The applicability of scanner method to investigate rhizosphere in wetlands

Abstract

Temporal changes in rhizosphere, including roots and rhizomes, are prerequisites for understanding plant community dynamics, while observation methods have room for development. Monitoring roots and rhizomes by non-destructive methods is desirable, particularly in wetlands, because plants often develop shallow roots that are determined by the water level. Here, we examined the applicability of flatbed scanner method, which allows for least destructive monitoring. The examination was performed on a post-mined peatland in Sarobetsu mire, northern Japan, where herbaceous plants are dominant. Photos (297 mm in height × 216 mm in width) were taken periodically using a scanner in transparent boxes installed in peat layers from 2020 to 2023. Most photos taken by the scanner showed clear for image analyses and were analyzed for temporal changes in root area and length of dominant species. Although root extraction was conducted automatically using open-source software, manual operations were required to increase root detectability and identification. The belowground plant organs were separated into main roots, fine roots, adventitious roots and rhizomes. The roots were mostly distributed within the photo planes, except for the deep rhizomes of Phragmites australis, indicating that this method captured most roots. In total, 62% of the roots were distributed above the groundwater level of which average was 7 cm below the peat surface. The examined species fluctuated in root area and length with upward trends and developed at different depths. We conclude that the scanner method proposed in this study is applicable to monitoring root dynamics, evaluated by the recruitment and growth at species level for the long term and provides a new insight into understanding rhizosphere dynamics in wetland ecosystems.