Heavy metal pollution improves allelopathic effects of Canada goldenrod on lettuce germination

Abstract

• Large amounts of heavy metals have been released into the environment. Thus, the allelopathic effects of invasive alien species on the germination performance of cooccurring indigenous species may be altered or even heightened with the rapid growth in heavy metal pollution. • This study evaluated the impacts of Canada goldenrod (Solidago canadensis L.) leaf extracts at concentrations of 0, 10 or 20 gl 1 on the germination of lettuce under different forms of heavy metal pollution (Cu 2+ , Pb 2+ or a combination of Cu 2+ and Pb 2+ ; 35 mgl 1) during incubation in Petri dishes for 10 days. • Goldenrod leaf extracts (high concentration) reduced growth of aboveground and belowground parts of lettuce as well as competition for light and soil nutrients. However, low concentrations of goldenrod leaf extracts dramatically improved growth of lettuce roots, competition for light, soil nutrient availability, leaf photosynthetic area and growth competitiveness. The combination of goldenrod leaf extracts and heavy metal pollution was synergistic on most lettuce germination parameters, probably because high concentrations of goldenrod leaf extracts together with heavy metal pollution had a synergistic negative impact on lettuce germination. • Consequently, increased levels of heavy metal pollution may favour invasion of invasive alien species while largely suppressing germination of indigenous species.

Drought Enhanced the Allelopathy of Goldenrod on the Seed Germination and Seedling Growth Performance of Lettuce

“…Thus, SGeSGrP performance of indigenous species will inevitably come down under the pressure from the allelopathy refereed by goldenrod, mostly due to the secretion of allelochemicals chiefly created from litter residues and/or root exudates [1,11]. Hence, the results are in accordance with previous studies [2,[8][9][10][12][13][14]. Further, as expected, SCH triggered a higher level of allelopathy on the competitive ability for sunlight acquisition as well as water and inorganic salt acquisition, leaf photosynthetic area, and plant growing ability of lettuce than SCL in this study.…”

“…After eight days of incubation, ten lettuce seedlings of lettuce per Petri dish (i.e., fifty seedlings of lettuce per bioassay treatment group) were chosen randomly to assess SGeSGrP parameters of lettuce, namely, germination percentage (represents the germination ability) [3,9,10,13], germination potential (represents the germination capacity and uniformity) [3,9,10,13], germination index (represents the germination speed and vitality) [37][38][39], germination rate index (represents the germination speed and vitality) [40][41][42], germination vigor index (represents the germination speed and vitality) [39,43,44], promptness index (represents the robust response capability of seedling's germination) [45][46][47], seedling height (represents the competitive ability for sunlight acquisition) [3,9,10,13,33], root length (represents the competitive ability for water and inorganic salt acquisition) [3, 9, 10, 13], leaf length and width (represents the competitive ability for sunlight acquisition) [3,6, 8-10, 13, 33, 48], green leaf area (represents leaf photosynthetic area) [49][50][51], singleplant fresh and dry weights (represents plant growing ability) [3,9,10,13,24,33,48] and plant moisture content (represents plant water content) [3,9,10,…”

“…Hence, plant ecologists are particularly interested in estimating the mechanism driving the successful invasion over the years. Previous results presented that numerous IAS can markedly prevent the growth performance of the surrounding plant species (mainly indigenous species) via the allelopathy triggered by the allelochemicals originated from litter residues and/or root exudates [1,2,11,12,13]. For instance, the allelopathy of the infamous IAS Solidago canadensis L. (goldenrod) occupy a decisive position in the process of effective establishment and flourishing expansion as well as the finally successful invasion [2, 8-10, 12, 13].…”

“…For instance, the allelopathy of the infamous IAS Solidago canadensis L. (goldenrod) occupy a decisive position in the process of effective establishment and flourishing expansion as well as the finally successful invasion [2, 8-10, 12, 13]. This fact is even more important as the allelopathy employed by IAS observably suppressed seed germination and seedling growth performance (SGeSGrP) of indigenous species [2,[8][9][10][12][13][14]. SGeSGrP constitute the core competence of plant life history, which determines the success of subsequently growth performance of the individuals and recruitment potential of the population [1,14].…”