Atmospheric CO2 concentrations are expected to continue increasing due to ongoing fossil fuel emissions, leading to innumerable climate impacts. These impacts are largely associated with the enhanced greenhouse effect, but recent work highlights that plant CO2 physiological responses can also strongly influence the climate. This study explores the impacts of plant responses on hydrological cycling at 2x preindustrial CO2 concentrations by analyzing simulations that separate plant physiology from climate responses to CO2 using the Community Earth System Model (CESM) versions 1 and 2. We find that CESM2 leaf area growth increases canopy evaporation, which offsets transpiration declines from reduced stomatal conductance, and dampens changes in precipitation, evapotranspiration, and runoff compared to CESM1 and a configuration of CESM2 with fixed leaf area. CESM2 better captures present-day leaf area magnitudes compared to observations but potentially over-estimates leaf area-CO2 sensitivity, highlighting the ongoing need to reduce plant allocation-related biases.