Thu, Aug 18, 2022: 11:00 AM-11:15 AM
518B
Background/Question/MethodsTrees continuously regulate leaf physiology to maximize carbon gains while simultaneously minimizing unavoidable water loss. The balance between these two processes, or water use efficiency (WUE), is fundamentally important to understanding changes in carbon uptake and transpiration from the leaf to the globe under increasing atmospheric CO2 (iCO2). Yet, additional environmental factors can modify the response of WUE to iCO2 through independent effects on carbon assimilation or stomatal conductance. Here, we couple annually-resolved long-term records of tree ring carbon isotope signatures with contemporary leaf physiological measurements of Quercus rubra and Liriodendron tulipifera in the eastern United States to reconstruct historical leaf physiology. We use a combination of linear mixed-effects models, generalized additive models, and hierarchical partitioning to ask the following questions: 1) Has the iWUE of Quercus rubra and Liriodendron tulipifera in the Central Appalachian Mountains changed since the mid-20th century? 2) If so, are changes in iWUE attributable to changes in Anet or gs? and 3) Which environmental factors are most important in driving trends and interannual variability in tree iWUE?
Results/ConclusionsWe first show 16 – 25% increases in tree intrinsic water use efficiency (iWUE), or the ratio of net photosynthesis (Anet) to stomatal conductance to water (gs), across both species since the mid-20th century. We find iCO2 to be one of the primary drivers of increasing iWUE, but also highlight the individual and interactive effects of nitrogen (NOx) and sulfur (SO2) air pollution overwhelming climate at four study locations spanning nearly 100 km. Reconstructions of seasonally-integrated Anet and gs revealed a ca. 43 – 50% stimulation of Anet was responsible for increasing iWUE in both tree species throughout ca. 79 – 86% of the chronologies with reductions in gs attributable to the remaining 14 – 21%. Our findings place into context the importance of considering local environmental conditions, including air pollution, on leaf physiology, and build upon a growing body of literature documenting stimulated Anet overwhelming reductions in gs as a primary mechanism of increasing iWUE of trees.
Results/ConclusionsWe first show 16 – 25% increases in tree intrinsic water use efficiency (iWUE), or the ratio of net photosynthesis (Anet) to stomatal conductance to water (gs), across both species since the mid-20th century. We find iCO2 to be one of the primary drivers of increasing iWUE, but also highlight the individual and interactive effects of nitrogen (NOx) and sulfur (SO2) air pollution overwhelming climate at four study locations spanning nearly 100 km. Reconstructions of seasonally-integrated Anet and gs revealed a ca. 43 – 50% stimulation of Anet was responsible for increasing iWUE in both tree species throughout ca. 79 – 86% of the chronologies with reductions in gs attributable to the remaining 14 – 21%. Our findings place into context the importance of considering local environmental conditions, including air pollution, on leaf physiology, and build upon a growing body of literature documenting stimulated Anet overwhelming reductions in gs as a primary mechanism of increasing iWUE of trees.