Impact of nitrogen additions on soil microbial respiration and temperature sensitivity in native and agricultural ecosystems in the Brazilian Cerrado.

Soil microbial respiration (SMR1 ) is a major flux of CO2 from terrestrial ecosystems into the atmosphere, which depends on several abiotic factors, including soil temperature and nutrient availability. A nutrient of great interest in soil ecology is nitrogen (N) because of its use in agriculture and an expected increase of depositions in soils. Models on the relationship between SMR and temperature may be able to describe the effects of N addition on the temperature sensitivity of soil respiration (Q10 2 ). Hence, this study aimed to investigate the effects of N addition on SMR and Q10 values in soils of native Brazilian Cerrado (NC3 ), and of an agricultural ecosystem (AE4 ) cultivated over the past 17 years. SMR was stimulated by N additions (100 and 200 mg N kg dwt soil-1 ) in samples of Cerrado sites depending on the land use type and temperature assessed. The addition of 200 N kg dwt soil-1 to NC showed higher SMR values at 25 °C compared to soil without N input, whereas the same happened in AE at 30 °C. Overall, NC presented higher Q10 values than AE. N inputs increased Q10 in the Cerrado sites. In NC, the highest Q10 value occurred when 200 mg N kg dwt soil-1 was added to soil, whereas in AE the greatest value was observed for a lower dose (100 mg N kg dwt soil-1 ). This study shows that N additions to tropical soils alter Q10 values depending on dose and land use. These are important findings to compare the fragility of pristine and cultivated Brazilian Cerrado ecosystems in the perspective of climate change.