Portell Xavier, Pot Valérie, Garnier Patricia, Otten Wilfred, Baveye Philippe C
School of Water, Energy and Environment, Cranfield University, Cranfield, United Kingdom.
UMR ECOSYS, Institut National de la Recherche Agronomique, AgroParisTech, Université Paris-Saclay, Paris, France.
Front Microbiol. 2018 Jul 27;9:1583. doi: 10.3389/fmicb.2018.01583. eCollection 2018.
There is still no satisfactory understanding of the factors that enable soil microbial populations to be as highly biodiverse as they are. The present article explores the hypothesis that the heterogeneous distribution of soil organic matter, in addition to the spatial connectivity of the soil moisture, might account for the observed microbial biodiversity in soils. A multi-species, individual-based, pore-scale model is developed and parameterized with data from 3 sp. strains, known to be, respectively, competitive, versatile, and poorly competitive. In the simulations, bacteria of each strain are distributed in a 3D computed tomography (CT) image of a real soil and three water saturation levels (100, 50, and 25%) and spatial heterogeneity levels (high, intermediate, and low) in the distribution of the soil organic matter are considered. High and intermediate heterogeneity levels assume, respectively, an amount of particulate organic matter (POM) distributed in a single (high heterogeneity) or in four (intermediate heterogeneity) randomly placed fragments. POM is hydrolyzed at a constant rate following a first-order kinetic, and continuously delivers dissolved organic carbon (DOC) into the liquid phase, where it is then taken up by bacteria. The low heterogeneity level assumes that the food source is available from the start as DOC. Unlike the relative abundances of the 3 strains, the total bacterial biomass and respiration are similar under the high and intermediate resource heterogeneity schemes. The key result of the simulations is that spatial heterogeneity in the distribution of organic matter influences the maintenance of bacterial biodiversity. The least competing strain, which does not reach noticeable growth for the low and intermediate spatial heterogeneities of resource distribution, can grow appreciably and even become more abundant than the other strains in the absence of direct competition, if the placement of the resource is favorable. For geodesic distances exceeding 5 mm, microbial colonies cannot grow. These conclusions are conditioned by assumptions made in the model, yet they suggest that microscale factors need to be considered to better understand the root causes of the high biodiversity of soils.
对于使土壤微生物种群具有如此高生物多样性的因素，目前仍没有令人满意的认识。本文探讨了这样一种假说：土壤有机质的非均匀分布，除了土壤水分的空间连通性之外，可能是造成土壤中观察到的微生物生物多样性的原因。开发了一个基于个体的多物种孔隙尺度模型，并用来自3种已知分别具有竞争性、通用性和低竞争性的菌株的数据进行了参数化。在模拟中，每种菌株的细菌分布在真实土壤的三维计算机断层扫描（CT）图像中，并考虑了三种水分饱和度水平（100%、50%和25%）以及土壤有机质分布中的三种空间异质性水平（高、中、低）。高异质性水平和中等异质性水平分别假设一定量的颗粒有机物质（POM）分布在单个（高异质性）或四个（中等异质性）随机放置的碎片中。POM按照一级动力学以恒定速率水解，并持续将溶解有机碳（DOC）输送到液相中，然后被细菌吸收。低异质性水平假设食物源从一开始就以DOC的形式存在。与三种菌株的相对丰度不同，在高资源异质性和中等资源异质性方案下，细菌总生物量和呼吸作用相似。模拟的关键结果是有机质分布的空间异质性影响细菌生物多样性的维持。在资源分布的低空间异质性和中等空间异质性情况下没有明显生长的竞争力最弱的菌株，如果资源放置有利，在没有直接竞争的情况下可以显著生长，甚至比其他菌株更丰富。对于超过5毫米的测地距离，微生物菌落无法生长。这些结论受到模型中所作假设的限制，但它们表明需要考虑微观尺度因素，以便更好地理解土壤高生物多样性的根本原因。
