Mechanism of increased plant uptake of Mn caused by steam sterilization of the soil

摘要

To clarify the mechanisms underlying increased plant uptake of Mn from steam-sterilized soil, we examined the effect of steam sterilization (SS) on Mn-oxide dissolution and its subsequent re-oxidization by Mn-oxidizing microorganisms. Experimental plots subjected to SS or no soil disinfection (CT) were set up in a greenhouse, and planted with tomato seedlings. The amounts of water soluble and exchangeable Mn in the soil after SS treatment were significantly higher than in the CT soil, while the amounts of Mn-oxide were significantly lower. Reducing sugars in the soil water extract were also increased after SS. The ratio of the SS-induced increase in galactose plus mannose to that in arabinose plus xylose was about 0.5, indicating the additional reducing sugars were mainly of plant origin. These results suggested that SS released reducing sugars from plant residues in the soil, in turn causing dissolution of soil Mn-oxide. On the other hand, the activity of Mn-oxidizing microorganisms was reduced by SS, and the slowness of their recovery would also contribute to the increased uptake of Mn by plants from steam-sterilized soils.