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Biotic processes explain diel hysteresis in soil respiration

The distribution of carbon fluxes in ecosystems is strongly influenced by soil CO2 fluxes that change with temperature. These fluxes generally show a daily hysteresis with respect to soil temperature, so that respiration shows highly variable levels for the same temperature depending on the daily cycle. These cycles are difficult to understand in real-life situations so we took advantage of the advanced control facility at Ecotron to independently manipulate biotic processes and soil temperature profiles. Using fine climate control, we simulated normal and fluctuating diurnal soil temperature conditions and conditions where we kept the soil temperature almost constant.

In a new study published in Scientific Reports with colleagues from Biosphere 2 research group at University of Arizona, we report about significant and nearly equal amplitudes of hysteresis regardless of the soil temperature regime. In addition, the amplitude of hysteresis was closely related to plant photosynthesis rates. These results suggest that a biological mechanism associated with the transport of leaf photosynthesis to the soil explains hysteresis. These temporal shifts in the ecosystem effects of daily temperature will need to be taken into account in future global models of ecosystem respiration partitioning.