摘要
本文逐日计算了土壤的生物学活动,使用的是非洲气象站的标准气象数据、一个简单的土壤水分模型,并且使用了关于温度、土壤含水量和生物学活动之间关系的一般性假设。活动系数r_(e_clim)由日土壤湿度和温度计算得出,从而考虑了温度与湿度之间的交互作用。瑞典中部(粘壤土,无作物)r_(e_clim)的年均值标准化为1,在那里进行了最初的校准。由于土壤在储水能力和植物覆被上的差异会对蒸腾作用产生影响,所以我们选择的样地均为无作物的该土壤,这样就只包括了气候差异。瑞典r_(e_clim)值,1,相当于诸如表土中含有的谷类秸杆等的年质量亏损约50%。非洲r_(e_clim)年均值在干热地点(法亚,乍得)为1.1,温湿地点(布拉柴维尔,刚果)为4.7之间变动。肯尼亚样地的r_(e_clim)值为2.1(高海拔,Matanya)至4.1(肯尼亚西部,Ahero)。这意味着假如土壤类型和经营相同,那么必须有4.1倍于瑞典的碳输入才能将Ahero的土壤碳水平维持在瑞典水平。对每一块样地都绘制了r_(e_clim)日动态图,并讨论了年内动态差异。模拟实验表明,如果将土壤碳平衡的瑞典土壤移至肯尼亚的Ahero,30年内其土壤碳将损失41%。如果将Ahero保持碳平衡的土壤移至瑞典,30年内其土壤碳含量将增加64%。本文讨论了方法与结论的有效性,并将r_(e_clim)与其它气候指数进行了对比。本文还提出了一种对r_(e_clim)值进行粗略估计的简易方法。
Soil biological activity was calculated on a daily basis,using standard meteorological data from African weather stations,a simple soil water model,and commonly used assumptions regarding the relations between temperature,soil water content,and biological activity.The activity factor r_(e_clim) is calculated from daily soil moisture and temperature,thereby taking the daily interaction between temperature and moisture into account.Annual mean r_(e_clim) was normalized to 1 in Central Sweden (clay loam soil,no crop),where the original calibration took place.Since soils vary in water storage capacity and plant cover will affect transpiration,we used this soil under no crop for all sites,thereby only including climate differences.The Swedish r_(e_clim) value,1,corresponds to ca.50% annual mass loss of,e.g., cereal straw incorporated into the topsoil.African mean annual r_(e_clim) values varied between 1.1 at a hot and dry site (Faya,Chad) and 4.7 at a warm and moist site (Brazzaville,Congo).Sites in Kenya ranged between r_(e clim)=2.1 at high altitude (Matanya) and 4.1 in western Kenya (Ahero).This means that 4.1 times the Swedish C input to soil is necessary to maintain Swedish soil carbon levels in Ahero,if soil type and management are equal.Diagrams showing daily r_(e_clim) dynamics are presented for all sites,and differences in within-year dynamics are discussed.A model experiment indicated that a Swedish soil in balance with respect to soil carbon would lose 41 % of its soil carbon during 30 y,if moved to Ahero,Kenya.If the soil was in balance in Ahero with respect to soil carbon,and then moved to Sweden,soil carbon mass would increase by 64% in 30 y.The validity of the methodology and results is discussed,and r_(e_clim) is compared with other climate indices.A simple method to produce a rough estimate of r_(e_clim) is suggested.
