Ecology of fungal denitrifiers in terrestrial ecosystems : global patterns and effects of management in agricultural soils

Sammanfattning: Denitrification is the dominant source of nitrous oxide (N2O) from terrestrial ecosystems, a potent greenhouse gas and stratospheric ozone-depleting agent. Fungi can perform denitrification and terminate the process with N2O, making them a potentially important source of N2O. This thesis aimed to broaden the understanding of the ecology of this understudied group in the nitrogen cycle by assessing their global abundance and distribution in terrestrial ecosystems and evaluating the effects of soil management practices on their abundance, community composition, and contribution to N2O production in agricultural soils.Fungi carrying the denitrification marker gene nirK were rare and cosmopolitan and compared to prokaryotic denitrifiers, they were most abundant in forests and croplands, although prokaryotes dominated in all biomes. Agricultural management practices affected the abundance and community composition of fungal denitrifiers through changes in the availability of carbon and nitrogen. Long-term fertilization increased their abundance, irrespective of soil type or climate, but did not affect fungal contributions to potential N2O production. Instead, the genetic potential of bacterial denitrifiers was more important. In unfertilized soils, biotic and abiotic controls of N2O production rates were important, but in fertilized soils only abiotic soil properties were involved. Inversion tillage, compared with other types of tillage, led to a reduction of the genetic potential for fungal denitrification relative to that of bacterial denitrifiers and selected for fungi with opportunistic lifestyles. These results highlight that fungal denitrifiers are found across all terrestrial ecosystems, are significantly influenced by soil management but contribute less to N2O emissions than their prokaryotic counterparts.