Microtome sectioning causes artifacts in rhizobox experiments

Experimental data on rhizosphere characteristics at high spatial resolution are required to improve our knowledge on phytoavailability of nutrients and pollutants. In numerous studies, sectioning using refrigerated microtomes has been employed to obtain thin soil layers at defined distances from the root surface. In this study, we assessed the effect of thin slicing and freezing on soil chemical characteristics. Two experimental soils were frozen at –20°C and sliced using a refrigerated microtome. In general, chemical changes relative to the non-sliced control were more pronounced as the trim thickness (thickness of a single slice) decreased. Maximum increases in pH and electrical conductivity (EC) for the smallest trim thickness used (20 m) were 0.9 units and 50%, respectively. Extractable fractions of P (0.5 M NaHCO₃) K, Mg, Mn, Na and Si (1 M NH₄NO₃) increased up to 40, 91, 19, 621, 50 and 100%, respectively. Based on these results, we suggest to use a trim thickness of 200 m. Apart from slicing, freezing (a prerequisite for the microtome technique) was found to bias soil chemical parameters. To circumvent microtome-related artifacts we present a home-made slicing device as a cost-effective alternative, which allows sectioning of non-frozen rhizosphere soil employing one single slice.