Combined effects of elevated temperature and CO2 alters epiphytic cyanobacterial community composition - consequences for nitrogen fixation activity and the host Pleurozium schreberi.
Authors: Warshan Denis , Kim Sea-Yong , Novotny Andreas , Andrésson Ólafur S. , Rasmussen Ulla 
Published: March 2022

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&lt;p&gt;&lt;span&gt;In&amp;#160;cold biomes,&amp;#160;N&lt;/span&gt;&lt;sub&gt;&lt;span&gt;2&lt;/span&gt;&lt;/sub&gt;&lt;span&gt;-fixation by&amp;#160;filamentous&amp;#160;heterocystous&amp;#160;cyanobacteria in symbiosis with&amp;#160;mosses&amp;#160;represents&amp;#160;one of&amp;#160;the main biological&amp;#160;inputs&amp;#160;of new nitrogen (N), and&amp;#160;greatly&amp;#160;&lt;/span&gt;&lt;span&gt;support&amp;#160;the&amp;#160;surrounding&amp;#160;ecosystem&amp;#160;productivity. In these ecosystems,&amp;#160;&lt;/span&gt;&lt;span&gt;climate&amp;#160;change&amp;#160;is expected to result in&amp;#160;2-9&amp;#176;C&amp;#160;increase&amp;#160;in&amp;#160;temperature and&amp;#160;two times&amp;#160;greater carbon dioxide (&lt;/span&gt;&lt;span&gt;CO&lt;/span&gt;&lt;sub&gt;&lt;span&gt;2&lt;/span&gt;&lt;/sub&gt;&lt;span&gt;)&amp;#8239;over the next century, yet&amp;#160;little is known about the&amp;#160;effects of these factors&amp;#160;&lt;/span&gt;&lt;span&gt;on&amp;#160;the&amp;#160;community composition of cyanobacteria in symbiosis with mosses.&amp;#160;&lt;/span&gt;&lt;span&gt;In particular, it&amp;#160;is unknown how&amp;#160;changes in the cyanobacterial community&amp;#160;will affect&amp;#160;N&lt;/span&gt;&lt;sub&gt;&lt;span&gt;2&lt;/span&gt;&lt;/sub&gt;&lt;span&gt;-fixation&amp;#160;activity&amp;#160;&amp;#160;and&amp;#160;the&amp;#160;resulting&amp;#160;impact on the moss growth rate (MGR).&amp;#160;Here,&amp;#160;we&amp;#160;reconstructed the&amp;#160;symbiosis between&amp;#160;the&amp;#160;common feathermoss&amp;#160;&lt;/span&gt;&lt;em&gt;&lt;span&gt;Pleurozium&amp;#160;schreberi&lt;/span&gt;&lt;/em&gt;&lt;span&gt;&amp;#160;and&amp;#160;cyanobacteria&amp;#160;isolated from feathermosses.&amp;#160;&lt;/span&gt;&lt;em&gt;&lt;span&gt;P.&amp;#160;schreberi&lt;/span&gt;&lt;/em&gt;&lt;span&gt;&amp;#160;gametophytes&amp;#160;were&amp;#160;inoculated with&amp;#160;1, 5 or&amp;#160;20 genetically&amp;#160;distinct&amp;#160;strains of&amp;#160;cyanobacteria&amp;#160;and&amp;#160;exposed to different temperature&amp;#160;(11&amp;#176;C and 19&amp;#176;C)&amp;#160;and CO&lt;/span&gt;&lt;sub&gt;&lt;span&gt;2&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; (500 ppm and 1000 ppm)&amp;#160;conditions.&amp;#160;&lt;/span&gt;&lt;span&gt;Changes in&amp;#160;MGR, N&lt;/span&gt;&lt;sub&gt;&lt;span&gt;2&lt;/span&gt;&lt;/sub&gt;&lt;span&gt;-fixation rate, and cyanobacterial&amp;#160;community structure and composition&amp;#160;were&amp;#160;measured at distinct time points:&amp;#160;5, 10, 20, and 30 weeks&amp;#160;of&amp;#160;exposure.&amp;#160;Our results indicate that both&amp;#160;elevated temperature and CO&lt;/span&gt;&lt;sub&gt;&lt;span&gt;2&lt;/span&gt;&lt;/sub&gt;&lt;span&gt;&amp;#160;levels&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;span&gt;can&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;span&gt;individually and&amp;#160;combined&amp;#160;have positive effects on the N&lt;/span&gt;&lt;sub&gt;&lt;span&gt;2&lt;/span&gt;&lt;/sub&gt;&lt;span&gt;-fixation activities, and consequently on&amp;#160;MGR.&amp;#160;The underlying&amp;#160;biotic&amp;#160;mechanisms&amp;#160;for&amp;#160;increased&amp;#160;N&lt;/span&gt;&lt;sub&gt;&lt;span&gt;2&lt;/span&gt;&lt;/sub&gt;&lt;span&gt;-fixation and MGR were changes in the cyanobacterial community diversity and composition. &amp;#160;In general, we observed a reduction in cyanobacterial diversity and an increase in cyanobacterial strain abundance that have adapted and dominated under the elevated temperature and CO&lt;/span&gt;&lt;sub&gt;&lt;span&gt;2&lt;/span&gt;&lt;/sub&gt;&lt;span&gt;&amp;#160;levels.&lt;/span&gt;&lt;/p&gt;
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