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Responses Of Soil Carbon Process To Different Forms Of Nitrogen Additions In Larix Gmelinii Plantation

Posted on:2018-03-15Degree:DoctorType:Dissertation
Country:ChinaCandidate:L L DongFull Text:PDF
GTID:1360330548474071Subject:Botany
Abstract/Summary:PDF Full Text Request
Atmospheric nitrogen(N)deposition has been considered as one major component of global change and is predicted to increase in the future,which has been demonstrated to have significantly altered forest carbon balance in the last several decades.However,the influence of different types of N on it still remained unclear.Most researchers have concentrated on inorganic N deposition and its biogeochemical cycling.In fact,the average contribution of organic N to total atmospheric N deposition can be as high as 33%.However,most studies about N deposition effects on soil carbon cycle process neglected the vital function of organic N.We hypothesized that fertilization using a single N source may not reflect the influence of atmospheric N deposition on C cycle of forest soils accurately because of the various N components in the atmosphere.Different ratios of inorganic N to organic N(10:0,7:3,5:5,3:7,0:10 and 0:0)were mixed with equal total amounts and then used to fertilize temperate forest soils in Larix gmelinii plantations in Northeastern China.In this project,ammonium nitrate was selected as an inorganic N source,while urea(45%),glycine(40%),and glutamate(15%)were chosen as organic N sources.Eighteen plots,each with 10 m×10 m dimensions were set up,surrounded by an approximately 10 m wide buffer strip.During each application,fertilizer was weighed,mixed with 25 L of water,and applied to each plot below the canopy using a backpack sprayer.Two passes were made across each plot in order to ensure an even distribution of fertilizer.The Control plot received 25 L water without N.This work aims to investigate the influence of fertilization with multiple forms of nitrogen on the soil carbon process(e.g.,fine root production and turnover,litter decomposition progress,soil respiration,soil enzyme activity,soil C stability and soil C sequestration potential)and its transfer(the transfer of soil labile carbon fractions to stable fractions)in temperate forest ecosystems,and also is expected to provide scientific contributions for understanding forest soil C sequestration potential and for developing mechanism underlying soil C stability.Our main results showed that:(1)The total amount of atmospheric nitrogen deposition from precipitation was 21.97 kg N hm-2 in 2011,2014 and 2015.The average contribution of ON to total N is 29%,which is usually ignored by most ecologists in current literature.(2)During the early simulated nitrogen deposition experiment in 2014,all forms of simulated N deposition significantly promoted soil respiration rates and cumulative soil surface CO2 flux during the growing seasons(P<0.05).Furthermore,soil respiration rate and cumulative soil surface CO2 flux increased as the percentage of organic N increased.(3)During the late simulated nitrogen deposition experiment in 2015 and 2016,addition of inorganic N deposition significantly decreased soil respiration rates,cumulative soil surface CO2 flux and Q10 during the growing seasons(P<0.05).However,the ratio of inorganic N to organic N impacted soil respiration and its cumulative soil surface CO2 flux.Soil respiration rates and its cumulative soil surface CO2 flux increased as the percentage of organic N increased.As a consequence,the pure addition of organic N deposition significantly increased soil respiration rates.Moreover,our results showed that the difference in soil respirations rates cased by ratio of inorganic N to organic N is due to its heterotrophic respiration,based on the data form the trenched technique.(4)Different ratios of inorganic N to organic N had different influence on leaf litter decomposition during a two-year experiment.Our results showed that addition of inorganic N decreased leaf litter decomposition rate.However,leaf litter decomposition rate in increased as the percentage of organic N increased.In fact,the pure addition of organic N deposition significantly increased leaf litter decomposition rates.(5)Different ratios of inorganic N to organic N had different influence on[1+2]roots and[3+4]roots decomposition because of their difference in carbon quality.Our results showed that all ratios of inorganic N to organic N had no influence on[1+2]roots decomposition.Addition of inorganic N decreased[3+4]roots decomposition rate.[3+4]roots decomposition rates increased as the percentage of organic N increased.In fact,the pure addition of organic N deposition significantly increased[3+4]roots decomposition rates.(6)Addition of inorganic N decreased fine root biomass.However,fine root biomass in increased as the percentage of organic N increased.In fact,the pure addition of organic N deposition significantly increased fine root biomass.Greater differences were observed in estimating the fine root production and turnover rate by minimum-maximum calculation,balancing transfers method and the ingrowth core method.The results from balancing transfers method and ingrowth core method showed that N addition of inorganic N decreased fine root biomass significantly reduced fine root production and turnover rates(P<0.05).Fine root production and turnover rates also increased as the percentage of organic N increased,and the pure addition of organic N deposition significantly increased fine root production and turnover rates.However,the results from balancing transfers method and ingrowth core method showed that N deposition did not significantly fine root production and turnover rates(P>0.05).Moreover,fine root biomass(<2 mm)explained an average of 82%variations of soil respiration rates.(7)As compared with the control,all ratios of inorganic N to organic N addition stimulated the activities of soil hydrolase(?-fructofuranosidase,cellulose,acid phosphatase,and urease)significantly after three years of N addition.However,the ratios of inorganic N to organic N addition had different influence on the activities of soil oxidases(polyphenol oxidase and peroxidase).Addition of inorganic N decreased the activities of polyphenol oxidase and peroxidase.However,their activities increased as the percentage of organic N increased.In fact,the pure addition of organic N deposition significantly increased the activities of polyphenol oxidase and peroxidase.(8)As compared with the control,all ratios of inorganic N to organic N addition increased dissolved organic carbon.However,the ratios of inorganic N to organic N addition had different influence on microbial biomass carbon and liable carbon contents.Addition of inorganic N decreased microbial biomass carbon and liable carbon contents and addition of organic N increased microbial biomass carbon and liable carbon contents.In summary,our results in this project indicated the importance of the inorganic N to organic N ratio in controlling the soil C cycle,which can consequently change the ecological effect of N deposition.
Keywords/Search Tags:Plantation
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