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Long‐term soil warming can decrease soil organic matter (SOM), resulting in self‐reinforcing feedback to the global climate system. We investigated additional consequences of SOM reduction for soil water holding capacity (WHC) and soil thermal and hydrological buffering. At a long‐term soil warming experiment in a temperate forest in the northeastern United States, we suspended the warming treatment for 104 days during the summer of 2017. The formerly heated plot remained warmer (+0.39 °C) and drier (−0.024 cm3 H2O cm−3 soil) than the control plot throughout the suspension. We measured decreased SOM content (−0.184 g SOM g−1 for O horizon soil, −0.010 g SOM g−1 for A horizon soil) and WHC (−0.82 g H2O g−1 for O horizon soil, −0.18 g H2O g−1 for A horizon soil) in the formerly heated plot relative to the control plot. Reduced SOM content accounted for 62% of the WHC reduction in the O horizon and 22% in the A horizon. We investigated differences in SOM composition as a possible explanation for the remaining reductions with Fourier transform infrared (FTIR) spectra. We found FTIR spectra that correlated more strongly with WHC than SOM, but those particular spectra did not differ between the heated and control plots, suggesting that SOM composition affects WHC but does not explain treatment differences in this study. We conclude that SOM reductions due to soil warming can reduce WHC and hydrological and thermal buffering, further warming soil and decreasing SOM. This feedback may operate in parallel, and perhaps synergistically, with carbon cycle feedbacks to climate change. Plain Language Summary: Soil warming in temperate deciduous forests of the northeastern United States may result in a series of consequences that ultimately reinforce climate change. Reduced soil carbon storage is one well‐studied consequence; changes in soil water holding capacity are less well studied. At a long‐term soil warming experiment in Harvard Forest, we suspended the warming treatment for 104 days to investigate how long‐term warming might have altered water holding capacity. We measured both reduced soil organic matter and reduced water holding capacity, as well as a statistically significant link between the two. We also observed the formerly heated plot remaining warmer and drier than the control plot throughout the suspension, despite having received no artificial warming for several months. This could have important implications for a warming world. Soil water storage plays a crucial role in holding water in an ecosystem between rain events, making water continuously available for both the ecological and for human use. Reduced soil water storage capacity could make both ecosystems and human infrastructure more sensitive to the weather variability, which is expected to increase with climate change. This could result in reduced forest growth and carbon storage, further reinforcing climate change. Key Points: Soil warming decreased soil organic matter and water holding capacity in a temperate deciduous forest in the northeastern United StatesDecreased soil organic matter content accounted for part but not all of the decrease in water holding capacityLower water holding capacity decreased thermal and hydrological buffering, leading to warmer and drier soil conditions [ABSTRACT FROM AUTHOR]

[i] Studies indicate that, historically, terrestrial ecosystems of the northern high-latitude region may have been responsible for up to 60% of the global net land-based sink for atmospheric CO2. However, these regions have recently experienced remarkable modification of the major driving forces of the carbon cycle, including surface air temperature warming that is significantly greater than the global average and associated increases in the frequency and severity of disturbances. Whether Arctic tundra and boreal forest ecosystems will continue to sequester atmospheric CO2 in the face of these dramatic changes is unknown. Here we show the results of model simulations that estimate a 41 Tg C yf' sink in the boreal land regions from 1997 to 2006, which represents a 73% reduction in the strength of the sink estimated for previous decades in the late 20th century. Our results suggest that CO2 uptake by the region in previous decades may not be as strong as previously estimated. The recent decline in sink strength is the combined result of (1) weakening sinks due to warming-induced increases in soil organic matter decomposition and (2) strengthening sources from pyrogenic CO2 emissions as a result of the substantial area of boreal forest burned in wildfires across the region in recent years. Such changes create positive feedbacks to the climate system that accelerate global warming, putting further pressure on emission reductions to achieve atmospheric stabilization targets. [ABSTRACT FROM AUTHOR]

The article presents a study that examines the net emissions of methane (CH4) in Alaska's ecosystem and atmosphere, and its contributions to carbon balance and greenhouse gas budget for the region. Under the investigation, (CH4) fluxes the 20th century to the 21st century were analyzed using the Terrestrial Ecosystem Model (TEM), a biogeochemistry model. A concept of global warming potentials was then used to convert net (CH4) emissions into carbon dioxide (CO2) equivalent units in terms of global warming effects. Results suggest that net methane emissions in the region will double by the end of the 21st century due to high-latitude warming and climate change, and that Alaska will be a net source of greenhouse gases to the atmosphere.

In terrestrial high-latitude regions, observations indicate recent changes in snow cover, permafrost, and soil freeze–thaw transitions due to climate change. These modifications may result in temporal shifts in the growing season and the associated rates of terrestrial productivity. Changes in productivity will influence the ability of these ecosystems to sequester atmospheric CO2. We use the terrestrial ecosystem model (TEM), which simulates the soil thermal regime, in addition to terrestrial carbon (C), nitrogen and water dynamics, to explore these issues over the years 1960–2100 in extratropical regions (30–90°N). Our model simulations show decreases in snow cover and permafrost stability from 1960 to 2100. Decreases in snow cover agree well with National Oceanic and Atmospheric Administration satellite observations collected between the years 1972 and 2000, with Pearson rank correlation coefficients between 0.58 and 0.65. Model analyses also indicate a trend towards an earlier thaw date of frozen soils and the onset of the growing season in the spring by approximately 2–4 days from 1988 to 2000. Between 1988 and 2000, satellite records yield a slightly stronger trend in thaw and the onset of the growing season, averaging between 5 and 8 days earlier. In both, the TEM simulations and satellite records, trends in day of freeze in the autumn are weaker, such that overall increases in growing season length are due primarily to earlier thaw. Although regions with the longest snow cover duration displayed the greatest increase in growing season length, these regions maintained smaller increases in productivity and heterotrophic respiration than those regions with shorter duration of snow cover and less of an increase in growing season length. Concurrent with increases in growing season length, we found a reduction in soil C and increases in vegetation C, with greatest losses of soil C occurring in those areas with more vegetation, but simulations also suggest that this trend could reverse in the future. Our results reveal noteworthy changes in snow, permafrost, growing season length, productivity, and net C uptake, indicating that prediction of terrestrial C dynamics from one decade to the next will require that large-scale models adequately take into account the corresponding changes in soil thermal regimes. [ABSTRACT FROM AUTHOR]

Focuses on a study which investigated the effects of increased atmospheric carbon dioxide concentration and temperatures on ericoid mycorrhizal colonization, functioning and below-ground carbon allocation in a subarctic forest. Correlation between ergosterol content of hair roots and ecosystem photosynthesis; Effects of global change factors on ergosterol content of hair roots; Relationship between ecosystem photosynthesis and ericoid mycorrhizal colonization.