Microstructure determines floating ability of weed seeds

BACKGROUND Weed seeds in rice‐wheat continuous cropping fields spread via flowing water during irrigation of the rice crop. However, the ability of their adaptation to water dispersal and their structural mechanisms remain unclear. One hundred and ten species of weed seeds from 35 families were selected for this study. Seed slices were made through freeze sectioning to observe and assess the proportions of parenchyma, aerenchyma and lignified tissue. Microstructure and morphological traits, such as relative size and appendages were integrated into an analysis. RESULTS Multivariate statistical analysis showed that floating time was significantly positively correlated with the shape, aerenchyma and parenchyma of the weed seeds and negatively with lignified tissue. Cluster analysis divided all the tested seeds into four categories. The first category was super floating weeds, which had a large proportion of parenchyma or air chamber and floated on water surfaces for > 400 h, including 16 species; the second category was strong floating weeds, which had a flat shape, parenchyma or air chamber structures and floated for 120 to 400 h, including 17 species; the third category was floating weeds, which were usually dense in structure with a floating time < 120 h, including 78 species; the fourth category showed no floating ability with a large size and mass, and dense structures including seven species. CONCLUSION Most weeds had floating ability, which was closely related to the adaptability of their anatomical structures. This study takes an insight into understanding ecological adaptation of weeds and the sustainable ecological weed control through removing floating weed seeds.