Effect of Soil Moisture on Growth and Transpiration in Helianthus Annuus

Abstract

Plants of the Russian Mammoth var. were grown in containers holding about 130 lbs. of dry soil under conditions of different holards, using 2 methods: (i) one group of plants was grown in soil in which the holard was maintained near the field capacity by frequent additions of water, while the other group was allowed to remove about [image] of the available soil moisture before the supply was replenished; (ii) 4 groups of plants were grown in soil mixed at predetermined holards, with no water added at any time during the series: in all series lower holard resulted in reduced growth in terms of stem diameter, leaf area, dry weight, and usually in stem height. In expts. using method (i) both water requirement and shoot-root ratio increased with greater available water; in the expts. employing method (ii), neither was altered appreciably. Growth rate in terms of leaf area was affected by even small differences in holard, and was altered by reduced holard long before any effect on stomatal opening or transpiration rate per unit leaf surface could be detected. The rate of transpiration per unit leaf area was ordinarily reduced when about -f of the available soil moisture had been removed, the actual point depending upon the transpiration rate. Stomatal opening appeared to be unaffected unless the holard was reduced to the point where the transpiration rate was lowered. In all cases in which the transpiration rate and stomatal opening were affected, the leaves showed signs of wilting.