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

Abstract

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 H 2 O h -1 ), transpiration per unit leaf area (E L ; mm day -1 ), stem CO 2 efflux (R stem ; lmol m -2 s -1 ) and soil CO 2 efflux (R soil ; lmol 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 opensystem 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.

Different responses of stem and soil CO2 efflux to pruning in a Chinese fir (Cunninghamia lanceolata) plantation

“…Statistically, our data on sap flow reached the lowest limit. In line with our results, Clinton et al (2011) did not find any change in sap flow of longleaf pine (P. palustris Mill.) after fire-induced leaf area reduction.…”

“…Previous studies have reported that changes in carbohydrate availability, which are caused by increasing atmospheric CO 2 concentration (Edwards et al 2002;Wertin and Teskey 2008), girdling (Maier et al 2010;Maunoury-Danger et al 2010), fire (Clinton et al 2011), and phloem chilling (Johnsen et al 2007), can significantly modify the stem CO 2 efflux within several days. Furthermore, pruning has the potential to influence stem CO 2 efflux by altering canopy transpiration, because CO 2 is transported via transpiration stream from soil or the lower part of the stem to the canopy .…”

Daytime depression in temperature‐normalised stem CO2 efflux in young poplar trees is dominated by low turgor pressure rather than by internal transport of respired CO2

“…It is therefore likely that carbon supply and demand is balanced in young trees of fast growing species such as P. × canadensis , so that stored carbon pools might be minimal to maintain cell growth and maintenance processes under unfavourable scenarios (Sala et al ., ). As a result, coupling between stem respiration and carbon supply is often observed when phloem transport is altered via stem girdling, canopy scorching or inhibition of photosynthesis (Wertin & Teskey, ; Maier et al ., ; Maunoury‐Danger et al ., ; Clinton et al ., ; De Schepper & Steppe, ; Bloemen et al ., ).…”

“…A two‐thirds defoliation was initially tested, but eventually the percentage of leaf area removal was increased due to the slight effect observed on sap flow at two‐thirds defoliation (probably explained by stomatal compensation; e.g. Maier & Clinton, ; Clinton et al ., ). The DEF 2 treatment consisted of 100% leaf area removal.…”

Partitioning Longleaf Pine Soil Respiration into Its Heterotrophic and Autotrophic Components through Root Exclusion

“…Likewise, Vogel and Valentine [8] suggest that measurements of R s from small root exclusion tubes within three weeks of installation may mitigate effects of root exclusion on soil moisture. However, three weeks of post-treatment incubation was insufficient to detect R h in longleaf pine, perhaps because of greater carbohydrate stores in longleaf pine roots relative to other species [24,25]. We suggest that the longer incubation did not profoundly change soil moisture dynamics or our overall estimate of R h to R s , because soils in this study were sandy with excessive drainage and the presence of the root exclusion tubes increased soil moisture on the final measurement date by only about 1%.…”