Effects of ammonium, phosphate, and salinity on growth, gas exchange characteristics, and ionic contents of seedlings of mangrove Kandelia candel (L.) Druce.

The effects of ammonium, phosphate, and salinity on growth, gas exchange ch aracteristics, and ionic content, of seedlings of mangrove Kandelia candel (L.) Druce were investigated in solution culture experiments over seven mon ths. High salinity at 20 ppt NaCl greatly reduced dry matter accumulation i n shoots and roots and leaf CO2 assimilation rate. Addition of ammonium-nit rogen (2 mM) significantly increased the growth of shoots and roots, leaf C O2 assimilation rate, and respiration rate at low salinity treatments. Phos phate amendment alone did not affect the growth of plants. However, when am monium-nitrogen was also added, phosphate improved the growth of plants, le af CO2 assimilation rate, and respiration rate in low salinity treatments. Kandelia candel tended to maintain a constant cation concentration in tissu es of leaves and roots at low salinity conditions. Potassium was the major cation in the tissues at the low salinity; however, it was replaced by sodi um as the salinity of the culture solution was increased. Kandelia candel a bsorbed ammonium-nitrogen luxuriously at all salinity treatments and some o f the ammonium accumulated in the tissues could he part of cations as the o smotic inorganic solute. Reasons for the difference in optimal growth salin ity fur K. candel between porewater in the field and the culture solution i n the greenhouse are discussed.