Climate-smart land management practices that replace shallow-rooted annual crop systems with deeply-rooted perennial plants can contribute to soil carbon sequestration. However, deep soil carbon accrual may be influenced by active microbial biomass and their capacity to assimilate fresh carbon at depth. Incorporating active microbial biomass, dormancy, and growth in microbially-explicit models can improve our ability to predict soil's capacity to store carbon. But, so far, the microbial parameters that are needed for such modeling are poorly constrained, especially in deep soil layers. Here, we used a lab incubation experiment and growth kinetics model to estimate how microbial parameters vary along 240 cm of soil depth in profiles under shallow- (soy) and deeply-rooted (switchgrass) plants 11 years after plant cover conversion. We also assessed resource origin and availability (total organic carbon, ¹⁴C, extractable organic carbon, specific UV absorbance of K₂SO₄ extractable organic C, total nitrogen, total dissolved nitrogen) along the soil profiles to examine associations between soil chemical and biological parameters. Even though root biomass was greater and rooting depth was deeper under switchgrass than soy, resource availability and microbial growth parameters were generally similar between vegetation types. Instead, depth significantly influenced soil chemical and biological parameters. For example, resource availability and total and relative active microbial biomass decreased with soil depth. Decreases in the relative active microbial biomass coincided with increased lag time (response time to external carbon inputs) along the soil profiles. Even at a depth of 210–240 cm, microbial communities were activated to grow by added resources within a day. Maximum specific growth rate decreased to a depth of 90 cm and then remained consistent in deeper layers. Our findings show that >10 years of vegetation and rooting depth changes may not be long enough to alter microbial growth parameters, and suggest that at least a portion of the microbial community in deep soils can grow rapidly in response to added resources. Our study determined microbial growth parameters that can be used in microbially-explicit models to simulate carbon dynamics in deep soil layers.

用深根多年生植物取代浅根一年生作物系统的气候智能型土地管理实践有助于土壤固碳。然而，深层土壤的碳积累可能受到活性微生物生物量及其在深层吸收新鲜碳的能力的影响。在微生物显性模型中结合活跃的微生物生物量、休眠和生长可以提高我们预测土壤储存碳能力的能力。但是，到目前为止，这种建模所需的微生物参数受到的限制很差，尤其是在深层土壤中。在这里，我们使用实验室孵化实验和生长动力学模型来估计在植物覆盖转换 11 年后，在浅（大豆）和深根（柳枝稷）植物下，微生物参数如何沿 240 厘米土壤深度变化。¹⁴ C，可萃取的有机碳，K ₂ SO _{4 的}特定紫外吸光度可提取的有机碳、总氮、总溶解氮）沿土壤剖面检测土壤化学和生物参数之间的关联。尽管与大豆相比，柳枝稷下的根生物量更大且生根深度更深，但植被类型之间的资源可用性和微生物生长参数通常相似。相反，深度显着影响土壤化学和生物参数。例如，资源可用性以及总和相对活跃的微生物生物量随着土壤深度的增加而降低。相对活跃微生物生物量的减少与沿土壤剖面的滞后时间（对外部碳输入的响应时间）的增加相吻合。即使在 210-240 厘米的深度，微生物群落也会在一天内被增加的资源激活生长。最大比生长率下降到 90 厘米的深度，然后在更深的层中保持一致。我们的研究结果表明，超过 10 年的植被和生根深度变化可能不足以改变微生物生长参数，并表明深层土壤中至少有一部分微生物群落可以响应增加的资源快速生长。我们的研究确定了微生物生长参数，这些参数可用于微生物显式模型以模拟深层土壤中的碳动态。