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item Sinclair, Thomas
item Ray, Jeffery - Jeff
item Premazzi, Monica
item Mislevy, Paul

Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/2002
Publication Date: 4/1/2004
Citation: Sinclair, T.R., Ray, J.D., Premazzi, M.L., Mislevy, P. 2004. Photon flux density influences grass responses to extended photoperiod. Journal of Experimental Botany. 51:69-74.

Interpretive Summary: Previous research has shown that the growth of four forage grasses was stimulated during the winter months by extending the daylength to which the plants were exposed. These results demonstrated that forage yields of these grasses in the winter could be enhanced by overcoming the daylength control of plant growth. This research, involving an ARS-USDA scientist located at Gainesville, FL, was undertaken to further elucidate the response of these grasses to the extended daylength. In particular, the influence of the light intensity during the period of extended daylength was studied for a possible influence on grass growth. It was found that there was a linear increase in plant growth as the light intensity increased. The light intensity influence, however, was eventually saturated but the saturation light intensity differed among the four grasses. These results document differences in behavior among the grasses that could be exploited to better understand the mechanisms controlling plant response to changes in daylength.

Technical Abstract: Plant sensitivity to extended photoperiod has been well documented, with little attention to the possibility that quantum flux density used to extend photoperiod has an influence on the expression of photoperiod response. This study was undertaken with 4 grass species under field conditions to examine their photoperiod response under a quantum flux density gradient. The experiment was undertaken during 2 seasons of short daylengths and plant response was measured as mass accumulation and height. All 4 species were sensitive to the extended photoperiod as shown by enhanced mass accumulation and greater height development as compared to a treatment without extended photoperiod. There was a linear increase in mass and height with increasing quantum flux density to a saturating quantum flux density. Saturating quantum flux density was generally consistent within a species for mass accumulation and height, but had substantial differences among species. Species with the greater relative increase in mass accumulation for the extended photoperiod also were found to require the greatest quantum flux density for saturation. These results highlighted an intriguing interaction between response to extended photoperiod and quantum flux density.