| Tropical cloud forest is a well-conserved with a unique environmental conditions and high plant diversity in Hainan Island.Trees in cloud forests are typically more malformed and elfine,and covered in more epiphytes.Environmental conditions in these forests are characterized by low air temperature,strong winds,frequent fog,and high levels of yltrabiolet radiation compared with lower altitude forests.The tropical cloud forests located in three different areas(i.e.,Bawangling Mountain(BWL)located at the west area,Jianfengling Mountain(JFL)located at the northwest area and Limushan Mountain(LMS)located at the centre area)in Hainan Island were investigated.The contents of carbon(C),nitrogen(N)and phosphorus(P)of soil sampled from 768 5 x 5 m plots were measured,and the contents of N,P and soluble sugars in twigs,leaves and roots of 282 plant species as well as those in leaf lettet of 256 plant species were determined.Finally,differences in nutrients among plants,leaf litters and soils were assessed,and correlations of the nutrients among the three pools were explored in the tropical cloud forests.The main findings were:(1)The contents of N,P and soluble sugars in the leaves of the three tropical cloud forests were significantly higher than twigs and roots.In twigs,leaves and roots,the contents of soluble sugars were(15.06±9.4)g/kg,(32.14±13.94)g/kg,(27.28± 18.83)g/kg,and the N contents were(3.48±1.02)g/kg,(9.51±5.26)g/kg,(3.71 ± 1.39)g/kg,and the P contents were(0.2±0.15)g/kg,(0.56±0.44)g/kg,(0.19±0.08)g/kg,respectively.The contents of N and soluble sugars in twigs of BWL were the highest while the contents of nutrients were the lowest in leaves of BWL;the contents of N and soluble sugars in twigs of LMS were the lowest while the contents of nutrients in leaves and roots of LMS were the highest.Affected by differences of rainfall and temperature,the differences in soluble sugars among different forest areas are significant.Overall,the N and P contents in twigs,leaves and roots were significantly positively correlated while P contents.(2)The soil nutrient contents of the three tropical cloud forests were C>N>P.There were significant differences in the nutrient contents among the three forest areas,with the nutrient contents in the soil of LMS were the highest.There were significantly positive correlations among the contents of N and P,C and P in all three forest areas.Overall,the soil contents of C,N,P of tropical cloud forests were significantly positive correlated.(3)The leaf letter nutrient contents of the three tropical cloud forests were soluble sugars>N>P.There were significant differences in the contents of the nutrients among the three forest areas.The contents of N and P were the highest while the contents of soluble sugars were the lowest in LMS.There were significantly positive correlations between the N and P contents in the leaf letter in all the three forest.Overall,there were significantly negative correlations between soluble sugars and N,soluble sugars and P.But there were significantly positive correlations between N and P in the leaf letter of the three tropical cloud forests.(4)There were significant differences in N and P contents among plant organs,leaf letters and soils of the three tropical cloud forests.The contents of N and P in leaves and leaf letters were significantly higher than twigs,roots and soils.The contents of soluble sugars were not significantly different between plant organs and leaf letters.There were significantly positive correlations in N contents between soils and roots,as well as in P contents between soil and leaves,and soil and leaf letters.Also,there were significantly positive correlations in the contents of soluble sugars among leaf letters and leaves and roots.There were close relationships in N contents between leaves and twigs,and between leaves and soil,as well as between leaves and roots,using structural equation model.Also,there were close relationships in P contents between soil and leaves,and between soil and leaf letter.In addition,close relationships in the contents of soluble sugars among leaves and leaf letter and roots were also found. |
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