Potassium Availability and Isotopic Fractionation in Arabidopsis thaliana: Exploring Nutrient Uptake Systems

Abstract

Potassium (K), magnesium (Mg), and calcium (Ca) are vital macronutrients in plant biochemistry, regulating plant growth, nutrient and metabolite transport, responses to environmental stresses, etc. K and N fertilizers are frequently applied to crops while Mg and Ca are usually applied when deficiency is expected. This thesis investigates how varying K concentrations affect nutrient uptake in plants, particularly in Arabidopsis thaliana, using a controlled hydroponic experiment setup. Plants regulate potassium uptake through specialized transport systems. When potassium is limited (<0.1 mM), plants tend to depend on high-affinity transport systems (HATS) to uptake potassium, whereas low-affinity transport systems (LATS) dominate when potassium levels are plentiful (>0.1 mM). Previous experiments revealed that at 0.10 mM external potassium, plants exhibited δ⁴¹K isotopic signatures in line with HATS, employed under stressed conditions without showing significant reductions in plant K acquisition relative to plants grown in more replete potassium environments. To address the gaps from the previous experiments, we examined intermediate potassium concentrations to evaluate whether a gradual transition or a step change would occur between HATS and LATS. Our results demonstrate that δ⁴¹K values become more negative with rising potassium availability. Plants grown at 0.33 mM potassium displayed intermediate δ⁴¹K, suggesting the concurrent operation of both transport systems. In contrast, δ⁴⁴/⁴⁰Ca and δ²⁶Mg remained stable across varying potassium conditions, indicating that their uptake is not dependent on external potassium availability. Additionally, based on the observed relationship between δ⁴¹K and δ15N, potassium availability may have an influence on nitrogen source utilization in plants (NO3 or NH+4). These findings demonstrate how nutrient availability affects uptake mechanisms and isotopic fractionation, providing new insights to achieve more sustainable agriculture practices.