Seedling establishment and modeling seedling root depth of Great Basin species

Background/Question/Methods

Millions of dollars are spent annually to seed damaged wildlands but many seeded species fail to establish. Thermal accumulation modeling of rate of root depth can serve as a tool to predict which seeded species are more likely to establish given site specific soil temperature and moisture patterns. In semi-arid areas, species that cannot put roots down as fast as the soil dries down cannot establish as soil resources are only available to plants if roots are in moist soil. Knowing which species are most likely to establish on a site should save money by avoiding the planting of species that are not likely to establish on particular sites. The following species were evaluated: Agoseris heterophylla, Agropyron cristatum X A. desertorum (Hycrest), Agropyron desertorum (Nordan), Astragalus utahensis, Bromus tectorum, Elymus elymoides, Elymus wawawaiensis (Secar), Linum perenne (Appar), Lupinus arbustus (Longspur), and Pseudoregneria spicata (Anatone). The completely randomized block split-plot design included six constant temperature trials at 7, 12, 15, 20, 25, and 30°C and three diurnal temperature trials at 4-12°C, 9-17°C, and 17-25°C. Each root trial had 4 blocks with Borvant gravelly loam and sand, 14 species collections, and 5 replicate tubes per block. Daily root depth was modeled as a function of constant temperature to derive the mean number of days to 15-cm root depth. The inverse of the mean number of days to 15-cm root depth for each constant temperature was used to fit a temperature response curve that predicted days to 15-cm root depth in diurnal temperature trials.

Results/Conclusions  

Most species temperature response curves had an r² greater than 0.9. Days to 15-cm root depth were converted to degree days by summing the daily average temperatures for each day of a root trial until the 15-cm root depth had been achieved. The results have shown that growth chamber thermal accumulation modeling accurately predicted degree days to 15-cm root depths for several species. Most species required 100 to 350 more degree days to achieve desired root depths in sand than soil. In the soil, Invasive annual B. tectorum required fewer degree days to 15-cm root depth with 150 to 200 degree days than the forbs with 350 to 750 degree days in the 4-12°C and 9-17°C root trials. Perennial grasses required an intermediate number of degree days to 15-cm root depth with 250 to 350 degree days.