The Regulating Effects Of Long-time Nitrogen Fertilization On Photosynthetic Characteristics Of Winter Wheat And Soil Respiration

Water and nitrogen nutrition deficit are the key factors limiting agricultural production in arid and semiarid region, thus it is essential to fertilize nitrogen for increasing agricultural productivity under rain-fed conditions. The experiment was composed of indoor experiment and outdoor experiment. First part is to discuss the changes of photosynthetic performance index and adverse resistance signal of wheat under water and nitrogen deficiency condition. Then four nitrogen levels were devised in the range of 0-360 kgN/hm² to survey the effects of the nitrogen level on the physio-ecological characteristics and soil respiration. The main conclusions of this study were as follows:(1) It indicated that the reason of the decline of Photosynthetic Performance Index is different between the two varieties under water and nitrogen deficiency condition. The main reason of Zhengmai 9023 was because of destoy of photosynthetic electron transport chain and the loss of leaf water. The photosynthetic electron transport of Changwu 134 was affected by drought stress. The capacity of light-harvesting of antenna pigment and the activity of reaction center decreased under nitrogen stress. The capacity of light-harvesting and photosynthetic electron transport were affected to some extent under drought and nitrogen stress. But the influence degree of drought and nitrogen stress on photosynthetic capacity was closely related with the contents of endogenous NO and CTK. NO signal of Changwu 134 was not weakened obviously and the high conversion of iP+iPA and Z+ZR to DHZ+DHZR was contributed to scavenge the ROS which produced under stress condition. Therefore, the tolerent degree of its photosynthetic apparatus was better than Zhengmai 9023. (2) Chlorophyll content, photosynthetic rate, photosynthetic capacity index of the different developmental stage was improved by increasing nitrogen after jionting stage in renge of 0-180 kgN/hm², it is different to need different nitrogen level for different wheat varieties. The regulative effect of nitrogen was obvious on photosynthesis of Changwu 134, for example, the Chl and PI of N180 and N360 were significantly higher than the other treatments. The chlorophyll content of Changwu 134 was higher than Zhengmai 9023 in filling stage and ripening stage, so it could maintain higher photosynthetic rate and PI value in late growth stage. With the nitrogen level increasing in the range of 0¹80 kgN/hm², the Chl and PI of Zhengmai 9023 were improved and the value of PI and its parameters and Pn in N360 were lower than that in N180.(3) The red edge parameters between nitrogen and no-nitrogen treatments had a significant difference. There was a significant negative correlation between photosynthetic characteristics, leaf nitrogen contents and biomass of wheat with Lwidth. It had a positive correlation with other red edge parameters and higher correlation coefficient with REP than others. With the N content or Chl content of leaf increasing, red shift was observed in REP fertilized nitrogen and Lo with N90 and N180. 350-680 nm and 750-1100 nm could serve as canopy spactra sensitive band to detecte nitrogen nutrition.(4) The accumulation and distribution of dry matter and N were the main reasons to determine wheat yield except higher photosynthetic capacity. Though Changwu 134 had an obvious drought resistance and photosynthetic duration in ripenning stage than Zhengmai 9023, its N transferation from pre-flowering vegetative organs to grain and the N distribution in grain was increased obviously only on 180 kg N/hm² and 360 kgN/hm². But it was lower than Zhengmai 9023 in general. Accordingly, Changwu 134 was a variety that needed high N and had lower efficiency. To increase nitrogen application(≤180 kgN/hm²)could promote the dry matter accumulation of different growth stages after jionting, the dry matter distribution to aerial part in harvest stage, reduce root-shoot ratio which was contributed to the dry matter transfer to grain and one of the main reasons why N could increase yield. In addition, the biomass of aerial part of Zhengmai 9023 in every N treatment was higher than that of Changwu 134. So the yeild of Changwu 134 was lower than Zhengmai 9023.(5) Soil CO₂ emission rate was affected by the root biomass, soil temperature and soil humidity and N levels in the growth stage of wheat. With the N application increasing in the range of 0-180 kg/hm², the total soil CO₂ emission and rate were increased significantly by N application. When nitrogen level was above 180 kg/hm², the total soil CO₂ emission was not increased significantly. Soil CO₂ emission rate had a positive correlation with soil temperature and a negative correlation with soil humidity. Besides, there was consistent season change between soil CO₂ emission rate and soil temperature. Soil temperature had a great influence than soil humidity on soil CO₂ emission rate. When soil humidity closing to soil wilting poin(t8.5%), the influence of soil temperature was not obvious on soil CO₂ emission rate. The soil CO₂ emission rate began to decrease. The total soil CO₂ emission rate of 0,90,180,360 kgN/hm² in wheat field were 42%, 65%, 90% and 95% higher than bare land respectively. It indicated that increasing N could promote the ratio of root respiration to soil respiration.