Impact of phosphorus mineral source (Al–P or Fe–P) and pH on cluster-root formation and carboxylate exudation in Lupinus albus L.

Abstract

Lupinus albus L. were grown in rhizoboxes containing a soil amended with sparingly available Fe-P or Al-P (100 μg P g −1 soil/resin mixture). Root halves of individual plants were supplied with nutrient solution (minus P) buffered at either pH 5.5 or 7.5, to assess whether the source of mineral-bound P and/or pH influence cluster-root growth and carboxylate exudation. The P-amended soil was mixed 3:1 (w/w) with anion-exchange resins to allow rapid fixation of carboxylates. Treatments lasted 10 weeks. Forty percent and 30% of the root mass developed as cluster roots in plants grown on Fe-P and Al-P respectively, but cluster-root growth was the same on root-halves grown at pH 5.5 or 7.5. Mineralbound P source (Al-or Fe-P) had no influence on the types of carboxylates measured in soil associated with cluster roots-citrate (and trace amounts of malate and fumarate) was the only major carboxylate detected. The [citrate] in the rhizosphere of cluster roots decreased with increased shoot P status (suggesting a systemic effect) and also, only for plants grown on Al-P, with decreased pH in the root environment (suggesting a local effect). In a separate experiment using anion exchange resins pre-loaded with malate or citrate, we measured malate (50%) and citrate (79%) recovery after 30 days in soil. We therefore, also conclude that measurements of [citrate] and [malate] at the root surface may be underestimated and would be greater than the 40-and 1.6-μmol g −1 root DM, respectively estimated by us and others because of decomposition of carboxylates around roots prior to sampling.

Genotypic variation in phosphorus acquisition from sparingly soluble P sources is related to root morphology and root exudates in Brassica napus

“…We believe that there may be two reasons for this: First, Al-P is more soluble than Fe-P. Similar results were reported in other studies, which suggested that because of its poor solubility, Fe-P was less available to a wide range of crops than either Ca-P or Al-P [29,30]. Second, the higher Al concentration resulting from soil acidification under the Al-P treatment might stimulate the release of organic acid anions and indirectly supplement the Al-P nutrition compared to the Fe-P treatment [31,32].…”

“…In some plant species, exudation of carboxylates can release P from sparingly soluble Fe and Al phosphate via ligand exchange or chelation of metal ions [30,42]. Hoffland [13] and Garden et al [43,44] suggested that carboxylates secreted by plant roots in the rhizosphere could increase P availability by mobilizing P from sparingly soluble Ca, Fe, and Al phosphates.…”

Effects of high concentrations of calcium salts in the substrate and its pH on the growth of selected rhododendron cultivars

“…Ciereszko and Barbachowska (2000) showed that elimination of phosphorus from the culture medium caused a significant increase in sugar content of roots and both young and older leaves of beans (Phaseolus vulgaris L.), as compared to the control, grown on a complete medium. Probably the increased concentration of sugars, in response to water deficit, can determine the carbon reserves in plants, which are used for construction of new tissues when phosphorus is available, but can also lower the osmotic potential in root cells, and in this way it can also affect the ability to take up some mineral salts form the substrate (Zohlen and Tyler 2004;Shane et al 2008). Such conclusions seem to be confirmed by a significant increase in carbon content (%) of roots of R. 'Cunningham's White' and R. 'Catawbiense Grandiflorum' cuttings, grown in the substrate with CaCO 3 (Table 3).…”

Long-term effect of different soil management systems and winter crops on soil acidity and vertical distribution of nutrients in a Brazilian Oxisol

“…patterns of cation uptake and ability of plants to accumulate carboxylic acids in root tissue. The acquisition of P of low lability due to exudation of organic acids has been observed in lupin (Lupinus albus L.) by several researchers (Bais, 2006;Bayon et al, 2006;Shane et al, 2008;Wang et al, 2008). Therefore, based on the above results, it can be expected that cultivating crops with different strategies to access soil nutrients over time may alter soil nutrients and acidity attributes, especially under NT system.…”