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1. Minerals limit the deep soil respiration response to warming in a tropical Andisol

   https://doi.org/10.1007/s10533-022-00965-1  

   McGrath, Casey R.; Hicks Pries, Caitlin E.; Nguyen, Nhu; Glazer, Brian; Lio, Stanley; Crow, Susan E. (November 2022, Biogeochemistry)

   Abstract Tropical regions hold one third of the world’s soil organic carbon, but few experiments have warmed tropical soils in situ. The vulnerability of these soils to climate change-induced losses is uncertain with many hypothesizing these soils would be less sensitive to climate change because already-high temperatures in tropical systems might limit microbial sensitivity or due to increased mineral protection of organic carbon in highly weathered tropical soils. Here we present the results of a deep soil (0–100 cm) warming experiment in a tropical Andisol. Andisols can store large, persistent pools of soil carbon that are protected from decomposition by poorly and non-crystalline minerals (PNCM). In 20 cm depth intervals, we measured key soil properties including carbon, nitrogen, pH, PNCM, bacterial and fungal richness along with temperature, moisture, and CO 2 production. Over a year of soil warming, CO 2 production significantly increased by 50–300% per degree of warming, but only in the top 40 cm of the soil profile in contrast to the results of other deep soil warming experiments. Multimodal analysis supported our hypothesis that high concentrations of PNCM was the primary driver of the lack of CO 2 response, followed by high relative soil moisture and low bacterial richness, which may be a proxy for organic carbon availability. The lack of elevated CO 2 production in response to warming suggests a limited positive feedback to climate change in Andisols driven by their strong mineral protection of organic matter. Therefore, Andisols should be considered high priority restoration or protection areas when considering the management of soil carbon stocks as part of climate action. 

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2. Drought re-routes soil microbial carbon metabolism towards emission of volatile metabolites in an artificial tropical rainforest

   https://doi.org/10.1038/s41564-023-01432-9  

   Honeker, Linnea K.; Pugliese, Giovanni; Ingrisch, Johannes; Fudyma, Jane; Gil-Loaiza, Juliana; Carpenter, Elizabeth; Singer, Esther; Hildebrand, Gina; Shi, Lingling; Hoyt, David W.; et al (August 2023, Nature Microbiology)

   Abstract Drought impacts on microbial activity can alter soil carbon fate and lead to the loss of stored carbon to the atmosphere as CO₂and volatile organic compounds (VOCs). Here we examined drought impacts on carbon allocation by soil microbes in the Biosphere 2 artificial tropical rainforest by tracking¹³C from position-specific¹³C-pyruvate into CO₂and VOCs in parallel with multi-omics. During drought, efflux of¹³C-enriched acetate, acetone and C₄H₆O₂(diacetyl) increased. These changes represent increased production and buildup of intermediate metabolites driven by decreased carbon cycling efficiency. Simultaneously,¹³C-CO₂efflux decreased, driven by a decrease in microbial activity. However, the microbial carbon allocation to energy gain relative to biosynthesis was unchanged, signifying maintained energy demand for biosynthesis of VOCs and other drought-stress-induced pathways. Overall, while carbon loss to the atmosphere via CO₂decreased during drought, carbon loss via efflux of VOCs increased, indicating microbially induced shifts in soil carbon fate. 

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3. Emerging climate impact on carbon sinks in a consolidated carbon budget

   https://doi.org/10.1038/s41586-025-09802-5  

   Friedlingstein, Pierre; Le_Quéré, Corinne; O’Sullivan, Michael; Hauck, Judith; Landschützer, Peter; Luijkx, Ingrid T; Li, Hongmei; van_der_Woude, Auke; Schwingshackl, Clemens; Pongratz, Julia; et al (January 2026, Nature)

   Abstract Despite the adoption of the Paris Agreement 10 years ago, carbon dioxide (CO₂) emissions from burning fossil fuels continue to increase, pushing atmospheric CO₂levels to 423 ppm in 2024 and driving human-induced warming to 1.36 °C, within years of breaching the 1.5 °C limit^1,2. Accurate reporting of anthropogenic and natural CO₂sources and sinks is a prerequisite to tracking the effectiveness of climate policy and detecting carbon-sink responses to climate change. Yet notable mismatches between reported emissions and sinks have so far prevented confident interpretation of their trends and drivers¹. Here we present and integrate recent advances in observations and process understanding to address some long-standing issues in global carbon budget estimates. We show that the magnitude of the natural land sink is substantially smaller than previously estimated, whereas net emissions from anthropogenic land-use change are revised upwards¹. The ocean sink is 15% larger than the land sink, consistent with recent evidence from oceanic and atmospheric observations^3,4. Climate change reduces the efficiency of the sinks, particularly on land, contributing 8.3 ± 1.4 ppm to the atmospheric CO₂increase since 1960. The combined effects of climate change and deforestation have turned Southeast Asian and large parts of South American tropical forests from CO₂sinks to sources. This underscores the need to halt deforestation and limit warming to prevent further loss of carbon stored on land. Improved confidence in assessments of CO₂sources and sinks is fundamental for effective climate policy. 

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4. Experimental warming accelerates positive soil priming in a temperate grassland ecosystem

   https://doi.org/10.1038/s41467-024-45277-0  

   Tao, Xuanyu; Yang, Zhifeng; Feng, Jiajie; Jian, Siyang; Yang, Yunfeng; Bates, Colin T; Wang, Gangsheng; Guo, Xue; Ning, Daliang; Kempher, Megan L; et al (December 2024, Nature Communications)

   Abstract Unravelling biosphere feedback mechanisms is crucial for predicting the impacts of global warming. Soil priming, an effect of fresh plant-derived carbon (C) on native soil organic carbon (SOC) decomposition, is a key feedback mechanism that could release large amounts of soil C into the atmosphere. However, the impacts of climate warming on soil priming remain elusive. Here, we show that experimental warming accelerates soil priming by 12.7% in a temperate grassland. Warming alters bacterial communities, with 38% of unique active phylotypes detected under warming. The functional genes essential for soil C decomposition are also stimulated, which could be linked to priming effects. We incorporate lab-derived information into an ecosystem model showing that model parameter uncertainty can be reduced by 32–37%. Model simulations from 2010 to 2016 indicate an increase in soil C decomposition under warming, with a 9.1% rise in priming-induced CO₂emissions. If our findings can be generalized to other ecosystems over an extended period of time, soil priming could play an important role in terrestrial C cycle feedbacks and climate change. 

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5. 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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