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土壤干旱引发植物木质部导管发生“空穴化”,对植物生长发育及抗旱生理具有重要影响。本研究通过检测小麦叶片超声波(AE)信号发射的变化,在田间充分灌水及控水条件下对冬小麦(Triticum aestivumL.)品种石新733主要生育期叶片木质部导管空穴化及气栓塞发生特性进行了研究。结果表明,叶片AE信号一般6:00~8:00开始发生,夜间21:00~3:00期间停止。土壤干旱时植株叶片木质部气栓塞发生程度显著高于良好供水的植株。拔节至灌浆盛期控水处理24 h AE总量高于足水处理,其中开花期至籽粒形成初期处理间差别最大,控水处理24 h AE平均为足水处理的4.6倍。但籽粒灌浆中后期控水处理土壤水分胁迫进一步加重时,24 h AE反而下降至接近甚至低于足水处理,出现“AE衰减现象”。叶片AE累积发生值和叶水势(Ψl)的变化关系符合Logistic曲线模型(脆弱曲线)。拟合结果表明,一般小麦Ψl降至约-1.00 MPa时导管空穴化发生速率最高。土壤干旱条件下植株叶片木质部脆弱性显著增高,木质部安全性明显降低。土壤干旱时叶片空穴化和气栓塞增高的主要原因是导管对空穴化的抵御能力下降,而叶水势的影响较小。
Soil drought leads to the occurrence of “cavitation” in xylem catheters of plants, which has an important impact on plant growth and drought resistance physiology. In this study, through the detection of the change of the ultrasonic signal transmitted by wheat leaves, the cavitation and embolism characteristics of the xylem in the leaves of winter wheat (Triticum aestivum L.) variety Shi Xin 733 Study. The results showed that the leaf AE signal usually started from 6:00 to 8:00 and stopped from 21:00 to 3:00 at night. Soil drought in plant leaves xylem embolism occurred significantly higher than the good water supply plants. The total AE at 24 h after watering from jointing stage to filling stage was higher than that of full water treatment, and the difference between the flowering stage and the initial stage of grain formation was the largest. AE at 24 h after watering treatment was 4.6 times of that of full water treatment. However, when soil water stress was further aggravated by controlled watering in the middle and late stages of grain filling, the 24 h AE decreased to near or even below that of the full water treatment, resulting in “AE decay phenomenon”. The relationship between cumulative value of leaf AE and leaf water potential (Ψl) accorded with Logistic curve model (fragile curve). The fitting results showed that when the average wheat Ψ1 dropped to about -1.00 MPa, the cavitation rate of the catheter was the highest. Under the soil drought conditions, the xylem vulnerability of plant leaves was significantly increased, and the xylem safety was significantly reduced. The main reason for the cavitation of leaves and the increase of air embolism in soil drought is that the resistance of catheters to cavitation decreases, but the influence of leaf water potential is small.