基于韧皮部纤维形态、树皮抗拉伸性能的橡胶树耐寒性研究

Cold Resistance of Hevea brasiliensis Based on Phloem Fiber Morphology and Bark Tensile Properties

为探索不同品种橡胶树幼龄树耐寒性与成龄树枝条韧皮部纤维形态、树皮抗拉伸性能之间的关系,分析不同品种橡胶树耐寒性与其相应生理、生物力学指标的相关性,从而比较不同品种橡胶树耐寒性的差异,以期建立不同品种橡胶树幼龄树茎段与成龄树枝条树皮相应指标之间的联系,并从细胞结构及树皮生物力学角度研究橡胶树耐寒性机理。以热研7-33-97、PB86、IAN873、大丰95、云研77-2等5个橡胶树品种1年生芽接苗茎段及相应品种成龄树2年生枝条树皮为材料,测定低温梯度下茎段韧皮部电导率及枝条韧皮部纤维形态、树皮抗拉伸性能指标,利用Logistic方程确定其低温半致死温度(L_(T50))的大小,得出不同品种耐寒性,并采用Spearman相关性分析法,得出L_(T50)与韧皮部纤维形态指标、树皮抗拉伸性能之间的相关性。结果表明,5个橡胶树品种韧皮部相对电导率呈“S”形曲线变化,相对电导率与胁迫温度之间呈极显著负相关,5个品种L_(T50)分别为-2.075℃、-2.240℃、-1.923℃、-1.900℃、-2.186℃;5个品种纤维长度在2921.013~4799.438μm,宽度在21.717~23.908μm,双壁厚度分别为11.504、10.271、10.873、12.715、10.401μm,腔直径分别为0.900、1.423、0.922、1.298、0.915μm,PB86的纤维双壁厚最小,腔直径最大;5个品种树皮厚度分别为0.709、0.564、0.886、0.935、0.774 mm,PB86的树皮厚度与其他品种的差异达到了显著水平(P<0.05),5个品种拉伸破坏荷载在4.935~11.064 N,PB86的抗拉伸强度与最大拉伸位移均为5个品种最大,分别为3.629 MPa、1.360 mm;1年生茎段韧皮部L_(T50)与成龄树2年生枝条韧皮部纤维双壁厚呈显著性正相关,与2年生树皮厚度、抗拉强度分别呈显著性正相关和显著性负相关。从细胞尺度与组织生物力学角度研究橡胶树耐寒性,以此搭建橡胶树幼龄树与成龄树联系的纽带,是橡胶树耐寒机理研究的有效途径。

In order to explore relationship between cold resistance of different immature Hevea brasiliensis varieties'stems and their mature tree branch phloem fiber morphology,bark tensile properties,correlation between cold resistance of different varieties and their physiological and biomechanical indicators were analyzed.By comparing the cold resistance of different varieties,the connection between different immature varieties'stem phloem and their mature tree branch barks could be construc.Moreover,it is useful for researching H.brasiliensis cold-resistance mechanisms from cell structure and biomechanical perspective.Firstly,electric conductivity of five varieties'(Reyan 7-33-97,PB86,IAN873,Dafeng 95,Yunyan 77-2)one-year-old seedling stem phloem under gradient low temperatures,phloem fiber morphology and bark tensile properties of mature two-year-old branches were studied.Then,semi-lethal temperature(L_(T50))of one-year-old seedling stem phloem were calculated respectively,by using Logistic equation.Thereupon,cold resistance orders of different varieties were ascertained.Consequently,the correlation between LT 50 and phloem fiber morphology indexes,bark tensile properties were analyzed with Spearman's correlation analysis method.The results showed that the variations of relative electric conductivity(REC)might be described as a typical S-shaped curve,and it appeared in an extremely significant negative correlation with the treatment temperatures.The L_(T50)of five varieties'(Reyan 7-33-97,PB86,IAN873,Dafeng 95,Yunyan 77-2)stem were as following,-2.075,-2.240,-1.923,-1.900,and-2.186℃.Moreover,the fiber lengths ranged from 2921.013 to 4799.438μm,their widths ranged from 21.717 to 23.908μm,their double wall thicknesses were 11.504,10.271,10.873,12.715,and 10.401μm,respectively,their lumen diameters were 0.900,1.423,0.922,1.298,and 0.915μm,respectively.Therefore,the fiber double wall thickness of the variety PB86 was the thinnest,and its lumen diameter was the largest in five varieties studied.For bark tensile properties,their bark thicknesses were 0.709,0.564,0.886,0.935,and 0.774 mm,respectively,during which the bark thickness of the variety PB86 reached significant level(P<0.05)with other varieties.The tensile breaking load ranged from 4.935 to 11.064N,bark tensile strength and maximal tensile displacement of the variety PB86 were the maximum in all the five varieties,they were 3.629 MPa,1.360 mm,respectively.L_(T50)of one-year-old seeding stem phloem was positively correlated with the phloem fiber double wall thicknesses of the two-year-old branches.In addition,bark thicknesses and tensile strength of mature two-year-old branches had positive correlation of significance and obviously negative correlation with L_(T50),respectively.Therefore,it is an effective way to research the cold-resistance mechanisms from the perspective of cell scale and tissue biomechanics,which is also an important link between immature and mature H.brasiliensis trees.