When the common plantation tree species A. nilotica is used in Sudan , the seed source is unknown or the seeds come from a mixed seed source. It is not well known how well the different subspecies are adapted to different ecological conditions.
The aim of the present study was to investigate the variation in adaptive morphological and physiological characteristics among three A. nilotica subspecies in Sudan (ssp. astringens, nilotica, tomentosa). Specifically, the aim was to clarify how these characteristics of each subspecies change under varying duration of drought and flooding stress. Parameters such as shoot height growth, shoot diameter, leaf area, number of leaves per seedling, branch forming, dry weight increment and transpiration were measured under nursery conditions. Furthermore, leaf shedding was monitored at different stress or watering intervals during the experimental period.
The experiment was carried out during the summer 2004 in the nursery of the Forest Research Center in Soba, Khartoum , Sudan (15 o 33 N, 32 o 32 E ) . The seeds of the three subspecies were collected in spring 2004 from different locations in Sudan .
Three different experiments were conducted in order to study the adaptation of the three subspecies to different watering regimes. More specifically, the experiments included a drought experiment, a flooding experiment and a recovery experiment. In the drought experiment three irrigation intervals and one control was used. Control seedlings were grown at field capacity, to insure favourable soil moisture conditions. Additionally, three watering regimes were applied in order to expose the seedlings to mild, medium and severe water stress.
In the flooding experiment three flooding periods were used and the experimental seedlings were compared with those of the control treatment. The seedlings were kept under artificial inundation for different periods of time, namely, two weeks, three weeks and four weeks. After the end of each flooding period 12 seedlings were removed from the flooding pool and left to recover for one week. Shoot height and daily transpiration rate were measured during the recovery period.
Publication Year: 2005