Differences in salinity tolerance and ion concentrations between Pinus densiflora Siebold et Zucc. and P. thunbergii Parl

Pinus densiflora Siebold et Zucc. and P. thunbergii Parl. are two representative pine species in the southern part of the Korean Peninsula that are often planted for reclamation purpose. In nature, P. thunbergii is distributed along the coastal areas, while P. densiflora is more inland. This study compared the growth and physiological performance of P. densiflora and P. thunbergii in different salinity levels. Seedling performance in root collar diameter growth, net photosynthetic rate and cation (Na, K, Ca and Mg) concentrations was examined at NaCl concentrations of 0, 50, 100, 150 and 200 mM for 95 days. Pinus densiflora showed significant decreases both in root collar diameter growth and net photosynthetic rate at a concentration of 50 mM NaCl (p < 0.001). On the otherhand, P. thunbergii maintained growth and photosynthesis at concentrations up to 100 mM NaCl treatment. Sodium and Mg concentrations in needles and stems of P. densiflora were more than twice the values of those in P. thunbergii in external salinity treatments (p < 0.05). However, the differences between the two species' root concentrations of Na and Mg were not statistically significant. The increased coverage of cuticular wax around stomata of P. densiflora needles with increasing external NaCl concentrations suggested the dehydration stress in the needles. Pinus densiflora needles at 200 mM NaCl had the plastoglobuli from thylakoid degradation and aging chloroplast. In saline conditions, P. densiflora uptakes and accumulates more ions such as sodium, in the aboveground organs than P. thunbergii, which contributes to the difference in their salinity tolerances, resulting in P. densiflora being salinity-sensitive and P. thunbergii being salinity-tolerant.