Multiple climate change treatments interact on germination thresholds of native and invasive species in the Mixed-grass Prairie

Background/Question/Methods:

The effects of global change conditions on seed germination and plant regeneration have been reported in many species. However, there are no consistent trends within and among plant functional groups (C3 vs C4) regarding how seed quality and germinability are affected by these climate change conditions. Seeds of three native and two invasive species were collected from the USDA-ARS Prairie Heating and CO₂ Enrichment Experimental plots in 2007 and 2008. This facility is located in the Mixed-grass Prairie near Cheyenne, WY. Field treatments include ambient (375 ppm) and enriched (600 ppm) CO₂, ambient and elevated (1.5/3.0°C day/night) temperature, and deep and shallow irrigations. Seed quality was evaluated and germination tests were conducted under alternating temperatures with the amplitude of 10°C. Thermal time requirements and base temperatures for germination were determined using thermal time models.

Results/Conclusions:

Treatment effects on seed quality and germination varied among species, years and germination temperatures. There were no treatment effects on seed fill percentage of Bouteloua gracilis (C4, 2007), Koeleria macrantha (C3), Stipa comata (C3), Chenopodium leptophyllum (C3), or Salsola iberica (C4). Heating increased seed fill percentage and seed viability of B. gracilis in 2008 compared to deep irrigation. Heating, either alone or combined with enriched CO₂, increased seed viability of K. macrantha. Enriched CO₂ and irrigation decreased while heating increased germination percentage of B. gracilis in 2008 at 15/5°C and 25/15°C. Enriched CO₂ and heating tended to increase germination percentage of S. iberica, while germination of C. leptophyllum was reduced by all treatments. Thermal time requirements of B. gracilis were decreased by all treatments, favouring early and fast germination. Heating and deep irrigation decreased the base temperature but increased thermal time requirements in S. iberica. Results suggest that species specific changes in seed quality and germinability as affected by climate change conditions will exert substantial cumulative effects on community composition in the long run. The distribution and abundance of invasive species C. leptophyllum (C3) may be reduced while native species B. gracilis (C4) may be favoured by global climate change.