Study On Soil CO₂ Emission Patterns And Influencing Factors During The Mulching Period Of Bamboo Shoot Forest

Soil respiration is one of the hot spots of carbon cycle research and the largest source of carbon emissions from terrestrial ecosystems into the atmosphere,among which forest soil respiration accounts for about 60%-90%of total carbon emissions from terrestrial ecosystems,and small changes in soil carbon pools can have an important impact on atmospheric carbon pools.Mulching is an important management measure in agriculture.Mulching raises soil temperature,changes soil physical and chemical properties,improves soil microbial breeding environment and plant root growth conditions,thus affecting soil respiration and CO₂ emission.Current studies on the effects of bamboo forest mulching on soil CO₂ emissions have mostly focused on the emission results and the dynamic change patterns measured in annual or monthly units.Studies on the response of soil CO₂ emission to bamboo shoot forest mulching measures and the dynamic changes of soil CO₂ emission rate during the mulching period and the main influencing factors have been rarely reported,failing to reveal the mechanism of the influence of bamboo forest mulching measures on soil CO₂ emission.In this study,Ph.Violascens and Ph.edulis‘Pachyloen’were used as research subjects,and we investigated the dynamic changes of soil CO₂ emission rate during the mulching period and analyzed the effects of mulching factors on soil CO₂ emission,such as the type and application amount of heating substances,the chaff layer thickness and the amount of water replenishment in the forest before mulching,in order to provide a reference for exploring an efficient and low-carbon mulching model for bamboo shoot forests.Research shows that:（1）The average rate of soil CO₂ emission from mulching bamboo shoot forests was21.92μmol·m^-2·s^-1 throughout the mulching period,with a total emission of 200.74 mol·m^-2.The emission rate showed a single-peaked curve dynamics,with a sharp increase in soil CO₂ emission rate in the first 3 weeks after mulching,slowing down in the 4th week and peaking in the 5th week,decreasing rapidly in the 6th-7th weeks,decreasing slowly in the8th-14th weeks,dropping to a minimum in the 15th week（March 2 of the following year）and then increasing slowly.In contrast,the CO₂ emission rate dynamics of the uncovered bamboo shoot forest was relatively smooth,with an average emission rate of 4.67μmol·m^-2·s^-1 and a total emission of 42.77 mol·m^-2.（2）The effect of chaff layer thickness on soil CO₂ emissions from the mulching bamboo shoot forest was highly significant（P<0.01）,and the difference in soil CO₂emissions between 15,25 and 35 cm of chaff layer thickness was highly significant（P<0.01）,and the effect on soil CO₂ emission rate throughout the mulching period was highly significant（P<0.01）.The thicker the chaff layer,the higher the soil CO₂ emission rate,and the soil CO₂ emission rate throughout the whole mulching period showed that the chaff layer was 15 cm<25 cm<35 cm.（3）The type of heating substance and the amount of oil cake（heating substance）applied mainly influenced the dynamic change pattern of soil CO₂ emission.Significant（P<0.05）or highly significant（P<0.01）differences in soil CO₂ emission rate were observed between different heating substances at most time points during the mulching period,but the effects on total soil CO₂ emissions were not significant（P>0.05）.The peak of soil CO₂emission rate appeared early when chicken manure was used as heating substance,the peak of soil CO₂ emission rate was high and varied widely when oil cake was used as heating substance,and the peak and variation of soil CO₂ emission rate were smaller when wheat ash was used as heating substance.Soil CO₂ emission rate increased with increasing application of oil cake（heating substance）,but the difference in soil CO₂ emission rate between the levels of 3.00 t·hm^-2,4.50 t·hm^-2,and 6.00 t·hm^-2 of oil cake application was not significant（P>0.05）.（4）The effect of the amount of water replenishment on soil CO₂ emissions before mulching stands varied depending on the type of heating substance.Under the conditions of applying different types of heating substances,the effect of water replenishment in the forest before mulching on the total and rate of soil CO₂ emission was significant（P<0.05）,rehydrating the forest floor to 10 cm of moist soil layer before mulching increased the peak,average and minimum values of soil CO₂ emission rate and total emissions.When using oil cake as heating substance,the amount of water replenishment on the forest before mulching only had significant effect（P<0.05）on the soil CO₂ emission rate in the early stage of mulching,and had no significant effect（P>0.05）on the total amount of emissions throughout the mulching period,but rehydrating the forest floor to 15 cm of moist soil layer before mulching could reduce the rate of the increasing of soil CO₂ emission rate,and delay the appearance of the peak soil CO₂ emission rate,and reduce the peak.A comprehensive analysis shows that the winter stand mulching of the bamboo shoot forest significantly increased the rate and amount of soil CO₂ emission,and changed the dynamic patterns of soil CO₂ emission rate.The chaff layer thickness is the dominant factor of affecting soil CO₂ emissions,and the thicker the chaff layer,the greater the soil CO₂emission amounts.Heating substances mainly affect the dynamic pattern of soil CO₂emissions,and the differences in soil CO₂ emission amounts between the three heating substances widely used in mulching and the application levels are not significant.The effect of water replenishment in the forest before mulching on soil CO₂ emissions stands varied depending on the type of heating substance.