Phosphorus: Back to the Roots

Abstract

Phosphorus (P) is a pivotal nutrient for all life on Earth. It is poorly mobile in soil and inorganic P concentrations in the soil solution are <0.6 to 11μM. Organic P concentrations in the soil solution tend to be higher, but organic P needs to be hydrolysed before it can be taken up by plant roots. Such hydrolysis involves phosphatases that are either released from the roots or derived from microorganisms in the rhizosphere. A large fraction of soil P is sorbed onto soil particles, and hence is unavailable to most plants. Roots that release large amounts of P‐solubilising carboxylates can access some of this sorbed P. Rates of P uptake from the soil solution are determined predominantly by the movement of P in soil. Root traits that enhance P movement in soil increase P acquisition; however, the kinetic properties of P transporters that take up this P have little effect on net P uptake. The downregulation of genes encoding these transporters is important to avoid P toxicity at a high P supply. Species or genotypes that lack the capacity to downregulate their P‐uptake capacity typically show P‐toxicity symptoms at a high P supply. Mycorrhizal symbionts increase the soil volume that is available for P acquisition. Attempts to select or engineer genotypes with greater P‐uptake capacities should consider both root and soil characteristics, including soil microorganisms such as mycorrhizal fungi.

Re-evaluation of the yield response to phosphorus fertilization based on meta-analyses of long-term field experiments

“…This is a phenomenon commonly observed in long-term fertilization trials (e.g., Köster and Schachtschabel 1983 ; Jungk et al 1993 ; Römer 2009 ; Kuchenbuch and Buczko 2011 ). Since the yield depressions observed here are more or less equal for all soil P content classes (A: 20%, B: 30.6%, C: 29%, D; 30.5%, E: 41% of datasets), and soil P toxicity is rare under field conditions (Zorn et al 2013 ; Lambers and Plaxton 2015 ), the negative YI cannot reasonably be explained directly by the effect of P fertilization. However, indirectly, high levels of plant-available P (as provided by mineral fertilizer) in general reduce root density (Forde and Lorenzo 2001 ), and the development of mycorrhiza (Mäder et al 2000 ; Williams et al 2017 ).…”

Identification and Characterization of the Phosphate-Solubilizing Bacterium Pantoea sp. S32 in Reclamation Soil in Shanxi, China

“…The average P content in soil is nearly 0.05% (w/w) with the main two forms being inorganic P (Pi) and organic P (Po). Nevertheless, only 0.1% of P can be utilized by plants, rendering available P a restrictive factor for plant growth (Lambers and Plaxton, 2018). Phosphate anions in chemical fertilizer available to plants are extremely reactive and become fixed through interactions with Ca 2+ , Fe 3+ , and Al 3+ ions in the soil to form insoluble phosphate salt complexes; however, the plant utilization efficiency for P in chemical fertilizers is only 5–25% (Schnug and Haneklaus, 2016), leading to P enrichment in the soil and the loss of soil fertility.…”

Seasonal Alterations in Organic Phosphorus Metabolism Drive the Phosphorus Economy of Annual Growth in F. sylvatica Trees on P-Impoverished Soil

“…P limitation for terrestrial plants is a consequence of pedogenesis over thousands of years (Lambers et al, 2008 ; Lang et al, 2016 ), associated with erosion and leaching processes combined with extremely low atmospheric P deposition (Peñuelas et al, 2013 ). Some of the most P impoverished soils of the world developed in Australia (Lambers et al, 2012 , 2015 ; Lambers and Plaxton, 2015 ) and in South Africa at the fynbos biome (Vitousek et al, 2010 ). Also soils in Central Europe show low P availability as indicated by high foliar N to P ratios of vegetation growing on these soils (Talkner et al, 2009 , 2015 ; Han et al, 2014 ; Jonard et al, 2015 ).…”