Enhancing Phytate Availability in Soils and Phytate-P Acquisition by Plants: A Review

Abstract

Phytate ( myo -inositol hexakisphosphate salts) can constitute a large fraction of the organic P in soils. As a more recalcitrant form of soil organic P, up to 51 million metric tons of phytate accumulate in soils annually, corresponding to ∼65% of the P fertilizer application. However, the availability of phytate is limited due to its strong binding to soils via its highly-phosphorylated inositol structure, with sorption capacity being ∼4 times that of orthophosphate in soils. Phosphorus (P) is one of the most limiting macronutrients for agricultural productivity. Given that phosphate rock is a finite resource, coupled with the increasing difficulty in its extraction and geopolitical fragility in supply, it is anticipated that both economic and environmental costs of P fertilizer will greatly increase. Therefore, optimizing the use of soil phytate-P can potentially enhance the economic and environmental sustainability of agriculture production. To increase phytate-P availability in the rhizosphere, plants and microbes have developed strategies to improve phytate solubility and mineralization by secreting mobilizing agents including organic acids and hydrolyzing enzymes including various phytases. Though we have some understanding of phytate availability and phytase activity in soils, the limiting steps for phytate-P acquisition by plants proposed two decades ago remain elusive. Besides, the relative contribution of plant- and microbe-derived phytases, including those from mycorrhizas, in improving phytate-P utilization is poorly understood. Hence, it is important to understand the processes that influence phytate-P acquisition by plants, thereby developing effective molecular biotechnologies to enhance the dynamics of phytate in soil. However, from a practical view, phytate-P acquisition by plants competes with soil P fixation, so the ability of plants to access stable phytate must be evaluated from both a plant and soil perspective. Here, we summarize information on phytate availability in soils and phytate-P acquisition by plants. In addition, agronomic approaches and biotechnological strategies to improve soil phytate-P utilization by plants are discussed, and questions that need further investigation are raised. The information helps to better improve phytate-P utilization by plants, thereby reducing P resource inputs and pollution risks to the wider environment.

Phytate and Arsenic Enhance Each Other’s Uptake in As-hyperaccumulator Pteris vittata: Root Exudation of Phytate and Phytase, and Plant Uptake of Phytate-P

“…However, the associated mechanisms regarding phytate hydrolysis in soils and its utilization by plants are poorly understood. 6 Phytase is a specialized phosphatase, which can catalyze phytate hydrolysis to release lower inositol phosphates and inorganic-P. 6 Some plants exude phytase into the rhizosphere and thereby helping their phytate-P acquisition. For example, under P deficiency, overexpression of phytase gene GmPAP14 in soybean results in high enzyme activity to facilitate its external phytate-P uptake.…”

“…5,10 Besides, phytase activity in soils is affected by soil pH and its strong sorption onto soils. 6 As such, studies on phytate-P acquisition by plants have often been conducted in sterile media or under hydroponics. It is known that phytase exudation by plants responds to P deficiency, but few studies focus on the impacts of As and/ or phytate on extracellular phytase activity and phytate-P uptake by plants.…”

“…As chemical analogues, AsV and P are taken up in plants via P transporters . Unlike As, P is an essential macronutrient for plant growth. , However, in many soils, inorganic-P only accounts for ∼1% of total P, with 30–80% consisting of the unavailable organic P. , As a result, low P availability in soils has been a constraint in limiting crop yields. It is estimated that ∼50% of organic P in soils is present as phytate (inositol hexakisphosphate) .…”

“…Therefore, phytate-P release may be crucial to enhance plant-available P in soils. However, the associated mechanisms regarding phytate hydrolysis in soils and its utilization by plants are poorly understood …”

State-of-the-Art Review on Engineering Uses of Calcium Phosphate Compounds: An Eco-Friendly Approach for Soil Improvement

“…[ 97 , 98 , 99 ]. It is estimated that annually, up to 51 million metric tons of phytate accumulate in the soil, making it a readily available resource [ 100 ]. Figure 9 schematically illustrates the structure of phytate.…”