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

Abstract

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 belowground C input, the spatial and temporal distribution of C, and the interactions between plants and soil microorganisms. Based on 14 C phosphor imaging, we visualized the allocation of assimilates into Lolium perenne roots and estimated the life time of hotspots at the root tips. Lolium shoots were labeled in a 14 CO 2 atmosphere, and herbariums of roots and shoots were prepared 6 h, 2 d, and 11 d after the 14 C pulse. The 14 C 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 14 C specific activity expressed as digital light units (DLU mm -2 ) of the imaging plates. Areas with high relative 14 C activity were classified as hotspots. Strong 14 C hotspots were detected mainly at the root tips already 6 h after the 14 C assimilation, and they remained active for at least 2 d. Eleven days after the 14 C assimilation, the hotspots at the root tips disappeared and the 14 C distribution was much more even than after 6 h or after 2 d. 14 C phosphor imaging proved to be a promising tool to visualize the allocation of photoassimilates into the roots and the rhizosphere and can be used to identify hotspots and their dynamics.

The flat-plate plant-microbial fuel cell: the effect of a new design on internal resistances

“…The bottom part of P-MFC 2, however, did contain at least one root-tip. Literature describes that so-called hotspots can occur in the rhizosphere [18,19]. A hotspot is a place in the root zone where microbial activity and exudation are enhanced compared to the rest of the rhizosphere [18].…”

Oxygen and redox potential gradients in the rhizosphere of alfalfa grown on a loamy soil

“…The rhizosphere, i.e. , the soil surrounding roots, which is influenced by its activity ( Darrah , 1993), represents only about 1% of the total soil volume, but has an enormous ecological importance ( Gregory , 2006; Pausch and Kuzyakov , 2011). It represents one of the hotspots in soil, where turnover of organic matter is increased compared to bulk soil due to higher microbial activity ( Jones and Hinsinger , 2008).…”

Substrate quality affects microbial‐ and enzyme activities in rooted soil

“…The release of labile compounds (including enzymes) by living roots or by lysis of root cells stimulates microbial activity ( Nannipieri et al, 2012) and microbial growth ( Panikov , 1995; Oger et al, 2004; Blagodatskaya et al, 2009) in the similar ways as rhizodeposits ( Kuzyakov and Domanski , 2000; Marschner et al, 2004). The release of root exudates and other rhizodeposits is ongoing and is localized in soil ( Pausch and Kuzyakov , 2011). Consequently, localization of easily available C produces hotspots of microbial abundance and activities, frequently termed as the “rhizosphere effect” ( Lynch , 1990; Sørensen , 1997).…”