Abstract:

Aims Winter soil respiration is reported to be a significant component of the annual carbon budgets. In order to understand how projected global warming affects winter soil respiration and soil microbial properties, we conducted a warming experiment in a young Pinus armandii plantation during the winter period to assess short-term response of winter soil CO₂ efflux and microbial properties to artificial warming. Methods We used an infrared heater and monitored soil temperature and relative air humidity in November 2009 and analyzed soil respiration, microbial biomass and inorganic nitrogen pools throughout the winter. Important findings The average daily air and soil temperatures were 2.1 and 6.7 ℃ higher in the warmed plots than in the control plots, respectively. Warming declined relative air humidity and soil water content by 15.2% and 7.2%, respectively. Across all measuring dates, simulated warming increased average soil CO₂ efflux by 31.4%. Warming significantly enhanced the soil microbial biomass carbon (SMB-C) and nitrogen (SMB-N) by 23.2% and 22.7%, respectively, but did not affect the ratio of SMB-C to SMB-N, which indicated that elevated temperature tended to accelerate the growth of SMB, but did not change the community structure of SMB. Likewise, warming tended to increase soil inorganic nitrogen pools. Nitrate (NO₃ ^--N) and ammonium (NH₄ ⁺-N) in the warmed soil increased 38.5% and 12.3%, respectively, compared with control soil. Results indicate that winter soil respiration, microbial activities and nutrient mineralization in the coniferous forest soils could be sensitive to future global warming.

Key words: experimental warming, inorganic nitrogen, Pinus armandii, soil microbial biomass, winter soil respiration