Root exudation composition changed by root zone but not by root
types
Root exudation can change significantly along the root axis and
different root types (Abenavoli et al. 2004; Tiziani et
al. 2021). However, only the targeted analyses revealed significantly
different metabolites in relation to the root zone. Aconitic acid, total
phenols, total flavonoids, as well as glycine, alanine and threonine
exudation has been significantly enhanced in maize apical root regions,
compared to subapical ones (Figure 2). Generally, the root tip is
considered to be very sensible to environmental stimuli (Baluška &
Mancuso 2013). Some studies suggested that the root tip functions as
control center for sensing external nutrient concentrations, inducing
alterations of root morphology and physiology (Baluška & Mancuso 2013;
Canarini, Kaiser, Merchant, Richter & Wanek 2019; Tiziani et al.2020a). Moreover, the elongation zone, which in our study is located in
the apical root zone, is known to be one of the physiologically most
active root zones being a sort of command center for root responses to
the environment (Baluska, Mancuso, Volkmann & Barlow 2010; Baluška &
Mancuso 2013; Tiziani et al. 2020a). The lack of root type
effects on the release of the exudates could be due to the restricted
soil volume of the potting system, which may have limited the soil
exploration of single root axes.