| Elevated tropospheric ozone concentration（[O3]）may substantially influence the belowground processes of the terrestrial ecosystem.Nevertheless,a comprehensive and quantitative understanding of the responses of soil C and N dynamics,soil greenhouse gas emissions,HONO and NO efflux to elevated[O3]remains elusive.In this study,the results of 41 peer-reviewed studies were synthesized using meta-analytical techniques,to quantify the impact of O3 on ten variables associated with soil C and N dynamics,i.e.,total carbon（TC）,total nitrogen（TN）,dissolved organic carbon（DOC）,ammonia nitrogen（NH4+）,nitrate nitrogen（NO3-）,microbial biomass carbon（MBC）and nitrogen（MBN）,rates of nitrification（NTF）and denitrification（DNF）,as well as C/N ratio.Meanwhile,77 pair of observations extracted from 16 peer-reviewed studies were synthesized using meta-analytical techniques to quantify the impact of O3 on soil CO2 emission.Furthermore,the results of 675 studies extracted from 11 peer-reviewed literatures were synthesized using meta-analytical techniques to quantify the impact of O3 on soil N2O emission.In addition,soil HONO,NO,pHzpc and ozone concentration were measured by wheat field experiment to study the effect of ozone concentration on soil HONO/NO efflux.The main results are as follows:1.The results depicted that all these variables showed significant changes（P<0.05）with[O3]increased by 27.6±18.7 nL/L（mean±SD）,including decreases in TC,DOC,TN,NH4+,MBC,MBN and NTF,and increases in C/N,NO3-and DNF.The effect sizes of TN,NTF,and DNF were significantly correlated with O3 fumigation level and experimental duration（P<0.05）.Soil pH and climate were essential in analyses of O3 impacts on soil C and N dynamics.However,the responses of most variables to elevated[O3]were generally independent of O3 fumigation method,terrestrial ecosystem type,and additional[CO2]exposure.The altered soil C and N dynamics under elevated[O3]may change the soil C source/sink status,and affect soil N availability thus influence plant growth and soil N losses.2.Soil CO2 efflux was significantly reduced under short-term O3 exposure（≤ 1 year,P<0.05）,while it was increased under extended duration（>1 year,P<0.05）.Particularly,soil CO2 emission was stimulated in nonagricultural ecosystem,in FACE experiment,and in the soils of lower pH.The effect sizes of soil CO2 efflux were significantly positively and negatively correlated with experimental duration and soil pH,respectively.Ozone effect on soil CO2 efflux would be enhanced at warm temperature and high precipitation.The duration of O3 exposure was the fundamental factor in analyzing O3 impacts on soil CO2 emission.3.Elevated O3 concentration significantly inhibited soil N2O emission（-8.0%,P<0.05）.The response of farmland soil was significant（-8.7%,P<0.05）,but the grassland soil response was not significant（P>0.05）.With the increase of O3 concentration level,the significance of soil N2O emission change gradually increased.The response based on the results of FACE system was not significant（P>0.05）due to the low O3 concentration in the experimental group,however,the response based on the research results of open-top chamber（OTC）is significant（-8.4%,P<0.05）due to the higher O3 concentration in the experimental group.the effect of elevated O3 concentration alone on soil N2O emission was significant（-8.0%,P<0.05）,while the results were not significant when coexisting with elevated CO2 concentration.In general,there were no significant differences among subgroups under different grouping modes（P>0.05）.The effect value of soil N2O emission was significantly correlated with annual mean air temperature（MAT）and O3 concentration（P<0.05）,the inhibition effect of O3 on soil N2O emission gradually increased with the increase of MAT and O3 concentration.4.Soil HONO and NO emissions were significantly different at different growth stages of wheat under elevated O3 concentration（P<0.05）,however,the effects of O3 on soil HONO and NO emissions were not significant.The results showed that HONO and NO emissions in the soil were poorly correlated with biochemical indices,but significantly correlated with chemical indices（pHzpc）.Therefore,HONO and NO emissions in the wheat rhizosphere soil were mainly controlled by chemical balance.In conclusion,the increase of atmospheric ozone concentration has a significant effect on the dynamic related variables of soil carbon and nitrogen and their cycle processes,but has no significant effect on the release of soil HONO and NO. |
