Displaying 1 - 2 of 2
Although large amounts of soil organic carbon (SOC) stored in the shrublands, information about SOC storage was little on the Tibetan Plateau. This study aims to evaluate the spatial patterns and storage of SOC in the shrublands and the relationships of climatic variables and soil pH on the Tibetan Plateau.<br>We used 177 profiles of soil samples obtained from 59 shrubland sites on the northeast Tibetan Plateau from 2011 to 2013. Ordinary least squares regressions, curve estimation, and multiple linear regressions were used to evaluate controlling factors on SOC stock. Kriging interpolation was used to upscale sit-level measurements to the whole study area.<br>We found that SOC storage in the northeast Tibetan shrublands was 1.36 Pg C in the top 1 m with an average SOC stock of 12.38 kg m<sup>−2</sup>. SOC stock decreased from east to west and south to north but generally increased significantly with the mean annual temperature (MAT) and the mean annual precipitation (MAP), and tended to decrease with soil pH. Although similar relationships were also observed in alpine shrublands, the trends among SOC stock, MAP, and MAT were not observed in desert shrublands. Our results indicate that a reduction in soil pH accelerates the C sequestration potential. Furthermore, global warming contributed to C sequestration in alpine shrublands, specifically, SOC stock increased 8.44 kg m<sup>−2</sup> with an increased unit of MAT in alpine shrublands just considering temperature effects. Meanwhile, the C sequestration was different among different regions due to the uneven increases in precipitation. However, in desert shrublands, MAP and MAT did not significantly affect SOC stock.<br>The results indicate that though a reduction in soil pH could contribute to C sequestration, MAT and MAP have different effects on SOC stock in different Tibetan Plateau shrublands. Increased MAT and MAP were 0.05 °C and 1.67 mm every year on the Tibetan Plateau, which will increase C sequestration in alpine shrublands, but might have limited impacts on desert shrublands, which help us comprehend soil C cycling in the global climate change scenario.
Emissions of nitrous oxide (N₂O) contribute to global warming and stratospheric ozone depletion. Anthropogenic N₂O emissions predominately result from the addition of synthetic nitrogen (N) fertilizers to terrestrial ecosystems. Usually, an exponential increase in N₂O emissions occurs as N addition rates increase to exceed plant demands. However, most evidence to date is from temperate areas, with little information available for alpine ecosystems. Here we examined the changes in N₂O flux under eight N addition levels and the mechanisms regulating these changes in a Tibetan alpine steppe. Our results showed that N₂O emission rate increased linearly with increasing N additions. Even when soil N availability exceeded plant N uptake, no sharp N₂O emissions were observed. The likely explanation was that decreased soil temperature limited the growth of nitrification-related microorganisms, mainly ammonia-oxidizing archaea, which further attenuated the positive response of N₂O emissions to excess N supply. These findings suggest that the N-induced changes in soil temperature regulate the growth of nitrifying microorganisms and the subsequent N₂O fluxes in this alpine steppe, and the exponential N₂O emission-N rate relationship observed in warm regions may not be simply extrapolated to alpine ecosystems.<br>N₂O emission exhibited a linear, rather than an exponential, response to increasing N additionsN₂O flux was explained by the changes in AOA along this N addition gradientDecreased soil temperature limited the growth of AOA, weakening the positive response of N₂O flux to excess N supplies