Print PageIt is estimated that there are 110 million landmines in 64 countries worldwide. Through time buried ordinance often leaks energetic compounds into soil. Apart from humanitarian issues, soil polluted with explosives, such as hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and 2,4,6-trinitrotoluene (TNT) is a crucial environmental problem. Vegetative cover plays an important role in the movement of explosives through the soil. Plants absorb explosive residuals, some of which accumulate in leaf tissues causing stress and disrupting photosynthetic processes. Physiological responses to explosives are poorly understood, especially relative to naturally occurring environmental stresses. Research into the methods with which explosives disrupts physiological processes could provide methods for discriminating anthropogenic and natural stresses. Through investigating effects of energetic compounds on plant physiology and functioning, we may be able to use non-invasive techniques to detect explosives contamination in soil. The objective of our research was to remotely distinguish stress caused by explosives from naturally occurring stress in plant canopies. Using the shrub Myrica cerifera, we conducted multiple stress experiments including drought, salinity, increased nitrogen, TNT exposure, and RDX exposure. Photosynthesis, stomatal conductance, water potential, chlorophyll fluorescence, reflectance and plant pigments were quantified over the course of each experiment.
Results/Conclusions
Physiological effects due to explosives exposure were markedly different from natural stress exposure. Natural stresses caused declines in water relations and photosynthesis in the absence of pigment changes, with impairment to electron transport. Stomatal control over photosynthesis was evident due to drought and salinity. Increased non-photochemical quenching and photorespiration were also seen as protective mechanisms to the photosystem. Reflectance indices primarily indicated changes in energy dissipative mechanisms. Exposure to explosives caused reduced photosynthesis with little effect on water relations. There was little effect on water relations. Electron transport was not impaired due to explosives and there was no evidence of stomatal control on photosynthesis, indicating declines due to biochemical changes and chlorophyll degradation. Fluorescence and reflectance measurements detected this change. Additional nitrogen (in concentrations analogous to the nitrogen in TNT) had very little effect on the physiology of this nitrogen-fixing species and there were no differences found in fluorescence or reflectance measurements. Under conditions of a constant leaching of explosives into the soil, as in the case of leaky landmines, plant uptake would be continuous. With further research into the effect of explosives on the photosystem, we can use various remote sensing methods to detect distinct signatures relative to uncontaminated plants.
