In addition to foliar manganese concentration, both iron and zinc provide proxies for rhizosheath carboxylates in chickpea under low phosphorus supply

Abstract

Plants deploying a phosphorus (P)-mobilising strategy via carboxylate release have relatively high leaf manganese concentrations ([Mn]). Thus, leaf [Mn] is a proxy for the amount of rhizosheath carboxylates. Whether the concentrations of other leaf micronutrient, such as iron ([Fe]), zinc ([Zn]) and copper ([Cu]), show a similar signal for rhizosheath carboxylates is unclear.Methods: We grew a large number of chickpea genotypes in two glasshouse studies with different growth media, P sources and P levels. Seven weeks after sowing, we determined concentrations of micronutrients in mature leaves, and the quantity and composition of rhizosheath carboxylates.Results: For 100 genotypes grown in river sand with low P supply, leaf [Fe] (R 2 =0.36) and [Zn] (R 2 =0.22), like leaf [Mn] (R 2 =0.38), were positively correlated with the total amount of rhizosheath carboxylates. For 20 genotypes grown in a soil mixture, leaf [Fe],[Zn], [Cu] and [Mn] showed positive correlations with total rhizosheath carboxylates that were stronger under moderately low P (R 2 =0.59, 0.59, 0.54, 0.72) than severely low P (R 2 =0.39, 0.28, 0.20, 0.36) or sufficient P (R 2 =0.36, 0.00, 0.01, 0.50) supply. Malonate was the predominant carboxylate in the rhizosheath and was significantly correlated with leaf micronutrient concentrations in both experiments.Conclusions: In addition to leaf [Mn], leaf [Fe] and [Zn] can be used as alternative and easily measurable proxies for belowground carboxylate-releasing processes in chickpea under low-P supply, particularly on moderately low-P soils.

Linking root exudation to belowground economic traits for resource acquisition

“…For example, protons released by roots acidify the rhizosphere and lead to the dissolution of inorganic phosphate complexes (Hinsinger et al ., 2003). Modulating the amount and composition of carboxylates may mobilize soil P by ligand exchange or chelating cations from mineral surfaces (Wang & Lambers, 2019; Wen et al ., 2021), and release of phosphatases (and phytases) into the rhizosphere may mobilize P from organic compounds (Richardson et al ., 2009a; Shen et al ., 2011). Overall, the supply of soil P to plants tends to be dominated by a range of equilibrium processes between different P pools, while P‐mobilizing exudates increase the availability of P in the rhizosphere by blocking/reversing a range of P‐sorbing processes (Fig.…”

Multiscale imaging on Saxifraga paniculata provides new insights into yttrium uptake by plants

“…Phosphate mobilising root exudates comprise protons, phosphatases and carboxylates 54 . It has been reported that carboxylates for instance, not only mobilise P, but also transition metal cations such as Mn, Fe, Cu and Zn 55 , 56 . The intensity of carboxylate production, however, depends on soil properties, plant species and phosphate supply 57 .…”

Ensuring future food security and resource sustainability: insights into the rhizosphere

“…Recent studies suggested that plants exude carboxylates not only for P acquisition, but also for effective mobilization of micronutrients such as Fe, Cu, Zn and Mn; in particular, Mn can significantly accumulate in leaves even when plants grow in low-P soils with low exchangeable Mn (Lambers et al, 2015;Wen et al, 2021). Therefore, an alternative method (measuring leaf Mn) to indicate rhizosphere processes (e.g., carboxylate secretion) was proposed, which might be a good screening tool for an assessment of the belowground root traits associated with nutrient acquisition strategies among species growing in low-P habitats (Lambers et al, 2015.…”