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Journal of Biological Sciences

Year: 2007 | Volume: 7 | Issue: 3 | Page No.: 496-505
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Authors

D.M. Musyimi

G.W. Netondo

G. Ouma

Keywords

Research Article

Effects of Salinity on Gas Exchange and Nutrients Uptake in Avocados

D.M. Musyimi, G.W. Netondo and G. Ouma
A study was conducted to evaluate the effect of different salinity levels on the growth, gas exchange, soil respiration and nutrient uptake of 8-month-old-avocado seedlings (var. Puebla) grown under naturally illuminated greenhouse conditions. Plants grown in 4.5 L plastic pots containing soil were subjected to 0 (control), 15, 30, 45 and 60 mM NaCl salinity treatments for eight weeks. The analysis of growth parameters such as stem diameter, leaf number, shoot height, root and shoot dry matter content showed that they were significantly affected by salinity of the growth media at (p<=0.05) at the end of the experiment. Net photosynthetic rate (PN), stomatal conductance (gs), transpiration rate (E), leaf water content and chlorophyll (chl) concentration decreased in response to increasing salt concentration in the growth medium. Intercellular CO2 concentration (Ci) and chloride ions content increased with increasing salt concentration of the growth medium. On the other hand, the uptake of other elements was inhibited by the increasing water salinity. Soil respiration of the rooting medium decreased with increasing salt concentration and this caused a decrease in shoot and root total biomass The high intercellular CO2 concentration observed at the higher salinity levels of 45 and 60 mM NaCl in comparison to control plants may indicate a greater inhibition of CO2 fixation or impairment of the photosynthetic apparatus by the sodium chloride toxicity, while the reduced soil respiration may imply low microbial activity and reduced root respiration in the soil rhizosphere caused by salt toxicity. The results obtained demonstrated that low salinity levels such as 45 and 60 mM NaCl highly inhibited avocado seedling growth, nutrients uptake and gas exchange capacity, under the set experimental conditions and that decline in stomatal conductance is accompanied by inhibition of PN due to salt stress. The results also suggest that soils which are saline or irrigating avocado plants with saline water may inhibit nutrient uptake, photosynthesis and hence retarded growth of the avocado seedlings.
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