Forest ecosystems sequester vast quantities of carbon (C) from the atmosphere, offsetting approximately 25% of fossil fuel emissions. Forests commit substantial fractions of this fixed C to long-term storage in soil and wood pools. Various individual plant and microbial C fluxes govern sequestration rates and storage, and human activities have altered factors that can control them at the global scale. In this dissertation, I investigate how two such factors – nutrient availability and soil acidity – impact aboveground and belowground productivity, soil respiration, and C allocation patterns in mixed temperate forests in New York. In Chapter 1, I examine how liming impacted fine root dynamics in a northern mixed temperate forest where calcium addition led to substantial forest floor C accumulation. Liming did not alter fine root biomass, but it markedly decreased fine root production and turnover, indicating that increased detrital fine root inputs have not contributed to the marked soil C accumulation at this site. In Chapter 2, I investigate how soil nitrogen (N) availability and pH impact soil respiration and its component plant- and decomposer-driven fluxes in mixed temperate forests in central NY. Soil acidification decreased heterotrophic respiration in surface organic soils, but did not affect the total soil respiration flux. In contrast, greater N availability decreased both heterotrophic and total soil respiration fluxes, driven largely by lower root-associated CO2 fluxes. In chapter 3, I explore how N availability and soil acidification affect wood production, aboveground net primary production (ANPP), fine root growth, and total belowground C flux (TBCF) by trees. Increased N availability stimulated ANPP and decreased TBCF, and reductions in TBCF could entirely explain ANPP gains. These effects were consistent in mid- and late-successional forests and occurred regardless of concurrent acidification. Overall, this dissertation demonstrates that nutrient availability exerts strong control over C allocation patterns in temperate forests. These changes in C allocation regulate soil respiration and can enable greater C storage in woody biomass. This research highlights that representing nutrient effects on forest C allocation in Earth system models will be critical for accurately predicting ecosystem C dynamics under global change.