The Effects Of Phyllostachys Edulis Expansion And Nitrogen Deposition On Fine Root Decomposition And Soil N₂O And CO₂ Emissions

In recent years,the expansion of Phyllostachys edulis has become a serious threat to the ecosystem of natural reserves in China.The expansion of Phyllostachys edulis has caused a series of ecological problems such as the impact on the greenhouse gas emissions of the soil.Phyllostachys edulis subterraneous stem have a strong horizontal expansion ability,and continue to spread to the surrounding habitats,and the decomposition of fine root litter is of great significance to soil nutrient cycling and greenhouse gas emissions.At present,the research on greenhouse gas emission changes caused by the expansion of Phyllostachys edulis mainly focuses on the litter parts of the ground,while the research on the underground fine root litter is little.The relevant change processes and mechanisms need to be studied.In this study,the mixed forest of Phyllostachys edulis and Cryptomeria japonica was used as the research object,and the static chamber technique was used to monitor soil N₂O and CO₂ emissions in situ.The decomposition of fine root litter adopts litter bag method.By in situ decomposition of moso bamboo fine roots,Japanese cedar fine roots,and the two mixed fine roots to study the effects of fine root input caused by Phyllostachys edulis expansion on soil N₂O and CO₂ emissions and fine root decomposition,and to simulate global nitrogen deposition to study the responses of fine root decomposition and soil N₂O and CO₂ flux to nitrogen deposition under the background of increased nitrogen deposition.Explore the ecological impact of moso bamboo fine root litter and provide a theoretical basis for sustainable forest development and greenhouse gas emission reduction.Through 12-15months observation,the conclusions of this study are as follows:（1）Moso bamboo and Japanese cedar and their mixed fine root litter mass and organic carbon（OC）loss faster in the early stage of decomposition（0-4 month）.The total nitrogen（TN）of moso bamboo and Japanese cedar fine root litter showed obvious enrichment,and the mixed fine root litter appeared to be released;in the late stage of decomposition（after the 9 month）,due to the increase in temperature,the fine root mass loss and nutrient release are accelerated.Mixed decomposition accelerates the attenuation of fine root mass and the release of OC,which produces a non-additive positive effect.Nitrogen deposition had no significant effect on the decomposition of fine roots of moso bamboo and Japanese cedar fine root litter,but significantly accelerated the attenuation of the quality of mixed fine roots.（2）Moso bamboo expansion reduces soil N₂O emission rate and cumulative emissions,and fine root litter input promotes soil CO₂ emissions and increases soil CO₂ cumulative emissions;after full expansion,the N₂O emission rate of the soil returns to the original emission level,and the cumulative emission increases significantly;with the expansion of moso bamboo,the CO₂ emission rate of soil gradually decreased.After the expansion,the CO2 emission rate of soil decreased significantly.（3）Simulated nitrogen deposition promoted soil N₂O emissions,significantly increased the soil N₂O emission rate during the expansion process of moso bamboo expansion process to full expansion,and increased cumulative soil N₂O emissions at various stages.Nitrogen deposition suppressed CO₂ emissions and reduced cumulative emissions.The treatment of mixed fine root litter under nitrogen deposition significantly increased the soil CO₂emissions rate.The N₂O and CO₂ emission rates of the treated soils changed significantly with time,with obvious seasonal changes.（4）Atmospheric temperature and soil temperature are significantly correlated with soil N₂O and CO₂ emission rates.Fine root input reduces the sensitivity of the soil CO₂ emission rate to temperature,and the rate of increase of soil N₂O emission rate gradually decreases with the increase of temperature during the expansion of moso bamboo.Therefore,the expansion of moso bamboo may be beneficial to soil carbon sequestration in a global warming environment.The residual rate of fine root litter mass,OC and TN were significantly negatively correlated with the cumulative CO₂ emissions of soil.The decomposition of fine roots increased the cumulative CO₂ emissions of soil.In conclusion,with the expansion of moso bamboo,the mixed of fine root litter accelerates the loss of mass and the release of OC and TN,resulting in a non-additive positive effect.Moso bamboo expansion inhibits N₂O emissions,fine root litter input promotes soil CO₂ emissions,and CO₂ emissions are suppressed after full expansion;Nitrogen deposition promotes soil N₂O emissions and suppresses CO₂ emissions,but has a positive effect on the soil CO₂ emission rate during the expansion of moso bamboo.Fine root input reduces the sensitivity of soil CO₂ emission rate to temperature,and the expansion of moso bamboo may be beneficial to soil carbon sequestration in a global warming environment.It can be seen that the expansion of moso bamboo has a significant effect on the decomposition of fine root litter and the emission of N₂O and CO₂ under the background of increased nitrogen deposition.While pursuing economic benefits,we should fully consider the ecological impact brought by the expansion of moso bamboo,and formulate reasonable forest management and greenhouse gas emission reduction measures.