Seasonal Dynamics Of Nitrogen, Phosphorus And Tannin Contents Of Rhizophora Stylosa And Avicennia Marina During Leaf Senescence

The seasonal dynamics of nitrogen and phosphorus concentrations,resorption efficiency(RE) and resorption proficiency(RP) of N and P,nitrogen to phosphorus ratios(N:P) in the leaves of Rhizophora stylosa and Avicennia marina were studied. In addition,the seasonal dynamics of total phenolics(TP),extractable condensed tannin(ECT),bound condensed tannin(BCT) and total condensed tannin(TCT) contents and protein precipitation capacity(PPC) of R.stylosa leaves at two sites were discussed.Furthermore,the relationships between TP and nutrient concentrations,TP and N:P of R.stylosa leaves were also studied.The results showed as follows:1.There was significant difference in the N and P concentrations of the leaves between R.stylosa and A.marina at Shankou,Guangxi province.The N concentrations of mature and senescent leaves averaged 9.35±0.88 mg·g^-1 and 1.45±0.92 mg·g^-1 for R.stylosa,and 17.26±1.43 mg·g^-1 and 6.07±1.34 mg·g^-1 for A. marina respectively.The P concentrations of mature and senescent leaves averaged 1.04±0.08 mg·g^-1 and 0.55±0.09mg·g^-1 for R.stylosa,and 1.58±0.26 mg·g^-1 and 0.67±0.08 mg·g^-1 for A.marina respectively.The N and P concentrations of A. marina leaves were significantly higher than those of R.stylosa leaves.The N and P concentrations both decreased with leaf senescence for R.stylosa and A.marina,indicating that N and P were resorbed before leaf abscission.The average N resorption efficiency was 84.79%for R.stylosa and 64.71%for A.marina, and the P resorption efficiency averaged 47.75%for R.stylosa and 57.05%for A. marina.The NRE of R.stylosa was higher than that of A.marina,but the PRE was lower than that of A.marina.The seasonal dynamics of N and P concentrations were similar for R.stylosa and A.marina,higher in winter and spring than that in summer and autumn.The N:P ratio in the mature leaves ranged from 9.02±0.90 to 11.20±2.14 for R. stylosa and from 9.21±0.91 to 13.98±1.87 for A.marina respectively,indicating both R.stylosa and A.marina were N-limited.The NRE was higher than PRE for two species at the same site.In addition,average N and P concentrations in senescent leaves were 0.15%and 0.06%for R.stylosa,and 0.61%and 0.07%for A.marina respectively,which were in the range indicative of complete resorption of N,and incomplete resorption of P.2.The N and P concentrations of R.stylosa leaves at Gaoqiao of Zhanjiang city in Guangdong province were higher than those of R.stylosa leaves at Shankou in Guangxi province.The N and P concentrations of R.stylosa at both sites decreased with leaf senescence.The NRE and PRE of R.stylosa at Gaoqiao were close to those at Shankou.The N and P concentrations of R.stylosa leaves at both sites were higher in winter and spring than that in summer and autumn.The N:P ratio in mature leaves of R.stylosa at Gaoqiao ranged from 8.72±0.46 to 9.76±0.79,also showing N-limitation.The NRE for R.stylosa at two sites were higher than PRE.In addition,average N and P concentrations in senescent leaves were 0.20%and 0.07%at Gaoqiao,and 0.15%and 0.06%at Shankou,which were in the range indicative of complete resorption of N,and incomplete resorption of P.3.There was no significant difference for TP,ECT,BCE,TCT of R.stylosa at both sites,except for the PPC in mature leaves of R.stylosa at Shankou and Gaoqiao. The TP and TCT contents of R.stylosa at both sites were from 125.13±37.06 mg·g^-1 to 286.55±58.06 mg·g^-1,and from 47.69±7.83 to 127.42±4.81 mg·g^-1 respectively. ECT accounted for 90%in TCT.The PPC of R.stylosa at both sites were from 182.76±54.19 to 1047.49±182.73 cm²Ã‚·g^-1.TP,ECT,TCT concents and PPC of R.stylosa leaves almost increased,while BCT decreased with senescence at two sites.TP,ECT, TCT contents were higher in autumn and winter than that in spring and summer, while,PPC,which was consistent with the observation of nutrients,was higher in spring and winter than in summer and autumn.4.There was a significantly negative linear relationship between TP and nutrient contents,while no significant relationships were observed between TP in mature and senescent leaves and N:P of R.stylosain leaves at both sites. 5.Compared to A.marina,R.stylosa had more advantage mechanisms of adaptation in the intertidal coastline surroundings,including higher resorption efficiency,lower nutrient losses and higher tannins level.