Effects Of Relative Supplies Of Nitrogen And Phosphorus On Growth And Stoichiometric Characteristics Of Suadea Salsa

The nitrogen(N)and phosphorus(P)status,including N :P supply ratio and overall supply level,has changed greatly in Yellow River Delta coastal wetland with increasing human disturbance.Ecological stoichiometry is an excellent research tool to study the plant response to nutrient status variation.Influenced by the nutrient demand characteristics and structure feature,plant ecological stoichiometry characteristics will change along with the variation of nutrient status and growth phase,and differ in different organs.In this research,the response of Suaeda Salsa,a dominant plant in Yellow River Delta,to the variations of N and P supply status was studied through a field control experiment.Three N :P supply ratios combined with three overall supply levels were set in the experiment.The respective effect of N :P supply ratio and overall supply level on the growth vigor,the C,N,P concentrations and C :N :P ratios in different organs,were examined at three growth phases.The relative impact strength of N and P supply status and growth phase on the stoichiometry of specific organ was compared as well.The results indicated that:(1)The morphological traits,including plant height,basal diameter and crow n size,as well as total biomass and biomass allocation of S.salsa were significantly related to overall nutrient supply level.Growing at low overall supply level,the plant was taller and thinner with a lower leaf biomass allocation in early vigorous growth phase;when come to later growth phase,it had smaller crown size with higher root biomass allocation and smaller total biomass.However,there was no significant change of all indicators between medium and high supply level.The N:P supply ratio alone had no significant effect on the morphological traits but had significant interaction with supply level on total biomass.The biomass increased significantly at high N :P supply ratio under low overall supply,with leaf biomass allocation increased simultaneously.(2)Under changing N and P supply status,C concentration varied least in S.sala organs compared with N and P concentration.Among different organs,N concentration varied least in root,while P concentration varied least in leaf.As for the C:N:P ratios,root C:N varied least while stem C:N varied most.Variation of both C:P and N:P was least in leaf and most in root.This result showed a significant organ difference of their stoichiometry characters responding to the changing N and P supply status.In addition,the variation of C,N and P stoichiometry was always the least in early growth phase and became greater over time,indicating that the response of C,N and P stoichiometry to nutrition condition was a cumulative process.(3)The N :P supply ratio and overall supply level had slight impacts on the C concentration in S.sala organs.At all growth phases,the tissue N concentration,C :N and the leaf P concentration as well as the leaf C :P were mainly determined by the overall supply level,while the root P concentration and root C :P depended most on the N :P supply ratio.The main factor of the tissue N :P,stem P concentration and stem C:P varied at different growth phases.O verall supply level affected them more at early growth phase,while N :P supply ratio had a greater influence at middle and late growth phase.The impact strength of N :P supply ratio on tissue N concentration and C:N decreased over time while increased on P concentration,C :P and N :P.O n the contrary,the impact strength of overall supply level showed opposite trend on N concentration,C :N and N :P over time.As for its impact strength on the P concentration and C :P,it increased first and then decreased.The relative impact strength of N :P supply ratio and overall supply level on stoichiometry characters varied obviously over time,pointing to that single sampling at specific phase may result in incomplete conclusion.(4)With the rise of overall supply level,the tissue N,P concentration and N :P increased while the tissue C :N,C:P ratio decreased significantly.With the increase of N:P supply ratio,the tissue N concentration,C :P and N :P ratio rose while C :N declined;the P concentration in specific organs decreased or kept stable,which differed among growth phases and organs.With the rise of N :P supply ratio and overall supply level,the N :P in all organs tended to increase.This consistent tendency in tissue N :P may reflect the long-term adapting strategy of S.salsa in Yellow River Delta where was mainly N-limited,which made it more sensitive to the increase of the N supply than to P supply.(5)When compared the impact strength of N and P supply condition and growth phase on the stoichiometry of specific organ of S.salsa under the circumstance that being 9-folds differences of N :P supply ratio and overall supply,the result showed obvious organ and elemental difference.Growth phase still contributed most to the variations of tissue C concentration,while N and P supply status impacted more on tissue P concentration.Leaf N concentration was more influenced by N and P supply status;however,root and stem N concentration were more impacted by growth phase.The N and P supply status had higher impact on leaf C :N,leaf C :P,stem C :P,stem N:P and root N :P,while growth phase influenced more on the leaf N :P,stem C :N,root C:N and root C :P.Compared within specific organs,leaf stoichiometry characteristics was influenced more by N and P supply status,while root stoichiometry characteristics was impacted more by growth phase.