Element Dynamics During Leaf Senescence Of Two Growth Forms Of Avicennia Marina Forest At Daguansha In Guangxi Province

Avicennia marina at Daguansha in Guangxi Province was divided into two growth forms:a dwarf form with tree height of below 1.5 m,and a transition form with tree height from 1.5 m to 2 m at maturity.Seasonal changes in the concentrations of Na,K,Ca,Mg,and Cl of mature and senescent leaves of two growth forms were studied.Meanwhile,the K/Na ratio and resorption efficiency(RE) of elements dring leaf senescence were also discussed in this paper.(1) Element concentration of A.marina leaves of two growth forms at Daguansha followed the order:Cl＞Na＞K＞Mg＞Ca,Na,Cl,K,and Mg followed the similar seasonal pattern,and were higher in spring and summer than in autumn and winter,but Ca fluctuated without significant seasonal pattern.(2) K concentration in the A.marina leaves of dwarf growth form(tree height of below 1.5 m at maturity) was lower than that of the transition form(tree height from 1.5 m to 2 m at maturity),K concentration decreased during leaf senescence for two growth froms,indicating K was resorbed from senescent leaves.There was no significant difference in Na,Mg,and Cl concentrations between two growth forms.Ca concentration in the A.marina leaves of dwarf growth form was lower than that of the transition form;K concentration and K/Na ratio in mature leaves of the transition form was higher than those of the dwarf form.(3) The amount of inorganic osmoregulator in the mature leaves of the transition form was higher than that of the dwarf form,but no significant difference of the amount of inorganic osmoregulator in the senescent leaves was found between two growth forms;The inorganic osmoregulator concentrations in the mature and senescent leaves of two growth froms increased in the spring,and rearch the highest in summer,and decreased the lowest in the autumn.(4) Resorption efficiency of K was positive,while resorption efficiencies of Na, Cl,Ca,and Mg were negative;Resorption efficiency of K of the dwarf growth form was higher than that of the transition form,no significant difference was found for resorption efficiency of Na,Cl,Ca and Mg between two growth forms.(5) As for K,Mg,there were significant positive relationships between reosrption efficiency and element concentration in mature leaves of two growth forms,the negative correlation between reosrption efficiency and element concentration in mature leaves of two growth forms was found for Na and Cl; however,there was the positive correlation between Ca reosrption efficiency and Ca concentration in mature leaves of the dwarf growth form,and no significant relationship between Ca reosrption efficiency and Ca concentration in mature leaves of the transition growth form.