Clipping effects on root architecture and morphology of 3 range grasses

Although defoliation is known to affect root growth in range plants, little information is available concerning the effect of defoliation on root architecture and its relationship to root morphological characteristics. This study evaluated the influence of clipping on root architecture and morphology of 3 range grasses from the Intermountain West: 'Whitmar', a cultivar of bluebunch wheatgrass [Pseudoroegneria spicata (Pursh) A. Love]; 'Hycrest', a cultivar of hybrid crested wheatgrass [Agropyron desertorum (Fisch. ex Link) Schult. X A. cristatum (L.) Gaert.]; and cheatgrass (Bromus tectorum L.). Greenhouse-grown seedlings were clipped once or twice at 3 intensities of defoliation (0, 50, and 70 %). The topology (pathlength-slope index), geometry (link length and root diameter), and morphology (total root length and specific root length) of roots of the 3 grasses were evaluated 28, 35, and 42 days after planting. Root topology (Peslope index) did not vary among defoliation treatments but did vary among species across harvests. Root branching of the grazing-tolerant Hycrest decreased through time, while root branching of the grazing-sensitive Whitmar increased through time. Cheatgrass maintained a highly branched root system throughout the experiment. Specific root length in Hycrest and Whitmar decreased through time, indicating that roots became coarser with age. Similar to its topological response, cheatgrass did not exhibit changes in specific root length through time. There were apparent tradeoffs between link lengths of the main axis and lateral roots of the seminal root, which may lead to important changes in root branching density, root production costs, and probably root function.