Print PageSoil respiration (Rsoil) is a large component of ecosystem carbon efflux. Thus, it is important to quantify how variations in the major exogenous abiotic (temperature and available moisture) and endogenous biotic (vegetative growth form, phenology) drivers might regulate Rsoil, under a range of current and projected climate scenarios. A growing body of evidence suggests that Rsoil can exhibit complex dynamics including hysteretic diurnal behavior, lag responses to environmental stimuli, and thermal acclimation. Moreover, antecedent environmental conditions can be important determinants of how Rsoil responds to environmental factors, and, thus, can be used to help explain rates of processes or patterns of interest. Hypothesized processes responsible for such antecedent effects, or legacy effects, range from allocation patterns of recent photosynthate, physiological upregulation, phenology, and dynamic storage and loss of labile carbon in response to variation in micro-meteorological conditions. We used a hierarchical Bayesian framework to quantify the duration of the ecological legacy effects (memory) in Rsoil under grasses and mesquite shrubs within a semiarid shrubland. We specifically focused on quantifying the endogenous memory (due to biotic inputs from previous days’ photosynthetic uptake) relative to the exogenous memory (as related to the importance of current and antecedent soil moisture and temperature conditions).
Results/Conclusions
Across an entire growing season, current-day Rsoil under mesquite shrubs appears to be significantly influenced by maximum photosynthetic rates (Amax), and thus carbon input, from up to four days prior. This lag was significantly shorter in soils under grasses, potentially because of shorter transport times of photosynthetic products. The magnitude of this endogenous memory effect was greatest during the primary growing season when plants had the greatest leaf area and were most physiologically active. The ecological memory of Rsoil under grasses was determined primarily by exogenous factors in that it was significantly affected by antecedent soil water conditions, which only minimally influenced Rsoil under shrubs. Inclusion of the biotic influence of Amax in an Rsoil model for this site increased the goodness-of-fit between observed and predicted Rsoil by 93% and 64% for shrubs and grasses, respectively, illustrating the importance of the endogenous memory. Continued efforts will aid our understanding of the relative contribution of autotrophic and heterotrophic respiration to total Rsoil, where each component may exhibit different endogenous and exogenous memories that are likely important for predicting total Rsoil. Exploration of the endogenous memory associated with Amax is expected to provide a quantifiable link between these above- and belowground fluxes.
