Measurements of H+ Fluxes and Concentrations in the Rhizosphere

Rhizosphere geometry and heterogeneity arising from root‐mediated physical and chemical processes

“…The rhizosphere is most often depicted as a soil cylinder of a given, rather small radius around the root, which extends outward from the smooth root surface. In many studies, including field and pot experiments, the soil adhering to the roots has been operationally defined as the rhizosphere (Gregory & Hinsinger, 1999; Jaillard et al ., 2002). This definition is similar to that of the rhizosheath, as defined by McCully (1999) (Fig.…”

“…The considerations noted above are challenges to the measurement of the rhizosphere, and especially to sampling. One dominant approach, used in both field and pot experiments, is based on an operational definition of the rhizosphere as that portion of the soil adhering to roots (Gregory & Hinsinger, 1999; Jaillard et al ., 2002). It is certainly relevant for studying physical rhizosphere processes such as adhesion/aggregation of soil particles to/by roots, but is a questionable sampling strategy when studying other processes.…”

“…In addition to microsampling and micro‐analytical techniques, novel in situ techniques, especially molecular probes, will facilitate quantitative assessments of rhizosphere processes at high spatial and temporal resolution (Killham & Yeomans, 2001; Mudge et al ., 2003; Boldt et al ., 2004). Coupling the use of spatially resolved information with image analysis is another powerful approach for quantitative insights into spatial heterogeneities of rhizosphere interactions, as achieved with pH dyes for measuring and locating the effluxes of protons from roots (Marschner et al ., 1982; Römheld, 1986; Jaillard et al ., 2002; Vansuyt et al ., 2003). The recent development of noninvasive techniques is even more promising for addressing temporal changes in rhizosphere processes.…”

“…An alternative approach that has been used extensively for studying rhizosphere gradients (Fig. 6) is the so‐called rhizobox or root‐mat approach (Gregory & Hinsinger, 1999; Jaillard et al ., 2002), in which a planar root mat (as initially proposed by Farr et al ., 1969) is separated from the soil by a fine mesh, enabling the collection of soil samples at defined distances from the root surface by slicing the soil parallel to the root mat (Kuchenbuch & Jungk, 1982; Wenzel et al ., 2001). However, this geometry is considerably oversimplified.…”

“…microsamplers) and/or that can be used for monitoring temporal patterns (e.g. microprobes: Gregory & Hinsinger, 1999; Jaillard et al ., 2002). In addition to microsampling and micro‐analytical techniques, novel in situ techniques, especially molecular probes, will facilitate quantitative assessments of rhizosphere processes at high spatial and temporal resolution (Killham & Yeomans, 2001; Mudge et al ., 2003; Boldt et al ., 2004).…”