Taklimakan desert carbon-sink decreases under climate change

The global carbon balance is a core issue in climate change research and a focus of international policy concern [1-3]. The missing carbon sink caused by approximately 1.6-2.0 Pg C a-1 (1 Pg = 1015 g) that is currently unaccounted for, has long plagued researchers [4,5]. Evidence is mounting those seemingly lifeless desert ecosystems, whose roles in the global carbon-cycle have long been neglected, exhibit the unconventional phenomenon of absorption of atmospheric CO_2, sequestering enormous amounts of CO_2 and thereby creating a significant carbon-sink [6-9]. This scenario appears to help narrow the gap in the missing carbonsink. However, this view has been questioned for the inaccurate carbon sequestration location [10]. The effects of abiotic processes, such as soil temperature gradient, moisture content, parent material, salt/alkali, and pH, on desert CO_2 exchange, have gradually revealed that the phenomenon of a desert carbon-sink is intimately associated with abiotic processes [11]. Thus far, the main processes, whereby, deserts act as carbon-sinks may include the following: (1) variation in the volume of gases caused by changes in pressure and temperature; (2) changes in solubility of CO_2 in soil water films; (3) pH-mediated CO_2 dissolution chemistry; and (4) surface adhesion of CO_2 onto soil minerals [11-13]. In ecosystems with relatively high productivity, the effects of abiotic processes on CO_2 exchange are often neglected because of strong biological respiration. In desert ecosystems, however, the effects of abiotic processes on CO_2 exchange cannot be ignored, although the CO_2 flux is extremely weak. The effects of abiotic processes are even greater than the effects of biological processes [11,14]. The latest research indicates that the absorbed CO_2 gradually, enters the desert groundwater layer by the process of leaching, and eventually converge in the underground saline water layer under the vast desert with the groundwater movement. This process is similar to the inorganic carbon sinks in the ocean [9].