Effect Of Soil Copper Contamination On Growth And Development Of Rice

Copper (Cu) is an essential element for plants, but the excessive soil Cu could have adverse effects on plant growth. According to soil quality assessment, the Cu concentration of the clean soil (first class farmland) was 35 mg·kg-1, light polluted soil (second class farmland) was 100 mg·kg-1, and heavy polluted soil (third class farmland) was 400 mg·kg-1. With the rapid development of industry and large-scaled using of herbicides and pesticides which contains Cu, the area of soil contaminated by Cu expanded every year. In order to clarify the effect of soil copper contamination on growth and development of rice, a soil culture experiment was conducted using 4 indica rice cultivars with 3 levels of soil Cu treatment(CK, none Cu addition, 30.13 mg·kg-1; 200 mg·kg-1; 400 mg·kg-1)under mimic-field conditions. Main results are as follows:(1) Soil Cu treatments significantly increased the Cu concentrations in roots, stem-sheaths, leaves and panicles of all test varieties at tillering, heading and maturity stages; but different varieties responded differently. There were little differences on the increase of root Cu concentrations between growth stages, but the stem-sheath concentration was increased more at tillering compared with heading and maturity stages; likely, panicle Cu concentration at heading was increased more than that at maturity stage. Significant interactive effects between varieties and Cu treatments were detected on the Cu concentration of roots, stem-sheaths and leafs at tillering stage, and on the panicle Cu concentration at heading stage.(2) At tillering and heading stages, the soil Cu treatments greatly decreased the ratio of Cu concentration of aerial parts (leaf, stem, and panicle) to the roots (RCAR) of all varieties. However, there were no significant differences on RCAR except the ratio of leaves to roots at tillering stages between varieties. At heading stage, no significant differences on all RCARs were detected between varieties. There was no significant interactive effect on RCAR between varieties and Cu treatments at different growth stages.(3) Soil Cu treatments significantly prolonged the growth period, decreased leaf area index (LAI) of four varieties at tillering and heading stages. Soil Cu treatments also greatly slowed down the speed of leave emergence of main stems, reduced the plant height and tillers number. The effects of soil Cu treatment on leaf emergence rate, the plant height and tiller number were disappeared 28 days after transplanting (DAT). Soil Cu treatments caused interveinal chlorosis symptoms on the functional leaves, but the effects were apparent only before 21 DAT. The impact of 400 mg·kg-1Cu treatment was greater than that of 200 mg·kg-1. In the middle and late growth stages, there were little effects of higher soil Cu concentration on the leaf emergence rate, functional leave color, plant height and total tiller number.(4) Soil Cu treatments significantly reduced the number and total length of adventitious roots per-plant, significantly decreased the dry weight of roots per-plant at tillering and heading stages, reduced the average length of adventitious roots andα-naphthylamine (α-NA) oxidizing capacity per-plant at tillering stage, significantly increased the diameter of adventitious root at heading stage; Soil Cu treatments affected little on the average length of adventitious root at heading stage andα-NA oxidizing capacity at tillering stage based on dry weight. There were significant differences between varieties on the number of adventitious roots per-plant, the root dry weight per-plant,α-NA oxidizing capacity per-gram dry weight at tillering and heading stages, as well as the diameter of adventitious root, total length of adventitious roots per-plant andα-NA oxidizing capacity per-plant at heading stage. Significant interactive effects between varieties and Cu treatments were detected on the root dry weight at heading stage, but no effect was detected on number and total length of adventitious roots per-plant, the average length of adventitious roots, the diameter of adventitious root,α-NA oxidizing per-weight,α-NA oxidizing per-plant at tillering and heading stages, and the plant root dry weight at tillering stage.(5) Both 200 mg·kg-1and 400 mg·kg-1 soil Cu treatments significantly reduced the dry weight at tillering stage of all tested varieties, and the higher the concentration, the greater the reduction. As to heading and maturity stages, 200 mg·kg-1 soil Cu treatment had no effects on dry weight of all tested varieties, while 400 mg·kg-1 had significant negative effects on dry weight (But the negetive effect was smaller than that at tillering stage). Soil Cu treatment had no effect on the dry matter distribution of different organs at all growth stages, except that the 200 mg·kg-1 treatment reduced the proportion of dry matter in panicles at harvest.(6) Soil Cu treatments significantly reduced the grain yield of all varieties, and the higher the concentration, the greater the yield decreased. There were significant differences on spikelet number per panicle and 1000-grain weight with different soil Cu treatments, while no effect was detected on the panicle number per area and filled grain percentage. There were significant differences between varieties of gain yield per area, panicle number per area, the spikelet number per panicle, seed setting rate and 1000-grain weight. There was significant interactive effect between varieties and Cu treatments on panicle number per area, the spikelet number per panicle and 1000-grain weight.