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Abstract
Forests in the Southeast U.S. are predicted to experience more variable precipitation in the future with more extreme daily precipitation events. Within these forests, the loblolly pine (Pinus taeda L.) is the most extensively planted and productive commercial pine species. Changes in climate could create more severe drying and re-wetting cycles in the forest soil profile to greater depths affecting stocks of soil C. To addresses this effect, a soil incubation experiment was established using soils from four loblolly pine plantations which span the full temperature and precipitation range of the species. Soils were incubated from as many as eight layers up to a depth of three meters. Results indicated that there were no significant changes to soil respiration in deep soils under repeated drying-wetting cycles.Change in precipitation could result in drought during the growing season. Deep soils help forests buffer the effects of water deficits during drought but the extent of deep rooting and quantity of plant available water at depth needs better quantification. Throughfall reduction x fertilization treatments were applied in a loblolly pine plantation in Taliaferro County, Georgia. Multiple layers of soil moisture were monitored to a depth of three meters from March 2013 to July 2015. Resultsdemonstrated soil water storage could satisfy evapotranspirational demand in the face of increasing dryness in the clay rich Piedmont soil of this research site when considering the whole soil profile. Possible climate change scenarios also include seasonal and frequency precipitation change. A hydrological model was used to quantify water fluxes and to test alternative precipitation regimes. Model outputs under year round reductions indicated sustained evapotranspiration to the detriment of soil drainage. With more seasonal precipitation redistribution and heavy storms, both evapotranspiration and drainage decreased, while surface runoff increased. Although root biomass measured both before and after the treatment had no significant difference between treatments, evapotranspiration increased with deeper roots under evenly reduced precipitation and seasonal precipitation redistribution scenarios. How deep root buffering capacity will persist in the face ofchanging precipitation may depend less on seasonal redistribution than rainfall frequency.