Physiological filters to vegetation establishment on contaminated soil
Anthropogenic soil contamination is a global issue which controls vegetation communities by acting as a physiological filter. Such filters inhibit both establishment and growth of vegetation. Explosive compounds in particular are highly mobile, toxic to a broad range of biota, and recalcitrant. Many studies have investigated explosive compound impacts on seed germination; however, successful germination is an inadequate predictor of successful establishment and subsequent growth due to physiological filtering. Our objective was to test germination success of local species which are known to occur on explosives contaminated sites and monitor health of those seedlings after germination. Propagules of Ulmus, Vitis, Ligustrum, Acer, and Cyperus genera were sown in soil containing 500 mg/kg (ppm) Composition B (Comp B); a mixture of RDX and TNT in a 6:4 ratio. Seed germination was recorded and health was monitored for 8 weeks post germination. Morphological impacts on post emergence individuals (leaf damage/deformation, shoot damage, height) were recorded on a weekly basis. Physiological measurements (photosynthesis, stomatal conductance, and electron transport rate) were also recorded. At the end of experiment biomass was harvested and used to measure fresh and dry weight, root to shoot ratios, and uptake analysis via high performance liquid chromatography (HPLC)
Emergence and establishment were both impacted by the presence of Comp B for all represented genera; however, the degree of the impact varied. Morphology and physiology of the seedlings was minimally impacted for Cyperus, while all other genera exhibited significant responses. Biomass for Comp B exposed plants was significantly lower than those in reference soil due to lower photosynthesis, stomatal conductance, and electron transport rate. Woody species also exhibited very different root to shoot ratios. Uptake analyses showed greatest presence of RDX relative to TNT in the tissues. Variability of emergence as well as post emergence morphology and physiology suggest that these compounds act as physiological filters, resulting in altered vegetative communities. Anthropogenic contaminants should be viewed through the lens of physiological ecology to understand how they impact function and stability of affected areas.