Replacing long-lived, rarely disturbed vegetation with short-lived, frequently disturbed vegetation is a widespread phenomenon in the Anthropocene that can influence ecosystem functioning and soil development by reducing the abundance of deep roots. We explore how sources and fate of soil CO₂ vary with organic substrate source, abundance of respiring biota (i.e., roots and soil microbes), season, and soil depth. We quantified multiple isotopic signatures of CO₂ (δ¹³C, Δ¹⁴C, δ¹⁸O) as well as concentrations and δ¹⁸O of free O₂ in the upper 5 m of soil at sites where root abundances and soil organic C have been previously quantified: in late-successional forests, cultivated fields, and ~ 80 y old regenerating pine forests growing on previously cultivated land. We hypothesized that soil CO₂sources would vary across soil depth and land cover, reflecting varying abundances of organic substrates, and seasonally as the dominance of root vs. microbial CO₂ production changes through the year. δ¹³C–CO₂ revealed respiration of C4-derived substrates in cultivated fields particularly during the growing season. This effect was not evident in soils of regenerating pine or older hardwood forests, suggesting that ~ 80 y of pine inputs to reforested soils have been sufficient to dominate microbial substrate selection over any remnant, historic agricultural C4 inputs. Δ¹⁴C–CO₂ diverged by land use at 3 and 5 m, indicating that more recently-produced photosynthate is available for mineralization in forests compared to cultivated plots, and in late-successional forests compared to regenerating pine forests. At 1.5, 3, and 5 m in forested plots we observed evidence of respiratory demands on soil pore space O₂. In these soils, we observed declines in [O₂] compared to other depths and to the agricultural plots and concurrent increases in δ¹⁸O of free O₂, consistent with the idea that roots and heterotrophic soil microbes are more active where photosynthate is more available. The δ¹⁸O–CO₂ values, a likely proxy for δ¹⁸O of soil porewater, exhibited ¹⁸O enrichment during the winter, when many sampling wells were flooded, compared to growing season values. These data suggest an isotopically-distinct and laterally-flowing source of CO₂-laden porewater during winter months. Combined, these datasets document how ~ 80 y of forest regeneration can provide sufficient C inputs to mask any microbial mineralization of decades-old organic inputs, but belowground C inputs still lag those of late successional forests. We also infer that lateral and vertical flows of water can serve as a sink for biotically-generated CO₂, and that where deep soil [CO₂] is lower due to lower root and microbial activities, production of carbonic acid is also diminished. Where reaction rates are weathering limited, a paucity of deep roots imposed by anthropogenic land cover change thus may limit the production of this agent of soil development and the C sink represented by the silicate weathering it can promote. The data suggest deep and persistent effects of the loss of deeply rooted long-lived vegetation on deep soil C storage and transformations that promote acid-dissolution weathering reactions that help form soil itself.

用寿命短、经常受干扰的植被取代寿命长、很少受干扰的植被是人类世的一个普遍现象，它可以通过减少深根的丰度来影响生态系统功能和土壤发育。我们探讨了土壤_CO2 的来源和归宿如何随有机基质来源、呼吸生物群（即根和土壤微生物）的丰度、季节和土壤深度而变化。我们量化了 CO₂ 的多种同位素特征 （δ¹³C、Δ¹⁴C、δ¹⁸O） 以及土壤上部 5 m 中游离 O₂ 的浓度和δ¹⁸O 在先前量化了根系丰度和土壤有机 C 的地点：在演替后期森林、耕地和 ~ 80 y 老的再生松林生长在以前的耕地上。我们假设土壤 CO₂来源会随着土壤深度和土地覆盖而变化，这反映了有机基质丰度的不同，并且随着根系与微生物 CO₂ 产生的优势在一年中的变化而变化。δ¹³C-CO₂ 揭示了 C4 衍生底物在耕地中的呼吸作用，尤其是在生长季节。这种影响在再生松树或老阔叶林的土壤中并不明显，这表明 ~ 80 y 的松树输入到重新造林的土壤中足以主导微生物基质的选择，而不是任何残留的、历史上的农业 C4 输入。Δ¹⁴C-CO₂ 在 3 m 和 5 m 处因土地利用而出现差异，表明与耕地相比，最近产生的光合产物可用于森林中的矿化，与再生松树林相比，在演替后期的森林中可用于矿化。在 1.在林地 5、3 和 5 m 中，我们观察到土壤孔隙空间 O₂ 的呼吸需求证据。在这些土壤中，我们观察到与其他深度和农业地块相比，[O₂] 有所下降，同时δ¹⁸O 的游离 O₂ 增加，这与根和异养土壤微生物在光合产物更容易获得的地方更加活跃的观点一致。δ¹⁸O-CO₂ 值可能是土壤孔隙水δ¹⁸O 的代表，与生长季节值相比，冬季许多采样井被淹没时，表现出 ¹⁸O 的富集。这些数据表明，在冬季，充满 CO₂ 的孔隙水存在同位素不同且横向流动的来源。这些数据集结合起来，记录了 ~ 80 y 的森林再生如何提供足够的 C 输入来掩盖几十年前有机输入的任何微生物矿化，但地下 C 输入仍然落后于晚期演替森林的输入。我们还推断，水的横向和垂直流可以作为生物产生的 CO₂ 的汇，并且在深层土壤 [CO₂] 由于根系和微生物活性较低而较低的地方，碳酸的产生也会减少。在反应速率风化受限的地方，人为土地覆盖变化造成的深根缺乏可能会限制这种土壤发育剂的产生，以及它可以促进的硅酸盐风化所代表的碳汇。数据表明，深根植被的丧失对深层土壤 C 储存和转化的深刻而持久的影响，这些转化促进了有助于形成土壤本身的酸溶风化反应。