Warming constrains bacterial community responses to nutrient inputs in a southern, but not northern, maritime Antarctic soil

We investigated the effects of increased soil temperature, water and nutrient availability on soil bacterial communities at Wynn Knolls on Signy Island (60 °S) in the northern maritime Antarctic and at Mars Oasis (71 °S) in the southern maritime Antarctic. After 10–12 months, analyses of the concentrations of ester linked fatty acids (ELFAs) in soil indicated that bacterial communities responded positively to single applications of substrates at both locations, with 20% and 49% increases in total Gram positive and Gram negative bacterial markers, respectively, in response to the application of tryptic soy broth (TSB; a complex substrate containing organic carbon and nitrogen, plus other nutrient elements) at Wynn Knolls, and 120% and 44% increases in Gram positive bacterial markers at Mars Oasis in response to the application of TSB and the amino acid glycine (a relatively simple source of organic carbon and nitrogen), respectively. Responses to the warming treatment were not detected at Wynn Knolls, where open top chambers (OTCs) increased mean monthly soil temperatures by up to 0.7 °C, but at Mars Oasis, where OTCs increased monthly soil temperatures by up to 2.4 °C, warming led to 41% and 46% reductions in the concentrations of Gram positive bacterial markers in soil to which glycine and TSB had been applied, respectively. Warming also led to 55% and 51% reductions in the ratio of Gram positive to Gram negative markers in soils at Mars Oasis to which glycine and TSB had been applied. These data suggest that warming may constrain the responses of bacterial communities to carbon and nitrogen inputs arising from dead plant matter entering maritime Antarctic soils in future decades.