Pasture degradation modifies the water and carbon cycles of the Tibetan highlands

Abstract

Abstract. The Tibetan Plateau has a significant role with regard to atmospheric circulation and the monsoon in particular. Changes between a closed plant cover and open bare soil are one of the striking effects of land use degradation observed with unsustainable range management or climate change, but experiments coupling changes of surface properties and processes with atmospheric feedbacks are rare and have not been undertaken in the world's two largest alpine ecosystems, the alpine steppe and the Kobresia pygmaea pastures of the Tibetan plateau. We coupled measurements of micro-lysimeter, chamber, 13C labeling, and eddy-covariance and combined the observations with land surface and atmospheric models, adapted to the highland conditions. This allowed us to analyze how three degradation stages affect the water and carbon cycle of pastures on the landscape scale within the core region of the Kobresia pygmaea ecosystem. The study revealed that increasing degradation of the Kobresia turf affects carbon allocation and strongly reduces the carbon uptake, compromising the function of Kobresia pastures as a carbon sink. Pasture degradation leads to a shift from transpiration to evaporation while the total sum of evapotranspiration remains unaffected. The results show an earlier onset of convection and cloud generation, likely triggered by enhanced evaporation. Consequently, precipitation starts earlier and clouds decrease the incoming solar radiation. In summary, the changes in surface properties by pasture degradation found on the highland have a~significant influence on larger scales.

Moderate grazing increased alpine meadow soils bacterial abundance and diversity index on the Tibetan Plateau

“…Global grasslands have been suffering from degradation owing to climate change and long‐term overgrazing (Babel, Biermann, & Coners, 2014; Che et al., 2018). Livestock grazing is considered to be the most important land‐use activity for grasslands (Akiyama, Yan, & Yagi, 2010; Du, Ke, Guo, Cao, & Zhou, 2019).…”

“…Livestock grazing is considered to be the most important land‐use activity for grasslands (Akiyama, Yan, & Yagi, 2010; Du, Ke, Guo, Cao, & Zhou, 2019). Moreover, grassland degradation drastically decreases the soil organic carbon and total nitrogen contents (Babel et al, 2014; Du, Ke, et al, 2019). Microbial abundance has an indirect impact on the grassland nitrogen and carbon turnover process (Chu et al., 2016; Hu, Nie, et al, 2019).…”

Decreased Soil Cation Exchange Capacity Across Northern China's Grasslands Over the Last Three Decades

“…First, a reduction in SOC content can lead to a decrease in CEC. Overgrazing and cultivation in past decades (Bridges & Oldeman, ; Mu et al, ; Yang et al, ; Yu et al, ) have increasingly degraded grasslands (Dai et al, ) and caused declines in grassland productivity (Babel et al, ). Consequently, the SOC stock of China's grasslands decreased by 3.56 Pg C (1 Pg = 10 15 g), dropping from approximately 37.71 to 34.15 Pg C from the 1980s to the 2000s, with particularly marked changes in Tibet, Qinghai, and Inner Mongolia (Xie et al, ).…”

“…First, along with the geographic gradient, grassland types are diverse (including both alpine and temperate grasslands) and environmental parameters such as precipitation and edaphic variables exhibit a wide range (Liao & Jia, ). Second, since the 1980s, northern China has experienced significant environmental changes, which mainly include the following: (1) Overgrazing and cultivation (Bridges & Oldeman, ; Yu et al, ) have led to soil desertification (Mu et al, ; Yang et al, ) and pasture degradation (Dai et al, ), thereby decreasing grassland productivity (Babel et al, ) and organic carbon storage (Dai et al, ; Xie et al, ) across the study area. (2) Elevated atmospheric acid deposition has induced soil acidification across northern China, with a decrease in soil pH of 0.63 units over the past two decades (Yang, Ji et al, ).…”

Modeling impacts of climate change and grazing effects on plant biomass and soil organic carbon in the Qinghai–Tibetan grasslands

“…Warming could significantly increase the net primary productivity of alpine meadows (Fan et al, 2010;Du et al, 2004;Chen et al, 2013). Other studies have found that warming also speeds up the decomposition rate for litter and manure, and increases soil respiration Luo et al, 2010), which could cause significant losses of soil organic carbon (SOC) and affect the alpine grassland ecosystem carbon pool balance (Tan et al, 2010;Pei et al, 2009;Babel et al, 2014;Liu et al, 2017). Although the ecological impact of warming on the QTP alpine grassland ecosystem has not been fully elucidated in previous studies, there is no doubt that warming will greatly accelerate the key processes in the alpine grassland ecosystem carbon cycle .…”