Transient changes in transpiration, and stem and soil CO2 efflux in longleaf pine (Pinus palustris Mill.) following fire-induced leaf area reduction

In 20-year-old longleaf pine, we examined short-term effects of reduced live leaf area (A(L)) via canopy scorching on sap flow (Q; kg H2O h(-1)), transpiration per unit leaf area (E-L; mm day(-1)), stem CO2 efflux (R-stem; mu mol m(-2) s(-1)) and soil CO2 efflux (R-soil; mu mol m(-2) s(-1)) over a 2-week period during early summer. R-stem and Q were measured at two positions (1.3-m or BH, and base of live crown-BLC), and R-soil was measured using 15 open-system chambers on each plot. E-L before and after treatment was estimated using Q measured at BLC with estimates of AL before and after scorching. We expected Q to decrease in scorched trees compared with controls resulting from reduced A(L). We expected R-stem at BLC and BH and R-soil to decrease following scorching due to reduced leaf area, which would decrease carbon supply to the stem and roots. Scorching reduced A(L) by 77%. Prior to scorching, Q at BH was similar between scorch and control trees. Following scorching, Q was not different between control and scorch trees; however, E-L increased immediately following scorching by 3.5-fold compared to control trees. Changes in E-L in scorched trees corresponded well with changes in VPD (D), whereas control trees appeared more decoupled over the 5-day period following treatment. By the end of the study, R-stem decreased to 15-25% in scorched trees at both stem positions compared to control trees. Last, we found that scorching resulted in a delayed and temporary increase in R-soil rather than a decrease. No change in Q and increased E-L following scorching indicates a substantial adjustment in stomatal conductance in scorched trees. Divergence in R-stem between scorch and control trees suggests a gradual decline in stem carbohydrates following scorching. The absence of a strong R-soil response is likely due to non-limiting supplies of root starch during early summer.