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Influences Of Urea Combined With Urease/Nitrification Inhibitor On Nitrogen Transformation And Its Mechanism Research Of Degraded Alpine Meadow In The Source Region Of Three Rivers

Posted on:2022-06-13Degree:DoctorType:Dissertation
Country:ChinaCandidate:P LiuFull Text:PDF
GTID:1483306722458484Subject:Physical geography
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Fertilization is one of the important measures to control and restore degraded alpine meadows,and it is an important measure to restore and improve the ecological functions of degraded alpine meadows.However,the utilization efficiency of nitrogen resources is low and will cause serious damage to the ecological environment.Therefore,this paper takes the moderately and lightly degraded alpine meadows in Maqin County,the source region of the Three Rivers as the research object to study the effect of urease combined with urease inhibitor NBPT and nitrification inhibitor DCD on nitrogen conversion in moderately degraded alpine meadows.The purpose is to study the following 3 aspects:(1)Based on plant nutrition and stable isotope technology,we studied the four major functional groups(Gramineae,Cyperaceae,legumes,weeds)on nitrogen use efficiency,aboveground/underground net primary productivity and forage nutrition to screen out the best urea+inhibitor combination treatment.The purpose is to realize the optimal utilization of resources and ensure the sustainable development of animal husbandry and provide technical support.(2)The paper research the basic characteristics of NH3,N2O,CO2,CH4 emissions from urea-N in the moderately degraded alpine grassland ecosystem by applying urea combined with NBPT and DCD,and obtain basic physical and chemical properties data in soil reservoirs to reveal gas emissions Mechanism.The purpose is to provide a scientific basis for the ecological environment protection of the Qinghai-Tibet Plateau.(3)Soil microorganisms are the central link of the ecosystem.It was determined that the diversity and community structure of fungi and bacteria in moderately degraded alpine meadow ecosystems by 16s and ITs techniques to explore the effect of urea combined with NBPT/DCD on key microorganisms.It provides a scientific basis for the mechanism of urease/nitrification inhibitors in moderately to mildly degraded alpine meadows.The research results of this paper are as follows:1)Species diversity:The addition of urea with NBPT and/or DCD did not significantly affect the species diversity of moderately and lightly degraded alpine meadows,but significantly improved the important value of dominant species and vegetation coverage.It shows that the addition of inhibitors will reduce the effect of urea on the plant diversity of moderately and lightly degraded alpine meadows.Vegetation productivity:The aboveground biomass of moderately degraded alpine meadow under single urea treatment was 277.01 g·m-1·y-1,U+NBPT treatment significantly increased by nearly 36.14%,and concentrated on grasses and weeds.The addition of urea inhibitors did not significantly change the biomass of mildly degraded alpine meadows.It shows that NBPT has a significant effect on the restoration and management of moderately degraded alpine meadows.2)Nitrogen utilization efficiency:In a mildly degraded alpine meadow,the 15N recovery rate of plants and roots under single urea treatment was only 33.44%,while U+NBPT and U+NBPT+DCD treatments increased the 15N recovery rates of plants and roots,30.44%and 19.44%,respectively.Pearson correlation analysis shows that NH4+-N,C/N ratio,TN and TP in soil are the main factors affecting nitrogen utilization.In the moderately degraded alpine meadow,the 15N recovery rate of plants and roots under single urea treatment was only 29.94%,and nearly 70%of nitrogen was not absorbed and utilized.U+NBPT treatment increased significantly by 44.20%.The U+DCD treatment significantly reduced 36.06%.Pearson correlation analysis shows that soil NH4+-N and NO3--N content are the main factors affecting moderately degraded alpine meadows.It is proved that the addition of NBPT can improve the effect of urea nitrogen in the soil and increase the internal circulation of N in the mildly degraded alpine meadow ecosystem.DCD has no effect on nitrogen utilization efficiency of moderately degraded alpine meadows.The effect is better in moderately degraded alpine meadows.3)Gaseous nitrogen loss:U+NBPT or U+NBPT+DCD has a significant effect on delaying the time and peak of NH3 volatilization from moderately and mildly degraded alpine meadows.Under mildly degraded alpine meadows,the cumulative loss of NH3 volatilization by single application of urea was 16.36 kg N·hm-2.The cumulative loss of N2O is 34.12 kg·hm-2.The cumulative loss of the two is as high as50.48 kg·hm-2,accounting for 33.65%of the nitrogen application rate.Among them,N2O loss is the main way for lose urea nitrogen.U+NBPT and U+NBPT+DCD treatments significantly reduced the cumulative loss of NH3 volatilization by 52.08%and 48.66%.The two treatments significantly reduced the cumulative loss of N2O by26.55%and 70.63%.U+DCD treatment did not reduce the loss of NH3 volatilization,but significantly reduced the cumulative loss of N2O by 38.10%.In the moderately degraded alpine meadow ecosystem,the cumulative loss of NH3 volatilization treated by U was as high as 18.77 kg N·hm-2.The cumulative loss of N2O is 26.40 kg·hm-2.The cumulative amount of the two is as high as 45.17 kg·hm-2,accounting for 30.11%of the nitrogen application rate.The addition of NBPT to urea inhibited NH3volatilization,and the addition of DCD to urea inhibited N2O emission.The addition of NBPT and DCD to urea significantly reduced both by 60.20%and 56.44%.Redundancy analysis shows that the addition of inhibitors has a significant positive correlation with soil NH4+-N and NO3--N content.It is proved that the inhibitor inhibits the activity of related microorganisms,reduces the loss of gaseous nitrogen of urea,and increases the accumulation of inorganic nitrogen in the soil.NBPT+DCD has a significant effect on inhibiting the loss of urea nitrogen in moderately degraded alpine meadows.4)Greenhouse gas emissions:In the slightly degraded alpine meadow ecosystem,different treatments have no impact on the CO2 emission rate and cumulative emissions.After applying urea,the weak CH4 sink in the mildly degraded alpine meadow was converted into a CH4 emission source,which was 1.10 kg·hm-2.However,after adding DCD to urea,CH4 emissions were weak CH4 sinks and significantly decreased to-0.44 kg·hm-2.In the moderately degraded alpine meadow ecosystem,U and U+DCD significantly reduced the cumulative CO2 emissions compared with the control without fertilization,by 21.29%and 17.20%,respectively.U+DCD and U+NBPT+DCD treatments had no significant difference in the cumulative amount of CH4 emissions,and both showed weak CH4 sinks.However,U+NBPT treatment significantly increased CH4 emissions,showing a positive growth.Through RDA analysis,there is a significant positive correlation between inhibitor addition and soil carbon and nitrogen content.The addition of NBPT makes the soil exist in the soil in the form of inorganic nitrogen.Although it inhibits urease-related microorganisms,it increases the relative abundance of other microorganisms,such as Acidobacteria and Ascomycota.As a result,soil CO2 and CH4 emissions have shown a significant positive increase.DCD has the most significant effect on reducing CO2and CH4 emissions from moderately degraded alpine meadows,especially in moderately degraded alpine meadow ecosystems.5)Soil fungi and bacterial communities in lightly degraded alpine meadow:Characteristics of bacterial community:Urea+different inhibitor treatments had no significant effect on the dominant phyla of soil bacteria,and the relative abundance of common phyla changed.U+NBPT increased the relative abundance of the dominant genus of Acidobacteria,RB41 by 1.28%.U+DCD would have a certain inhibitory effect on Nitrospira of the Nitrospira phylum.Fungal community characteristics:The relative abundance of Ascomycota in the dominant phyla of soil fungi increased by urea+different inhibitors,while the relative abundance of Basidiomycota and Zygomycota decreased.Under U+DCD treatment,the relative abundance of Archaeorhizomyces of Ascomycota significantly increased by 26.66%(p<0.05),while U,U+NBPT inhibited Hygrocyb of Basidiomycota.6)Soil fungi and bacterial communities in moderately degraded alpine meadow:Characteristics of bacterial community:The relative abundance of the dominant genera and rare genera of soil bacteria changed.Under U treatment,the relative abundance of Proteobacteria Rhodoplanes increased by 0.34%.U+NBPT,U+DCD+NBPT inhibited the Actinomycete Solirubrobacteralesf?67-14.Fungal community characteristics:The relative abundance of Ascomycota under U+NBPT+DCD was 31.79%,which was the lowest.The relative abundance of Basidiomycota under CK treatment was 4.86%,which was significantly lower than other treatments(p<0.05).Urea+urease/nitrification inhibitor can promote the growth of Clitopilus.7)According to the structural equation model,urea+inhibitor directly affects the aboveground biomass of lightly and moderately degraded alpine meadows by directly affecting the content of soil ammonium nitrogen,but has no significant effect on the content of nitrate nitrogen.8)The results of RDA and SEM analysis show that urea+inhibitors ultimately affect NH3 volatilization by affecting the content of soil NH4+-N and NO3--N;the other pathway is urea+inhibitors by affecting the relative abundance of soil fungi dominance,and above-ground biomass,ultimately affect NH3 volatilization.Urea+inhibitor affects the relative abundance of soil dominant bacteria,NH4+-N and NO3--N content,and ultimately affects N2O emissions.
Keywords/Search Tags:Degraded alpine meadows, Urea, Urease/Nitrification Inhibitor, Soil Nutrient, Nitrogen Fertilizer Utilization, Greenhouse gas emission, Ammonia volatilization, Soil fungi and bacterial communities
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