Fertilizer Potential of Struvite as Affected by Nitrogen Form in the Rhizosphere

Abstract

Struvite is increasingly considered a promising alternative to mined phosphorus (P) fertilizer. However, its solubility is very low under neutral to alkaline pH while it increases with acidification. Here, we investigated whether supplying ammonium to stimulate rhizosphere acidification might improve struvite solubility at the vicinity of roots and, ultimately, enhance P uptake by plants. Using a RHIZOtest design, we studied changes in soil pH, P availability and P uptake by ryegrass in the rhizosphere and bulk soil supplied with either ammonium or nitrate under three P treatments: no-P, triple super phosphate and struvite. We found that supplying ammonium decreased rhizosphere pH by more than three units, which in turn increased soluble P concentrations by three times compared with nitrate treatments. However, there was no difference between P treatments, which was attributed to the increase of soluble Al concentration in the rhizosphere, which subsequently controlled P availability by precipitating it under the form of variscite-like minerals (predicted using Visual MINTEQ). Moreover, although ammonium supply increased soluble P concentration, it did not improve P uptake by plants, likely due to the absence of P deficiency. Further studies, especially in low-P soils, are thus needed to elucidate the role of nitrogen form on P uptake in the presence of struvite. More generally, our results highlight the complexity of manipulating rhizosphere processes and stress the need to consider all the components of the soil-plant system.

Interactions between below‐ground traits and rhizosheath fungal and bacterial communities for phosphorus acquisition

“…Spatially uneven pools of available inorganic P can be acquired via P‐foraging traits such as specific root length (SRL), root length density (RLD) or root hair length and abundance (Fort, 2013; Haling et al., 2018; Ma et al., 2018), allowing plants to develop an extensive surface for absorption to efficiently explore larger soil volumes (Hinsinger et al., 2018). P‐mobilisation traits such as root exudation of protons, carboxylates or enzymes can also allow plants to mobilise poorly available P, that is increase soil inorganic P concentration and thus P availability by transforming P forms such as precipitates, P bound to soil particles or organic P. Precipitated inorganic P forms such as Ca/Mg‐phosphate can be dissolved via proton release in the rhizosheath soil (Gómez‐Suárez et al., 2020; White & Hammond, 2008). Plant‐released carboxylates, by competing with P for binding sites and complexing cations (e.g.…”

Can arbuscular mycorrhizal fungi speed up carbon sequestration by enhanced weathering?

“…In the rhizosphere however, H + release due to uptake of base cations can locally reduce pH by multiple units compared to bulk soil (e.g. Gómez-Suárez et al, 2020), and thus still increase mineral dissolution even in case of higher bulk soil pH. The weathering process involves the dissolution of silicates which consumes H + , releases geogenic nutrients such as P, Ca, Mg, K, and Si (depending on the source material) and increases the alkalinity of the environment.…”

Metal immobilization and nitrate reduction in a contaminated soil amended with zero-valent iron (Fe0)

“…The design of the biotest used in this study was described in details by Houben and Sonnet (2015). The principle of this device is similar to that used by other authors (Bravin et al, 2012;Couder et al, 2015;Gómez-Suárez et al, 2020) and consists in separating plant roots from soil with a 20-μm polyamide mesh to facilitate the collection of plants and rhizosphere. Briefly, 6 sterilized (10 min in 2 mol L -1 H2O2) seeds of Lupinus albus L. or 1.5 g sterilized seeds of Lolium multiflorum Lam., per pot were germinated in demineralized water for three days in darkness.…”

“…Numerous studies have investigated the ability of Fe 0 to immobilize metals in soils (Guan et al, 2015;Xue et al, 2018a). Hanauer et al (2011) reported that Fe 0 has initially no binding capacity for ions.…”

“…The main process responsible for change of rhizosphere pH is the release of H + or OHby roots to compensate charge imbalance due to unequal uptakes of cation and anions (Hinsinger et al, 2003). In particular, N uptake by roots greatly impacts rhizosphere pH as a higher uptake of NH4 + relative to NO3 -increases the release of H + from roots (Gómez-Suárez et al, 2020). As a result, by promoting the reduction of NO3 -into NH4 + , the application of Fe 0 increased the uptake of NH4 + relative to NO3 -, which explains the pH decrease in Fe 0 -amended rhizosphere compared to the bulk soil.…”