Growth and Development in Range Grasses. II. Early Development of Bouteloua curtipendula as Affected by Drought Periods

Seedlings of Bouteloua curtipendula in 2-gallon glazed crocks, grown under wet to dry conditions as regulated by watering at intervals of 3, 6, 12, or 20 days, were subjected to soil-drought periods from 48 to 88 days in length. Plants in the first three series were subjected to drought when 18, 30, and 42 days old, and in the last at 26 and 46 days. Watering was resumed in some pots of each series after 48 days of drought, at intervals of 3 and 12 days. Others were left on drought until approximately 110 days old and were then watered amply to test survival. All plants were harvested at 119 days, except those harvested at the beginning, at the close, and 3 days after the close of the 48-day drought. 2. The few seedlings which failed to survive the 48-day drought, and many of the larger number failing to survive for longer periods, had failed in establishment of adventitious roots, either because of having been placed on drought prior to, or just at, the time of initiation of such roots, or because infrequent watering prevented their establishment. Such establishment seemed to be dependent upon 3 consecutive days of soil-surface wetness. A number of small plants, however, survived 48 days of drought with no established adventitious roots. 3. All stem meristems nearest the ground, and the young foliage surrounding them, were equally and most resistant to the effects of internal water deficit, resuming growth rapidly after watering. Older foliage died during the 48-day drought period. Initiated adventitious root primordia, buried in stem tissues, either died or failed to grow effectively after subjection to 2-3 weeks of water deficit. Many root tips, established in the soil, had apparently survived but resumed growth very slowly after drought, in contrast to stem meristems. 4. There was little differential effect of drought at different ages on the growth produced by all stem meristems which survived. At 119 days, numerous growth measurements were correlated closely with total amount of water supplied during the entire experiment. In general, size was reduced by drought to a greater degree than were numbers of organs differentiated, at least in the 48-day period, as compared with continuously watered controls. 5. Drought, when it prevented establishment of adventitious roots, tended to stimulate the initiation of root primordia on the various axes, both by acceleration of rate of initiation and by increase in total numbers produced on an axis, after watering was resumed.