Seed Viability of <i>Heracleum mantegazzianum</i> (Apiaceae) Is Quickly Reduced at Temperatures Prevailing in Biogas Plants

Abstract

Heracleum mantegazzianum is an invasive plant species with enormous effect on ecosystems and human health. Mechanical weed management often results in large amounts of biomass. Fermentation in biogas plants can be used for disposal of this biomass contaminated with seeds and for energetic utilization, if spreading of viable seeds with fermentation residues is prevented. Our aim is to quantify the risk of seed survival in mesophilic biogas plants. Seeds were harvested at three ripening stages in central Germany. They were incubated for 0, 0.5, 1, 2, 4, and 8 days at 35 and 42 °C in water baths. Thereafter, seed viability was assessed by a tetrazolium test. Furthermore, germinative capacity of seeds which had passed an incubation of 48 h at 35 °C were tested. After eight days in water bath none of the 1199 tested seeds were viable anymore. The time until half of the seeds died (ED50) ranged from 9 to 65 h, whereby high temperature accelerated the mortality. Germinative capacity was similar to the seed survival rate. The results suggest that fermentation of H. mantegazzianum biomass poses only a low risk of viable seed spread, if the operating temperature of the biogas plant achieves 42 °C and a high retention time is ensured.

Keywords

• giant hogweed
• biogas reactor
• biomass disposal
• germinative capacity
• invasive plant management
• water bath