Climate controls on soil respired CO_2 in the United States: Implications for 21st century chemical weathering rates in temperate and arid ecosystems

摘要

The most recent IPCC (2007) report predicts that regional-scale precipitation patterns will change significantly in the 21st century as a result of increasing atmospheric CO_2. The amount of respired CO_2 stored in the soil atmosphere is heavily influenced by climate, and the concentration of CO_2 in soils controls the concentration of dissolved CO_2 ([CO_(2aq)]) in pore water involved in chemical weathering. Therefore, we can expect changes to chemical weathering rates as a result of climate change, which can influence the global carbon cycle through the consumption of CO_2 during continental silicate weathering. These changes may even be important on human timescales. To predict changes to the [CO_(2aq)] of soil water, we have produced an extensive literature review of soil respired CO_2 measurements to study the spatial variability of soil respired CO_2. We show that respired CO_2 concentrations and [CO_(2aq)] vary with precipitation. This study focuses on the western United States, where we find a strong relationship between summer average soil-respired CO_2 and mean annual precipitation for soils forming in or below 900mmyr~(-1) precipitation (R~2=0.91). The correlation breaks down when higher mean annual precipitation rates are considered, restricting the use of this relationship to arid to subhumid precipitation regimes.We estimate the response of [CO_(2aq)] in soil pore water in the western United States to projected anthropogenic CO_2 emissions using this new relationship and projected changes in precipitation simulated by the North American Regional Climate Change Assessment Program for the decade 2051-2060. According to our model, [CO_(2aq)] in soil pore water is expected to decrease by up to 50% in the southwestern United States and to increase by up to 50% in areas of the Northern and Central Great Plains. These results have important implications for CO_2 consumption and changes to terrestrial carbon cycling in the next century.