Defining an Adequate Sample of Earlywood Vessels for Retrospective Injury Detection in Diffuse-Porous Species

Vessels of broad-leaved trees have been analyzed to study how trees deal with various environmental factors. Cambial injury, in particular, has been reported to induce the formation of narrower conduits. Yet, little or no effort has been devoted to the elaboration of vessel sampling strategies for retrospective injury detection based on vessel lumen size reduction. To fill this methodological gap, four wounded individuals each of grey alder (Alnus incana (L.) Moench) and downy birch (Betula pubescens Ehrh.) were harvested in an avalanche path. Earlywood vessel lumina were measured and compared for each tree between the injury ring built during the growing season following wounding and the control ring laid down the previous year. Measurements were performed along a 10 mm wide radial strip, located directly next to the injury. Specifically, this study aimed at (i) investigating the intra-annual duration and local extension of vessel narrowing close to the wound margin and (ii) identifying an adequate sample of earlywood vessels (number and intra-ring location of cells) attesting to cambial injury. Based on the results of this study, we recommend analyzing at least 30 vessels in each ring. Within the 10 mm wide segment of the injury ring, wound-induced reduction in vessel lumen size did not fade with increasing radial and tangential distances, but we nevertheless advise favoring early earlywood vessels located closest to the injury. These findings, derived from two species widespread across subarctic, mountainous, and temperate regions, will assist retrospective injury detection in Alnus, Betula, and other diffuse-porous species as well as future related research on hydraulic implications after wounding

In search of an ice core signal to differentiate between source-driven and sink-driven changes in atmospheric methane

The concentration of atmospheric methane increased from around 360 ppbv at the last glacial maximum (∼20 ka before present) to about 700 ppbv in the pre-industrial era (∼200 years before present). The sources and/or sinks of methane must therefore have changed during this period; however, the relative sizes of the source- and sink-driven changes in methane concentration remain uncertain. We take the first “bottom-up” approach to identifying any chemical signals preserved in the ice record that could help us to determine these. Using an atmospheric chemistry-transport model, we explore the effects of source- and sink-driven changes in methane on a wide range of chemical species in the Antarctic boundary layer. Though we identify several potentially useful atmospheric signals, a simple and robust constraint on the sizes of the source- and sink-driven changes cannot be readily identified, owing to their preservation in the ice, limitations to the information they hold, and/or ambiguity surrounding their interpretation. This includes the mass-independent fractionation of oxygen isotopes in sulfates, and the concentration of formaldehyde, in which there has been considerable interest. Our exploration is confined to a domain in which NOx emissions and climate remain constant. However, given the uncertainties associated with the changes in these factors, we would anticipate that their inclusion would make it harder still to identify a robust signal. Finally, though formaldehyde cannot provide this, we propose how it might be used to synchronize the gas- and aqueous-phase Antarctic ice records and thus determine the relative phasing of glacial-interglacial changes in Southern Hemisphere CO2 and temperature