The potential nitrous oxide emissions in a permanent grassland chronosequence

Sammanfattning: As a part of a larger project (Belowground biodiversity of grasslands – conservation needs and potential to promote sustainable agriculture), this study aims to investigate potential nitrous oxide (N2O) emissions and microbial gene abundances needed for the production (nirS and nirK) and reduction (nosZI and nosZII) of nitrous oxide in soil of permanent grasslands of various age. Thegrasslands have at different times been converted to permanent grasslands and are of interest because of the possibility to shed more light about the passage of time’s affects on the soil microbialcommunities and their activity. Three farms around Uppsala that manage permanent grasslands of various ages were selected and 24 soil samples were taken at dept 0 – 10 cm. These regions have similar backgrounds in cultivation, but they differ in soil type and some soil parameters. The prediction was that the permanent grasslands with the highest age have the lowest production of nitrous oxide gas, because of the lack of the availability of nutrient N over time in permanent grasslands due to no fertilizers being added and what is present will be in high demand by plants and microorganisms. In addition, the gene abundances for nirS and nirK are expected to become lower with age along with the lower production of nitrous oxide. The results however, thought not significant, showed an increase in N2O production with age, that possibly could be linked to significantly increasing organic matter content in soil over time. Instead a difference in N2O production was found between regions. Neither the age or the region of the permanent grasslands had a significant effect on the dynamics of different gene abundances, but the genes nirS and nirK showed a slight decrease with age and the opposite was found for the gene nosZII’s abundance.