冬小麦叶片气栓塞与叶水势日变化的关系

Relationship Between Occurrence of Daily Embolism and Changes of Leaf Water Potential in Winter Wheat

应用超声波(AE)信号测定技术,对冬小麦叶片木质部气栓塞发生与叶水势(ψl)日变化关系进行了研究。结果表明,AE信号在24 h周期内3个活跃期的出现与ψl变化密切相关。上午第一AE活跃期伴随ψl的下降,傍晚第二AE活跃期对应ψl的恢复,午夜前后的第三活跃期对应夜间ψl的进一步恢复,午夜后土壤和植株水势基本达到平衡后,AE信号终止。AE信号发生量和ψl变化量为非线性关系,表现出水势临界值效应,即ψl达到临界值时,微小的ψl变化会引发AE信号峰值。午后最低叶水势出现前的ψl下降期,ψl临界值起身拔节期平均为-1.08 MPa,孕穗至灌浆期平均为-1.60 MPa。叶水势变化是引发小麦叶片气栓塞发生的直接因素之一。

The relationship between xylem embolism occurrence and leaf water potential change in winter wheat leaves was investigated by ultrasound acoustic emission (AE) monitoring technique during 1996 ?2000. The results indicated a close relationship among the 3 high AE rate periods, which characterized the 24 h AE occurrence course, and changes of leaf water potential (Ψl). The first high AE rate period corresponded to a sharp decline in Ψl in the morning, the second, which occurred at dust, was related to a remarkable increase in Ψl, and the third accompanied a further recovery of Ψl around midnight. After midnight, AEs ceased when water equilibrium was reached between soil and plant. Positive non-linear relationships between AEs and concurrent absolute value of changes in Ψl were found for most observations. The results identified a ' Ψl threshold effect' i. e. , bursts of AEs would be triggered when Ψl declined to this value. Threshold values of Ψl, determined during Ψl decline before midday averaged -1. 08 MPa at wheat erecting and jointing stages, and -1. 60 MPa for booting and grain filling stages. Change in Ψl was one of the direct causes for embolism occurrence.