Among-provenance diversity and phenotypic plasticity of water-use efficiency in sessile oak populations growing in a mesic common garden.
Authors: Rabarijaona Arivoara , Ponton Stéphane , Bert Didier , Ducousso Alexis , Richard Béatrice , Levillain Joseph , Brendel Oliver 
Published: March 2022

&lt;p&gt;Abstract:&lt;/p&gt;&lt;p&gt;As a widespread species, sessile oak (&lt;em&gt;Quercus petraea&lt;/em&gt;)&lt;em&gt; &lt;/em&gt;populations occupy a wide range of ecological conditions with different local selection pressures, especially different drought exposure, which would have favoured different locally adapted populations. Water-use efficiency (WUE), which is defined at the tree level as the ratio between the biomass produced and the quantity of water transpired during the same period of time, is an interesting candidate trait for adaptation to drought. Six hundred trees from sixteen different provenances planted in 1993 in a common garden in the North-Eastern of France were harvested during the 2014-2015 winter. Intrinsic WUE (WUE&lt;sub&gt;i&lt;/sub&gt;), estimated from carbon isotope composition (&amp;#948;&lt;sup&gt;13&lt;/sup&gt;C) measurements of tree-rings, was compared among and within provenances for three contrasted years: (i) 2000, a wet year; (ii) 2003, a severely dry year; (iii) and 2005, a moderately dry year. The main purpose was to assess the drought-adaptive character of WUE&lt;sub&gt;i&lt;/sub&gt; for sessile oak trees. For this, (i) the adaptive character of WUE&lt;sub&gt;i&lt;/sub&gt; was evaluated by relating population mean WUE&lt;sub&gt;i&lt;/sub&gt; to the mean pedoclimatic conditions of their provenance sites. (ii) The phenotypic plasticity of WUE&lt;sub&gt;i&lt;/sub&gt; to drought was evaluated by comparing &amp;#160;the values observed in 2003 and 2005 to those of &amp;#160;2000 ; this plasticity was also related to the mean pedoclimatic conditions of their provenance sites. (iii) The contribution of WUE&lt;sub&gt;i&lt;/sub&gt; to tree and population fitness was assessed from the relationship between WUE&lt;sub&gt;i&lt;/sub&gt; and tree growth. Significant differences in &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C (thus WUE&lt;sub&gt;i&lt;/sub&gt;) were found among populations. However, no linear relationship was established between mean population &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C and the mean pedoclimatic conditions of the provenance sites. Based on these results observed on juvenile sessile oak trees in the relatively wet conditions of the common garden, no local adaptation in terms of WUEi was detected. An increase in drought intensity resulted in an increase in population WUE&lt;sub&gt;i&lt;/sub&gt; and all provenances displayed a similar plasticity of WUE&lt;sub&gt;i&lt;/sub&gt; to drought, suggesting no among population diversity for drought responses. A significant correlation between WUE&lt;sub&gt;i&lt;/sub&gt; and tree growth was detected only during the wet year, when populations with a higher WUE&lt;sub&gt;i&lt;/sub&gt; also had a higher growth index. Moreover, a much larger variability in WUE&lt;sub&gt;i&lt;/sub&gt; was demonstrated within populations (2&amp;#8211;4&amp;#8240;) than among-population (0.6&amp;#8240;).&lt;/p&gt;&lt;p&gt;Key words : Climate change, assisted migration, local adaptation, water-use efficiency, fitness, diversity&lt;/p&gt;