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; μmol m⁻² s⁻¹) and soil CO₂ efflux (R _soil; μmol 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 A _L 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.