Effects of Salt on Root Aeration, Nitrification, and Nitrogen Uptake in Mangroves

Abstract

The potential effects of salt on the growth, root anatomy, radial oxygen loss (ROL), and nitrogen (N) dynamics in mangroves were investigated using the seedlings of Avicennia marina (Forsk.) Vierh. The results showed that a moderate salinity (200 mM NaCl) appeared to have little negative effect on the growth of A. marina. However, higher salt stresses (400 and 600 mM NaCl) significantly inhibited the biomass yield. Concentrations of N in the roots and leaves decreased sharply with increasing salinity. Nevertheless, the presence of salt directly altered root anatomy (e.g., reduced root porosity and promoted suberization within the exodermis and endodermis), leading to a significant reduction in ROL. The results further showed that reduced ROL induced by salt could restrain soil nitrification, resulting in less ammonia-oxidizing archaea and bacteria (AOA and AOB) gene copies and lower concentrations of NO3− in the soils. While increased root suberization induced by salt inhibited NH4+ and NO3− uptake and influx into the roots. In summary, this study indicated that inhibited root aeration may be a defense response to salt, however these root symptoms were not advantageous for rhizosphere nitrification and N uptake by A. marina.

Nitrogen Cycling and Mass Balance in the World’s Mangrove Forests

“…Additional evidence indicates that adjacent mudflat sediments usually have higher porewater concentrations of NH 4 + than in mangrove soils, suggesting that the difference is due to tree uptake [11]. These data are circumstantial, but support experimental data showing a strong preference by mangroves for ammonium (and nitrate) for their growth and nutrition [12][13][14][15]. Nitrite and nitrate are often found in mangrove porewater [4,11], but concentrations show very irregular patterns with increasing soil depth.…”

“…Abbreviations: DNRA= dissimilatory nitrate reduction to ammonium; anammox = anaerobic ammonium oxidation. Source: [9,15,[55][56][57][58]129,.…”

Differential Response of Macrobenthic Abundance and Community Composition to Mangrove Vegetation

“…It has been shown that sea-level rise caused by climate change may affect the growth and distribution of mangroves [72][73][74]. Large-scale planting of mangroves has been applied as a mitigation strategy for mangrove loss [34].…”