CH4 uptake flux of Leymus chinensis steppe during rapid growth season in Inner Mongolia, China

Abstract

The influence of near ground atmosphere CH 4 concentration, soil water content, soil Eh, plants, soil temperature, and pH on CH 4 uptake flux of Leymus chinensis steppe during rapid growth season was studied using field in-situ measurement in Xilin River basin of Inner Mongolia, China. The results showed that CH 4 uptake flux was positively correlated with near ground atmosphere CH 4 concentration and soil Eh but negatively correlated with soil water content. Precipitation may decrease the CH 4 flux by increasing the soil water content. The average fluxes of three treatments during the observation period were 1.52 (natural conditions, 1.51 (aboveground plants were excluded), and 2.00 mg m −2 d −1 (all plants were removed), respectively. The difference between the CH 4 flux of natural condition treatment and that of removing aboveground plants treatment is small, whereas the flux of removing all plants treatment is larger than the other two treatments. This means that the contribution of aboveground plants to CH 4 uptake flux is smaller than that of roots or roots-removing process. CH 4 uptake flux is not sensitive to soil temperature and the narrow-ranged soil pH (6.36-7.86). The Leymus chinensis steppe acts as a sink for CH 4 , and thus more studies should be focused on its affecting factors and related mechanisms. The global atmospheric concentration of CH 4 has increased from a pre-industrial value of about 715 to 1732 ppb in the early 1990s, and was 1774 ppb in 2005 [1]. CH 4 is a long-lived greenhouse gas (it lasts about 8.4 years in the atmosphere) [2] and can absorb more infrared radiation than CO 2 . The warming potential of CH 4 is 26 times of that of CO 2 [3, 4] and the current direct radioactive forcing of CH 4 is 20% of the total from all of the long-lived and globally mixed greenhouse gases [5]. Emission of CH 4 has a long-term effect on climate change. CH 4 concentration in atmosphere lies mainly on the balance between natural and artificial emission and uptake of CH 4 . The persistently increased CH 4 concentration is caused not only by the increased sources but also by the decreased sink [6]. Aerobic soil environment can oxidize the CH 4 diffusing from atmosphere to soil, which is the biggest sink for CH 4 of terrestrial ecosystem except for atmospheric photochemical reactions [7]. This oxidation process is very important for regulating the quantity of CH 4 in atmosphere. The increase rate of CH 4 concentration in atmosphere would be 1.5 times of value right now if there were no soil sink for CH 4 [8]. Up to now, most of our studies about CH 4 uptake are focused on forest [9-11], grassland [12-14], and paddy field [15,16], and also concerned with the influence of land use change on CH 4 uptake [17,18]. Research on CH 4 uptake process in grassland ecosystem focused on the variation pattern of flux, but its affecting factors are not yet clear.

Effects of enclosure time on the community composition of methanotrophs in the soils of the Inner Mongolia grasslands

“…Previous studies demonstrated that the Inner Mongolia grassland is a CH 4 sink (Ma et al 2006;Liu et al 2007;Holst et al 2008;Chen et al 2010;Geng et al 2010) with USC-γ as the main methanotrophic cluster oxidizing atmospheric CH 4 (Zhou et al 2008a). Different from those results, this study found in all three treatments only one genotype (OTU1) belonging to USC-γ cluster.…”

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

“…Recent evidence suggests that semiarid grassland is an important sink for atmospheric CH 4 ( [40][41][42]) and results from our study). With a mean annual CH 4 uptake of 26.1 µg C m −2 h −1 (Table 8), mean CH 4 uptake from all three treatments ranged from 25.1 to 27.9 µg C m −2 h −1 ( Table 2).…”

Soil methane uptake by grasslands and forests in China

“…More than three fourths of all published measurements from grasslands of China were taken in the semi-arid steppe ecoregion of the NASD. Based on 306 data collected in this region we estimated the mean CH 4 uptake rate by grasslands as 74.31 AE 62.51 mg CH 4 m À2 h À1 Wang et al, 1998Wang et al, , 2000Wang et al, , 2005Ma et al, 2006;Liu et al, 2007Liu et al, , 2009aGeng et al, 2010;Zhou and Hao, 2010;Luo and Jiao, 2012), which is also the highest mean CH 4 uptake rate of grasslands for all ecoregions in China (Fig. 2).…”

“…So far to the best of our knowledge, there is no synthesis study on a comprehensive CH 4 budget for either grasslands or forests in China, which is indispensable for a general CH 4 uptake estimate for this country. Multiple studies on CH 4 fluxes of grasslands in China have already been carried out Wang et al, 1998Wang et al, , 2000Wang et al, , 2005Wang et al, , 2007Wang et al, , 2009bDong et al, 2000Dong et al, , 2005Ma et al, 2006;Li et al, 2007;Liu et al, 2007Liu et al, , 2011Liu et al, , 2012aHolst et al, 2008;Sun, 2008;Chen et al, 2010;Geng et al, 2010;Zhou et al, 2011;Luo and Jiao, 2012;Wei et al, 2012;Zhang et al, 2012), some even making efforts to estimate the total emission for specific regions Liu et al, 2009a;Wang et al, 2009c). Relatively fewer studies on CH 4 fluxes of forests in China have been published (Xu et al, 1995;Sun, 2000;Dong et al, 2003;Du et al, 2004;Mo et al, 2005;Yang et al, 2010;Liu et al, 2010bLiu et al, , 2012bGuan et al, 2012;Yang, 2012).…”