Analysis and experimentation on ecosystems

{\textless}p{\textgreater}{\textless}strong{\textgreater}Abstract.{\textless}/strong{\textgreater} At a local level, biogenic isoprene emissions can greatly affect the air quality of urban areas surrounded by large vegetation sources, such as in the Mediterranean region. The impacts of future warmer and drier conditions on isoprene emissions from Mediterranean emitters are still under debate. Seasonal variations of \textit{Quercus pubescens} gas exchange and isoprene emission rates (ER) were studied from June 2012 to June 2013 at the {\textless}span class="inline-formula"{\textgreater}O$_{\textrm{3}}${\textless}/span{\textgreater}HP site (French Mediterranean) under natural (ND) and amplified (AD, 32{\textless}span class="thinspace"{\textgreater}{\textless}/span{\textgreater}%) drought. While AD significantly reduced stomatal conductance to water vapour throughout the research period excluding August, it did not significantly preclude {\textless}span class="inline-formula"{\textgreater}CO$_{\textrm{2}}${\textless}/span{\textgreater} net assimilation, which was lowest in summer ({\textless}span class="inline-formula"{\textgreater}{\textless}math xmlns="http://www.w3.org/1998/Math/MathML" id="M3" display="inline" overflow="scroll" dspmath="mathml"{\textgreater}{\textless}mrow{\textgreater}{\textless}mo{\textgreater}≈{\textless}/mo{\textgreater}{\textless}mo{\textgreater}-{\textless}/mo{\textgreater}{\textless}mn mathvariant="normal"{\textgreater}1{\textless}/mn{\textgreater}{\textless}/mrow{\textgreater}{\textless}/math{\textgreater}{\textless}span{\textgreater}{\textless}svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="26pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="9d569a8130c156bf00f8fd937bb9bdae"{\textgreater}{\textless}svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-15-4711-2018-ie00001.svg" width="26pt" height="10pt" src="https://www.anaee.eu/bg-15-4711-2018-ie00001.png"/{\textgreater}{\textless}/svg:svg{\textgreater}{\textless}/span{\textgreater}{\textless}/span{\textgreater}{\textless}span class="thinspace"{\textgreater}{\textless}/span{\textgreater}{\textless}span class="inline-formula"{\textgreater}µ{\textless}/span{\textgreater}mol{\textless}span class="inline-formula"{\textgreater}{\textless}math xmlns="http://www.w3.org/1998/Math/MathML" id="M5" display="inline" overflow="scroll" dspmath="mathml"{\textgreater}{\textless}msub{\textgreater}{\textless}mi/{\textgreater}{\textless}mrow class="chem"{\textgreater}{\textless}msub{\textgreater}{\textless}mi mathvariant="normal"{\textgreater}CO{\textless}/mi{\textgreater}{\textless}mn mathvariant="normal"{\textgreater}2{\textless}/mn{\textgreater}{\textless}/msub{\textgreater}{\textless}/mrow{\textgreater}{\textless}/msub{\textgreater}{\textless}/math{\textgreater}{\textless}span{\textgreater}{\textless}svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="18pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="da4b9860380d886174733d1b63fe73da"{\textgreater}{\textless}svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-15-4711-2018-ie00002.svg" width="18pt" height="10pt" src="https://www.anaee.eu/bg-15-4711-2018-ie00002.png"/{\textgreater}{\textless}/svg:svg{\textgreater}{\textless}/span{\textgreater}{\textless}/span{\textgreater}{\textless}span class="thinspace"{\textgreater}{\textless}/span{\textgreater}m{\textless}span class="inline-formula"{\textgreater}$^{\textrm{−2}}${\textless}/span{\textgreater}{\textless}span class="thinspace"{\textgreater}{\textless}/span{\textgreater}s{\textless}span class="inline-formula"{\textgreater}$^{\textrm{−1}}$){\textless}/span{\textgreater}. ER followed a significant seasonal pattern regardless of drought intensity, with mean ER maxima of 78.5 and 104.8{\textless}span class="thinspace"{\textgreater}{\textless}/span{\textgreater}{\textless}span class="inline-formula"{\textgreater}µ{\textless}/span{\textgreater}gC{\textless}span class="thinspace"{\textgreater}{\textless}/span{\textgreater}g{\textless}span class="inline-formula"{\textgreater}{\textless}math xmlns="http://www.w3.org/1998/Math/MathML" id="M9" display="inline" overflow="scroll" dspmath="mathml"{\textgreater}{\textless}mrow{\textgreater}{\textless}msubsup{\textgreater}{\textless}mi/{\textgreater}{\textless}mi mathvariant="normal"{\textgreater}DM{\textless}/mi{\textgreater}{\textless}mrow{\textgreater}{\textless}mo{\textgreater}-{\textless}/mo{\textgreater}{\textless}mn mathvariant="normal"{\textgreater}1{\textless}/mn{\textgreater}{\textless}/mrow{\textgreater}{\textless}/msubsup{\textgreater}{\textless}/mrow{\textgreater}{\textless}/math{\textgreater}{\textless}span{\textgreater}{\textless}svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="15pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="6efaa4f6738e6edd1054c17c8e813756"{\textgreater}{\textless}svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-15-4711-2018-ie00003.svg" width="15pt" height="17pt" src="https://www.anaee.eu/bg-15-4711-2018-ie00003.png"/{\textgreater}{\textless}/svg:svg{\textgreater}{\textless}/span{\textgreater}{\textless}/span{\textgreater}{\textless}span class="thinspace"{\textgreater}{\textless}/span{\textgreater}h{\textless}span class="inline-formula"{\textgreater}$^{\textrm{−1}}${\textless}/span{\textgreater} in July (ND) and August (AD) respectively and minima of 6 and <{\textless}span class="thinspace"{\textgreater}{\textless}/span{\textgreater}2{\textless}span class="thinspace"{\textgreater}{\textless}/span{\textgreater}{\textless}span class="inline-formula"{\textgreater}µ{\textless}/span{\textgreater}gC{\textless}span class="thinspace"{\textgreater}{\textless}/span{\textgreater}g{\textless}span class="inline-formula"{\textgreater}{\textless}math xmlns="http://www.w3.org/1998/Math/MathML" id="M12" display="inline" overflow="scroll" dspmath="mathml"{\textgreater}{\textless}mrow{\textgreater}{\textless}msubsup{\textgreater}{\textless}mi/{\textgreater}{\textless}mi mathvariant="normal"{\textgreater}DM{\textless}/mi{\textgreater}{\textless}mrow{\textgreater}{\textless}mo{\textgreater}-{\textless}/mo{\textgreater}{\textless}mn mathvariant="normal"{\textgreater}1{\textless}/mn{\textgreater}{\textless}/mrow{\textgreater}{\textless}/msubsup{\textgreater}{\textless}/mrow{\textgreater}{\textless}/math{\textgreater}{\textless}span{\textgreater}{\textless}svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="15pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="2c27f0681d740946c3059801ae51d88c"{\textgreater}{\textless}svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-15-4711-2018-ie00004.svg" width="15pt" height="17pt" src="https://www.anaee.eu/bg-15-4711-2018-ie00004.png"/{\textgreater}{\textless}/svg:svg{\textgreater}{\textless}/span{\textgreater}{\textless}/span{\textgreater}{\textless}span class="thinspace"{\textgreater}{\textless}/span{\textgreater}h{\textless}span class="inline-formula"{\textgreater}$^{\textrm{−1}}${\textless}/span{\textgreater} in October and April respectively. The isoprene emission factor increased significantly by a factor of 2 in August and September under AD (137.8 and 74.3{\textless}span class="thinspace"{\textgreater}{\textless}/span{\textgreater}{\textless}span class="inline-formula"{\textgreater}µ{\textless}/span{\textgreater}gC{\textless}span class="thinspace"{\textgreater}{\textless}/span{\textgreater}g{\textless}span class="inline-formula"{\textgreater}{\textless}math xmlns="http://www.w3.org/1998/Math/MathML" id="M15" display="inline" overflow="scroll" dspmath="mathml"{\textgreater}{\textless}mrow{\textgreater}{\textless}msubsup{\textgreater}{\textless}mi/{\textgreater}{\textless}mi mathvariant="normal"{\textgreater}DM{\textless}/mi{\textgreater}{\textless}mrow{\textgreater}{\textless}mo{\textgreater}-{\textless}/mo{\textgreater}{\textless}mn mathvariant="normal"{\textgreater}1{\textless}/mn{\textgreater}{\textless}/mrow{\textgreater}{\textless}/msubsup{\textgreater}{\textless}/mrow{\textgreater}{\textless}/math{\textgreater}{\textless}span{\textgreater}{\textless}svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="15pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="453577aa284ae9a8e4231cc2ab178b14"{\textgreater}{\textless}svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-15-4711-2018-ie00005.svg" width="15pt" height="17pt" src="https://www.anaee.eu/bg-15-4711-2018-ie00005.png"/{\textgreater}{\textless}/svg:svg{\textgreater}{\textless}/span{\textgreater}{\textless}/span{\textgreater}{\textless}span class="thinspace"{\textgreater}{\textless}/span{\textgreater}h{\textless}span class="inline-formula"{\textgreater}$^{\textrm{−1}}$){\textless}/span{\textgreater} compared with ND (75.3 and 40.21{\textless}span class="thinspace"{\textgreater}{\textless}/span{\textgreater}{\textless}span class="inline-formula"{\textgreater}µ{\textless}/span{\textgreater}gC{\textless}span class="thinspace"{\textgreater}{\textless}/span{\textgreater}g{\textless}span class="inline-formula"{\textgreater}{\textless}math xmlns="http://www.w3.org/1998/Math/MathML" id="M18" display="inline" overflow="scroll" dspmath="mathml"{\textgreater}{\textless}mrow{\textgreater}{\textless}msubsup{\textgreater}{\textless}mi/{\textgreater}{\textless}mi mathvariant="normal"{\textgreater}DM{\textless}/mi{\textgreater}{\textless}mrow{\textgreater}{\textless}mo{\textgreater}-{\textless}/mo{\textgreater}{\textless}mn mathvariant="normal"{\textgreater}1{\textless}/mn{\textgreater}{\textless}/mrow{\textgreater}{\textless}/msubsup{\textgreater}{\textless}/mrow{\textgreater}{\textless}/math{\textgreater}{\textless}span{\textgreater}{\textless}svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="15pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="d4a046b56a13488879e986af4cdaffdb"{\textgreater}{\textless}svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-15-4711-2018-ie00006.svg" width="15pt" height="17pt" src="https://www.anaee.eu/bg-15-4711-2018-ie00006.png"/{\textgreater}{\textless}/svg:svg{\textgreater}{\textless}/span{\textgreater}{\textless}/span{\textgreater}{\textless}span class="thinspace"{\textgreater}{\textless}/span{\textgreater}h{\textless}span class="inline-formula"{\textgreater}$^{\textrm{−1}}${\textless}/span{\textgreater}), but no significant changes occurred on ER. Aside from the June 2012 and 2013 measurements, the MEGAN2.1 (Model of Emissions of Gases and Aerosols from Nature version 2.1) model was able to assess the observed ER variability only when its soil moisture activity factor {\textless}span class="inline-formula"{\textgreater}\textit{γ}$_{\textrm{SM}}${\textless}/span{\textgreater} was not operating and regardless of the drought intensity; in this case more than 80{\textless}span class="thinspace"{\textgreater}{\textless}/span{\textgreater}% and 50{\textless}span class="thinspace"{\textgreater}{\textless}/span{\textgreater}% of ER seasonal variability was assessed in the ND and AD respectively. We suggest that a specific formulation of {\textless}span class="inline-formula"{\textgreater}\textit{γ}$_{\textrm{SM}}${\textless}/span{\textgreater} be developed for the drought-adapted isoprene emitter, according to that obtained for \textit{Q. pubescens} in this study ({\textless}span class="inline-formula"{\textgreater}\textit{γ}$_{\textrm{SM}}$={\textless}/span{\textgreater}{\textless}span class="thinspace"{\textgreater}{\textless}/span{\textgreater}0.192e{\textless}span class="inline-formula"{\textgreater}$^{\textrm{51.93 SW}}${\textless}/span{\textgreater} with SW the soil water content). An isoprene algorithm ({\textless}span class="inline-formula"{\textgreater}\textit{G}{\textless}/span{\textgreater}14) was developed using an optimised artificial neural network (ANN) trained on our experimental dataset (ER{\textless}span class="thinspace"{\textgreater}{\textless}/span{\textgreater}{\textless}span class="inline-formula"{\textgreater}+{\textless}/span{\textgreater}{\textless}span class="thinspace"{\textgreater}{\textless}/span{\textgreater}{\textless}span class="inline-formula"{\textgreater}O$_{\textrm{3}}${\textless}/span{\textgreater}HP climatic and edaphic parameters cumulated over 0 to 21 days prior to the measurements). {\textless}span class="inline-formula"{\textgreater}\textit{G}{\textless}/span{\textgreater}14 assessed more than 80{\textless}span class="thinspace"{\textgreater}{\textless}/span{\textgreater}% of the observed ER seasonal variations, regardless of the drought intensity. ER{\textless}span class="inline-formula"{\textgreater}$_{\textrm{\textit{G}14}}${\textless}/span{\textgreater} was more sensitive to higher (0 to {\textless}span class="inline-formula"{\textgreater}−7{\textless}/span{\textgreater} days) frequency environmental changes under AD in comparison to ND. Using IPCC RCP2.6 and RCP8.5 climate scenarios, and SW and temperature as calculated by the ORCHIDEE land surface model, ER{\textless}span class="inline-formula"{\textgreater}$_{\textrm{\textit{G}14}}${\textless}/span{\textgreater} was found to be mostly sensitive to future temperature and nearly insensitive to precipitation decrease (an annual increase of up to 240{\textless}span class="thinspace"{\textgreater}{\textless}/span{\textgreater}% and at the most 10{\textless}span class="thinspace"{\textgreater}{\textless}/span{\textgreater}% respectively in the{\textless}span id="page4712"/{\textgreater} most severe scenario). The main impact of future drier conditions in the Mediterranean was found to be an enhancement ({\textless}span class="inline-formula"{\textgreater}+40{\textless}/span{\textgreater}{\textless}span class="thinspace"{\textgreater}{\textless}/span{\textgreater}%) of isoprene emissions sensitivity to thermal stress.{\textless}/p{\textgreater}