Temporal and spatial effects of elevated CO2 on greenhouse gas fluxes from tree stems in an upland temperate forest

Josep Barba,Vincent Gauci,Giulio Curioni

doi:10.5194/egusphere-egu22-12003

Abstract

&lt;p&gt;Tree stems emit CO&lt;sub&gt;2&lt;/sub&gt; and can exchange CH&lt;sub&gt;4&lt;/sub&gt; with the atmosphere (either emitting or uptaking), with a significant contribution to the C budgets from local to regional scales. However, there is still a need to better understand the spatial and temporal variability of stem CO&lt;sub&gt;2&lt;/sub&gt; and CH&lt;sub&gt;4&lt;/sub&gt; fluxes to quantify the role of vegetation on the C cycle and how these fluxes will behave under future environmental conditions such as atmospheric elevated CO&lt;sub&gt;2&lt;/sub&gt;. An increment of atmospheric CO&lt;sub&gt;2&lt;/sub&gt; concentrations might result in higher photosynthetic rates, which would spin the C cycle in the trees, potentially increasing stem CO&lt;sub&gt;2&lt;/sub&gt; emissions due to higher stem respiration and higher soil-derived CO&lt;sub&gt;2&lt;/sub&gt; contribution. Higher photosynthetic rates might also stimulate fine roots exudation, which could stimulate methanotrophic or methanogenic communities. Additionally, elevated CO&lt;sub&gt;2&lt;/sub&gt; would increase water use efficiency at the leaf level, reducing the amount of water transpired, and potentially increasing soil moisture, which would favour conditions for CH&lt;sub&gt;4&lt;/sub&gt; production. In this study, we present one year of monthly measurements of stem CO&lt;sub&gt;2&lt;/sub&gt; and CH&lt;sub&gt;4&lt;/sub&gt; fluxes from mature oaks (&lt;em&gt;Quercus robur&lt;/em&gt;) growing under elevated CO&lt;sub&gt;2&lt;/sub&gt; (~150 ppm above atmospheric concentrations) and ambient conditions, in a second-generation FACE experiment (Free Air CO&lt;sub&gt;2&lt;/sub&gt; Enrichment; BIFoR-FACE UK). Trees growing under ambient conditions emitted 76% more CO&lt;sub&gt;2&lt;/sub&gt; than those under elevated atmospheric CO&lt;sub&gt;2&lt;/sub&gt;, which was not what we hypothesized. Despite stem CH&lt;sub&gt;4&lt;/sub&gt; fluxes have been reported in multiple upland ecosystems for lots of tree species, our preliminary results did not show clear evidence of CH&lt;sub&gt;4&lt;/sub&gt; stem fluxes (emissions or uptake) for the oaks at our study site. Similar measurements in other FACE experiments are needed to determine if our results on the effect of elevated CO&lt;sub&gt;2&lt;/sub&gt; on stem CO&lt;sub&gt;2&lt;/sub&gt; and CH&lt;sub&gt;4&lt;/sub&gt; fluxes could be extrapolated to other ecosystems and species.&amp;#160;&lt;/p&gt;

Full Text