Soil water content as a critical factor for stable bacterial community structure and degradative activity in maritime Antarctic soil

Abstract

Recent increases in air temperature across the Antarctic Peninsula may prolong the thawing period and directly affect the soil temperature (Ts) and volumetric soil water content (SWC) in maritime tundra. At a Ts of 8°C, two customized microcosm systems were created using maritime Antarctic soil to investigate the differential influence of SWC on the bacterial community on degradation of humic substances (HS), the largest pool of recalcitrant soil organic carbon. When the microcosm soil (KS1-4Feb) was incubated for 90 days at a constant SWC of ~32%, the initial HS content (167.0 mg-g-1 of dried soil) decreased to 156.0 mg (approximately 6.6% loss, p<0.05). However, when another microcosm soil (KS1-4Apr) was incubated with SWCs that gradually decreased from 37% to 9% for 90 days, HS degradation was undetected. The low HS degradative activity persisted, even after the SWC was restored to 30% for an additional 30 days. Overall bacterial community structure remained relatively stable at a constant SWC setting (KS1-4Feb). In contrast, we saw marked shifts in the bacterial community structure with the changing SWC regimen (KS1-4Apr), suggesting that soil bacterial communities are vulnerable to drying and re-wetting conditions. These microcosm experiments provide new information regarding the effects of constant SWC and higher Ts on stable bacterial communities and higher HS degradation rate in maritime Antarctic tundra soil.