Composition and activity of nitrifier communities in soil are unresponsive to elevated temperature and CO2, but strongly affected by drought

Abstract

Nitrification is a fundamental process in terrestrial nitrogen cycling. However, detailed information on how climate change affects the structure of nitrifier communities is lacking, specifically from experiments in which multiple climate change factors are manipulated simultaneously. Consequently, our ability to predict how soil nitrogen (N) cycling will change in a future climate is limited. We conducted a field experiment in a managed grassland and simultaneously tested the effects of elevated atmospheric CO2, temperature, and drought on the abundance of active ammonia-oxidizing bacteria (AOB) and archaea (AOA), comammox (CMX) Nitrospira, and nitrite-oxidizing bacteria (NOB), and on gross mineralization and nitrification rates. We found that N transformation processes, as well as gene and transcript abundances, and nitrifier community composition were remarkably resistant to individual and interactive effects of elevated CO2 and temperature. During drought however, process rates were increased or at least maintained. At the same time, the abundance of active AOB increased probably due to higher NH4+ availability. Both, AOA and comammox Nitrospira decreased in response to drought and the active community composition of AOA and NOB was also significantly affected. In summary, our findings suggest that warming and elevated CO2 have only minor effects on nitrifier communities and soil biogeochemical variables in managed grasslands, whereas drought favors AOB and increases nitrification rates. This highlights the overriding importance of drought as a global change driver impacting on soil microbial community structure and its consequences for N cycling.

Nitrification is a minor source of nitrous oxide (N2O) in an agricultural landscape and declines with increasing management intensity

“…Similarly, both abundance and community structure of amoA genes of AOA and AOB have been shown to be stable across seasons in two acid forest soils (Qin et al, 2019 ). Thus, it seems reasonable to conclude that long‐term management practices in our ecosystems have selected soil nitrifier populations that are adapted to seasonal environmental fluctuations such as soil temperature (Séneca et al, 2020 ).…”

The effect of increased temperature and CO2 air enrichment on the nutritive value of orchard grass (Dactylis glomerata) in permanent grassland

“…There were no alterations of precipitation considered in this study, and all plots were exposed equally to the naturally occurring precipitation. However, further studies in the ClimGrass-project also dealt with the effects of simulated drought on growth (Küsters et al ., 2021), as well as on soil chemical and soil ecological processes (Seneca et al ., 2020; Meeran et al ., 2021).…”

Long‐term manipulation of mean climatic conditions alters drought effects on C‐ and N‐cycling in an arable soil

“…However, there have been other studies in which drought decreased N mineralization at least during summer (Novem Auyeung et al, 2013). NH 4 + oxidizing bacteria and archaea, which govern the rate limiting step in nitrification (Lehtovirta‐Morley, 2018) have been shown to be drought resistant within grassland ecosystems (Fuchslueger et al, 2014; Séneca et al, 2020). Accordingly, even in our arable system, ongoing nitrification might explain why NH 4 + did not accumulate during the drought phase of our experiment.…”