| Chinese fir(Cunninghamia lanceolata(Lamb.)Hook)is one of the most important artificial afforestation species in southern China.Due to the long-term cultivation of single pure forests,the woodland has suffered from land degradation,poor resistance,poor natural regeneration and so on.These problems severely restrict the sustainable management and ecological environment construction of Chinese fir plantation.Converting Chinese fir plantation into mixed broadleaf-conifer forest may be one of the important ways to solve these problems.Shade tolerance of tree species is a significant basis for the construction of multi-layer mixed forest of different ages.It is necessary to select shade-enduring plants which could growth well and adapt to specific light environment.To strengthen the research on the growth and living strategies of shade-enduring plants will help to solve this problem.At present,the basis of tree species selected as mixed tree species of Chinese fir plantation was mostly based on practical experience.It is necessary to make a deep research on the shade tolerance of different tree species and take some measures of interplanting transformation according to the shade tolerance of tree species.In this study,the typical interplanting trees of Chinese fir plantation,Schima superba Gardn.et Champ,Phoebe zhennan S.Lee and Liquidambar formosana were chosen as experimental materials.Different shade environments(0% of full sunlight,40%,60%,85%,95% of shading degree)were constructed by using shade houses covered with black nylon shade cloth at increasingly higher mesh gauges.It is an important way to explore the best growth environment of Schima,Phoebe and Liquidambar seedlings by studying the the response strategies of morphogenesis and physiological characteristics of three seedlings under different shading degrees.To explore the shade tolerance ability and mechanism of three seedlings can provide theoretical basis for the construction of multi-layer mixed forest of different ages.The major results were as follows:1.The effects of different shading degree on the morphogenesis and biomass distribution of Schima,Phoebe and Liquidambar.With the increase of shading degree,the basal diameter increment of Schima,Phoebe and Liquidambar decreased gradually.Except for the treatment of95% shading degree,the seedlings height increment of other treatments increased gradually with the increase of shading degree.In the treatment of full sunlight,40%,60% and 85% shading degree,the morphological characteristics of seedlings changed from “short and thick” to “fine and high” with the increase of shading degree.The leaf area and specific leaf area of the three seedlings increased with the increase of shading degree.The specific leaf weight decreased with the increase of shading degree.That is to say,the leaves of seedlings are small and thick under strong light but large and thin under weak light.The accumulation of total biomass and underground part biomass of Schima seedlings decreased with the increase of shading intensity.The total biomass of Phoebe and Liquidambar seedlings increased first and then decreased with the increase of shading degree.2.The effect of different shading degree on the change of nonstructural carbohydrate(NSC)content in the leaves of three kinds of plants.The NSC content in the leaves of Schima,Phoebe and Liquidambar all reached the maximum value under the full sunlight,and then gradually decreased with the increase of shading degree.The trend of starch content in leaves of three seedlings was decreased with the increase of shading degree,which was consistent with that of NSC.The content of soluble sugar in the leaves of Phoebe and Liquidambar seedlings had the maximum and minimum values under natural shading degree and 95%shading degree,respectively.The adjustment of NSC content is conducive to the improvement of survival suitability of seedlings and the competitiveness of scarce resources in the shade environment.In this study,95% shading degree significantly inhibited the accumulation of NSC in seedlings.3.The effects of different shading degree on the chemical characteristics of three seedlings.With the increase of shading degree,the content of carbon(C)in the roots and leaves of Schima seedlings decreased gradually,but the content of nitrogen(N)and phosphorus(P)in each organ increased gradually.The content of N and P in all organs of Phoebe seedlings increased with the increase of shading degree.The content of C element in all organs of Liquidambar seedlings decreased with the increase of shading degree,and the shade environment promoted the accumulation of N and P elements in roots,stems and leaves of Liquidambar seedlings.Under the same shading degree,the content of C element in all organs of Phoebe seedlings was significantly higher than that of Schima and Liquidambar seedlings.There was no significant difference in the content of N element among the three seedling leaves under the same shading degree.P content in leaves of Schima seedlings was significantly lower than that of Phoebe and Liquidambar,while P content in stems of Schima seedlings was significantly higher than that of the other two seedlings.The ratio of C: N,C: P and N: P decreased with the increase of shading degree among the three seedlinds.4.The effects of different shading degree on the photosynthetic characteristics of three seedlings.The net photosynthetic rate(Pn)of Schima,Phoebe and Liquidambar seedlings was higher under 40% shading degree.And the Pn of the three seedlings under 95% shading degree was lower.The light saturation point(LSP)and light compensation point(LCP)of Schima seedlings decreased with the increase of shading degree.The LSR and LCR of Phoebe and Liquidambar seedlings reached the maximum value under 40% shading degree.The trend of light use efficiency(LUE)of three seedling was same under different shade environment.Under low light quantum flux density(PPFD),the LUE of seedlings increased rapidly,then reached the peak value,and then decreased gradually with the increase of PPFD.The higher the PPFD,the slower the LUE decreased.With the increase of shading degree,the range of spontaneous fluorescence and average fluorescence intensity of chloroplasts increased,while the peak value of fluorescence decreased.The chlorophyll content of three seedlings under 85% and 95% shading degree was significantly higher than that of other treatments.The increase of chlorophyll content was conducive to the efficiency of light energy utilization of three seedlings under shade environment.5.Comprehensive evaluation of shade tolerance of 3 species interplanting under Chinese fir plantation.Each index of three seedlings under different shading degrees was standardized firstly.The comprehensive evaluation of shade tolerance of three species under different shade treatments was carried out by using membership function method combined with weight.The result showed that the order of shade tolerance of three seedlings under different shading degrees was as follow,Schima > Phoebe > Liquidambar.The seedlings of Schima belong to the high shade tolerance type.The seedlings of Phoebe and Liquidambar belong to the medium shade tolerance type. |
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