The Role of Cell Wall Esters and Foliar Emissions of Methanol and Acetic Acid in the Response of Trees and Ecosystems to Abiotic Stress

Abstract:

Ecosystem dynamics and abiotic stresses are predicted to dramatically alter with climate change. Understanding the mechanisms that drive plant responses to environmental change is vital for predicting how the structure and function of natural and managed ecosystems will react to such changes including alterations in carbon, water, and energy cycling, at the individual leaf to whole ecosystem levels. A common thread among many of the biochemical and physiological processes that determine ecosystem dynamic responses to climate change variables are alterations in plant cell wall chemical composition, structure, and function. A large proportion of the plant cell wall can be modified with methyl and O-acetyl ester groups which may play important roles in cell growth and tissue development, proper xylem and stomatal functioning, central carbon and energy metabolism, and stress communication and signaling. The hydrolysis of these esters leads to rapid physiological changes in the cell wall and the emission of methanol and acetic acid to the atmosphere. Thus, cell wall methylation and acetylation, and their corresponding de-esterification, underpin plant responses to environmental stress, and facilitate forest response to climate¹. Here we use coupled online PTR-MS and GC-MS as well as colorimetric assays to provide evidence that methanol (meOH) and acetic acid (AA) emissions derive from cell wall de-esterification in poplar leaves². We present a new concept of leaf cell wall O-acetyl/methyl ester ratios and demonstrate that under abiotic stress they are quantitatively reflected in the AA/meOH emission ratios, which also change as a function of leaf age. We further explore the AA/meOH emission ratio from rapidly growing and drought stressed poplar trees using a dynamic branch enclosure and contrast this with eddy covariance fluxes above a citrus orchard and forested ecosystems in California, Colorado, and Belgium to help distinguish emissions associated with vegetation growth from those linked with plant stress. We evaluate the hypothesis that the production and emission of acetic acid is enriched during stress conditions compared to that of methanol, which may be more enriched during the growth phase.

¹ Dewhirst et al (2020) Trends in Plant Science, 25(8), 729-732

² Dewhirst et al (2020) PLoS One, 15(5), e0227591