Acoustic Emissions in Tomato Plants under Water Stress Conditions

Abstract

Acoustic emissions (AE) could be used as an indicator of plant water stress as speaking plant. The objective of this study was to observe AE of tomato plant and to analyze relationship between AE and plant waterconsumption associated with transpiration. Three glasshouse experiments were conducted with potted tomato plants. The AE, transpiration rate and the plant transpiration transfer coefficient (h a t ) as an indicator of plant water stress level were determined with h a t being calculated based on sunlit leaf temperature, temperature of an artificial leaf without transpiration (hereafter, referred to as non-transpiration leaf temperature) and air temperature. The results showed that daily patterns of AE varied depending on water stress level, which was indicated by h a t . Under mild or moderate water stress (h a t ? 0) conditions, AE increased with decrease in amount of soil water but decreased with decrease in amount of soil water under severe water stress conditions (0 <h a t ? 1). To analyze hourly changes in relationship between AE and transpiration, concept of change of transpiration rate (AT) was introduced. Under mild or in absence of water stress conditions (h a t ? 0), AE increased linearly with increase of AT with a significant regression coefficient (r 2 = 0.85 and slope = 0.61). Then, as water stress level increased, r 2 gradually decreased, as well as slope of regression line between AE and AT. When water stress level increased further, slope continuously decreased. However, r 2 started to increase gradually. Thus, when water stress increased to a critical level (0 < h a t ? 1), a significant inverse linear relationship between AE and AT, with r 2 = 0.64 and slope = -0.73 could be observed. On basis of these results. AE tended to be differently affected by AT depending on water stress level.