Ecological controls on moss, microbial, and root respiration in burned black spruce soils of interior Alaska

Authors: O Neill, Katherine; RITCHER, DANIEL - DUKE UNIVERSITY; KASISCHKE, ERIC - UNIVERSITY OF MARYLAND

Submitted to: Biogeochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2005
Publication Date: 8/25/2006
Citation: O Neill, K.P., Ritcher, D., Kasischke, E. 2006. Ecological controls on moss, microbial, and root respiration in burned black spruce soils of interior Alaska. Biogeochemistry 80:1-20. DOI 10.1007/s10533-005-5964-7.

Interpretive Summary: Boreal forests contain large amounts of stored soil carbon and are currently believed to function as a small net sink for atmospheric CO2. These northern landscapes are highly susceptible to wildfire, and post-fire changes in soil temperature and moisture have the potential to transform large areas of the landscape from a net sink to a net source of carbon. Understanding the ecological controls that regulate these disturbance effects is critical to developing models of carbon cycling in northern latitudes. This study evaluated changes in soil C dynamics along a 140-yr age-sequence of burned black spruce stands. Moss species exhibited a distinct successional pattern in the first five decades after fire disturbance -- a pattern that largely regulated soil temperature, decomposition, and carbon accumulation as these systems recovered from disturbance. Models indicated that changes in substrate quality and temperature increased decomposition in humic organic materials after fire. Residual sources of CO2 (those not attributed to moss respiration or decomposition of humic materials) increased as a function of stand age, reflecting increased contributions from roots and decreased decomposition as the stand recovered from disturbance. Since soil temperature may be perturbed for more than a decade following fire, these results suggest that fire may convert upland black spruce soils to a net source of CO2 and result in the loss of stored soil C in the decades following disturbance.

Technical Abstract: Boreal forests are highly susceptible to wildfire, and post-fire changes in soil temperature and moisture have the potential to transform large areas of the landscape from a net sink to a net source of carbon (C). Understanding the ecological controls that regulate these disturbance effects is critical to developing models of ecosystem response to changes in fire frequency and severity. This paper combines laboratory and field measurements along a chronosequence of burned black spruce stands with mass-balance and physiological models to assess the ecological relationships between moss succession, soil microclimate, decomposition, and C source-sink dynamics. Bryophyte species exhibited a distinct successional pattern in the first five decades after fire that corresponded to decreases in soil temperature and increased C accumulation in organic soil profiles. Potential rates of C exchange in mosses were greatest in early successional species and declined as the stand matured. Post-fire changes in temperature and substrate quality indicate increased modeled rates of decomposition in humic organic material by a factor of 0.6 to 4.0 in the first 10 years after fire. Residual sources of CO2 (those not attributed to moss respiration or decomposition of humic materials) increased as a function of stand age, in part reflecting increased contributions from roots as the stand recovered from disturbance. Together, the field measurements, laboratory experiments, and models provide strong evidence that interactions between moss and plant succession, soil temperature, and soil moisture largely regulate C source-sink dynamics from black spruce systems in the first century following fire disturbance.