Impact of Roots, Microorganisms and Microfauna on the Fate of Soil Phosphorus in the Rhizosphere

Abstract

Phosphorus (P) occurs at low concentrations in soils because of the numerous processes responsible for P sorption or immobilisation. Soil P is also characterised by its restricted mobility, and thus the most limiting step of P acquisition is not its absorption by plant roots, but rather the many processes that determine the fate of soil P in the rhizosphere. This chapter describes these various processes, including those directly mediated by plants (which vary considerably with plant species), and those related to soil microbial and microfaunal activities. In order to overcome the restricted mobility of soil P, plants have evolved several features aimed at increasing the rhizosphere volume by increasing the absorptive surfaces, notably root elongation and branching. The formation of root hairs and mycorrhizas is also triggered by interactions with plant growth promoting microorganisms. Plants have also evolved strategies aimed at increasing soil P concentrations via the mobilisation of inorganic and organic pools of soil P. These imply changes in pH, and the release of P‐mobilising compounds such as carboxylates and phosphatases, that are exuded by the roots themselves or by rhizosphere microorganisms. Finally, the soil microfauna (especially the predators of bacteria and fungi) play an important role in the cycling of soil P in the rhizosphere that deserves further consideration.

Phosphorus facilitation and covariation of root traits in steppe species

“…In addition, Apase is more active at low pH (Fig. 1d), which may account for the acidification of the rhizosphere (Hinsinger et al , 2015). Therefore, covariation of root physiological traits is tightly correlated with the efficiency to mobilize Po and sorbed P (Fig.…”

A Critical Review on Soil Chemical Processes that Control How Soil pH Affects Phosphorus Availability to Plants

“…Adjusting pH in either direction resulted in an increase in water extractable P, likely due to the fact that samples were only equilibrated for 48 h. A similar example is found in the studies of Gustafsson et al [16] and Devau et al [75], in which soils were only equilibrated for 144 and 84 h, respectively. Examples of soil pH changes in the rhizosphere that disrupt the equilibrium between non-labile and labile P fractions arising from the activities of microorganisms and plant roots were described by Hinsinger et al [76]. Prior to the additional 2-week equilibration period, the P solubility was determined to be a function of Ca phosphates, as partly evidenced by the similarity in shape to pure Ca phosphate minerals (Figure 2).…”

Hidden miners – the roles of cover crops and soil microorganisms in phosphorus cycling through agroecosystems

“…The exudation of different organic anions and acidification may be complementary (Gerke and Meyer 1995), but the mechanisms are complex and the result depends strongly on soil chemistry and P level (Oburger et al 2011). Complicating the system further, microorganisms function as both potential sinks and alternative sources of carboxylates (Deubel et al 2000), and soil fauna remobilize P from the microbial biomass (Hinsinger et al 2015). The identification of pH as the principal driver of microbial diversity in soils (Philippot et al 2009) paired with substantial changes in pH in the rhizosphere led Hinsinger et al (2009) to the hypothesis that rootinduced pH changes shape the structure of the rhizosphere microbial community equally or more importantly than root C deposition.…”