杉木人工林去除根系土壤呼吸的季节变化及影响因子

Seasonal variation of soil respiration by root exclusion and its controlling factors in a Cunninghamia lanceolata plantation

2007年1月至2008年12月,在长沙天际岭国家森林公园内,采用挖壕法研究杉木人工林去除根系后土壤呼吸速率季节动态及其与5 cm土壤温、湿度的相关关系。结果表明:去除根系与对照5 cm土壤温度的差异性不显著(P=0.987),5 cm土壤湿度差异显著(P=0.035)。杉木林去除根系处理后土壤呼吸速率明显降低,2007至2008两年实验期间去除根系与对照处理变化范围分别为0.19-2.01μmol.m-2s-1和0.26-2.61μmo.lm-2s-1,年均土壤呼吸速率分别为0.90μmo.lm-2s-1和1.30μmol.m-2s-1。去除根系土壤呼吸速率降低幅度为9.4%-59.7%,平均降低了30.4%。去除根系和对照的土壤呼吸速率与5 cm土壤温度之间均呈显著指数相关,模拟方程分别为:y=0.120e0.094t(R2=0.882,P=0.000),y=0.291e0.069t(R2=0.858,P=0.000)。Q10值分别为2.56和2.01。

Soil respiration（Rs）,the emission of CO2 from the soil surface,is one of major carbon fluxes from terrestrial ecosystems to the atmosphere,and is therefore an important component of the global carbon balance.Total respiration from soils is mainly comprised of both the heterotrophic respiration of microorganisms（soil bacteria,fungi,and fauna） and autotrophic respiration from roots and their associated mycorrhizae.While Rs has received considerable attention in recent decades,much less is known about the contribution of heterotrophic or autotrophic component to the total Rs.A large part of gross primary production is consumed in heterotrophic respiration,and published estimates of the contribution of heterotrophic respiration to total Rs vary greatly and ranged from 10% to 90%.As a result,precise assessment of the contribution of autotrophic respiration to the total Rs is important to understand the effects of global climate change and human management practices on carbon sequestration and cycling in terrestrial ecosystems.This study aimed to reveal seasonal changes of Rs and the contribution of root respiration to total Rs in a Cunninghamia lanceolata plantation in the Tianjiling Forestry Park（113°01′-113°02′ E,28 °06′-28°07′ N） of Changsha,Hunan Province,China.A trenching method,in which the roots existing in a given area are severed at the plot boundary but not removed,was used to determine the contribution of root respiration to total soil CO2 efflux.The Rs rates were measured from January 2007to December 2008 by using infrared gas exchange analyzer of Li-Cor 6400-09.The results showed that the soil temperature at 5cm depth between trenched plots（without living roots） and control plots（with living roots） was not significant difference（P=0.987）,but soil moisture at 5cm depth between these two types of plots was significant difference（P=0.035）.The Rs rates in control plots increased from May to August and then decreased during autumn.A similar seasonal pattern of Rs process was found in the trenched plots,but the Rs rates in the trenched plots were lower than the controls,and the difference was significant in 2008（P=0.021）.The rates of soil CO2 efflux within the trenched and control plots ranged 0.19-2.01 and 0.26-2.61μ mol·m-2s-1 respectively.The annual Rs in the trenched and control plots averaged 0.90 and 1.30μ mol·m-2s-1,respectively.The Rs rates were decreased 9.4%-59.7% with an annual value of 30.4% in trenched plots when compared with the control plots.There was a significant exponential relationship（R2=0.882,P=0.000） between Rs within the trenched plots and soil temperature.The Q10 value,representing the sensitivity of Rs to soil temperature was higher in the trenched plots（2.56） than the control plots（2.01）.It was worth mentioning that great decreases of Rs within the trenched plots was suppressed in September 2008 due to natural distribution of precipitation and the variation of soil moisture in the study area.