Effect of tea compost and potassium humate on sunflower (Helianthus annuus L.) resistance to the toxicity of lead

Lead is an unnecessary elements that have highly toxic effects on plants and humans. Severe effects of this heavy element on physiological and morphological aspects of seedling have been reported. Lead prevents the seed germination, root elongation and seedling development, so creates disruption in essential elements uptake such as magnesium and iron, and reduces the amount of carbon dioxide capture. In contaminated soils poor establishment and thus reduce plant biomass, reduces the efficiency of phytoremediation. The seed priming is one of the important ways of seed enhancement before planting. Which that seeds are emerged into the water or osmotic solution and then soaked seeds remains in lag phase and don’t sprout.
This research was conducted in research greenhouse, college of agriculture, University of Shahrekord in 2016. Sunflower seeds was purchased from Seed and Plant Improvement Institute, Karaj, Iran. To study the effect of potassium humate and compost tea on sunflower seedling tolerance to toxic concentrations of lead factorial experiment in a completely randomized design with three replications done. Treatments were control, potassium humate and compost tea and four levels of lead concentrations (0, 200, 400 and 600 mg of lead/kg of soil). The concentration of compost tea (1: 5) and potassium humate was 300 mmol/L.
Results showed that increasing of lead concentration significantly reduced the root dry weight, stem dry weight and leaf dry weight, chlorophyll a, chlorophyll b and increased carotenoids, proline content and electrolyte leakage. Seed priming with potassium humate and compost tea alleviated the damage effect of contaminated soil with lead on mentioned parameters. In lead stress, potassium humate increased root dry weight (733 mg), leaf dry weight (73 mg), chlorophyll a, chlorophyll b and lead concentration of root and aboveground of sunflower. However, compost tea increased proline (27 µm/l) and carotenoids (0.7 mm/g fw) and decreased electrolyte leakage (5.54 %) compared with control.
Generally in past researches indicated that reducing of seedling weight can be due to decline of essential nutrients uptake such as K, Ca, Mg and Fe (Gogorcena et al, 2002) and decline of biomass production due to disruptions in the photosynthesis, respiration and nitrogen metabolism (Balestrasse et al, 2001) induced by toxic concentrations of lead.
Potassium humate in the most toxic lead concentration prevented the loss of dry weight of roots and leaves by 51% and 28% in compared to control, respectively. Because the potassium increases permeability of cell walls, which makes it facilities the translocation of seed reserves from the endosperm to the embryo axis. Additionally it causes the synthesis of proteins, nucleotides, and more growth of embryo (Umair et al, 2010) and resulted increasing of seedling weight. In general, the replacement of lead instead of magnesium in the chlorophyll causes chlorophyll degradation. Iincrease of concentrations of chlorophyll a (171%) in the most toxic lead and chlorophyll b (381%) at 400 mg/kg of lead by ppotassium humate can be related to the role of potassium. Potassium increases chlorophyll concentration and enhances the CO2 fixation.
In general, it can be concluded that with potassium humate and compost tea with increasing photosynthesis pigments and proline content and reducing electrolyte leakage increased of sunflower tolerance in contaminated soils with lead.