Effects of the coordination mechanism between roots and leaves induced by root-breaking and exogenous cytokinin spraying on the grazing tolerance of ryegrass |
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Authors: | Xiao-Ling Wang Dan Liu Zhen-Qing Li |
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Institution: | (1) State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing, 100093, China;(2) College of Agronomy, Henan University of Science and Technology, Luoyang, Henan, 471003, China |
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Abstract: | The grazing tolerance mechanism of ryegrass was investigated by examining the effects of roots on leaves under frequent defoliation.
The study consisted of four treatments: (1) with root breaking and cytokinin spraying, (2) root breaking without cytokinin
spraying, (3) cytokinin spraying with no root breaking, and (4) no root breaking and no cytokinin spraying. Results showed
that root breaking or frequent defoliation inhibited the ryegrass regrowth, which resulted in low biomass of the newly grown
leaves and roots, as well as low soluble carbohydrate content and xylem sap quantity in the roots. Spraying with exogenous
cytokinin promoted the increase in newly grown leaf biomass, but decreased root biomass, root soluble carbohydrate content,
and root xylem sap quantity. Determination of gibberellic acid, indole-3-acetic acid, abscisic acid, and zeatin riboside (ZR)
in roots, newly grown leaves, and stubbles showed that cytokinin is a key factor in ryegrass regrowth under frequent defoliation.
Root breaking and frequent defoliation both decreased the ZR content in roots and in newly grown leaves, whereas spraying
with exogenous cytokinin increased the ZR content in roots and in newly grown leaves. Therefore, cytokinin enhances the above
ground productivity at the cost of root growth under frequent defoliation. |
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