Soil Organic Matter Dynamics in Eurasian Steppes

包括哈萨克斯坦、乌克兰和匈牙利在内的欧亚草原土壤表面CO_2通量变化很大。在一些草地生态系统（哈萨克斯坦南部），土壤水分含量高于大部分农田。然而，原位年土壤呼吸与生物环境因子（即“湿度和SOM积累”和“生物量积累”因子）之间的关系相当简单。与此同时，实验室确定SOM分解速率的方法显示出各生态系统（如草原或森林）内速率常数的总体相似性。这可能是迄今为止建立的模拟模型明显成功的主要原因之一，在这些模型中，几种有机物质的池被认为主要基于分解速率常数顺序的差异。初步观察到，在种植生态系统下，降低土壤呼吸有利于缓解土壤有机质相关特性的主动退化。天然草地复垦后的显著变化主要表现在有机质较不稳定组分（如轻组分C或C_0）的减少。在区域尺度上，C_0值可用于预测CO_2的排放。相对而言，化学化土壤对环境条件和/或土地利用的变化似乎是稳定的，不像森林生态系统，在森林生态系统中，开垦后经常观察到SOM的加速分解。地质统计分析表明，哈萨克斯坦北部农业景观中SOM的总体积累主要受土壤水分状况和土地利用/管理导致的累积初级生产的影响。在乌克兰草原土壤中也指出了地形和水状况造成的这种变化。初级生产最重要的决定因素是可利用水，而在所调查的草原生态系统中，分解的决定因素通常是温度。农业实践通常会改变土壤水分状况，以实现最大作物产量，然后将初级生产作为收获，但它不会从根本上改变土壤有机质和/或养分的动态。如果农业实践对草原环境下土壤有机质的不利影响是有限的，那么基于有机质动态空间格局的因地制宜的农业管理将是通过减少有机质分解来协调可持续农业生产与环境保护的现实选择。少

The CO_2 flux from soil surfaces in Eurasian steppes, including Kazakhstan, Ukraine and Hungary, varied widely. It was higher in some grassland ecosystems (southern Kazakhstan) than in most of the cropland. Nonetheless a rather simple relationship was obtained between the in situ annual soil respiration and bio-environmental factors (namely "humidity and SOM accumulation" and "biomass accumulation" factors). At the same time, the laboratory approach to fix decomposition rates of SOM showed an overall similarity of the rate constants within each respective ecosystem such as steppe or forest. This might be one of main reasons for an apparent success of simulation models ever established, in which several pools of organic materials are supposed primarily based on the difference in the order of decomposition rate constants.Lowering soil respiration under cropped ecosystems tended to alleviate an active degradation of SOM-related properties of soils, which was initially observed. A signific … More ant change after reclamation of natural grassland mostly appeared in the decrease of more labile fractions of SOM, such as light fraction C or C_0. In the regional scale, the value of C_0 was useful for predicting CO_2 emission. Chemozem soils seemed to be, relatively speaking, stable against changes in environmental conditions and/or land use, not like as forest ecosystems, in which accelerated decomposition of SOM was often observed after reclamation.The geostatistical analysis suggested that the overall accumulation of SOM in agro-landscape in northern Kazakhstan was primarily affected by the cumulative primary production as a result of soil moisture regime and land use/management. Such a variation caused by topography and water regime was also pointed out for Ukrainian steppe soils. The most important determinant for primary production is water availability, whereas that of decomposition is usually temperature in the steppe ecosystems investigated. Agricultural practices usually modifies soil water regime for achieving maximum crop production, followed by removal of primary production as harvest, but it does not essentially change the dynamics of SOM and/or nutrients. If the adverse effects of agricultural practices on SOM regime under steppe environment are actually limited, as suggested from different approaches, a site-specific agricultural management based on the spatial patterns of organic matter dynamics would be a suitable option in reality for harmonizing sustainable agricultural production with environmental conservation by reducing organic matter decomposition. Less