Effects of Grazing Pattern on Ecosystem Respiration and Methane Flux in a Sown Pasture in Inner Mongolia, China

Abstract

The establishment of sown pasture is an important agricultural practice in many landscapes. Although both native grassland and sown pasture play a key role in the global carbon cycle, due to lack of data and field experiments, our understanding of grassland CH4 fluxes and CO2 emissions remains limited, especially when it comes to sown pasture. We measured ecosystem respiration and CH4 fluxes in response to a variety of potential drivers (soil temperature, soil moisture, ammonium nitrogen, nitrate nitrogen and dissolved organic carbon) in CG (continuous grazing), RG (rotational grazing) and UG (ungrazed) plots in sown grassland for one year in Inner Mongolia. Fluxes of CH4 and ecosystem respiration were measured using static opaque chambers and gas chromatography. Grazing significantly reduced ecosystem respiration (p < 0.01), and grazing pattern significantly influenced respiration in CG and RG plots (p < 0.01). We find that the sown grassland is a net sink for atmospheric CH4. No influence of grazing pattern was observed on CH4 flux in CG, RG and UG (p > 0.05). Soil temperature is the most important factor influencing ecosystem respiration and CH4 flux in the sown grassland, with soil moisture playing a secondary role to soil temperature. Variation in levels of ammonium nitrogen, nitrate nitrogen and dissolved organic carbon had little influence on ecosystem respiration or CH4 flux (except in UG plots). The values obtained for ecosystem respiration of grasslands have a large uncertainty range, which may be due to spatial variability as well as differences in research methods. Mean CH4 fluxes measured only during the growing season were much higher than the annual mean CH4 fluxes.

Soil carbon flux research in the Asian region: Review and future perspectives

“…For this analysis, we used open data sources Wang and Fang, 2009;Bond-Lamberty and Thomson, 2018;Feng et al, 2018;Steele and Jian, 2018;Mei et al, 2019;Yang et al, 2019a . In arid and semi-arid environments, biological soil crusts significantly influence ecological processes, including soil C flux.…”

“…, 73 of which is stored in the solid phase of the soil Liu et al, 2015a . There has been much less reporting on the CH 4 flux than CO 2 flux in arid and semi-arid environments. The few studies on this topic Wang et al, 2014c;Mei et al, 2019;Yang et al, 2019a , have…”

“…These studies reported on the differential responses of R r and R h to warming, such as decreasing trends in the warming effect over time Noh et al, 2016a;Fang et al, 2018 . Other warming studies resulted in sustained stimulations of the warming effects on R h due to sufficient soil moisture conditions or the negligible depletion of C substrate Aguilos et al, 2013;Teramoto et al, 2016a;Wu et al, 2016 . In the Asian monsoon region, the sustained stimulatory warming effects on R h in the long-term have outcomes that contrast the decline in the initial stimulatory warming effect after several years of warming treatment in other ecosystems Melillo et al, 2002;Eliasson et al, 2005 . A five-year warming study by Teramoto et al 2018 had demonstrated that inter-annual variation in the magnitude of the annual warming effect was positively related to the number of rainy days associated with precipitation. Despite the accumulation of this evidence from the field, there is still a critical need to conduct multi-factorial manipulation experiments associated with natural or anthropogenic disturbances Zhu et al, 2015;Li et al, 2017;Sun et al, 2018a;Zhou et al, 2019b , and long-term experiments including extreme climate events to better integrate experiments and models to contribute toward global synthesis Rustad, 2008 . Global warming also generally enhances CH 4 uptake in grassland, tundra and forest ecosystems due to the stimulated activity of methane-oxidising methanotrophs with increasing soil temperature Luan et al, 2019;Yue et al, 2019 . As the influence of increasing temperature on CH 4 uptake is dependent on the soil water content/level, N deposition and their interaction Yue et al, 2019;Li et al, 2020 , the impacts of warming on CH 4 uptake may be inconsistent across different ecosystems. Previous studies have reported that experimental warmings enhanced CH 4 uptake in arid alpine grasslands in the Tibetan Plateau and in a tundra ecosystem at Changbai Mountain, China Lin et al, 2015;Zhou et al, 2016;Chen et al, 2017;Li et al, 2020 . In contrast, they had no significant effect on CH 4 emissions from alpine meadows on the Qunghai-Tibetan Plateau, and a temperate desert in China Zhao et al, 2017a;Yue et al, 2019;Li et al, 2020;…”

“…Despite the accumulation of this evidence from the field, there is still a critical need to conduct multi-factorial manipulation experiments associated with natural or anthropogenic disturbances Zhu et al, 2015;Li et al, 2017;Sun et al, 2018a;Zhou et al, 2019b , and long-term experiments including extreme climate events to better integrate experiments and models to contribute toward global synthesis Rustad, 2008 . Global warming also generally enhances CH 4 uptake in grassland, tundra and forest ecosystems due to the stimulated activity of methane-oxidising methanotrophs with increasing soil temperature Luan et al, 2019;Yue et al, 2019 . As the influence of increasing temperature on CH 4 uptake is dependent on the soil water content/level, N deposition and their interaction Yue et al, 2019;Li et al, 2020 , the impacts of warming on CH 4 uptake may be inconsistent across different ecosystems. Previous studies have reported that experimental warmings enhanced CH 4 uptake in arid alpine grasslands in the Tibetan Plateau and in a tundra ecosystem at Changbai Mountain, China Lin et al, 2015;Zhou et al, 2016;Chen et al, 2017;Li et al, 2020 . In contrast, they had no significant effect on CH 4 emissions from alpine meadows on the Qunghai-Tibetan Plateau, and a temperate desert in China Zhao et al, 2017a;Yue et al, 2019;Li et al, 2020;Wu et al, 2020 . This highlights the need for future research to consider the interactive impacts of N deposition, precipitation and warming manipulations on CH 4 uptake Zhu et al, 2015;Chen et al, 2017;Yue et al, 2019;Wu et al, 2020 .…”

“…There are a few studies on the effects of grazing on soil CH 4 uptake. Studies on grassland ecosystems located in Haibei and Inner Mongolia, China, have indicated that grazing reduced CH 4 uptake due to a decrease in air permeability Liu et al, 2007;Chen et al, 2011 , whilst grazing did not significantly affect CH 4 flux with no changes to the bacterial community Lin et al, 2015;Zhu et al, 2015;Mei et al, 2019 . In the Asian region, few studies have explored how grassland management may be able to regulate the combined and interactive effects of grazing and other global change factors on R s components and CH 4 flux Zhu et al, 2015;Wang et al, 2020b . The absence of research on the impact of land-use changes such as deforestation or reforestation on R s components and CH 4 emissions had created greater uncertainty in predicting future soil C sequestration in Asian regions Hergoualc'h and Verchot, 2011;Jauhiainen et al, 2012;Sun et al, 2018a;Wu and Mu, 2019;Zhang et al, 2020 . Further research are still needed in vulnerable ecosystems such as peatlands Couwenberg et al, 2010;Jauhiainen et al, 2012;Sundari et al, 2012;Ishikura et al, 2019, sub-tropical wetlands Philipp et al, 2017, and deserts Wang et al, 2014aFa et al, 2018 Kaupper et al, 2019. Wong et al 2020 reported that the conversion of a peat swamp forest to a drained oil palm plantation decreased CH 4 emissions from tropical peatlands in Malaysia.…”