| As one of the main afforestation tree species around the world, Populus with ideal plant type has very important significance for cultivation and breeding. Branching angles are the key factor to form the crown, and the angles and morphology of branches are regulated by endogenous hormones. Taking the annual narrow crown black Yang II [Populus deltoides‘Lux'× ? Populus deltoides‘Shanhaiguan'× Populus simonii) ‘Zhaiguan?'],Populus euramericana I-107( Populus×euramericana cv.‘74/76'), Populus tomentosa02-9-22(Populus tomentosa) as the test material, this study, tested the content of four kinds of endogenous hormones(ZR, GA, IAA, ABA) in shoot tip, base(upper and lower) and upper(upper and lower) in natural condition and artificial pull branches case with HPLC according to the its growth process. Effect of endogenous hormones on variation of branching angle was analyzed, which provided theoretical basis for the mechanism of branching angle development and formation of crown type and plant type. The main conclusions are as follows:(1) Branch is the important part composed of tree crown type, plant type. Branch angles are important parameters in terms of the crown structures, affecting the size and structure of crown, reflecting the morphological characteristics of the canopy structure, and determining the overall plant type structure. In the whole process of growth, the base angle of the 3 kinds of test materials were significantly different: the narrow crown black Yang < poplar I-107 <Populus Populus 02-9-22; Branches grow changing original growth direction into negative geotropism, and differences of degrees of bending were significantly in later stage: Narrow crown black poplar II extending angle was significantly less than that of Populus euramericana I-107 and Populus tomentosa02-9-22. These two aspects jointly decided different forms of three test material, resulting in the difference of crown type, and plant type.Therefore, the branch angles were of great significance for evaluation of the crown and plant type as important parameters of the types of branches.(2) The changing of GA and IAA content is important internal reason for the differenceof branching angle, and different GA, IAA content on both sides of branches lead to different growing speed, and content of GA and IAA underside was higher than top right, also the same to speed. And GA was able to induce underside secondary xylem development and provide bending mechanical force for branches upward, which led to negative geotropism. As a result,the branching angle becomes smaller. The larger upper and lower content variation was, the smaller branching angle between them was. This case occurred in crown black poplar II.(3) Artificial pulling process artificially branches after, branching angle becomes larger and growth direction was changed, causing increasing content of the GA and IAA upperside,and underside decreasing significantly, which applied to same branch as well. This means GA and IAA have important influence on the development of poplar branches.(4) The narrow crown black poplar II owed largest new shoot length and basal diameter and the strongest growth, the weakest was Populus tomentosa 02-9-22, Populus euramericana107 between the two in the entire growth process. Each hormone content in shoot tip mainly influenced shoot length and base diameter growth, and these two increased to some extent,and that means more exuberant state of branches. Such promoting hormones as ZR, GA and IAA content was higher, and ABA(suppression of growth hormone) content was low in branch tip.With analasis of content and distribution of the hormone, the changes of ZR and ABA contents were mainly affected by the new shoot length and basal diameter, which had no significant effect on the branch angles. IAA, GA has an important influence on the development of the branchbranch, and the GA and IAA content of the branches on both branch sides was an important internal reason for the different branch angles. |
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