Effect Of Different Phosphorus Levels On The Growth Of Kosteletzky Virginica Under NaCl Stress

By pot experiment, we tried to explore the impact of different phosphorus leveltreatments（0.1mM,0.5mM,1mM,1.5mM,2mM,3mM,4mM）on the growth,physiological characteristics, photosynthetic gas exchange, as well as photochemicalcharacteristics of PSII and ion distribution of Kosteletzkya virginica under salt stress(200mM NaCl), in order to confirm optimum phosphorus level under salt stress andto provide theoretical basis for reasonable application of fertilizer in the cultivation ofKosteletzkya virginica in saline land.The experimental results were as follows:1. Effect of different phosphorus levels on the growth of Kosteletzkya virginicaunder NaCl stressUnder0mM NaCl and200mM NaCl treatment, the fresh weight, dry weight,stem length and total length of branches of Kosteletzkya virginica first rose and thenfell with the phosphorus level; Under0mM NaCl treatment, they achieved maximumunder1mM-2mM phosphorus level, under200mM NaCl treatment, however, themaximum was achieved under1.5mM-3mM phosphorus level, and then the growthdecreased under high phosphorus level both under0mM NaCl and200mM NaCltreatment; The results showed that Kosteletzkya virginica increased its demand forphosphorus under NaCl treatment.2.Effect of different phosphorus levels on the photosynthetic characteristics ofKosteletzkya virginica under NaCl stressUnder0mM NaCl and200mM NaCl treatment, the Pn, Gs, Tr and actualphotochemical efficiency (ΦPSII) of Kosteletzkya virginica first rose and then fellwith the phosphorus level, while Ci showed the oppisite trend, Kosteletzkya virginicaincreased its demand for phosphorus level under NaCl treatment on photosyntheticcharacteristics. Under NaCl treatment, Pn and Gs decreased obviously, but Ciincreased a little, indicating that non-stomatal limiting factor and stomatal limitingfactor at this time are both responsible for the decrese of Pn under salt stress.Under low phosphorus level, Pn was low, the limitation of CO2assimilation ledto the increase of Ci; Under suitable phosphorus level, Pn increased, accompanyingthe decrease of Ci. NaCl treatment increase the demand for phosphorus in Kosteletzkya virginica level, indicating that phosphorus nutrition can alleviate saltstress.3.Effect of different phosphorus levels on light energy allocation of Kosteletzkyavirginica under NaCl stressqP decreased and NPQ increased gradually under salt stress, NPQ increasedremarkably compared to the control when it came to200mM NaCl concentration;Indicating that the photochemical conversion efficiency was inhibited by salt stress,and more excited energy was dissipated through NPQ. As a result, the PSII reactioncentre wouldn’t be damaged badly.Under low phosphorus level, PSII photochemical conversion efficiency was low,the assimilation of CO2was low, then more excited energy was dissipated throughNPQ remarkably; Under suitable phosphorus level, with the photochemicalconversion efficiency increased, NPQ decreased simultaneously. Phosphorus nutritioncan contribute to energy dissipating through chemical quenching, which is an efficientway to protect the reaction centre of PSII in Kosteletzkya virginica.4.Effect of different phosphorus levels on the photochemical characters of PSIIof Kosteletzkya virginica under NaCl stressPHI (Po) decreased slightly under salt stress, indicating that the influence of saltstress on the maximum photochemical efficiency was neglectable; PHI(Eo) overalltrends similar to PHI (Po), but significantly different from CK；The changing trends ofPHI(Do) is just the opposite to PHI(Eo), increased significantly under salt stress,indicating that thermal dissipation of Kosteletzkya virginica significantly increased.ETo/CSm and DIo/CSm Trends in contrast，ETo/CSm decreased while DIo/CSmincreased under salt stress. It showed that thermal dissipation increased with thedecrease of the efficiency of photochemistry.The relative variable fluorescence atJ-step(Vj) showed a remarkably increased under salt stress.Both PHI(Po) and PHI(Eo) increased gradually with the increase of phosphorusconcentration, and a decrease slightly was found at high level phosphorusconcentrations. The maximum of PHI(Po) and PHI(Eo) of the control group wasachieved at1mM-2mM phosphorus concentration. Different from the control group,PHI(Po) and PHI(Eo) of the experimental group achieved the maximum at aphosphorus concentration of1.5mM-2mM and2mM-3mM, respectively. Theresults indicated that low phosphorus level inhibited the transformation of electrochemical energy. Phosphorus level has a greater impact on PHI(Po) than saltstress.PHI(Do) decreased gradually as the phosphorus concentration increased uner thesame salinity, and a small fluctuation was found at high phosphorus level. High levelphosphorus promoted the proportion of quantum yield that used in electron transportand decreased the proportation of quantum yield to thermal dissipation. The minimumPHI(Do) was found in the control group at1mM-2mM phosphorus, while appearedat2mM-3mMphosphorus under salt stress.Vj decreased gradually as the phosphorus concentration increased under thesame salinity for a certain range of phosphorus concentration. The difference betweenlow phosphorus (0.1mM、0.5mM) and optimal phosphorus level was significant,indicating that increased phosphorus played an important role in the opening degreeof reaction center and in promoting the transfering of excitation engery. The minimumVj of the control group appeared at1mM-2mM phophorus, while appeared at1.5mM-3mM under salinity.From the above analyses, the demand of phosphorus of Kosteletzkya virginicaincreased to some extent under salt stress.5.Effect of different phosphorus levels on ion distribution of Kosteletzkyavirginica under NaCl stressUnder salt stress, the Na+concentration in roots is much higher than that inleaves, which indicated that Kosteletzkya virginica could accumulate Na+in root andtransport K+to leaf selectively. With an appropriate concentration range, phosphrusenhanced selectivity of the absorption of K+to Na+, therefore, a lower ratio of Na+: K+in leaf could be achieved.Phosphrus-involved photoprotection system is believed to be an importantmechanism for plants to deal with excessive light engery under salt stress byphotochemical and non-photochemical energy dissipation. And more phosphrus isneeded under salt stress to protect the photosynthetic apparatus by decreasing the loadof PSII reaction center.