Effects of a long‐term anoxic warming scenario on microbial community structure and functional potential of permafrost‐affected soil

Sizhong Yang,Alexander J. Probst,Josefine Walz,Christian Knoblauch,Michiel H. in ‘t Zandt,Mike S. M. Jetten,Till L. V. Bornemann,Susanne Liebner,Dirk Wagner

doi:10.1002/ppp.2131

Abstract

AbstractPermafrost (PF)‐affected soils are widespread in the Arctic and store about half the global soil organic carbon. This large carbon pool becomes vulnerable to microbial decomposition through PF warming and deepening of the seasonal thaw layer (active layer [AL]). Here we combined greenhouse gas (GHG) production rate measurements with a metagenome‐based assessment of the microbial taxonomic and metabolic potential before and after 5 years of incubation under anoxic conditions at a constant temperature of 4°C in the AL, PF transition layer, and intact PF. Warming led to a rapid initial release of CO2 and, to a lesser extent, CH4 in all layers. After the initial pulse, especially in CO2 production, GHG production rates declined and conditions became more methanogenic. Functional gene‐based analyses indicated a decrease in carbon‐ and nitrogen‐cycling genes and a community shift to the degradation of less‐labile organic matter. This study reveals low but continuous GHG production in long‐term warming scenarios, which coincides with a decrease in the relative abundance of major metabolic pathway genes and an increase in carbohydrate‐active enzyme classes.

Highlights

Permafrost (PF), which is classified as ground that stays frozen for at least two consecutive years, is widespread in the Arctic and subarctic regions
High initial CO2 production was observed in a 4-year incubation study on deep PF deposits from the Lena River delta, Siberia, whereas CH4 production rates were much lower, which is consistent with our study.[63]
This study used an anaerobic incubation system to investigate the potential of microbial response to environmental changes in which labile carbon is steadily depleted, and older carbon fractions are solely available in the long run

Summary

| INTRODUCTION

Permafrost (PF), which is classified as ground that stays frozen for at least two consecutive years, is widespread in the Arctic and subarctic regions. Hydrology plays an important role in regulating the soil redox potential and the conditions for aerobic and anaerobic microbial metabolism.[13] In particular, anaerobic microbial carbon turnover processes remain poorly understood.[6] In addition, changes in soil temperature, nutrient availability, and vegetation influence soil organic carbon (SOC) decomposition and the resulting ratio of CO2 to CH4 emissions.[13,14,15] The SOC quality is important to influence carbon release from PF; a labile carbon pool is usually degraded immediately after PF thawing, and slow decomposing carbon fraction determines the long-term decomposition of PF SOC on a scale of 5–15 years.[16] After the initial degradation of labile organic matter fractions, microbes have access to less-labile organic matter fractions. Soil water contents were calculated as the weight difference between wet and dried (105C) samples. pH values were measured in a suspension of 5 g of thawed soil in 12.5 mL of distilled water (CG820, Schott Geräte GmbH, Hofheim, Germany)

| MATERIALS AND METHODS

Findings

| DISCUSSION

| CONCLUSIONS