Nonstructural Carbohydrates and Spring Regrowth of Two Cool-season Grasses: Interaction of Drought and Clipping

The role that accumulated carbohydrates play in plant regrowth has been discussed for over 60 years. However, few quantitative studies have been published on the importance of carbohydrates for regrowth in early spring after plants have been exposed to periods of either drought or drought plus defoliation. We examined the relationship between total nonstructural carbohydrate (TNC) concentrations and pools (biomass × concentration) and spring regrowth for crested wheatgrass [Agropyron desertorum Fisch. ex Link) Schult.] and bluebunch wheatgrass [Pseudoroegneria spicata (Pursh) A. Löve ssp. spicata; Syn: A. spicatum (Pursh) Scribn. and Smith] with and without clipping under drought, natural, and irrigated conditions. In spring 1985 and early spring 1986, after 1 or 2 years of clipping, crown and root TNC concentrations and TNC pools per tiller were generally similar for clipped and unclipped plants of both species. Nonstructural carbohydrate concentrations in crowns and roots did not relate to rate or total production of dark regrowth in mid-spring 1985 and early spring 1986. In early spring 1986 following 2 years of repeated treatments, crown and root TNC pools were on average 7 times higher under drought, in both clipped and unclipped plants, than they were under the higher moisture-level treatments for both species. The large pools of TNC in drought-treated plants appeared to enhance the production of dark regrowth when meristematic limitations on growing tillers did not exist in early spring. These results suggest that plants exposed to prolonged periods of drought or drought plus defoliation may have rapid initial regrowth upon alleviation of these stresses because high amounts of TNC may have accumulated in their storage organs during stress. In addition, the results suggest that high TNC availability facilitates growth only when meristematic activity is high