lower capacity to invest in roots than shoots, suffered greater mortality when exposed to inundation and salinity stress
Summary
Mangroves inhabit the land-sea interface where tidal inundation and salinity gradients are a natural phenomenon. Inundations and salinity are among the problems that confront mangroves when their optimal levels are exceeded, often causing a proliferation of anaerobic microbes and draining of essential nutrients [1]-[3]. How to cite this paper: Mangora, M.M. (2016) Nutrient Enrichment and Saline Conditions Decreases Growth and Photosynthesis of the Mangrove Heritiera littoralis Dryand. Open Journal of Marine Science, 6, 293-301.
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