Environmental Effects On Tannin Production Of Casuarina Equisetifolia Branchlets

Casuarina equisetifolia is an important shelter tree in coastal sandy areas.Changesin the N and P concentrations,N:P ratios and tannin content in C.equisetifoliabranchlets during development and senescence across a coastal gradient,and seasonalchanges in tannin content were studied at Chishan Forestry Center of DongshanCounty,Fujian Province,China.In addition,the effects of fertility,pH and soilmoisture on tannin contents of C.equisetifolia seedlings were discussed in a sandculture system,so as to find proof about secondary metabolism production.The results showed as follows:1.Nutrients and tannin contents of C.equisetifolia branchlets varied significantly inresponse to changes in a coastal gradient.Nutrient contents of senescent branchlets atseaward sites were higher,while tannin contents and nutrient resorption efficiencywere lower than those at inland sites.The coastal gradients have no significant effectson nutrient and tannin contents of young and mature branchlets.2.N:P ratios of mature branchlets was firstly used to indicate the nutrient limitationin C.equisetifolia forests.Based on N:P ratios(above 28),C.equisetifolia forestswere P-limited.Accordingly,phosphorus resorption efficiency was higher thannitrogen resorption efficiency of corresponding coastal gradient.Nutrient deficiencymay be one of the important reasons for high tannin levels in C.equisetifolia.3.The seasonal variation of tannin and nitrogen contents of C.equisetifoliabranchlets at different developmental and senescent stages were studied firstly.Indifferent seasons,total phenolics(TP),extractable condensed tannins(ECT) contentand protein precipitation capacity(PPC) in young and mature branchlets were higherthan those in senescent branchlets,but protein-bound condensed tannins(PBCT) weresignificantly higher in senescent branchlets than in young and mature branchlets.Thehighest of TP in young and mature branchlets occurred in summer,when TCT contentwas lowest.Nitrogen content in young branchlets was highest,and decreased withmaturity and senescence.The lowest of nitrogen content also was in summer,but thenitrogen resorption efficiency(51.01±3.94% to 63.00±8.61%) didn't change withseason.In this study,TP contents were inversely related to N contents.However,therewas a positive correlation between TCT and N contents.The high TCT:N ratios in senescent branchlets was one of the important nutrient conservation strategies for C.equisetifolia.4.In fertilized soil treatment plots,TP and ECT contents of branchtets of C.equisetifolia seedlings decreased,soluble sugars increased,while nutrient contentschanged little with nitrogen fertilizer addition.TP:N and ECT:N ratios decreased.TPand ECT contents remained stable,while starch,chlorophyll,carotenoid and nutrientcontents increased with phosphorus fertilizer addition.5.In pH and fertilized soil treatment plots,TP and ECT contents significantlydecreased with nitrogen fertilizer addition.Nitrogen contents and ECT:N ratios werealso inversely related to levels of nitrogen fertilizer.Phosphorus fertilizer applicationhas no significant effects on TP and ECT contents.TP contents increased,and ECTcontents remained unchange with the increasing of pH.But starch,chlorophyll a,chlorophyll a/b ratios,carotenoid and nutrient contents decreased significantly,Accordingly,TP:N and ECT:N ratios significantly increased.6.In moisture and fertilized soil treatment plots,nitrogen and phosphorus fertilizerhave significant effects on TP and ECT contents of branchlets of C.equisetifoliaseedlings.TP and ECT contents decreased with nitrogen and phosphorus fertilizeraddition.TP and ECT contents increased under drought-stressed conditions.In controlled experiments,TP contents increased,and ECT contents decreased withprolonged treatment time.Both TP and ECT contents decreased with nitrogenfertilizer addition.This pattern lends to support source-sink hypotheses such as thecarbon-nutrient balance(CNB) hypothesis and the growth-differentiation(GDB)hypothesis.The discrepancy of relationship between nutrition with TP or ECT showedthat the biosynthetic route of different tannins were different.In this study,nosignificant correlation between TP and N,or ECT and N did not support proteincompetition model(PCM).TP:N and ECT:N ratios were higher under nutrientdeficiency and arid conditions,which was one of the important nutrient conservationstrategies for C.equisetifolia.