دانلود مقاله شماره  20

تحمل به خشکی در گیاهان گوشنی و ابدار

Salinity Tolerance of Cacti and Succulents

Abstract
The salinity tolerance of golden barrel cactus (Echinocactus grusonii), ocotillo (Fouquieria splendens), saguaro cactus (Carnegiea gigantea), and Gentry’s agave (Agave parryi truncata) was tested.  Plants were irrigated with a solution of EC 0.6, 5.0, 10.0, and 15.0 dS/m. Duration of treatments were 18 weeks for saguaro and 26 weeks for the other three species.  In general, fresh weight, dry weight, and moisture content decreased with increasing salinity levels, with the exception of saguaro dry weight which was not affected by the treatments, and ocotillo moisture content which increased with increasing salinity.  Runoff was collected three times during the experiment and indicated that ion uptake was higher for barrel cactus than the other three species.  EC of runoff averaged for all dates and species showed an increase of 17%, 54%, 46%, and 64% over the salinity treatment solutions  of 0.6, 5.0, 10.0, and 15.0 dS/m, respectively.  

Introduction
Salinity is a problem in many arid regions of the world, including the Southwestern United States.  Deteriorating water quality exposes cacti and succulents in urban landscapes to increasing salinity conditions.  Unless higher leaching fractions are used, salts will accumulate in the root zone of plants when irrigation water of higher salinity is used. In addition, with drought becoming a common occurrence each year in the arid southwest, it is possible that water restrictions will be imposed in response to drought emergencies, which will cause potential issues of both salinity and drought for plants in urban landscapes.  Large numbers of cacti and succulents are already established in Southwest landscapes and many more are planted each year in the rapidly increasing urban developments.  Although these plants are generally considered tolerant to drought, no data exists as to their salinity tolerance.  It is well established that drought tolerance and salinity tolerance have different mechanisms and therefore tolerance to one stress does not confer tolerance to another. With the likelihood of increasing soil and water salinity in the Southwest, it seems prudent to obtain knowledge regarding the salinity tolerance of commonly planted cacti and succulents.  The ive of this research was to determine the salt tolerance of four species of succulents and cacti and to determine ion concentration in runoff.

Materials and Methods
Golden barrel cactus (Echinocactus grusonii), saguaro cactus (Carnegiea gigantea), ocotillo (Fouquieria splendens), and Gentry’s agave (Agave parryi truncata) were transplanted into 2-gallon (5.4 L) containers with a mix of sand and pumice (50/50 vol.).  Plants were grown outdoors in full sun at the Campus Agriculture Center of
he University of Arizona in Tucson, Arizona from May to November 2006.  Duration of treatments were 18 weeks for saguaro and 26 weeks for the other three species.  Plants were irrigated with a fertilizer solution containing 50 ppm N augmented with a 3:1 ratio of sodium chloride and calcium chloride to obtain salinity levels of EC 0.6, 5.0, 10.0, and 15.0 dS/m.  Eight replicate plants per species were assigned to each salinity treatment.  Plant dry weight, moisture content of shoots and mineral tissue analysis were determined at the end of the experiment.  Runoff was captured and analyzed three times at 7-week intervals.

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