Effects Of Light Utilization Capacity On Seedlings Of Eucalyptusurophylla ×E.grandis Mixed With Native Tree Species

Long-term operation of pure forests will bring about many negative impacts on ecological environment. In order to promote the transformation of forestry in China from timber production to forestry ecological construction, it is demanded that forest stands should be transformed according to local conditions by changing the traditional management model of pure forests to near-natural mixed forests with more levels and higher ecological value and economic potential. In this paper, the study on the effects of Eucalyptus seedlings mixed with 5 native tree species including Erythrophleum fordi, Schima superb, Castanopsis hystrix, Michelia macclurei and Castanopsis fissa was carried out with two mixed patterns of single and double. The indices to study the mixed effects included the growth condition, photosynthetic characteristics, chlorophyll, chlorophyll fluorescence.The results were as follows.(1) Mixed planting can improve the growth condition of each seedling and tree species within the mixed combination, and promote the growth of seedling and tree height, diameter, crown, etc. Among all mixed combinations, Combination 2A, Combination 2B, Combination 2C, Combination 2D, Combination 3C, Combination 3D and Combination 3J are relatively better. Not only a multilevel structure is formed in them but also the growth condition of seedlings and trees is pretty good.(2) Net photosynthetic rates(Pn) of the same tree species in each test group differ significantly. Its regularity is significant, mostly in the case that Pn of the mixed group is more than that of the control group and meanwhile the mixed condition has much more impact on Pn. By comparing the Pn of each tree species, we find the high-to-low order is Eucalyptus, Schima superb, Michelia macclurei, Erythrophleum fordi, Castanopsis hystrix, and Castanopsis fissa. The change trend of stomatal conductance(Gs) and inter-cellular carbon dioxide concentration(Ci) is nearly consistent in the same tree species of the each mixed combination, being mostly in the case that the data in mixed group are more than that of the corresponding control group. As to the leaves utilization of energy(LUE), in the same tree species, the changes of LUE are highly consistent with the change trend of Pn, suggesting that mixed planting can enhance the light utilization of plants in mixed combinations. Form the perspective of water use efficiency(WUE), Eucalypust in mixed group makes use of water more adequately compared to the control group; while for other tree species, only a few tree species in a few mixed group make use of water less adequately. In summary, mixed planting can enhance photosynthetic ability, light utilization capacity and water use capacity of plants. In the aspect of photosynthetic ability, Mixed Combination 3B, Mixed Combination 3C, Mixed Combination 3D and Mixed Combination 2B are relatively excellent.(3) Mixed planting has significant influence on the chlorophyll content of plants. Chlorophyll A content, chlorophyll B content as well as total chlorophyll content of plants in mixed combinations are all significantly higher than those of the pure forestry, as a result enhancing the photosynthetic ability of plants. Viewing comprehensively the chlorophyll content in each test group, we find Mixed Combination 2A, Mixed Combination 2B, Mixed Combination 3A and Mixed Combination 3C and Mixed Combination 3G play a significant role in improving chlorophyll content of plants.(4) There are some differences in chlorophyll fluorescence parameters of each species in all mixed group which as well has strong regularity. Mixed planting can significantly enhance PS maximum energy conversion efficiency Fv / Fm, PS potential activity Fv / ? ?Fo, the electron transfer rate ETR, PS ?actual quantum yield Y(II) of plants, thus enhancing the light transfer and utilization ability of seedlings and trees. Concluding from the Cluster Analysis of each mixed group, we find that in the aspect of chlorophyll fluorescence, Mixed Combination 2A, Mixed Combination 2B, Mixed Combination 2D, Mixed Combination 2E, Mixed Combination 3C, Mixed Combination 3D and Mixed Combination 3J are relatively better.(5) We adopt Principal Component Analysis to comprehensively evaluate light use efficiency(LUE) of different mixture types. The result shows that mixed planting trial enhances photosynthetic ability, light transfer and use efficiency and water use efficiency. The more excellent mixed combinations include Combination 2A(Eucalyptus + Erythrophleum fordii)(2.79), Combination 2B(Eucalyptus + Schima superba)(2.55), Combination 2E(Eucalyptus + Michelia macclurei)(2.33), Combination 3C(Eucalyptus + Erythrophleum fordii + Michelia macclurei)(2.08), Combination 3D(Eucalyptus + Michelia macclurei + Castanopsis hystrix)(1.86), and Combination 3J(Eucalyptus + Castanopsis hystrix + Castanopsis fissa)(1.54).