The Infection Of Arbuscular Mycorrhizal Fungi At The Paddy Fields With Different Nitrogen Levels And The Effects On The Nitrogen Loss

The Taihu Lake Basin is a densely planted area of paddy rice.As a typical wetland crop,the agricultural non-point source pollution and the spread of pollutants due to the farming of paddy rice are very serious.It has become a key issue to control the non-point source pollution when considering the loss of nitrogen and phosphorus in the paddy field during the paddy rice growth process.A large number of studies has shown that AMF can significantly improve the host plant mineral nutrition(phosphorus,nitrogen,sulfur and trace elements,etc.),and promote the absorption and assimilation of the plant nitrogen,the mineralization of the organic nitrogen,nitrogen fixation and many other soil nitrogen cycle Process.It shows that the use of arbuscular mycorrhizal fungi to enhance the absorption and utilization of nutrients in paddy soil is an effective way to control non-point source pollution of farmland.In this paper,a field experiment was conducted at the Changshu Agricultural Ecological Experiment Station of the Chinese Academy of Sciences to study the effects of nitrogen application rates and external environmental factors on the AMF infection rate in rice roots during different growth periods.A simulated rainfall experiment was conducted on the collected undisturbed soil from the paddy fields to study the relationship between AMF infection rate and nitrogen loss,the external environmental factors in paddy fields.The main work and conclusions are as follows:(1)Four treatment groups were designed: 1)N0(0kgN /(ha · a));2)N270(270kgN /(ha · a));4)N375(375 kg N /(ha · a))nitrogen with organic fertilizer.The rice roots and their surrounding soil in the field were collected during fallow,seedling,tillering,sunning,heading,filling,maturing and fallow before transplanting periods.The AMF infection rate in rice roots was measured by the staining method.The changes of AMF infection rate in rice roots at different growth stages were investigated.The AMF infection rate in the seedling stage without nitrogen fertilizer was the lowest,which was only 6%.The trend of the AMF infection rate from the seedling stage to the sunning stage was an upward,the highest value in the whole growth stage was 55.96%.AMF infection rate fluctuated within the range of 20% ~ 50% after the sunning stage.The effects of applying nitrogen fertilizer and organic fertilizer on AMF infection rate in rice roots varied in different growth stages,but AMF infection rates which were varied in different growth stages were not influenced by the amount of nitrogen fertilizer and organic manure,and all showed the general trend which is the increase from seedling to sunning stage,the decrease from sunning to heading stage,the increase from heading to filling stage and the decrease from filling to fallow stage.(2)To explore the influence of external environmental factors on arbuscular mycorrhizal fungi,the soil moisture content,soil pH,soil temperature,soil NH3-N and NO3-N and rice leaf area index under different N treatments were measured.The correlation between environmental factors and rice root AMF infection rates under different nitrogen treatments at different growth stages was investigated using Spss20.0.Correlation results showed that soil moisture,soil pH and rice root AMF infection rate showed a certain degree of positive correlation;soil temperature and rice AMF infection rate was not significantly correlated;soil ammonia nitrogen,nitrate nitrogen and rice leaf area There was a negative correlation between soil ammonia nitrogen,nitrate nitrogen,rice leaf area index and root AMF infection rate.(3)This research is to build rainfall-soil-runoff system,study the influence of AMF infection rate on nitrogen spillover output in paddy field,collect original undisturbed soil in paddy field with different growth stages by using soil ring knife,design soil splash plate based on the hydrological data of Suzhou.The intensity and duration of artificial rainfall were determined to simulate small-area runoff experiments.Soil erosion and rainfall runoff were collected to determine the amount of nitrogen loss in the runoff.The results show that the loss of the proportion of soil particles and the total nitrogen in runoff fluid is negatively correlated with the AMF infection rate,and AMF plays a certain role in reducing soil nitrogen output and soil erosion.The amount of total nitrogen loss in runoff during sunning period was lower than that in fallow period.The amount of nitrogen loss in runoff after adding nitrogen fertilizer was higher than that without nitrogen fertilizer.The amount of total nitrogen loss was the highest in N300 treatment,which was 1.98 mg / L,accounting for 6.75% of nitrogen application.The lowest total nitrogen loss under N0 treatment was 1.975 mg / L,and the highest nitrogen loss under N270 was 2.20 mg / L,accounting for 7.33% of the amount of nitrogen applied.The amount of total nitrogen loss was the lowest under N0 treatment with a loss of 2.06 mg / L.Nitrate loss in runoff was mainly dominated by nitrate nitrogen,accounting for more than 90% of total nitrogen loss,followed by ammonia nitrogen and nitrite nitrogen.Therefore,nitrate nitrogen was the key to reducing farmland nitrogen loss.The results of the experimental study in this paper can guide the rational arrangement of paddy fields in the rainy season of the Yangtze River Delta region and effectively reduce nitrogen losses.It can guide the scientific design of non-point source pollution control systems for paddy fields,such as river ponds,biological retention ponds,and ecological ditch,and also instruct Rational Combination of Fertilization and AMF Intensified Infection to Reduce Nitrogen Loss in Rice Fields.