Effects of throughfall reduction and fertilization on soil CO2 efflux and total below-ground carbon flux in a loblolly pine (Pinus taeda) plantation

Background/Question/Methods

Total below-ground carbon flux (TBCF) is the sum of metabolic fluxes to support root production, respiration, root exudates, herbivory, and symbionts. Together, TBCF and litterfall can be used to estimate soil CO₂ efflux (E_S) in forest ecosystems. However, little is known about how TBCF and its components respond to decreasing soil moisture and changes in soil fertility. This response was examined from 2012 to 2014 in a loblolly pine plantation in Washington, GA, as part of the PINEMAP Project. The experiment was a 2 × 2 factorial combination of fertilization (2 levels, control and one-time fertilizer application) and precipitation throughfall reduction (2 levels, control and 30% reduction) replicated in four blocks. We measured E_S and litterfall along with soil temperature and soil moisture. We also measured fine root and coarse root production in 2014. Our objectives were to (1) quantify impacts of throughfall reduction and fertilization on E_S, and (2) determine TBCF response to these treatments.

Results/Conclusions

Fertilization decreased E_S by 22%. There were no significant effects of throughfall reduction on E_S. These results indicated that aboveground carbon processes and root growth should be considered in assessing and modeling E_S and its components. Fertilization slightly decreased TBCF but increased annual litterfall and coarse root production. Throughfall reduction increased TBCF mainly by increasing fine root production. We conclude that nutrient supply and water availability had differing effects on Es and TBCF, and that TBCF was more sensitive than Es to fertilization and throughfall exclusion treatments.