Abstract
Abstract. Lack of understanding of the effects of warming and winter grazing on soil fungal contribution to the nitrous oxide (N2O) production process has limited our ability to predict N2O fluxes under changes in climate and land use management, because soil fungi play an important role in driving terrestrial N cycling. A controlled warming and winter grazing experiment that included control (C), winter grazing (G), warming (W) and warming with winter grazing (WG) was conducted to investigate the effects of warming and winter grazing on soil N2O production potential in an alpine meadow on the Tibetan Plateau. Our results showed that soil bacteria and fungi contributed 46 ± 2 % and 54 ± 2 % to nitrification, and 37 ± 3 % and 63 ± 3 % to denitrification in the control treatment, respectively. We conclude that soil fungi could be the main source of N2O production potential for the Tibetan alpine grasslands. In our results, neither warming nor winter grazing affected the activity of enzymes responsible for overall nitrification and denitrification. However, warming significantly increased the enzyme activity of bacterial nitrification and potential of N2O production from denitrification to 53 ± 2 % and 55 ± 3 %, respectively, but decreased them to 47 ± 2 % and 45 ± 3 %, respectively. Winter grazing had no such effects. Warming and winter grazing may not affect the soil N2O production potential, but climate warming can alter biotic pathways responsible for N2O production process. These findings confirm the importance of soil fungi in the soil N2O production process and how they respond to environmental and land use changes in alpine meadow ecosystems. Therefore, our results provide some new insights into ecological controls on the N2O production process and contribute to the development of an ecosystem nitrogen cycle model.
Highlights
N2O emissions from soil contribute to climate warming as N2O is a potent greenhouse gas (IPCC, 2015); it is mainly produced in soils through microbial nitrification and denitrification (Zumft, 1997)
The effects of climate warming and grazing on the aboveground vegetation, soil physicochemical properties, litter mass loss, bacterial communities and N2O fluxes of Tibetan alpine grasslands have been extensively investigated (Hu et al, 2010; Li et al, 2016; Luo et al, 2010; Rui et al, 2012; Wang et al, 2012; Zhu et al, 2015); most of these studies were focused on the effect of summer grazing; little is shown on the effect of winter grazing on them (Zhu et al, 2015; Che et al, 2018)
Many studies of Tibetan alpine grasslands are mainly focused on bacterial nitrifiers and denitrifiers or their activities, taking these to be the key factors in N2O emission in alpine grasslands
Summary
N2O emissions from soil contribute to climate warming as N2O is a potent greenhouse gas (IPCC, 2015); it is mainly produced in soils through microbial nitrification and denitrification (Zumft, 1997). The effects of climate warming and grazing on the aboveground vegetation, soil physicochemical properties, litter mass loss, bacterial communities and N2O fluxes of Tibetan alpine grasslands have been extensively investigated (Hu et al, 2010; Li et al, 2016; Luo et al, 2010; Rui et al, 2012; Wang et al, 2012; Zhu et al, 2015); most of these studies were focused on the effect of summer grazing; little is shown on the effect of winter grazing on them (Zhu et al, 2015; Che et al, 2018). While many studies have explored N mineralization, nitrification and even denitrification as well as bacterial nitrifiers and denitrifiers for better understanding of N2O emission and ecosystem functioning (Yang et al, 2013; Yue et al, 2015), few studies have been conducted to distinguish whether bacteria or fungi dominate in N2O emission and N cycling (Kato et al, 2013), especially under warming and grazing conditions
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