Sensitivity of soil methane ̄uxes to reduced precipitation in boreal forest soils

In order to better predict soil sinks of methane, we need to examine soil methane ̄ux patterns and responses to altered soil moisture regimes. Estimates of the global atmospheric CH4 budget must also account for ̄uxes in the vast boreal region. We measured methane ̄uxes into the soil surface, methane concentrations, water content, and temperature in the soil pro®le in two interior Alaskan forests, over two growing seasons. At each site, a 0.10 ha rain-shelter limited summer precipitation from entering the soil. Limiting summer precipitation at the upland site generally increased that site's soil uptake of methane. Average rates of soil methane uptake among upland plots ranged from 0.10 to 0.95 mg mÿ2 dayÿ1. At the ̄oodplain site, limiting precipitation decreased the soil methane uptake of that site, and the rates here ranged from ÿ0.02 to 0.57 mg mÿ2 dayÿ1. Using soil pro®le methane concentrations, we calculated CH4 ̄uxes using Fick's Law. Our inability to precisely measure the concentration gradient across the soil surface resulted in calculated ̄ux estimates that more likely represent ̄uxes within the soil pro®le. Methane sources and sinks in the soil pro®le also confounded the comparison of measured and calculated ̄uxes. 7 2000 Elsevier Science Ltd. All rights reserved.