Transpiration directly regulates the emissions of water‐soluble short‐chained OVOCs

Abstract

Most plant-based emissions of volatile organic compounds are considered mainly temperature dependent. However, certain oxygenated volatile organic compounds (OVOCs) have high water solubility; thus, also stomatal conductance could regulate their emissions from shoots. Due to their water solubility and sources in stem and roots, it has also been suggested that their emissions could be affected by transport in the xylem sap. Yet further understanding on the role of transport has been lacking until present. We used shoot-scale long-term dynamic flux data from Scots pines (Pinus sylvestris) to analyse the effects of transpiration and transport in xylem sap flow on emissions of 3 water-soluble OVOCs: methanol, acetone, and acetaldehyde. We found a direct effect of transpiration on the shoot emissions of the 3 OVOCs. The emissions were best explained by a regression model that combined linear transpiration and exponential temperature effects. In addition, a structural equation model indicated that stomatal conductance affects emissions mainly indirectly, by regulating transpiration. A part of the temperature's effect is also indirect. The tight coupling of shoot emissions to transpiration clearly evidences that these OVOCs are transported in the xylem sap from their sources in roots and stem to leaves and to ambient air.

Radon as a natural tracer of gas transport through trees

“…Radon is a natural tracer with a wide variety of applications to tree‐gas research including studies of greenhouse gas emissions (Fig. ), volatile organic carbon emissions (Rissanen et al ., ), hypoxia effects on physiology and development (Spicer & Holbrook, ), and forest regulation of aerosol production (Jayaratne et al ., ). Patterns in stem radon emissions across species, seasons, and diurnal periods suggested that tree transport of soil‐produced and plant‐produced gases is controlled by plant hydraulics, and that trees emit soil gases during the night when transpiration rates are negligible.…”

Interannual and Seasonal Dynamics of Volatile Organic Compound Fluxes From the Boreal Forest Floor

“…In trees, methanol production is connected to growth and is produced mainly in leaves and needles in spring, and in stem and root expansion in summer. Soil VOC production can also influence the canopy fluxes, because methanol produced in the stem and roots during their growth, can be transported to the canopy via transpiration stream (Rissanen et al, 2018), and hence be emitted through stomata (Folkers et al, 2008). Peaking acetone and acetaldehyde fluxes above a hardwood forest in autumn were speculated to result from leaf senescence and decaying biomass (Karl et al, 2003).…”

Insect Odorscapes: From Plant Volatiles to Natural Olfactory Scenes

“…During the day, they can fluctuate rapidly, in response to changes in cloud cover and shading by the canopy (Singsaas and Sharkey, 1998). Light influence on stomatal conductance constrains emissions of polar water-soluble VPCs such as methanol, which can be further modified by diurnal changes in transpiration and water transport (Rissanen et al, 2018). On the other hand, emissions of apolar hydrophobic VPCs are independent of stomatal conductance, even though these VPCs diffuse principally through stomata (Niinemets et al, 2002).…”