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1. Permafrost Carbon: Progress on Understanding Stocks and Fluxes Across Northern Terrestrial Ecosystems

   https://doi.org/10.1029/2023JG007638  

   Treat, Claire C; Virkkala, Anna‐Maria; Burke, Eleanor; Bruhwiler, Lori; Chatterjee, Abhishek; Fisher, Joshua B; Hashemi, Josh; Parmentier, Frans‐Jan W; Rogers, Brendan M; Westermann, Sebastian; et al (March 2024, Journal of Geophysical Research: Biogeosciences)

   Abstract Significant progress in permafrost carbon science made over the past decades include the identification of vast permafrost carbon stocks, the development of new pan‐Arctic permafrost maps, an increase in terrestrial measurement sites for CO₂and methane fluxes, and important factors affecting carbon cycling, including vegetation changes, periods of soil freezing and thawing, wildfire, and other disturbance events. Process‐based modeling studies now include key elements of permafrost carbon cycling and advances in statistical modeling and inverse modeling enhance understanding of permafrost region C budgets. By combining existing data syntheses and model outputs, the permafrost region is likely a wetland methane source and small terrestrial ecosystem CO₂sink with lower net CO₂uptake toward higher latitudes, excluding wildfire emissions. For 2002–2014, the strongest CO₂sink was located in western Canada (median: −52 g C m⁻² y⁻¹) and smallest sinks in Alaska, Canadian tundra, and Siberian tundra (medians: −5 to −9 g C m⁻² y⁻¹). Eurasian regions had the largest median wetland methane fluxes (16–18 g CH₄m⁻² y⁻¹). Quantifying the regional scale carbon balance remains challenging because of high spatial and temporal variability and relatively low density of observations. More accurate permafrost region carbon fluxes require: (a) the development of better maps characterizing wetlands and dynamics of vegetation and disturbances, including abrupt permafrost thaw; (b) the establishment of new year‐round CO₂and methane flux sites in underrepresented areas; and (c) improved models that better represent important permafrost carbon cycle dynamics, including non‐growing season emissions and disturbance effects. 

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2. Surface‐Atmosphere Carbon Dioxide Exchange and Ecosystem Water Use Efficiency in a Multi‐Functional Perennial Polyculture Agroecosystem

   https://doi.org/10.1002/sae2.70182  

   Shrestha, Ojaswee; De_La_Roca, Gabriela; Ramsey, Philip W; Hoffman, Sophie; Stoy, Paul C (June 2026, Journal of Sustainable Agriculture and Environment)

   ABSTRACT Perennial polycultures, with a combination of perenniality and vegetation diversity, have carbon mitigation potential and water conservation benefits, via increased plant carbon uptake and improved ecosystem water use efficiency (EWUE). Few studies have assessed the coupled carbon and water balance in perennial polyculture agroecosystems that are not yet a widespread agricultural practice. We measured net ecosystem carbon dioxide (CO₂) exchange (NEE) and evapotranspiration (ET) using eddy covariance, partitioned measurements into gross primary productivity (GPP), ecosystem respiration (R_ECO), evaporation (E) and transpiration (T), to assess annual carbon sinks and EWUE in a fruit orchard with diverse forbs and grass understory cover in Southern California's Mediterranean climate. Seasonal trends showed peak CO₂uptake and EWUE from late spring through summer. The agroecosystem functioned as a modest yet statistically significant net carbon sink compared to a hypothesised net zero carbon balance (no carbon storage), sequestering 58 g C m⁻² year⁻¹(Z(standardised variability) = −2.41,p = 0.016) in 2022 (January–December) and 174 g C m⁻² year⁻¹(Z = −7.31,p < 0.001) in 2023 (January–October). Smaller net CO₂losses from January to March when trees were dormant underscored the critical role of understory vegetation during winter and early spring in maintaining the net annual carbon sink. Cumulative ET was 664 mm (2022) and 617 mm (January–October 2023) with T dominating E, particularly from April to July during peak tree activity. Monthly EWUE ranged from 1.4 to 4.7 g C m⁻² mm⁻¹H₂O. EWUE stayed above half of the maximum observed value throughout the tree dormant season, beyond October until apricot leaf‐out in April, due to photosynthetically active understory cover. Staggered complementary phenologies between trees and understory cover vegetation can extend the carbon uptake period, making perennial polyculture agroecosystems a net CO₂sink with high water‐use efficiency. 

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3. Lateral Dissolved Organic Carbon Losses Represent ∼10% of Upland Tundra Carbon Losses and Include Seasonal Permafrost Contributions

   https://doi.org/10.1029/2025JG009067  

   Kelley, A K; Axler, Z; Ledman, J; De_La_Torre, M; Ebert, C H; Springer, A E; Kaufman, D S; Schuur, E_A G (November 2025, Journal of Geophysical Research: Biogeosciences)

   Abstract We investigated lateral dissolved organic carbon (DOC) fluxes from lower‐order streams in upland tundra underlain by permafrost to assess their contribution to carbon (C) sink or source strength. The study site, located in Healy, Alaska, is within the Panguingue Creek watershed (66 km²), where permafrost acts as a confining layer for soil pore water. We examined how seasonal hydrology affects DOC export to understand lateral C flux contributions to the site's net ecosystem C balance. Previous estimates of vertical gas exchange (net CO₂uptake and release) indicated a loss of 52.5 g C m⁻² yr⁻¹and methane was estimated to lead to an additional loss of 6.4 ± 0.20 CO₂‐equivalent (g CO₂–C m⁻² yr⁻¹) suggesting the site is a net C source. We found that a second‐order stream exported an additional 5.0 g DOC m⁻² yr⁻¹laterally, which is approximately 10% of the vertical CO₂loss, reinforcing the site's source status. Accounting for CO₂, CH₄, and DOC, total C losses were estimated to be 64 g C m⁻² yr⁻¹. Further, we found that shoulder seasons played a key role in C export, with the spring freshet alone accounting for 59% of total DOC flux. Seasonality also influenced DOC age, with older, permafrost‐derived DOC exported primarily during spring and fall. These findings underscore the significance of lateral pathways in permafrost C budgets and highlight DOC as a critical, seasonally variable component of C loss. 

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4. Resolving the Carbon‐Climate Feedback Potential of Wetland CO ₂ and CH ₄ Fluxes in Alaska

   https://doi.org/10.1029/2022GB007524  

   Ma, Shuang; Bloom, A Anthony; Watts, Jennifer D; Quetin, Gregory R; Donatella, Zona; Euskirchen, Eugénie S; Norton, Alexander J; Yin, Yi; Levine, Paul A; Braghiere, Renato K; et al (September 2023, Global Biogeochemical Cycles)

   Abstract Boreal‐Arctic regions are key stores of organic carbon (C) and play a major role in the greenhouse gas balance of high‐latitude ecosystems. The carbon‐climate (C‐climate) feedback potential of northern high‐latitude ecosystems remains poorly understood due to uncertainty in temperature and precipitation controls on carbon dioxide (CO₂) uptake and the decomposition of soil C into CO₂and methane (CH₄) fluxes. While CH₄fluxes account for a smaller component of the C balance, the climatic impact of CH₄outweighs CO₂(28–34 times larger global warming potential on a 100‐year scale), highlighting the need to jointly resolve the climatic sensitivities of both CO₂and CH₄. Here, we jointly constrain a terrestrial biosphere model with in situ CO₂and CH₄flux observations at seven eddy covariance sites using a data‐model integration approach to resolve the integrated environmental controls on land‐atmosphere CO₂and CH₄exchanges in Alaska. Based on the combined CO₂and CH₄flux responses to climate variables, we find that 1970‐present climate trends will induce positive C‐climate feedback at all tundra sites, and negative C‐climate feedback at the boreal and shrub fen sites. The positive C‐climate feedback at the tundra sites is predominantly driven by increased CH₄emissions while the negative C‐climate feedback at the boreal site is predominantly driven by increased CO₂uptake (80% from decreased heterotrophic respiration, and 20% from increased photosynthesis). Our study demonstrates the need for joint observational constraints on CO₂and CH₄biogeochemical processes—and their associated climatic sensitivities—for resolving the sign and magnitude of high‐latitude ecosystem C‐climate feedback in the coming decades. 

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5. Hydrologic connectivity with peatland soils drives very high carbon fluxes in a tropical, mountain stream

   https://doi.org/10.1007/s10533-026-01327-x  

   Whitmore, Keridwen M; DelVecchia, Amanda G; Jaramillo, Ricardo; Chimbolema, Segundo; Suárez, Esteban; Riveros-Iregui, Diego A (June 2026, Biogeochemistry)

   Abstract Inland waters receive large quantities of carbon from the surrounding landscape and are active sites of carbon transport, transformation, and emission. Global carbon emission estimates are limited by sparse and unevenly distributed carbon flux observations, particularly in the tropics. We evaluated hydrological and metabolic controls on carbon export variability from a large peatland in a tropical ecosystem typical of the Northern Andes mountains. We recorded dissolved CO₂(pCO₂), dissolved oxygen (DO), and discharge at 15-min intervals 5 m downstream of a peatland outlet (Station 1) and at 3 additional locations downstream (Stations 2, 3 and 4) from July 2019 until Jan 2020 and from June 2021 until March 2023. Continuous measurements of DO and discharge were also measured 2 km away in a stream draining an adjoining catchment (Station 5). Discrete measurements of dissolved organic carbon (DOC) and dissolved methane (pCH₄) were collected in June-July of 2021 and 2022. Stream discharge was a primary control onpCO₂and DOC in the stream network at both seasonal and event scales. DOC concentration increased with discharge and whilepCO₂decreased during higher flows, CO₂loading increased. Pronounced seasonal changes were observed with lowestpCO₂recorded at the peatland outlet in wet months (June–August: 5845 ± 2325 ppm, mean ± standard deviation), and the highest in dry months (Nov-Feb, 16,677 ± 3685 ppm). Anoxic or hypoxic conditions persisted for over half of our study and measurements ofpCH₄at the peatland outlet were very high (982 ± 797 ppm), underscoring the importance of anaerobic activity in this system. Aerobic processes also influencedpCO₂dynamics. Aquatic metabolism at Station 5 (29 July–19 Oct 2021) was net heterotrophic, with ER exceeding GPP and netpCO₂production (mean ER: − 6.5 g O₂m⁻²d⁻¹, GPP: 0.44 g O m⁻²d⁻¹). Our study highlights the role of hydrologic connectivity and diverse biogeochemical processes in shaping carbon export and cycling in páramo streams, which results inpCO₂andpCH₄levels among the highest reported in streams and rivers worldwide. 

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