Effects of trichlorethylene, plant sex and site of origin on modular demography in Vallisneria americana.
Abstract
The demographic effects of an organochlorine contaminant on the dioecious aquatic macrophyte Vallisneria americana are reported. Plants were sampled from two natural populations in the Huron-Erie corridor of the Great Lakes Basin and placed in experimental treatments of high (396 mg per litre), medium (132 mg per litre), low (66 mg per litre) and zero concentrations of trichloroethylene (TCE). Plant responses were determined in terms of genet mortality (i.e. death of the entire genetic individual), ramet production (clonal growth) and mortality, leaf birth and death rates, leaf area and sexual reproduction. TCE in the water caused significant ramet and genet mortality, and reduced the growth of surviving plants. Control plants produced significantly more leaves than contaminated plants. Contaminant-exposed plants continued producing their leaves for 4-6 weeks longer than controls, and showed greater rates of leaf death. The total leaf area of genets exposed to TCE was significantly lower than that of unexposed plants. TCE was associated with a significant decrease in flower production. The concentration of TCE was determined in plant tissues, water and sediment. Levels of TCE were greatest in the sediment, and sediment originating from each site absorbed TCE to differing degrees. TCE was more concentrated in the underground storage tissues (roots and turions) than it was in leaves. Root and turion tissues of plants from one site contained significantly less TCE than those of plants from the other site, despite an identical concentration of TCE in the water; differences may have been due to contrasting sediment affinities for TCE, and/or different rates of TCE accumulation by the plants from each site. TCE was bioaccumulated, particularly in roots. This appeared to be attributable to the fact that TCE accumulated, in the first instance, in sediments. The log10 of TCE concentrations in sediment were linearly correlated with TCE concentrations in roots, suggesting that TCE uptake is through the root system rather than the leaves, and that uptake is driven by the concentration gradient between sediment and plant. Plants that survived the TCE treatment appeared to be resistant to the chemical; they were as likely to flower as surviving untreated plants. Males were more likely than females to survive TCE treatment. It is concluded that modular demography can be used to characterize the performance of plants that are stressed by exposure to various concentrations of the organochlorine solvent trichloroethylene, and that plants from different sites differ in their ability to survive contaminant stress.