Effects of soil nitrogen and phosphonium on leaf nitrogen and phosphonium stoichiometric characteristics and chlorophyll content of <I>Oligostachyum lubricum</I>

Abstract

Aims Organ stoichiometric characteristics are the bridge that connects environment and plant organ traits.The relationships among environment,organ stoichiometric characteristics and organ traits reveal mechanisms of environmental effects on plant organ traits and make it possible to regulate plant traits.Our objective was try to find the relationships among soil and leaf nitrogen(N),phosphonium(P) stoichiometric characteristics and leaf chlorophyll content for Oligostachyum lubricum.Methods Total N,P concentrations of the original soil in pots were 421.76 and 37.35 mg.kg –1,respectively,and the original soil was treated as the control(1N1P).Total experimental N,P concentration were two,three and four times as high as the control.Different N,P levels were combined into 10 combinations(2N2P,2N3P,2N4P,3N2P,3N3P,3N4P,4N2P,4N3P,4N4P and 1N1P) and every combination except the control was achieved by adding different amounts of NH 4 NO 3 and NH 4 H 2 PO 4.Leaf samples were collected from ramets of O.lubricum after grown in the pot soil with different N,P level combinations for 45 days.Leaf total N concentration was determined by employing the Kjeldahl method and leaf total P concentration by the acid melt-molybdenum stibium anti-color method.Leaf chlorophyll concentrations were measured based on acetone-ethanol mixture(1 : 1) extraction method.Soil and leaf total N,P concentrations were expressed as mg.kg –1 DW.Important findings Soil total N concentration was significantly positively correlated with leaf total N concentration and leaf N : P ratio,whereas soil total P concentration had no significant correlation with leaf total P concentration and leaf N : P ratio.Leaf N : P ratio increased with the increasing of soil N : P ratio,and the rate of increase of soil N : P ratio was faster than that of leaf N : P ratio.At the same soil condition,leaf N : P ratio of ramets growing in soil with 2N2P and 3N3P had no significant difference,but the both were higher than the control(1N1P) and lower than that growing in soil with 4N4P.Leaf N : P was the main factor that affected leaf chlorophyll content.Results suggested that soil total N concentration had more effect on leaf N,P stoichiometric characteristics than soil total P.Sufficient supply of soil total N lead to the luxury uptake of N by leaves of O.lubricum.The growth of O.lubricum was limited by low soil total N concentration before N and P addition.