Photosynthetic responses of Microstegium vimineum (Trin.) A. Camus, a shade-tolerant, C 4 grass, to variable light environments

Abstract

Microstegium vimineum (Trin.) A. Camus, a shade-tolerant C grass, has spread throughout the eastern United States since its introduction in 1919. This species invades disturbed understory habitats along streambanks and surrounding mesic forests, and has become a major pest in areas such as Great Smoky Mountains National Park. The focus of this study was to characterize the photosynthetic induction responses of M. vimineum, specifically its ability to utilize low light and sunflecks, two factors that may be critical to invasive abilities and survival in the understory. In addition, we were curious about the ability of a grass with the C photosynthetic pathway to respond to sunflecks. Plants were grown under 25% and 50% ambient sunlight, and photosynthetic responses to both steady-state and variable light were determined. Plants grown in both 25% and 50% ambient sun became 90% light saturated between 750-850 μmol m s; however, plants grown in 50% ambient sun had significantly higher maximum steady-state photosynthetic rates (16.09 ± 1.37 μmol m s vs. 12.71 ± 1.18 μmol m s). Both groups of plants induced to 50% of the steady-state rate in 3-5 min, while it took 10-13 min to reach 90% of maximum rates, under both flashing and steady-state light. For both groups of plants, stomatal conductance during induction reached maximum rates in 6-7 min, after which rates decreased slightly. Upon return to low light, rates of induction loss and stomatal closure were very rapid in both groups of plants, but were more rapid in those grown in high light. Rapid induction and the ability to induce under flashing light may enable this species to invade and dominate mesic understory habitats, while rapid induction loss due to stomatal closure may prevent excess water loss when low light constrains photosynthesis. The C pathway itself does not appear to present an insurmountable barrier to the ability of this grass species to respond to sunflecks in an understory environment.

Performance and reproduction of an exotic invader across temperate forest gradients

“…Yet, as noted, these associations cannot fully decouple cause and effect in M. vimineum establishment. Admittedly, seed output is less likely an influence upon the abiotic environment than M. vimineum biomass; but there is an established correlation between M. vimineum vegetative biomass and seed output (Horton and Neufeld 1998, Claridge and Franklin 2002, Cheplick 2005), and we found a similar relationship (coeff. ¼ 4.8, f-value ¼ 14.47, p , 0.0006).…”

“…Microstegium vimineum is one of many exotic species currently invading deciduous forest, understory habitats (Horton and Neufeld 1998, Cole and Weltzin 2005, Martin et al 2009 (Warren et al 2011) synthesized disparate research pertaining to potential niche limitations in M. vimineum and informed the structuring of our observational and experimental work. Most notably, the Warren et al (2011) review suggested that as multiple environmental gradients shift concurrently across woodland boundaries, individual assessment of potential niche resources (e.g., light) fails to take interactions between abiotic drivers into consideration.…”

Plasticity of Chasmogamous and Cleistogamous Reproductive Allocation in Grasses

“…Although it is a summer annual C 4 grass, it is shade tolerant (Horton and Neufeld 1998) and tends to grow in mesic deciduous forests where it can form a dense, lawn-like monoculture underneath the canopy. In temperate regions, it recruits from seed in early spring and produces culms that can branch and root from the lowermost nodes.…”

Assessment of Nonnative Invasive Plants in the DOE Oak Ridge National Environmental Research Park

“…Microstegium is shade tolerant and can grow in variable light conditions because of its low-light compensation points and lowdark respiration rates. These allow the plant to continue to assimilate COz in the darkness of the understory (Horton and Neufeld 1998). In fact, microstegium has been observed growing in areas that receive only 5% full sunlight Microstegium is found throughout the ORR.…”