Decreased Soil Organic Matter in a Long‐Term Soil Warming Experiment Lowers Soil Water Holding Capacity and Affects Soil Thermal and Hydrological Buffering

• Published in: Journal of geophysical research. Biogeosciences Vol. 125; no. 4
• Main Authors: Werner, W. J., Sanderman, J., Melillo, J. M.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-04-2020; American Geophysical Union (AGU)
• Subjects: Buffers; Carbon capture and storage; Carbon cycle; Carbon sequestration; Climate change; Climate system; Composition; Control; Deciduous forests; Experiments; Feedback; Forest growth; Fourier transforms; Global climate; Horizon; Hydrology; Infrared spectra; Infrared spectroscopy; Moisture content; Organic matter; Organic soils; Reduction; Soil; Soil horizons; Soil investigations; Soil organic matter; Soil water; Soil water storage; Soils; Spectra; Statistical analysis; Storage capacity; Storage conditions; Temperate forests; Water; Water storage; Weather; United States > US
• ISSN: 2169-8953; 2169-8961
• DOI: 10.1029/2019JG005158

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 States
Decreased soil organic matter content accounted for part but not all of the decrease in water holding capacity
Lower water holding capacity decreased thermal and hydrological buffering, leading to warmer and drier soil conditions