N balance and cycling of Inner Mongolia typical steppe: a comprehensive case study of grazing effects

Abstract

Increasing grazing pressure and climate change affect nitrogen (N) dynamics of grassland ecosystems in the Eurasian steppe belt with unclear consequences for future delivery of essential services such as forage production, C sequestration, and diversity conservation. The identification of key processes responsive to grazing is crucial to optimize grassland management. In this comprehensive case study of a Chinese typical steppe, we present an in‐depth analysis of grazing effects on N dynamics, including the balance of N gains and losses, and N cycling. N pools and fluxes were simultaneously quantified on three grassland sites of different long‐term grazing intensities. Dust deposition, wind erosion, and wet deposition were the predominant but most variable processes contributing to N losses and gains. Heavy grazing increased the risk of N losses by wind erosion. Hay‐making and sheep excrement export to folds during nighttime keeping were important pathways of N losses from grassland sites. Compared to these fluxes, gaseous N losses (N2O, NO, N2, and NH3) and N losses via export of sheep live mass and wool were of minor relevance. Our N balance calculation indicated mean annual net N losses of 0.9 ± 0.8 g N/m2 (mean ± SD) at the heavily grazed site, whereas the long‐term ungrazed site was an N sink receiving mean annual inputs of 1.8 ± 1.1 g N/m2, mainly due to dust deposition. Heavy grazing reduced pool sizes of topsoil organic N, above‐ and belowground biomass, and N fluxes with regard to plant N uptake, decomposition, gross microbial N turnover, and immobilization. Most N‐related processes were more intensive in seasons of higher water availability, indicating complex interactions between land use intensity and climate variability. The projected increase of atmospheric N depositions and changes in rainfall pattern imposed by land use change will likely affect N sink–source pathways and N flux dynamics, indicating high potential impact on grassland ecosystem functions. Land use practices will be increasingly important for the management of N dynamics in Chinese typical steppe and, therefore, must be considered as key component to maintain, restore or optimize ecosystem services.

Effect of rest-grazing management on soil water and carbon storage in an arid grassland (China)

“…Among paired grazing and rest grazing management, the former has been previously found to have significantly reduced community coverage (from 32.06 to 27.48), infiltration rate (from 9.85 to 6.00 cm h À1 ), SWC (from 24% to 15%) and greater soil loss to erosion in the arid environment (from 288.74 to 525.91 kg ha À1 ) (Jones, 2000;Jia et al, 2006;Teague et al, 2011;Giese et al, 2013). In this study, rest-grazing increased the ANPP and coverage (Table 2), which could enhance infiltration and buffer temperatures, while decreasing evaporation and radiation, so that SWC increased (Jones, 2000;Felzer et al, 2011;Merritt and Bateman, 2012;Deng et al, 2014).…”

Effects of grazing exclusion on soil carbon and nitrogen storage in semi-arid grassland in Inner Mongolia, China

“…Thirdly, the decreased loss of C and N from soils could also lead to the accumulation of SOC and TN after grazing exclusion. Because grazing is known to simulate soil mineralization, nitrification and ammonification, which in turn resulted in higher soil respiration rates and N 2 O emissions (Polley et al, 2008;Giese et al, 2013). These losses of SOC and TN are thought to be reduced when the disturbance is stopped by grazing exclusion (Qiu et al, 2013).…”

Restoration of ecosystem carbon and nitrogen storage and microbial biomass after grazing exclusion in semi-arid grasslands of Inner Mongolia

“…However, grazing by domestic livestock, one of the major human activities in grassland worldwide, has been found to cause grassland degradation and have significant effects on C and N cycles and storage (Giese et al, 2013;Mcsherry and Ritchie, 2013).…”

“…Soil microbial biomass was found to be a sensitive indicator of the dynamics of soil C and N cycles (Giese et al, 2013;Liu et al, 2012). Moreover, litter composition, soil carbon pool and microbial biomass are highly interlinked during carbon accumulation by soil (Fliebbach and Mader, 2000;Shrestha and Stahl, 2008).…”

“…Descheemaeker et al (2006) observed an increase of organic matter input from 20 g m also support the influence of organic matter input from vegetation to the soil. On the other hand, long-term grazing is known to stimulate soil mineralization, nitrification and ammonification (Giese et al, 2013;Hassink, 1994), which in turn could result in higher ecosystem respiration rates and N 2 O emissions (Giese et al, 2013;Polley et al, 2008). However, these losses of ecosystem C and N, as well as the outflow of energy and nutrient from the soil-plant system to livestock, are thought to be reduced when the disturbance is stopped by grazing exclusion (Qiu et al, 2013Zhou et al, 2011.…”