Analyzing CO 2 Exchange Between the Soil / Atmosphere Interface in Arid Soils at the Wrigley Institute for Environmental Studies ( WIES )

CO2 exchange between soil and the atmosphere plays a dramatic and continually evolving role in the Earth’s carbon cycle. Areas of land can become a net source of CO2 or a net sink of CO2 depending on a variety of factors such as soil moisture, soil chemistry, vegetation levels, organic matter concentration, and prevailing climatic conditions. Utilizing a vented flux chamber, we collected soil CO2 flux data from the campus of the Wrigley Institute for Environmental Studies (WIES) under varying conditions. Our findings displayed that the soil of the WIES campus acts as a net source of CO2 due to high levels of soil respiration and low levels of photosynthesis, which persist during drought conditions. In addition, we found that adding water to soils under drought conditions enhances CO2 output considerably on the time scales of hours due to increased soil respiration. 1.0 Introduction Given that greenhouse gas induced climate change is becoming more evident, quantifying the rates of exchange of CO2 between soils and the atmosphere can serve to resolve our understanding of CO2 budgets and projections based on them. On human time scales, the terrestrial biosphere acts as a net sink for carbon. Plant life fixes CO2 during photosynthesis and stores it as organic carbon. Soil respiration is the major driver that returns fixed CO2 back to the atmosphere [1]. CO2 is returned to the atmosphere through three main respiration components: root respiration, surface-litter respiration, and the respiration of soil organic matter (including root detritus). Globally, soil respiration flux is estimated to add a total 50-75 Pg C/yr to the atmosphere [2]. In comparison, anthropogenic fossil fuel emissions only add about 5 Pg C/yr [2]. Therefore even a minor shift in soil respiration can match the scale of global anthropogenic emissions from burning fossil fuels [2]. A greater understanding of how CO2 is traded across the atmosphere/soil interface is necessary in understanding the local and global patterns of CO2 movement [3]. Both present and future land management practices affect atmospheric CO2 exchange. For example, Schlesinger and Andres [4] demonstrated that soil tillage and increased temperatures will enhance soil microbe respiration and release more CO2 into the atmosphere. In addition, Nakano et al. [5] and Wania et al. [6] have shown that another greenhouse gas, CH4, can be released from arctic permafrost in a positive feedback loop when temperatures increase in conjunction with increased CO2 release due to higher soil microbe respiration. Understanding the factors that drive CO2 exchange between the soil and the atmosphere can be helpful in timing land management practices to mitigate the release of CO2 from soil or even stimulate CO2 sequestration. By analyzing diurnal cycles of soil CO2 fluxes, experimentation, presented below, displayed the variability of CO2 uptake and release of various vegetation and soil types over the course of a day. These experiments consistently display that soils released more CO2 at night and during the early morning hours, but released much less or even absorbed CO2 during the midday, afternoon, and early evening. The application of water to arid soils greatly increased the release of CO2 on a timescale of hours; therefore, it is reasonable to conclude that human additions of water to arid soils will lead