Soil respiration and ecosystem carbon stocks in New England forests with varying soil drainage

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Northern temperate forests play an important role in the global carbon (C) cycle. Individual stands can differ in C content and storage, based on characteristics such as vegetation type, site history, and soil properties. These site differences may cause stands to vary in their response to extreme weather events such as droughts. We examined ecosystem C pools, soil respiration, and litterfall in four hardwood stands with widely varying soil drainage in Rhode Island. Total ecosystem C increased as soils became more poorly drained, ranging from 181 Mg C ha-in the excessively drained Entisol to 547 Mg C ha-in the very poorly drained Histosol. The proportion of ecosystem C contained in the soil was much higher in the poorly drained soils, and ranged from 57% in the excessively drained Entisol to 91% in the poorly drained Histosol. While total ecosystem C stocks varied by a factor of three, rates of litterfall and soil respiration were similar among sites. Soil carbon content was highest in the very poorly drained site, and respiration was lowest from this site. During the summer drought of 1999, all soils except the Histosol had lower respiration rates than predicted from temperature alone. Rain events that ended the drought produced a pulse of soil respiration in all mineral soils, stimulating soil C flux more than expected from temperature alone. The effect of drought and rewetting on soil respiration varied by site, suggesting that the response to climate variability will depend upon soil drainage to some extent. Soil respiration rates were most variable in dry conditions, and current and antecedent soil moisture conditions played an important role during those times. In general, soil respiration was much more variable over time than across sites, even among these sites with very different total soil C content, indicating that climatemainly temperatureis the main determinant of soil CO2 release even across soils with widely varying drainage.

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Northeastern Naturalist