Leaf thickness and electrical capacitance as measures of plant water status

Restricted (Penn State Only)
Author:
Afzal, Sayed Amin
Graduate Program:
Agronomy
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
January 24, 2017
Committee Members:
  • Sjoerd W. Duiker, Jack Watson, Dissertation Advisor
  • Sjoerd W. Duiker, Jack Watson, Committee Chair
  • Jack Watson, Committee Member
  • Dawn Luthe, Committee Member
  • Paul Heinemann, Outside Member
Keywords:
  • plant-based sensor
  • irrigation scheduling
  • leaf sensor
  • water stress
  • photosynthesis
  • soil water
  • leaf water
Abstract:
Three experiments were conducted to study the feasibility of using leaf thickness (LT) and leaf electrical capacitance (CAP) for monitoring of plant water status. LT and CAP were measured by a developed leaf sensor. In the first experiment, the relationship between leaf relative water content (RWC) and relative LT (RLT) was determined on cut leaves of four crops in a lab condition. Linear piecewise modeling explained 86-97% of the variations, but the estimated parameters varied by species. The second experiment was conducted on tomato (Solanum lycopersicum) in a growth chamber at a constant temperature and on/off photoperiod. The plant was irrigated to the saturation level and allowed to dehydrate thereafter. The daily LT variations were minor for θ above the wilting point, but more noticeable below it. CAP was at a minimum value during the dark periods and rapidly increased by illumination, implying that CAP was a reflection of photosynthesis. The extent of daily CAP variations decreased when θ was below the wilting point, suggesting that the effect of water stress on CAP would be through its negative impact on photosynthesis. In the last experiment, eight tomato plants were grown in a controlled greenhouse. One leaf sensor was clipped on a leaf of each plant. The irrigation regime was designed based on observed visual wilting stages such that water stress level was increased over time. Daily LT variations increased by water stress. CAP was at a minimum value during the nights and rapidly increased by light, but the extent of daily variations decreased by water stress. The relative values of daily night- and noon-time LT and noon-time CAP had strong piecewise linear relationships with θ. Overall, θ and soil matric potential could not identify the water stress levels, while a transition from a stress level to the next level could be identified by at least one of the relative values of LT or CAP. The results promise that LT and CAP are suitable gauges for precision monitoring of plant water status. However, further studies are required to assess these techniques in various environmental conditions and on different crops.