Effect of lead on growth of warm season turf grasses

The ability to tolerate metals targeted for remediation in existing soil conditions is one of the important features possessed by plants used in phytoextraction programs. Pot experiments were conducted using Stenotaphrum dimidiatum (L.) Brongn, Zoysia matrella var. pacifica Goudsw and Axonopus compressus (Sw.) P. Beauv plants to identify ability of these turf grasses to withstand and tolerate lead when grown in contaminated soil from across Musi River region of Hyderabad which had lead metal in concentrations higher than permissible limits. Plants were exposed to 131.2, 223.3 and 326.2 mg kg-1of lead in contaminated soil and examined under three metal exposure periods of 120, 240, and 360 days. Control samples were obtained by growing plants in normal soil with 42.2 mg kg-1of lead. The pot cultures were maintained at a nursery under normal day light conditions and shoots were harvested every 60 days during the 360 days of study period from June 2017 to June 2018. Results showed that for all three grasses a decrease in heights was seen with an increase in soil lead concentrations and exposure time. Decrease in lengths was more for roots than shoots.Zoysia matrella was the most lead affected plant with a mean phytotoxicity of 14.7% compared to 10.9 and 8.5% seen in Stenotaphrum dimidiatum and Axonopus compressus. Lead tolerance was highest for Axonopus compressus with Metal tolerance index (MTI) of 91.5%, followed by Stenotaphrum dimidiatum (89.1%) and least by Zoysia matrella (85.3%). At the highest given soil lead concentration of 326.2 mg kg-1with Axonopus compressus was found significantly better having higher tolerance index compared to Zoysia matrella. The study concludes that Axonopus compressus popularly known as Carpetgrass has a greater scope for use in lead phytoextraction programs compared to the other two tested grasses as it had the ability to tolerate and withstand lead in contaminated soil at higher concentration