Effect Of Gap Size On Soil CO₂ Efflux In A Mixed Broadleaved-korean Pine Forest

Forest gap is critical component of uneven-aged natural forests.Changes of micro-climate and micro-topography in partial area of forests could enhance or restrain the biogeochemical processes,and so as to alter the carbon budgets of forest ecosystems.We aimed to investigate the effects of gap size on soil respiration and corresponding biotic and abiotic factors in twelve natural gaps(separated from ? level to ? level with sizes ranged from 25 m2 to 600 m2).The results showed that:(1)The soil respiration within different gap sizes exhibited obviously seasonal dynamics,which was in accordance with the change of soil temperature.The maximum values occurred between July and August,and the minimum appeared in May or October.The average value of spatial coefficient of variation(CV)among measurement collars for soil respiration across all gaps was 50%,which was approximately 2 times higher than that among different gaps(26%).There was no pronounced relationship between soil respiration rates and gap size.Compared to the control(canopy),the soil respiration rates within gaps of I level(0-100 m2)were similar to that of control.However,the average soil respiration rates within the gaps of II level(100-200 m2)and ?-? levels(300-600 m2)declined 21%and 12%,respectively.(2)On average,soil moisture within gaps increased 17%compared to that under canopy.Soil organic carbon and total nitrogen firstly increased with canopy gap size,reached highest within ? and ? levels canopy gap(100-300 m2),and then decreased.Both soil microbial biomass carbon and nitrogen were lowest in ?-? levels canopy gap(400-600 m2).The differences of soil nutrients and microbial biomass between control and canopy gaps may be caused by changes of soil moisture,root exudates and litter input.Fine root biomass were negatively correlated with gap size(p<0.05).At the phylum level,the relative abundances of main fungal species varied with gap size,while the relative abundances of main bacterial species were similar between treatments;The enzymatic activities of five soil enzymes related to carbon,nitrogen and phosphorous cycling tended to decrease with increasing gap size.(3)Soil temperature can account for 14-97%of the seasonal variation of soil respiration across all gaps.The temperature sensitivity(Q10)ranged from 1.2 to 3.8.Across all forest gaps,soil respiration and soil moisture exhibited significant parabolic relationship(p<0.5),and soil moisture alone explained 56%variation of soil respiration among different gaps.We also found there was a significant relationship between soil respiration and fine root biomass across gaps(p = 0.01).In addition,the Q10 values within different gaps increased with soil moisture until it reached 30-40%,then the Q10 decreased.