Submitted to: Biological Invasions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/31/2011
Publication Date: 7/1/2012
Citation: Matlaga, D.P., Quinn, L.D., Davis, A.S., Stewart, R. 2012. Light response of native and introduced Miscanthus sinensis seedlings. Biological Invasions. 5:363-374. Interpretive Summary: One of the goals of invasion biology is to understand why invasive species undergo explosive population growth and range expansion in their introduced habitats. In the Eastern and Midwest U.S., the exotic ornamental Chinese silver grass (Miscanthus sinensis) has escaped from cultivation and formed self-sustaining populations. Chinese silver grass grows in open areas with high light levels in both its native range (east Asia) and in the U.S. However, naturalized populations of Chinese silver grass in the U.S. are also found along forest edges and in the shady understory of young forests. This has created concern that Chinese silver grass has evolved greater shade tolerance and in the future may spread into older forest with deep shade. To test the hypothesis that populations of Chinese silver grass in its introduced range vary in their tolerance of shade from those in its native range, we conducted a greenhouse experiment in which seedlings from introduced (U.S.) and native (Japan) seed sources were grown under varying light levels. We observed several differences in seedling light response but few were linked to the region where the seeds originated. Seedlings from Japanese populations had wider leaves compared to seedlings from U.S. populations. For all populations, a greater percent of the biomass of the plant was invested in the leaves, and less in the roots, under low light compared to plants in high light. Additionally, the leaves of seedlings growing under low light levels were thinner, capturing light more efficiently per unit mass, than those growing in high light. Our results do not support the hypothesis that Chinese silver grass range expansion in the U.S. is driven by increased tolerance of shade in the introduced range. Therefore, efforts to determine the potential geographic limits of this species in the U.S. should not assume a different light requirement than for the native range.
Technical Abstract: Miscanthus sinensis is an Asian grass introduced to the U.S. for ornamental purposes, which has formed naturalized populations across the Eastern and Midwest regions. In both its native and exotic ranges M. sinensis is found in open habitats with high light levels. Within its exotic range M. sinensis is also found in forest edge habitats and in the understory of secondary forest, creating concern that shade-tolerance has evolved and in the future populations may spread into undisturbed forest understories. To understand how seedling growth and biomass allocation are influenced by light availability in populations of M. sinensis within its native and exotic range we conducted a greenhouse experiment. We placed seed collected from four populations in the native range (Japan) and three populations in the exotic range (U.S.) under 7%, 17%, 30% and 50% full sunlight and measured growth and biomass of the resulting seedling after four months. Several seedling attributes differed between populations, but few of these differences were explained by the region (Japan vs. U.S.) where the population originated. Generally, seedlings from Japanese populations had wider leaf blades, shown in a steeper slope in the relationship between leaf length and leaf area, compared to seedlings from U.S. populations. Light treatments influenced seedling size and the allocation of biomass within a seedling. Seedlings from all populations produced more leaves and greater leaf area and biomass as light levels increased. Seedlings allocated a greater proportion of biomass to leaves, and less to roots, under lower light conditions compared to the high light treatments. Leaves of a given mass had leaf area, and were therefore thinner, on seedlings growing under low light. Our results indicate that M. sinensis seedlings alter their growth and allocation patterns in response to light availability, but do not support the hypothesis that greater shade tolerance has evolved in U.S. populations of this exotic species.