以8年生银杏为试材,采用不同程度的断根处理,测定处理后树体超声(ultrasound acoustic emission,UAE)信号、枝条栓塞程度(percentage loss of hydraulic conductance,PLC)、树干液流通量、气孔导度、蒸腾速率以及叶片水势等生理指标,分...以8年生银杏为试材,采用不同程度的断根处理,测定处理后树体超声(ultrasound acoustic emission,UAE)信号、枝条栓塞程度(percentage loss of hydraulic conductance,PLC)、树干液流通量、气孔导度、蒸腾速率以及叶片水势等生理指标,分析断根对银杏树体水力特征及生长状况的影响.结果表明:断根处理后,在短时间内有大量UAE信号产生,且随断根程度的加重而增大,在6h出现最大值,随后逐渐降低;枝条的PLC在起初的12h迅速增加,24h后增速趋于停滞;银杏树干液流通量、叶片气孔导度、蒸腾速率和水势明显降低,各处理间差异显著.经统计分析,累积UAE(cumulative number of UAE,cUAE)信号量与PLC呈现显著的正相关关系,与液流通量和叶片水势呈负相关关系.次年的单叶面积、新生枝条长度显著下降,下降程度随断根处理的加重而加剧.断根处理在短时间内增加了银杏管胞气穴数量和木质部栓塞的程度,影响到水分输送和叶片蒸腾,最终对叶片和枝条的生长产生负面影响.展开更多
Cavitation in plant conduits only involves two processes of air bubbles: the gradual expansion and elongation, and the explosion event. An explosion event of cavitation, which can only occur in intact conduit at water...Cavitation in plant conduits only involves two processes of air bubbles: the gradual expansion and elongation, and the explosion event. An explosion event of cavitation, which can only occur in intact conduit at water tension, trigs acoustic (or ultrasound) emission and induces air to diffuse with high speed, simultaneously. Synchrotron X-ray phase contrast microscopy (XPCM) was used to capture cavitation event in intact conduits of leaves of corn and rice. Cavitation events occur in certain areas of leaves and have a certain time frame. Before XPCM experiment, several preliminary experiments were done as follows: 1) Paraffin sections of leaves of different species were observed to select samples and to determine the occurrence area of cavitation event of leaves. 2) The time frame of cavitation occurrence was determined by ultrasonic emission. 3) The water potentials of leaves were determined, to know the water state of the leaves during cavitation. Locked the area and time frame of cavitation event in the leaves, consecutive XPCM images of cavitation process were more easily acquired. The images show that the phenomenon of gas bubble fully filling conduits for an instant took place in intact conduits of detached leaves of corn and rice more easily. It is that the gas diffusing in a moment was caused by the explosion of the air seeds which had entered in the intact conduits of the leaves. For living plants, it is suggested that the explosion event of cavitation is the most important for embolism formation.展开更多
For a short closed conduit with smooth (streamline pattern) boundary, the comparison of minimum pressure coefficient at boundary, - Cpm , which obtained from model tests, with flow cavitation number a is possible to d...For a short closed conduit with smooth (streamline pattern) boundary, the comparison of minimum pressure coefficient at boundary, - Cpm , which obtained from model tests, with flow cavitation number a is possible to describe the property of preventing cavitation in the closed conduit.In this paper, analytical results show that the ratio σ/ - Cpm decreases with increasing Reynolds number Re, when the configuration of the conduit is designed, and this ratio approaches a constant when Re = 106 or so. The model test data for five engineering cases of the short closed conduit with various configuration indicates that the analytical results are reliable. Therefore, the value of the ratio σ/ - Cpm corresponding to that of Reynolds number in model (Re)m ≥106 must be taken so as to correctly describe the cavitation property of the studied conduit. The condition of Lr ≥ 10-4[(Re)p]2/3 should be satisfied ( Lr is model length scale; (Re)p is Reynolds number in prototype) when the model is designed by Froude criterion of similarity.展开更多
文摘以8年生银杏为试材,采用不同程度的断根处理,测定处理后树体超声(ultrasound acoustic emission,UAE)信号、枝条栓塞程度(percentage loss of hydraulic conductance,PLC)、树干液流通量、气孔导度、蒸腾速率以及叶片水势等生理指标,分析断根对银杏树体水力特征及生长状况的影响.结果表明:断根处理后,在短时间内有大量UAE信号产生,且随断根程度的加重而增大,在6h出现最大值,随后逐渐降低;枝条的PLC在起初的12h迅速增加,24h后增速趋于停滞;银杏树干液流通量、叶片气孔导度、蒸腾速率和水势明显降低,各处理间差异显著.经统计分析,累积UAE(cumulative number of UAE,cUAE)信号量与PLC呈现显著的正相关关系,与液流通量和叶片水势呈负相关关系.次年的单叶面积、新生枝条长度显著下降,下降程度随断根处理的加重而加剧.断根处理在短时间内增加了银杏管胞气穴数量和木质部栓塞的程度,影响到水分输送和叶片蒸腾,最终对叶片和枝条的生长产生负面影响.
文摘Cavitation in plant conduits only involves two processes of air bubbles: the gradual expansion and elongation, and the explosion event. An explosion event of cavitation, which can only occur in intact conduit at water tension, trigs acoustic (or ultrasound) emission and induces air to diffuse with high speed, simultaneously. Synchrotron X-ray phase contrast microscopy (XPCM) was used to capture cavitation event in intact conduits of leaves of corn and rice. Cavitation events occur in certain areas of leaves and have a certain time frame. Before XPCM experiment, several preliminary experiments were done as follows: 1) Paraffin sections of leaves of different species were observed to select samples and to determine the occurrence area of cavitation event of leaves. 2) The time frame of cavitation occurrence was determined by ultrasonic emission. 3) The water potentials of leaves were determined, to know the water state of the leaves during cavitation. Locked the area and time frame of cavitation event in the leaves, consecutive XPCM images of cavitation process were more easily acquired. The images show that the phenomenon of gas bubble fully filling conduits for an instant took place in intact conduits of detached leaves of corn and rice more easily. It is that the gas diffusing in a moment was caused by the explosion of the air seeds which had entered in the intact conduits of the leaves. For living plants, it is suggested that the explosion event of cavitation is the most important for embolism formation.
文摘For a short closed conduit with smooth (streamline pattern) boundary, the comparison of minimum pressure coefficient at boundary, - Cpm , which obtained from model tests, with flow cavitation number a is possible to describe the property of preventing cavitation in the closed conduit.In this paper, analytical results show that the ratio σ/ - Cpm decreases with increasing Reynolds number Re, when the configuration of the conduit is designed, and this ratio approaches a constant when Re = 106 or so. The model test data for five engineering cases of the short closed conduit with various configuration indicates that the analytical results are reliable. Therefore, the value of the ratio σ/ - Cpm corresponding to that of Reynolds number in model (Re)m ≥106 must be taken so as to correctly describe the cavitation property of the studied conduit. The condition of Lr ≥ 10-4[(Re)p]2/3 should be satisfied ( Lr is model length scale; (Re)p is Reynolds number in prototype) when the model is designed by Froude criterion of similarity.
