Chemical Sensing of Plant Stress at the Ecosystem Scale
ACD and TIIMES scientists detected significant fluxes and concentrations of methyl salicylate (MeSA) in a tree plantation atmosphere using micrometerological techniques in combination with highly sensitive mass spectrometry (Karl et al., BGD, in review). Methylsalicylate, a volatile form of aspirin, is synthesized by plants in response to biotic and abiotic stresses and gives plants the ability to communicate through the atmosphere. Measurements shown in Figure 1 demonstrate, for the first time, that MeSA can be present in the forest atmosphere and that MeSA emissions are elevated in response to temperature and drought stress. These measurements show that plant internal defense mechanisms can be activated in response to temperature stress and are modulated by water availability on large scales. Highest MeSA fluxes (up to 0.25 mg/m2/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). Under these conditions estimated night-time leaf temperatures were as low as ~ 4.6°C, likely inducing a response to prevent chilling injury (2). Unlike humans, who are advised to take aspirin to regulate body temperature (e.g. as a fever suppressant), plants have the ability to produce their own mix of aspirin-like chemicals triggering the formation of proteins which reduce injury resulting from temperature stress. By doing so, organic carbon is added to the atmosphere which could have ramifications for air quality and climate.
Figure 1:
MeSA flux plotted versus ΔT (daily maximum temperature – daily minimum temperature)
before irrigation (black) and after irrigation (gray).
These observations showing that MeSA can make a major contribution to the total biogenic volatile organic compound (VOC) flux from a forest come as a surprise. This finding of a new category of semivolatile organic emissions may help to explain previous studies indicating that there is a “missing source” of biogenic VOCs. These findings also provide tangible proof that plant to plant communication occurs on the ecosystem level and connect two separate scientific communities on plant volatile research that have co-evolved over the past years: One has historically focused on biogenic VOCs important for atmospheric chemistry (e.g. isoprene, monoterpenes); the second community has targeted the ecology of plant volatiles (e.g. floral scents). The finding of significant plant hormone emissions is expected to transform the research approaches of these separate scientific communities and result in more integrated and multi-disciplinary studies.