The Effects Of Long-term Film Mulching On Soil Carbon Pools And Greenhouse Gas Emissions In Rainfed Farmlands

Film mulching represents a prominent strategy for augmenting crop yields in arid regions.As crops thrive beneath the mulch,inducing alterations in the soil microenvironment,there is a consequential impact on the processes governing the carbon cycle and greenhouse gas emissions within the ecosystem.In the context of mounting climate change concerns and burgeoning populations,the domain of agricultural production necessitates a nuanced equilibrium amidst a confluence of complex global imperatives.The escalating prevalence of plastic films has exacerbated the predicament of"white pollution",underscoring the urgency to expound upon the ecological and environmental merits conferred by plastic film mulching.Furthermore,there exists an imperative to investigate the temporal and spatial suitability of employing degradable films as a sustainable alternative to plastic counterparts.Drawing on a comprehensive nine-year positioning experiment conducted in the Loess Plateau,this study instituted three distinct treatments:conventional plastic film mulching,degradable film mulching,and a control group devoid of any mulching.Focusing on the spring corn community as the subject of scrutiny,the study meticulously explored the ramifications of plastic film mulching on soil respiration and its constituent elements.The underlying mechanism unveiled discernible variations in the responses exhibited by diverse carbon components and sources in the soil to mulching film.Furthermore,we quantified alterations in the ecosystem’s carbon budget under diverse mulching materials.Augmented by the DNDC（Denitrification-Decomposition）model,we extended our evaluation to encompass the temporal trends in the agricultural impacts of various plastic film mulching within the context of forthcoming climate shifts.To elucidate spatial disparities and discern controlling factors,we harnessed meta-analysis and machine learning methodologies,shedding light on the effects of the two mulching techniques on crop yields and greenhouse gas emissions.The findings of this research contribute a theoretical framework conducive to a profound comprehension of the dynamic mechanisms governing soil carbon pools and pivotal pathways in the carbon cycle under mulching.Additionally,they provide theoretical underpinning for the advancement of agriculture characterized by high yield,efficiency,and environmental sustainability.The principal research findings are outlined as follows:（1）Differences emerge in the regulatory impacts of plastic film mulching and degradable film mulching on distinct components and origins of carbon within the soil.In the PM and DM,carbon storage in the surface soil（0-30 cm）increased by 2.3%and6.6%respectively,as compared to the control treatment.Notably,both particulate organic carbon storage and plant-derived carbon exhibited a substantial surge.As observation depth extended to 100 cm,carbon storage beneath the degradable film mulching rose by 1.9 Mg ha^-1compared to the control,while it decreased by 4.4 Mg ha^-1 beneath the plastic film mulching.This can be attributed to a marked reduction in plant-derived carbon input in the deeper soil（30-100 cm）,coupled with significant decreases in mineral-bound carbon stocks（5.3%）and microbial-derived carbon（9.6%）in the PM treatment.Examination of soil physical and chemical properties revealed alterations induced by plastic film mulching in microbial traits and community structure.Specifically,this measure led to a notable augmentation in extracellular enzyme activity（both oxidative and hydrolytic）and total phosphoric acid fatty acid content（PLFA）,accompanied by a substantial reduction in the Gram-positive bacteria/Gram-negative bacteria PLFA ratio,as well as soil microbial carbon utilization efficiency（CUE）.Conversely,degradable film mulching significantly boosted soil hydrolytic extracellular enzyme activity and CUE.Both the random forest model and partial least squares path model underscored the pivotal roles of CUE and underground biomass as primary driving factors of microbial-derived carbon and plant-derived carbon,respectively,indicating a positive linear correlation for both.（2）Long-term mulching induces alterations in soil respiration carbon emissions within spring corn farmland and influences its responsiveness to shifts in annual precipitation.Both plastic and degradable film mulching exhibit noteworthy enhancements in above-ground biomass,below-ground biomass,leaf area index（LAI）,and corn grain yield.A substantial surge in autotrophic respiration carbon emissions linked to plant growth is discernible.Concurrently,mulching exerts considerable influence on the physical and chemical attributes of the soil,resulting in a notable upswing in carbon emissions from heterotrophic respiration.Upon comparing various mulching materials,it is evident that carbon emissions from soil respiration,heterotrophic respiration,and autotrophic respiration demonstrate variable reductions under degradable film mulching in contrast to plastic film measures.Soil carbon emissions,across diverse management approaches,exhibit a linear upward trajectory with escalating annual precipitation.Additionally,the adoption of plastic film mulching heightens the sensitivity of heterotrophic respiration to shifts in annual precipitation,while dampening the sensitivity of autotrophic respiration.Structural equation modeling reveals that mulching measures directly foster carbon emissions in both heterotrophic and autotrophic respiration through ameliorations in soil hydrothermal conditions and augmented mineral nitrogen content.Specifically,plastic film mulching predominantly amplifies carbon emissions in heterotrophic respiration,whereas the surge in emissions under degradable film mulching is primarily attributable to autotrophic respiration.（3）Film mulching precipitates an elevation in greenhouse gas emissions and accentuates the carbon input and output of the farmland ecosystem.In comparison to uncovered farmland,the adoption of plastic film mulching resulted in a significant escalation of N₂O and heterotrophic respiration CO₂ emissions,accompanied by a17%reduction in CH₄ absorption.Noteworthy increments were also observed in ecosystem carbon input and output,along with a consequential augmentation in net global warming potential（NGWP）,while the carbon budget witnessed a 21%reduction relative to the control treatment.In contrast to the PM treatment,the degradable membrane mulching method（DM）manifested a reduction of 12.7%and 12.3%in N₂O and heterotrophic respiration CO₂ emissions respectively,alongside a year-on-year increase of 6.1%in CH₄ absorption.Both NGWP and greenhouse gas emission intensity（GHGI）per unit of output experienced a significant decrease.It is worth noting that the carbon budget of the farmland ecosystem in DM ranked highest among all measures.（4）The farmland responses to mulching films of varying materials exhibit distinct reactions to climate change under four scenarios.In the forthcoming period（2021-2100）,the Loess Plateau region is anticipated to experience an upward trend in both precipitation and temperature,with the most pronounced increases projected under high emission scenarios（SSP 3-7.0 and SSP 5-8.5）.Different climate scenarios have yielded a favorable impact on corn yields in the region.While ordinary plastic film mulching initially yields the highest corn output in the simulation’s early stages,its rate of increase over time is the lowest.Conversely,the yield of degradable film mulching benefits from heightened precipitation and temperature,rendering it the highest among all treatments under the SSP 5-8.5 scenario.Across the four emission scenarios,the greenhouse gas emissions associated with the degradable film mulching measures were notably lower than those of the PM treatment,and soil carbon storage registered the highest values among all measures.（5）Noteworthy spatial disparities emerge in the optimal application areas for plastic film mulching and degradable film mulching measures.Examination of global datasets revealed that conventional plastic film mulching measures gave rise to augmented N₂O,CH₄,and global warming potential（GWP）.Conversely,greenhouse gas emissions exhibited varying degrees of reduction under degradable film mulching.Concerning crop yield,the yield-enhancing effect of PM is particularly pronounced in cold,arid,and nutrient-deficient regions,indicative of robust spatial heterogeneity.In specific climatic conditions（MAP>400 mm,MAT>8℃）or specific soil environments（SOC>10 g kg-1;TN>1.2 g kg-1）,degradable film mulching measures yield higher outputs.Machine learning output results illustrate that both PM and DM can bolster the yield of major cereal crops（maize and wheat）by 647 and 495 Tg yr^-1,respectively.From a regional standpoint,degradable film mulching measures exhibit higher yield gains in Asia and Africa.Latitude-wise,the average yield increase with the application of DM between 30°S-30°N surpasses that of PM.Moreover,the implementation of degradable film mulching significantly diminishes global warming potential（GWP）on a global scale.This underscores the potential for employing degradable film mulching in specific climatic regions as a means of balancing food security with greenhouse gas emissions.In conclusion,the implementation of degradable film mulchinging strategies serves to optimize crop yields while concurrently mitigating the acceleration of greenhouse gas emissions.This approach proves advantageous for soil carbon sequestration,and enhancing climate adaptability.