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.
Highlights
Mangroves are special saline plants that occur in tropical and subtropical costal shores [1,2,3].Previous study [4] has reported that potential global warming and sea level rise may further aggravate coastal salinization due to possible increases in saltwater intrusion
In the higher salt treatments (400 and 600 mM salt treatments), all growth parameters sharply decreased when compared to the controls (Table 1)
The results of this study showed that a moderate salinity (200 mM NaCl) appeared to have little negative effect on the growth of A. marina
Summary
Mangroves are special saline plants that occur in tropical and subtropical costal shores [1,2,3].Previous study [4] has reported that potential global warming and sea level rise may further aggravate coastal salinization due to possible increases in saltwater intrusion. Mangroves are special saline plants that occur in tropical and subtropical costal shores [1,2,3]. Mangroves are generally considered as salt tolerant plants [5,6,7,8], high salinity and excessive salt may inhibit growth of the plants and disturb the nutrient dynamics within mangrove ecosystems [9]. In contrast to terrestrial ecosystems, nitrification and micro-formation of NO3 − in the sediments of mangroves are greatly inhibited [11,12,13,14]. Most inorganic N in mangrove sediments exists in the NH4 + form [15,16,17]. Shiau et al [9]
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