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Effect Of Growing Season N Addition And Reduced Precipitation On Soil C Dynamics During The Non-Growing Season

Posted on:2021-02-08Degree:DoctorType:Dissertation
Country:ChinaCandidate:G Y YanFull Text:PDF
GTID:1360330605967126Subject:Ecology
Abstract/Summary:PDF Full Text Request
The increasing nitrogen deposition and redceuing precipitation caused by climate change affect the carbon budget of forest soil by changing the availability of soil water and nitrogen.Up to now,there are many studies on the effects of increasing nitrogen deposition and redceuing precipitation on the carbon budget of forest soil in the growing season.To a large extent,these results reveal the change rule of soil carbon budget in growing season under the scenario of increasing nitrogen deposition and reduceing precipitation,but the change rule of soil carbon budget in non growing season is rarely concerned.However,in order to truly understand the annual dynamic change of forest soil carbon budget,it is necessary to understand the response of soil carbon budget to increasing nitrogen deposition and redceuing precipitation in non growing season.Therefore,in this study,the short-term legacy effects of nitrogen addition(50 kg N hm-2 yr-1)and precipitation reduction(-30%penetration rain)in the growth season on non-growing season soil respiration,methane emission,fine root dynamics,litter decomposition and microbial community were studied by using the field in-situ control plots simulating long-term climate change.The main results are as follows:(1)Nitrogen addition and precipitation reduction significantly increased the average soil respiration in non-growing season by changing heterotrophic respiration and autotrophic respiration,while their combined effect did not significantly change the average soil respiration in non-growing season.Under all treatments,there was a significant linear correlation between soil respiration and soil temperature in non-growing season,and a significant logarithmic correlation between soil moisture and soil respiration.Compared with the normal years,the extreme climate conditions with almost no snow cover in non-growing season significantly reduced soil respiration,but increased the impact intensity of nitrogen addition and precipitation reduction on soil respiration,and also changed the impact direction of their combined effect on soil respiration.(2)Although nitrogen addition and precipitation reduction significantly reduced the average methane flux in non-growing season,their effect on methane flux is regulated by sampling time and different years.Extreme weather in non-growing season of 2018-2019 year counteracts the negative effect of precipitation reduction on methane flux.However,methane flux was positively correlated with soil nitrate nitrogen content,which indicated that nitrogen addition and precipitation reduction might change soil methane flux in non-growing season by affecting soil nitrogen dynamics.(3)The nitrogen addition and precipitation reduction decreased the length of fine root per unit area in early winter and increased the length of fine root per unit area in late winter,indicating that the nitrogen addition and precipitation reduction increased the death of fine root in early winter and the growth of fine root in late winter.The increase of fine root mortality in early winter may be due to the increase of root cortex thickness and the increase of temperature sensitivity of fine root due to nitrogen addition and precipitation reduction;the increase of fine root growth in late winter may be partly due to the large number of early root death,which reserves a large amount of nutrients for the growth of root in late winter.Based on the principle of compensation,the root system in late winter can quickly heal in a short time make up for the early losses in non-growing season.(4)Litter decomposition has a weak positive response to nitrogen addition,but a significant negative response to precipitation reduction and their combined effect.Litter quality regulates the response of litter decomposition to nitrogen addition,precipitation reduction and their combined effect.Nitrogen addition,precipitation reduction and their combined effect had a trend of increasing nitrogen and phosphorus retention in the early stage of litter decomposition,which may be conducive to the stability and balance of nutrients in the ecosystem and mitigate the impact of climate change on the soil ecosystem.There was a significant linear or exponential correlation between nitrogen retention and phosphorus retention in low-quality litter,but not in high-quality litter.(5)The combination effect of nitrogen addition and precipitation reduction increased the microbial biomass in winter,changed the microbial diversity,community structure and relative abundance of functional groups in winter;although the precipitation reduction did not significantly change the microbial biomass in winter,it also changed the microbial diversity,community structure and relative abundance of functional groups in winter.Nitrogen addition significantly increased some eutrophic bacteria,indicating that our research site may still not reach nitrogen saturation.The precipitation reduction increased the bacterial community with high anti-interference ability,which indicated that the decrease of precipitation may have a certain degree of pressure on the bacterial community.Nitrogen application could transform the fungi community from Basidiomycetes with high decomposing ability to Ascomycetes,which may explain that litter decomposition does not increase significantly under the condition of nitrogen addition.The precipitation reduction and their combined effect increased the saprophytic fungi community,which may be caused by the increase of fine root death.Sampling time regulated the effects of nitrogen addition,precipitation reduction and their combined on microbial community structure.During the freeze-thaw period,the composition and diversity of microorganisms and the relative abundance of functional groups of bacteria and fungi were significantly reduced,but the decomposition rate of organic matter could still high,which may indicate that the decomposition of litter during the freeze-thaw period may be mainly caused by physical fragmentation.In this paper,conventional methods are used for the first time to study the legacy effects of climate change factors(nitrogen addition and precipitation reduction)on some main ecological processes in non-growing season.The results show that the nitrogen addition and precipitation reduction may promote the carbon cycle in non-growing season by affecting soil nutrient and physical structure,fine root morphology and anatomical structure,litter quality,microbial community structure and functional team.In non-growing season,extreme climate conditions(such as snow being reduced)can adjust the impact of climate change factors(nitrogen addition and precipitation reduction)on soil ecological processes.This study not only increases our understanding of the short-term legacy effect of climate change on non-growing season ecological process,but also provides some data and theoretical reference for understanding the impact of future climate change on non-growing season carbon cycle.
Keywords/Search Tags:Nitrogen addition, Reduced precipitation, Temperate forest, Non-growing season, Carbon cycle
PDF Full Text Request
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