HEAVY METAL PHYTOEXTRACTION POTENTIAL OF INDIGENOUS TREE SPECIES OF FAMILY FABACEAE

Abstract

The present study highlights the possibility of using wastewater for forest irrigation. This study was conducted in 2 phases, first phase was the seed germination study of the five selected species and the second phase was of growth of plants through pot experiment. Five tree species selected for the study were, Dalbergia sissoo Roxb., Albizia lebbeck (L.) Benth, Pongamia pinnata (L.) Pierre, Bauhinia purpurea L. and Millettia peguensis Ali. Three types of wastewater were collected, first from industrial wastewater (IWW), second from hospital wastewater (HWW) and third from domestic wastewater (DWW). Germination experiment was set up in Petri dishes and seeds were irrigated with different concentrations of WWs. In pot experiment the five tree species were planted in pots and were irrigated with 5 different concentrations (0%, 25%, 50%, 75% and 100%) of WWs. Germination study results revealed that the five plant species survived in the WW irrigation and showed sufficient tolerance. The maximum germination was of Dalbergia sissoo i.e. 74%. The toxicity of different WWs is as follows: IWW > HWW > DWW The mean time to germination of Millettia peguensis was 95 hrs and of Albizia lebbeck was 80 hrs. Similarly, all the five species showed positive increase in seedling fresh weight, dry weight and seedling length. Maximum fresh weight was observed in Dalbergia sissoo (0.64 g) and the lowest fresh weight was reported in Millettia peguensis (0.35). The order of tolerance index and vigor index among the five species is as follows; Dalbergia sissoo > Albizia lebbeck > Bauhinia purpurea > Pongamia pinnata > Millettia peguensis In pot experiment, the DWW showed positive impact on height, fresh and dry weight, where as, the HWW showed positive impact on height upto 50% concentration and the further increase in concentration decreased the height. The maximum negative impact was observed with IWW irrigation. Pongamia pinnata showed 90% increase xiii in height in DWW compared to control set up. Albizia lebbeck showed 35% increase in fresh weight, 45% increase in fresh weight by Dalbergia sissoo. The photosynthetic rate, transpiration rate and stomatal conductance of all the five species decreased significantly. In HWW the decrease in photosynthetic rate was as follows; Pongamia pinnata (-80%), Albizia lebbeck (-60%), Dalbergia sissoo (-45%), Millettia peguensis (-45%) and Bauhinia purpurea (-58%). The proline content in all treatments was measured as a sign of oxidative stress. Maximum proline was observed in Bauhinia purpurea (6.33) in IWW, where as the least quantity of proline was observed in Pongamia pinnata (3.89). The metal uptake and translocation results are also very promising. Maximum uptake was observed for Pb in IWW by Dalbergia sissoo (107.06 mg/day). Uptake of Cr and Cu uptake was slow in all species. Translocation factor of Albizia lebbeck was maximum i.e. 3.03 in HWW. Untreated IWW seems to create number of problems in ecosystem by disturbing both biotic and abiotic (soil properties, soil osmotic potential) components. This study seems to be successful in combating wastewater problem. This study indicates that, Dalbergia sissoo, Albizia lebbeck, Bauhinia purpurea, Pongamia pinnata and Millettia peguensis are much tolerant in IWW and can be successfully used for phytoextraction processes. The tolerance index is as follows: Dalbergia sissoo > Albizia lebbeck > Bauhinia purpurea > Pongamia pinnata > Millettia peguensis The idea is to utilize WW to generate urban forests with the said five species. This idea can reduce multiple and serious problems like, IWW toxicity, WW treatment, and air pollution through urban forestry. The most prominent benefit is that this urban forest is eco-friendly and sustainable solution for multiple problems.