Non-additive effects of day- and night-time warming on ecosystem C fluxes in a temperate steppe

A field experiment was conducted in a semiarid temperate steppe in northern China to examine differential impacts on ecosystem carbon (C) and water fluxes of day and night warming associated with climate change. Net ecosystem exchange (NEE) and soil respiration were both greatly enhanced by night warming, possibly resulted from photosynthetic over-compensation. However, day warming, through intensifying water and heat stresses and suppressing stomatal conductance and photosynthesis, counterbalanced the positive effects of night warming, leading to intermediate changes in NEE and soil respiration under whole-day warming. Day and night warming additively affected NEE, but non-additively influenced soil respiration and evapotranspiration. Our observations are critical for model projecting the responses and feedbacks of terrestrial C cycling to global climate change.