Abstract
AimsWe imaged the sub-mm distribution of labile P and pH in the rhizosphere of three plant species to localize zones and hot spots of P depletion and accumulation along individual root axes and to relate our findings to nutrient acquisition / root exudation strategies in P-limited conditions at different soil pH, and to mobilization pattern of other elements (Al, Fe, Ca, Mg, Mn) in the rhizosphere.MethodsSub-mm distributions of labile elemental patterns were sampled using diffusive gradients in thin films and analysed using laser ablation inductively coupled plasma mass spectrometry. pH images were taken using planar optodes.ResultsWe found distinct patterns of highly localized labile P depletion and accumulation reflecting the complex interaction of plant P acquisition strategies with soil pH, fertilizer treatment, root age, and elements (Al, Fe, Ca) that are involved in P biogeochemistry in soil. We show that the plants respond to P deficiency either by acidification or alkalization, depending on initial bulk soil pH and other factors of P solubility.ConclusionsP solubilization activities of roots are highly localized, typically around root apices, but may also extend towards the extension / root hair zone.
Highlights
Plants actively modify their rhizosphere to render soil P plant-available by releasing protons, carboxylate anions and enzymes (Hinsinger and Gilkes 1995; LópezArredondo et al 2014)
In the non-calcareous soil, soil porewater pH tended to increase in the planted pots compared to the nonplanted controls
Our findings reveal several reproducible patterns of the spatial distribution of labile P and its solubility controls at sub-mm scale
Summary
Plants actively modify their rhizosphere to render soil P plant-available by releasing protons, carboxylate anions and enzymes (Hinsinger and Gilkes 1995; LópezArredondo et al 2014). The root apices and younger root sections are highly active zones of P uptake (Colmer and Bloom 1998; Fang et al 2007; Marschner et al 2011), and have been shown to be hot spots of organic anion exudation and proton release (Neumann and Römheld 1999; Raghothama and Karthikeyan 2005). The occurrence of Al, Fe and Ca, and of Mn, in regions of elevated P concentrations in the vicinity of roots can serve as indicator of plant-mediated element solubilization
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