A Meta-analysis And A Field Experiment Of Logging On Forest Soil N₂O Flux

Global warming and ozone depletion caused by the rising of N₂O concentration are two global important issues.How to mitigate the increase of atmospheric N₂O concentration has been a major challenge.Forest soil is one of the main sources of N₂O.Currently,it is still unclear whetherforest loggingelevatesor inhibits soil N₂O emission.In this study,we collected data of forest loggingon soil N₂O emission over the world from the previous studies and established the related database after one by one screening.A Meta-analysis was conducted to explore the effects of logging on soil N₂O emission with effect size of Hedges'd and on related soil environmental variables with effect size of lnR,aiming to reveal the mechanism of the effect of loggingon soil N₂O.Then,an experiment was carried on Chinese subtropical chinese fir plantation with four treatments:Control?UC?,Clear-cutting and natural regeneration?CN?,Clear-cutting and soil spot preparation regeneration?CAS?,and Clear-cutting and whole soil preparation regeneration?CAO?,aiming to explore the effects of clear-cutting and regeneration on soil N₂O emission.Main findings of Meta-analysis are as following:?1?Clear-cutting increased Soil N₂O emission flux significantly in the early and medium stage of recovery.Light and moderate logging did not change N₂O flux significantly.The long-term effects of clear-cutting on N₂O emission flux were complicated,depending on the newly formed forest types.Logging had no statistically significant effect on soil N₂O flux in mixed species and coniferous forest,but it increased N₂O flux in broadleaved forest significantly.?2?Among the nine soil environmental variables,such as soil pH,temperature,TN,SOC,NO₃^--N,NH₄⁺-N,MBC and MBN,logging caused a marked positive change in soil NO₃^--N and temperature,but had a significant negative change in pH.Compared with light and moderate logging,clear-cutting had statistically significant effect on soil NO₃^--N,NO₃^--N,pH and temperature.For different recovery stages,there was a dramatical increase in soil temperature and NO₃^--N in the early stage,and there was an obvious increase of NO₃^--N in the medium stage.In the long stage of recovery,there was a decline in SOC and pH,while there was an increase in MBN and an uncertainty in NO₃^--N.In general,logging elevated N₂O emission flux by increasing soil NO₃^--N and temperature.?3?For different forest types,logging resulted in a significant increase in soil NO₃^--N,temperature and moisture,while decreased soil pH in broadleaved forest.And it increased soil temperature in coniferous forest.Overall,logging had a bigger impact on soil environmental variables in broadleaved forest.Main findings of field experiment are as following:?1?Clear-cutting?CN?increased N₂O emission in the early stage of recovery.Soil spot preparation after clear-cutting did not change N₂O significantly,but whole soil preparation after clear-cutting had a marked increase in N₂O.?2?A single regression analysis showed,N₂O emission flux were positively with soil temperature,moisture,NO₃^--N,MBC,MBN,WSOC,WSON,and NH₄⁺-N.Among these soil emvironmental variables,soil temperature,moisture,MBC,MBN,NO₃^--N,SOC and WSON are important factors affecting N₂O flux,and soil temperature has the greatest impact on it.?3?Although clear-cutting and regeneration decreased soil pH and moisture,it increased soil temperature,NO₃^--N,MBC,MBN,WSOC and WSON,and accelerated nitrification and denitrification processes.Finally,N₂O emission flux was elevated.