Reponses of CO2, CH4, and N2O fluxes from soils to temperature, soil nitrogen, and aboveground photosynthesis in a temperate forest
Soil respiration (CO2 fluxes from soils) plays a major role in global carbon cycling. It is well accepted that soil respiration responds positively to soil temperature, but the constraint of other confounding factors, such as moisture, on the soil respiration-temperature response is still not clear. In addition, the responses of other greenhouse gas emissions, including methane (CH4) and nitrous oxide (N2O), to temperature and the relationship between CH4, N2O, and CO2 fluxes is of increasing interest. These gas flux responses to temperature are further connected with nitrogen availability and aboveground photosynthesis. Our research goal is to understand how CO2, CH4, and N2O fluxes from soils respond to temperature, soil nitrogen, and aboveground photosynthesis, and how these fluxes are related to each other.
We take advantage of an existing long-term multifactorial warming and nitrogen addition experiment at Harvard Forest, a temperate forest in Massachusetts. The treatments include warming, low nitrogen addition, high nitrogen addition, the control, and the combination. We measured CO2, CH4, and N2O fluxes with a recently assembled mobile in-situ gas flux measurement system.
We found when moisture was not limited, CO2, CH4, and N2O fluxes responded positively to temperature. N2O fluxes increased with nitrogen addition, but the response of CO2 and CH4 to nitrogen is not significantly. The response of N2O fluxes to nitrogen addition peaked within 5 days after nitrogen was added, and the response faded gradually. Seasonal variation in photosynthesis regulates these gas fluxes in combination with seasonality in climate.