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Effects of Temperature and Clipping on Growth, Carbohydrate Reserves, and Root Exudation of Western Wheatgrass in Hydroponic Culture¹

The objective was to investigate the influence of three temperature regimes (13/7C, 24/13C, 29.5/18C day/night) and clipping (moderate and severe) treatments on the growth, total nonstructural carbohydrates (TNC), and root exudations of western wheatgrass (Agropyron smithii Rydb.). The mean growth rate of unclipped plants continued to increase with increasing temperature (from 13/7 to 29.5/18C) up to 50 days followed by a decline during subsequent growth at 24/13 and 29.5/18C. The growth rate of clipped plants was higher than the unclipped controls except for the short duration of 10 days following the clippings. Greatest growth rate occurred under moderate clipping and the next greatest under severe clipping compared to the unclipped (control) plants; crown and root growth of clipped and unclipped plants was greater at 24/13 than at 13/7 or 29.5/18C. Shoots of clipped plants continued to grow throughout the 80-day experimental period, but those of unclipped plants ceased to show any positive dry matter accumulation after 50 days.

The TNC concentrations in the shoots, crowns, and roots of control plants were greater at 24/13 than at 13/7 or 29.5/18C. Concentrations in the three organs of clipped plants declined following clippings, more so in severely than in moderately clipped plants. Severe clipping and high temperature treatments appeared to have a stimulatory effect on root exudations.

This study indicated that decline in the growth rate of this cool season grass following maturity was more marked at higher temperatures (29.5/18C) than at lower temperatures, giving a higher overall growth rate for plants at 13/7C. In general, clipping treatments stimulated shoot growth and also increased the potential growth period of the plant. Evidence suggested that reserves in crowns and roots were not utilized to any marked degree for the regrowth of shoots following clipping.

Key Words: Relative growth rate • Total nonstructural carbohydrates (TNC) • Growth analysis • Agropyron smithii Rydb.

² U.S. International Biological Program Grassland Biome, Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO 80523. Dr. Singh was on leave from Department of Botany, Kurukshetra University, Kurukshetra, India.

Received for publication January 9, 1974.

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