• Dehydration effects on seedling development of four range species

      Bassiri, M.; Wilson, A. M.; Grami, B. (Society for Range Management, 1988-09-01)
      The effects of temporary drought periods of semiarid regions were simulated by dehydration of germinating seeds of crested wheatgrass (Agropyron desertorum), Russian wildrye (Elymus junceus), alfalfa (Medicago sativa), and cicer milkvetch (Astragalus cicer) in 8 constant humidity environments, ranging from -10 to -220 MPa for 4 days. Combined effects of root excision and temporary dehydration at -22 to -160 MPa were also studied. Subsequent growth of seedlings was evaluated in growth performance tests under favorable soil moisture conditions. When the initial roots were killed by dehydration, survival of grasses depended on the development of seminal lateral root(s) from the scutellar nodes, and survival of legumes depended on development of a new meristem at the distal end or along the side of hypocotyl-root axis. The effect of dehydration was more drastic on the legumes than on the grasses, particularly at more severe conditions. While temporary dehydration of -59 MPa had little effect on grasses, it reduced the percent emergence of the legumes by about 70%. In the -220 MPa treatment, emergence percentages of crested wheatgrass, Russian wildrye, alfalfa, and cicer milkvetch were 59, 35, 6, and 1, respectively, and percentages of rooted seedlings were 58, 12, 3, and 1, respectively. Under combined effects of excision and dehydration at -160 MPa, emergence percentages of the 4 species were 50, 34, 14, and 0, respectively, and their root lengths decreased by 37, 42, 44, and 100%, respectively. Within species variation in tolerance of dehydration suggested opportunities to select and breed for this characteristic.
    • Root excision and dehydration effects on water uptake in four range species

      Bassiri, M.; Wilson, A. M.; Grami, B. (Society for Range Management, 1988-09-01)
      Germinating seeds of crested wheatgrass (Agropyron desertorum), Russian wildrye (Elymus junceus), alfalfa (Medicago sativa), and cicer milkvetch (Astragalus cicer) were dehydrated for 4 days at -22 MPa, and/or their roots were excised, and used as treated materials. In an experiment in root growth boxes, where the seedlings depended for 60 days on the initial soil water supply, seminal primary and seminal lateral roots of grasses penetrated to the same depth. Both types of roots were similarly effective in taking up water, mainly from the upper 50 cm of the soil profile. In a sealed pot experiment under favorable moisture conditions, water uptake increased with seedling age up to 34 and 41 days for crested wheatgrass and Russian wildrye, respectively, and up to the end of the experiment (53 days) for the legume species. Leaf area of grasses was not affected by root excision alone, but it decreased due to the combined effects of root excision and temporary dehydration. Leaf area was generally proportional to water uptake within each species. In all 4 species, root excision and temporary dehydration did not affect transportation rates, while transportation rate decreased as a function of age. Transportation rates were higher in legumes than grasses and were higher in Russian wildrye than crested wheatgrass.