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. (Résumé d'auteur

Mycorrhizal Phosphorus Efficiencies and Microbial Competition Drive Root P Uptake

“…Ectomycorrhizas produce hyphal networks that overcome zones of P depletion by hyphal tunneling (Jongmans et al, 1997;Hoffland et al, 2003;Jansa et al, 2011). Mycorrhizal fungi further contribute to bioweathering by secretion of organic acids (Wallander, 2000;Balogh-Brunstad et al, 2008;Jansa et al, 2011) and to the recycling of organic-bound P by production of acidic phosphatases (Hinsinger et al, 2015;Smith et al, 2015). Already early tracer studies with radioactive P i showed that mycorrhizal roots of pine and beech accumulate more P than non-mycorrhizal roots (Kramer and Wilbur, 1949;Harley et al, 1954).…”

Cultivation of vetiver in saline tailings contaminated with arsenic under phosphorus doses

“…The lower damages observed in the leaves and the greater deepening of the roots in the substrate, although it is a strategy of the plant to increase its ability to access and absorb P (Hinsinger et al, 2015), suggest that doses lower than or equal to 560 mg kg -1 of P 2 O 5 reduced As toxicity. The contents and total amounts of As in the dry matter increased with the doses of P (Figure 1), corroborating Tu & Ma (2003), who observed that the addition of phosphate to the soil increased the accumulation of arsenate by Pteris vittata.…”

Mycorrhizal fungi alleviate acidification‐induced phosphorus limitation: Evidence from a decade‐long field experiment of simulated acid deposition in a tropical forest in south China

“…The ECM can even directly produce extracellular enzymes such as phosphomonoesterase (Smith & Reed, 2008). Some of mycorrhizal fungi can also solubilize relatively complex organic P or occluded P that is bound to Al/Fe oxides by secreting organic acids, phenolic compounds and protons (Hinsinger et al, 2015;Rosling et al, 2016). However, little information is available so far on whether the plant-microbe interactions could be enhanced under long-term acid deposition and how it regulates soil P transformation in the already highly acidic soils.…”