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a USDA-ARS, Crop Genetics and Production Res. Unit, P.O. Box 345, Stoneville, MS 38776 USA
bpettigr{at}ag.gov
Potassium deficiency reduces lint yield and causes fiber quality problems for cotton (Gossypium hirsutum L.) producers throughout the U.S. production regions. This deficiency produces plants exhibiting reduced leaf area but increased specific leaf weights (SLW). The objectives of this research were (i) to determine whether the alterations in leaf growth produced by a K deficiency are associated with changes in leaf carbohydrate levels or leaf water status and (ii) to determine if a K deficiency alters the carbohydrate concentration in root tissue. Field studies were conducted in 1993 and 1994 using four genotypes (`DES 119', `MD 51 ne', `Prema', and `STV 825') and two levels of K fertilization (0 and 112 kg K ha-1). Glucose, fructose, sucrose, and starch concentrations were quantified for leaves collected at three different dates in both years. Root carbohydrate concentrations were determined once in each growing season. Leaf water potential and its components were determined once each growing season using thermocouple psychrometers. Glucose was the only carbohydrate whose leaf concentration was consistently altered by the K deficiency; it was increased an average of 84% across all leaf harvest dates. Leaf concentrations of starch, sucrose, and fructose were inconsistent in their response to variation in K levels. The K deficiency increased root tissue concentrations of starch by 82%, glucose by 14%, and fructose by 27%, averaged across years. Although leaf water potential (
l) and leaf osmotic potential (
) were unaffected by varying the level of K fertilization, leaf turgor (t) averaged across both years was increased 17% in leaves from the K-deficient plants. The elevated carbohydrate concentrations remaining in source tissue, such as leaves, appear to be part of the overall effect of K deficiency in reducing the amount of photosynthate available for reproductive sinks and thereby producing reductions in lint yield and fiber quality seen in cotton.
Abbreviations: CDT, central daylight time • DAP, days after planting • gs, stomatal conductance • LAI, leaf area index • SLW, specific leaf weight • l, leaf water potential • t, leaf turgor potential • , leaf osmotic potential
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