Physiological Responses of Grapevine Shoots to Water Stress and the Development of a Microtensiometer to Continuously Measure Water Potential

Download or read book Physiological Responses of Grapevine Shoots to Water Stress and the Development of a Microtensiometer to Continuously Measure Water Potential written by Vinay Vijay Pagay and published by . This book was released on 2014 with total page 167 pages. Available in PDF, EPUB and Kindle. Book excerpt: Water availability plays a key role in growth processes in grapevines (Vitis vinifera L.), moderating the balance between vegetative and reproductive growth. It was hypothesized that differences in vegetative growth of individual shoots within a grapevine on a single cane were due to differences in the water status of those shoots as indicated by their midday stem water potentials, [PSI]md. A combination of leaf pressure chamber, leaf gas exchange, ultrasonic acoustic emissions, stem hydraulic measurements, and histology techniques were used on field-grown 'Riesling' grapevines that were subjected to progressive soil moisture deficits during the 2011 and 2012 growing seasons. Differences in [PSI]md were not large enough to explain the large differences in shoot length within a single vine. Longer shoots had greater hydraulic conductivities, but shorter shoots were found to have higher rates of xylem acoustic emissions occurring under less water stress (higher [PSI]md) than longer shoots. Longer shoots had larger cross-sectional xylem vessel area and somewhat less inter-vessel pitting compared to shorter shoots. These differences could contribute to the higher hydraulic efficiency of long shoots, and with fewer pits per vessel, there may be fewer embolisms. Stomatal conductance and photosynthetic responses to increasing water stress were not different in relation to shoot length. In summary, although there were differences in water status between long and short shoots on the same vine, the differences were not great enough to explain the differences in growth rate of the shoots. Tensiometry is a technique to measure the chemical potential of stretched liquid water based on a thermodynamic equilibrium between liquid water and its vapor. It provides the most sensitivity in the range of (high) water potentials relevant to plants and soils, and is compatible with miniaturization for embedding in plants. Based on this technique, we developed a i microelectromechanical system (MEMS)-based microtensiometer in which a piezoresistive pressure sensor coupled to a nanoporous silicon membrane was able to measure large internal negative pressures of liquid when exposed to sub-saturated vapors. We demonstrated its function in sub-saturated vapors across a range of activities (aw) or relative humidities (RH), measuring internal hydrostatic pressures approaching -33 MPa (aw=0.78 or 78% RH), the largest negative liquid pressure directly measured by any method. The extended range of measurement combined with a small form factor make the microtensiometer an attractive instrument for the measurement of water activity in a variety of materials (e.g. concrete), physical, biological, and environmental systems. The microtensiometer can also be embedded in the stems of woody plants and in soils for the continuous measurement of water potential. Scalable microtensiometer arrays in conjunction with wireless networks offer the potential to provide continuous, high-resolution data to geographic information system (GIS) centers to aid in irrigation decisions and optimize water resource management for sustainable crop production. ii.