How does rising atmospheric CO2 affect marine organisms?

Click to locate material archived on our website by topic

Native vs. Nonnative Invasive Plants in a CO2-Accreting Atmosphere
Belote, R.T., Weltzin, J.F. and Norby, R.J.  2003.  Response of an understory plant community to elevated [CO2] depends on differential responses of dominant invasive species and is mediated by soil water availability.  New Phytologist 161: 827-835.

The authors state that "an increase in atmospheric CO2 may increase the success of nonnative invasive plants by directly enhancing their growth or by altering the availability of resources (Dukes and Mooney, 1999; Smith et al., 2000; Weltzin et al., 2003)."  It could also be stated that just the opposite may occur.  Belote et al. thus sought to investigate this matter in the understory plant community of the FACE facility at the Oak Ridge National Environmental Research Park, Tennessee, USA, which is located within a sweetgum (Liquidambar styraciflua L.) stand that was established in 1998.  The trees of this stand were 17 meters tall when the study was conducted in 2002 and comprised a closed canopy that reduced the light in the understory plant community by 70-95% during the growing season.

What was done
In early September of each of two years (2001, characterized as wet; 2002, characterized as dry), the authors determined the total seasonal above-ground net primary productivity of each plant species in both the ambient (365 ppm) and CO2-enriched (550 ppm) FACE plots.  In the case of herbaceous species, this was accomplished by clipping the plants at ground level and drying and weighing the collected material; while for woody perennials, new shoots that had been marked early in the spring of each year were clipped, dried and weighed.

What was learned
The vast bulk of the understory biomass production (approximately 90% in the ambient CO2 treatment in both years of the study) came from two nonnative invasive species: Nepal grass (Microstegium vimineum (Trin.) A. Camus), a shade-tolerant C4 annual grass, and Japanese honeysuckle (Lonicera japonica Thunb.), a C3 evergreen woody vine.  The less prominent of these two "problematic invasives" (L. japonica) experienced a dramatic three-fold CO2-induced increase in production in both years of the study.  The considerably more prominent M. vimineum, on the other hand, exhibited no change in production in response to atmospheric CO2 enrichment in the dry year, and actually suffered a 40% reduction in productivity in the elevated CO2 treatment in the wet year.

So how did the rest of the understory community fare, i.e., the non-weeds?  From the bar graphs presented in the paper, we calculate that their productivity was increased by about 80% in the CO2-enriched treatment in the dry year and by approximately 150% in the wet year, so that their total share of community production increased from about 9.5% in ambient air to approximately 14% in the elevated CO2 treatment in the dry year, and from about 10.5% in ambient air to approximately 25% in the elevated CO2 treatment in the wet year.  Hence, the non-weed community significantly increased its share of total ecosystem productivity in the CO2-enriched treatment in both the wet and dry year of the two-year study.

What it means
In this study, native understory vegetation in a closed canopy forest made significant advances against the huge productivity advantage currently enjoyed by two nonnative invasive species as a consequence of an approximate 185-ppm increase in the air's CO2 concentration.

Dukes, J.S. and Mooney, H.A.  1999.  Does global change increase the success of biological invaders?  Trends in Ecology and Evolution 14: 135-139.

Smith, S.D., Huxman, T.E., Zitzer, S.F., Charlet, T.N., Houseman, D.C., Coleman, J.S., Fenstermaker, L.K., Seemann, J.R. and Nowak, R.S.  2000.  Elevated CO2 increases productivity and invasive species success in an arid ecosystem.  Nature 408: 79-82.

Weltzin, J.F., Belote, R.T. and Sanders, N.J.  2003.  Biological invaders in a greenhouse world: Will elevated CO2 fuel plant invasions?  Frontiers in Ecology and the Environment 1: 146-153.

Reviewed 9 June 2004