Science et changements planétaires / Sécheresse


Influence of moderate or severe water stress on the growth of Casuarina glauca Sieb. seedlings Volume 14, issue 3, JUILLET-AOÛT-SEPTEMBRE 2003


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Institut national de recherches en génie rural, eaux et forêts, BP 10, Ariana 2080, Tunisie <Albouchi.aliiresa.agrinet.tn> Faculté des sciences de Bizerte, Jarzouna 7021, Tunisie

The fast growing Casuarina glauca Sieb. tree species, originating from the southeastern coastal regions of Australia, enjoys a wide geographical distribution thanks to its multi‐use potential. In Tunisia, the species was introduced around 1960, initially in the northern humid regions, then its plantation was expanded to include sub‐humid areas, where C. glauca is mainly used for the fixation of coastal sand dunes, the forestation of marginal lands, and as windbreaks in irrigated perimeters. The establishment of the species in the arid regions of Southern Tunisia was not, however, as successful as in the North due to a lack of information on its drought resistance capability. Studying the effects in time of either moderate or severe water stress on some growth parameters of C. glauca may provide some answers for improving the spread of the use of the species in dry zones. To that end, seedlings of C. glauca grown in plastic pots were subjected to two levels of water stress, with pre‐dawn water potentials of either ‐ 0.5 MPa (moderate) or ‐ 1.0 MPa (severe), in addition to a control treatment (no stress) under which the pre‐dawn water potential was maintained at ‐ 0.2 MPa. Relative water content (RWC), plant height, and biomass of roots and shoots were monitored during a 6‐month period following the treatment imposition. Water stress caused a decline in RWC, a reduction in height and total dry biomass. It also caused a greater biomass allocation towards roots to the detriment of shoots. Greater amplifications of these responses were observed as the level of water stress was intensified, particularly during the first 4 months of the study period. Under moderate and severe water stress, the seedlings RWC amounted to 86 and 63%, respectively, while height lagged at 23 and 32% behind that of control plants. The same treatments caused a reduction of 27 and 41% in total dry biomass. During the first months, root biomass of stressed plants was similar to that of unstressed ones, while shoot biomass was reduced by 24 and 45% under moderate and severe water stress, respectively. After four months, these responses were progressively attenuated, indicating an increase over time in the tolerance to drought acquired by the species stressed seedlings. By the end of the study period, no significant reduction in RWC, height, and dry biomass was detected, suggesting that a preconditioning treatment to drought of at least four months before transplantation can effectively contribute to a successful establishment of C. glauca seedlings in arid regions.