Growth and nutrition of rice seedlings when phosphorus or silicon was applied to a soil heavily contaminated with both arsenic and cadmium

Abstract

There is a lack of affordable and effective strategies to mitigate multiple heavy metal contamination in lowland rice production. We tested phosphorus (P) or silicon (Si) addition to a soil contaminated with both arsenic (As) and cadmium (Cd) for their mitigation potential in rice seedlings. Rice variety IR64 was grown in pots with either P (0, 2.5, 5, 10, 20 (recommended rate), 40 and 80 mg P kg−1 soil), or Si (0, 0.15, 0.3, 0.6, 1.2 and 2.4 g Si kg−1 soil) addition until the end of tillering phase (nine weeks). Over this period, growth of rice was enhanced by up to 35% with the addition of P until the recommended rate, whereas growth was reduced beyond 0.3 g Si kg−1 application. Photosynthetic rate and maximum PSII quantum yield of the youngest fully expanded leaves were similar among P and Si treatments. Phosphorus addition increased shoot [As] and decreased shoot [Cd] by up to 59% and 63%, respectively, and both effects were visible only after plants reached P sufficiency. Silicon addition from 0 to 2.4 mg Si kg−1 soil increased shoot [As] by up to 28% and decreased [Cd] by up to 25%. Accumulation of As and Cd in the leaves from top to bottom of the canopy increased by factors of 10 and 7.6, respectively. Therefore, P or Si application cannot generally be recommended as remedy for rice production on multiple heavy metal contaminated soil. However, rice plants have efficient mechanisms to translocate As and Cd to mature leaves.