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Calcium and Strontium Transport to Plant Roots¹

ABSTRACT

Mass-flow and diffusion of Ca and Sr to tomato (Lycopersicon esculentum) roots were studied in two exchange resin rooting media. Six harvests were made from plants grown over a 26-day period under low and high humidities in a growth chamber. With low humidity, the rate of supply of Ca and Sr by mass-flow exceeded uptake rate during the entire growth period. Under high humidity, the rate of mass-flow supply exceeded uptake only until the second harvest, thereafter diffusion became the dominant supply mechanism.

The Ca/Sr ratio of uptake was compared with the Ca/Sr ratios on the resins and in solutions to determine the source of Ca and Sr. Supply by mass-flow came from the solution, where-as supply by diffusion apparently came mainly from the exchangeable fraction indicating exchange diffusion was important. Both log of root length and log of water uptake were linearly correlated with time for the 26-day growth period investigated. The rate of water absorption ranged from 1.1 x 10^-7 to 6.0 x 10^-7 cm³/cm of root per sec.

The root uptake coefficient for Ca uptake varied between 1.43 x 10^-6 and 2.72 x 10^-6 cm/sec and for Sr 1.0 x 10^-6 to 2.38 x 10^-6 cm/sec where an average root radius of 0.015 cm was used in the calculations.

Contribution from the Dep. of Agronomy, Purdue Univ. Agr. Exp. Sta., Lafayette, Ind. 47907. Journal Paper no. 4705. This research was supported in part by the US Atomic Energy Commission under contract AT (11-1)-1495.

² Research Associate, Graduate Assistant, and Professor of Agronomy, Purdue University, respectively. The senior author is now Associate Professor of Environmental Science, Dep. of Natural Resources and Environmental Science, Alabama A&M Univ., Huntsville.

Received for publication March 28, 1972. Accepted for publication June 9, 1972.