Inhibition of photosynthesis and transpiration in relation to mercury‐induced root damage in spruce seedlings

Abstract

Spruce seedlings [Picea abies (L.) Karst.] were exposed in nutrient solutions to a range of concentrations of HgCl2 and CH3HgCl for 7 weeks. The mineral, chlorophyll and water contents of the needles, and dry weights of root and needles were then estimated. The rates of photosynthesis, transpiration and dark respiration of the intact plants were determined using a Li‐cor portable photosynthesis‐measuring system. CO2 uptake decreased as the supply of both forms of Hg increased. Rates of transpiration were significantly reduced only after exposure to CH3HgCl. Similar concentrations of Hg were found in needles independent of the form of Hg supplied. Decreased rates of CO2 uptake at 100 nM HgCl2 and 1 nM CH3HgCl could be explained by lower levels of chlorophyll, and by lower levels of chlorophyll and closed stomata at all other CH3HgCl concentrations. Only at 1000 nM HgCl2 were other photosynthetic parameters affected. Decreased rates of transpiration and the lower chlorophyll levels in the needles did not appear to be due to the direct action of Hg, but rather to root damage that leads to a decrease in water supply and nutrient levels in the needles.

Detection and Quantification of Unbound Phytochelatin 2 in Plant Extracts of Brassica napus Grown with Different Levels of Mercury

“…Pea (Pisum sativum) and spearmint (Mentha spicata) absorb Hg from solution, and roots accumulate much greater amounts of Hg than shoots (Beauford et al, 1977). Similar results have been found in Norway spruce (Picea abies; Godbold and Hü tterman, 1988), willow (Wang and Greger, 2003), and aquatic plants (Coquery and Welbourn, 1994).…”

Changes in Hg fractionation in soil induced by willow

“…The shoot/root Hg concentration ratio was low and rather stable since it was not dependent on time (Table 2). A low distribution of Hg to the shoots was also found in willow grown in hydroponics and in other plant species, which is probably due to the roots having strong affinities for Hg, thereby trapping most of the available Hg (Beauford et al, 1977;Godbold and Hu¨tterman, 1988;Greger et al, 2005;Wang and Greger, 2004). Accumulation of Hg in all parts of plants significantly increased with time (Table 2), whereas the readily exchangeable Hg fractions accessed by 1 M MgCl 2 extraction in the rhizospheric soil decreased with time (Table 4).…”

Effects of humic acid on transport and transformation of mercury in soil-plant systems

“…Hg can be washed away through watering the plants, since there is a small hole on the bottom of the pot. Hg can also escape to the air in the form of Hg ~ which is formed through biochemical processes both in the soils and the plants (Du and Fang, 1982;Godbold and Htittermann 1988;Boudou et al, 1991). It can be seem that a very small fraction of Hg was transported into the plant (all less than 0.1%).…”