The Response Of Different S.salsa Populations To Low Nitrate Nitrogen Concentration

The effect of different nitrate nitrogen levels on the growth, ion accumulationand root morphology of two S. salsa populations were investigated in this paper, forthe purpose of understanding the mechanism of nitrate uptake and reutilization underhigh salt concentration and low NO₃^-concentration in two S. salsa populations.Results are as follows:1. Effects of salinity and nitrogen interaction on the growth and ionaccumulation of S. salsa from different habitats.The contents of Na⁺、Cl-and amino acid （AA） in the leaves of S. salsa weresignificantly increased under high salinity （500mM NaCl）. In both salinity levels （1and500mM NaCl）, the Cl-content decreased in two S. salsa populations with thesupply of5mM NO₃^--N, while the Cl-content in leaves of the inland population washigher than that in the intertidal population in all treatments. The supply of5mMNO₃^--N significantly increased NO₃^-content and NR activity in leaves of two S. salsapopulations. At the same NO₃^--N concentration, high salinity decreased the NO₃^-content in S. Salsa from saline inland, while salinity had no significant effect on thevalue in S. Salsa from intertidal zone. At the0.1mM NO₃^--N concentration, thechlorophyll content of S. Salsa from saline inland decreased with the increase of NaClconcentration, while no adverse effect of salinity on S. Salsa from intertidal zone wasobserved. The biomass and root/shoot ratio of two S. salsa populations decreasedunder500mM NaCl treatment. With higher NO₃^-and AA content and lower Cl-content, the intertidal population is competent to survive in the environment withhigher salt concentration and lower NO₃^-concentration. 2. The response of two S. salsa populations to nitrogen starvationIn the present experiment, with0.3mM or5mM NO₃^--N pretreatment, the NO₃^-content in leaves of the intertidal population was higher than that in the inlandpopulation during the whole time course. Nitrogen starvation decreased chlorophyllcontents, NR activity and photosynthetic oxygen evolution rate in leaves of the inlandpopulation more sever than the intertidal population, especially when seedlings werepretreated with0.3mM NO₃^--N. As for S. salsa from saline inland soils, theroot/shoot ratio decreased significantly after nitrogen starvation, while nitrogenstarvation had no adverse effect on the value for the intertidal population afterseedlings were pretreated with0.3mM NO₃^--N.The present results suggest that S. salsa from intertidal zone may have higherNO₃^-storage capacity and nitrogen assimilation capacity under low nitrogen condition.Therefore, the seedlings of the intertidal population have higher NO₃^--N reutilizationability to maintain nitrogen metabolism and normal photosynthesis ability, whichindicates that S. salsa from intertidal zone can better adapt to low nitrogen habitatcompared to the inland population. These traits may affect the distribution of S. salsain natural saline environments.3. Effects of salinity and nitrogen interaction on the growth and ionaccumulation of young seedings in two S. salsa populationsThe contents of Na⁺and Cl-increased markly with increasing NaCl supply inyoung seedings （seedlings were collected14days after seeds were moistened indifferent concentrations of NO₃^--N and NaCl）of two S. salsa populations, while theopposite trend was found in the contents of K⁺and NO₃^-. Elevated NO₃^--N supplyincreased the NO₃^-content, while decreased the content of Na⁺and Cl-at400mMNaCl. Compared with the seedings of the inland population, the seedings from theintertidal population always had lower contents of Na⁺and Cl-and higher NO₃^-content. High salinity inhibited the roots elongation, while the low NO₃^--N supplyincreased the root length, dry weight and fresh weight of the roots in seedings of twoS. salsa populations, especially for the intertidal population. Salinity and nitrogen interaction had no obvious effect on shoot growth of two populations,. Shoot length ofseedings from intertidal population was higher than that in seedings of inlandpopulation. The results suggest that low NO₃^--N concentration can promote theenlongation and NO₃^-uptake of roots, especially in seedlings from intertidalpopulation. This trait may maintain the growth of plants from two populations at highsalinity and low nitrogen environment, especially for the intertidal population. Thismay be the mechanism of two populations to adapt high salinity and low nitrogenhabitat, especially for the intertidal population.