Quantifying the timescales over which exogenous and endogenous conditions affect soil respiration

Understanding how exogenous and endogenous factors and above-ground-below-ground linkages modulate carbon dynamics is difficult because of the influences of antecedent conditions. For example, there are variable lags between above-ground assimilation and below-ground efflux, and the duration of antecedent periods are often arbitrarily assigned. Nonetheless, developing models linking above- and below-ground processes is crucial for estimating current and future carbon dynamics. We collected data on leaf-level photosynthesis (A(sat)) and soil respiration (R-soil) in different microhabitats (under shrubs vs under bunchgrasses) in the Sonoran Desert. We evaluated timescales over which endogenous and exogenous factors control R-soil by analyzing data in the context of a semimechanistic temperature-response model of R-soil that incorporated effects of antecedent exogenous (soil water) and endogenous (A(sat)) conditions. For both microhabitats, antecedent soil water and A(sat) significantly affected R-soil, but R-soil under shrubs was more sensitive to A(sat) than that under bunchgrasses. Photosynthetic rates 1 and 3d before the R-soil measurement were most important in determining current-day R-soil under bunchgrasses and shrubs, respectively, indicating a significant lag effect.Endogenous and exogenous controls are critical drivers of R-soil, but the relative importance and the timescale over which each factor affects R-soil depends on above-ground vegetation and ecosystem structure characteristics.