| Soil Cu concentration is one of the evaluation criterions on soil environmental quality. According to Chinese standard, it is 35 mg/kg for the first class of field soil (soil Cu background), 100 mg/kg for the second class and 400 mg/kg for the third class. Owning to fast development of industry and the application of Cu chemicals, the area of Cu-contaminated soil is extending, and soil Cu level is increasing. Soil Cu concentrations are even higher than 1000 mg/kg in some places.Up to present, the effects of soil Cu stress on rice growth, development, yield and quality are far from clear, especially in the area showed below. (1) Many researches were conducted under short-term Cu stress, thus the tolerance and adaptation mechanisms of plant to Cu stress were neglected. (2) The number of rice cultivars in some experimrnts were small, so it cannot represent different rice types. (3) Soil Cu concentrations were under 300 mg/kg in most experiments, below the third class of field soil. (4) The majority of the work on Cu effects on rice has been focused on yield, yield components, and aboveground biomass accumulation, but few examined the reason related to yield, the matter accumulation of different stages, and the underground part: roots. Furthermore, the principle of rice reaction to Cu stress in N and P accumulation and rice quality were rarely studied. To investigate these issues, a series of experiments were conducted with 20 rice cultivars as materials and soil Cu concentrations from 100 mg/kg to 1000 mg/kg. The aim was to understand the effects of soil Cu contamination on the growth and development of aboveground parts, root growth, root activities, yield, yield components, rice quality, matter production and distribution, N and P uptake and utilization, and Cu accumulation in rice plant. The results of the experiments explained the main causes of rice yield reduction under soil Cu contamination, and provide technical foundation to rice cultivars selection and cultivation methods for soil Cu-contaminated area.The major results were showed as follows:1. The yields of all the 20 rice were reduced under soil Cu level of 400 mg/kg (the third class of field soil), and the reducing rates ranged from 4.63% to 64.08%. According to yield reducing significantly , the 20 rice cultivars were divided into three classes. The cultivars with no significant yield reduction were belong to the first class, including Yang dao 6, Feng you xiang zhan and IR8. Their average yield reducing rate was 8.65%. The number of cultivars in the first kind occupied 15% of the 20 cultivars. The second class covered the cultivars with significant yield reduction at P0.05 level, including Nan jing 11, Wu yun jing 7 and Te qing. Their average yield reducing rate was 22.95%. The number of cultivars in the second kind occupied 15% of the 20 cultivars. The third class were cultivars with significant yield reduction at P0.01 level, including Ri ben qing, Ai zi zhan, Zao feng 9, Shan you 63, Gui chao 2, Lian jing 3, Nong ken 57, Wu xiang jing 14, Liang you pei jiu, Huang jing qing, IR 24, Wu yu jing 3, Zhen dao 88 and Yan jing 2. Their average yield reducing rate was 41.35%. The number of cultivars in the third class occupied 70% of the 20 cultivars. These results indicate that most cultivars (85%), in the investigated 20 cultivars, are sensitive to soil Cu stress (400 mg/kg), only a few cultivars (15%) are relatively tolerant to Cu stress.2. The basic characteristics of the cultivars without significant yield reduction under soil Cu concentration of 400 mg/kg were below: small number of panicles, more spikelets per panicle, higher weight per 1000-grain, higher biomass, lower harvest index, more N accumulation in plant, and lower Cu concentration in plant at maturity.3. The main causes of yield loss under soil Cu contamination were below: less and smaller panicle, less N accumulation and lower biomass. The cultivars with larger degrees of yield reduction would have larger degrees of decrease in panicle number, spikelet per panicle, N accumulation and biomass, and vice versa.4. The yields of Wu xiang jing 14 and Shan you 63 were all significantly reduced under soil Cu levels of 100 mg/kg to 1000 mg/kg, and higher was soil Cu level, the more in yield reducing rate.On rice growth and development, plant height, leaf number on main stem, the number of elongated inter-nodes and heading date were not significantly affected by soil Cu level below 200 mg/kg. But the indexes were significantly reduced or delayd by soil Cu levels of 400 mg/kg and above.On yield components, the yield reductions under soil Cu levels of 100 mg/kg and 200 mg/kg were resulted from the decrease of spikelets per panicle. But the yield reductions under soil Cu levels of 400 mg/kg and above were resulted from both the decrease of panicle number and spikelets per panicle. Further researches indicated that the reduction of panicle number was resulted from slower regreen after transplanting, delayed tillering, smaller number of tillers; and the reduction of spikelets per panicle was resulted from delayed tillering, smaller dry weight per stem, and less spikelets per unit of dry matter.On the matter production and distribution, the effect of soil Cu stress on the biomass production of rice was significant, the higher was soil Cu lever, the more reduction in biomass. The effects of Cu on matter accumulation, leaf area and leaf chlorophyll content were larger at earlier stage of rice growth than at middle and late stages. There was no clear effects of Cu on harvest index.On the uptake and utilizaton of N and P, soil Cu treatment significantly reduced N and P accumulation in rice plant, and N and P efficiency in grain production. The effects of Cu on N and P accumulation were larger than on N and P efficiency in grain production.On the Cu concentration, Cu concentration in rice plant increased with the elevation of soil Cu levels, and they correlated negatively and significantly (P<0.05 or P<0.01) with panicle numbers, spikelets per panicle, biomass, N accumulation, P accumulation, root weight per plant and root activities per plant.5. Along with the elevation of soil Cu levels, the brown rice and polished rice rates in grain processing decreased obviuosly. The contents of protein, Fe, Zn, Mn, Mg and Cu increased first and then decreased, with peak protein content at soil Cu level of 400-600 mg/kg, peak Fe, Zn, Mn, Mg contents at soil Cu level of 100-200 mg/kg. Cu concentrations in brown rice reached top at soil Cu level of 200 mg/kg for Wu xiang jing 14 (11.3 mg/kg), and 400 mg/kg for Shan you 63 (12.1 mg/kg), and they all exceeded Chinese Food Standard.The Cu concentrations in different parts of rice grain were in the order: cortex > brown rice > grain > polished rice > chaff. After grain processing, the maximum Cu concentration in polished rice was below Chinese Food Standard for Wu xiang jing 14, but exceeded Chinese Food Standard for Shan you 63. The Cu concentrations in cotex were below Chinese Feedstuff Standard for the two cultivars.6. The root generation and growth were inhibited, root contents of zeatin and zeatin ribosede (Z+ZR) and root activity was decreased under soil Cu contamination, nevertheless, physiological metabolism was disturbed due to more Cu uptake by root and more Cu accumulation in rice plant. Due to the root activity decreased and toxic effects of Cu in rice plant, the regreen of rice seeding and leaf generation was delayed, the uptake of N and P were affected, leaf area, chlorophyll contents, matter production were reduced. These lead to delayed tillering and panicle heading date, shorter plant height, decreased leaf number on main stem and elongated inter-nodes. Finally, less and smaller panicle, less N and P accumulation, reduced N and P efficiency in grain production and decreased biomass may be the important causes for rice yield loss under soil Cu contamination.
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