From cradle to grave: The impacts of RDX across three life stages of Morella cerifera

Background/Question/Methods

Environmental integrity has risen to the foreground of the public mind with relation to anthropogenic activities. Explosives contamination has been a particular topic of interest because of its unique biological interactions. The objective of this study was to determine whether explosive contamination in soils would impact seed germination, seedling establishment, and adult plant physiology for the shrub Morella cerifera. Understanding age related differences in sensitivity could assist current attempts to detect contaminants using plants. Royal Demolition Explosive (RDX) was chosen as the test contaminant as it is readily identifiable and one of the most commonly used explosive compounds. Seeds were prepared and then germinated on soil containing varied concentrations of RDX up to 1500 mg kg^-1 dry soil. Juveniles were tested for 8 weeks in soil amended with various concentrations up to 750 mg RDX kg^-1 dry soil and adults were treated for 8 weeks in soil contaminated up to 1500 mg RDX kg^-1 dry soil. All were measured against standard controls in uncontaminated soil. Germination rate, seedling survival, and seedling growth characteristics were quantified. Leaf drop, necrosis, reduction, curling, fluorescence, and shoot:root length were quantified for juveniles. Gas exchange, fluorescence, and leaf drop were measured for adult plants.

 Results/Conclusions

All groups showed a significant response to contamination. Seeds germinated properly but succumbed to effects of the contamination after emergence. Juveniles and adults responded with significant leaf drop and deformation. Juveniles reacted at concentrations of 400 mgkg^-1 and higher while adult plants reacted when exposed to concentrations of 500 mgkg^-1 and above. Adults also showed significant alterations by week 6 in photosynthesis, fluorescence, and stomatal conductance. Higher mortality was observed in adult plants than juveniles at higher concentrations, possibly due to the extensive root system and increased water need. The adult plants exhibited decreased carbon fixation yet exhibited no significant decrease in electron transport rate (ETR) pointing to a disruption in the Calvin-Benson cycle as opposed to the light dependent portion of photosynthesis. Additionally the reaction of the leaves matched that of a physical attack response possibly due to the accumulation of toxic compounds in the aerial portions of the leaves. Overall concentration played a larger role in plant response than age, implying that M. cerifera remains sensitive to this anthropogenic toxin throughout its life stages.