Salinity and temperature effects on CO2 assimilation in leaves of avocados.

Abstract

Young avocado plants were cultured in a glasshouse and subjected to salt stress or were well watered at Maseno University between September 2003 and September 2004. Three-month-old avocado seedlings were grown in 4.5 L pots containing soil and daily irrigated with 300 mL of NaCl concentrations of 0 (control), 15, 30, 45 and 60 mM NaCl. Growth conditions in the greenhouse were: temperature: min/max 20/40°C and relative humidity: min/max 50/95%. The data collected included shoot height, number of leaves per plant, stem diameter growth, root fresh and dry weight, shoot fresh and dry weight, chlorophyll concentration and gas exchange parameters. There were significant differences in growth parameters measured except plant height. A slight increase in shoot height and stem diameter was observable at low salt concentrations (15 and 30 mM NaCl) within the first sixteen days of salt application. Chlorophyll concentration decreased with increasing salt concentration of the growth medium. Photosynthetic rate, stomatal conductance, transpiration rate and intercellular CO2 concentration decreased significantly with increasing salt concentration. The decrease in photosynthetic rate was only partially to stomatal closure. Salt stress was found to cause irreversible and visible damage, such as leaf tip burn, leaf scorching and death of the plants.