Temporal patterns of fine‐root dynamics have little influence on seasonal soil CO₂ efflux in a mixed, mesic forest

Abstract

Among the contributors to soil CO2 efflux, there remains uncertainty about the contribution of root activity to the overall soil efflux. Soil water and temperature frequently have been used to predict a large portion of the variation in soil CO2 efflux. We hypothesized that fine‐root dynamics explain most of the remaining variability in soil CO2 efflux that cannot be explained by soil temperature and water content. We anticipated that seasonal increases in root production, mortality via decomposition, and standing crop would result in corresponding increases in soil CO2 efflux. We tested our hypotheses by collecting and analyzing two years of minirhizotron and soil chamber CO2 flux data from plots distributed throughout the Shale Hills Catchment of the Susquehanna‐Shale Hills Critical Zone Observatory in Central Pennsylvania, USA. Here we showed that: (1) seasonal fluctuations in fine‐root dynamics yielded only a very small increase in the predictability of soil CO2 efflux; (2) fine‐root mortality effects on soil CO2 efflux were strongly tied to soil temperature; (3) fluctuations in fine‐root presence or standing mass independent of temperature and moisture had little effect on soil CO2 efflux; and (4) new fine‐root length and root length mortality had limited impacts on soil CO2 efflux rates. We conclude that, at least in temperate forests on rocky soils, characterizing fine‐root dynamics may provide only limited improvement in the estimation of soil CO2 efflux.