| Forest litter plays an important role in maintaining soil fertility and promoting nutrient cycling and energy flow in forest ecosystems.Nutrient cycling is an important physiological and ecological process in forest ecosystem.Therefore,five typical species of the subtropical coastal sand were selected as the research object.The five species(Eucalyptus grandis x E.urophylla,Acacia crassicarpa,Pinus elliottii,Casuarina equisetifolia and Secondary forest)litterfall,litter composition,nutrient content,litter return and so on.At the same time,Eucalyptus grandis x E.urophylla,Acacia crassicarpa,Pinus elliottii,Casuarina equisetifolia and Secondary forest were researched nutrient transfer.The characteristics of nutrient transfer in different forest types,the use of efficiency and the difference of return,the characteristics of nutrient transfer in different forest types,the restoration and reconstruction techniques of coastal sand ecosystem,and the coastal sand ecology system of sustainable management to provide theoretical basis and practical guidance.The results are as follows:1.The annual litter fall of Eucalyptus grandis x E.urophylla,Acacia crassicarpa,Pinus elliottii,Casuarina equisetifolia and Secondary forest were 8.41 t·hm-2,7.31 t·hm-2,9.41 t·hm-2,10.10 t·hm-2,8.86 t·hm-2,showing Casuarina equisetifolia>Pinus elliottii>Secondary forest>Eucalyptus grandis x E.urophylla>Acacia crassicarpa.In the composition of litter in different forest types,the litter branches accounted for 6.34%-19.83%of the total litter,litter leaves accounted for 66.84%-76.03%of the total litter,litter flowers accounted for 0.14-2.20%of the total litter,litter cones accounted for 0.78%-7.89%of the total litter,litter the other accounted for the total litter of 7.00%-12.13%.The litter of different forest types showed obvious monthly dynamic changes,the litterfall of Eucalyptus grandis x E.urophylla,Acacia crassicarpa,Pinus elliottii and Casuarina equisetifolia were the single peak type,and the litter peaked at September.The monthly variation of Secondary forest was bimodal,the first peak appeared in May,and the second peak appeared in September.Pearson correlation analysis showed that there was a significant negative correlation between litter branches and litter flowers,and there was a significant positive correlation between litter leaves and total litterfall.2.The nutrient content of each component of different forest types was basically as follows:Ca>N>K>Mg>Na>P.The nutrient contents of litter leaves were the highest,and the nutrient content of litter flowers and cones was the lowest.There were differences in the annual return of macroelement in five forest types,Casuarina equisetifolia(5120.27 kg·hm-2)>Pinus elliottii(4826.88 kg·hm-2)>Eucalyptus grandis x E.urophylla(4444.92 kg·hm-2)>Secondary forest(4372.58 kg·hm-2)>Acacia crassicarpa(4015.01 kg·hm-2).The largest component of the nutrient return was the leaves,and the second largest component was the branch,and the second largest component of Eucalyptus grandis x E.urophylla and Pinus elliottii was the other.The monthly dynamic changes of the macroelement returned in different forest types were single peak and bimodal,and the peak appeared basically in May and September.3.The average contents of trace elements in litter of different forest types were as follows:Fe>Al>Mn>Zn>Cu.Different forest types were basically litter leaves and the other components of the nutrient content were higher,litter flowers and cones nutrient content were low.The total amount of trace elements in the litter of different forest types was 5522.17-18924.65 g-hm'2,which was characterized by Secondary forest>Pinus elliottii>Casuarina equisetifolia>Eucalyptus grandis x E.urophylla>Acacia crassicarpa.The annual total amount of trace elements was:Al>Fe>Mn>Zn>Cu.There were significant differences in the annual amount of trace elements in different components of litter in different forest types,and the litter leaves>the litter other>the litter branches>the litter cones>the litter flowers.The dynamic changes of trace elements in different forest types showed single peak and bimodal,and the peak appeared basically in the period from May to September.4.The ratio of total litter and the amount of litterfall in different forest types could be used to understand the nutrient use efficiency of litter.In the case of Eucalyptus grandis x E.urophylla,Acacia crassicarpa and Pinus elliottii,the utilization efficiency of Cu was the highest,and Casuarina equisetifolia was the most efficient in using Zn,and the Secondary forest had the highest utilization efficiency for P.The Pinus elliottii had the highest utilization efficiency for N,Ca,Mg,Fe and Cu.The Acacia crassicarpa had the highest utilization efficiency for Mg,Mn,A1 and Zn.The Casuarina equisetifolia had the highest utilization efficiency for P and K.The Secondary forest had the highest utilization efficiency for C and Ca.5.The average contents of nutrient macroelement in the fresh branches of different forest types were as follows:K>N>Ca>Na>Mg>P.The nutrient content of macroelement in different forest types showed different laws,and basically showed the laws of single peak and bimodal,and the peak value of nutrient content was basically in the period from May to September.The nutrient contents of trace elements in fresh branches of different forest types were as follows:Fe>Al>Mn>Zn>Cu.The dynamic changes of the different branches were different,and the dynamic changes were not the same.The average content of nutrients in fresh leaves of different forest types was as follows:N>K>Ca>Na>Mg>P,which was consistent with the average nutrient content of fresh elements in different forest types.The nutrient content of leaves of fresh leaves in different forest types showed different laws,and the laws of single peak and bimodal were basically presented.The average content of trace elements in fresh leaves of different forest types was as follows:Fe>Al>Mn>Zn>Cu.The dynamic changes of fresh leaves in different forest types were single peak and bimodal,and only the dynamic change of Fe content in fresh leaves was similar to that of the three peaks.6.The nutrient concentrations of N,P,K and Na in litter were observed after comparison with the nutrient concentration of fresh leaves and litter in different forest types.The contents of Ca in the five forest types were higher than those in the fresh Ca indicating that the Ca element might not have any nutrient transfer.In the trace element nutrients,the Eucalyptus grandis x E.urophylla branches in the litter when the Fe element occurred in the nutrient transfer.The Pinus elliottii branches in the litter when the Mn element occurred in the nutrient transfer.The Pinus elliottii,Casuarina equisetifolia and Litsea glutinosa(Lour.)C.B.Rob.branches in the litter when the Cu element occurred in the nutrient transfer.There was no nutrient transfer of Al in different forest types.The Pinus elliottii branches in the litter when the Zn element occurred in the nutrient transfer.A comparative analysis of the nutrient contents of fresh leaves and litter leaves showed that nutrient transfer occurred in N,P and K at different forest types.Five litter leaves occurred a certain degree of nutrient transfer.The results showed that the contents of Fe,Mn and Al in leaves of different forest types were significantly higher than those of fresh leaves(p<0.05),which indicated that the five forest types were litter leaves,Fe and Mn did not develop nutrient transfer.7.The nutrient transfer rate of 5 forest types branches was as follows:K>P>Na>N>Mg>Ca.The contents of N,P,K,Mg and Na were all positively transferred in the average nutrient transfer rate of different forest types.However,Mg and Na contents were transfer in the year in the dynamic change of macroelement transfer rate in different forest types.And Mg,Na elements in some months of the year had negative transfer.The monthly dynamic changes of nutrient transfer rate and nutrient transfer rate of trace elements in different forest types were basically the negative transfer,but positive transfer occurred in some months of the year.The nutrient transfer rate of five forest types leaves was K>P>N>Na>Mg>Ca.The contents of N,P,K and Na were all positively transferred in the average nutrient transfer rate of different forest types.However,Na elements in some months of the year was negative transfer,in the dynamic change of macroelement transfer rate in leaves of different forest types.The nutrient transfer rate and the monthly dynamic change of leaves trace elements in different forest types were basically negative transfer,but they would be transferred in some months of the year.8.The nutrient contents N,P and K of fresh and litter branches,fresh and litter leaves were related to their physiological and biochemical processes,and the nutrient contents of branches and leaves were closely related to their physiological and biochemical processes. |
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