Seedling growth of intermountain perennial and weedy annual grasses

Abstract

Squirreltail [Elymus elymoides (Raf.) Swezey] is a native cool-season grass that has been observed to invade rangelands dominated by the weedy annual grasses, cheatgrass (Bromus tectorum L.) and medusahead wildrye [Taeniatherum caput-medusae (L.) (Nevski]. Our objective was to determine if growth characteristics could account for this squirreltail trait. We used growth analysis to examine differences in seedling growth and tissue allocation of 5 squirreltail entries, 2 long-lived perennial grasses ('Goldar' bluebunch wheatgrass [Pseudoroegneria spicata (Pursh) A. Löve] and 'Hycrest' crested wheatgrass [Agropyron desertorum (Fisch. ex Link) Schult. X A. cristatum (L.) Gaertn.]), cheatgrass, and medusahead wildrye. We monitored the 9 entries in a greenhouse for mean relative growth rate, net assimilation rate, leaf area ratio, specific leaf area, leaf weight ratio, root relative growth rate, specific root length, root-to-shoot dry-mass ratio, and root length-to-leaf area ratio beginning 10 days after sowing at 9 destructive harvests at 3-day intervals. Cheatgrass had high relative growth rate for both shoot and root. Only medusahead wildrye equalled the shoot relative growth rate of cheatgrass, and only Hycrest equalled its root relative growth rate. Cheatgrass seedlings were larger than squirreltail seedlings by 2 to 3 weeks after emergence. Few differences were detected among perennials and medusahead wildrye. Cheatgrass displayed the highest leaf area ratio and specific leaf area of the 9 entries but was similar to medusahead wildrye and Red Deer River squirreltail for specific root length. Growth characteristics cannot account for squirreltail's observed ability to invade annual grass stands. However, the combination of high specific leaf area and specific root length in squirreltail germplasm, as found in cheatgrass, may enhance squirreltail survival under competition with annual grasses, especially medusahead wildrye.