Abstract
The soil bioavailability of phosphorus (P) is often low because of its poor solubility, strong sorption and slow diffusion in most soils; however, stress due to excess soil P can occur in greenhouse production systems subjected to high levels of P fertilizer. Silicon (Si) is a beneficial element that can alleviate multiple biotic and abiotic stresses. Although numerous studies have investigated the effects of Si on P nutrition, a comprehensive review has not been published. Accordingly, here we review: (1) the Si uptake, transport and accumulation in various plant species; (2) the roles of phosphate transporters in P acquisition, mobilization, re-utilization and homeostasis; (3) the beneficial role of Si in improving P nutrition under P deficiency; and (4) the regulatory function of Si in decreasing P uptake under excess P. The results of the reviewed studies suggest the important role of Si in mediating P imbalance in plants. We also present a schematic model to explain underlying mechanisms responsible for the beneficial impact of Si on plant adaption to P-imbalance stress. Finally, we highlight the importance of future investigations aimed at revealing the role of Si in regulating P imbalance in plants, both at deeper molecular and broader field levels.
Highlights
Silicon (Si) is the second most abundant element in the Earth’s crust, and its content within plants ranges from 0.1% to 10% depending on species
Many studies have been conducted to illustrate the mechanisms of Si alleviation of Pdeficiency or excess-P stress. These investigations have collectively shown the beneficial effects of Si supplementation on P-imbalance stress in different plant species
In regard to the diversity of the Si-mediated P-imbalance stress resistance mechanisms, the abovedescribed studies in this review have demonstrated that exogenous Si application is able to alleviate P-deficiency stress by increasing P mobility, decreasing exchangeable Al3+ in acid soils, increasing the exudation of both malate and citrate, upregulating P transporter genes and enhancing internal P utilization by decreasing Fe and Mn uptake (Figure 1)
Summary
Silicon (Si) is the second most abundant element in the Earth’s crust, and its content within plants ranges from 0.1% to 10% depending on species. Several authors have systematically reviewed research progress on the elucidation of mechanisms of Si-mediated alleviation of biotic and abiotic stresses in plants [2,3,4,5,6,7]. In these reviews, the beneficial effects of Si on nutrient imbalance have received relatively little attention. The cytoplasmic membrane of plant roots may provide a channel for the absorption of silicic acid by non-ionic diffusion, the permeability coefficient of silicic acid through the plasma membrane is only 10−10 m·s−1 [28]. The tissue and cellular locations of these genes, which differ among plant species, determine the different roles of Si transporters in plant Si uptake, transport and accumulation
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