Biogeochemistry of Fluoride in a Plant–Solution System

Abstract

Fluoride (F-) pollutants can harm plants and the animals feeding on them. However, it is largely unknown how complexing and chelating agents affect F bioavailability. Two studies were conducted that measured F- bioavailability and uptake by rice (Oryza sativa L.). In the first study, rice was grown in solution culture (pH 5.0) with 0, 2, or 4 mM F- as KF to compare the interaction of F- with humic acid (HA) and with a conventional chelating agent, N-hydroxyethylenthylenediaminetriacetic acid (HEDTA). In the second study, F was supplied at 0, 0.5, 1.0, and 2.0 mM KF with an additional 2 mM F- treatment containing solution Ca at 2x (2 mM Ca) the level used in the first study, to test the effect added Ca had on F- availability and uptake. Total biomass was greatest with HEDTA and F- < 1 mM. Leaf and stem F concentrations increased exponentially as solution F- increased linearly, with nearly no F partitioning into the seed. Results suggest that F was taken up as HF0 while F- uptake was likely restricted. Additionally, F- competed with HA for Ca, thus preventing the formation of Ca-HA flocculents. The addition of soluble Ca resulted in the precipitation of CaF2 solids on the root surface, as determined by tissue analysis and energy dispersive X-ray spectroscopy.

Changes of leaf antioxidant system, photosynthesis and ultrastructure in tea plant under the stress of fluorine

“…Fluorine, a phytotoxin in air, water, soil, and vegetation, is released into the environment from a number of industrial sources (Mackowiak et al 2003), application of phosphate fertilizers in agriculture (Loganathan et al 2001), and weathering of volcanic ashes (Cronin et al 2003). F is transferred from soil to roots, and then to above ground parts, or absorbed by leaves from the air.…”

Crop Effects on Closed System Element Cycling for Human Life Support in Space

“…Rice growth was affected by all levels of F, where biomass decreased linearly with increasing solution F − (Figure 2a). This study did not continue through seed maturity but results from a previous study showed that rice seed F was less than 0.5% of shoot tissue concentrations (Mackowiak et al, 2003). Plants from this study had begun seed fill at the time it was terminated (63 days).…”

“…The nutrient solution composition and maintenance methods used for the Na studies are the same used in a previous study with tomato and soybean . Details of nutrient solution , Mackowiak et al (2003) and Mackowiak and Grossl (1999), respectively.…”

“…composition and maintenance for the F and I studies are described in detail elsewhere (Mackowiak et al, 2003;Mackowiak and Grossl, 1999). The hydroponic system descriptions and pH set points are given ( Table 2).…”

“…In addition, F − is incorporated into phosphorus (P) solid-phases to form fluoroapatite. Plants do not appear to profit from F nutrition and several reports have shown F − supplied to plants above 1 mM may be toxic (Bar-Yosef and Rosenberg, 1988;Hara et al, 1977;Mackowiak et al, 2003;Stevens et al, 1997).…”