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1. Decadal increases in carbon uptake offset by respiratory losses across northern permafrost ecosystems

   See, C (August 2024, Nature Climate Change)

   Tundra and boreal ecosystems encompass the northern circumpolar permafrost region and are experiencing rapid environmental change with important implications for the global carbon (C) budget. We analysed multi-decadal time series containing 302 annual estimates of carbon dioxide (CO2) flux across 70 permafrost and non permafrost ecosystems, and 672 estimates of summer CO2 flux across 181 ecosystems. We find an increase in the annual CO2 sink across non-permafrost ecosystems but not permafrost ecosystems, despite similar increases in summer uptake. Thus, recent non-growing-season CO2 losses have substantially impacted the CO2 balance of permafrost ecosystems. Furthermore, analysis of interannual variability reveals warmer summers amplify the C cycle (increase productivity and respiration) at putatively nitrogen-limited sites and at sites less reliant on summer precipitation for water use. Our findings suggest that water and nutrient availability will be important predictors of the C-cycle response of these ecosystems to future warming. 

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2. Mycorrhiza—Saprotroph Interactions and Carbon Cycling in the Rhizosphere

   https://doi.org/10.1111/gcb.70173  

   Tripathi, Binu M; Piñeiro, Juan; Dang, Chansotheary; Brzostek, Edward; Morrissey, Ember M (April 2025, Global Change Biology)

   Labile carbon (C) inputs in soils are expected to increase in the future due to global change drivers such as elevated atmospheric CO2 concentrations or warming and potential increases in plant primary productivity. However, the role of mycorrhizal association in modulating microbial activity and soil organic matter (SOM) biogeochemistry responses to increasing below‐ground C inputs remains unclear. We employed 18O–H2O quantitative stable isotope probing to investigate the effects of synthetic root exudate addition (0, 250, 500, and 1000 μg C g soil-1) on bacterial growth traits and SOM biogeochemistry in rhizosphere soils of trees associated with arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) fungi. Soil respiration increased proportionally to the amount of exudate addition in both AM and ECM soils. However, microbial biomass C (MBC) responses differed, increasing in AM and decreasing in ECM soils. In AM soils, exudate addition increased taxon‐specific and community‐wide relative growth rates of bacteria, leading to enhanced biomass production. Conversely, in ECM soils, relative growth rates were less responsive to exudate addition, and estimates of MBC mortality increased with increasing exudate addition. In the AM soils, aggregated bacterial growth traits were predictive of soil respiration, but this relationship was not observed in ECM soils, perhaps due to substantial MBC mortality. These findings highlight the distinct responses of bacterial communities in AM and ECM rhizosphere soils to exudate addition. Considering that microbial products contribute to the formation of stable soil organic carbon (SOC) pools, future increases in labile exudate release in response to global change may consequently lead to greater SOC gains in AM soils compared to ECM soils. 

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3. A Wireless Sensor Network for High Spatial and Temporal Resolution Soil Gas Emission Monitoring

   https://doi.org/10.3390/s26144605  

   Biradavolu, Yoganand; Winanto, Hendri Yuda; Shahid, Muhammad Osama; Krishnaswamy, Bhuvana; Huang, Jingyi (July 2026, Sensors)

   Wide-scale, spatio-temporal quantification of soil CO2 efflux is essential for understanding terrestrial carbon dynamics, predicting climate change, and evaluating the carbon balance in managed and natural ecosystems. Rising global temperatures, changing land use patterns, and other activities aimed at boosting crop productivity have resulted in an increase in microbial activity, increasing the impact of soil on gas exchange. Therefore, it is important to measure CO2 gas exchange in situ, over wide areas and extended periods without manual intervention. However, current approaches such as remote sensing lacks sufficient spatial and depth resolution, while other direct measurements such as eddy covariance demand expensive infrastructure, limiting wide-scale deployment. In this work, we propose a low-cost, battery-operated CO2 sensing system that provides long-term and scalable monitoring of soil respiration and carbon flux, with the promise for high-resolution measurements. Our innovative design features a PVC-based gas chamber that periodically opens and closes to allow for gas exchange, and a sensor module with low-cost temperature, moisture, pressure, and CO2 sensors, with a low-power wireless LoRa network for real-time monitoring. Our system was rigorously validated through multiple outdoor deployments, over long periods to demonstrate its practicality. We observe that temperature, air pressure, and humidity trends show responsiveness to the environment. We also observe that CO2 emission flux rate vary significantly across different modules, underscoring the need for fine-grained spatial and temporal resolution in monitoring. 

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4. Amplifying feedback loop between drought, soil desiccation cracking, and greenhouse gas emissions

   https://doi.org/10.1088/1748-9326/ad2c23  

   Vahedifard, Farshid; Goodman, C Clay; Paul, Varun; AghaKouchak, Amir (March 2024, Environmental Research Letters)

   The continuous escalation of carbon dioxide (CO2) emissions into the atmosphere is recognized as the primary catalyst for anthropogenic climate change. In 2021, CO2 emerged as the predominant contributor to the warming effect of all human-made greenhouse gases (GHGs), accounting for two-thirds of their global heating impact. While the primary anthropogenic source of increased atmospheric CO2 concentration is the combustion of fossil fuels, the largest terrestrial source of CO2 emissions is soil where 80% of the total terrestrial carbon is stored. Approximately 62% of soil carbon is in organic form and readily released as CO2, while the remaining is made up of inorganic carbon (SIC). Here, we postulate that there is an amplifying feedback loop between drought, soil desiccation cracking, and CO2 emission in a warming climate – a critical aspect that has been overlooked in the existing literature. Further, we argue that the postulated feedback loop affects the emissions of other GHGs, such as methane (CH4) and nitrous oxide (N2O), from soils. The urgent need to recognize and characterize this exacerbating feedback loop is twofold. Firstly, it is widely acknowledged that drought accelerates the oxidation of soil organic carbon (SOC) and, thus, increases CO2 emissions into the atmosphere. Drought-induced soil moisture deficits differentially affect plant processes; while photosynthesis rates may be reduced in plants, leading to decreased carbon uptake, respiration rates can vary. Initially, drought may cause a slight increase in respiration, despite a decline in photosynthesis, leading to increased carbon emissions from the soil. These effects can differ based on ecosystem types, highlighting the complex interplay between drought, photosynthesis, and respiration. Secondly, drought triggers soil desiccation cracking, substantially increasing the permeability of the soil and the interfacial exchange area between the atmosphere and the soil, which, in turn, can considerably increase CO2 efflux in soil by exposing deeper and older stores of soil carbon. Desiccation cracking threatens earthen infrastructure systems and the natural environment. The problems associated with desiccation cracks are becoming more prevalent as anthropogenic climate change exacerbates the severity and frequency of droughts, heatwaves, and drought-heavy precipitation cycles (4). As the warming trends continue, more (and possibly older) CO2 is released from the soil, which can further contribute to global warming. Thus, a chain of events happens in a cascading manner. Failure to consider the hypothesized feedback loop can result in significant inaccuracies when modeling and predicting GHG emissions from soil. It may also lead to underestimating the overall impact of climate change on critical aspects such as soil health, crop production, and the structural integrity of earthen infrastructure. 

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5. Responses of tundra soil microbial communities to half a decade of experimental warming at two critical depths

   https://doi.org/10.1073/pnas.1901307116  

   Johnston, Eric R.; Hatt, Janet K.; He, Zhili; Wu, Liyou; Guo, Xue; Luo, Yiqi; Schuur, Edward A.; Tiedje, James M.; Zhou, Jizhong; Konstantinidis, Konstantinos T. (July 2019, Proceedings of the National Academy of Sciences)

   Northern-latitude tundra soils harbor substantial carbon (C) stocks that are highly susceptible to microbial degradation with rising global temperatures. Understanding the magnitude and direction (e.g., C release or sequestration) of the microbial responses to warming is necessary to accurately model climate change. In this study, Alaskan tundra soils were subjected to experimental in situ warming by ∼1.1 °C above ambient temperature, and the microbial communities were evaluated using metagenomics after 4.5 years, at 2 depths: 15 to 25 cm (active layer at outset of the experiment) and 45 to 55 cm (transition zone at the permafrost/active layer boundary at the outset of the experiment). In contrast to small or insignificant shifts after 1.5 years of warming, 4.5 years of warming resulted in significant changes to the abundances of functional traits and the corresponding taxa relative to control plots (no warming), and microbial shifts differed qualitatively between the two soil depths. At 15 to 25 cm, increased abundances of carbohydrate utilization genes were observed that correlated with (increased) measured ecosystem carbon respiration. At the 45- to 55-cm layer, increased methanogenesis potential was observed, which corresponded with a 3-fold increase in abundance of a single archaeal clade of the Methanosarcinales order, increased annual thaw duration (45.3 vs. 79.3 days), and increased CH 4 emissions. Collectively, these data demonstrate that the microbial responses to warming in tundra soil are rapid and markedly different between the 2 critical soil layers evaluated, and identify potential biomarkers for the corresponding microbial processes that could be important in modeling. 

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