Effects of red/far-red light ratio on hybrid knotweed (Reynoutria x bohemica) seed germination and seedling growth

Citation

Anderson D., Critchley R., Bae J., Clements D.R. 2019. Effects of red/far-red light ratio on hybrid knotweed (Reynoutria x bohemica) seed germination and seedling growth. Proceedings of the 73rd Annual meeting of the Canadian Weed Science Society. November 18-21, 2019. Kelowna, British Columbia, Canada (Oral Presentation).

Plain language summary

Bohemian knotweed (Reynoutria x bohemica) is an invasive hybrid species resulting from the crossing of Japanese (Reynoutria japonica) and giant knotweed (Reynoutria sachalanensis). The hybridization of the two species allows for increased genetic diversity in R. bohemica, making it an aggressive invader. Despite the presence of viable seeds in wild specimens, seedling emergence and establishment of Bohemian knotweed are rarely observed. It was hypothesized that environmental conditions may influence seed germination and seedling growth. This growth chamber study investigated germination and seedling growth under different light quality, ranging from deep shade to full sunlight. Seeds from multiple collection sites throughout the Lower Mainland, British Columbia were used. Germination rates differed among sites. The deep shade had lower germination rates than higher light quality. The moderate and full sunlight produced mean germination of 61.33% and 60.83% respectively, while the deep shade resulted in 50% germination success. As a seedling vigor parameter, chlorophyll contents were not different among sites. However, chlorophyll levels were lower at the deep shade than the moderate/full sunlight. No significant difference in biomass was found between sites or light quality. Leaf number was lower in the deep shade than full sunlight. Seedling height was not reduced by lower light quality; however, significant difference was found between sites. This study suggests that the presence of a canopy may reduce the number of successful germinants of Bohemian knotweed but would not inhibit seedling emergence. This data could help explain the lack of seedlings found in proximity to established stands of Bohemian knotweed.

Abstract

Bohemian knotweed (Reynoutria x bohemica) is an invasive hybrid species resulting
from the crossing of Japanese (Reynoutria japonica) and giant knotweed (Reynoutria
sachalanensis). The hybridization of the two species allows for increased genetic
diversity in R. bohemica, making it an aggressive invader. Despite the presence of viable
seeds in wild specimens, seedling emergence and establishment of Bohemian
knotweed are rarely observed. It was hypothesized that environmental conditions may
influence seed germination and seedling growth. In this experiment, red to far-red light
ratios (R:FR) of 0.3, 0.6, and 1.0 were utilized to investigate germination and seedling
growth under different light quality, ranging from deep shade (R:FR of 0.3) to full
sunlight (R:FR of 1.0). Seeds from multiple collection sites throughout the Lower
Mainland, British Columbia were used. Germination rates differed among sites (p <
0.01). The 0.3 R:FR had lower germination rates than both higher ratios (p < 0.01). The
0.6 and 1.0 R:FR produced mean germination of 61.33% and 60.83% respectively, while
the 0.3 ratio resulted in 50% germination success. As a seedling vigor parameter,
chlorophyll contents measured by a SPAD meter were not different among sites.
However, chlorophyll levels were lower at the 0.3 ratio (p = 0.0327) than the higher
ratios. No significant difference in biomass was found between sites or ratios. Leaf
number was lower in the 0.3 R:FR than the 1.0 ratio (p = 0.0447). Seedling height was
not reduced by lower R:FR ratios; however, significant difference was found between
sites (p = 0.0002). This study suggests that the presence of a canopy may reduce the
number of successful germinants of R. bohemica but would not inhibit seedling
emergence. This data could help explain the lack of seedlings found in proximity to
established stands of Bohemian knotweed.

Publication date

2019-11-18

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