Grazing-induced reduction of natural nitrous oxide release from continental steppe

Abstract

Atmospheric concentrations of the greenhouse gas nitrous oxide (N(2)O) have increased significantly since pre-industrial times owing to anthropogenic perturbation of the global nitrogen cycle, with animal production being one of the main contributors. Grasslands cover about 20 per cent of the temperate land surface of the Earth and are widely used as pasture. It has been suggested that high animal stocking rates and the resulting elevated nitrogen input increase N(2)O emissions. Internationally agreed methods to upscale the effect of increased livestock numbers on N(2)O emissions are based directly on per capita nitrogen inputs. However, measurements of grassland N(2)O fluxes are often performed over short time periods, with low time resolution and mostly during the growing season. In consequence, our understanding of the daily and seasonal dynamics of grassland N(2)O fluxes remains limited. Here we report year-round N(2)O flux measurements with high and low temporal resolution at ten steppe grassland sites in Inner Mongolia, China. We show that short-lived pulses of N(2)O emission during spring thaw dominate the annual N(2)O budget at our study sites. The N(2)O emission pulses are highest in ungrazed steppe and decrease with increasing stocking rate, suggesting that grazing decreases rather than increases N(2)O emissions. Our results show that the stimulatory effect of higher stocking rates on nitrogen cycling and, hence, on N(2)O emission is more than offset by the effects of a parallel reduction in microbial biomass, inorganic nitrogen production and wintertime water retention. By neglecting these freeze-thaw interactions, existing approaches may have systematically overestimated N(2)O emissions over the last century for semi-arid, cool temperate grasslands by up to 72 per cent.

Evaluating the lingering effect of livestock grazing on functional potentials of microbial communities in Tibetan grassland soils

“…However, grazing reallocates N between aboveground and belowground ecosystems, which could compensate soil N loss. Indeed, a continental survey indicated that grazing increased both the rates of N cycling and soil N content (Wolf et al 2010). In our study, soil TN contents decreased at the 3200-m site and increased at the 3400-m site (Table 2), which might have resulted from differential microbial mediation of N cycles at different sites.…”

Potential for reduced methane and carbon dioxide emissions from livestock and pasture management in the tropics

“…The focus is on the mitigation of CO 2 and CH 4 . The role of N 2 O emissions from certain grazing systems is currently undergoing reevaluation (8).…”

Spatiotemporal Variations in Nitrous Oxide Emissions from an Open Fen on the Qinghai–Tibetan Plateau: a 3-Year Study

“…Though there was no significant relation between standing water depths and N 2 O emissions, we still considered this related to the temporal dynamics of soil water regime (water tables or standing water depths), which is usually regarded as one of the most important factors controlling N 2 O emissions in variable ecosystems (Mosier et al 1991;Yu et al 2008;Wolf et al 2010). Moreover, temporal dynamics of soil water regime in wetland soils is sensitive to seasonal and inter-annual weather patterns, which will affect the environmental drivers for N-transformation processes (Jørgensen et al 2012).…”

“…Therefore, after seasonal or inter-annual drainage, more easily grazing for livestock is believed to stimulate N 2 O fluxes from wetlands on the plateau. However, it is of great uncertainty that the interaction of abovementioned climate change and grazing on N 2 O fluxes (Lin et al 2009;Wolf et al 2010). …”