不同供水条件下田间冬小麦气栓塞发生基本特征

Characteristics of Xylem Embolism in Leaves of Winter Wheat Under Different Irrigation Conditions

应用超声波技术,在田间灌水及干旱条件下对冬小麦品种9195叶片木质部气栓塞发生特征进行了研究。结果表明,超声波(AE)信号发生的基本特征为1d内一般有3个活跃期,第一活跃期以上午10:00～11:00出现频率最多,第二、三活跃期多分别出现在18:00左右和0:00前后,一般夜间0:00～2:00后信号终止。3个活跃期的AE信号发生强度可随生育进程、土壤水分及气候状况等条件变化。土壤干旱时,第三活跃期减弱或消失。灌水当日第二活跃期有增强的趋势。拔节初期,干旱小麦的AE信号发生量高于灌水小麦的。抽穗后土壤过度干旱时,AE信号量却常低于灌水小麦,笔者称其为“AE信号衰减现象”。灌水后土壤水分充足时,气栓塞也有相当程度的发生。气栓塞是伴随气孔开启、光照增强和温度升高而出现的植株水势快速下降的一种生理性反映。

Using ultrasonic acoustic emission (AE) technique (equipment type: 4615 Drought Stress Monitor, Physical Acoustics Corp. USA) , a study was conducted for three years on the characteristics of leaf xylem embolism in dry and irrigated winter wheat (cv. 9195) under field conditions. It was found that there were three AE active periods di-urnally. The first active period usually occurred around 10:00 - 11:00, the second around 18:00, and the third around 00:00, AE signals usually stopped after 0:00-2:00. The relative AE intensity of the three active periods changed with soil moisture, weather condition and growth stages etc . Under dry conditions, the third active period could disappear. On newly irrigated soil, AE rate often became higher during the second active period. The total 24 h AEs and the degree of embolism were higher for dry than for irrigated wheat during early jointing stages. However, the total 24 h AEs of the dry wheat frequently became far less than that of the irrigated one in later stages. This phenomenon is called 'AE signal exhaustion' . This was an implication of a more severe soil moisture stress. It happened when part of the embolized conduits remained unrepaired overnight due to severe soil water stress, therefore, the number of water conduits which were able to cavitate the next day would decrease. Considerable amounts of AE signals were recorded in plants with very high soil moisture, such as that newly irrigated. The authors regarded cavitations and embolism as a physiological response to the quick decline in plant water potentials, which happened daily accompanying stomatal opening and increasing in sunlight and temperature.