Soils provide the substrate for important microbial mechanisms that moderate a variety of processes in both managed and natural terrestrial ecosystems. Australian soils are particularly ‘stressed’ and are considered to be highly weathered and nutrient deficient. This places increased pressure on the Australian cotton industry to sustainably increase productivity to support the fibre demands of a growing global population. We explored Vertosol subsoils (>30 cm) under rotational cotton crops, measuring the distribution of soil microbial activity (SMA) and biomass (SMB) to 100 cm depth, as influenced by crop system and time, using respiration-based experiments. Seasonal SMA fluctuations were considered by capturing the long-term SMA between systems using stable oxygen isotope methodology. Our results indicate that subsoils contributed 47% of SMA, regardless of system, but subsoil SMB (26%) was constrained by resource availability. Long-term SMA was not significantly influenced by depth and system, presumably as a consequence of the shrink–swell nature of Vertosols facilitating organic matter movement down the profile. The impact of this organic matter on the activity of indigenous microorganisms below the top 30 cm of the profile highlights a need to consider deeper soil when unravelling the potential microbial benefits to our cropping systems.

中文翻译：

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受系统、作物状况和季节影响的澳大利亚轮作棉下土壤微生物活性和生物量分布

土壤为重要的微生物机制提供了基质，这些机制可以调节受管理的和自然的陆地生态系统中的各种过程。澳大利亚的土壤特别“受压”，被认为是高度风化和营养不足的土壤。这给澳大利亚棉花产业带来了更大的压力，需要持续提高生产力，以满足不断增长的全球人口对纤维的需求。我们探索了轮作棉花作物下的 Vertosol 底土 (>30 cm)，使用基于呼吸的实验测量土壤微生物活性 (SMA) 和生物量 (SMB) 到 100 cm 深度的分布，受作物系统和时间的影响。通过使用稳定氧同位素方法捕获系统之间的长期 SMA，考虑了季节性 SMA 波动。我们的结果表明，底土贡献了 47% 的 SMA，无论系统如何，但底土 SMB (26%) 受到资源可用性的限制。长期 SMA 不受深度和系统的显着影响，可能是由于 Vertosols 的收缩膨胀性质促进了有机物质沿剖面移动。这种有机物质对剖面顶部 30 厘米以下的本地微生物活动的影响突出表明，在阐明微生物对我们种植系统的潜在益处时，需要考虑更深的土壤。