Establishment capacity of rhizoidal tubers of the moss Bryum billarderii Schwagr. (Bryaceae, Bryophyta) under copper-induced stress

Vegetative propagules are key to moss persistence, yet their responses to metal stress remain poorly understood. This study provides the first experimental evidence of copper (Cu) effects on moss rhizoidal tubers. We experimentally assessed the response of rhizoidal tubers of Bryum billarderii Schwägr. (Bryaceae) to Cu by exposing tubers to 0, 0.5, 1, and 2 mmol/L Cu for 60 days. Establishment was evaluated through filament production and bud formation, and both traits declined sharply with increasing Cu. In controls, tubers initiated filaments by day 6 and all formed both filaments and buds by day 60. At 0.5 mmol/L Cu, filament formation was infrequent and buds appeared only late in the experiment, occasionally accompanied by abnormal tuber production at bud apices. At 1–2 mmol/L Cu, development was almost completely inhibited, with only a single tuber producing filaments at 2 mmol/L and no bud formation at any higher concentration. These results show that copper markedly reduces, but does not completely inhibit, early morphogenesis in moss tubers, thereby impairing clonal establishment through reduced filament and bud production, even at low concentrations.