Temperature and CO2 Affect Yield, Root Biomass, and Nutritive Value of Canadian Tame and Native Forage Species.

Atmospheric CO₂ concentration could reach between 500 and 800 μmol mol^-1 by the end of the century while summer temperature is predicted to increase by 2 to 3ºC. Plants grown under elevated CO₂ generally exhibit enhanced photosynthesis and biomass production while growth and nutritive value may be negatively affected by air temperatures slightly above current values. In Canada, range and forage species occupy 36 million ha and understanding the impact of climate change on these sustainable plant communities is required. The objective of this project was to determine the impact of IPCC-predicted climate change scenarios (temperature, CO₂, and their interactions) on yield and nutritive value of tame and native forage species used in Canada. We also wanted to assess the impact of temperature and CO₂ on C sequestration by assessing root biomass and degradability. Ten forage species were tested including the C3 grasses Kentucky bluegrass, western wheatgrass, timothy, meadow brome, tall fescue and reed canary grass, the C4 grasses little bluestem and blue gramma, and the legumes alfalfa and red clover. Plants were grown from seeds in growth chambers under either 400 or 500 ppm of CO₂ and under 22/10 or 25/15^oC D/N temperatures. Yield, nutritive value, root biomass, and degradability were measured on two growth cycles. Inoculated legumes showed the largest yield increase (+40%) in response to an increase in atmospheric CO₂. Yield of C4 grasses was higher under the 25/15ºC than under the 22/10ºC temperature regime while for C3 grasses, the response was reversed. Root biomass responded similarly but to a lesser extent to increased CO₂ and temperature. Our results also highlight a complex interaction between CO₂, temperature, and species.

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