Nutrients unlocked from permafrost thaw affect microbial methane metabolism
Authors: Kashi Natalie N. , Varner Ruth K. , Thorp Nathan R. , Knorr Melissa A. , Wymore Adam S. , Ernakovich Jessica G. , Hobbie Erik A. , Giesler Reiner 
Published: March 2020

&lt;p&gt;The biological conversion of frozen carbon-rich soil (permafrost) into greenhouse gases such as carbon dioxide could cause a positive feedback to climate change. Another significant consequence of permafrost thaw is the collapse of soil structure and subsequent higher water table that can shift vegetation toward water-adapted plant communities that emit high concentrations of methane (CH&lt;sub&gt;4&lt;/sub&gt;). Plants and microbes respond rapidly to labile carbon (C) and nitrogen (N) released from permafrost thaw, however, the microbial response to phosphorus (P) is unknown. &amp;#160;Here we investigated how the nutrient status of permafrost and peat affect microbial activities in four minerotrophic communities in a peatland undergoing permafrost thaw. We experimentally fertilized soils in vitro with a permafrost soil slurry, inorganic P, organic N, or organic N and P. This method isolated the effect of permafrost thaw on microbial processes by removing the confounding effect of plant-soil interactions. The four peatland communities include 1. palsas (intact permafrost mounds rising above the surrounding peatlands), 2. pockets of collapsed palsas dominated by &lt;em&gt;Sphagnum fuscum&lt;/em&gt;, 3. adjacent eutrophic &lt;em&gt;Sphagnum&lt;/em&gt;-dominated lawns with thawing permafrost and 4. inundated, sedge-dominated minerotrophic fens with no permafrost remaining. Permafrost had high extractable inorganic N concentrations, averaging 30 &amp;#181;g N g-1 soil dry weight (dw), whereas extractable P concentrations were low, averaging 1.4 &amp;#181;g P g-1 soil dw. While N concentrations in the permafrost were over four times the concentration in adjacent peatland communities, extractable P concentrations were relatively lower. &lt;em&gt;Sphagnum&lt;/em&gt; lawns positioned at the base of palsas, had nine times the extractable P concentrations averaging 12.6 &amp;#181;g P g-1 soil dw compared to the permafrost, suggesting that P availability increases as permafrost thaws. However, in the fen where no permafrost remains, extractable P concentrations were again low, 2.4 &amp;#181;g P g-1 soil dw, despite high total P. These fen communities are also marked by higher iron concentrations, likely resulting in P immobilization by higher concentrations of metals. The addition of inorganic P and the combination of organic N and P in these fen sites strongly enhanced CH&lt;sub&gt;4&lt;/sub&gt; oxidation rates while organic N did not, indicating the importance of P for these energy intensive transformations. Nutrient amendments did not have a significant effect on CH&lt;sub&gt;4&lt;/sub&gt; production rates, however, permafrost slurries significantly decreased CH&lt;sub&gt;4&lt;/sub&gt; production in &lt;em&gt;Sphagnum&lt;/em&gt; lawn communities, suggesting an unknown inhibitory effect of permafrost chemistry on CH&lt;sub&gt;4&lt;/sub&gt; production. The results of our study highlight the effects of permafrost degradation on nutrient release and provide new insight into how nutrients unlocked from permafrost affects greenhouse gases.&amp;#160;&lt;/p&gt;