Kuzyakov Y: Photoassimilate allocation and dynamics of hotspots in roots visualized by 14 C phosphor imaging

Understanding photoassimilate allocation into the roots and the release of organic substances from the roots into the rhizosphere is an important prerequisite for characterizing the below-ground C input, the spatial and temporal distribution of C, and the interactions between plants and soil microorganisms. Based on 14C phosphor imaging, we visualized the allocation of assim-ilates into Lolium perenne roots and estimated the life time of hotspots at the root tips. Lolium shoots were labeled in a 14CO2 atmosphere, and herbariums of roots and shoots were prepared 6 h, 2 d, and 11 d after the 14C pulse. The 14C distribution in roots and leaves revealed that pulse labeling does not yield homogeneously labeled plant material. The spatial distribution of assimilate allocation was evaluated based on the 14C specific activity expressed as digital light units (DLU mm–2) of the imaging plates. Areas with high relative 14C activity were classified as hotspots. Strong 14C hotspots were detected mainly at the root tips already 6 h after the 14C assimilation, and they remained active for at least 2 d. Eleven days after the 14C assimilation, the hotspots at the root tips disappeared and the 14C distribution was much more even than after 6 h or after 2 d. 14C phosphor imaging proved to be a promising tool to visualize the allocation of photoassimi-lates into the roots and the rhizosphere and can be used to identify hotspots and their dynamics