Author: Siyu ZhuPublisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
Many studies have elucidated the importance of water stress on plant growth, yield, quality and susceptibility to disease. Via the vascular network of xylem, a water conductive tissue, plant water stress responds dynamically to variations in evaporative demand defined by micrometeorological conditions over minutes to hours, and soil water availability over hours to months. Stem water potential is believed to be an integrator of water stress across the soil-plantatmosphere-continuum (SPAC), and is difficult to measure. Despite its destructive nature, 50 years after its invention, the manually operated Schölander pressure chamber (SPC) is still the most widely accepted tool for stem water potential measurements. Limitations in available techniques have hindered the study of dynamic water stress in plants. In this dissertation, we introduce a micro-tensiometer (μTM) as a new technique, for probing the dynamic water stress of plants in an accurate and continuous manner. We examine the reliability of μTM against SPC, on apple (2 months), grapevine (12 months), and almond (4 months), to represent woody species in wet, semi-arid, and arid environments respectively. We observe: 1) nighttime disequilibrium in stem water potential that is challenging to acquire with the labor-intensive SPC; 2) rapid response of stem water potential to evaporative demand in wet environment; and 3) slow dynamics and persistent disequilibrium of the water-stressed almond in dry environment. With the advantage of continuous measurements and inspired by van den Honert, we use circuit models to interpret the observed dynamics. In a wet environment, a simple circuit with a single hydraulic resistance and a single hydraulic capacitance, is sufficient for elucidating the rapid response of plants to the high frequent variations in environmental demand. In a dry environment,an additional soil compartment defined by the soil retention properties, is used to address the long transient of soil dehydration. We now have models as new tools to resolve the complex dynamics of water stress. We also measure the dynamic water stress in maize, the first examination on herbaceous crops with this tool. The measured stress is less coupled to the rapid variations in evaporative demand, but more to the soil water potential around the roots. In fact, we extract an empirical water retention curve for the soil that coincides with the theoretical prediction. The μTM, therefore, opens up an opportunity to monitor the root-zone soil stress, a challenging property to access. Finally, we explore the response of plants to fine control of irrigation events, and discover that the transient of root response to irrigation events is shorter when less stressed (nighttime) and longer when more stressed (daytime). This phenomenon suggests more effective irrigation events when plants are less stressed with reduced water loss. The micro-tensiometer and the developed circuit models, together, provide opportunities to unveil the full dynamics of plant water stress, address the transient factor in plant physiological responses to both short and long-term dehydration processes, and guide more efficient management of agricultural water use.
