Long Tao, Or Dani
Department of Civil and Environmental Engineering, Tufts University, Medford, MA 02155, USA.
Microb Ecol. 2009 Aug;58(2):262-75. doi: 10.1007/s00248-009-9510-3. Epub 2009 Apr 8.
The high degree of microbial diversity found in soils is attributed to the highly heterogeneous pore space and the dynamic aqueous microenvironments. Previous studies have shown that spatial and temporal variations in aqueous diffusion pathways play an important role in shaping microbial habitats and biological activity in unsaturated porous media. A new modeling framework was developed for the quantitative description of diffusion-dominated microbial interactions focusing on competitive growth of two microbial species inhabiting partially saturated rough surfaces. Surface heterogeneity was represented by patches with different porosities and water retention properties, yielding heterogeneous distribution of water contents that varies with changes in relative humidity or soil matric potential. Nutrient diffusion and microbial growth on the variably hydrated and heterogeneous surface was modeled using a hybrid method that combines a reaction diffusion method for nutrient field with individual based model for microbial growth and expansion. The model elucidated the effects of hydration dynamics and heterogeneity on nutrient fluxes and mobility affecting microbial population growth, expansion, and coexistence at the microscale. In contrast with single species dominance under wet conditions, results demonstrated prolonged coexistence of two competing species under drier conditions where nutrient diffusion and microbial movement were both limited. The uneven distribution of resources and diffusion pathways in heterogeneous surfaces highlighted the importance of position in the landscape for survival that may compensate for competitive disadvantages conferred by physiological traits. Increased motility was beneficial for expansion and survival. Temporal variations in hydration conditions resulted in fluctuations in microbial growth rate and population size. Population growth dynamics of the dominant species under wet-dry cycles were similar to growth under average value of diffusion coefficients for dry and wet conditions, respectively, suggesting that the time-averaged diffusion coefficient could serve as a useful indicator for estimation of microbial activities in a highly dynamic system such as that found in soils.
土壤中发现的高度微生物多样性归因于高度异质的孔隙空间和动态的水相微环境。先前的研究表明，水相扩散途径的时空变化在塑造非饱和多孔介质中的微生物栖息地和生物活性方面起着重要作用。开发了一个新的建模框架，用于定量描述以扩散为主的微生物相互作用，重点关注栖息在部分饱和粗糙表面的两种微生物的竞争生长。表面异质性由具有不同孔隙率和保水特性的斑块表示，产生随相对湿度或土壤基质势变化而变化的含水量非均匀分布。使用一种混合方法对可变水合和异质表面上的养分扩散和微生物生长进行建模，该方法将养分场的反应扩散方法与基于个体的微生物生长和扩展模型相结合。该模型阐明了水合动力学和异质性对养分通量和迁移率的影响，这些影响在微观尺度上影响微生物种群的生长、扩展和共存。与潮湿条件下单物种占主导地位相反，结果表明在较干燥条件下两种竞争物种长期共存，此时养分扩散和微生物移动均受到限制。异质表面上资源和扩散途径的不均匀分布突出了景观位置对生存的重要性，这可能弥补生理特征带来的竞争劣势。增加的移动性有利于扩展和生存。水合条件的时间变化导致微生物生长速率和种群大小的波动。干湿循环下优势物种的种群增长动态分别类似于在干燥和潮湿条件下扩散系数平均值下的生长，这表明时间平均扩散系数可作为估计土壤等高度动态系统中微生物活动的有用指标。
