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Chemical sensing of plant stress at the ecosystem scale

T. Karl,A. Guenther,A. Turnipseed,E. Patton,K. Jardine

Published 2008 in Biogeosciences

ABSTRACT

Significant ecosystem-scale emissions of methyl- salicylate (MeSA), a semivolatile plant hormone thought to act as the mobile signal for systemic acquired resistance (SAR), were observed in an agroforest. Our measurements show that plant internal defence mechanisms can be acti- vated in response to temperature stress and are modulated by water availability on large scales. Highest MeSA fluxes (up to 0.25 mg/m 2 /h) were observed after plants experienced ambient night-time temperatures of 7.5 C followed by a large daytime temperature increase (e.g. up to 22 C). Un- der these conditions estimated night-time leaf temperatures were as low as 4.6 C, likely inducing a response to pre- vent chilling injury. Our observations imply that plant hor- mones can be a significant component of ecosystem scale volatile organic compound (VOC) fluxes (e.g. as high as the total monoterpene (MT) flux) and therefore contribute to the missing VOC budget. If generalized to other ecosystems and different types of stresses these findings suggest that semivolatile plant hormones have been overlooked by inves- tigations of the impact of biogenic VOCs on aerosol forma- tion events in forested regions. Our observations show that the presence of MeSA in canopy air serves as an early chem- ical warning signal indicating ecosystem-scale stresses be- fore visible damage becomes apparent. As a chemical met- ric, ecosystem emission measurements of MeSA in ambient air could therefore support field studies investigating factors that adversely affect plant growth.

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