Factors affecting the soil organic carbon pool in marshes along the Yarlung Zangbo River, Tibet, China

Marshes in high plateaus are critical in governing carbon cycle because of their huge but labile soil organic carbon (SOC) storage, which of even a small proportion of carbon contained in SOC can lead to high variations in the atmospheric CO2 levels. The Yarlung Zangbo River (YZR) is the world's highest river, flowing from west to east across Tibet. There are widespread alpine marshes and meadows along the YZR basin, with huge SOC storage but extremely vulnerable to climate change. However, few studies were carried out to explore the potential effects of environmental factors on SOC pool along the YZR. In the present work, effects of climate, plant biomass, soil nutrients, and molecular features of organic matter on SOC storage were systematically evaluated. Results indicated that SOC contents varied from 0.86% to 29.68%, with an average of 7.29%, and an estimated 5887 Gg (10(9)g) of carbon was stored in marsh soils along the YZR. Soil accretion rates ranged from 1.66 to 2.73 mm yr(-1), while carbon sequestration rates ranged from 43.65 gC m(-2) yr(-1) to 125.4 gC m(-2) yr(-1), with an average of 75.89 gC m(-2) yr(-1). It was estimated that 34.58 Gg of carbon was sequestrated by wetlands along the YZR every year. The abundance of lignin-derived components, total nitrogen, and soil moisture contents (SWC) were the main drivers promoting SOC contents. SOC storage was significantly related to mean annual temperature (Temp) but decreased with the ratio of annual precipitation (Pre) to Temp. Compared with the chemical decomposition resistance of organic matter, more SOC variations arose from climate, and climate warming had adverse impacts on SOC pool. SWC were proved to be the most powerful promoter of SOC increase. Rising temperatures are expected to have a detrimental impact on SOC storage when the climate is warming in the future.

Automated summary

Marshes in high plateaus play a critical role in governing the carbon cycle due to their large yet unstable soil organic carbon (SOC) storage. The Yarlung Zangbo River (YZR) is the world's highest river, and it harbors widespread alpine marshes and meadows with huge SOC storage but high vulnerability to climate change. This study systematically evaluated the effects of environmental factors on SOC storage along the YZR and found that climate, plant biomass, soil nutrients, and molecular features of organic matter all have significant impacts. The findings suggest that rising temperatures and decreased precipitation relative to temperature could have adverse effects on SOC storage in the future.