Effects of throughfall exclusion and fertilization on soil CO2 efflux and its components in a loblolly pine (Pinus taeda) plantation
Soil CO2 efflux (RS) is an important component of forest ecosystem carbon budgets and net ecosystem CO2 exchange, but little is known about RS and its components responding to throughfall exclusion and optimal fertilization. The experiment design was a 2 X 2 factorial combination of fertilization (2 levels) and precipitation (throughfall exclusion, 2 levels) replicated in four blocks. We measured RS along with soil temperature (Ts) and soil moisture (WS) at a 10 cm depth from 2012 to 2014 in a loblolly pine plantation in Washington, GA. The autotrophic (RA) and heterotrophic (RH) components of soil CO2 efflux were separated with trenched plots and were taken measurements in 2014. Our objectives were to (1) quantify impacts of throughfall exclusion and fertilization on RS and its components (RA, RH).and (2) determine soil CO2efflux and its components individually response to environmental factors and biological factors in throughfall exclusion and fertilization treatments.
Annual mean RS were 2.11, 1.73, 2.09 and 1.92 for control, fertilization, throughfall exclusion and combination between fertilization and throughfall exclusion, respectively from 2012 to 2013. The apparent Q10 for RS was 2.26, 2.25, 2.12 and 2.35 in four treatments, respectively. There were no significant differences for RS and TS in all treatments except Ws. However, there was slight reduction in RS and RA in fertilization and combination between fertilization and throughfall exclusion treatment. In all treaments, Ts explained more than 80% of variation in RS. There was a weak relationship between RS and WS. RS and RH was better predicted by TS in the dormant season than the growing season, indicating that additional factors such as root growth, photosynthesis became more important contributors to RS during the growing season. Fertilization slight decreased RS mainly from RA. The nonsignificant throughall exclusion effects due to the abnormal precipitation in 2013. We concluded that aboveground carbon assimilation, root growth should be considered in assessing and modeling RS and its components.