Eco-Physiological responses of Sunflower (Helianthus annuus L.) against various levels of Rhizospheric Arsenic (As) and Associated Metals in the Soil

Abstract

A series of four experiments was performed to evaluate effect of different levels of two inorganic arsenicals on seed germination, vegetative and reproductive growth or yield of sunflower cultivars. First experiment conducted in climatic room using seeds of four sunflower cultivars revealed adverse effects of higher levels of arsenic (6, 8 and 10 mg As/L) on seed germination. Reduction in germination percentage, increased mean germination time, more days to 50 % germination and stunted plumule and radicle growth with poor seedling vigour index depicted stressful effects of arsenic for sunflower seedlings while lower levels of arsenic (2 and 4 mg As/L) proved to be a little bit promoting for seeds to germinate. In further three pot experiments arsenic was applied through soil, irrigation water as well as in combination to two sunflower cultivars and different morphological, physiological and plant water relation parameters were recorded. Arsenic bio-accumulative potential as well as concentrations of 26 different micro, trace and heavy metal ions were also determined in root, shoot, leaves and seeds of sunflower cultivars at crop maturity using ICP-OES. As observed during the experimentation and concluded from physio-chemical analysis of the plant organs, roots were found substantial sink for arsenic in sunflower and least accumulation was recorded in seeds or achenes. Arsenic application in soil proved more stressful than irrigation water alone and overall arsenic application in combination was proved most deterrent for sunflower growth and development. Plant accumulated arsenic according to its levels in rooting medium and availability to plant because in aqueous rhizospheric environment it transforms into various complex compounds and just a fraction is phytoextracted by sunflower roots. Yield was also affected due to deleterious effects of higher concentrations of arsenicals (80 and 100 mg As/kg soil) either as arsenate or arsenite with lower capitulum diameter and reduced hundred achene weight. Both, cultivars or hybrids of sunflower showed similar behavior towards its ability to cope with arsenic levels more than 100 mg As/kg soil with very little phytoextraction potential and accumulation in above ground biomass.