What was done
A FACE experiment utilizing atmospheric CO2 concentrations of 360 and 475 ppm was established on a sheep-grazed pasture located in Manawatu, New Zealand, to study the long-term effects of elevated CO2 on community dynamics in this dry-land ecosystem.  This paper specifically reports on the effects of elevated CO2 on seed production, seedling recruitment and species compositional changes within this community following two-years of daytime atmospheric CO2 enrichment.

What was learned
In both years of the study, elevated CO2 increased seed production and dispersal in seven of the eight most abundant pasture species, including the grasses Anthoxanthum odoratum, Lolium perenne and Poa pratensis, the legumes Trifolium repens and Trifolium subterranean, and the herbs Hypochaeris radicata and Leontodon saxatilis.  In some species, elevated CO2 increased the number of seeds per reproductive structure (inflorescences), while all species exhibited CO2-induced increases in the number of reproductive structures per unit area.

Such increases in seed production contributed to CO2-induced increases in the numbers of species present within CO2-enriched experimental plots.  Greater biodiversity, for example, was found in CO2-enriched plots due to the presence of several short-lived annual species that were absent from plots fumigated with ambient air.  In addition, atmospheric CO2 enrichment helped maintain biodiversity by increasing the number of H. radicata, L. saxatilis, T. repens, and T. subterranean seedlings that survived for at least seven months in both study years, while it additionally lengthened the survival time of A. odoratum and L. perenne in the initial year of experimentation.

What it means
As the atmospheric CO2 concentration increases, dry-land pasture plants common to New Zealand will likely grow more robustly due to increased seed production, dispersal and extended seedling survival periods, in spite of repeated grazing by sheep.  Thus, these pastures will likely increase their carbon-sequestering prowess as these CO2-mediated changes continue to occur.  In addition, the rising CO2 content of the air should help to maintain, and even increase, the biodiversity of these unique pasture communities by increasing the numbers of both common and uncommon species they contain.