Development of soil microbial communities is driven by local abiotic and biotic conditions, yet our current understanding of their ecology is limited to studies in modified or young and relatively fertile ecosystems. In nutrient-impoverished soils, microbial communities may be predominantly structured by availability of key elements such as phosphorus (P) or nitrogen, regardless of the taxa (bacteria, archaea or fungi). Here, we determined if shifts in bacterial communities and biomass occurred along a long-term soil chronosequence in south-western Australia, and whether such shifts were related to changes in soil nutrient availability along the retrogressive phase of this chronosequence. We quantified shifts in the biomass and abundance of major soil microbial groups using phospholipid fatty acids and quantitative polymerase chain reaction. We found that declining soil P availability limited microbial growth and community structure. Common cations, notably magnesium, showed strong relationships with the abundance of most bacterial and archaeal taxa. In the oldest most severely impoverished soils, the fungal to bacteria ratio was higher than in the young soils, indicating fungi are better adapted to such environments. Finally, archaeal copy numbers decreased more strongly than bacterial copy numbers with increasing nutrient-impoverishment of soils. The study enhances our understanding of the ecology of soil bacteria, archaea, and fungi during ecosystem development and retrogression.

土壤微生物群落的发展是由当地的非生物和生物条件驱动的，但我们目前对其生态学的理解仅限于对改良或年轻且相对肥沃的生态系统的研究。在营养贫乏的土壤中，微生物群落可能主要由磷（P）或氮等关键元素的可用性构成，而与分类群（细菌、古细菌或真菌）无关。在这里，我们确定细菌群落和生物量的变化是否沿澳大利亚西南部的长期土壤时间序列发生，以及这种变化是否与沿该时间序列的倒退阶段土壤养分有效性的变化有关。我们使用磷脂脂肪酸和定量聚合酶链反应量化了主要土壤微生物群的生物量和丰度的变化。我们发现土壤磷可用性的下降限制了微生物的生长和群落结构。常见的阳离子，特别是镁，与大多数细菌和古细菌类群的丰度表现出很强的关系。在最古老最严重的贫困土壤中，真菌与细菌的比率高于年轻土壤，表明真菌更适应这种环境。最后，随着土壤养分贫化程度的增加，古菌拷贝数下降的幅度大于细菌拷贝数。该研究增强了我们对生态系统发展和退化过程中土壤细菌、古细菌和真菌生态学的理解。在最古老最严重的贫困土壤中，真菌与细菌的比率高于年轻土壤，表明真菌更适应这种环境。最后，随着土壤养分贫化程度的增加，古菌拷贝数下降的幅度大于细菌拷贝数。该研究增强了我们对生态系统发展和退化过程中土壤细菌、古细菌和真菌生态学的理解。在最古老最严重的贫困土壤中，真菌与细菌的比率高于年轻土壤，表明真菌更能适应这种环境。最后，随着土壤养分贫化程度的增加，古菌拷贝数下降的幅度大于细菌拷贝数。该研究增强了我们对生态系统发展和退化过程中土壤细菌、古细菌和真菌生态学的理解。