Dynamic changes in solar radiation have an important influence on ecosystem carbon sequestration,but the effects of changes caused by sky conditions on net ecosystem CO2 exchange(NEE)are unclear.This study analyzed th...Dynamic changes in solar radiation have an important influence on ecosystem carbon sequestration,but the effects of changes caused by sky conditions on net ecosystem CO2 exchange(NEE)are unclear.This study analyzed the effects of sunny,cloudy,and overcast sky conditions on NEE using carbon flux and meteorological data for a subtropical coniferous plantation in 2012.Based on one-year data,we found no seasonal variation in the light response curve under various sky conditions.Compared with sunny sky conditions,the apparent quantum yield(α)and potential photosynthetic rate at a light intensity of 150 and 750 W m^-2(P150 and P750)under cloudy sky conditions increased by an average of 82.3%,217.7%,and 22.5%;αand P150 under overcast sky conditions increased by 118.5%and 301%on average.Moderate radiation conditions were more favorable for maximum NEE,while low radiation conditions inhibited NEE.In most cases,when the sunny NEE was used as a baseline for comparison,the relative change in NEE(%NEE)was positive under cloudy sky conditions and negative under overcast sky conditions.The average maximal%NEE under cloudy sky conditions was 42.4% in spring,34.1% in summer,1.6% in autumn and –87.3% in winter.This study indicates that cloudy sky conditions promote photosynthetic rates and NEE in subtropical coniferous plantations.展开更多
Fluctuations in soil greenhouse gas(GHG)are an important part of the terrestrial ecosystem carbon-nitrogen cycle,but uncertainties remain about the dynamic change and budget assessment of soil GHG flux.Using high freq...Fluctuations in soil greenhouse gas(GHG)are an important part of the terrestrial ecosystem carbon-nitrogen cycle,but uncertainties remain about the dynamic change and budget assessment of soil GHG flux.Using high frequency and consecutive soil GHG fluxes measured with an automatic dynamic chamber system,we tested the applicability of the current Forest-DNDC model in simulating soil CH4,CO2 and N2O fluxes in a temperate broad-leaved Korean pine forest at Changbai Mountain.The results showed that the Forest-DNDC model reproduced general patterns of environmental variables,however,simulated seasonal variation in soil temperature,snow melt processes and soil moisture partly deviated from measured variables,especially during the non-growing season.The modeled CH4 flux was close to the field measurement and co-varied mainly with soil temperature and snowpack.The modeled soil CO2 flux had the same seasonal trend to that of the observation along with variation in temperature,however,simulated CO2 flux in the growing season was underestimated.The modeled N2O flux attained a peak in summer due to the influence of temperature,which was apparently different from the observed peak of N2O flux in the freeze-thaw period.Meanwhile,both modeled CO2 flux and N2O flux were dampened by rainfall events.Apart from consistent estimation of annual soil CH4 flux,the annual accumulation of CO2 and N2O was underestimated.It is still necessary to further optimize model parameters and processes using long-term high-frequency observation data,especially transference of heat and water in soil and GHG producing mechanism.Continues work will improve modeling,ecosystem carbon-nitrogen budget assessment and estimation of soil GHGs flux from the site to the region.展开更多
基金National Key Research and Development Program of China(2017YFC0503801 2016YFA0600104)
文摘Dynamic changes in solar radiation have an important influence on ecosystem carbon sequestration,but the effects of changes caused by sky conditions on net ecosystem CO2 exchange(NEE)are unclear.This study analyzed the effects of sunny,cloudy,and overcast sky conditions on NEE using carbon flux and meteorological data for a subtropical coniferous plantation in 2012.Based on one-year data,we found no seasonal variation in the light response curve under various sky conditions.Compared with sunny sky conditions,the apparent quantum yield(α)and potential photosynthetic rate at a light intensity of 150 and 750 W m^-2(P150 and P750)under cloudy sky conditions increased by an average of 82.3%,217.7%,and 22.5%;αand P150 under overcast sky conditions increased by 118.5%and 301%on average.Moderate radiation conditions were more favorable for maximum NEE,while low radiation conditions inhibited NEE.In most cases,when the sunny NEE was used as a baseline for comparison,the relative change in NEE(%NEE)was positive under cloudy sky conditions and negative under overcast sky conditions.The average maximal%NEE under cloudy sky conditions was 42.4% in spring,34.1% in summer,1.6% in autumn and –87.3% in winter.This study indicates that cloudy sky conditions promote photosynthetic rates and NEE in subtropical coniferous plantations.
基金National Key Research and Development Program of China(2017YFC0503801)National Natural Science Foundation of China(31570446)
文摘Fluctuations in soil greenhouse gas(GHG)are an important part of the terrestrial ecosystem carbon-nitrogen cycle,but uncertainties remain about the dynamic change and budget assessment of soil GHG flux.Using high frequency and consecutive soil GHG fluxes measured with an automatic dynamic chamber system,we tested the applicability of the current Forest-DNDC model in simulating soil CH4,CO2 and N2O fluxes in a temperate broad-leaved Korean pine forest at Changbai Mountain.The results showed that the Forest-DNDC model reproduced general patterns of environmental variables,however,simulated seasonal variation in soil temperature,snow melt processes and soil moisture partly deviated from measured variables,especially during the non-growing season.The modeled CH4 flux was close to the field measurement and co-varied mainly with soil temperature and snowpack.The modeled soil CO2 flux had the same seasonal trend to that of the observation along with variation in temperature,however,simulated CO2 flux in the growing season was underestimated.The modeled N2O flux attained a peak in summer due to the influence of temperature,which was apparently different from the observed peak of N2O flux in the freeze-thaw period.Meanwhile,both modeled CO2 flux and N2O flux were dampened by rainfall events.Apart from consistent estimation of annual soil CH4 flux,the annual accumulation of CO2 and N2O was underestimated.It is still necessary to further optimize model parameters and processes using long-term high-frequency observation data,especially transference of heat and water in soil and GHG producing mechanism.Continues work will improve modeling,ecosystem carbon-nitrogen budget assessment and estimation of soil GHGs flux from the site to the region.
