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Title: EFFECT OF TEMPERATURE AND CO2 ON FORAGE NUTRITIVE VALUE OF 'PETE' EASTERN GAMAGRASS

Author
item Gitz, Dennis
item Ritchie, Jerry
item Krizek, Donald
item Springer, Timothy
item Reeves Iii, James
item Reddy, Vangimalla

Submitted to: Eastern Native Grass Symposium
Publication Type: Proceedings
Publication Acceptance Date: 7/15/2006
Publication Date: 10/10/2006
Citation: Gitz, D.C., Ritchie, J.C., Krizek, D.T., Springer, T.L., Reeves III, J.B., Reddy, V. 2006. Effect of Temperature and CO2 on Forage Nutritive Value of 'Pete' Eastern Gamagrass. IN: Sanderson, M.A., Adler, P., Goslee, S., Ritchie, J.C., Skinner, H., and Soder, K. (Editors). Proceedings of the Fifth Eastern Native Grass Symposium, October 10-13, 2006, Harrisburg, Pennyslvania. p107-114.

Interpretive Summary: Eastern gamagrass is a warm season perennial C4 bunchgrass native to the Americas. It is also of interest as a potential forage plant because it can be grown on a range of soils and is tolerant to drought and flooding. It has been suggested as a forage crop which could be used to extend forage production into the Summer, when heat and drought become a problem with more traditional cool season grasses. We investigated how gamagrass forage quality would respond to high carbon dioxide and high temperature, conditions associated with global warming. We found that gamagrass is extremely responsive to temperature, but less sensitive to carbon dioxide levels. Forage harvested from low temperature grown gamagrass is more nutritious and more digestible than high temperature grown gamagrass. We found that with increasing carbon dioxide, lignin content increased slightly in all portions of the plant (leaves, crowns, and roots). First cuttings of gamagrass in the Spring might be more nutritious than later harvests simply because of lower temperatures during production. This may explain, at least in part, why warm season grasses grown in northern climates, exhibit superior forage nutritive value to those grown in warmer regions. Results of this work are expected to benefit growers and breeders.

Technical Abstract: It is becoming generally accepted that two features of future global climate will be increased temperatures and carbon dioxide levels. The potential for such climate change effects on forage quality in native grass species has not been investigated. Eastern gamagrass [Tripsacum dactyloides (L.) L.] was grown in one cubic meter bins filled with a sand:vermiculite mix with regular fertigation with a complete nutrient solution in closed transparent cuvettes (Soil Plant Atmosphere Research (SPAR) chambers) at 370 or 740 mol mol-1 CO2 and 20/14°, 27.5/21.5° or 35/29°C day/night temperatures. Plants were allowed to develop from mid-May to mid-October. Leaves were clipped at 8 and 16 weeks and whole plants (roots, crowns, leaves) were harvested at 21 weeks. Eastern gamagrass leaves grown at 20°C had the highest in vitro dry matter digestibility (68% IVDMD), the least fiber (69% NDF, 34% ADF, 3.9% Lignin), and the highest protein content (18% crude protein by combustion). Growth at 35°C reduced both IVDMD and protein content by about 17%. On average, forage from plants grown at the current ambient CO2 level was slightly higher in IVDMD (about 62%) than that of enhanced CO2 grown plants (IVDMD of about 61%). Levels of CO2 had no effect on crude leaf protein content. We found a slight but consistent and significant effect of CO2 on forage nutritive value for this native grass species. Temperature effects were much more pronounced. The results suggest that the higher protein content of first cuttings of eastern gamagrass, and of eastern gamagrass grown in cooler climates, might result from a developmental response to temperature in addition to such generally recognized factors as water availability and canopy phenology.