Tree proximity affects soil respiration dynamics in a coastal temperate deciduous forest.

Soil respiration (R_s), the flow of CO₂ from the soil surface to the atmosphere, is one of the largest carbon fluxes in the terrestrial biosphere. The spatial variability of R_s is both large and poorly understood, limiting our ability to robustly scale it in time and space. One factor in R_s spatial variability is the autotrophic contribution from plant roots, but it is uncertain how the proximity of plants affects the magnitude and temperature sensitivity of R_s. This study examined the effect of tree proximity on R_s in the growing and dormant seasons, as well as during moisture-limited times, in a temperate, coastal, deciduous forest in eastern Maryland, USA. In a linear mixed-effects model, tree basal area within 5 m (BA₅) exerted a significant positive effect on the temperature sensitivity of soil respiration. Soil moisture was the dominant control on R_s during the dry portions of the year while soil moisture, temperature, and BA₅ all exerted significant effects on R_s in wetter periods. Our results suggest that autotrophic respiration is more sensitive to temperature than heterotrophic respiration at these sites, although we did not measure these source fluxes directly, and that soil respiration is highly moisture-sensitive, even in a record-rainfall year. The R_s flux magnitudes (0.3-16.6 µmol m^-2 s^-1) and variability (coefficient of variability 10 %-22 % across plots) observed in this study were comparable to values observed over decades in similar forests. We estimate that four R_s observations were required to be within 50 % of the stand-level mean, and 311 to be within 5 %, at 90 % confidence. A better understanding of the spatial interactions between plants and microbes that results in measured R_s is necessary to link these processes with large scale soil-to-atmosphere C fluxes. [ABSTRACT FROM AUTHOR]