Effects of phosphite, a reduced form of phosphate, on the growth and phosphorus nutrition of spinach (Spinacia oleraceaL.)

Abstract

Phosphite (Phi) may potentially supply phosphorus (P) nutrition to plants and is widely marketed as a super P fertilizer for many crops. This study investigated the effects of Phi on growth and P nutrition in spinach (Spinacia oleracea L.). High-rate foliar application experiments designed to evaluate the phytotoxicity and P nutritional potential of different Phi formulations by foliar application at two rates (0.15 and 0.3% P 2 O 5 ) showed that all Phi formulations did not improve plant growth under different available P-soils, but rather significantly decreased shoot dry weight (DW) at the higher rate. In two other soil and hydroponic experiments, Phi was foliar applied at a low rate (0.05% P 2 O 5 ) and root P treatments were combinations of Phi and phosphate (Pi) at different Pi : Phi ratios for a high P level (the soil experiment) or a low P level (the hydroponic experiment). In both experiments, shoot DW decreased markedly as the Pi : Phi ratios decreased from 100:0 to 0:100 and Phi foliar application did not improve plant growth. In the soil experiment, plants grew poorest at 0:100, but grew well when both Phi and Pi were applied at a high rate of 115 mg P pot -1 , indicating that at this level Phi had a negative effect on only severely P-deficient plants. Root growth of no Pi-fertilized plants was strongly inhibited by Phi from either root or foliar application. In both experiments, P concentration drastically decreased with decreasing Pi : Phi ratios from 100:0 to 0:100, but increased substantially with foliar application of Phi compared with Pi, suggesting that Phi was absorbed poorly by the roots, but was well absorbed by the leaves compared to Pi. We conclude that Phi cannot be used as a P fertilizer for spinach via either root or foliar applications at low or high levels, and also that Phi has no beneficial effect on the growth of spinach. As Phi is now widely marketed as a P fertilizer for many crops, care should be taken in selecting Phi as a P fertilizer for a given crop.

Physiological and Nutritional Evaluation of the Application of Phosphite as a Phosphorus Source in Cucumber Plants

“…These results were expected, as the P deficiency spurs root growth and formation of root hairs and root caps, which serves to increase uptake of this macronutrient (Ruiz, Belakbir, and Romero 1996;Williamson et al 2001;Maathuis 2009). We found results similar to those reported by Thao et al (2008b) in experiments with hydroponic crops such as spinach (Spinacia oleracea L.) treated with four application rates of Phi (0, 0.05, 0.2, and 2 mM) in combination with four rates of Pi (0.05, 0.1, 0.15, and 0.3 mM), finding the greatest value of fresh biomass (FB) in the root for the most P-deficient treatment. Ticconi, Delatorre, and Abel (2001) found an increase in root hairs in Arabidopsis thaliana when lower rates of P were applied to the growth medium.…”

“…The experiments made by Thao et al (2008b), in which they applied the same quantity of P to the plants using five different Pi/Phi ratios, showed that the total P concentration tended to decline as lower Pi/Phi ratios were applied. This occurred when applying descending Pi/Phi ratios, although, contrary to this trend, the lowest Pi/Phi ratio (which contained more P in the form of Phi) resulted in the greatest values for the total P concentration.…”

Phosphite and Phosphate Have Contrasting Effects on Nutrient Status of Plants

“…Phosphorus (P) in the reduced form (phosphite, Phi) cannot replace the anion phosphate (Pi) in plant metabolism, with subsequent risks of phytotoxicity and growth impairment in plants under Phi nutrition (Ratjen and Gerendás 2009;Thao et al 2008aThao et al , 2008bZambrosi, Mattos Jr., and Syvertsen. 2011).…”

In vitro growth of sweet potato fed with potassium phosphite

“…Although Phi compounds are marketed as fertilisers containing phosphorus, an increase in productivity is not expected from application of this nutrient. McDonald et al (2001), Thao and Yamakawa (2008) have all argued that Phi cannot be used as a phosphorus source, either by crops or by growing cells. According to Singh et al (2003), cell cultures grown using Phi as a nutrient have exhibited increased cell death, protein deterioration and DNA damage, perhaps owing to the erroneous incorporation of Phi in place of Pi.…”