Effects of temperature and relative humidity on growth and calcium uptake, translocation, and accumulation in sorghum1

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Abstract
Differences in temperature or relative humidity may partially explain some of the visual appearances of calcium (Ca) deficiency disorders found in sorghum [ Sorghum bicolor (L.) Moench] plants grown in controlled conditions. Independent temperature and relative humidity (R.H.) experiments were conducted using ‘Redlan’ and ‘Martin’ sorghum genotypes grown in three identical growth chambers with temperature treatments of 21/16, 28/23, and 35/30°C or R.H. regimes of 30, 60, and 90% at nutrient solution Ca levels of 25, 50, and 300 mg Ca L‐1. Calcium deficiency symptoms appeared on plants grown with the lowest Ca level at each temperature or R.H. Symptoms became progressively more severe as the temperature increased and were most severe at 60% R.H. The severity of deficiency was higher in Redlan than Martin in the R.H. experiment, but no differences between genotypes appeared with changing temperatures. Plant dry matter and Ca concentrations in plants increased with increasing Ca levels. Lower leaves had higher Ca concentrations than upper leaves reflecting Ca immobility. Mean Ca concentrations in plants was highest at the lowest temperature and more dry matter was accumulated in roots at this temperature. Reduction in root growth at the 35/30°C temperature and a subsequent reduction in Ca absorption could explain the lower plant Ca concentrations for this temperature treatment. Dry matter yield of plants grown with 300 mg L‐1 Ca was greatest at the medium temperature although dry matter yield generally increased as temperature declined. Lowest mean Ca concentration in leaves of plants occurred in plants at 90% R.H. Maximum dry matter yields occurred at 30% and minimum yields at 60% R.H. These results suggested that Ca absorption may be slowed in sorghum at high temperatures and relative humidities. A high rate of transpiration appears to enhance Ca mobility. Conditions detrimental to root growth inhibit adequate Ca absorption.