Short-Term Response Of Winter Soil Respiration To Snow Removal In A Picea Asperata Forest Of Western Sichuan

With the global warming,increased winter temperature and altered seasonal snow cover patterns will become more obvious,which will have a significant impact on soil respiration and soil carbon cycle in winter.The subalpine forest in western Sichuan is a sensitive region of global warming and also sensitive to climate change.It is great importance to study the response of winter soil respiration to global warming in the region.In this study,a Picea asperata forest of western Sichuan was studied.The effect of snow removal on the environmental factors in winter was evaluated by using wooden roof method and to study the mechanism's response of winter soil respiration and soil active organic carbon fractions?SAOCs?in different periods?early snow cover period?ESC?,deep snow cover period?DSC?and snow cover melt period?SCM??to snow removal.Results showed that:?1?The average thickness of snow was 17.2 cm throughout the winter and a maximum was 40.1 cm in February 2016.Snow showed a marked insulation effect,which is better in the nighttime than that daytime.Compared with the natural plot,snow removal reduced soil temperature?T?in each soil depth,resulting in a serious soil freezing and significantly increased the number of freeze-thaw cycles?FTCs?in ESC and SCM periods.Correlation analysis showed that snow depth was significantly positively correlated with FTCs,but significantly negatively correlated with T and soil moisture?W?.Moreover,W fluctuates most violently when T was from-0.5? to0.5?.?2?Different SAOCs responded to snow removal differently.Repeated-measure analysis showed that time effect had a significant effect on particulate organic carbon?POC?but no significant impact on easily mineralizable carbon?EMC?,however,POC and EMC increased slightly in winter.Snow effect and interactions had no significant effect on EMC and POC,but EMC in each period was significantly lower than that in control.POC had no significant difference.Light fraction organic carbon?LFOC?showed a decrease trend in winter.This may be due to the fact that winter LFOC was depleted by the continued decomposition of microorganisms.Removal of early snow resulted in the difficulty of adapting microorganisms during ESC and DSC periods,and the microbial mortality rate increased,resulting in the snow being removed.The LFOC content was stable in the early stage.There was no significant change in easily oxidized carbon?EOC?and labile carbon pool?LCP?content throughout the winter,which may be due to low microbial enzyme levels in winter and slight consumption of EOC and LCP.The study found that the snow removal will reduce the correlation of most SAOC and may change the inherent mechanisms of SAOCs conversion,and which will furtherly have a significant impact on soil carbon cycle.?3?Winter CO₂ flux is an important part of soil-atmosphere carbon cycle.The average R_S and carbon fluxes under natural snow cover were 0.52mmol?m^-2?s^-1 and88.44 g m^-2,respectively,snow removal reduced R_S and carbon fluxes by 21.02%and25.99%,respectively.Repeated measures analysis showed that time effect and snow effect have a significant effect on R_S,while the interactions of time and snow had no significant effect.The inhibition of R_S by snow removal mainly occurred at the ESC period.There was a significant positive exponential relationship between R_S and T and W in winter.T could explain the variations of R_S 54%and 65%in snow removal and control,respectively,and 64%and 83%were explained by W in control,respectively.Additionally,snow removal significantly reduced the temperature sensitivity(Q₁₀)of R_S?11.02 vs 4.95?.?4?Correlation analysis showed that the correlations R_S and SAOCs and environmental factors were significantly different during the three key periods in winter.During the ESC period,except for LCP-II,R_S was slightly positively correlated with SAOCs and significantly positively correlated with T,W and snow depth,but negatively correlated with FTCs.During the DSC period,except for EOC,R_S was slightly negatively correlated with SAOCs,positively correlated with T and snow depth,and negatively correlated with FTCs.In the SCM period,R_S was not significantly associated with LCP-II and EMC,but were significantly negatively correlated with other SAOCs and W.Taken together,snow removal in a Picea asperata forest of western Sichuan significantly reduced soil temperature,increased soil freeze-thaw cycles,and worsened winter soil environment,thereby changed different SAOCs and reduced its correlation relationships.Ultimately,snow removal reduced winter soil CO₂ flux and the temperature sensitivity of soil respiration.