Water salinity effects on growth and nitrogen assimilation rate of mangrove (Kandelia candel) seedlings

Mangrove is one of the dominant plants in tropical and sub-tropical estuarine ecosystems. The understanding of growth and nitrogen (N) assimilation rates of mangrove at different water salinities can be beneficial for evaluating the response of mangroves to increased anthropogenic N loading into these systems. We investigated the effect of salinity on growth and N assimilation of Kandelia candel (L) Druce under the phytotron conditions at alternating temperatures of 25 °C (day) and 20 °C (night) with 16-h light at ∼300 μmol photons m−2 s−1. The experiment included four salinity treatments (0, 8.8, 17.5 and 35 psu) and two N sources (NO3− and NH4+). With increasing salinity, mangrove shoot and root biomass decreased, but its hypocotyl biomass increased. Thus, the total biomass yield of mangrove remained unchanged in different salinity treatments. Nevertheless, N assimilation rate measured by the 15N stable isotope technique was significantly reduced from about 2.2 mg N g−1 biomass hr−1 under control conditions (0 psu) to 0.9 mg N g−1 biomass hr−1 under 35 psu. Mangrove favored nitrate than ammonium at low salinity (0 psu), but preferred NH4+ to NO3− at higher salinity (17.5 and 35 psu).