Most of our terrestrial carbon (C) storage occurs in soils as organic C derived from living organisms. Therefore, the fate of soil organic C (SOC) in response to changes in climate, land use, and management is of great concern. Here we provide a unified conceptual model for SOC cycling by gathering the available information on SOC sources, dissolved organic C (DOC) dynamics, and soil biogeochemical processes. The evidence suggests that belowground C inputs (from roots and microorganisms) are the dominant source of both SOC and DOC in most ecosystems. Considering our emerging understanding of SOC protection mechanisms and long-term storage, we highlight the present need to sample (often ignored) deeper soil layers. Contrary to long-held biases, deep SOC—which contains most of the global amount and is often hundreds to thousands of years old—is susceptible to decomposition on decadal timescales when the environmental conditions under which it accumulated change. Finally, we discuss the vulnerability of SOC in different soil types and ecosystems globally, as well as identify the need for methodological standardization of SOC quality and quantity analyses. Further study of SOC protection mechanisms and the deep soil biogeochemical environment will provide valuable information about controls on SOC cycling, which in turn may help prioritize C sequestration initiatives and provide key insights into climate-carbon feedbacks.

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Core Ideas Clod and core bulk density measurements were significantly different at all depths. The core sampling method underestimated the soil organic carbon (SOC) stock. Calculating SOC stocks on a mass basis did not overcome sampling method bias. Using clod and core methods interchangeably adds uncertainty to SOC databases. Regional and global SOC stocks may be largely underestimated. Changing climate, land use, and management can impact both surface and deep soil organic carbon (SOC) stocks on decadal timescales, highlighting the importance of accurate measurements of SOC stocks and comparisons. This study compared three soil sampling methods for estimating SOC stocks: clod, core, and excavation. The excavation method was used as the standard by which the other methods were compared. Sampling took place at an intensively managed Douglas‐fir [Pseudotsuga menziesii (Mirb.) Franco] plantation in northwestern Oregon, USA. Soil samples were collected by depth to 150 cm. Clod and core method soil bulk density measurements were significantly different at all depths, with the core method consistently resulting in lower soil bulk density. The core method significantly underestimated soil bulk density at all depths deeper than 20 cm and underestimated the SOC stock to a depth of 150 cm by 36%. Most of this difference occurred deeper than 20 cm, where the majority of SOC stocks were contained across all soil sampling methods. The underestimation of soil mass by the core method similarly affected the fixed depth, genetic horizon, and mass based approaches to quantify SOC stocks. This study demonstrated that (1) commonly used soil sampling methods for measuring soil properties should not be assumed to be interchangeable; and (2) regional and global SOC stocks may be largely underestimated due to shallow sampling and the frequent use of core methods.

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ObjectiveTo present an unusual case of spontaneous pneumomediastinum subsequent to recreational amphetamine use.Case reportA young African American adult male was admitted to internal medicine service for treatment of rhabdomyolysis secondary to methamphetamine use. On admission, he was complaining of chest pain in addition to nausea and generalized muscle aches. By his second hospital day, chest pain had resolved yet physical exam demonstrated crepitation of the anterior chest and left axilla. Portable chest x-ray revealed subcutaneous emphysema in addition to pneumomediastinum.ConclusionSpontaneous pneumomediastinum is a rare complication of amphetamine use that is often associated with subcutaneous emphysema and can be diagnosed with chest x-ray. Management is conservative, with observation, pain control, and supplemental oxygen as needed.

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Forests provide valuable ecosystem and societal services, including the sequestration of carbon (C) from the atmosphere. Management practices can impact both soil C and nitrogen (N) cycling. This study examines soil organic C (SOC) and N responses to thinning and fertilization treatments. Soil was sampled at an intensively managed Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) plantation in north-western Oregon, USA. Management regimes-thinning, fertilization plus thinning, and no (control) treatment-were randomly assigned to nine 0.2-ha plots established in 1989 in a juvenile stand. Prior to harvest, forest floor and soil bulk density and chemical analysis samples were collected by depth to 150 cm. During a single rotation of~40 years, thinning treatments significantly reduced SOC and N stocks by 25% and 27%, respectively, compared to no treatment. Most of this loss occurred in deeper soil layers (below~20 cm). Fertilization plus thinning treatments also reduced SOC and N stocks, but not significantly. Across all management regimes, deeper soil layers comprised the majority of SOC and N stocks. This study shows that: (1) accurately quantifying and comparing SOC and N stocks requires sampling deep soil; and (2) forest management can substantially impact both surface and deep SOC and N stocks on decadal timescales.

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