Root System Development of Prosopis Seedlings under Different Soil Moisture Conditions

Prosopis juliflora (Swartz) DC is one of the most economically and/or ecologically important legumes in arid and semi-arid regions of the world. Prosopis was introduced into Sudan in early 20 century, and succeeded in controlling the expansion of desert in northern Sudan. Recently, however, this species distributes widely and rapidly in eastern Sudan, and induces many problems in human subsistence. To clarify the mechanism of rapid invasion of Prosopis, we investigated the response of seedling roots to different soil moisture conditions. Prosopis seedlings were cultivated twice (seven weeks each) in Desertification Mechanism Analysis System of Arid Land Research Center, Tottori University. Seedlings were cultivated in columns with sandy soils and dripping irrigation once per day. Second experiment was done in columns with four drip irrigations (top, top and middle, middle and bottom, or bottom of columns). Seedlings were carefully harvested, and dry weight and root structure were analyzed. Results were (1) seedlings developed two root systems, one was horizontal root just below the soil surface, and the other was tap root penetrated beyond 1m depth, (2) water supply on the surface increased dry weight and total root length of seedling, (3) seedling developed lateral roots vigorously at higher soil moisture areas. These results suggest that seedling responds sensitively to the increase of soil moisture after the rain, and develops root system flexibly against patches of soil moisture. These properties may enable Prosopis to invade easily into new habitats and distribute widely and rapidly in eastern Sudan.