Ionomic response of Lotus japonicus to different root-zone temperatures

Abstract

The effects of root-zone temperature (RZT) on the ion uptake, distribution and interactions of 21 (11 essential and 10 non-essential) elements using Lotus japonicus were studied. After acclimation in hydroponics at ambient (25°C) RZT for three weeks, seedlings were exposed to sub-optimal (15°C and 20°C) and ambient RZTs. After one week, plants were harvested and then growth and mineral elements were analyzed. The highest shoot and root biomass was at 25°C and lowest at 15°C RZT. In shoots, the highest concentrations of all elements, except for nickel (Ni), were at 25°C RZT. At lower RZTs, the reductions in concentrations were more evident especially for trace elements and heavy metals. Except for magnesium (Mg), the highest root concentrations were at 15°C RZT for all essential elements. Unlike other non-essential elements, the highest cadmium (Cd) and cobalt (Co) concentrations in roots were at 25°C RZT. The shoot/root ratios of almost all elements were affected by sub-optimal RZTs. Only manganese (Mn) and Co showed increased shoot/root ratio at sub-optimal RZTs; and this ratio decreased for other elements. Nickel in shoots and Mn, Co and Cd in roots tended to be negatively correlated with most other elements (either, essential or non-essential) in each respective organ. The present study showed that RZT significantly changed the ion profile of L. japonicus and suggests possible connection between global warming and phyto-accumulation of heavy metals, especially in temperate regions, since most metals tended to accumulate in shoots at higher RZT.