Studies On Greenhouse Gas Emissions And Influencing Factors Of Three Middle-Season Paddy Fields

The continuous increase of greenhouse gas concentrations in the atmosphere has caused widespread concern.Human agricultural activities are one of the main reasons for this result.Natural conditions such as water and temperature,soil conditions such as soil carbon and nitrogen,management measures,and utilization methods will all affect greenhouse gas emissions.This study selected cold waterlogged paddy fields?representing the“single-season rice-winter leisure”model?,rice-crayfish coculture?representing the new“single-season rice-breeding in paddy”model?,and rice-wheat rotation?representing the“rice field-dryland rotation”model?as three types single-season rice paddy fields.These three rice fields are all“One Single Season Rice-”pattern,that is,one season of middle rice crops was planting on the annual scale,which covers most of the rice field types in Hubei Province.In this study,we continuously monitor the greenhouse gases?CO₂,CH₄,and N₂O?and related environmental factors?temperature,moisture,inorganic nitrogen,DOC?,determine the structure and abundance of functional gene communities related to CH₄emissions after rice harvesting,calculate carbon balance,carbon footprint,and carbon efficiency.This study aims to provide evidence for measures of greenhouse gas emissions reduction in different single-season rice fields and can provide scientific basis and data support for the compilation of greenhouse gas emission inventories in Hubei Province.It is essential to fully understand the impact of environmental conditions on greenhouse gas and carbon emissions in rice fields.The main research conclusions are as follows:1. CH₄emissions from cold waterlogged paddy fields?CW?are significantly higher than the normal paddy fields?NW?.At the annual scale,the temperature is mainlycontrolling factor to the CH₄ fluxes.Long-term flooded promotes increasing ofmethanogens,and methanogens can increase a large amount of CH₄ produced in theCW rice fields.CH₄ fluxes in the NW paddy field is significantly related to the soilmoisture at the annual scale.Planting rice increased CH₄emissions from both ricefields.The soil anaerobic respiration?R_h?in the CW rice fields is significantlylower than that in the NW rice fields.Still,there is no difference in ecosystemrespiration(R_eco)between them.The cumulative emissions of R_hand R_eco are 70-80%of the total emissions in the wet management stage and the flooded stage.R_ecoin the CW rice fields is mainly affected by soil temperature and NH₄⁺-N,and moreaffected by rice planting in the NW rice fields.Regardless of rice planting or not,the two types of paddy fields are carbon sinks on the yearly scale.N₂O emissionsin CW rice fields are significantly lower than in NW rice fields.N₂O emissions fromCW rice fields are mainly affected by temperature and NH₄⁺-N,while in NW ricefields are affected by NO₃^--N,NH₄⁺-N,soil moisture,soil temperature,and DOCsimultaneously.2. Flooding significantly increased CH₄emissions after straw return in the non-rice season.The non-rice season flooding significantly increased the OTU numbers ofmcr A'and pmo A'.The farming crawfish can change the soil methanogencommunity structure and close to the drainage mode.NH₄⁺-N inhibits CO₂emissions,and drainage increases CO₂ emissions at flooded conditions in the non-rice season.Straw return increases gaseous carbon emissions and increases systemcarbon sink significantly.CO₂ emissions are mainly affected by air temperature,soil DOC and NO₃^--N in the WSC treatment.Straw return can promote N₂Oemissions in flooded conditions at the non-rice season,and inorganic nitrogencontent and form change are the critical drivers of N₂O emissions in all treatments.3. In the rice-crayfish paddy fields,farmed crayfish can substantially reduce the increase of CH₄ caused by flooding and straw return,and the emission reductioneffect mainly occurs in the non-rice season flooding stage and rice planting stage.Farmed crayfish can change the soil methanogen community structure and close tothe drainage mode.Farmed crayfish can increase the gross primary productivity?GPP?,reduce CO₂ and the total N₂O emissions,and increase the system's carbonsink capacity significantly.4. In the rice-wheat rotation system,fertilization significantly increases the cumulative CH₄ emissions in rice season,which accounts for 98.7%-100.5%of the total yearlyCH₄ emissions.Air temperature noticeably increases on CH₄ emissions in alltreatments,and NO₃^--N contents negatively affects CH₄ emissions in all treatments.NH₄⁺-N contents positively affects CH₄ emissions significantly in composted strawtreatment and composted straw-fertilizer treatments.Compared with CK,fertilization significantly changes the methanogens community structure.Fertilization increases pmo A'copies number in all fertilization treatments,andpmo A copies number significantly negative correlation with mean CH₄ fluxes.Thecopies number ratio of mcr A and pmo A has a significant quadratic relationship withaccumulate CH₄ emissions.Fertilizations significantly increased the annual averageCO₂ fluxes and CO₂cumulative emissions.Air temperature significantly promotedCO₂ fluxes in all treatments,except 2MNPK.Soil water content significantlyinhibited CO₂ emissions in all treatments.Air temperature negatively affects N₂Oemissions in all chemical fertilization treatments and negatively affects all non-chemical fertilization treatments.On an annual scale,GWP_CO2 accounts for morethan 90%of the total GWP.CO₂ emission intensity is 15-30 times that of CH₄,andCH₄ emission intensity is 3-7 times that of N₂O.5. Indirect carbon emissions of chemical fertilizer account for the most substantial proportion of the total indirect carbon emissions and indirect carbon emissions ofnitrogen fertilizer are the highest.The annual carbon footprint of the rice-wheatrotation is the lowest,rice-crayfish coculture and NW field are the second,and theCW field is the highest.The rice-wheat rotation has the highest carbon efficiency,followed by rice-crayfish coculture and NW treatment,and the lowest is coldwaterlogged rice fields.