Effects Of Zinc On Photosynthetic Performance, Grain Yield And Quality In Winter Wheat

In order to clarify the effects of zinc on photosynthetic performance, grain yield and quality in winter wheat, a field experiment with four zinc fertilization levels (ZnSO4 7H2O 0, 11.25, 22.5 and 33.75 kg hm-2) was conducted on the Teaching and Demonstration Farm of Agricultural University of Hebei, Baoding, during 2001-2002, with field-grown winter wheat of two varieties, 8901-11 and 4185, as experimental materials. The changing dynamics of carbonic anhydrase (CA) activity, chlorophyll content (Chl) and net photosynthesis rate (Pn) in leaves of winter wheat were determined. The accumulation and translocation of nitrogen, phosphorus, potassium and zinc in different organs, the community photosynthetic parameters and the grain yield formation were investigated. The grain quality parameters at different Zn levels were also determined after maturity. The main results were summarized as follows:1. The activity of CA reached the maximum value at anthesis, and rapidly decreased thereafter with an exception of slowly-decreasing period during 10~20 days after anthesis. Among the different treatments, CA activity increased with the increase of Zn level and the highest value occurred at the Zn level of 11.25 kg hm-2, and the activity decreased when zinc fertilization amount exceeded the 22.5 kg hm-2. The CA activity in flag leaf and the 3rd leaf from top all reached the maximum at the 7th or 14th day after full expansion. The CA activity in the 3rd leaf from top was higher than that in flag leaf when they were just expanding, but the maximum value of CA activity in flag leaf was much higher compared with that in the 3rd leaf from top. Among the different treatments, the CA activity in flag leaf was highest at the Zn levels of 11.25-22.5 kg hm-, and the CA activity in the 3rd leaf from top, however, increased with the increasing zinc fertilization.2. There were differences in Chl between the two varieties, 8901-11 and 4185. TheChl in the two varieties were all increased by zinc fertilization, and the Chl highest in top function leaves and in flag leaf occurred at the Zn level of 11.25 kg hm-2.3. Affected by such factors as Chl and CA activity, the Pn of all leaves were also increased by zinc fertilization, and the highest Pn also occurred at the Zn level of 11.25 kg hm-2, just as the Chl and CA activity were. However, the responses of the two varieties to zinc fertilization were slightly differences in photosynthetic performances.4. The absorption of nitrogen, phosphors, potassium and zinc by wheat plants was boosted up, and the amounts of accumulation of the nutrients in all above-ground organs and their translation from vegetative organs to grains after anthesis were increased by fertilizing zinc. Leaf area index (LAI), community photosynthetic potential and crop growth rate (CGR) were all enhanced after fertilizing zinc, but there were small differences in zinc fertilization amounts for different community photosynthetic parameters to reach their highest value. It was not sensitive to zinc fertilization for the production of biological yield of 8901-11 or during its vegetative growth period, but very sensitive to zinc fertilization for the production of economic yield or during its reproduction growth period. The zinc level for 8901-11 to get its highest dry matter production was lower compared with that for 4185.5. In a suitable range of zinc fertilization, spike number per hm-2, grain number per spike and 1000-grain weight were all increased by zinc fertilization. Because of the interaction of the three yield components, the Zn levels for different yield components to reach their highest value were different in the two varieties. In 8901-11, spike number per hm-2 reached the maximum at the Zn level of 33.75 kg hm-2, grain number per spike reached the maximum at Zn 22.5 kg hm-2, and 1000-grain weight at Zn 11.25 kg hm-2. In 4185, spike number per hm-2 reached the maximum at the Zn level of 11.25 kg hm-2, but grain number per spike and 1000-grain weight at the level of 33.75kg hm-2.