Effect of Herbicides in Paddy Runoff on Seed Germination of Vallisneria asiatica and Ammannia multiflora

Abstract

Although rice production provides stable environments for aquatic plants, the wide use of herbicides is a concern for wild plants inhabiting the surroundings of rice paddies. Because commercial herbicides are typically a cocktail of chemicals, they may pose a threat to wild plants even when the constituent chemicals do not individually have detrimental effects. We sampled water from a rice paddy and a river receiving the paddy drainage immediately after the transplanting period to identify and compare the concentrations of herbicides. We also examined the effect of the sampled water on the germination of two plants: Ammannia multiflora (hygrophyte) and Vallisneria asiatica (submerged). We found that the concentrations of glufosinate in the paddy and river waters were 0.0015 and 0.0013 mg L -1 , respectively, and those of pyraclonil were 0.0010 and 0.0009 mg L -1 in the same waters, indicating that these chemicals persist outside the rice paddy. The germination rate of A. multiflora was significantly diminished with exposure to river and paddy water under fluctuating temperature conditions, whereas no difference was observed for V. asiatica. For a comprehensive understanding of the influences of residual herbicides on wetland biodiversity, it is necessary to analyse the effects of herbicides on a wide range of aquatic plants and at various stages of growth.

Comparison of Biological and Genetic Characteristics between Two Most Common Broad-Leaved Weeds in Paddy Fields: Ammannia arenaria and A. multiflora (Lythraceae)

“…The genus comprises upright and solid stems extending approximately 150 cm high, flowers have four petals, and seeds are inverted pyramidal; one side is round, and the other is irregularly concave [2]. This genus is the most common broad-leaved weed in rice fields and is a successful competitor for nutrition and space during the rice growth period [3][4][5]. The most common Ammannia weeds in China's paddy fields are selected; however, no more than three plants were sampled from each paddy field.…”