Energy Levels of Water in a Community of Plants as Influenced by Soil Moisture

Free energy levels of plant water were measured during July and August in two communities of annual plants. One set of plants was irrigated, while the other grew on a silt loam soil that became increasingly drier. The different species of plants had widely varying levels of water potential on both the moist and dry soils. The more drought-tolerant plants on the dry soil had the lowest afternoon plant water potentials even though they had the most vigorous root systems (lamb's quarter, kochia, sugar beets, and sunflower). Some of the more drought-tolerant plants also had low water free energies when growing on moist soil. Most of the plants growing in the dry sea gained enough water during the night to raise their water potentials above that of the soil surrounding the bulk of their roots.