Regulation Of Phosphorus Supplying Rates On The Winter Wheat-Maize Seedling Growthing Process

Phosphorus stress is one of the key factors to limit crop production. Screening of crops varieties which efficiently use phosphate is important to increase the crops capacity to utilize soil phosphate. Few researchers reported the differences of response to phosphate between wheat and maize.Two varieties of wheat (Xiaoyan 22 with more tillerings, and Lankao 4 with less tillerings) and maize (Tunyu 65 with potentially higher yield, and Hudan 4 with potentially lower yield) were grown in Hoagland solution to investigate the effects of phosphate concentration on biomass of shoot and root, P uptake, Chlorophyll fluorescence parameters and root morphological character of them at different seedling stage. Phosphate levels referred to 0 (P0), 0.05 (P1), 0.3 (P2), 0.5 (P3) P2O5 mmol·L^-1. The main results of the research are as follows:1. Both of wheat and maize responded to low phosphorus stress. However, the responses were different in growth period and genotypes. Shoot biomass and root biomass of crops also responded differently. During the early stage of seedling (40 days after emergence), shoot biomass of crops didn't decrease significantly with the low concentration of phosphate comparing with normal phosphate (0.5 P₂O₅ mmol·L^-1) while opposite results were found during the later stage of seedling (40～50 days after emergence). Under low-phosphate stress, root biomass of maize increased while root biomass of wheat was found to be decreased. Total biomass of maize was more sensitive to the reduction of phosphate concentration than that of wheat during the early stage of seedling while the reverse was true during the later stage of seedling.2. There were different effects of phosphate level on P uptake by wheat and maize. They also depended on genotypes, organs and time of measuring. P uptake in different parts of crop mainly depended on biomass rather than P concentration of crop. The maximum P uptake by wheat was higher than maize during the early seedling stage (25 days after seedling emergence), while no difference was found during the later seedling stage (40-50 days after seedling emergence). When 0.05 mmol·L^-1 treatment was used as a control, P uptake of whole plant for maize was more sensitive to P in medium than for wheat, Lankao 4 was more sensitive than Xiaoyan 22, and no difference was found between Tunyu 65 and Hudan 4. 3. Leaf net photosynthetic rate (Pn), stomatal conductance (Gs) and stomatal limiting value (Ls) of wheat and maize were gradually reduced while intercellular CO₂ concentration (Ci) was enhanced because of P deficiency, suggesting that the decreased photosynthetic rate might be controlled by non-stomatal limitation. When no phosphate was applied, leaf net photosynthetic rate (Pn) of wheat was higher than maize while Pn of maize was significantly higher than wheat and it was also more sensitive to phosphate when phosphate was supplied. Leaf net photosynthetic rate (Pn) of Tunyu 65 was always greater than Hudan 4 while the difference of Pn between two wheat genotypes was fluctuant with the phosphate levels. Comparing with normal phosphate level (P3), lack of phosphate (P0) caused reduces of maximum fluorescence (F_m), variable fluorescence (F_v), the intrinsic photochemical efficiency (F_v/ F_m) and potential activities (F_v/ F₀) of wheat and maize leaves and increases of original fluorescence (F0), indicating that the photo change and PSâ…¡use efficiency decreased. F_v / F_m of maize leaf was reduced due to P deficiency (P1) while that of wheat leaf wasn't. This suggested that photo-inhibition of photosynthesis happened to maize under low phosphorus stress. Hudan 4 showed greater tolerance to low phosphorous stress than Tunyu 65.4. Root dry weight, length, surface area and volume of wheat and maize increased significantly when phosphate was applied, comparing with P0. Increase of root length attributed mainly to fine roots. Xiaoyan 22 had greater root biomass and root shoot ratio under low-P stress than Lankao 4 while Tunyu 65 had greater root biomass and root shoot ratio than Hudan 4.5. When phosphate was applied, Lankao 4 had greater tillers number, height and leaf area than Xiaoyan 22 while Hudan 4 had greater leaves number, height and leaf area than Tunyu 65.