The impact of land use change and agricultural management on the cycling of soil organic carbon (SOC) is not well understood, limiting our ability to manage for, and accurately model, soil carbon changes at both local and regional scales. To address this issue, we combined long-term soil incubations with acid-hydrolysis and dry combustion to parse total SOC (C_t) into three operationally defined SOC pools (active, slow, and recalcitrant) from 9 long-term sites with varying land uses on current and former tallgrass prairie soil. Land uses represented a gradient of soil disturbance histories including remnant prairie, restored prairie, grazed pasture, annual crop rotations, and continuous maize. Dry combustion was used to estimate total carbon (C_t, physical), while acid hydrolysis of both the active (C_a) and slow (C_s) pools was used to estimate a recalcitrant carbon pool (C_r, chemical). Non-linear modeling of CO₂ efflux data from the long-term incubations was then used to estimate C_a, and the decomposition rates of both C_a and C_s (k_a and k_r, biological). The size of the slow pools C_s was then defined mathematically as C_t-(C_a + C_r). Remnant prairie had the highest C_t, while cool-season pasture and a 35-y-old restored prairie had higher C_t than the other agricultural systems. All agricultural systems, including pasture, had the highest fraction of C_t as C_r (∼50%), whose mean residence time (MRT) in these soils is ≥500 years (Paul et al., 2001a) demonstrating that this fraction persists, while the more labile fractions were lost over the course of a few months (C_a) to a few decades (C_s) as a result of tillage-intensive agriculture. The two- to four-decade MRT time of C_s indicated a pool likely to be more responsive to the 20 to 40 years of land-use practices used at some of the sites. The C_s pool was largest in the remnant- and 35-y-old prairies indicating significant C accrual and stabilization compared to the agricultural ecosystems. Interestingly, the remnant prairie maintained the highest C_a pool as well, demonstrating the strong connection between the quantity of fresh C inputs and the potential for long-term C stabilization and accrual. The accumulation of C in active (≈labile) pools as a first step toward long-term stabilization highlights the tenuous nature of early carbon gains, which can be quickly lost in response to climate change or poor management.

土地利用变化和农业管理对土壤有机碳 (SOC) 循环的影响尚不清楚，这限制了我们在地方和区域尺度上管理和准确模拟土壤碳变化的能力。为了解决这个问题，我们将长期土壤孵化与酸水解和干燃烧相结合，将总 SOC (Ct) 解析为_来自9 个不同土地的长期站点的三个操作定义的 SOC 池（活跃、缓慢和顽固）用于当前和以前的高草草原土壤。土地利用代表了土壤扰动历史的梯度，包括残余草原、恢复的草原、放牧牧场、一年生轮作和连续玉米。干式燃烧用于估算总碳（C _t，物理的），而活性（C _a）和慢速（C _s）池的酸水解用于估计顽固碳池（C _r，化学）。然后使用来自长期孵育的 CO ₂流出数据的非线性建模来估计C _a以及C _a和C _s（k _a和k _r，生物）的分解速率。然后，慢池C _s的大小在数学上定义为C _t -( C _a  + C _r )。残余草原的C _t最高，而凉季牧场和 35 年恢复的草原的C _t高于其他农业系统。所有农业系统，包括牧场， C _t的最高比例为C _r (~50%)，其在这些土壤中的平均停留时间 (MRT) ≥ 500 年 (Paul et al., 2001a) 表明这一比例持续存在，而由于耕作密集型农业，在几个月 ( C _a ) 到几十年 ( C _{s ) 的过程中，更不稳定的部分会丢失。}C _s的两到四个十年的捷运时间表明一个水池可能对某些地点使用的 20 到 40 年的土地使用实践更敏感。C _s池在残余和 35 岁大草原中最大，表明与农业生态系统相比，C 积累和稳定显着。有趣的是，残余草原也保持了最高的C _a池，表明新鲜 C 输入的数量与长期 C 稳定和积累的潜力之间存在密切联系。作为实现长期稳定的第一步，活跃（≈不稳定）池中的 C 积累突出了早期碳增益的脆弱性，这些增益可能会因气候变化或管理不善而迅速丧失。