Tree Canopies Influence Ground Level Atmospheric Electrical and Biogeochemical Variability

Abstract

Static electric fields in the atmosphere are increasingly recognized as interacting with various organisms over several levels of biological organization. Recently, a link between atmospheric electrical variations and biogeochemical processes has been established in the context of open fields, yet biological structures like trees produce substantial alterations in atmospheric electric properties. Here, we assess whether these structural changes affect the dynamics of the electrical landscape and its relation to geochemical processes. To this end, we theoretically assess how trees alter their surrounding electric fields and empirically compare the temporal dynamics of atmospheric potential gradients, positive ions in the near-ground level atmosphere and soil electrochemical properties in an open field and under a tree. The developed model of electric fields around trees provides insight into the extent to which trees shield the underlying electric landscape, revealing that a substantial increase in atmospheric potential gradient only marginally affects the electric field under the canopy. We further show that soil electrochemical properties are tied to the temporal dynamics of positive ion in the near-ground level atmosphere, and that the presence of a tree reduces the temporal variability in both ground level positive ion concentrations and soil redox potential. This suggests that a tree can alter the temporal variability in atmospheric electricity and soil electro-chemistry, thereby likely indirectly influencing soil microorganisms and processes as well as electro-sensitive organisms that perceive and utilize atmospheric electric fields.

Prey can detect predators via electroreception in air

“…These two animal representations were both assigned the material properties of “Insect tissue.” The remainder of the model was assigned the material properties of “Air.” The surface of the wasp representation was assigned a charge of +10 pC, while the surface of the caterpillar representation was assigned a charge of −2 pC, based on the means of the charge measurements made in this study for V. vulgaris and A. io respectively. The surface of the plant stem cylinder was defined as electrical ground ( 5 , 12 , 37 , 40 , 52 , 53 ).…”

Observed electric charge of insect swarms and their contribution to atmospheric electricity

“…The honeybee swarm was represented as an ellipsoid with semi-axes 2 m x 1 m x 0.5 m ellipsoid at a height of 3 m, and the locust swarm an ellipsoid with semi-axes 4 m x 1 m x 1 m at a height of 15 m. The swarm charge was distributed evenly as a volume charge within the ellipsoids, with the total charge calculated respectively as the sum of 500 bees each carrying +100 pC (order of magnitude from ( England and Robert, 2022 )) and 1000 locusts carrying +850 pC each. An approximately 8 m tall deciduous tree was included in each model to provide scale and an electrical landmark for comparison ( Hunting et al., 2021a ). The remainder of the model domain was assigned as air.…”

“…The upper surface of this air column was given an electrical potential typical of a 40 m altitude in fair-weather conditions (+4 kV), with the bottom surface defined as zero potential, equivalent to the established surface (first meter) atmospheric potential gradient of 100 V/m ( Bennett and Harrison, 2007 ; Wilson, 1903 ). The surface of the tree was also defined as ground ( Hunting et al., 2021a ). Meshing of the geometry was physics-controlled, set to “extremely fine”.…”

“…Meshing of the geometry was physics-controlled, set to “extremely fine”. The relative permittivity, ε r , was defined as ε r = 12 for living trees ( Hunting et al., 2021a ; Suojanen et al., 2001 ), ε r = 1 for air, and ε r = 80 inside the insect swarms (likely an overestimate, based on the permittivity of water). Model outputs presented for this study were produced by plotting data from two-dimensional slices through the centre of the three-dimensional dataset.…”

“…The atmospheric PG has proved important in understanding large-scale drivers of the global atmospheric electric circuit (e.g. from climate and space weather) ( Harrison, 2015 ), and in causing migration of biologically relevant ions (e.g., nitrate, sulphate, radon) ( Hunting et al., 2019 , 2021a , 2021b ) as well as facilitating animal dispersal or navigation ( Clarke et al., 2013 ; Hunting et al., 2022 ; England and Robert, 2022 ; Morley and Robert, 2018 ). The continuous monitoring of atmospheric electric fields is therefore essential in developing a detailed understanding of a wide array of atmospheric, biological, and geological processes.…”