干湿交替频率对不同土壤CO_2和N_2O释放的影响

Impacts of drying-wetting cycles on CO_2 and N_2O emissions from soils in different ecosystems

干旱、半干旱和地中海气候区,乃至一些湿润地区,由干湿交替引起的土壤碳、氮的短暂脉冲式释放很大程度上决定着长时间尺度温室气体释放的总量,是土壤碳、氮温室气体释放的关键过程。选择我国降雨梯度下的森林、农田、草地和荒漠生态系统,采集土样进行实验室统一控制条件下的多重干湿交替循环,对比探讨不同生态系统土壤干湿交替频率对CO2和N2O释放的影响模式。结果表明:(1)干湿交替能够显著的激发土壤中CO2和N2O的释放,森林、农田、草地和荒漠土壤CO2和N2O释放速率对干湿交替的响应模式基本一致,其响应强度与土壤本底中碳和氮的含量有关;(2)在一定培养时间内,随着干湿交替频率的增加,土壤再湿润阶段CO2释放速率降低,但是,气体释放的总量较之于恒湿对照组有所增加。(3)不同土壤N2O的释放总量对干湿交替频率的响应模式表现出很大的差异,其中农田和荒漠土壤响应模式类似。

In the context of climate change impacts on the rainfall patterns,understanding the effects of soil drying-rewetting cycles on green-house gas emission has become increasingly important in many ecosystems.Soil carbon and nitrogen releases caused by drying and rewetting cycles largely determine the total amount of greenhouse gases emission for a long time in an ecosystem.Such kind of influence is particularly important in arid,semi-arid and Mediterranean regions.The soil drying-rewetting cycle is a natural phenomenon that the soil experiences drying,then wetting,and then drying and rewetting again and again.When a dry soil is being rewetted,the amount of soil microbial biomass and its activity can be sharply increasing in a short time period,and then a large amount of gaseous carbon（C） and nitrogen（N） erupts from the soil.The sudden release of gaseous C and N is caused by the stimulation of the soil microbes.Such a phenomenon is called ＂Birch effect＂.The drying-rewetting cycles play an important role in the feedbacks of terrestrial ecosystems.In this study,soil samples were taken from four field sites of forest,agriculture,grassland and desert ecosystems along the precipitation gradient in China.These four sites are Beijing Forest Ecosystem Study,Ansai Agricultural Ecosystem Study,Inner Mongolia Grassland Study and Fukang Desert Ecosystem Study sites of the Chinese Ecosystem Research Network（CERN）.Based on the laboratory experiment with 0,2,5,7 and 14 drying-rewetting cycles in the controlling temperature,we examed the patterns of drying-rewetting impacts on soil CO2 and N2O emission.Our results showed that：（1） Drying and rewetting cycles significantly stimulated the CO2 and N2O releases from soil.For example,in comparison with the control experiment with constant soil moisture in the grassland soil,the average respiration rate of 14-cycle,7-cycle,5-cycle and 2-cycle treatments increased 43%、103%、116% and 192%,respectively.We also found that response patterns in CO2 and N2O release rates to drying and rewetting frequencies were similar among different ecosystem soils.The initial rewetting pulses were the highest,and then declined over time.（2） The total amount of CO2 released from the cycling soil was higher than that from its corresponding control treatment with constant soil moisture.In the forest soil,the 14-cycle soil released a total of 360.11μg C-CO2/g soil in comparison with the control treatment with constant soil moisture,which released 284.56 μg C-CO2/g soil.The cycling increased respiration by 27%.In the grassland soil,the 14-cycle soil released a total of 339.88μg C-CO2/g soil in comparison with the control treatmen,which released 244.01 μg C-CO2/g soil,increased by 39%.In the agriculture soil,the 14-cycle soil released a total of 299.31μg C-CO2/g soil in comparison with the control treatment,which released 143.27 μg C-CO2/g soil,increased respiration by 109%.In the desert soil,the 14-cycle soil released a total of 167.54μg C-CO2/g soil in comparison with the control treatment,which released 142.79 μg C-CO2/g soil,increased respiration by 17%.（3） Cumulative N2O release among different ecosystem soils had different drying-rewetting response patterns,but soils from the agriculture and desert ecosystems have similar response patterns.