Microbial community composition is linked to Sphagnum acclimation to warming
Authors: Živković Tatjana , Carell Alyssa A , Granath Gustaf , Nilsson Mats B , Helbig Manuel , Warshan Denis , Klarenberg Ingeborg Jenneken , Gilbert Daniel , Shaw A. Jonathan , Kostka Joel E , Weston David J 
Published: March 2021

&lt;p&gt;Peatlands store about third of the terrestrial carbon (C) and exert long-term climate cooling. Dominant plant genera in acidic peatlands, &lt;em&gt;Sphagnum&lt;/em&gt; mosses, are main contributors to net primary productivity. Through associative relationships with diverse microbial organisms (microbiome), &lt;em&gt;Sphagnum&lt;/em&gt; mosses control major biogeochemical processes, namely uptake, storage and potential release of carbon and nitrogen. Climate warming is expected to negatively impact C accumulation in peatlands and alter nutrient cycling, however &lt;em&gt;Sphagnum&lt;/em&gt;-dominated peatland resilience to climate warming may depend on &lt;em&gt;Sphagnum&lt;/em&gt;-microbiome associations. The ability of the microbiome to rapidly acclimatize to warming may aid &lt;em&gt;Sphagnum&lt;/em&gt; exposed to elevated temperatures through host-microbiome acquired thermotolerance. We investigated the role of the microbiome on &lt;em&gt;Sphagnum&lt;/em&gt;&amp;#8217;s ability to acclimate to elevated temperatures using a microbiome-transfer approach to test: a) whether the thermal origin of the microbiome influences acclimation of &lt;em&gt;Sphagnum&lt;/em&gt; growth and b) if microbial benefits to &lt;em&gt;Sphagnum&lt;/em&gt; growth depend on donor &lt;em&gt;Sphagnum&lt;/em&gt; species.&lt;/p&gt;&lt;p&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160; Using a full-factorial design, microbiomes were separated from &lt;em&gt;Sphagnum&lt;/em&gt; &amp;#8220;donor&amp;#8221; species from four different peatlands across a wide range of thermal environments (11.4-27&amp;#176;C). The microbiomes were transferred onto germ-free &amp;#8220;recipient&amp;#8221; &lt;em&gt;Sphagnum&lt;/em&gt; species in the laboratory and exposed to a range of experimental temperatures (8.5 &amp;#8211; 26.5&amp;#176;C) for growth analysis over 4 weeks.&lt;/p&gt;&lt;p&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160; Normalized growth rates were maximized for plants that received a microbiome from a matched &amp;#8220;donor&amp;#8221; and with a similar origin temperature (&amp;#916;T&lt;sub&gt;treatment-origin&lt;/sub&gt;: 0.3&amp;#177;0.9&amp;#176;C [&amp;#177;standard error], p = 0.73). For non-matched &amp;#8220;donor-recipient&amp;#8221; &lt;em&gt;Sphagnum&lt;/em&gt; pairs, &amp;#916;T&lt;sub&gt;treatment-origin&lt;/sub&gt; was slightly negative with -4.1&amp;#177;2.1&amp;#176;C (p = 0.06). The largest growth rate of the &amp;#8220;recipient&amp;#8221; was measured when grown with a microbiome from a matching &amp;#8220;donor&amp;#8221; &lt;em&gt;Sphagnum&lt;/em&gt; species and was 252% and 48% larger than the maximum growth rate of the germ-free &lt;em&gt;Sphagnum&lt;/em&gt; and the non-matched &amp;#8220;donor-recipient&amp;#8221; &lt;em&gt;Sphagnum&lt;/em&gt; pairs, respectively.&lt;/p&gt;&lt;p&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160; Our results suggest that the composition of the &lt;em&gt;Sphagnum&lt;/em&gt; microbiome plays a critical role in host plant temperature acclimation. We found that microbially-provided benefits to the host plant were most pronounced when: 1) the thermal origin of the microbiome is similar to experimental temperatures, and 2) when donor and recipient &lt;em&gt;Sphagnum&lt;/em&gt; species are the same. Together, these results suggest that &lt;em&gt;Sphagnum&lt;/em&gt; temperature acclimation can be modulated, in part, by microbial interactions and may potentially play a role in peatland resilience to climate warming.&lt;/p&gt;