Interaction of Arsenic and Phosphate on Their Uptake and Accumulation in Chinese Brake Fern

Abstract

Interactive effects of arsenate (As (V)) and phosphate (Pi) were investigated under hydroponic culture. Arsenic concentrations in fronds and roots of Chinese brake fern (Pteris vittata L.) significantly (p<0.05) increased with increasing As (V), but decreased (p<0.05) with increasing Pi in nutrient solution. Phosphate uptake was significantly (p<0.05) inhibited by 1000 μmol L⁻¹ As (V). Under 100 μmol L⁻¹ As (V), frond phosphorus (P) increased at 100 and 1000 μmol L⁻¹ Pi, and root P increased at 250 μmol L⁻¹ Pi exposures. Arsenic and P concentrations in fronds and roots of Chinese brake fern were negatively correlated (p<0.05). Arsenate treatments enhanced As and P transport to fronds, while increasing Pi inhibited their transportation, with highest frond P and As (%) obtained under 100 μmol L⁻¹ treatment.

pH values in nutrient solution increased with increasing exposure time, but decreased with increasing Pi levels. Dissolved organic carbon (DOC) contents (dry weight) in nutrient solution decreased with increasing Pi levels, both for treatments with and without As (V). Arsenate at 1000 μmol L⁻¹ significantly (p<0.05) increased DOC contents, especially for treatment without Pi. Six organic acids were detected in root exudates of Chinese brake fern, with oxalic and malic acids being most dominant.

KEY WORDS:

• arsenate
• phosphate
• Chinese brake fern
• dissolved organic acid
• root exudates
• pH

ACKNOWLEDGMENTS

The authors would like to thank Dr. H.B. Wang and Dr. B. Yang of Sun Yat-sen University, P.R. China for their assistance. Financial support from the Research Grants Council of University Grants Committee of Hong Kong (HKBU 2181/03M) is gratefully acknowledged.