An evaluation of soil–plant–water interactions based on the ⁸⁷Sr/⁸⁶Sr, 1/Sr, Ca/Sr, K/Rb and K/Ca ratios of the respective components

Abstract

A 6-month experiment reports on the ⁸⁷Sr/⁸⁶Sr, 1/Sr, Ca/Sr and K/Rb ratios of soil materials, rainwater, soil solutions after percolation through the upper horizon of an alluvial substrate covered by grass, and of the leaves and roots from grass. A correlation between the ⁸⁷Sr/⁸⁶Sr and 1/Sr ratios of the rainwater, soil materials, soil solutions, and grass roots suggests an interconnected supply. Only the data point of the grass leaves plots outside this correlation, suggesting a mix for the Sr, namely from rainwater and soil materials with a different combination. On top of the rainwater supply to the leaves, 0.25 μg/g Sr from atmospheric dust with an ⁸⁷Sr/⁸⁶Sr ratio of 0.7105 is suspected. Based on the Sr contents and ⁸⁷Sr/⁸⁶Sr ratios, the grass roots take up 72 % of Sr from soil solutions and 28 % from rainwater in the case of a dominant interaction between soil solutions and rainwater. If the soil materials and soil solutions are considered dominant in the interaction with the roots, 67 % of the Sr comes from formers and 33 % from latters. If the plants do not only take up but also contribute to the interactions, the feedback represents 33 % of the uptake. In combining the ⁸⁷Sr/⁸⁶Sr and Ca/Sr ratios of the different contributors to the soil/plant/rainwater interactions, 7.4 times more Ca is supplied to the plants by the soil solutions than Sr, its trace equivalent. In the detail, the roots take up 2.4 times more Ca than Sr and the leaves 5.0 times more. Also, about 2.8 times more K is taken up than its trace equivalent Rb, the soil solutions releasing 2.8 times more K than Rb, the roots taking 9.0 times more K and the leaves 18.0 times more K than Rb. Also noteworthy is the fact that the grass roots pick up 2.5 times less K than the leaves compared to Ca. These values apply only to grass.