Bioavailability of zinc and phosphorus in calcareous soils as affected by citrate exudation

Abstract

Aims Zinc (Zn) and phosphorus (P) deficiency often occurs at the same time and limits crop production in many soils. It has been suggested that citrate root exudation is a response of plants to both deficiencies. We used white lupin (Lupinus albus L.) as a model plant to clarify if citrate exuded by roots could increase the bioavailability of Zn and P in calcareous soils. Methods White lupin was grown in nutrient solution and in two calcareous soils in a rhizobox. Rhizosphere soil solution was sampled to determine citrate, metals and P. Based on the measured citrate concentrations, a soil extraction experiment with citrate as extractant was done. Results Absence of Zn triggered neither cluster root formation nor citrate exudation of white lupin grown in nutrient solution, whereas low P supply did. The maximum citrate concentration (∼1.5 mM) found in the cluster rhizosphere soil solution of one soil mobilized P, but not Zn. In the other soil the highest citrate concentration (∼0.5 mM) mobilized both elements. Conclusions White lupin does not respond to low Zn bioavailability by increasing citrate exudation. Such a response was observed at low P supply only. Whether Zn and P can be mobilized by citrate is soil-dependent and the possible controlling mechanisms are discussed.

Can citrate efflux from roots improve phosphorus uptake by plants? Testing the hypothesis with near‐isogenic lines of wheat

“…Citrate concentrations around the cluster roots of white lupin are estimated to be 5–50 µmol g −1 soil (Dinkelaker et al , Gerke et al ), which probably corresponds to 1–10 m M in solution. These concentrations are consistent with other results obtained using ceramic suction cups (Dessureault‐Rompre et al , Duffner et al ) and could be sufficient to benefit plant nutrition according to various in vitro studies (Bar Yosef , Jones et al , , Jones , Kirk et al , Strom et al , Jones et al , Khademi et al , Oburger et al ).…”

Testing decontaminated sediments as a substrate for ornamentals in field nursery plantations

“…Moreover, the dynamics of the micronutrients in the rhizosphere can be quite different from the one farther away from roots (Rengel, 2002;Pinton, 2007;Dotaniya and Meena, 2015), where the samples have been taken. For instance, plants can excrete organic acids which stimulate the microorganisms, whose respiration, together with the root respiration, may change the soil pH of the rhizosphere (Soltani et al, 2014;Duffner et al, 2012;Dotaniya and Meena, 2015;Rengel, 2015) and favour the solubility of ions. In addition, organic acids in soils like humic or fulvic acids can form salts, work as important ion exchange or metal chelating system (Hinsinger et al, 2003), and be absorbed by the plant together with the cations (Clark and Baligar, 2000;Rengel, 2002;Tang and Rengel, 2003).…”

How a phosphorus‐acquisition strategy based on carboxylate exudation powers the success and agronomic potential of lupines (Lupinus, Fabaceae)

“…Chelation of iron by the exuded carboxylates might play an additional role (Broadley et al, 2012). Zinc deficiency does not induce cluster‐root formation or carboxylate release in white lupine, but, depending on soil type, the carboxylates that are released under P deficiency can enhance the availability of zinc as well (Duffner et al, 2012). It is likely that other micronutrients, e.g., copper, are also mobilized and taken up by lupines, as shown for cluster roots of Hakea prostrata R.Br.…”