| It is widely recognized that zinc deficiency is one of major nutrition problem in calcareous soils of North China, and drought is also a stress factor to crop productivity in these areas. There was little investigation about mechanism of soil zinc supply under soil drought and relationship between zinc supply and crop response to water stress. Pot trial under greenhouse condition was conducted using a zinc deficient cumulic cinnamon soil from North China to study soil zinc availability and effect of zinc application on maize plant growth and physiological response to different soil moisture regimes. The ultrastucture of leaf cells of maize plants under different soil water conditions and zinc application was examined using transmission electron microscope.The experiment with split culture systems was conducted to examine maize plant roots distribution, plant nutrient uptake, and plant water use from subsoil as affected by zinc application in topsoil and different soil water treatments. Rhizobox experiment was conducted to study the status of zinc and transformation of various zinc forms in rhizosphere under different soil water conditions. The results are as following:1. Zinc application and adequate soil moisture significantly enhanced dry matter weight of roots, stems, leaves and total plants, especially shoot growth. Root to shoot ratio trended to increase by zinc deficiency and soil drought stresses. There was little difference of plant growth among zinc application rates (3.0-27.0 mg Zn/kg). However, plant biomass of would decrease with Sl.Omg Zn/kg zinc application.2. Zn concentration and Zn content hi roots, stems, leaves and total plants significantly increased with zinc application. Zn translocation from roots to shoots was stimulated by zinc application and adequate soil moisture supply. Higher Zn concentration in roots and stems was found in plants grown under drought while Zn content in plants decreased.3. The positive interactive effect of applied zinc and soil moisture treatments on plant growth and Zn uptake was observed. The highest biomass of plants was found under zinc application and adequate soil moisture. Under adequate soil water supply, especially water supply in topsoil, increase of plant growth and Zn uptake due to zinc application was more remarkable.4. The more pronounced effect of water supply on plants growth and Zn content was found in early grown plants with adequate water supply in topsoil than in subsoil. Plant dry matter weight and Zn uptake increased with adequate water supply in subsoil if plants were stressed by drought in topsoil. However, there was little influence of adequate water supply-3-in subsoil on plant biomass and Zn uptake when plants were grown on the condition of adequate water in topsoil. Moreover, root biomass and Zn content had a slight decrease.5. The distribution of early grown plant roots in different soil layers was not influenced by zinc application in topsoil but was affected by soil water supply. Under drought stress in topsoil dry matter weight of roots in upper soil layer decreased and the ratio of root biomass in upper soil layer to that in lower soil layer also decreased, indicating that roots tended to distribute in subsoil. On the contrary, root biomass in the upper soil layer increased with adequate water supply in topsoil and tended to distribute in topsoil. On the condition of drought in subsoil, root biomass in topsoil and subsoil all increased but the ratio of root biomass in upper soil layer to that in lower soil layer decreased, suggesting that roots tended to distribute in topsoil when plants were stressed by the drought in subsoil o6. With zinc application in topsoil, N, P, K, Ca, Mg content in plants and their translocation to shoots significantly increased but plant Fe, Mn, Cu uptake decreased and Fe, Mn, Cu translocation to shoots was not affected. N, P, K, Ca, Mg, Mn, Cu content in plants under drought in topsoil all decreased except that plant Fe uptake increased. On the condition of adequate water suppl...
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