伊犁河谷退化野果林中新疆野苹果茎的水力结构

为揭示伊犁河谷退化野果林中新疆野苹果植株个体的死亡机理,对比研究3种长势(Ⅰ级,20%枯枝率;Ⅱ级,40%~60%枯枝率;Ⅲ级,>80%枯枝率)新疆野苹果茎的水力结构特征的差异以及水分运输有效性和安全性及其影响因素。结果表明: 随野果林退化程度的增加,3种长势的新疆野苹果茎的边材比导水率和叶比导水率呈下降趋势,但差异不显著;傍晚时的栓塞程度、栓塞脆弱性呈显著增加的趋势,其中Ⅰ、Ⅱ和Ⅲ级长势个体的导水率损失50%时木质部水势分别为-1.87、-1.35和-0.53 MPa;黎明前和正午叶水势、水力安全边际均为Ⅰ级>Ⅱ级>Ⅲ级;与水力学相关的木质部解剖结构以及枝叶性状在3种长势个体之间存在显著差异。相关性分析表明,新疆野苹果茎木质部水分运输的有效性和安全性之间存在弱的权衡关系。新疆野苹果茎的水力结构变化伴随着新疆野果林的衰退过程。野果林的退化会加剧新疆野苹果木质部导管的栓塞化程度,降低其抵抗空穴化栓塞的能力,新疆野苹果面临水力失衡的威胁更大。

Stem hydraulic architecture of Malus sieversii in degraded wild fruit forest in Ili valley,China

To reveal mechanisms underlying the dieback of Malus sieversii in degraded wild fruit forest in Ili valley of China, we compared the differences in stem hydraulic architecture, water transport effectiveness and safety, as well as their influencing factors among three growth classes of dead branches ratios, including Class Ⅰ (<20%), Class Ⅱ (40%-60%) and Class Ⅲ (>80%), respectively. With the increases in degradation degree of Xinjiang wild fruit forest, sapwood-specific hydraulic conductivity and leaf-specific hydraulic conductivity decreased, without significant differences among the three growth classes. Branch embolism at dusk and hydraulic safety significantly increased. The xylem water potential at 50% loss of hydraulic conductivity was -1.87, -1.35 and -0.53 MPa for Class Ⅰ, Ⅱ and Ⅲ, respectively. Predawn and midday leaf water potential and the hydraulic safety margin exhibited an order of Ⅰ>Ⅱ>Ⅲ. Xylem anatomical cha-racteristics and branch and leaf traits related to hydraulics were significantly different among the three growth classes. Results from correlation analysis revealed a weak tradeoff between xylem-specific hydraulic efficiency and xylem safety of M. sieversii. Stem hydraulic architecture of M. sieversii altered with the decline of Xinjiang wild apple forest. With increasing degrees of degradation, the severity of xylem embolisms aggravated, resistance to cavitation embolisms reduced, and the risk of water imbalance increased.