The effect of a freeze–thaw cycle on dissolved nitrogen dynamics and its relation to dissolved organic matter and soil microbial biomass in the soil of a northern hardwood forest

• Published in: Biogeochemistry Vol. 142; no. 3; pp. 319 - 338
• Main Authors: Watanabe, Tsunehiro, Tateno, Ryunosuke, Imada, Shogo, Fukuzawa, Karibu, Isobe, Kazuo, Urakawa, Rieko, Oda, Tomoki, Hosokawa, Nanae, Sasai, Takahiro, Inagaki, Yoshiyuki, Hishi, Takuo, Toda, Hiroto, Shibata, Hideaki
• Format: Journal Article
• Language: English
• Published: Cham Springer Science + Business Media 01.02.2019; Springer International Publishing; Springer Nature B.V
• Subjects: Amplification; Availability; Bacterial leaching; Biogeosciences; Biomass; Carbon; Climate change; Climate models; Cycles; Dissolved organic carbon; Dissolved organic matter; Dynamics; Earth and Environmental Science; Earth Sciences; Ecosystems; Environmental Chemistry; Forests; Freeze-thawing; Freezing; Frost; Global warming; Gravimetry; In situ leaching; Insulating materials; Insulation; Leaching; Life Sciences; Mineralization; Moisture content; Nitrification; Nitrogen; Organic matter; Organic soils; ORIGINAL PAPERS; Reduction; Removal; Snowpack; Soil; Soil depth; Soil dynamics; Soil investigations; Soil microorganisms; Soil moisture; Soil surfaces; Soil water; Water content; Winter; Freeze–thaw cycle; Winter climate change; N mineralization; Soil microbe; Biogeochemical cycles; Nitrification
• ISSN: 0168-2563; 1573-515X
• DOI: 10.1007/s10533-019-00537-w

Recent global warming models project a significant change in winter climate over the next few decades. The decrease in snowpack in the winter will decrease the heat insulation function of the snowpack, resulting in increased soil freeze–thaw cycles. Here, we examined the impact of winter freeze–thaw cycles on year-round dissolved nitrogen (N) and carbon (C) dynamics and their relationship with dissolved organic matter and microbial biomass in soil by conducting an in situ experimental reduction in snowpack. We investigated dissolved inorganic N ( N H 4 + and N O 3 − ), dissolved organic N (DON), dissolved organic carbon (DOC), inorganic N leaching, soil microbial biomass, and microbial activities (mineralization and nitrification) in the surface soil of a northern hardwood forest located in Japan. Experimental snowpack reduction significantly increased the number of soil freeze–thaw cycles and soil frost depth. The N H 4 + content of the surface soil was significantly increased by the amplified soil freeze–thaw cycles due to decreased snowpack, while the soil N O 3 − content was unchanged or decreased slightly. The gravimetric soil moisture, DON and DOC contents in soil and soil microbial biomass significantly increased by the snowpack removal in winter. Our results suggest that the amplified freeze–thaw cycles in soil increase the availability of DON and DOC for soil microbes due to an increase in soil freezing. The increases in both DON and DOC in winter contributed to the enhanced growth of soil microbes, resulting in the increased availability of N H 4 + in winter from net mineralization following an increase in soil freeze–thaw cycles. Our study clearly indicated that snow reduction significantly increased the availability of dissolved nitrogen and carbon during winter, caused by increased soil water content due to freeze–thaw cycles in winter.