Studies On The Regulation Mechanism Of Nitrogen And Phosphorus On Wheat Photosynthetic Performance

Many researchers have studied the photosynthetic performances for many crops. But the systemic studies combining the mechanism of photosynthesis with temporal and spatial changes of photosynthetic performances were rarely done, especially the temporal and spatial experiment of photosynthetic performances in wheat and the regulating mechanism by nitrogen and phosphorus fertilization were hardly studied. Therefore, this study was conducted in Agricultural University of Hebei, Baoding, during 1999-2001, using field-grown Henong859 as materials. The purpose of the study was to clarify some mechanism of photosynthesis under different fertilizing amount of nitrogen and phosphorus through determinations of photosynthetic rate, physiological and senescent properties, and population growth property, so as to provide some experimental foundation for reasonable fertilization of wheat in Hebei Plain. The results were summarized as follows:1 In certain rang of nitrogen application (N 75~225 kg ?hm"2), the more the nitrogen amount was fertilized, the higher values were the photosynthetic rate (PJ, stomatal conductance (gj, chlorophyll content(Chl), Hill reaction activity, ATPase activity and soluble protein content (pro) of the third leaf from top and flag leaf and unicycle photophosphorylation activity of flag leaf, while lower the intercellular CO2 consentrationCCj) was. The results demonstrate that nitrogen delayed the degradation of chlorophyll and soluble protein, increased the photosynthetic rate of leaves. But for the highest nitrogen treatment (N 375 kg ?hnr2) Chi content, ATPase activity, pro content, SOD and POD activities of flag leaf decreased and MDA content increased drastically from the 20th day after flag leaf full expansion, and the Hill reaction and unicycle photophosphorylation activities were lower than other treatments.2 With the increasing of nitrogen application (N 75~225kg ?hm"2), activities of superoxide dismutase (SOD) and peroxide dismutase of the third leaf from the top and flag leaf (POD) increased, but malondialdehyde(MDA) content decreased with nitrogen application(75~225 kg ?hm-2) so that RSP, PAD, LAI and LSC had higher values, which indicted that nitrogen fertilization increased activities of protective enzymes, retarded senescence and prolonged the photosynthetic function period. However, the activities of SOD decreased and MDA content increased for the highest nitrogen treatment.3 With the increase of phosphorus application (75~225 kg ?hm"2), Pn, Chi content, Hill reaction activity, ATPase activity, pro content of the third leaf from the top and flag leaf were higher. However, Chlb content, Hill reaction and unicycle photophosphorylation activities of flag leaf were retarded under high phosphorus treatment (375 kg ?hm"2), which indicated that their dynamics of Chlb content, Hill reaction and unicycle photophosphorylation activities of flag leaf were uniform, and the three parameters were more sensitive to phosphorus than other parameters. The Pn of flag leaf, however, still kept higher.4 Increased phosphorus fertilization (75~375 kg ?hm"2) resulted in that activities of SOD and POD increased, MDA content decreased, Moreover, the activities or contents of most of the physiological performances of the third leaf from top and flag leaf increased, so that the RSP, PAD, LSC, PDW and grain yield had higher values. These results were probably due to that phosphorus facilitated nitrogen metabolism, increased the activities of protective enzyme, delayed the degradation of chlorophyll, so that phosphorus retarded senescence and photosynthetic decline of the leaves and increased ear number, PDW, LAI and yield.