Quantifying erosion rates and weathering pathways that maximize soil organic carbon storage

Primary minerals that enter soils through bedrock weathering and atmospheric deposition can generate poorly crystalline minerals (PCM) that preferentially associate with soil organic carbon (SOC). These associations hinder microbial decomposition and the release of CO₂ from soils to the atmosphere, making them a critical geochemical control on terrestrial carbon abundance and persistence. Studies that explore these relationships are typically derived from soil chronosequences that experience negligible erosion and thus do not readily translate to eroding landscapes. Here, we propose a theoretical framework to estimate steady-state PCM density and stocks for hilly and mountainous settings by coupling geochemical and geomorphic mass balance equations that account for soil production from bedrock and dust, soil erosion, PCM formation from weathering, and the transformation of PCMs into crystalline phases. We calculate an optimal erosion rate for maximum PCM abundance that arises because PCMs are limited by insufficient weathering at faster erosion rates and loss via “ripening” into more crystalline forms at slower erosion rates. The optimal erosion rate for modeled hilltop soil is modulated by reaction rate constants that govern the efficiency of primary mineral weathering and PCM ripening. By comparing our analysis with global compilations of erosion and soil production rates derived from cosmogenic nuclides, we show that landscapes with slow-to-moderate erosion rates may be optimal for harboring abundant PCM stocks that can facilitate SOC sequestration and limit turnover. Given the growing array of erosion-topography metrics and the widespread availability of high-resolution topographic data, our framework demonstrates how weathering and critical zone processes can be coupled to inform landscape prioritization for persistent SOC storage potential across a broad range of spatial and temporal scales

Antarctic subglacial lake exploration: a new frontier in microbial ecology

To date, wherever life has been sought on Earth, it has almost always been found—from high in the stratosphere (Imshenetskii et al., 1975, 1978, 1986; Wainwright et al., 2003) to deep in the ocean trenches (Takamia et al., 1997; D'Hondt et al., 2004) and even within the Earth's crust itself (Pedersen, 2000). Microorganisms have also been found in some of the most extreme environments. They have been found to exist in ice, boiling water, acid, salt crystals, toxic waste and even in the water cores of nuclear reactors (Rothschild and Mancinelli, 2001). Antarctic subglacial lake ecosystems have the potential to be one of the most extreme environments on Earth, with combined stresses of high pressure, low temperature, permanent darkness, low-nutrient availability and oxygen concentrations derived from the ice that provided the original meltwater (Siegert et al., 2003), where the predominant mode of nutrition is likely to be chemoautotrophic. Yet, to date, the identification of significant subglacial bacterial activity in the Arctic, beneath glaciers (Skidmore et al., 2000, 2005) and in subglacial lakes (Gaidos et al., 2004), as well as extensive work on permafrost communities and work in the deep sea, suggests that life can survive and potentially thrive in these types of environment. Microbial life has been shown to function at gigapascal pressures (Sharma et al., 2002) and bacteria recovered from the deep ocean at around 4000 m have been shown to retain both structural integrity and metabolic activity. They have shown activity in the Antarctic at −17 °C (Carpenter et al., 2000) and to exist in the pore spaces between ice crystals (Thomas and Dieckmann, 2002)

Invasive earthworms unlock arctic plant nitrogen limitation

Abstract Arctic plant growth is predominantly nitrogen (N) limited. This limitation is generally attributed to slow soil microbial processes due to low temperatures. Here, we show that arctic plant-soil N cycling is also substantially constrained by the lack of larger detritivores (earthworms) able to mineralize and physically translocate litter and soil organic matter. These new functions provided by earthworms increased shrub and grass N concentration in our common garden experiment. Earthworm activity also increased either the height or number of floral shoots, while enhancing fine root production and vegetation greenness in heath and meadow communities to a level that exceeded the inherent differences between these two common arctic plant communities. Moreover, these worming effects on plant N and greening exceeded reported effects of warming, herbivory and nutrient addition, suggesting that human spreading of earthworms may lead to substantial changes in the structure and function of arctic ecosystems

Metallochaperones Regulate Intracellular Copper Levels

Copper (Cu) is an important enzyme co-factor that is also extremely toxic at high intracellular concentrations, making active efflux mechanisms essential for preventing Cu accumulation. Here, we have investigated the mechanistic role of metallochaperones in regulating Cu efflux. We have constructed a computational model of Cu trafficking and efflux based on systems analysis of the Cu stress response of Halobacterium salinarum. We have validated several model predictions via assays of transcriptional dynamics and intracellular Cu levels, discovering a completely novel function for metallochaperones. We demonstrate that in addition to trafficking Cu ions, metallochaperones also function as buffers to modulate the transcriptional responsiveness and efficacy of Cu efflux. This buffering function of metallochaperones ultimately sets the upper limit for intracellular Cu levels and provides a mechanistic explanation for previously observed Cu metallochaperone mutation phenotypes