A ⁸⁶Rb BIOASSAY TO DETERMINE THE POTASSIUM STATUS OF TREES

Abstract

SUMMARYA bioassay method has been developed to test for potassium deficiency in forest trees; it is based on the metabolic uptake by excised roots of ^*Rb from 5 x 10~® M rubidium chloride solution during a period of 15 min. Betula pubescens Ehrh. seedlings were grown in sand culture supplied with Hewitt's nutrient solution containing K at concentrations between 1 and 200 mg T^ A negative curvilinear relationship was demonstrated between uptake by the seedlings of ^*Rb from the rubidium chloride solution and the concentration of K previously supplied in the growth medium. When roots of intact plants were immersed in ^*Rb-labelled solution for 15 min, less than 1 % of *®Rb taken up was translocated to the shoots. A similar response curve, relating ^®Rb uptake to K supplied to growing plants, was demonstrated when Picea sitchensis (Bong.) Carr seedlings were grown in peat culture with K added at 0 to 400 mg T^ In three field trials of the bioassay, roots were excised from P. sitchensis and Pinus contorta Douglas ex Loud, growing on peat or peaty gley plots where different amounts of fertilizer had been added to give a range of degrees of K deficiency or from unfertilized, control plots. The patterns of ^®Rb uptake by excised roots indicated that the method is potentially useful for the rapid determination of K deficiency in forest trees.

Radial movement of sapwood-injected rubidium into heartwood of Japanese cedar (Cryptomeria japonica) in the growing period

“…This expectation is supported by some experiments, one of which reported that the ratio of radioactively labeled Rb to K was almost constant, regardless of their contents, through the parts of sugar cane [21]. Similar behavior of K and Rb is also reported in uptake via roots by rice plant [22] and tree seedlings [23], indicating validity of using Rb as an analog for K.…”

Uptake of 24Mg by excised pine roots: A preliminary study

“…If this is true, the results is in contrast to the response of plants deficient to P, K and N, which have significantly increased capacity for uptake of these elements (Harrison and Helliwell, 1979;Jones et al, 1987Jones et al, , 1991. The larger increase in atom % 24Mg in Mg-deficient plants during incubations in tracer solutions was reflecting the dilution of tracer in a smaller initial Mg pool, as previously discussed for 15N (H~3gberg et al, 1994), and was borne out when uptake was calculated per unit root dry weight.…”

Nutrient acquisition from different soil depths by pedunculate oak

“…It has been shown in root bioassay studies that the uptake rate of specific nutrients is correlated to the nutrient status of the tree (Jones et al 1987(Jones et al , 1991. However, this should not be a problem when investigating the uptake of nutrients from different soil depths within a tree species, but may cause difficulties when comparing different tree species.…”