Ion selective electrodes for measurement of sodium and chloride in salinity experiments

Abstract

A method of measuring sodium (Na⁺) and chloride (Cl^‐) content of plant tissue and root uptake of these ions using ion selective electrodes (ISE) was developed and tested. Peach [Prunus persica (L.) Batsch.] and barley (Hordeum vulgare L.) plants were grown for 52 days in solution culture with up to 50 and 100 mM NaCl added, respectively. During this time, samples of nutrient solution were collected at the beginning and end of four time periods to estimate the amount of Na⁺ and Cl^‐ extracted. At the end of the experiment, plants were destructively harvested to determine the concentration of Na⁺ and Cl^‐ in tissues. Values obtained with Na⁺ and Cl^‐ ISEs were compared against inductively coupled plasma spectrometry (for Na⁺) or Bran‐Leubbe autoanalyzer (for Cl") at independent laboratories. Readings of Na⁺ and Cl^‐ in plant tissue obtained by ISEs were highly correlated with those obtained from independent labs, with average errors of 1.3% for Na⁺ and 6.3% for Cl^‐. Both ISEs also read nutrient solution samples with 25,50, and 100 mM added NaCl to within 5% of known values. Cumulative uptake during the study (calculated by summing Na⁺ and Cl^‐ uptake during the 4 time periods) over‐predicted the total amount of these elements found in plant tissue at the end of the study. However, total ion content estimates from cumulative uptake and plant tissue analysis were highly correlated (r²>0.90), suggesting that nondestructive measurements of ion uptake would allow separation of plant species with differing capacities for Na⁺ or Cl^‐ exclusion. Collectively, the data suggest that ISEs provide a simple, inexpensive, and accurate alternative to standard methods of Na⁺ and Cl^‐ measurement in salinity studies.