Hazardous waste leachates induced changes in plant water relation, photosynthetic pigments, heavy metal accumulation and yield of mustard (Brassica juncea L.) plant

Abstract

Chromium (Cr) contamination by industrial sites in water and agricultural soils is common and responsible for the human body being at risk from this heavy metal. The present study aims to assess the plant growth, yields, photosynthetic pigments, water relation, and heavy metal accumulation to understand the nature of the adaptation of Cr overload in mustard plants. An experiment was conducted at different levels of Basic Chrome Sulphate (BCS) sludge leachates i.e., T1 (control without leachates), T2 (25% leachates+75% DW); T3 (50% leachates + 50% DW); T4 (75% leachates + 25% DW) and T5 (100% leachates) on mustard (Brassica juncea L.) plant in completely randomized design (CRD). The primary leachates were collected from the dumping site of BCS sludge which was situated at 26⁰24′57′' NL and 80⁰3′28′' EL at Khanchandpur Kharanja, Rania, Kanpur Dehat district of Uttar Pradesh, India. Results indicated that the vegetative growth and yield were significantly decreased on increasing the dose of leachates. The linear regression coefficient (R2) values showed that the number of seeds, biomass, and seed yields per plant were more significantly affected (R2 = 0.963, R2 = 0.955, and R2 = 0.872 respectively) than vegetative growth (R2 = 0.706). The photosynthetic pigments like chlorophyll `a' (Chl. a), chlorophyll `b' (Chl. b), and carotenoid contents were significantly increased on increasing the dose of leachates while the Chl.`a'/Chl.`b' ratio decreased but carotenoid/ chlorophyll ratio increases. The leaf surface area and relative water contents (RWC) were significantly decreased while the degree of succulence and specific water content were significantly increased. Maximum Cr concentration was observed in the root up to T4 levels and further sharply declined while shoot and seed, it was not detected up to T4 but further sharply increased which may be due to Cr being restricted in the root up to a certain limit of Cr load in mustard plant and further on increasing the load it enters into the shoot and affects to growth and yields. The accumulation of Cr, Ni, and Pb was increased on increasing leachate dose because leachates also contain these heavy metals. The results of the Pollution Load Index (PLI) indicated that Cr scored maximum (1.792) pollution load and showed descending order as Cr > Zn >Pb>Cu>Cd>Ni.